The Role of Oxytocin in Bovine Satellite Cell Proliferation and Differentiation

Abstract

Steroid hormones are reported to increase oxytocin (OXT) expression in skeletal muscle. It is possible that OXT may play essential roles in satellite cell (SC) proliferation and differentiation, which further contribute to skeletal muscle development and growth. In this dissertation, we tested this hypothesis with in-vivo and in-vitro studies in intrauterine growth restriction (IUGR) sheep, caloric restricted (CR) calves, tamoxifen (TAM) treated heifers, and bovine satellite cells (BSCs), respectively. In the in-vivo studies, we collected (1) longissimus dorsi muscle (LM) from IUGR sheep; (2) infraspinatus muscle (INF), LM, and semitendinosus muscle (ST) from CR calves; (3) LM muscle from TAM heifers. In all samples, mRNA abundance of targeted genes, such as OXT, were measured. Muscle fiber size and BSC number were also determined in skeletal muscle from TAM treated heifers. For the in-vitro studies, different treatments including 17β-estradiol (E2), trenbolone (TBA), TAM, OXT, and atosiban were applied to wild-type BSC and OXT knockout BSC (CRISPR-OXT) separately to investigate OXT's functions on BSC activity. For in-vivo studies, OXT expression significantly decreased (P<0.05) in IUGR LM muscle. Caloric restriction decreased OXT expression (P<0.05) in INF, LD, and ST muscle. Expression of OXT in LM from TAM animals decreased 50% (P<0.05). Moreover, TAM caused a small statistical reduction (P<0.05) in cross-sectional area (CSA). In in-vitro studies, OXT alone increased (P<0.05) fusion index but not proliferation in the wild-type BSC, whereas both proliferation and differentiation were stimulated (P<0.05) by OXT treatment in the CRISPR-OXT cell. By contrast, E2 and TBA increased (P<0.05) both proliferation rate and fusion index in wild-type BSC. However, E2 and TBA only stimulated proliferation rate (P<0.05) but not fusion index for CRISPR-OXT cells. Atosiban treatment resulted in lower proliferation and differentiation (P<0.05) in both wild-type BSC and CRISPR-OXT cell compared with OXT and E2 treatment groups. Together, our in-vivo studies indicate that OXT may play important roles in skeletal muscle development and growth. Our in-vitro studies demonstrate that OXT plays important roles in BSC proliferation and differentiation, and it is involved in steroid hormone stimulated BSC activity.