Altered synaptic and astrocytic proteins in Lewy body disorders associated with GBA mutations

Mutations in the glucocerebrosidase (GBA) gene, originally implicated in Gaucher's disease, are now recognized as a major risk factor for developing Parkinson's disease (PD). While up to 70% of PD patients eventually progress to dementia, GBA mutations further increase the risk of Lewy body dementias (LBD), an umbrella term encompassing both dementia with Lewy bodies and Parkinson's disease dementia. Collectively, these disorders are classified as synucleinopathies. To date, there is no clear understanding of the mechanistic relationships between GBA mutations and synucleinopathies, although, synaptic protein changes have been shown to correlate with cognitive change in LBD as well as in Alzheimer's disease (AD). The aim of this study was to examine synaptic dysfunction in α-synucleinopathies with GBA mutations. The research cohort consisted of 10 controls, 7 PD/LBD-GBA N370S, and 20 PD/LBD-wild type (WT) where seven synaptic markers including four pre-synaptic [synaptosomal-associated protein 25; (SNAP25), synaptophysin; (SYP), ras-related protein; (Rab3A), and vesicle associated membrane proteins 2; (VAMP2)], two post-synaptic [post-synaptic density protein 95; (PSD95), and neurogranin; (NRGN)], and one astrocytic [vesicle associated membrane proteins 3; (VAMP3)] protein were investigated in four cortical regions (prefrontal, temporal, anterior cingulate and parietal) using immunoblot technique. Four markers (NRGN, SNAP25, VAMP2, and VAMP3) were found to be significantly and regionally altered between the three groups. The expression of pre-synaptic (SNAP25), post-synaptic (NRGN), and the astrocytic protein (VAMP3) is different between PD/LBD with GBA mutation and PD/LBD-WT suggesting the potential role of GBA gene due to mutations which could alter the levels of some synaptic markers. Our study is the first to validate several synaptic markers in human post-mortem-associated GBA N370S mutation.