Hesam Hakim

Assistant Professor l Solving the bottleneck in digital diagnostics using AI & Data Science 🧬🔬

[Hesam Hakim @hesamhakim]

@biogerontology Forcing pyruvate into the TCA cycle via PDH activation is an elegant rescue of OCR, but does this shift truly restore basal crypt stemness, or does it trigger metabolic differentiation cues? The balance between glycolytic stem maintenance and TCA commitment remains delicate.

[Hesam Hakim @hesamhakim]

We usually frame succinate pooling around HIF-1α stabilization or broad demethylase inhibition. Zhu et al. (Metabolism) uncover an elegant structural role: succinate directly binds VDAC1 at Leu150 (Kⅆ = 8.63 𝜇M), triggering oligomeric pores that release both mtRNA and mtDNA into the cytosol.

The key mechanistic friction: does VDAC1 oligomerization alone suffice for outer membrane nucleic acid transit, or does it require inner-membrane herniation (mPTP opening or BAX/BAK cooperation) to liberate matrix dsRNA to RIG-I/MAVS?
Outstanding breakdown from @changmyung1981 linking TCA failure directly to sterile innate inflammation.
🔗https://t.co/6hnIfWBKKE

[오창명 @changmyung1981]

🧬🫘 What if renal fibrosis begins not simply with mitochondrial energy failure—but when a TCA-cycle metabolite turns mitochondria into a source of “viral-like” RNA that activates innate immunity?

A compelling 2026 study in Metabolism identifies an E2F4–SDHB–succinate–VDAC1–mtRNA–RIG-I/MAVS axis linking tubular metabolic dysfunction directly to inflammation and renal fibrosis.

The proposed mechanism is striking:

E2F4 ↓ → SDHB ↓ → succinate ↑

↓

succinate binds VDAC1-L150

↓

VDAC1 oligomerization

↓

mitochondrial RNA leaks into cytosol

↓

RIG-I → MAVS

↓
innate inflammation
↓
RENAL FIBROSIS
🔬 SDHB is selectively lost in injured renal tubules

Single-cell analysis of UUO kidneys showed that Sdhb was strongly reduced across acute-injury, repairing, and failed-repair proximal tubular populations, while fibrotic genes including Acta2, Col1a1 and Fn1 increased.

The phenotype extended beyond UUO: renal SDHB was also reduced in diabetic and angiotensin-II models. Meanwhile, succinate increased in kidney, serum and urine.

This establishes an important metabolic signature:

Fibrotic kidney = SDHB↓ / succinate↑

But is SDHB loss causal?

🧪 Tubule-specific Sdhb deletion provides the answer

Interestingly, deleting Sdhb specifically in renal tubular cells did not immediately produce overt renal failure.

Creatinine and BUN remained relatively normal, and there was little baseline fibrosis.

Yet underneath that apparently normal kidney:

succinate ↑

mitochondrial swelling/cristae disruption ↑

TNF/NF-κB/chemokine signaling ↑

were already present.

This suggests SDHB deficiency acts as a:

METABOLIC PRIMING EVENT

rather than immediately destroying the kidney.

Add a second injury—UUO—and the phenotype becomes dramatic.

Tubule-specific Sdhb loss increased:

tubular damage
Masson/Sirius-red fibrosis
α-SMA
macrophage infiltration
Cxcl2/Cxcl5/Il36a/Ccl2
and severe mitochondrial structural abnormalities.

Conversely, tubular SDHB overexpression protected the kidney, reducing fibrosis, mitochondrial damage, macrophage infiltration and inflammatory cytokines.

So SDHB is not simply a fibrosis-associated marker.

Manipulating SDHB changes disease severity in both directions.

🤯 The key mechanistic discovery: mitochondrial RNA escapes
SDHB deficiency was associated with increased:
urinary mtRNA
and
cytosolic mitochondrial dsRNA.
The same phenomenon occurred in TGF-β-treated HK-2 cells.

Importantly:

SDHB overexpression → mtRNA leakage ↓

while:

SDHB loss → mtRNA leakage ↑.

The images in Figure 5, page 23 make this particularly clear: dsRNA progressively separates from the mitochondrial compartment during injury, whereas restoring SDHB suppresses that cytosolic signal.

And the authors also found:

urinary mtRNA ↑ in patients with CKD

compared with healthy controls.

That raises an intriguing translational possibility:

Could urinary mtRNA become a non-invasive marker of mitochondrial injury in CKD?

The current study is not sufficient to establish it as a clinical biomarker, but the concept is worth pursuing.

🦠 Why does mtRNA matter?

Mitochondria retain their bacterial evolutionary ancestry.

Once mitochondrial RNA escapes into the cytoplasm, its structures can resemble foreign/viral RNA.

The cell therefore recognizes mtRNA through:

RIG-I

↓

MAVS aggregation

↓
TBK1 / IRF3 / NF-κB signaling
↓

INFLAMMATION

Indeed, UUO and TGF-β increased RIG-I and MAVS aggregation, while SDHB overexpression suppressed both.

This creates a fascinating bridge:

METABOLISM → MITOCHONDRIAL DAMP → INNATE IMMUNITY

rather than metabolism simply altering ATP availability.

🔥 But how does succinate make mtRNA escape?

The investigators systematically tested several mitochondrial-release mechanisms:

VDAC1
BAX
SNX9/mitochondrial-derived vesicles.

Only:

VDAC1 knockdown

substantially prevented succinate-induced mtRNA leakage.
Succinate itself was sufficient to:
induce VDAC1 oligomerization

and

increase cytosolic mtRNA dose-dependently.

Then came the biochemical result:

Succinate directly binds VDAC1.

SPR measured:

Kd = 8.63 μM

considerably stronger than related metabolites including:

α-ketoglutarate: 25.9 μM
itaconate: 36.4 μM
fumarate: 53.1 μM.

So succinate is doing more than acting as a metabolic substrate or signaling metabolite.
It directly engages a mitochondrial membrane protein.
🎯 And they map the interaction to a single VDAC1 residue

Molecular docking predicted four candidate residues:

H122
G148
L150
K174.

Mutational analysis identified:

L150

as critical.

The VDAC1-L150Q mutant markedly suppressed:

SDHB-loss-induced VDAC1 oligomerization

and

succinate-induced mtRNA leakage.

Figure 6 on page 26 provides the mechanistic centerpiece:

SDHB↓

→ succinate↑
→ VDAC1-L150 binding
→ VDAC1 oligomerization
→ mtRNA escape

This gives the study an unusually direct metabolic-to-structural mechanism.
💊 VBIT-4 pharmacologically interrupts the pathway
The investigators next used:

VBIT-4

an inhibitor of VDAC1 oligomerization.

In Sdhb-deficient mice, VBIT-4 reduced:

cytosolic/urinary mtRNA

macrophage infiltration

Cxcl2/Cxcl5/Il36a/Ccl2
RIG-I/MAVS activation.
Figure 7 on page 29 visually shows the rescue: VBIT-4 suppresses dsRNA accumulation and inflammatory macrophage infiltration despite persistent Sdhb deficiency.
Interestingly, the biology extends beyond RNA.

SDHB loss also caused:

mtDNA leakage → cGAS-STING activation

and VBIT-4 reduced this pathway as well.

Thus VDAC1 oligomerization may function as a broader mitochondrial DAMP gateway:

VDAC1 oligomerization

↙︎　　　　　　　　　↘︎
mtRNA leakage mtDNA leakage
↓　　　　　　　　　　 ↓
RIG-I–MAVS cGAS–STING
↘︎　　　　　　　　　↙︎

INNATE INFLAMMATION

🧬 Finally, what causes SDHB loss?

The investigators screened predicted transcriptional regulators of the SDHB promoter.

Among seven candidates:
E2F4
showed the strongest effect.
E2F4 knockdown decreased SDHB mRNA and protein, and E2F4 itself was substantially reduced in UUO kidneys. Promoter-reporter experiments supported direct transcriptional regulation of SDHB by E2F4.

Even better, restoring E2F4 in renal tubules:

SDHB ↑

succinate ↓

mtRNA leakage ↓

RIG-I/MAVS ↓

mitochondrial damage ↓

fibrosis ↓.

This completes the pathway:

E2F4 ↓

↓

SDHB ↓

↓

SUCCINATE ↑

↓

VDAC1-L150 binding

↓

VDAC1 oligomerization

↓
mtRNA + mtDNA leakage
↙︎　　　　　　　　　↘︎
RIG-I–MAVS cGAS–STING
↘︎　　　　　　　　　↙︎

INFLAMMATION
↓
RENAL FIBROSIS
🧠 The broader conceptual message
Kidney fibrosis is usually framed around:

TGF-β
FAO failure
glycolytic reprogramming
fibroblast activation
and
ECM deposition.

This study adds another dimension:

TCA-cycle metabolites can directly control mitochondrial membrane permeability and innate immunity.

Succinate is therefore not simply:

“a metabolite that accumulates when SDH fails.”

In this model it becomes an active molecular messenger:

METABOLITE → VDAC1 → mtRNA → IMMUNE SENSOR → FIBROSIS

That is an elegant example of immunometabolism becoming organ fibrosis.

⚠️ Important limitations

The causal work remains predominantly based on UUO mice and HK-2 cells. Human evidence is limited mainly to increased urinary succinate/mtRNA in CKD; the study does not establish that the complete E2F4–SDHB–VDAC1–RIG-I/MAVS pathway drives human CKD progression.

The authors also show that VDAC1 releases both mtRNA and mtDNA, but they did not directly quantify which pathway—RIG-I/MAVS versus cGAS-STING—contributes more strongly to fibrosis, or whether the two operate synergistically.

And although VBIT-4 provides an attractive proof-of-concept, this remains preclinical pharmacology.

Still, several highly testable translational questions emerge:

Is SDHB reduced in human failed-repair proximal tubules?

Does urinary mtRNA track CKD progression or treatment response?

Does the SDHB-low/succinate-high phenotype define a particular CKD endotype?

Can VDAC1 inhibition prevent AKI→CKD transition?

And perhaps most interestingly:

Could mitochondrial nucleic-acid leakage become a common mechanistic bridge connecting metabolic dysfunction to fibrosis across kidney, heart, liver, and aging tissues?

📄 Zhu Z, Chen P, Shu H, et al.
SDHB deficiency promotes renal fibrosis by triggering mtRNA leakage and activating the RIG-I-MAVS pathway.
Metabolism. 2026. Accepted September 14, 2026.

DOI: 10.1016/j.metabol.2026.156778

#KidneyDisease #CKD #RenalFibrosis #SDHB #Succinate #Mitochondria #mtRNA #VDAC1 #RIGI #MAVS #Immunometabolism #MetabolicReprogramming #KidneyResearch #Fibrosis #Metabolism

[Hesam Hakim @hesamhakim]

Key data from this human multi-omic atlas in @ScienceAdvances comparing regular exercisers vs. sedentary controls:

• Cellular Epigenetics: Cytotoxic CD8⁺ T cells and mature NK cells display an epigenetic "pre-activation" state with increased chromatin accessibility at effector loci.
• Transcriptomics & Lipids: Monocytes show lower basal inflammatory gene programs, coupled with systemic remodeling of circulating lipid species.

Regular exercise doesn’t just broadly "boost" immunity—it rewires chromatin accessibility in cytotoxic lymphocytes while dampening basal innate inflammation.

🔗 https://t.co/J2dePwgbqU

[Eric Topol @EricTopol]

How regular exercise enhances our immune response.
A multiomic blood assessment (single-cell RNA, epigenetics, metabolites, lipids, and cells) with distinct signature for exercise vs sedentary lifestyle @ScienceAdvances
https://t.co/mcgPrLSyJ5

[Hesam Hakim @hesamhakim]

Brilliant engineering from @peterdu_ @Satpathology @BassikLab. Beyond immuno-oncology, deploying match-seq to screen what cell-surface ligands govern the physical interaction between aged/senescent tissue niches and patrolling phagocytes in vivo would be transformative for geroscience.

[Hesam Hakim @hesamhakim]

We typically view succinate accumulation through metabolic or epigenetic lenses—HIF-1α stabilization or broad demethylase inhibition.
This study in Metabolism uncovers a direct structural role: succinate physically binds VDAC1 at Leu150, driving oligomeric pore formation that leaks both mtRNA and mtDNA into the cytosol.

The compelling tension: does VDAC1 oligomerization alone suffice for nucleic acid escape across the outer membrane, or does it require coordinated inner-membrane herniation (via mPTP or BAX/BAK macropores) to liberate inner matrix transcripts to RIG-I/MAVS?
A powerful breakdown from @changmyung1981 showing how TCA metabolite pooling directly triggers sterile innate immunity.
🔗https://t.co/6hnIfWBKKE

[오창명 @changmyung1981]

🧬🫘 What if renal fibrosis begins not simply with mitochondrial energy failure—but when a TCA-cycle metabolite turns mitochondria into a source of “viral-like” RNA that activates innate immunity?

A compelling 2026 study in Metabolism identifies an E2F4–SDHB–succinate–VDAC1–mtRNA–RIG-I/MAVS axis linking tubular metabolic dysfunction directly to inflammation and renal fibrosis.

The proposed mechanism is striking:

E2F4 ↓ → SDHB ↓ → succinate ↑

↓

succinate binds VDAC1-L150

↓

VDAC1 oligomerization

↓

mitochondrial RNA leaks into cytosol

↓

RIG-I → MAVS

↓
innate inflammation
↓
RENAL FIBROSIS
🔬 SDHB is selectively lost in injured renal tubules

Single-cell analysis of UUO kidneys showed that Sdhb was strongly reduced across acute-injury, repairing, and failed-repair proximal tubular populations, while fibrotic genes including Acta2, Col1a1 and Fn1 increased.

The phenotype extended beyond UUO: renal SDHB was also reduced in diabetic and angiotensin-II models. Meanwhile, succinate increased in kidney, serum and urine.

This establishes an important metabolic signature:

Fibrotic kidney = SDHB↓ / succinate↑

But is SDHB loss causal?

🧪 Tubule-specific Sdhb deletion provides the answer

Interestingly, deleting Sdhb specifically in renal tubular cells did not immediately produce overt renal failure.

Creatinine and BUN remained relatively normal, and there was little baseline fibrosis.

Yet underneath that apparently normal kidney:

succinate ↑

mitochondrial swelling/cristae disruption ↑

TNF/NF-κB/chemokine signaling ↑

were already present.

This suggests SDHB deficiency acts as a:

METABOLIC PRIMING EVENT

rather than immediately destroying the kidney.

Add a second injury—UUO—and the phenotype becomes dramatic.

Tubule-specific Sdhb loss increased:

tubular damage
Masson/Sirius-red fibrosis
α-SMA
macrophage infiltration
Cxcl2/Cxcl5/Il36a/Ccl2
and severe mitochondrial structural abnormalities.

Conversely, tubular SDHB overexpression protected the kidney, reducing fibrosis, mitochondrial damage, macrophage infiltration and inflammatory cytokines.

So SDHB is not simply a fibrosis-associated marker.

Manipulating SDHB changes disease severity in both directions.

🤯 The key mechanistic discovery: mitochondrial RNA escapes
SDHB deficiency was associated with increased:
urinary mtRNA
and
cytosolic mitochondrial dsRNA.
The same phenomenon occurred in TGF-β-treated HK-2 cells.

Importantly:

SDHB overexpression → mtRNA leakage ↓

while:

SDHB loss → mtRNA leakage ↑.

The images in Figure 5, page 23 make this particularly clear: dsRNA progressively separates from the mitochondrial compartment during injury, whereas restoring SDHB suppresses that cytosolic signal.

And the authors also found:

urinary mtRNA ↑ in patients with CKD

compared with healthy controls.

That raises an intriguing translational possibility:

Could urinary mtRNA become a non-invasive marker of mitochondrial injury in CKD?

The current study is not sufficient to establish it as a clinical biomarker, but the concept is worth pursuing.

🦠 Why does mtRNA matter?

Mitochondria retain their bacterial evolutionary ancestry.

Once mitochondrial RNA escapes into the cytoplasm, its structures can resemble foreign/viral RNA.

The cell therefore recognizes mtRNA through:

RIG-I

↓

MAVS aggregation

↓
TBK1 / IRF3 / NF-κB signaling
↓

INFLAMMATION

Indeed, UUO and TGF-β increased RIG-I and MAVS aggregation, while SDHB overexpression suppressed both.

This creates a fascinating bridge:

METABOLISM → MITOCHONDRIAL DAMP → INNATE IMMUNITY

rather than metabolism simply altering ATP availability.

🔥 But how does succinate make mtRNA escape?

The investigators systematically tested several mitochondrial-release mechanisms:

VDAC1
BAX
SNX9/mitochondrial-derived vesicles.

Only:

VDAC1 knockdown

substantially prevented succinate-induced mtRNA leakage.
Succinate itself was sufficient to:
induce VDAC1 oligomerization

and

increase cytosolic mtRNA dose-dependently.

Then came the biochemical result:

Succinate directly binds VDAC1.

SPR measured:

Kd = 8.63 μM

considerably stronger than related metabolites including:

α-ketoglutarate: 25.9 μM
itaconate: 36.4 μM
fumarate: 53.1 μM.

So succinate is doing more than acting as a metabolic substrate or signaling metabolite.
It directly engages a mitochondrial membrane protein.
🎯 And they map the interaction to a single VDAC1 residue

Molecular docking predicted four candidate residues:

H122
G148
L150
K174.

Mutational analysis identified:

L150

as critical.

The VDAC1-L150Q mutant markedly suppressed:

SDHB-loss-induced VDAC1 oligomerization

and

succinate-induced mtRNA leakage.

Figure 6 on page 26 provides the mechanistic centerpiece:

SDHB↓

→ succinate↑
→ VDAC1-L150 binding
→ VDAC1 oligomerization
→ mtRNA escape

This gives the study an unusually direct metabolic-to-structural mechanism.
💊 VBIT-4 pharmacologically interrupts the pathway
The investigators next used:

VBIT-4

an inhibitor of VDAC1 oligomerization.

In Sdhb-deficient mice, VBIT-4 reduced:

cytosolic/urinary mtRNA

macrophage infiltration

Cxcl2/Cxcl5/Il36a/Ccl2
RIG-I/MAVS activation.
Figure 7 on page 29 visually shows the rescue: VBIT-4 suppresses dsRNA accumulation and inflammatory macrophage infiltration despite persistent Sdhb deficiency.
Interestingly, the biology extends beyond RNA.

SDHB loss also caused:

mtDNA leakage → cGAS-STING activation

and VBIT-4 reduced this pathway as well.

Thus VDAC1 oligomerization may function as a broader mitochondrial DAMP gateway:

VDAC1 oligomerization

↙︎　　　　　　　　　↘︎
mtRNA leakage mtDNA leakage
↓　　　　　　　　　　 ↓
RIG-I–MAVS cGAS–STING
↘︎　　　　　　　　　↙︎

INNATE INFLAMMATION

🧬 Finally, what causes SDHB loss?

The investigators screened predicted transcriptional regulators of the SDHB promoter.

Among seven candidates:
E2F4
showed the strongest effect.
E2F4 knockdown decreased SDHB mRNA and protein, and E2F4 itself was substantially reduced in UUO kidneys. Promoter-reporter experiments supported direct transcriptional regulation of SDHB by E2F4.

Even better, restoring E2F4 in renal tubules:

SDHB ↑

succinate ↓

mtRNA leakage ↓

RIG-I/MAVS ↓

mitochondrial damage ↓

fibrosis ↓.

This completes the pathway:

E2F4 ↓

↓

SDHB ↓

↓

SUCCINATE ↑

↓

VDAC1-L150 binding

↓

VDAC1 oligomerization

↓
mtRNA + mtDNA leakage
↙︎　　　　　　　　　↘︎
RIG-I–MAVS cGAS–STING
↘︎　　　　　　　　　↙︎

INFLAMMATION
↓
RENAL FIBROSIS
🧠 The broader conceptual message
Kidney fibrosis is usually framed around:

TGF-β
FAO failure
glycolytic reprogramming
fibroblast activation
and
ECM deposition.

This study adds another dimension:

TCA-cycle metabolites can directly control mitochondrial membrane permeability and innate immunity.

Succinate is therefore not simply:

“a metabolite that accumulates when SDH fails.”

In this model it becomes an active molecular messenger:

METABOLITE → VDAC1 → mtRNA → IMMUNE SENSOR → FIBROSIS

That is an elegant example of immunometabolism becoming organ fibrosis.

⚠️ Important limitations

The causal work remains predominantly based on UUO mice and HK-2 cells. Human evidence is limited mainly to increased urinary succinate/mtRNA in CKD; the study does not establish that the complete E2F4–SDHB–VDAC1–RIG-I/MAVS pathway drives human CKD progression.

The authors also show that VDAC1 releases both mtRNA and mtDNA, but they did not directly quantify which pathway—RIG-I/MAVS versus cGAS-STING—contributes more strongly to fibrosis, or whether the two operate synergistically.

And although VBIT-4 provides an attractive proof-of-concept, this remains preclinical pharmacology.

Still, several highly testable translational questions emerge:

Is SDHB reduced in human failed-repair proximal tubules?

Does urinary mtRNA track CKD progression or treatment response?

Does the SDHB-low/succinate-high phenotype define a particular CKD endotype?

Can VDAC1 inhibition prevent AKI→CKD transition?

And perhaps most interestingly:

Could mitochondrial nucleic-acid leakage become a common mechanistic bridge connecting metabolic dysfunction to fibrosis across kidney, heart, liver, and aging tissues?

📄 Zhu Z, Chen P, Shu H, et al.
SDHB deficiency promotes renal fibrosis by triggering mtRNA leakage and activating the RIG-I-MAVS pathway.
Metabolism. 2026. Accepted September 14, 2026.

DOI: 10.1016/j.metabol.2026.156778

#KidneyDisease #CKD #RenalFibrosis #SDHB #Succinate #Mitochondria #mtRNA #VDAC1 #RIGI #MAVS #Immunometabolism #MetabolicReprogramming #KidneyResearch #Fibrosis #Metabolism

[Hesam Hakim @hesamhakim]

The crucial breakthrough from Bingwei Lu's group is identifying the exact target: hyperphosphorylated tau translocates into mitochondria and binds NDUFS3 in Complex I, driving reverse electron transport (RET). Breaking that specific RET-ROS feedback loop is the real therapeutic advance.

[Hesam Hakim @hesamhakim]

The conditional genetics here are clean: proving sobetirome requires cell-autonomous Ppargc1a in both AECs and fibroblasts confirms it's not just systemic dampening. The real hurdle: will THRβ-driven biogenesis resolve established, age-associated matrix crosslinking, or just prevent acute injury?

[Hesam Hakim @hesamhakim]

The PM-Mito phenotype is a fascinating convergence point. Perifascicular COX-negative fibers preceding sIBM suggest that respiratory chain collapse isn't just collateral damage but an active driver of clonal TEMRA CD8+ T-cell homing and local cGAS-STING-mediated Type I IFN persistence.

[Hesam Hakim @hesamhakim]

@Lo_Zanzi @SciImmunology A brilliant mechanistic paradox: while aging cells leak mtDNA via unbuffered ROS to drive chronic cGAS-STING inflammaging, tumors hijack glutaminolysis-derived GSH to suppress mtDNA herniation and evade acute immune surveillance. Organelle redox as an innate immune rheostat.

[Hesam Hakim @hesamhakim]

The NIA Interventions Testing Program (ITP) set the benchmark for rigorous geroscience pharmacology, but waiting three years for terminal mouse mortality curves is fundamentally throttling drug discovery. Austad, Kaeberlein, and Richard Miller lay out an essential roadmap in Frontiers: identifying early-adulthood "aging rate indicators" to screen candidate geroprotectors in months rather than years.

The central tension is separating cause from consequence. Can we develop functional or organellar surrogate readouts—like composite metabolic flexibility or mitochondrial quality control flux—that genuinely predict altered intrinsic aging trajectories across distinct genotypes, rather than simply measuring transient, pathway-specific compensatory stress responses?

Essential reading for anyone working on translational intervention pipelines.

🔗 https://t.co/EI5lpWR9QE

[Agingdoc🩺Dr David Barzilai🔔MD PhD MS MBA DipABLM @agingdoc1]

Aging rate indicators and the search for anti-aging drugs

🔑"By discriminating normal mice from slow-aging mice (even in early adulthood), aging rate indicators could enable more rapid screening of candidate anti-aging drugs in mice and, potentially, in human clinical trials of relatively short duration."

https://t.co/TVaWkHTytp

By @StevenAustad, @mkaeberlein, and Richard Miller @FrontScience

[Hesam Hakim @hesamhakim]

Crucial synthesis @LukensJohnR. Oligodendrocytes are far more than passive insulators—their MCT1/MCT2-mediated lactate shuttling to sustain axonal mitochondria is a critical metabolic lifeline. When this fails, whether via aging or neuroinflammation, axonal collapse is inevitable.

[Hesam Hakim @hesamhakim]

@LauraMinquini @BBParis1984 @BBParis1984’s work on ovarian aging as an accelerated geroscience pacemaker is critical. The key mechanistic puzzle: are microbial shifts driving primordial follicle depletion via circulating inflammatory DAMPs or by disrupting local ovarian steroidogenic mitochondrial flux?

[Hesam Hakim @hesamhakim]

@SatchinPanda The real bottleneck for native Urolithin A has always been rapid Phase II hepatic glucuronidation and dismal CNS penetrance. If UA-30 achieves sustained nanomolar free fractions across the BBB to induce PINK1/Parkin or BNIP3 flux in motor neurons, that’s a massive step forward.

[Hesam Hakim @hesamhakim]

Excellent paper @smartelegans @SimranM14914635! Delineating how RICTOR coordinates the methionine cycle across host-microbe boundaries to selectively tune mitophagic clearance—rather than relying on canonical bulk autophagy—is a brilliant mechanistic advance for longevity biology.

[Hesam Hakim @hesamhakim]

Fission and mitophagy aren't just housekeeping—they function as an active innate immune weapon.

New in @LSAjournal from @RutgersU & @Waksman_Inst:
• The Mechanism: An antimicrobial compound promotes coordinated mitochondrial fission, rapidly routing damaged fragments into downstream mitophagy.
• The Macrophage Phenotype: Rather than compromising host energy, this clearance program sharpens macrophage bactericidal efficacy against intracellular bacterial infection.
• Organismal Geroscience: In C. elegans, the same organellar quality-control cascade extends systemic lifespan, confirming that mitohormetic clearance drives both pathogen defense and longevity.

Further proof that mitochondrial fragmentation is context-dependent: when paired with intact autophagic flux, targeted fission preserves host defense and tissue resilience.
🔗 https://t.co/1c6ML7llBs

[LifeScienceAlliance @LSAjournal]

A potent antimicrobial promotes mitochondrial fission and mitophagy, boosting the effectiveness of macrophages in defending against bacterial infection and promoting lifespan extension in C. elegans.
@RSUinfo @RutgersU @RutgersNB @Waksman_Inst
https://t.co/rOCjRAb0Do

[Hesam Hakim @hesamhakim]

Critical advance. Decoupling TMRM intensity from FLIM lifetime signatures and exposing coverslip hypoxia as an imaging artifact resolves a massive blind spot. Proving that axonal vs. somatic mitochondria age along divergent biophysical trajectories changes how we define geroscience endpoints.

[Hesam Hakim @hesamhakim]

Superb mechanistic breakdown from @changmyung1981 on the landmark 2026 @Nature study establishing MFF as a central execution switch in ferroptosis:

Organelle fragmentation is not merely a passive byproduct of dying cells—it is an active, coordinated death program:
• The Post-Translational Switch: Lipid peroxidation generates CYP4A11-derived 17-HETE, driving PKCβ activation and DUSP22 suppression to selectively phosphorylate MFF at Ser155.
• Multi-Organelle Coordination: MFF-Ser155 phosphorylation recruits DRP1 to drive synchronized fission across both mitochondria and peroxisomes, establishing a reciprocal ROS-amplification loop at contact sites.
• The Nucleic Acid Cascade: Downstream cristae collapse and mtROS trigger VDAC1 oligomerization, driving cytosolic mtDNA extrusion and secondary cGAS–STING signaling.

Rigorous proof that organelle contact kinetics and structural fission machinery directly dictate cell fate and innate immune sensing.

[오창명 @changmyung1981]

🧬🔥 Ferroptosis may not simply damage mitochondria—it actively recruits an organelle-fission program that helps drive cells past the point of no return.

A major 2026 Nature study identifies mitochondrial fission factor (MFF) as a ferroptosis-selective signaling node linking lipid peroxidation to coordinated mitochondrial + peroxisomal fragmentation, oxidative amplification, and ultimately cell death.

The proposed pathway is remarkably coherent:

Ferroptotic stress

↓
CYP4A11 → 17-HETE ↑
↓
PKCβ activation + DUSP22 suppression
↓
MFF-Ser155 phosphorylation
↓
DRP1 recruitment
↓
mitochondrial + peroxisomal fission
↓
organelle ROS amplification + metabolic dysfunction
↓

FERROPTOSIS

And the authors go beyond mechanism: they develop MFF–SPARK, a live-cell biosensor for this phosphorylation event, then use it for drug screening and identify avermectin B1 as a pharmacological activator of the PKCβ–MFF axis.
🔬 The story began with unbiased phosphoproteomics
The investigators compared phosphorylation landscapes during:

ferroptosis
apoptosis
necroptosis

and quantified:
7,587 phosphosites
across

3,144 phosphoproteins.

PCA separated the different death modalities, suggesting that regulated cell-death programs carry distinct phosphorylation signatures.

Among candidate ferroptosis-associated phosphoproteins, MFF stood out.

MFF overexpression increased sensitivity to both RSL3 and erastin, whereas MFF knockdown provided the strongest protection among tested candidates. Most importantly:

MFF Ser155 phosphorylation was selectively enriched during ferroptosis.

Figure 1 on page 2 provides a nice visual summary of this discovery pipeline—from phosphoproteomics to functional screening and genetic validation.
🧬 MFF appears surprisingly selective for ferroptosis
CRISPR deletion of MFF markedly reduced cell death caused by:

RSL3
erastin
genetic GPX4 loss

and re-expression of MFF restored sensitivity.

Yet MFF loss had little effect on experimentally induced:

apoptosis

or

necroptosis.

The effect also generalized across multiple cell types, including:

HeLa
HT-1080
SH-SY5Y
HepG2
A549.

MFF deficiency preserved several classical ferroptosis phenotypes:

lipid peroxidation ↓
ROS ↓
LDH release ↓
long-term clonogenic survival ↑.

This makes MFF more than another mitochondrial morphology protein.

It functions as a selective regulator of ferroptotic susceptibility.

🔥 The critical partner is DRP1
MFF is an outer-membrane adaptor that recruits DRP1, the canonical mitochondrial fission GTPase.
Deleting either:

MFF

or

DRP1

strongly protected cells against RSL3-induced ferroptosis.

And the genetic epistasis experiment was particularly informative:

in MFF/DRP1 double-KO cells, ferroptotic sensitivity could be restored only when:

MFF + DRP1 were re-expressed together.
Other DRP1 adaptors—FIS1, MIEF1 and MIEF2—did not reproduce this effect.
So ferroptotic fission appears to use a surprisingly specific:
MFF → DRP1
module.

🤯 But MFF does not control only mitochondria

This may be the paper's most important conceptual advance.
MFF also participates in peroxisomal fission.
During ferroptosis, the authors observed:
mitochondrial fragmentation

AND

peroxisomal fragmentation.

Both compartments accumulated ROS, and deleting MFF or DRP1 suppressed fragmentation in both organelles.

Even more interestingly, ferroptotic stress increased physical contact between:

MITOCHONDRIA ↔ PEROXISOMES

and compartment-specific ROS sensors showed reciprocal ROS amplification between them.

This crosstalk was already detectable within approximately:

60 minutes after RSL3 exposure.

Figure 2 on page 4 captures this beautifully: mitochondrial and peroxisomal fragmentation, ROS generation, organelle proximity, and MFF dependence are integrated into one model.

Thus ferroptosis may involve an:

inter-organelle oxidative feed-forward loop.

⚡ Mitochondrial fission becomes functional failure

MFF deletion preserved:

ATP

oxygen consumption

ETC complex I–V activity

during ferroptotic stress.

Electron microscopy also showed that RSL3-induced cristae disruption depended specifically on the MFF–DRP1 axis.

So the sequence is not simply:

ferroptosis → dying mitochondria fragment.

The data support something closer to:

MFF-mediated fission

↓
cristae disruption
↓
ETC dysfunction
↓
mtROS ↑
↓

ferroptotic amplification.

In this framework, organelle fragmentation is part of the execution machinery, not merely a morphological consequence of dying cells.

🧬 MFF also opens another amplification pathway: mtDNA

MFF-dependent mitochondrial dysfunction increased:

mtROS

↓

VDAC1 oligomerization

↓

cytosolic mtDNA release

↓

cGAS–STING activation.

Inhibiting VDAC oligomerization suppressed mtDNA release and reduced ferroptosis.

Mito-TEMPO similarly prevented VDAC1 oligomerization and mtDNA release, placing mitochondrial ROS upstream.

Because mtDNA release occurred relatively late, the authors interpret cGAS–STING primarily as an amplifier downstream of mitochondrial dysfunction, rather than the initiating ferroptotic event.

This adds an intriguing inflammatory dimension:

lipid peroxidation → organelle remodeling → mtDNA danger signaling

may be mechanistically connected within ferroptotic cells.

🧪 Peroxisomes contribute through metabolism as well as ROS

MFF deficiency increased expression of:

ACOX1

and

catalase

through a compensatory program involving:

PPARα activation.
Disrupted peroxisomal fission enhanced β-oxidation-associated signaling, while targeted peroxisomal ROS activated NRF2 and catalase expression.
Thus MFF appears to coordinate two metabolically specialized organelles:
mitochondria → ETC / ATP / mtROS
and
peroxisomes → fatty-acid oxidation / ROS / lipid metabolism.
Their coordinated remodeling may help explain why ferroptosis is so intimately linked to cellular metabolism.

🔥 What activates MFF?

Targeted eicosanoid metabolomics identified an unexpected lipid signal:

17-HETE

Among accumulated eicosanoids, 17-HETE specifically enhanced MFF-dependent ferroptosis.

17-HETE alone induced:

mitochondrial fragmentation
peroxisomal fragmentation
increased organelle association

and during ferroptotic stress further increased:

organelle ROS
and
mtDNA release.

The authors then traced endogenous 17-HETE production upstream to:

CYP4A11.

CYP4A11 deletion reduced endogenous 17-HETE accumulation and ferroptosis, while exogenous 17-HETE bypassed CYP4A11.

That establishes:

CYP4A11 → 17-HETE → MFF

as a lipid-metabolism-to-organelle-dynamics axis.

🎯 Ser155 is the critical molecular switch

The authors engineered:

MFF-WT

MFF-S155A — non-phosphorylatable

MFF-S155D — phosphomimetic.

Only the S155A mutant preserved elongated mitochondrial and peroxisomal morphology and strongly resisted ferroptosis.

Meanwhile, MFF-Ser155 phosphorylation progressively increased after:

RSL3
and
erastin

but disappeared with ferroptosis inhibitors:

liproxstatin-1
ferrostatin-1
DFO.

It was not induced during apoptosis or necroptosis.

Intriguingly, increased MFF-S155 phosphorylation was also observed in mouse models of:

cardiac ischemia–reperfusion

and

high-fat/high-cholesterol diet-induced fatty liver disease.

That raises the possibility that MFF-S155 phosphorylation could become a useful tissue ferroptosis biomarker, although this clearly requires broader validation.

👀 Then they built a live ferroptosis sensor

The investigators converted this phosphorylation event into:

MFF–SPARK

a phase-separation-based biosensor.

When MFF Ser155 becomes phosphorylated, phosphopeptide-binding interactions drive formation of visible:

🟢 green fluorescent droplets.

Dephosphorylation reverses them.

With RSL3:

signal appeared within ~20 minutes
and reached approximately:
4.2-fold activation.

Other ferroptosis triggers—including ML162, erastin, FINO2 and iron—also activated the sensor, whereas apoptosis and necroptosis stimuli did not.

Figure 4 on page 7 is one of the most visually compelling parts of the paper: ferroptotic signaling is literally converted into dynamic phase-separated fluorescent droplets.
That makes MFF–SPARK potentially useful for:
real-time ferroptosis kinetics
single-cell heterogeneity
drug screening
and
pathway discovery.

🧬 MFF phosphorylation is controlled by a kinase–phosphatase pair

Using the biosensor, the investigators identified:

PKCβ = kinase

and

DUSP22 = phosphatase.

PKCβ was necessary and sufficient for MFF-S155 phosphorylation, and kinase-dead PKCβ failed to activate the pathway.

Conversely, DUSP22 directly interacted with MFF and dephosphorylated Ser155.

Loss of DUSP22:

MFF phosphorylation ↑

lipid peroxidation ↑

ferroptosis ↑.

And ferroptotic stress does both simultaneously:

PKCβ activation ↑

while

DUSP22 expression ↓.
So the molecular switch is pushed strongly toward phosphorylation:
PKCβ → MFF-S155 ←| DUSP22

The mechanistic diagram in Figure 4, page 7 summarizes this particularly well.

💊 Then MFF–SPARK becomes a drug-discovery platform
The authors screened approximately:
1,000 mitochondria-targeted compounds

using MFF–SPARK.

The strongest hit was:

avermectin B1

a macrocyclic compound traditionally used for antiparasitic/insecticidal applications.

Avermectin B1:

MFF-S155 phosphorylation ↑
mitochondrial fission ↑
peroxisomal fission ↑
organelle ROS ↑
ferroptotic sensitivity ↑.

All of these effects were strongly dependent on MFF.

Even better, the authors identified its direct upstream target:

PKCβ

with microscale thermophoresis showing:

Kd ≈ 0.22 μM.

Figure 5 on page 9 elegantly links the screening platform to PKCβ binding and ultimately tumor experiments.

🐭 Can this actually sensitize tumors to ferroptosis?

In HCT-116 xenografts, the investigators tested:

avermectin B1

IKE

and

avermectin B1 + IKE.

Either monotherapy produced relatively modest tumor effects.

But:

AVM B1 + IKE → substantially stronger tumor suppression

with increased:
lipid peroxidation
MDA
4-HNE
in tumor tissue.
Adding liproxstatin-1 reversed the effect, supporting ferroptosis as the relevant mechanism.
The tumor-growth curves and histology in Figure 5, page 9 make this combination effect particularly clear.

At the tested dose and schedule, the authors reported no obvious body-weight changes, major-organ histopathology, or detectable abnormalities in ALT, AST, BUN, or creatinine.

🧠 The conceptual shift is important

The canonical ferroptosis model emphasizes:

GPX4 / FSP1

SLC7A11

iron

PUFA lipid peroxidation.

This study adds another layer:

ORGANELLE DYNAMICS

The authors propose that GPX4 failure initiates oxidative stress, but:

MFF-dependent organelle remodeling acts as an executional amplifier.

So ferroptosis may be better represented as:

GPX4/SLC7A11 failure

↓
lipid peroxidation
↓

CYP4A11–17-HETE

↓
PKCβ ↑ / DUSP22 ↓
↓

MFF-S155-P

↓
DRP1
↙︎　　　　　　　　　↘︎
MITOCHONDRIAL FISSION PEROXISOMAL FISSION
↓　　　　　　　　　　　　 ↓
ETC failure / mtROS ROS / metabolic remodeling
↘︎　　　　　　　　　　　 ↙︎
mitochondria–peroxisome oxidative crosstalk

↓
VDAC → mtDNA → cGAS–STING
+
lipid ROS amplification
↓

FERROPTOTIC COMMITMENT

The full model shown in Extended Data Figure 10, page 35 is particularly effective: it visually integrates the lipid signal, PKCβ/DUSP22 switch, MFF phosphorylation, DRP1 recruitment, both organelles, and the pharmacological entry point.

⚠️ Translation requires caution

The therapeutic tumor experiments used HCT-116 xenografts in immunodeficient mice, not spontaneous or immunocompetent tumor models. The xenograft experiment used female BALB/c nude mice, while systemic safety testing used male C57BL/6 mice; sex was not treated as a biological variable.

The authors also acknowledge that PKCβ is probably not the only upstream regulator of MFF. Even when PKC activity was absent, wild-type MFF retained some ferroptosis-promoting activity compared with MFF deletion or the phospho-dead mutant.

And avermectin B1 should not be interpreted as a ready-to-use anticancer ferroptosis therapy. The study establishes preclinical proof-of-concept for pharmacologically engaging PKCβ–MFF, not clinical efficacy.

🎯 The most interesting discovery may ultimately be MFF itself

This paper turns MFF from a conventional mitochondrial-fission adaptor into something much more interesting:

a sensor

an executional amplifier

[Hesam Hakim @hesamhakim]

Excellent mechanistic overview from @dantawfik on mitochondria as central gatekeepers of innate immune activation:

The transition from metabolic organelle to sterile pathogen proxy depends on membrane integrity and quality control thresholds:

• The Molecular Breach: Sub-lethal stress drives BAX/BAK macropores and VDAC oligomerization, allowing unmethylated mtDNA nucleoids and externalized cardiolipin to escape mitochondrial containment.
• Dual PRR Activation: Cytosolic mtDNA engages cGAS–STING to drive Type I interferons, while cardiolipin mislocalization directly seeds the NLRP3 inflammasome platform to mature IL-1β.
• Mitophagy as an Immune Checkpoint: Autophagosomal capture and lysosomal degradation of depolarized mitochondria prevent DAMP extrusion before pattern recognition receptors can trigger a feed-forward inflammatory loop.

In aging and chronic disease, loss of organellar clearance is functionally indistinguishable from chronic, low-grade intracellular infection.

[Daniel Tawfik @dantawfik]

Your mitochondria can trigger the same inflammatory alarms your immune system uses to fight bacteria. That's because mitochondria are bacteria, or at least they were 1.5 billion years ago.

A Nature Reviews Immunology paper maps the molecular mechanisms of how mitochondria control inflammation, the safeguards that normally prevent false alarms, and what happens when those systems fail.

The core problem: mitochondria are ancient bacteria that your cells absorbed roughly 1.5 billion years ago. They still carry bacterial signatures. Your immune system evolved to recognize bacterial molecules as threats. When mitochondria get damaged and leak their contents, your immune system can't distinguish between a broken mitochondrion and an actual infection.

Mitochondria contain multiple damage-associated molecular patterns, or DAMPs. These are molecules that trigger immune responses when detected outside their normal location:

• Mitochondrial DNA (mtDNA): Unmethylated, circular DNA that resembles bacterial genomes
• Cardiolipin: A phospholipid normally confined to the inner mitochondrial membrane
• N-formyl peptides: Proteins with bacterial-style chemical signatures
• ATP and other metabolites: Energy molecules that signal danger when released

These molecules activate pattern recognition receptors, the sensors your immune system uses to detect threats.

The most studied pathway involves mitochondrial DNA activating a detection system called cGAS-STING. Here's how it works:

When mitochondria become damaged, their outer membrane develops holes. Think of it like a breach in a container. The mitochondrial DNA, which normally stays sealed inside, leaks out into the cytosol, the liquid interior of your cell.

An enzyme called cGAS patrols the cytosol looking for DNA that shouldn't be there. When it finds mitochondrial DNA floating around, it produces a signaling molecule called cGAMP. This molecule activates another protein called STING, which sits on the endoplasmic reticulum, a membrane network inside cells.

STING activation triggers the production of interferons, immune signaling proteins your body normally makes to fight viral infections. Your cell responds to leaked mitochondrial DNA the same way it responds to a virus.

A second pathway involves cardiolipin, a fat molecule that normally stays on the inner membrane of mitochondria. When cardiolipin appears on the outer surface or leaks into the cytosol, it activates the NLRP3 inflammasome. This is a multi-protein assembly that acts like an alarm system. Once activated, it produces inflammatory molecules called cytokines, specifically IL-1β, which trigger inflammation throughout surrounding tissue.

Your cells have multiple safeguards to prevent mitochondria from triggering these inflammatory pathways:

Apoptosis suppresses inflammation. Apoptosis is programmed cell death, a controlled self-destruction process. When a cell commits to dying, it activates enzymes called caspases. These enzymes act like molecular scissors, rapidly cutting up mitochondrial DNA and other inflammatory molecules before they can activate immune sensors. Two key studies demonstrated that strong caspase activation prevents the cGAS-STING pathway from turning on during cell death.

Mitophagy removes damaged mitochondria. Mitophagy is selective autophagy, meaning cellular recycling that targets only mitochondria. When mitochondria lose their electrical charge, called membrane potential, or accumulate too much damage, they get tagged with molecular markers. These tags signal cellular machinery to engulf the damaged mitochondrion inside a double-membrane structure called an autophagosome. The autophagosome fuses with a lysosome, which contains digestive enzymes that break down the damaged mitochondrion completely. This happens before its contents can leak out and trigger inflammation.

Chromatin packaging inhibits cGAS. Your nuclear DNA is wrapped around proteins called histones and packaged into a structure called chromatin. This packaging prevents cGAS from detecting it. Mitochondrial DNA lacks this protective packaging, which makes it a much stronger activator of cGAS when it reaches the cytosol. This difference explains why leaked mitochondrial DNA triggers inflammation while nuclear DNA, even when exposed during normal cell division, generally does not.

The pathological consequences emerge when these safeguards fail or get overwhelmed.

Insufficient mitophagy allows damaged mitochondria to accumulate. Their contents gradually leak into the cytosol, triggering chronic low-grade inflammation. This process contributes to age-related inflammatory diseases, neurodegenerative disorders, and metabolic dysfunction.

Defective apoptosis prevents proper DAMP degradation. Cells that can't complete programmed death release intact mitochondrial components that activate stronger inflammatory responses. This mechanism appears in some autoimmune conditions where defective clearance of dying cells drives chronic inflammation.

Excessive mitochondrial stress overwhelms quality control. When mitochondrial damage happens faster than mitophagy can remove it, cells release mitochondrial DAMPs even with functioning safeguards. This occurs during ischemia-reperfusion injury, severe metabolic stress, and certain infections that specifically target mitochondria.

The inflammation can become bidirectional. Inflammatory signals like TNF-α and interferons feed back to impair mitochondrial function, creating cycles where inflammation damages mitochondria and damaged mitochondria amplify inflammation.

Several human diseases show clear links to dysregulated mitochondria-driven inflammation:

Parkinson's disease involves mitochondrial dysfunction in dopaminergic neurons. Defective mitophagy allows damaged mitochondria to trigger inflammatory responses that accelerate neurodegeneration.

Systemic lupus erythematosus shows elevated mtDNA in circulation and enhanced cGAS-STING activation. Defective clearance of dying cells releases mitochondrial contents that drive autoantibody production.

COVID-19 severity correlates with cGAS-STING pathway activation. Viral infection triggers mitochondrial DNA release, and excessive type I interferon responses contribute to immunopathology.

Cancer cells sometimes exploit insufficient mitochondria-driven inflammation. Tumors with defective inflammatory signaling evade immune surveillance, while therapeutic interventions that trigger controlled mitochondrial DAMP release can enhance anti-tumor immunity.

The therapeutic implications point in two directions.

For inflammatory diseases, blocking mitochondrial DAMP signaling could reduce pathological inflammation. cGAS-STING inhibitors are in development for autoimmune conditions. Enhancing mitophagy might prevent DAMP accumulation before inflammation starts.

For cancer and infections, activating mitochondrial DAMP release could boost immunity. Some chemotherapy drugs work partly by triggering immunogenic cell death that releases mitochondrial DAMPs. Radiation therapy activates similar pathways.

The central insight is that mitochondrial quality control and inflammation are mechanistically linked. The same cellular machinery that maintains energy metabolism also determines inflammatory state. When mitochondria function properly and damaged ones get cleared efficiently, inflammation remains appropriately regulated. When quality control fails, mitochondrial DAMPs drive pathological inflammatory responses.

Your immune system treats broken mitochondria like invading bacteria because, evolutionarily, that's exactly what they once were. The molecular signatures persist. What determines health versus disease is how effectively your cells maintain mitochondrial integrity and clear damaged mitochondria before they trigger inappropriate immune activation.

[Hesam Hakim @hesamhakim]

@Deep_Chora Superb breakdown. Tracing mitochondrial fragmentation upstream of DRP1 to ER-anchored INF2/Spire1 actin nucleation and MFF oligomerization provides the exact structural framework needed to test whether transferable serum/IgG factors are acting directly on MAM tethering.

[Hesam Hakim @hesamhakim]

Rigorous human bioenergetics in @JPhysiol (Motanova et al.):

What happens to mitochondrial phenotype during 10-day bed rest in older adults?

• The Paradox: Mitochondrial volume density (mass) drops, but OXPHOS capacity per unit organelle actually increases—intrinsic respiratory efficiency is conserved.
• The Primary Insult: A marked rise in non-phosphorylating H₂O₂ emission occurs upstream of any respiratory complex or supercomplex degradation, driven by impaired antioxidant clearance.
• The Dynamics: Dephosphorylation of DRP1 at Ser637, priming fission and mitophagy pathways to trim mitochondrial mass under disuse.

Critical evidence that disuse-driven metabolic decline in aging is initiated by redox uncoupling and structural turnover, not immediate ETC failure.

[Nick Krontiris @nick_krontiris]

Preserved mitochondrial respiration in presence of oxidative stress and reduced mitochondrial mass after 10-day bed rest in older adults (open access)

https://t.co/BibPwOtWKN