Hypothesis

In metabolic dysfunction‑associated steatotic liver disease (MASLD), zone 3 hepatocytes undergo mitochondria‑dependent ferroptosis that releases lipid‑peroxidation‑rich exosomes. These exosomes carry damaged mitochondrial DNA, oxidized phospholipids, and specific microRNAs (e.g., miR‑122‑5p, miR‑192) that induce ferroptosis susceptibility and an aging gene signature in neighboring zone 1 and 2 hepatocytes. Blocking mitochondrial ferroptosis or exosome secretion will therefore prevent the zonated propagation of hepatocyte aging and reverse systemic metabolic dysfunction even after fibrosis has begun.

Mechanistic Rationale

Zone 3 hypoxia stabilizes HIF‑2α, which upregulates transferrin receptor 1 (TFRC) and downregulates ferritin heavy chain (FTH1), expanding the labile iron pool and sensitizing mitochondria to ferroptosis [1]. Mitochondrial ferroptosis generates 4‑hydroxynonenal (4‑HNE)–adducted phospholipids that are packaged into exosomes via the ESCRT‑III pathway. Exosomal 4‑HNE adducts modify KEAP1 in recipient cells, causing transient NRF2 activation that paradoxically upregulates SREBP‑1c–driven lipogenesis, creating a feed‑forward loop of lipid overload and further iron mobilization [2]. Simultaneously, exosomal miR‑122‑5p suppresses SIRT1 in target hepatocytes, deacetylating PGC‑1α and impairing mitochondrial antioxidant defenses, thereby lowering the threshold for ferroptosis [3]. This mechanism explains why over 17% of hepatocytes acquire an aging signature in MASLD livers despite the original insult being confined to zone 3.

Predictions

1. In MASH mice, zona‑restricted mitochondrial ferroptosis (measured by mitochondrial C11‑BODIPY oxidation) will exceed cytosolic ferroptosis by 2‑fold in zone 3.
2. Exosomes isolated from zone 3 hepatocytes will contain elevated 4‑HNE‑phospholipids, mtDNA fragments, and miR‑122‑5p/miR‑192, and will induce AHGS+ markers and mitochondrial iron uptake when applied to zone 1/2 hepatocytes in vitro.
3. Genetic or pharmacological blockade of mitochondrial ferroptosis (using MitoFerrox) or exosome release (using GW4869 or Rab27a knock‑down) will reduce the proportion of AHGS+ hepatocytes by >50% in advanced MASH livers, decrease fibrosis area by ~40%, and improve glucose tolerance compared with ferroptosis inhibition alone.
4. Circulating exosomal 4‑HNE‑phospholipid levels will correlate with AHGS+ burden (AUC >0.85) and will decline following combined MitoFerrox + GW4869 treatment.

Experimental Design

• Model: Male C57BL/6J mice fed a choline‑deficient, high‑fat, high‑fructose (CDHFHF) diet for 20 weeks to establish advanced MASH.
• Interventions: (a) Vehicle, (b) Liproxstatin‑1 (ferroptosis inhibitor), (c) MitoFerrox (mitochondrial iron chelator), (d) GW4869 (exosome secretion inhibitor), (e) MitoFerrox + GW4869.
• Readouts: Zone‑specific mitochondrial ferroptosis (mito‑C11‑BODIPY + immunofluorescence), exosome characterization (NTA, western blot for CD63, 4‑HNE‑phospholipid dot blot, small‑RNA seq), AHGS+ quantification (RNAscope for p16, SASP markers), fibrosis (Sirius Red area), glucose tolerance test, plasma exosome analytics.
• Statistical: Two‑way ANOVA with Tukey post‑hoc; n=8 per group to detect 30% effect size with 80% power.

Potential Pitfalls and Alternatives

If mitochondrial ferroptosis inhibition fails to reduce exosome release, we will test whether inhibiting ACSL4 (with ferrostatins) diminishes 4‑HNE‑phospholipid loading into exosomes. Conversely, if exosome blockade does not affect distal AHGS+ spread, we will examine tunneling nanotube‑mediated transfer of oxidized mitochondria as an alternative route.

This hypothesis is directly falsifiable: a lack of exosomal 4‑HNE‑phospholipid or miRNA transfer, or absence of improvement in AHGS+ burden and systemic metabolism after combined mitochondrial ferroptosis and exosome inhibition, would refute the proposed mechanism.