CSPα knockout causes neurodegeneration by impairing SNAP-25 function

Abstract

At a synapse, the synaptic vesicle protein cysteine-string protein-a (CSPa) functions as a co-chaperone for the SNARE protein SNAP-25. Knockout (KO) of CSPa causes fulminant neurodegeneration that is rescued by a-synuclein overexpression. The CSPa KO decreases SNAP-25 levels and impairs SNARE-complex assembly; only the latter but not the former is reversed by a-synuclein. Thus, the question arises whether the CSPa KO phenotype is due to decreased SNAP-25 function that then causes neurodegeneration, or due to the dysfunction of multiple as-yet uncharacterized CSPa targets. Here, we demonstrate that decreasing SNAP-25 levels in CSPa KO mice by either KO or knockdown of SNAP-25 aggravated their phenotype. Conversely, increasing SNAP-25 levels by overexpression rescued their phenotype. Inactive SNAP-25 mutants were unable to rescue, showing that the rescue was specific. Under all conditions, the neurodegenerative phenotype precisely correlated with SNARE-complex assembly, indicating that impaired SNARE-complex assembly due to decreased SNAP-25 levels is the ultimate correlate of neurodegeneration. Our findings suggest that the neurodegeneration in CSPa KO mice is primarily produced by defective SNAP-25 function, which causes neurodegeneration by impairing SNARE-complex assembly.

α-Synuclein Membrane Association Is Regulated by the Rab3a Recycling Machinery and Presynaptic Activity*

“…Interestingly, CSP␣ deficiency is known to cause progressive and lethal neurodegeneration that is exacerbated by ␣-syn gene deletion and rescued by ␣-syn overexpression, suggesting overlapping but probably independent functions for ␣-syn and CSP␣ (53,54). Indeed, both proteins appear to modulate SNARE complex assembly (55)(56)(57)(58). Although triple knock-out mice lacking all three synucleins (␣, ␤, and ␥) are viable, they too display agedependent sensorimotor deficits and increasing mortality at 1 year of age.…”

Reduced SNAP-25 increases PSD-95 mobility and impairs spine morphogenesis

“…Finally, miniature excitatory postsynaptic current (mEPSC) analysis in SNAP-25 Het networks revealed a significant reduction in both the frequency and the amplitude relative to controls (Figure 2i). Notably, no difference in mEPSC frequency and amplitude occurs in primary hippocampal cultures at earlier SNAP-25 in spine formation and function G Fossati et al developmental stages, 18,20 thus confirming that morphological and functional postsynaptic defects become evident only at later stages during neuronal development.…”

“…17 Finally, reduction of SNAP-25 levels has been found to cause neurodegeneration in mice lacking the synaptic vesicle protein Cysteine-string protein-α, possibly due to the impaired SNARE-complex assembly produced by the decreased SNAP-25. 18 The mechanisms by which reduced SNAP-25 expression may result in a psychiatric disease are still undefined, although alterations in neurotransmitter release have been indicated as potential causative processes. 19,20 Recently an unexpected postsynaptic role of SNAP-25 has been described, with the protein controlling NMDA and kainate receptor trafficking.…”

Expanding Proteostasis by Membrane Trafficking Networks

“…Moreover, genetic evidence suggests a role for Hsp90 in the assembly and function of the tether "congenital disorders of glycosylation" (COG) TRaCKS components, which regulate the compartmentalization of Golgi glycosylation biology (see below) (Banfield 2011; Freeze and Ng 2011;Geller et al 2012;Rosnoblet et al 2012). Finally, increasing evidence implicates a general role for Hsc/p70 and Hsp90 in vesicle tethering and fusion, mediated by sequential RAB GTPase and SNARE TRaCKS found in the Golgi (Chen and Balch 2006) and at the synapse (Sakisaka et al 2002;Sharma et al 2012b). In the latter case, we have a snapshot of integration of synapse-specific TRaCKS (Fig.…”

“…In the latter case, we have a snapshot of integration of synapse-specific TRaCKS (Fig. 4A) involving the SNARE fusion components syntaxin1 (STX1), vesicle-associated membrane proteins 2 (VAMP2) with the the cytosolically oriented PN component cysteine string protein (CSP) through a-synuclein (aSYN) (Chandra et al 2005;Burre et al 2010;Sharma et al 2011Sharma et al , 2012bSudhof and Rizo 2011), and the PN component Hsp90 (Sakisaka et al 2002). When defective, aSYN triggers neurodegenerative disease, implicating a role for TRaCKS in Parkinson's (Auluck et al 2010;Chua and Tang 2011).…”