Promotion of insulin-induced glucose uptake in C2C12 myotubes by osteocalcin

作者：Tsuka Shintaro; Aonuma Fumiko; Higashi Sen; Ohsumi Tomoko; Nagano Koki; Mizokami Akiko; Kawakubo Yasukochi Tomoyo; Masaki Chihiro; Hosokawa Ryuji; Hirata Masato; Takeuchi Hiroshi^*

来源：Biochemical and Biophysical Research Communications, 2015, 459(3): 437-442.

DOI：10.1016/j.bbrc.2015.02.123

• Akt
• ERK
• Glucose metabolism
• Insulin
• Osteocalcin
• Skeletal muscle

A close relationship between the bone and systemic glucose metabolism has recently been the center of attention, since the uncarboxylated form of osteocalcin (GluOC), a bone-derived protein, but not the gamma-carboxylated form, is involved in glucose metabolism. However, the analysis of GluOC effect using isolated organs and related cell lines are required to understand its roles in a whole systemic metabolic status. In the present study, we examined the effect of GluOC on cell lines derived from skeletal muscle to explore the mechanisms by which GluOC regulates glucose uptake. In the differentiated C2C12 myotubes, GluOC dose-dependently induced the phosphorylation of ERK without affecting intracellular cAMP and Ca2+ levels. This effect was inhibited by U0126, an inhibitor of ERR kinase (MEK). Additionally, U73122, an inhibitor of phospholipase C tended to inhibit it as well. Furthermore, cell treatment with GluOC for a long period promoted insulin-induced Akt phosphorylation and glucose uptake in the myotubes, which was abolished by ERR signaling inhibition. These results indicate that GluOC does not triggered Ala phosphorylation and glucose uptake by itself but promotes insulin-induced glucose uptake in myotubes, probably by up-regulating Akt signaling through ERK activation.

• 出版日期2015-4-10