IF AAV8 vectors encoding (i) a signal-peptide-fused secretable Insulin-Degrading Enzyme (sIDE; native IDE CDS with the murine Igκ secretion signal prepended) and (ii) full-length human Neprilysin (NEP), both under the rat insulin promoter (RIP), are delivered by intraductal cannulation at a combined dose of 1×10¹¹ vg each to 16-week-old hemizygous hIAPP transgenic male mice (FVB/N-Tg(Ins2-IAPP)RHFSoel) placed on 60% HFD starting at 8 weeks,

THEN at 10 months post-injection, treated mice will show ≥60% reduction in islet soluble IAPP oligomer burden (ELISA with conformation-specific antibody), ≥50% reduction in ThioS⁺ amyloid area per islet cross-section, preservation of β-cell mass (≥70% of young reference), and improved glucose excursion (AUC-GTT reduced ≥30% vs. AAV8-GFP controls), with the additional novel prediction that pancreatic innervation (assessed in intra-islet peri-autonomic nerve fibers by phospho-tau AT8 immunostaining) will show significantly lower accumulation of IAPP-seeded protease-resistant tau compared to untreated hIAPP-HFD controls,

BECAUSE the following causal chain operates across two previously unlinked compartments:

1. Intracellular pre-secretory degradation: Native IDE in β-cells cleaves IAPP monomers within the regulated secretory pathway before granule packaging; restoring declining IDE activity in aged islets reduces the flux of amyloidogenic IAPP entering the interstitium, directly addressing the amyloidogenic pool at source (IDE activity declines with age and insulin resistance, and IDE inhibition accelerates IAPP fibril formation, as summarized in the Research Context).
2. Extracellular post-secretory degradation via sIDE: Critically, wild-type IDE is a cytosolic enzyme and cannot access the extracellular islet interstitium where IAPP oligomerization and nucleation occur. By fusing the Igκ signal peptide to IDE, the enzyme is routed through the secretory pathway and released into the pericellular space. This extracellular sIDE constitutes a novel second line of defence, degrading secreted IAPP monomers in the interstitium before nucleation-competent oligomers form — a compartment entirely unaddressed by any existing therapeutic strategy.
3. Membrane-anchored NEP provides complementary extracellular coverage: NEP, naturally a type II membrane protein, cleaves IAPP at the cell surface and in the islet interstitium. While NEP degrades IAPP ~30× slower than Aβ40 (Research Context), overexpression via AAV achieves supraphysiological enzyme density sufficient to compensate for lower catalytic efficiency. NEP's substrate promiscuity also degrades any local Aβ that enters pancreatic tissue via circulation or IAPP-Aβ cross-seeding dynamics (IAPP-Aβ hetero-oligomers are documented to be more cytotoxic than homo-oligomers of either peptide, as reviewed in the Research Context).
4. Dual-enzyme synergy eliminates the kinetic gap: IDE is sterically incapable of accommodating β-sheet oligomers (IDE's c...

SENS category: GlycoSENS

Key references: • doi.org/10.1186/s13024-022-00518-y]. • doi.org/10.1007/s00401-015-1477-1]. • doi.org/10.1523/jneurosci.0705-15.2015]; • doi.org/10.1038/s41467-023-38640-0]; • doi.org/10.1038/s41467-023-38640-0].