Pregnancy induced a fiber type switch to a glycolytic phenotype in SKM, and it is enhanced by SMTNL1 deletion.
A, expression of SMTNL1 in non-pregnant (NP), pregnant (PRE), and pseudopregnant (PSPRE) plantaris muscle by SQ-WB. B, phosphorylation of SMTNL1 Ser-301 in non-pregnant (NP) and pregnant (PRE) plantaris muscle. Means + SEM (n = 4–5/group), t test, *, p < 0.05. C and D, pregnancy reduces MHC2a expression (C) and increases expression of MHC2b (D) in SKM. Protein expression levels in non-pregnant, pregnant, and pseudopregnant by SQ-WB. n = 4–13/group, data are presented as the mean ± S.E., GLM with Tukey's test. Different letters indicate significant differences, p < 0.05. E, fiber typing by IHC and confocal microscopy of plantaris muscle. SMTNL1 (green) is expressed in type2a fibers (red) in control SKM. SMTNL1 expression shows localization in fibers different from type2a (arrows). Insets show secondary antibody controls. Scale bars = 20 μm. F, analysis of MHC2b expression (white) in plantaris muscle. Scale bar = 10 μm. G, SMTNL1, MHCI, MHC2a, and MHC2b expression in human SKM in pregnancy. H, quantitative Periodic Acid Schiff staining for glycogen content of human rectus abdominis sections. G and H, means ± S.E. (n = 4–5/group), t test. *, p < 0.05. I, quantitative fiber counting of plantaris muscle of non-pregnant, pregnant, and pseudopregnant (smtnl1+/+ and smtnl1−/− animals. PAS, Periodic Acid Schiff. Data are the means ± S.E. (n = 14–15/group), t test. #, p < 0.1; *, p < 0.05; **, p < 0.001.