Combined Effects of Androgen and GH on BMP-Induced Expression of Osteoblast Markers in C2C12 and MC3T3-E1 Cells

Presentation Number: SAT 348
Date of Presentation: April 1st, 2017

Kosuke Kimura, Nahoko Iwata and Fumio Otsuka*
Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan

Abstract

Osteoblasts undergo differentiation in response to various factors including growth factors and steroids. Bone mass is diminished in androgen- and/or growth hormone (GH)-deficient patients. Replacement of testosterone for male patients with androgen deficiency improves their bone density and architecture. These changes are mediated, at least in part, by conversion of testosterone to estradiol. GH replacement for male cases with GH deficiency also improves bone mineral density. Although it was shown that testosterone and GH act synergistically to induce protein synthesis and elicit anabolic effects, it has been recently reported that combined treatment for males with hypopituitarism did not improve bone parameters more than did treatment with testosterone alone. Hence, the functional relationship between androgen and GH and their combined and/or mutual effects on bone metabolism remain unclear. Here we investigated the mutual effects of androgen and GH on osteoblastic marker expression using mouse myoblastic C2C12 and osteoblast-like MC3T3-E1 cells. Combined treatment with dihydrotestosterone (DHT) and GH enhanced BMP-2-induced expression of Runx2, ALP and osteocalcin mRNA compared with the individual treatments in C2C12 cells. Co-treatment with DHT and GH activated BMP-2-induced Smad phosphorylation and Id-1 transcription in C2C12 cells but not in MC3T3-E1 cells. Insulin-like growth factor (IGF-I) mRNA level was amplified by GH and BMP-2 treatment and was restored by co-treatment with DHT in C2C12 cells. The mRNA level of the IGF-I receptor was not significantly altered by GH or DHT, while it was increased by IGF-I treatment. In addition, IGF-I treatment increased collagen-1 mRNA expression, whereas blockage of endogenous IGF-I activity using an anti-IGF-I antibody failed to suppress the effect of GH and DHT on BMP-2-induced Runx2 expression in C2C12 cells, suggesting that endogenous IGF-I was not substantially involved in the underlying GH actions. On the other hand, androgen receptor and GH receptor mRNA expression was suppressed by BMP-2 treatment in both cell lines, implying the existence of a feedback action. Collectively, the results showed that combined effects of androgen and GH facilitated BMP-2-induced osteoblast differentiation at the early stage by upregulating BMP receptor signaling.

 

Nothing to Disclose: KK, NI, FO