硫氧还蛋白及其还原酶通过胰岛素/脂联素信号通路参与胰岛素抵抗的机制研究

Insulin resistance, a major characteristic feature of type 2 diabetes, has been bringing many serious health problems to a large amount of people. It is thus important to further clarify the mechanism underlying the development of insulin resistance. We found that thioredoxin (Trx)/thioredoxin reductase (TrxR) activities elevated in the sera of insulin-resistant mice, which however contained the reduction of hepatic Trx/TrxR activities in parallel with increased degree of palmitoylated Trx/TrxR. In addition, Trx was found to interact with adiponectin in human serum. In view of the ability for Trx/TrxR to catalyze the reduction of disulfide bond, the latter is critical to maintaining insulin, insulin receptor and high-molecular-weight adiponectin structure and functions, we thus speculated that the increased Trx/TrxR in serum would affect hepatic sugar and lipid metabolisms via insulin and adiponectin signaling pathways, leading to increased levels of free fatty acids, which may modify and inhibit Trx/TrxR. To confirm our speculation, we are planning to study: (1) the relationship among human serum Trx/TrxR activity, type 2 diabetes, the levels of serum insulin and high-molecular-weight adiponectin; (2) the effects of extracellular Trx/TrxR on insulin/adiponectin binding to corresponding receptors, and activating classic downstream proteins; (3) the mechanism underlying the interaction between Trx/TrxR and adiponectin; (4) the molecular mechanism and modification site(s) behind the inhibition of Trx/TrxR by palmitate. Our results are expected to provide new insights into the prevention and treatment of insulin resistance.

胰岛素抵抗是2型糖尿病的主要特征，严重威胁着人类健康，其发病机制急需深入研究。我们发现，硫氧还蛋白（Trx）及其还原酶（TrxR）活性，在胰岛素抵抗小鼠血清中增高，在肝脏中降低可脂酰化程度增高；人血清中Trx与脂联素相结合。于是思索：Trx/TrxR具有促二硫键还原的能力，而调控糖脂代谢的胰岛素及其受体、高分子量脂联素需二硫键维持结构与功能；血清Trx/TrxR活性异常增高，很可能会干扰胰岛素/脂联素信号通路，导致肝内游离脂肪酸积累，修饰和抑制Trx/TrxR，促进氧化应激。为此拟研究：（1）人血清中Trx/TrxR活性与2型糖尿病、胰岛素、高分子量脂联素含量的相关性；（2）细胞外液中Trx/TrxR对胰岛素/脂联素与肝细胞膜相应受体结合、激活下游经典蛋白的影响；（3）Trx/TrxR与脂联素互作的分子机制；（4）软脂酸抑制Trx/TrxR的机制及修饰位点。以期为2型糖尿病防治提供新思路。

2型糖尿病/胰岛素抵抗是最常见的代谢性疾病，发病率居高不下。这里，我们部分揭示与该病有关的硫氧还蛋白（Trx1）及其还原酶（TrxR1）的改变，以期为防治该疾病提供新思路。（1）2型糖尿病患者血清Trx1/TrxR1含量/活性显著高于健康人。血清中的Trx1既能促进肝细胞胰岛素受体β亚基（IRβ）磷酸化又能促进PTP1B活性。细胞外Trx1对肝胰岛素信号的影响，取决于IRβ磷酸化程度/PTP1B活性的平衡。值得关注的是，血清Trx/TrxR活性有助于2型糖尿病诊断。（2）2型糖尿病患者血清总脂联素水平显著低于健康人。高分子量（HMW）脂联素具有胰岛素增敏作用。在血清中加入Trx1系统引起HMW脂联素向低分子量（LMW）脂联素转变；单独的Trx1可以和脂联素形成稳定复合物，在导致自身活性下降的同时，影响脂联素和其受体结合，进而缓解脂联素对Trx1表达的抑制作用。脂联素与Trx1相互调控。（3）胰岛素抵抗小鼠，肝脏TrxR1/Trx1 活性和含量下降，但它们棕榈酰化水平增高。TrxR1 活性中心硒半胱氨酸以及Trx1 分子中结构半胱氨酸Cys62，Cys69 或/和Cys73 发生棕榈酰化，导致其抗氧化活性降低，引起氧化应激。肝脏Trx1/TrxR1 变化是高脂饮食引起胰岛素抵抗的一个新特征。（4）胰岛素抵抗小鼠，小肠TrxR1/Trx1含量/活性均降低。以人小肠上皮细胞为模型的研究结果显示，Trx1系统损伤，破坏小肠细胞的紧密连接；Trx1系统活性增高，维护小肠细胞紧密连接完整性。Trx1系统的这种保护作用，至少与三方面的分子机制有关：（i）保护Na+-K+ATPase活性；（ii）保护紧密连接蛋白ZO-1；（iii）降低活性氧对紧密连接的破坏作用。该结果，为胰岛素抵抗伴随肠粘膜上皮细胞通透性增高的现象提供了新的分子机制。总之，Trx1/TrxR1异常与代谢性疾病密切相关。