Hypothesis

The membrane‑catalyzed nucleation mechanism that drives toxic hIAPP aggregation in pancreatic β‑cells is a conserved structural failure motif present in other metabolic tissue proteins. Under chronic nutrient excess, these proteins undergo analogous anionic‑lipid‑mediated amyloid formation on organelle membranes (ER, mitochondria, plasma membrane) in hepatocytes, adipocytes, and myocytes, triggering a coordinated UPR^ER‑UPR^mt response, inflammasome activation, and systemic insulin resistance.

Mechanistic Reasoning

1. Shared amphipathic segments – Bioinformatic scanning of highly expressed metabolic proteins (e.g., adiponectin, apolipoprotein B, myosin heavy chain) reveals short segments with high β‑propensity and clustered acidic residues analogous to the hIAPP core (residues 20‑29). These segments are predicted to interact preferentially with anionic lipids such as phosphatidylserine and cardiolipin, which are enriched in stress‑exposed membranes of liver, adipose, and muscle.

2. Membrane‑catalyzed nucleation – As shown for hIAPP, anionic lipids lower the critical nucleus size, promoting primary nucleation and secondary fibrillization at membrane surfaces. We propose that lipid‑induced conformational switching of these metabolic proteins creates seeding‑competent oligomers that can cross‑seed each other, propagating proteostatic stress across tissues via extracellular vesicles or interstitial fluid.

3. UPR coupling – In β‑cells, PERK‑eIF2α‑ATF4 signaling coordinates UPR^ER with mitochondrial UPR by upregulating chaperones like GRP75 and Lon protease. Similar chaperone induction is expected in hepatocytes and adipocytes when membrane‑bound oligomers accumulate, leading to a chronic, low‑grade UPR that blunts transcriptional identity (e.g., reduced HNF4α in liver, PPARγ in adipose) and impairs autophagy.

4. Macrophage amplification – Resident tissue macrophages (Kupffer cells, adipose tissue macrophages, muscle‑associated macrophages) possess inflammasome sensors that detect amyloid‑like oligomers, resulting in caspase‑1 activation and IL‑1β release. This creates a feed‑forward loop where macrophage‑derived cytokines exacerbate ER stress in parenchymal cells, mirroring the β‑cell–macrophage axis observed in islets.

5. Cross‑tissue propagation – Oligomers released from one tissue can seed aggregation in another, explaining the observed correlation between hepatic steatosis, adipose fibrosis, and muscle insulin resistance in obesity and T2D. The cross‑seeding of hIAPP with tau suggests that similar prion‑like mechanisms may operate metabolically.

Testable Predictions

• Prediction 1: Synthetic peptides corresponding to the candidate motifs from adiponectin, ApoB, and myosin will exhibit lipid‑dependent aggregation kinetics comparable to hIAPP when incubated with liposomes containing phosphatidylserine or cardiolipin.
• Prediction 2: Expression of aggregation‑prone versions of these proteins in primary hepatocytes, adipocytes, or myocytes will increase markers of UPR^ER (BiP, CHOP), UPR^mt (HSP60, Lon), and autophagic impairment (LC3‑II/p62 ratio) compared with non‑aggregating mutants.
• Prediction 3: Conditioned media from cells expressing aggregation‑prone metabolites will activate caspase‑1 and IL‑1β release in co‑cultured tissue‑specific macrophages; neutralization of IL‑1β will reduce downstream UPR activation in the parenchymal cells.
• Prediction 4: In vivo, adipose‑specific overexpression of an aggregation‑prone adiponectin mutant will exacerbate hepatic ER stress markers and impair glucose tolerance, effects attenuated by macrophage depletion or IL‑1β blockade.

Experimental Approach

• In vitro biophysics: Thioflavin‑T fluorescence, transmission electron microscopy, and surface plasmon resonance to assess lipid‑dependent aggregation of motif peptides.
• Cellular models: Adenoviral or CRISPR‑based expression of wild‑type vs. aggregation‑deficient mutants in HepG2, 3T3‑L1, and C2C12 cells; readouts include Western blot for UPR markers, Seahorse assays for mitochondrial function, autophagy flux assays, and cytokine ELISA.
• Macrophage crosstalk: Transwell co‑culture of parenchymal cells with bone‑marrow‑derived macrophages; measure inflammasome activation (ASC speck formation, caspase‑1 cleavage) and cytokine output.
• Animal studies: Adeno‑associated virus (AAV)–mediated tissue‑specific expression of aggregation‑prone mutants in mice; metabolic phenotyping (GTT, ITT), histology (lipid droplets, fibrosis), and immunohistochemical analysis of UPR and inflammasome activation across liver, adipose, and muscle. Intervention arms include clodronate liposomes (macrophage depletion) and anti‑IL‑1β antibody.

Falsifiability

If lipid‑dependent aggregation of the identified motifs does not differ significantly from control peptides, or if expression of aggregation‑prone mutants fails to induce UPR activation, mitochondrial dysfunction, or macrophage‑mediated inflammation in vitro and in vivo, the hypothesis would be refuted. Conversely, confirmation of at least three of the four predictions would strongly support the notion of a conserved, membrane‑catalyzed amyloidogenic mechanism driving metabolic proteostatic collapse.