Endoplasmic reticulum membrane protein complex subunit 10 (EMC10) is an evolutionarily conserved and multifunctional factor across species. We previously reported that Emc10 knockout (KO) leads to mouse male infertility. Emc10-null spermatozoa exhibit multiple aspects of dysfunction, including reduced sperm motility. Two subunits of a Na/K-ATPase, ATP1A4 and ATP1B3, are nearly absent in Emc10 KO spermatozoa. Here, two isoforms of EMC10 were characterized in the mouse testis and epididymis: the membrane-bound (mEMC10) and secreted (scEMC10) isoforms. We present evidence that mEMC10, rather than scEMC10, is required for cytoplasm sodium homeostasis by positively regulating ATP1B3 expression in germ cells. Intra-testis mEMC10 overexpression rescued the sperm motility defect caused by Emc10 KO, while exogenous recombinant scEMC10 protein could not improve the motility of spermatozoa from either Emc10 KO mouse or asthenospermic subjects. Clinically, there is a positive association between ATP1B3 and EMC10 protein levels in human spermatozoa, whereas no correlation was proven between seminal plasma scEMC10 levels and sperm motility. These results highlight the important role of the membrane-bound EMC10 isoform in maintaining cytoplasm sodium homeostasis and sperm motility. Based on the present results, the mEMC10-Na, K/ATPase α4β3 axis is proposed as a novel mechanism underlying the regulation of cytoplasmic sodium and sperm motility, and its components seem to have therapeutic potential for asthenospermia.

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Skeletal muscle is one of the most important organs involved in the glucose metabolism, and is mainly responsible for postprandial glucose uptake. We have previously shown that overexpression of the secreted isoform of endoplasmic reticulum protein complex subunit 10 (scEMC10) impairs, while Emc10 knockout (KO) or antibody neutralization of circulating scEMC10 improves glucose tolerance in mice. In this study, we presented evidence the regulation of glucose metabolism is achieved through the impacts of scEMC10 on skeletal muscle. PET-CT analyses showed Emc10 KO increased, whereas overexpression of scEMC10 decreased glucose uptake of skeletal muscle in mice, which can be accounted for by the corresponding changes in GLUT4 expression in their skeletal muscle tissues. Recombinant scEMC10 protein reduced both expression and membrane translocation of GLUT4, thus inhibiting glucose uptake in L6-GLUT4myc skeletal muscle cells. Mechanistically, scEMC10 decreased phosphorylations of both AMPK and its downstream target TBC1D1 in both skeletal muscle cells and tissues. Intraperitoneal administration of a scEMC10 neutralizing antibody increased both expression and membrane translocation of GLUT4 accompanied by increased uptake of glucose in gastrocnemius in mice. These data support scEMC10 as an inhibitor of glucose uptake in skeletal muscle and suggest the inhibition of scEMC10 will be a promising way to lower blood glucose in diabetes. Disclosure S.Jin: None. Y.Wang: None. K.Chen: None. J.Dai: None. L.Chen: None. S.Liu: None. X.Wang: None. Funding National Natural Science Foundation of China (81873645); Science and Technology Commission of Shanghai Municipality (22140902700)