BACKGROUND: Vimentin (VIM) is an intermediate filament that plays a key role in development and regeneration of various tissue types, however the role of VIM during skeletal muscle hypertrophy, to our knowledge has not been fully elucidated. Therefore, the purpose of this study was to determine the role and response of VIM following mechanical overload (MOV) induced skeletal muscle hypertrophy. METHODS: C57BL/6 mice (age 4mo) were subjected to 10 or 20 days of synergist ablation to induce overload of the plantaris muscle, time matched sham surgery mice served as controls. Following overload, the plantaris was removed and either sectioned for immunohistochemistry (IHC) or placed in Trizol for RNA/protein isolation. VIM expression was examined via RT-qPCR, western blotting, and IHC. To examine expression of VIM in stromal cells occupying the muscle environment, the Tabula Muris single cell transcriptome data set was used for stromal cell target selection, and IHC was performed to examine co-expression of stromal cells and VIM (area of VIM per stromal cell) in response to overload. Data were checked for normality via Shapiro-Wilks tests and one-way ANOVAs were performed with Tukey post-hoc tests. Western blotting data and RT-qPCR data were normalized to sham mice and IHC derived data were expressed as a percentage. RESULTS: VIM mRNA and protein expression was significantly upregulated following 10 and 20 days of MOV (p<0.001). Cross-sectional muscle area occupied by VIM and VIM area per fiber significantly increased following 10 and 20 days of MOV (p<0.001). Based on the Tabula Muris data set, mesenchymal stem cells (e.g. fibro-adipogenic progenitors; FAPs), satellite cells, and macrophages presented the highest expression of VIM in skeletal muscle in the basal state. Area of VIM per stromal cell with satellite cells, FAPs (FAPs), and macrophages increased following 10 and 20 days of MOV (p=0.0012, p<0.001, and p<0.001, respectively). Interestingly, area of VIM per fibroblast did not significantly change following 10 or 20 days of MOV (p=0.581). CONCLUSION: VIM expression is upregulated following MOV induced skeletal muscle hypertrophy. Furthermore, VIM is co-expressed with various stromal cells, and appears to be predominantly produced by fibroblast in response to overload.

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