Genetic and physiological causes of inherited Vascular and Metabolic Diseases

描述（由申请人提供）：冠状动脉疾病（CAD）是全球发病和死亡的最常见原因。一组代谢表型称为代谢综合征，已被确定为CAD的主要危险因素。将这些表型彼此联系起来以及与CAD联系起来的机制还没有很好地理解。我们在一个常染色体显性遗传早发性冠状动脉疾病（CAD）、糖尿病、高脂血症和高血压的大家族中发现了致病基因。该突变在LDL受体样蛋白（LRP 6）中第二表皮生长因子前体结构域的高度保守残基处用半胱氨酸取代精氨酸（R611 C），该蛋白编码Wnt信号传导途径中的辅助受体。第二个突变（R473 Q）是在一个大的家族中发现的早发性CAD和表型与代谢综合征的整体情况一致。体外研究表明，这些突变损害Wnt信号传导。基因型表型相关性表明，突变影响这些激酶中存在的代谢表型的数量。这些发现已经建立了LRP 6突变引起的Wnt信号传导障碍与冠状动脉/代谢综合征之间的因果关系，并提出了突变的复杂下游效应的可能性，这需要进一步研究。非糖尿病R611 C突变携带者的口服葡萄糖耐量试验表明，他们是高胰岛素血症，表明胰岛素抵抗可能是突变携带者糖耐量受损的主要原因。LRP 6突变导致胰岛素抵抗的机制尚不清楚。骨骼肌糖原合成缺陷被认为是胰岛素抵抗的主要原因之一。糖原合成的限速酶糖原合成酶（GS）被糖原合成酶激酶3ss（GSK 3ss）磷酸化并失活。GSK 3 β受Wnt信号传导激活负调控。突变携带者的淋巴母细胞样细胞中GSK 3 β的表达和活性增加。我们推测LRP 6突变通过损害糖原合成酶活性直接影响糖原合成。为了验证这一假设并确定胰岛素抵抗的主要部位，将通过输注[6，6- 2 H]-葡萄糖同位素来测量两种激酶中非糖尿病突变携带者和非携带者家族成员的胰岛素刺激葡萄糖处置率和对胰岛素抑制肝脏葡萄糖输出的敏感性。肝脏和肌肉中的糖原合成将使用13 C MRS评估，并且肌内葡萄糖-6-磷酸浓度的胰岛素刺激的变化将使用31 P MRS测量。将比较突变携带者和健康对照的骨骼肌活检中的糖原合成和GS活性。此外，为了探索LRP 6突变在代谢综合征和CAD患者中的患病率和谱，将对200例早发CAD、糖尿病和代谢综合征患者的队列进行LRP 6编码区非保守突变筛查。这些研究为代谢综合征和CAD的病理生理学提供了重要的见解，并为这些疾病确定了新的生物标志物和治疗靶点。

DESCRIPTION (provided by applicant): Coronary artery disease (CAD) is the most common cause of morbidity and mortality worldwide. A cluster of metabolic phenotypes known as metabolic syndrome has been established as a major risk factor for CAD. The mechanisms that link these phenotypes to one another and to CAD are not well understood. We have identified the disease causing gene in a large family with autosomal dominant early onset coronary artery disease (CAD), diabetes, hyperlipidemia, and hypertension. The mutation, substitutes cysteine for arginine (R611C) at a highly conserved residue of the second epidermal growth factor precursor domain in the LDL receptor like protein (LRP6), which encodes a co-receptor in the Wnt signaling pathway. A second mutation (R473Q) was identified in a large kindred with early onset CAD and phenotypes that are consistent with the overall picture of the metabolic syndrome. In vitro studies have indicated that these mutations impair Wnt signaling. Genotype phenotype correlation showed that the mutations impact number of the metabolic phenotypes that are present in these kindreds. These findings have established a causal link between Wnt signaling impairment caused by LRP6 mutation and coronary artery/metabolic syndrome and raise the possibility of complex downstream effects of the mutation which warrants further investigation. Oral glucose tolerance tests in nondiabetic R611C mutation carriers have shown that they are hyperinsulinemic, indicating that insulin resistance is likely the major cause of impaired glucose tolerance in the mutation carriers. The mechanisms of insulin resistance caused by LRP6 mutation are not known. Defect in glycogen synthesis of the skeletal muscle is thought to be one of the major causes of insulin resistance. The rate limiting enzyme for glycogen synthesis, glycogen synthase (GS), is phosphorylated and inactivated by glycogen synthase kinase 3ss (GSK3ss). GSK3ss is negatively regulated by Wnt signaling activation. The expression and activity of GSK3ss is increased in lymphoblastoid cells of the mutation carriers. We hypothesize that LRP6 mutation directly affect glycogen synthesis by impairment of glycogen synthase activity. To examine this hypothesis and to identify the major site of insulin resistance, insulin-stimulatedglucose disposal rate and sensitivity to insulin suppression of hepatic glucose output will be measured with infusion of [6, 6- 2H]-glucose isotope in both nondiabetic mutation carriers and non-carrier family members in the two kindreds. Glycogen synthesis in liver and muscle wil be assessed using 13C MRS and insulin stimulated changes in intramuscular glucose-6-phosphate concentration will be measured using 31P MRS. Glycogen synthesis and GS activity in the skeletal muscle biopsies of the mutation carriers and healthy controls will be compared. In addition, to explore the prevalence and spectrum of LRP6 mutations in patients with metabolic syndrome and CAD, a cohort of 200 cases with early onset CAD, diabetes and metabolic syndrome will be screened for non conservative mutation(s) in the coding region of LRP6. These studies hold great promise in providing important insight into the pathophysiology of metabolic syndrome and CAD and identifying novel biomarkers and therapeutic targets for these disorders.