SMPD1 mutations, activity, and α‐synuclein accumulation in Parkinson's disease

Abstract

Background SMPD1 (acid‐sphingomyelinase) variants have been associated with Parkinson's disease in recent studies. The objective of this study was to further investigate the role of SMPD1 mutations in PD. Methods SMPD1 was sequenced in 3 cohorts (Israel Ashkenazi Jewish cohort, Montreal/Montpellier, and New York), including 1592 PD patients and 975 controls. Additional data were available for 10,709 Ashkenazi Jewish controls. Acid‐sphingomyelinase activity was measured by a mass spectrometry‐based assay in the New York cohort. α‐Synuclein levels were measured in vitro following CRISPR/Cas9‐mediated knockout and siRNA knockdown of SMPD1 in HeLa and BE(2)‐M17 cells. Lysosomal localization of acid‐sphingomyelinase with different mutations was studied, and in silico analysis of their effect on acid‐sphingomyelinase structure was performed. Results SMPD1 mutations were associated with PD in the Ashkenazi Jewish cohort, as 1.4% of PD patients carried the p.L302P or p.fsP330 mutation, compared with 0.37% in 10,709 Ashkenazi Jewish controls (OR, 3.7; 95%CI, 1.6‐8.2; P = 0.0025). In the Montreal/Montpellier cohort, the p.A487V variant was nominally associated with PD (1.5% versus 0.14%; P = 0.0065, not significant after correction for multiple comparisons). Among PD patients, reduced acid‐sphingomyelinase activity was associated with a 3.5‐ to 5.8‐year earlier onset of PD in the lowest quartile versus the highest quartile of acid‐sphingomyelinase activity (P = 0.01‐0.001). We further demonstrated that SMPD1 knockout and knockdown resulted in increased α‐synuclein levels in HeLa and BE(2)‐M17 dopaminergic cells and that the p.L302P and p.fsP330 mutations impair the traffic of acid‐sphingomyelinase to the lysosome. Conclusions Our results support an association between SMPD1 variants, acid‐sphingomyelinase activity, and PD. Furthermore, they suggest that reduced acid‐sphingomyelinase activity may lead to α‐synuclein accumulation. © 2019 International Parkinson and Movement Disorder Society

Higher Urine bis(Monoacylglycerol)Phosphate Levels in LRRK2 G2019S Mutation Carriers: Implications for Therapeutic Development

“…Interestingly, variants in the gene encoding sphingomyelinase are also risk factors for PD. 15 In this study, urinary di-18:1-BMP and di-22:6-BMP and their 2,2 0 isoforms were elevated in LRRK2 G2019S mutation carriers (with and without PD), compared with noncarriers. In contrast, mice with germline deletion of LRRK2 and cynomolgus monkeys treated with 3 distinct LRRK2 kinase inhibitors show decreases in urinary di-22:6-BMP levels.…”

“…Both di‐18:1‐BMP and di‐22:6‐BMP are elevated in patients with Niemann‐Pick disease, a lysosomal disorder caused by diminished acid sphingomyelinase levels. Interestingly, variants in the gene encoding sphingomyelinase are also risk factors for PD …”

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“…Some forms of ceramide in the plasma of PD patients are higher in individuals with dementia when compared with nondemented patients . In addition, mutations in the SMPD1 gene that encode sphingomyelinase is correlated with an increased risk of PD . Mutations in the GBA gene that encodes glucocerebrosidase, which produces ceramide from glucocerebroside, are also associated with PD .…”

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The Vicious Cycle Between α‐Synuclein Aggregation and Autophagic‐Lysosomal Dysfunction

“…aSMase belongs to the sphingomyelinase family, responsible for catalyzing the breakdown of sphingomyelin to Cer and phosphorylcholine. A recent study showed that reduced aSMase activity in blood samples is associated to a 3.5‐ to 5.8‐year earlier onset of PD …”