Phosphorylated SARM1 is involved in the pathological process of rotenone-induced neurodegeneration

Abstract

Sterile alpha and Toll/interleukin receptor motif-containing protein 1 (SARM1) is a NAD+ hydrolase that plays a key role in axonal degeneration and neuronal cell death. We reported that c-Jun N-terminal kinase (JNK) activates SARM1 through phosphorylation at Ser-548. The importance of SARM1 phosphorylation in the pathological process of Parkinson's disease (PD) has not been determined. We thus conducted the present study by using rotenone (an inducer of PD-like pathology) and neurons derived from induced pluripotent stem cells (iPSCs) from healthy donors and a patient with familial PD PARK2 (FPD2). The results showed that compared to the healthy neurons, FPD2 neurons were more vulnerable to rotenone-induced stress and had higher levels of SARM1 phosphorylation. Similar cellular events were obtained when we used PARK2-knockdown neurons derived from healthy donor iPSCs. These events in both types of PD-model neurons were suppressed in neurons treated with JNK inhibitors, Ca2+-signal inhibitors, or by a SARM1-knockdown procedure. The degenerative events were enhanced in neurons overexpressing wild-type SARM1 and conversely suppressed in neurons overexpressing the SARM1-S548A mutant. We also detected elevated SARM1 phosphorylation in the midbrain of PD-model mice. The results indicate that phosphorylated SARM1 plays an important role in the pathological process of rotenone-induced neurodegeneration.

Keywords: JNK; PARK2; Parkinson’s disease; Phosphorylation; SARM1.Abbreviations: ARM, armadillo/HEAT motif; DMSO, dimethyl sulfoxide; EGTA, ethylene glycol-bis(2-aminoethelether)-N: N: N: N-tetraacetic acid; iPSC, induced pluripotent stem cell; JNK, c-Jun N-terminal kinase; NAD, nicotinamide adenine dinucleotide; NSC, neural stem cell; NF-L, neurofilament-L; NF-M, neurofilament-M; PD, Parkinson’s disease; PINK1, PTEN-induced kinase 1; ROS, reactive oxygen species; SAM, sterile alpha motif; SARM1, sterile alpha and Toll/interleukin receptor motif-containing protein 1; SNpc, substantia nigra pars compacta; TH, tyrosine hydroxylase; TIR, Toll/interleukin receptor; WT, wild type.