高磷环境导致血管平滑肌生物节律紊乱的机制研究

Circadian rhythms exist in most living organisms, strongly influence human biology and pathology. An endogenous timing mechanism, circadian clock, causes rhythmic expression of a considerable fraction of the genome of most organisms to optimally align physiology and behavior with their environment. .Disrupted circadian rhythm of vascular smooth muscle cells(VSMCs) showed a novel function of the internal clock in the pathogenesis of cardiovascular events. It is now accepted that hyperphosphatemia, a distinct syndrome of chronic kidney disease(CKD),plays vital role in abnormality of vascular structure and function, however, little is known about how the peripheral clock in the vasculature contributed to this process.We have reported an important role for PPARγ in VSMCs as a peripheral factor participating in regulation of cardiovascular rhythms, deficiency of PPARγ in VSMCs was responsible for a significant reduction of circadian variations in blood pressure and heart rate in parallel with impaired rhythmicity of the clock genes. Furthermore, we discovered that TGF-β1 pathway was activated and expression of PPARγ was promptly inhibited in VSMCs under high phosphate conditions, with obviously disrupted circadian rhythm of VSMCs in vitro;supplement of PPARγ agonist can upregulate circadian genes in thoracic aortae in mice model.It has been proved that PPARγ abrogates Smad-dependent TGF-β1 pathway by targeting the ATp300 transcriptional coactivator,therefore,this project will highlight how circadian gene expression in VSMCs is modulated under high phosphate conditions and how about the regulation mechanisms in this pathologic process.Discovery of the pathogenesis and tools to manipulate the phase of each biological clock in VSMCs under high phosphate conditions, will be of great help in establishing a novel chronotherapeutic approach to the prevention and treatment of cardiovascular disorders in hyperphosphatemia CKD patients.

生物节律指哺乳动物组织器官的生理功能呈现精密的24小时昼夜变化规律。高磷血症作为慢性肾脏病常见的内环境紊乱，是导致血管结构和功能异常的独立危险因素，但有关高磷与血管生物节律的研究尚无人涉足。申请人已证实当血管平滑肌的过氧化物酶增殖物激活受体γ（PPARγ）表达缺陷时，血管的生物节律发生紊乱；高磷可诱导血管平滑肌的PPARγ水平降低、TGF-β1信号通路活化、血管生物节律异常；PPARγ激动剂明显上调高磷血症小鼠主动脉节律基因的水平。文献报道PPARγ通过ATp300抑制TGF-β1的信号通路，由此我们提出假说：高磷导致血管平滑肌生物节律的紊乱，PPARγ通过ATp300对抗TGF-β1的作用而调节血管的生物节律。课题组拟在已有的工作基础上，论证高磷-血管平滑肌-血管生物节律三者间的关系，我们将从全新视角探索高磷导致血管功能异常的机理，为寻求慢性肾脏病心血管并发症的防治措施提供更广阔的视野。

本研究证实转化生长因子β1（transforming growth factor-β,TGF-β1)在高磷诱导血管平滑肌细胞（vascular smooth muscle cells, VSMCs）转分化的过程中有重要地位，高磷刺激可导致VSMCs的PPARgamma表达异常和生物节律紊乱，是诱发心血管疾病(cardiovascular disease, CVD)的重要危险因素。本课题进一步从时间生物学的角度论证了慢性肾脏病-矿物质骨代谢紊乱(chronic kidney disease-mineral and bone disorder, CKD-MBD)与心血管节律异常的关系。继发性甲状旁腺功能亢进（Secondary hyperparathyroidism, SHPT）是CKD-MBD的重要临床表现，心率变异性（heart rate variability，HRV）是评价心血管生物节律的有效手段，HRV降低反映了心脏自主神经功能的损害，对多种心血管并发症有良好的独立预测价值。我们以慢性肾脏病5期患者为研究对象，发现升高的血清全段甲状旁腺激素（intact parathyroid hormone, iPTH)、钙、磷及钙磷代谢调节因子—成纤维细胞生长因子23（Fibroblast growth factor 23, FGF23）水平与降低的HRV密切相关，提示矿物质骨代谢紊乱直接导致慢性肾脏病患者的心率变异性异常；随访证实成功的甲状旁腺切除术（parathyroidectomy,PTX）可纠正患者的骨矿物质代谢紊乱、逆转降低的HRV。我们的临床和基础研究工作对于认识CKD-MBD心血管生物节律紊乱的发病机理、探索其防治措施、维护心血管功能稳态提供了有益的资料。