Kisspeptin在小鼠萊迪氏細胞中對排卵素誘發類固醇生合成作用之調控

Abstract

現今已知Kisspeptin在哺乳動物的生殖生理調控中作為下視丘-腦垂腺-性腺軸(Hypothalamus-pituitary-gonad axis)之上游調節因子，以驅使動物發身及調控生殖周期。除下視丘外，Kiss1及Kiss1r基因亦在睪丸與卵巢等性腺組織中均有表現，然其中生理作用尚未完全瞭解。本研究目的將探討kisspeptin及其受體KISS1R在睪丸中的表現調控與其調節生殖之功能。 在小鼠動物模式中，Kiss1基因表現起始於發身時期並與睪丸發育同步，而Kiss1r基因表現則沒有時程上的差異。由於kisspeptin主要表現於萊迪氏細胞中，故排卵素(Luteinizing hormone, LH)可視為刺激睪丸分泌Kisspeptin之可能因子。透過MA-10細胞株及初代小鼠萊迪氏細胞之離體試驗，我們證實人類絨毛膜激性腺素(Human chorionic gonadotropin, hCG)與8-Br-cAMP(Protein kinase A活化劑)均可刺激細胞增加kisspeptin表現，其中，此調控作用涉及轉錄因子CREB (cAMP responsive element binding protein)之參與。為探討Kisspeptin是否參與類固醇生合成(Steroidogenesis)和精子發生(Spermiogenesis)之調節功能，以慢病毒傳遞shRNA系統(Lentiviral delivery shRNA system)將發身中ICR小鼠之睪丸予以組織特異性Kiss1及Kiss1r基因表現減量(Gene knockdown)。於手術12週後，Kiss1與Kiss1r基因表現減量成年小鼠均具有正常睪丸與附睪重量，且組織型態亦無異樣。然而，此兩組小鼠之血漿睪固酮濃度均有下降，此結果顯示kisspeptin可能參與萊迪氏細胞類固醇生合成之調節。為驗證此假設，將MA-10細胞株給予kisspeptin-10與不同濃度之hCG共處理，並分析處理後培養液中孕酮(Progesterone)濃度。結果顯示kisspeptin-10可促使細胞孕酮分泌助於hCG低中劑量之處理；而抑制作用發生於hCG高劑量之處理。此外，使用小分子干擾核醣核酸(Small interfering RNA, siRNA)將細胞Kiss1r基因表現減量，該處理造成細胞中類固醇合成相關基因的基因表現下降，同時孕酮之分泌作用亦受到抑制。 綜合以上所述，LH可透過cAMP/PKA/CREB訊息傳遞途徑以刺激小鼠萊迪氏細胞分泌kisspeptin。由於萊迪氏細胞亦表現對應受體KISS1R，細胞可能透過自分泌kisspeptin之途徑，以調節自身類固醇生合成作用，而使睪固酮濃度範圍持恆。然而，KISS1R之胞內分子機制及其與LH受體訊息傳遞途徑之交互作用，則需要更多的研究來闡明。

Kisspeptin has been found to act as an upstream regulator of the hypothalamus-pituitary-gonad axis (HPG axis), which is the main regulatory system of animal reproduction. In addition to the hypothalamus, multiple reproductive tissues including testis and ovary are also found to express Kiss1 and Kiss1r. However, the possible physiological role of kisspeptin/KISS1R in testis remain unclear. The aim of this study is to investigate the regulations and local functions of kisspeptin in rodent testis. Based on previous observations which kisspeptin expression is correlated to the testicular development and is dominantly in the Leydig cells, luteinizing hormone (LH) may be a potential factor to stimulate testicular kisspeptin secretion. Consistent with the hypothesis, kisspeptin expression was increased in the MA-10 cell, a mouse tumor Leydig cell line, and primary mouse Leydig cell after hCG or 8-Br-cAMP, a PKA activator, treatment. Furthermore, this stimulated Kiss1 expression is dependent on cAMP response element binding protein (CREB) regulation. To investigate the local function of kisspeptin in testis, pubertal ICR mice were given testicular-specific Kiss1 or Kiss1r knockdown by using lentiviral delivery shRNA system. After 12 weeks, mice were sacrificed and reproductive tissues were collected for further analysis. The Kiss1 and Kiss1r shRNA transduced mice had normal testis weight, epididymis weight, testicular morphology. However, the abnormal rate of epididymal sperm morphology was increased, and fertility was decreased in the testicular Kiss1 knockdown mice. Importantly, both Kiss1 and Kiss1r shRNA transduced mice had decreased plasma testosterone levels. These results suggested that testicular kisspeptin may regulate steroidogenesis and spermiogenesis. To address this hypothesis, MA-10 cell was treated with kisspeptin-10 alone or combined with hCG. Kisspeptin-10 could induce progesterone production under the middle or lower concentrations of hCG but suppressed effect occurs under the high concentration of hCG. When the cell was knockdown in Kiss1r, the expression of steroidogenesis-related genes was decreased, and progesterone production was also suppressed. In summary, LH could induce kisspeptin expression in mouse Leydig cells through cAMP/PKA/CREB pathway. As Leydig cell also expressing KISS1R, the autocrine kisspeptin could modulate steroidogenesis to control the dynamic range of hormone concentration. However, the intracellular molecular mechanism of Kisspeptin/KISS1R and its interaction with LH/CG-R signaling pathway need more studies to elucidate.