Hypothesis

In early MASLD, zone‑specific hypoxia stabilizes HIF‑1α, which directly represses Nrf2 transcriptional activity and downstream GPX4 expression. Loss of GPX4 sensitizes pericentral hepatocytes to lipid‑peroxide‑driven ferroptosis. Ferroptotic hepatocyte death releases DAMPs (e.g., HMGB1, oxidized phospholipids) that activate TLR4 on hepatic stellate cells, triggering their transition to a fibrogenic phenotype and collagen deposition. Thus, the hypoxia‑HIF‑1α‑Nrf2‑GPX4 axis couples metabolic stress to ferroptosis‑initiated fibrosis before extensive steatosis accumulates.

Mechanistic Rationale

• HIF‑1α is known to compete for CBP/p300 co‑activators, limiting Nrf2‑driven antioxidant gene transcription.
• Nrf2 normally upregulates GPX4, SLC7A11, and glutathione synthesis; its inhibition lowers the lipid‑repair capacity.
• Zone 3 oxygen gradient already limits fatty acid oxidation, raising intracellular lipid peroxides; HIF‑1α‑mediated Nrf2 suppression pushes cells over the ferroptosis threshold.
• Ferroptotic DAMPs are potent activators of TLR4‑MyD88‑NFκB signaling in stellate cells, a pathway shown to drive collagen‑I production.

Testable Predictions

1. Genetic or pharmacologic HIF‑1α inhibition in zone 3 hepatocytes (e.g., using AAV8‑HIF‑1α shRNA under a CYP2E1 promoter) will:

   • Increase Nrf2 target gene expression and GPX4 protein.
   • Reduce lipid‑peroxide markers (C11‑BODIPY581/591, 4‑HNE) and ferroptosis death (liproxstatin‑1 sensitive) despite unchanged steatosis.
   • Lower hepatic stellate cell activation (α‑SMA, collagen‑1) and fibrosis scores in aged mice fed a methionine‑choline deficient diet.

2. Pharmacologic Nrf2 activation (e.g., sulforaphane) will rescue GPX4 expression and attenuate ferroptosis even when HIF‑1α remains high, placing Nrf2 downstream of HIF‑1α.

3. Biomarker correlation: In human MASLD biopsies, AHGS enrichment will inversely correlate with nuclear Nrf2 and GPX4 levels specifically in pericentral regions, and this correlation will be strongest in patients with mild‑to‑moderate steatosis (<67% hepatocytes) but elevated HIF‑1α staining (pimonidazole adducts).

4. Falsification: If HIF‑1α knock‑down fails to improve GPX4, reduce ferroptosis markers, or attenuate fibrosis despite clear zone‑specific hypoxia, the hypothesis is refuted; alternative drivers (e.g., mitochondrial ROS independent of Nrf2) would then be implicated.

Experimental Approach

• Use lineage‑tracing CYP2E1‑CreERT2;Rosa26‑tdTomato mice to target zone 3.
• Administer tamoxifen to induce Cre, then inject AAV8‑HIF‑1α shRNA or control.
• Feed mice a Western diet supplemented with fructose to induce MASLD, assess at 12 weeks.
• Measure steatosis (Oil‑Red‑O), hypoxia (pimonidazole), AHGS (snRNA‑seq or qPCR for signature genes), ferroptosis (GPX4 Western, lipid‑ROS), and fibrosis (Sirius Red, hydroxyproline).
• Parallel human cohort: obtain laser‑capture pericentral hepatocytes from MASLD biopsies, perform immunostaining for HIF‑1α, Nrf2, GPX4, and correlate with AHGS score and fibrosis stage.

Implications

Confirming this link would reveal a pre‑fibrotic, hypoxia‑driven ferroptosis checkpoint that can be intercepted by HIF‑1α antagonists or Nrf2 activators, widening the therapeutic window beyond ferroptosis inhibitors alone and providing a mechanistic bridge between metabolic zonation and early fibrogenesis.