雄激素缺乏导致肝脏胰岛素抵抗中FoxO1的调控机制研究

Patients with hypogonadism often accompanied with insulin resistance and metabolic disorders. Abdominal obesity caused by IR makes further lower testosterone, which form a vicious circle. The targets and mechanisms of how testosterone deficiency leads to IR are still not very clear, and the clinical safety of testosterone replacement therapy is controversial so far. So it is in emergency to reveal the mechanism of how androgen deficiency leading to insulin resistance. In our previous study we found for the first time that castration-induced.testosterone deficiency leading to impaired fasting glucose associated with hepatic insulin resistance in old-aged male rats; FoxO1 is a key transcription factor for insulin to regulate hepatic glucose and lipid metabolism. By activating IP3K-Akt signaling pathway, insulin leads to FoxO1 phosphorylated thereby reducing its activity. While in our preliminary experiments， the results showed that the expression and activity of FoxO1 in the liver tissues of the castrated rats were dramatically increased despite the high levels of insulin. Previous studies suggested that approximately 70% of AR binding sites are present in junction with FOXA1 binding sites genome-wide in LNCaP cells. Analysis of FoxO1.promoter sequence showed that there are AR binding sites in the FoxO1 promoter. Co-Immunoprecipitation results showed that AR interacted with FoxO1 when over expressed in 293T cells.Therefore, we hypothesized that androgen receptor directly activated FoxO1 by interactions when androgen deficiency, which counteracted the effect of insulin, and thus leading to hepatic insulin resistance. This study for the first time to investigate the mechanism of how to regulate FoxO1 while in low androgen, which would to provide new ideas and possible targets for the prevention and treatment of LOH patients with metabolic disorders.

雄激素缺乏患者常有胰岛素抵抗，而胰岛素抵抗导致的腹型肥胖使睾酮进一步降低，形成恶性循环，导致男性心血管疾病高发。目前雄激素缺乏导致胰岛素抵抗的靶点及机制均不清楚，临床睾酮替代治疗的安全性存在争议。我们前期研究首次发现，肝脏是低雄激素引起胰岛素抵抗的主要靶点，但其机制尚未明了。叉头框蛋白1（FoxO1）是胰岛素调控肝脏糖脂代谢的关键转录因子，正常胰岛素抑制其活性，但在雄激素缺乏机体，我们发现FoxO1的活性不被所升高的胰岛素抑制，且雄激素受体（AR）表达升高。前人研究提示雄激素受体可调控转录因子活性，我们预实验显示AR与FoxO1相互作用，故我们推测雄激素缺乏时配体缺失后，AR直接活化 FoxO1，抵消胰岛素对其抑制，导致肝脏胰岛素抵抗。本项目在前期工作基础上，从AR与FoxO1的相互作用角度，采用多种手段研究雄激素缺乏时FoxO1的调控机制，为雄激素缺乏患者代谢紊乱的防治提供新的思路。

雄激素缺乏患者常有胰岛素抵抗，而胰岛素抵抗导致的腹型肥胖使睾酮进一步降低，形成恶性循环，导致男性心血管疾病高发。目前雄激素缺乏导致胰岛素抵抗和心血管疾病的靶点及机制均不清楚，临床睾酮替代治疗的安全性存在争议。我们前期研究首次发现，肝脏是低雄激素引起胰岛素抵抗的主要靶点，但其机制尚未明了。本项目拟从FoxO1的角度研究雄激素缺乏导致肝脏胰岛素抵抗及心血管疾病的机制。在研究中我们发现，雄激素缺乏虽在晚期导致空腹血糖升高，但血脂紊乱症状的出现远早于血糖升高。而对血脂的影响中，雄激素缺乏后胆固醇的升高程度大于甘油三脂的升高。利用同位素示踪的方法，我们发现雄激素缺乏后肠道胆固醇的吸收影响并不大，主要影响肝脏对胆固醇的摄取及肝脏内胆固醇的合成。另一方面，雄激素缺乏导致动脉斑块形成，Masson染色表明动脉中内膜层纤维化明显。在机制上，我们发现雄激素缺乏后，肝脏FoxO1和p-FoxO1的表达均明显增加，与胆固醇摄取相关的PCSK9表达明显异常。通过本项目的研究，有助于针对性地降低雄激素缺乏患者血液中胆固醇浓度，从而对老年男性心血管疾病进行防治。