Global phosphoproteomic profiling of skeletal muscle in ovarian-hormone deficient mice

Background: Phosphorylation is important in skeletal muscle development, growth, regeneration, and contractile function. Alterations in the skeletal muscle phosphoproteome due to aging have been reported in males; however, studies in females are lacking. We have demonstrated that estrogen deficiency decreases muscle force which correlates with decreased myosin regulatory light chain phosphorylation. Thus, we questioned whether the decline of estrogen in females that occurs with aging might alter the skeletal muscle phosphoproteome. Methods C57BL/6J female mice randomly assigned to a sham-operated (Sham) or ovariectomy (Ovx) group to investigate the effects of estrogen deficiency on skeletal muscle protein phosphorylation in a resting, non-contracting condition. After 16 weeks of estrogen deficiency, the tibialis anterior muscle was dissected and prepped for label-free nano-liquid chromatography tandem mass spectrometry phosphoproteomic analysis. Results We identified 4,780 phosphopeptides in tibialis anterior muscles of ovariectomized (Ovx) and Sham-operated (Sham) control mice. Further analysis revealed 647 differentially regulated phosphopeptides (Benjamini – Hochberg adjusted p-value < 0.05 and 1.5-fold change ratio) that corresponded to 130 proteins with 22 proteins differentially phosphorylated (3 unique to Ovx, two unique to Sham, six upregulated, and 11 downregulated). Differentially phosphorylated proteins associated with the sarcomere, cytoplasm, and metabolic and calcium signaling pathways were identified. Conclusion Our work provides the first global phosphoproteomic analysis in females and how estrogen deficiency impacts the skeletal muscle phosphoproteome. Future work into specific phosphorylation events on sarcomeric proteins and phosphoproteins pertaining to calcium signaling may offer insight on the molecular mechanism(s) of skeletal muscle strength loss in females.