A role for kit receptor signaling in Leydig cell steroidogenesis
A role for kit receptor signaling in Leydig cell steroidogenesis
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DOI：
10.1095/biolreprod.102.014548
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发表时间：
2003-09-01
影响因子：
3.6
通讯作者：
Besmer, P
中科院分区：
文献类型：
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作者：
Rothschild, G;Sottas, CM;Besmer, P
Kit 及其配体 Kitl 在造血、黑素生成和配子发生中发挥作用。在睾丸中，Kitl由支持细胞表达，Kit由精原细胞和间质细胞表达。试剂盒功能由受体自身磷酸化以及随后与信号分子（包括磷酸肌醇 (PI) 3-激酶）的关联介导。我们之前描述了在 Kit(Y719F)/Kit(Y719F) 敲入突变雄性小鼠中阻断 Kit 介导的 PI 3 激酶激活的生殖后果。这些小鼠中只有配子发生受到影响，而雄性小鼠由于精原细胞阶段精子发生受阻而无法生育。在本研究中，我们研究了 Kit(Y719F) 突变对 Leydig 细胞发育和类固醇生成功能的影响。尽管突变动物睾丸中的生精小管已耗尽生殖细胞，但睾丸含有正常数量的间质细胞，并且这些动物中的间质细胞似乎已经经历了正常分化。对突变动物中类固醇生成的评估表明，外周睾酮水平并未显着降低，但 LH 水平增加了 5 倍，这意味着突变动物中类固醇生成受到损害。因此，在体外寻找 Kit 信号在 Leydig 细胞类固醇生成中的作用。将来自C57Bl6/J雄性小鼠的纯化Leydig细胞与Kit1一起温育，并测量睾酮产生。 Kit1刺激的睾酮产生量比未处理的对照组高2倍。 Leydig细胞中Kit1介导的睾酮生物合成是PI 3激酶依赖性的。在体外，来自突变小鼠的 Leydig 细胞比正常 Leydig 细胞对 LH 的类固醇生成能力更强。相反，这些细胞中Kit1介导的睾酮生成与正常细胞中的相当。由于突变男性的 LH 水平升高，并且已知 LH 会刺激睾酮生物合成，因此我们提出了一个模型，其中血清睾酮水平由升高的 LH 分泌控制。突变雄性的间质细胞无法对 Kitl 刺激做出有效反应，最初产生较低水平的睾酮，从而减少下丘脑-垂体轴上睾酮的负反馈。根据这一假设，随后分泌的额外 LH 会导致血清睾酮恢复正常水平。 Kitl 通过 PI 3 激酶发挥作用，是体内 Leydig 细胞类固醇生成功能的旁分泌调节剂。
Kit and its ligand, Kitl, function in hematopoiesis, melanogenesis, and gametogenesis. In the testis, Kitl is expressed by Sertoli cells and Kit is expressed by spermatogonia and Leydig cells. Kit functions are mediated by receptor autophosphorylation and subsequent association with signaling molecules, including phosphoinositide (PI) 3-kinase. We previously characterized the reproductive consequences of blocking Kit-mediated PI 3-kinase activation in Kit(Y719F)/Kit(Y719F) knockin mutant male mice. Only gametogenesis was affected in these mice, and males are sterile because of a block in spermatogenesis during the spermatogonial stages. In the present study, we investigated effects of the Kit(Y719F) mutation on Leydig cell development and steroidogenic function. Although the seminiferous tubules in testes of mutant animals are depleted of germ cells, the testes contain normal numbers of Leydig cells and the Leydig cells in these animals appear to have undergone normal differentiation. Evaluation of steroidogenesis in mutant animals indicates that testosterone levels are not significantly reduced in the periphery but that LH levels are increased 5-fold, implying an impairment of steroidogenesis in the mutant animals. Therefore, a role for Kit signaling in steroidogenesis in Leydig cells was sought in vitro. Purified Leydig cells from C57Bl6/J male mice were incubated with Kitl, and testosterone production was measured. Kitl-stimulated testosterone production was 2-fold higher than that in untreated controls. The Kitl-mediated testosterone biosynthesis in Leydig cells is PI 3-kinase dependent. In vitro, Leydig cells from mutant mice were steroidogenically more competent in response to LH than were normal Leydig cells. In contrast, Kitl-mediated testosterone production in these cells was comparable to that in normal cells. Because LH levels in mutant males are elevated and LH is known to stimulate testosterone biosynthesis, we proposed a model in which serum testosterone levels are controlled by elevated LH secretion. Leydig cells of mutant males, unable to respond effectively to Kitl stimulation, initially produce lower levels of testosterone, reducing testosterone negative feedback on the hypothalamic-pituitary axis. The consequent secretion of additional LH, under this hypothesis, causes a restoration of normal levels of serum testosterone. Kitl, acting via PI 3-kinase, is a paracrine regulator of Leydig cell steroidogenic function in vivo.