下丘脑饥饿素系统对代谢综合征血压和交感神经活动的增强效应及其机制的研究

Matabolic syndrome(MS) is a common disease with high morbility and wide impact on public health. It is widely accepted that MS significantly increases the incidence of cardiovascular diseases.However,the pathogenesis of MS is unclear and thus receives extensive studies. Previous studies have suggested that the enhancement of sympathetic nerve activity is a patho-physiological basis for MS. The increases in sympathetic activity itself and consequent hypertension may lead to severe heart, brain, kidney deseases. However,the cellular and molecular mechanism for enhanced sympathetic activity and hypertension in MS is unclear. Paraventricular nucleus of hypothalamus(PVN) and Orexin system play important role in metabolism，neuroendocrine, and central control of sympathetic activity and arterial blood pressure.Our pilot studies revealed that the expression of Orexin receptor in PVN was increased in a rat MS model，suggesting Orexin system is a one of the key components which link metabolic disordes and cardiovascular disturbance such as hypertension. In this study,we will use a rat MS model induced by high-fat dietto investigate the mechanism underlying increased sympathetic nerve activity in MS. We will performed a series of experiments in molecular, cellular, organism,and overall levels to test our hypotheses. This proposal will provide signficant insights into the central mechanisms involved in enhanced sympathetic vasomotor tone and hypertension in MS. These findings will have important theoretical significance and potential clinical theraputic value.

代谢综合征(MS）为一种发病率高、影响范围广的常见病，可显著增加心血管疾病发病率。有关MS的发病机制是目前的研究热点。研究提示交感神经活性增强是MS发病机制的共同病理生理基础。而交感神经活性增强及其导致的血压增高可引起严重的心、脑、肾疾病。然而，对于代谢综合征中交感神经活性增强的细胞及分子机制仍不清楚。下丘脑室旁核（PVN）和下丘脑饥饿素（Orexin）系统在机体能量代谢、神经内分泌和交感神经活动及动脉血压的调控中起重要作用。我们前期研究显示，MS大鼠下丘脑PVN中 Orexin受体表达增多，提示下丘脑Orexin系统是连接代谢紊乱和交感神经活性增强及高血压的重要纽带。本研究拟采用高脂饮食诱导的MS大鼠模型，通过整体、细胞和分子水平的系列研究，探讨Orexin系统对MS交感神经活动增强的机制。本研究将有助于深入理解MS高血压和交感神经活性增强的中枢机制，具有重要的理论意义和潜在应用价值。

本研究采用肥胖Zucker大鼠（OZRs），探讨下丘脑Orexin(饥饿素)及其受体对代谢综合征交感活动增强的机制。结果显示：1. OZRs基础平均动脉压 (MAP) 及心率 (HR) 显著高于瘦Zucker大鼠（LZRs）。2. PVN微注射Orexin受体1（OXR1）选择性阻断剂SB334867显著降低OZRs的MAP、HR及肾交感神经活动（RSNA），而OXR2阻断剂无作用。3. PVN微量注射orexin A剂量依赖性增加MAP、HR及RSNA，但 对OZRs的升压效应显著高于LZRs。4. OZRs PVN中OXR1表达显著升高。5. OZRs高血压与肥胖无关。6. OZRs PVN基础交感前神经元膜电位（MP）和自发放电频率（FR）显著高于LZRs。7. 阻断OXR1显著降低OZRs大鼠交感前神经元MP和FR。8. orexin A剂量依赖性地兴奋大鼠PVN交感前神经元，增强MP和FR。orexin A对OZRs的兴奋性增强效应显著高于LZRs。orexin A的兴奋增强效应可被SB334867预处理所阻断。9. orexin A 对交感前神经元mEPSC无显著影响。11. orexin A显著增大OZRs PVN 交感前神经元非选择性阳离子电流 (NSCC)。12. PVN注射OXR1-shRNA1（下调OXR1）后，OXR1-SHR大鼠MAP显著降低。13. 虽然三组大鼠心率变异度总频谱能量无差异，但OXR1-SHR大鼠LF/HF比值显著低于其余两组大鼠。14. PVN注射OXR1-shRNA1显著降低OXR1-SHR 大鼠PVN中OXR1受体含量。15. PVN给予SB334867显著降低OZRs和OXR1-SCR大鼠MAP、HR和RSNA。16. OXR1-SHR大鼠PVN注射orexin A 引起的升压效应显著降低。17. OXR1-SHR大鼠PVN逆行标记的交感前神经元放电频率显著降低，orexin A引起的兴奋效应明显减弱。综上所述，OZRs下丘脑PVN中OXR1受体表达上调通过增强突触后非选择性阳离子通道电流，提高下丘脑PVN交感前神经元兴奋性，使外周交感神经传出活动增多，导致心率加快、血压升高；相反，通过OXR1-shRNA下调OZRs下丘脑PVN OXR1，显著降低交感前神经元兴奋性，进而引起外周交感传出活动降低、血压降低。