Pathologic Alterations in the Proteome of Synaptosomes from a Mouse Model of Spinal Muscular Atrophy

Abstract

Spinal muscular atrophy (SMA) is a human genetic disorder characterized by muscle weakness, muscle atrophy, and death of motor neurons. SMA is caused by mutations or deletions in a gene called survival motor neuron 1 (SMN1). SMN1 is a housekeeping gene, but the most prominent pathologies in SMA are atrophy of myofibers and death of motor neurons. Further, degeneration of neuromuscular junctions, of synapses, and of axonal regions are features of SMA disease. Here, we have investigated the proteome dynamics of central synapses in P14 Smn 2B/– mice, a model of SMA. Label-free quantitative proteomics on isolated synaptosomes from spinal cords of these animals identified 2030 protein groups. Statistical data analysis revealed 65 specific alterations in the proteome of the central synapses at the early onset stage of disease. Functional analysis of the dysregulated proteins indicated a significant enrichment of proteins associated with mitochondrial dynamics, cholesterol biogenesis, and protein clearance. These pathways represent potential targets for therapy development with the goal of providing stability to the central synapses, thereby preserving neuronal integrity in the context of SMA disease. Data are available via ProteomeXchange with identifier PXD012850.

Quantitative Proteomics Reveal an Altered Pattern of Protein Expression in Brain Tissue from Mice Lacking GPR37 and GPR37L1

“…In further studies, it would be interesting to explore whether changes in intracellular Ca 2+ levels result in specific conformational changes in S100A5 that promote secretion or conversely exert general effects on the secretion machinery. Several studies show that S100 calcium-binding proteins exposed to high intracellular Ca 2+ levels can bind Ca 2+ and subsequently adopt a conformation that exposes hydrophobic sites that then enables them to bind target proteins or membranes. , Interestingly, S100 proteins have also been reported to be associated with synaptosomes, including several recent proteomic studies that reveal the presence of S100 proteins in the synaptosome. − Several other studies show that S100 proteins are able to form tight complexes with binding sites in synaptosomal particulate fractions in both time- and temperature-dependent manners − and are shown to also localize to the synaptosome in mouse brain cortex. , Additionally, two studies that investigated the localization of S100 proteins in synaptosomal fractions showed that divalent cations such as Ca 2+ and Mg 2+ were necessary for S100 proteins to interact directly with synaptosomes. , While these studies highlight the role of S100 proteins in the neuronal synaptosome, it is possible that the binding of Ca 2+ can affect the function and/or secretion of S100 proteins from glial cells as well.…”

The Ubiquitin Proteasome System in Neuromuscular Disorders: Moving Beyond Movement

“…The SMN protein is known to play key roles in several core canonical cellular pathways, including snRNP biogenesis and pre-mRNA splicing [90], actin dynamics [91,92], phosphatase and tensin homolog-mediated (PTEN-mediated) protein synthesis pathways [93], and translational regulation [94]. Furthermore, functional analysis of synaptosomes from the SMA mouse model Smn 2B/− revealed a significant increase in proteins involved in the cholesterol biogenesis and mitochondrial dynamics [95].…”

Alterations in the Proteome of Developing Neocortical Synaptosomes in the Absence of MET Signaling Revealed by Comparative Proteomics

“…Over the past 2 decades, mass spectrometry interrogation of synaptosomes as a whole, or postsynaptic density, active zone, and synaptic vesicle subfractions, has revealed the extraordinary molecular complexity of the synaptic proteome that includes, in addition to classically defined synapse-specific proteins, proteins associated with signaling pathways and organelles required for synapse formation, maturation, and function (e.g., [29][30][31][32][33][34][35][36][37][38][39]). Similar approaches have also identified alterations in the synaptic proteome in response to genetic and environmental perturbations in animal models (e.g., [40][41][42][43][44][45][46][47]) and in postmortem tissue from clinical populations, including schizophrenia and Alzheimer's disease (e.g., [48,49]), providing insight into potential molecular mechanisms underlying disease pathology. Here, we used a discovery-based proteomics approach to determine molecular changes in the mouse neocortical synaptosomal proteome at the peak of synaptogenesis following the conditional deletion of Met.…”