Hypothesis

IAPP oligomers released from stressed beta cells act as cross‑tissue seeds that bind mitochondrial surfaces in liver, skeletal muscle and adipose tissue, impairing mitochondrial protein import and activating the PERK‑eIF2α‑ATF4 axis of the mitochondrial unfolded protein response (UPR^mt^). This UPR^mt^ activation amplifies reactive oxygen species production, worsens insulin signaling and feeds back to increase beta cell stress, creating a vicious cycle that accelerates islet aging and systemic insulin resistance.

Mechanistic Rationale

Chronic ER stress in aged beta cells upregulates PERK signaling, which already coordinates ER and mitochondrial UPR via the PERK‑eIF2α‑ATF4 axis [2]. Simultaneously, toxic IAPP oligomers—rather than mature fibrils—are secreted into the extracellular space and have been detected in blood, brain, heart and kidney [3][4]. We propose that these oligomers possess an exposed hydrophobic motif that preferentially associates with the outer mitochondrial membrane of metabolically active tissues, disrupting the TIM/TOM import machinery and causing accumulation of misfolded mitochondrial precursors. The resulting mitochondrial proteostatic stress triggers ATF4‑dependent transcription of mitochondrial chaperones (e.g., HSP60, HSP70, LONP1) as a compensatory UPR^mt^ response. However, chronic activation shifts the balance toward CHOP‑mediated apoptosis and ROS overproduction, thereby impairing tissue‑specific insulin uptake and secretion. This links the beta‑cell‑centric proteostatic decline described in recent work [1] to a broader tissue‑wide mechanism, addressing the noted gap in cross‑tissue mechanistic comparisons [5].

Key Predictions

1. In aged or diabetic mouse models, liver, muscle and adipose will show elevated levels of IAPP oligomers co‑localizing with mitochondrial markers (TOM20) prior to detectable increases in classic ER stress markers (p‑PERK, CHOP).
2. Genetic or pharmacological blockade of oligomer uptake (e.g., using a monoclonal antibody against the oligomer‑specific epitope or CRISPR knockout of the putative mitochondrial receptor) will reduce UPR^mt^ activation (lower HSP60/LONP1, phospho‑eIF2α) and improve insulin tolerance without altering beta cell ER stress markers.
3. Overexpression of mitochondria‑targeted chaperones (mtHSP70) or proteases (LONP1) will rescue insulin signaling in peripheral tissues even when beta cell IAPP oligomer production remains high.
4. Conversely, forced expression of oligomer‑secreting beta cells in young mice will induce peripheral UPR^mt^ markers and systemic insulin resistance within weeks, an effect abolished by mitochondrially directed antioxidant (MitoQ) treatment.

Experimental Approach

• In vivo: Use RIP‑Cre;IAPP‑overexpressing mice crossed with tissue‑specific mito‑GFP reporters. Quantify oligomer‑mitochondria proximity by proximity ligation assay (PLA) in liver, muscle, adipose at 3, 6, 12 months.
• In vitro: Treat primary hepatocytes, myotubes and adipocytes with synthetic IAPP oligomers (trimers‑pentamers) labeled with Alexa‑647; measure mitochondrial import assays (radiolabeled precursor uptake) and UPR^mt^ readouts (qPCR for HSP60, LONP1, ATF4; western for phospho‑eIF2α).
• Intervention: Administer oligomer‑specific antibody or small‑molecule sequesterer (e.g., Epigallocatechin‑3‑gallate) and assess glucose tolerance, insulin tolerance, and tissue‑specific UPR^mt^ markers.
• Readouts: Blood glucose, insulin, HOMA‑IR, tissue ROS (MitoSOX), apoptosis (cleaved caspase‑3), and beta cell mass.

Potential Outcomes and Falsifiability

If oligomer blockade fails to diminish peripheral UPR^mt^ activation or improve insulin sensitivity, while beta cell ER stress remains unchanged, the hypothesis that IAPP oligomers drive cross‑tissue mitochondrial UPR^mt^ is falsified. Conversely, a selective rescue of peripheral metabolism without affecting beta cell stress would support the proposed mechanism and highlight mitochondria‑targeted therapies as a means to break the islet‑periphery vicious cycle in aging and T2D.