Sfrp5 and Wnt5a: novel regulators of cytokine release and insulin action through the non-canonical Wnt-signalling pathway in primary human adipocytes and hepatocytes?

分泌型卷曲相关蛋白（Sfrp）5是无翅型MMTV整合位点家族成员Wnt 5a的抑制剂，其激活非经典Wnt信号传导途径。几项主要的临床前研究最近报道了Sfrp 5和Wnt 5a在2型糖尿病（T2 D）发病机制中的作用，但越来越清楚的是，来自小鼠模型的数据不能转化为人类。小鼠研究将Sfrp 5描述为抗炎和胰岛素增敏，而Wnt 5a显示出相反的作用。人类研究的初步结果表明，这些因素与炎症和葡萄糖代谢的相互作用更为复杂。因此，拟议的项目旨在阐明这种蛋白质二重奏如何影响这些糖尿病相关过程以及人类T2 D事件的风险。我假设肥胖改变了Sfrp 5和Wnt 5a从不同细胞类型进入循环的分泌模式。从那里，两种蛋白质到达胰岛素靶组织并影响细胞因子释放、胰岛素敏感性葡萄糖和能量代谢。我预计潜在的机制是基于非经典的Wnt信号通路，因为已知5个Wnt信号成员调节细胞因子释放和/或胰岛素抵抗：JNK，PKC，NFAT，NF κ B和CREB。我进一步假设Sfrp 5和Wnt 5a的比例决定了非经典Wnt信号通路的激活状态的程度，因此决定了T2 D的风险。我计划在三个不同的水平上接近这一假设，这允许对Sfrp 5和Wnt 5a在T2 D发病机制中的作用进行翻译分析：我的第一个分析是基于临床水平，以确定肥胖和体重减轻如何调节Sfrp 5和Wnt 5a（目标1）。我将在腹部手术前后测量从Bariatrix研究的瘦对照和肥胖参与者获得的血清和胰岛素靶组织（如肝脏、骨骼肌和脂肪组织）中Sfrp 5和Wnt 5a的浓度。我的第二个分析是基于体外细胞水平，以研究Sfrp 5和Wnt 5a的失衡如何以及通过非经典Wnt信号通路的哪些组分影响分泌模式和胰岛素敏感的葡萄糖和能量代谢（目标2和3）。在这一部分，我将使用原代人脂肪细胞和肝细胞。我的第三个分析是基于流行病学水平，以评估在何种程度上Sfrp 5和Wnt 5a的全身水平作为预测事件T2 D在一个前瞻性的人群为基础的研究（目标4）。我将测量KORA研究的1000名表型良好的参与者的血清样本中Sfrp 5和Wnt 5a的浓度，并将其与7年随访时的T2 D状态相关联。该项目旨在揭示Sfrp 5/Wnt 5a，非经典Wnt信号通路和T2 D之间迄今未知的联系。深入了解这些相互作用可能会揭示预防和治疗T2 D的新治疗靶点。

Secreted frizzled-related protein (Sfrp)5 is an inhibitor of the wingless-type MMTV integration site family member Wnt5a which activates the non-canonical Wnt-signalling pathway. Several mainly preclinical studies recently reported a role of Sfrp5 and Wnt5a in the pathogenesis of type 2 diabetes (T2D), but it has become increasingly clear that data from mouse models cannot be translated to humans. Mouse studies described Sfrp5 as anti-inflammatory and insulin-sensitising, whereas Wnt5a showed opposite effects. Preliminary results from human studies indicate a more complex interaction of these factors with inflammation and glucose metabolism. Thus, the proposed project aims to clarify how this protein duo influences these diabetes-associated processes and the risk of incident of T2D in humans. I hypothesise that obesity alters the secretion pattern of Sfrp5 and Wnt5a from different cell types into the circulation. From there both proteins reach insulin target tissues and affect cytokine release, insulin-sensitive glucose and energy metabolism. I expect that the underlying mechanism is based on the non-canonical Wnt-signalling pathway because 5 Wnt-signalling members are known to regulate cytokine release and/or insulin resistance: JNK, PKC, NFAT, NFkappaB and CREB. I further assume that the ratio of Sfrp5 and Wnt5a determines the degree of the activation status of the non-canonical Wnt-signalling pathway and therefore the risk of T2D. I plan to approach this hypothesis on three different levels which allow a translational analysis of the role of Sfrp5 and Wnt5a in the pathogenesis of T2D: My first analysis is based on a clinical level to determine how obesity and weight loss regulate Sfrp5 and Wnt5a (objective 1). I will measure the concentrations of Sfrp5 and Wnt5a in serum and insulin target tissues such as liver, skeletal muscle and adipose tissues obtained from lean controls and obese participants of the Bariatrix study before and after abdominal surgery. My second analysis is based on a cellular level in vitro to study how and by which component(s) of the non-canonical Wnt-signalling pathways an imbalance of Sfrp5 and Wnt5a affects secretion pattern and insulin-sensitive glucose and energy metabolism (objective 2&3). For this part, I will use primary human adipocytes and hepatocytes. My third analysis is based on an epidemiological level to evaluate to what extent systemic levels of Sfrp5 and Wnt5a serve as predictors of incident T2D in a prospective population-based study (objective 4). I will measure concentrations of Sfrp5 and Wnt5a in serum samples from 1000 well-phenotyped participants of the KORA study and relate them to the T2D status at the 7-year follow-up. The proposed project aims to shed light on the hitherto unknown link between Sfrp5/Wnt5a, non-canonical Wnt-signalling pathway and T2D. A deeper insight into these interactions might reveal novel therapeutic targets in the prevention and treatment of T2D.