α-Synuclein binds and sequesters PIKE-L into Lewy bodies, triggering dopaminergic cell death via AMPK hyperactivation

Abstract

The abnormal aggregation of fibrillar α-synuclein in Lewy bodies plays a critical role in the pathogenesis of Parkinson's disease. However, the molecular mechanisms regulating α-synuclein pathological effects are incompletely understood. Here we show that α-synuclein binds phosphoinositide-3 kinase enhancer L (PIKE-L) in a phosphorylationdependent manner and sequesters it in Lewy bodies, leading to dopaminergic cell death via AMP-activated protein kinase (AMPK) hyperactivation. α-Synuclein interacts with PIKE-L, an AMPK inhibitory binding partner, and this action is increased by S129 phosphorylation through AMPK and is decreased by Y125 phosphorylation via Src family kinase Fyn. A pleckstrin homology (PH) domain in PIKE-L directly binds α-synuclein and antagonizes its aggregation. Accordingly, PIKE-L overexpression decreases dopaminergic cell death elicited by 1-methyl-4-phenylpyridinium (MPP + ), whereas PIKE-L knockdown elevates α-synuclein oligomerization and cell death. The overexpression of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or α-synuclein induces greater dopaminergic cell loss and more severe motor defects in PIKE-KO and Fyn-KO mice than in wild-type mice, and these effects are attenuated by the expression of dominant-negative AMPK. Hence, our findings demonstrate that α-synuclein neutralizes PIKE-L's neuroprotective actions in synucleinopathies, triggering dopaminergic neuronal death by hyperactivating AMPK.neurodegenerative disease | dopamine | Lewy bodies

Targeting AMPK Signaling as a Neuroprotective Strategy in Parkinson’s Disease

“…However, the relationship between AMPK and αSyn is not straightforward. Some studies have noted that αSyn decreases AMPK phosphorylation at Thr172 [187], while others have observed that αSyn increases it [189]. One possible explanation for these contradictory findings is that αSyn and phosphorylated αSyn differentially affect AMPK.…”

“…Unphosphorylated αSyn activates the phosphatase PP2A, which promotes the dephosphorylation of both αSyn and AMPK, whereas pS129-αSyn inhibits PP2A [192,193]. Furthermore, pS129-αSyn was found to sequester PIKE-L, an inhibitor of AMPK, leading to increased AMPK activity in mice and in SH-SY5Y cells overexpressing αSyn [189]. Thus, unphosphorylated αSyn may inhibit AMPK function through PP2A, but as αSyn becomes increasingly phosphorylated this inhibition declines and other AMPK regulating proteins become inhibited, leading to increased AMPK activity [193].…”

“…Interestingly, AMPK may be one of the endogenous kinases that phosphorylates αSyn. Expression of AMPK-CA in vitro increased pS129-αSyn, while expression of AMPK-DN deceased it [189,194]. However, treatment with metformin either in vitro or in vivo has repeatedly been shown to decrease phosphorylation of αSyn, and this effect is apparently through an AMPK-independent mechanism [171,174,196,197].…”

“…Likewise, 6-OHDA increased autophagy, ROS, and apoptotic cell death in SH-SY5Y cells, and inhibiting macroautophagy with 3-MA or an AMPK inhibiting neurotrophic factor ameliorated these deficits and increased cell viability [199]. MPP+ similarly increased macroautophagy and markers of PCD in SH-SY5Y cells, and expression of AMPK-DN attenuated these effects, while 3-MA prevented cell death as measured by LDH release [189]. In both primary neurons and PC12 cells, administration of 6-OHDA, rotenone, or MPP+ each increased AMPK activity, decreased cell viability, and promoted apoptosis.…”

“…Lentiviral expression of AMPK-DN in the SNc of mice decreased MPTP-induced macroautophagy, ameliorated TH loss in the striatum and SNc, and attenuated motor deficits [189]. Treatment of mice with metformin for 1-week reduced MPTP-induced reactive microglia and pro-inflammatory cytokines in the SNc (indicating a strong anti-inflammatory effect), but metformin treatment did not attenuate the loss of SNc DA neurons, and it actually worsened MPTP-induced DA and DOPAC depletion.…”