Fu S-P, Liu B-R, Wang J-F, Xue W-J, Liu H-M, Zeng Y-L, Huang B-X, Li S-N, Lv Q-K, Wang W, Liu J-X
College of Veterinary Medicine, Jilin University, Changchun, China.
J Neuroendocrinol. 2015 Mar;27(3):212-22. doi: 10.1111/jne.12256.
β-Hydroxybutyric acid (BHBA) has recently been shown to regulate hormone synthesis and secretion in the hypothalamus. However, little is known about the effects of BHBA-mediated hormone regulation or the detailed mechanisms by which BHBA regulates growth hormone-releasing hormone (GHRH) synthesis and secretion. In the present study, we examined the expression of the BHBA receptor GPR109A in primary hypothalamic cell cultures. We hypothesised that BHBA regulates GHRH via GPR109A and its downstream signals. Initial in vivo studies conducted in rats demonstrated that GHRH mRNA expression in the hypothalamus was strongly inversely correlated with BHBA levels in the cerebrospinal fluid during postnatal development (r = -0.89, P < 0.01). Furthermore, i.c.v. administration of BHBA acutely decreased GHRH mRNA expression in rats. Further in vitro studies revealed a decrease in GHRH synthesis and secretion in primary hypothalamic cells after treatment with BHBA; this effect was inhibited when hypothalamic cells were pretreated with pertussis toxin (PTX). BHBA had no effect on GHRH synthesis and secretion in GT1-7 cells, which do not exhibit cell surface expression of GPR109A. Furthermore, BHBA acutely decreased the transcription of the homeobox gene for Gsh-1 in the hypothalamus in both in vivo and in vitro, and this effect was also inhibited by PTX in vitro. In primary hypothalamic cells, BHBA activated the extracellular signal-regulated kinase (ERK)1/2, p38 and c-Jun N-terminal kinase mitogen-activated protein kinase (MAPK) kinases, as shown by western blot analysis. Moreover, inhibition of ERK1/2 with U0126 attenuated the BHBA-mediated reduction in Gsh-1 expression and GHRH synthesis and secretion. These results strongly suggest that BHBA directly regulates GHRH synthesis and secretion via the GPR109A/ERK1/2 MAPK pathway, and also that Gsh-1 is essential for this function.
β-羟基丁酸（BHBA）最近被证明可调节下丘脑激素的合成与分泌。然而，关于BHBA介导的激素调节作用或其调节生长激素释放激素（GHRH）合成与分泌的详细机制，我们所知甚少。在本研究中，我们检测了原代下丘脑细胞培养物中BHBA受体GPR109A的表达。我们推测BHBA通过GPR109A及其下游信号调节GHRH。最初在大鼠中进行的体内研究表明，出生后发育期间，下丘脑GHRH mRNA表达与脑脊液中BHBA水平呈强烈负相关（r = -0.89，P < 0.01）。此外，脑室内注射BHBA可使大鼠GHRH mRNA表达急性降低。进一步的体外研究显示，用BHBA处理后，原代下丘脑细胞中GHRH的合成与分泌减少；当用百日咳毒素（PTX）预处理下丘脑细胞时，这种作用受到抑制。BHBA对不表达GPR109A细胞表面的GT1-7细胞的GHRH合成与分泌无影响。此外，BHBA在体内和体外均可使下丘脑中Gsh-1同源框基因的转录急性降低，且在体外这种作用也被PTX抑制。在原代下丘脑细胞中，蛋白质免疫印迹分析显示，BHBA激活了细胞外信号调节激酶（ERK）1/2、p38和c-Jun氨基末端激酶丝裂原活化蛋白激酶（MAPK）激酶。此外，用U0126抑制ERK1/2可减弱BHBA介导的Gsh-1表达降低以及GHRH合成与分泌减少。这些结果有力地表明，BHBA通过GPR109A/ERK1/2 MAPK途径直接调节GHRH的合成与分泌，并且Gsh-1对于该功能至关重要。
