胰島素路徑調控肝臟雄激素受體表現的分子機制研究

Abstract

雄激素受體(androgen receptor, AR基因)除了在生殖器官內扮演非常重要的角色外，目前研究也發現男性的肝臟也是一個會受到雄激素所調控的器官之一。我們實驗室過去發現了雄激素訊息傳遞路徑可以刺激B型肝炎病毒(HBV)在肝臟細胞內轉譯層面的調控機制。然而，雄激素受體在肝臟內一般的生理功能以及其調控機制仍然還未被釐清。不過從其他團隊的研究中發現當肝臟雄激素受體剔除小鼠在餵食高脂飼料後，可以觀察到有胰島素阻抗的現象產生，這樣的發現似乎點出了肝臟中的雄激素受體可能參與了葡萄糖的代謝調控。為了進一步探討雄激素受體在肝臟中的代謝功能，我們實驗室首先建立了在肝臟中會大量表現AR基因的轉殖基因小鼠模式。而在進行代謝相關的檢測實驗中，我們發現禁食後AR蛋白質的表現會大幅減少，但當我們注射insulin後短時間內AR又會大量表現。這代表肝臟中的AR是會受到insulin pathway所調控的基因之一。因此本論文的研究主要會專於探討insulin pathway在肝臟內調控AR基因表現的機制。 選用在飢餓狀態下注射不同時間insulin的H-ARTG小鼠作為我們的實驗樣品，利用西方墨點法以及RT-qPCR檢測蛋白質以及RNA的表現差異。結果發現AR在insulin刺激後短時間內表現即會大量提高，主要可能是受一個非轉譯層面的調控機制所影響。緊接著我們利用IHC staining的染色技術去觀察此時期AR在肝臟中的分佈情形，發現受到insulin刺激的AR主要會出現在肝臟中pericentral的區域 (zone 3 區域)。 這樣的結果表示男性肝臟中的AR可能會有一調控肝臟pericentral的區域代謝機制的生理功能。而這個特殊的分佈現象在進行去勢手術後就消失了，代表insulin調控AR在pericentral的區域表現是要有androgen的存在下才會發生。而相關的調控機制我們目前也正在進行研究中。我們預期這次研究的結果可以幫助我們在未來更深一步釐清AR在pericentral的區域的生理功能為何。

In addition to the sex organs, liver is also identified as an androgen responsive organ in men, as our previous finding showed that the androgen/androgen receptor (AR) pathway can stimulate the transcription of HBV in hepatocytes. However, the physiological function of this pathway in liver is still remained unclear. Some clues from the conditional AR knockout mice suggested that hepatic AR might function in glucose metabolism, under the insulin resistance condition induced by high fat diet. Aiming to further study the function of hepatic AR in metabolism, our previous study established a hepatic specific AR transgenic (H-ARtg) mouse model. In this animal model, we found that the hepatic AR was significantly decreased by fasting, which however was increased by the insulin treatment. It suggests that the hepatic AR is a putative target gene responsive to the insulin pathway in liver. This study thus aims to study the mechanism for the elevation of AR stimulated by insulin pathway in liver. The RNA and protein analysis for AR in male H-ARtg injected with insulin after fasting indicated that the AR protein is elevated shortly by insulin stimulation, mainly at the post-transcriptional level. We have established the immunohistochemistry staining procedure for detecting the AR in liver tissues, which showed that the hepatic AR protein induced by insulin preferentially locates in hepatocytes at the pericentral area in liver lobules. It thus suggests a physiological function of AR in specific pericentral metabolic zone in male livers. Such a unique pattern is diminished by castration, indicating its dependence on the androgen ligand. The mechanism to restrict the AR at pericentral zonal region is currently under investigation. We expect the results will form the basis for future investigate on the metabolic functions of AR in hepatocytes at the specific pericentral metabolic zone.