The PKCι-β-arrestin2 axis disrupts SORLA retrograde trafficking, driving its degradation and amyloid pathology in Alzheimer's disease.

Background: Variants of SORL1 have been associated with both late and early onset of Alzheimer's disease (AD). SORL1 encodes the sorting-related receptor with A repeat (SORLA) protein, which belongs to the VPS10 receptor family. SORLA protects against AD pathogenesis through its sorting function, and reduced SORLA levels have been consistently observed in sporadic AD. Although the importance of SORLA in AD pathogenesis is well recognized, how it can be targeted for AD treatment remains to be established, owing to the inadequate understanding of its regulation by intracellular signaling.

Methods: We employed combined biochemical, cell biological, and pharmacological approaches to investigate how SORLA trafficking and stability are regulated. Additionally, we used an AD mouse model, postmortem tissue samples, and iPSC-derived neurons to examine the functional outcomes of this regulation.

Results: We identified a novel direct interaction between SORLA and β-arrestin2 (βARR2), which impedes the interaction of SORLA with the retromer complex, thus reducing the retrograde trafficking of SORLA. βARR2 promotes the interaction between SORLA and the ESCRT0 complex, leading to the lysosomal localization and degradation of SORLA. We also found that PKCι/λ induces SORLA phosphorylation and enhances its interaction with βARR2, promoting SORLA degradation. Importantly, blocking PKCι/λ with auranofin disrupts the SORLA-βARR2 interaction, elevates SORLA levels, decreases amyloidogenic processing of APP, and improves cognition in the App AD mouse model. Furthermore, PKCι is hyperactive in human AD brains, and auranofin reduces Aβ production in AD iPSC-derived neurons through increasing SORLA levels.

Conclusion: Our study reveals the PKCι/λ-βARR2 axis as a key molecular mechanism that disrupts SORLA retrograde trafficking and drives its degradation. Our findings represent the first evidence that SORLA levels can be pharmacologically manipulated through blocking PKCι/λ to reduce Aβ production and alleviate AD-related phenotypes. Notably, repurposing auranofin, an FDA-approved drug for rheumatoid arthritis, may offer the potential for AD treatment.