CNP对慢性高眼压性RGCs细胞损伤神经保护作用的机制研究

Glaucoma is a leading cause for vision loss worldwide which is following cataract. It is a kind of progressive disease characterized by distinctive defects of optic disk cupping (retinal nerve fibers) and visual field loss associated with or without elevated intraocular pressure (IOP). Glaucoma is a progressive optic neuropathy and retinopathy, contributed by IOP and other possible risk factors, such as age, race, family history, diabetes, and pathological myopia, and so on, resulting in the exceptional apoptosis of retinal ganglion cells (RGCs) and eventually irreversible functional visual defects. Lowering intraocular pressure, which has been recognized as the only effective anti-glaucoma treatment currently, can not yet completely prevent the optic nerve progressive damages. So the research on the glaucomatic neuropathy and neuroprotection becomes a new focus. Otherwise, the pathophysiologic mechanism underlying glaucomatous RGCs death remains unclear. Several theories have been proposed, for example, excitotoxicity, deprivation of trophic factors, vascular insufficiency, reactive gliosis, and immunological abnormality, and so on. It was indicated that the family of natriuretic peptides (NPs), including ANP (Atrial natriuretic peptide), BNP (Brain natriuretic peptide) and CNP (C-type natriuretic peptide), and their natriuretic peptide recptors (NPRs) of particulate guanylyl cyclase, including NPRA, NPRB and NPRC, had some important neuroprotective effects on the ischemic, traumatic, regressive diseases relevant to neurons apoptosis of central nervous system. Some other researchs had showed that there were plentiful expressions of NPs and NPRs in the tissues of retina and optic nerve, and NPs and cGMP had potent neuroprotective effects on the retinal neurons injuries, especially on the excitotoxicity-induced RGCs death. These neuroprotective mechanisms were yet unclear. Our preliminary study has showed that, except the decrease of IOP, CNP provided a neuroprotective effect on NMDA-induced RGCs apoptosis in the excitotoxic retinopathy model. Therefore, we plan series of functional, pathomorphological and molecular biological studies to evaluate whether pretreatment with CNP can inhibit the rat RGCs apoptosis under pressure in vitro, and in the retina and optic nerve damages of rats with chronic ocular hypertension. Furthmore, we also plan to discuss the neuroprotective mechanisms of CNP in the hypertensive damages, which may function through the inhibition of the apoptotic cascade pathway eruption of "μ-Calpain - BAX/Bcl-xL homodimer - mitochondrial outer membrane permeabilization increasing - Cytochrome C and Caspase-9/3" induced by intracellular calcium overload. We hope that these studies can facilitate the possible implementation that natriuretic peptides family become a new way of anti-glaucoma treatment, with double effects of not only hypotension but also neuroprotection.

青光眼是以视网膜神经节细胞（RGCs）凋亡为特征的严重退行性致盲性眼病，除降眼压外，视神经损伤和保护已成青光眼研究热点。利钠肽家族对中枢神经系统神经细胞凋亡相关病变有重要保护作用，但机制不清。前期工作表明，C型利钠肽（CNP）不仅可降低眼内压，还对兴奋性氨基酸所致大鼠视网膜神经兴奋性毒性有明显抑制的神经保护作用。本课题拟进一步从病理形态学和分子生物学角度，研究CNP对压力诱导体外培养大鼠RGCs凋亡有无抑制作用，对大鼠慢性高眼压视神经损害有无抑制RGCs凋亡的作用，探讨CNP保护机制，可能是通过"CNP→结合NPRB→cGMP↑→PKGs→L-Ca2+通道↓→[Ca2+]i↓→μ-Calpain↓→BAX↓/ BcL-xL↑→线粒体膜通透性↓→细胞色素C↓和 Caspase-9/3↓"通路，来抑制细胞凋亡产生神经保护作用。为利钠肽家族成为既降眼压又保护视神经的抗青光眼治疗新途径打下基础。

青光眼是人类第二大致盲眼病，是以视网膜神经节细胞（RGCs）凋亡为特征的严重退行性致盲性眼病，其可能通过多种机制诱导视网膜神经节细胞凋亡，同时累及其胞体和神经纤维，发生进行性的退行性病变，最终产生伴有或不伴有眼压增高的不可逆性视觉功能损害。降低眼内压虽是目前唯一公认有效的青光眼治疗方法，但其并不能完全阻止青光眼性视神经的进行性损害。除降眼压外，视神经损伤和保护已成青光眼研究热点。利钠肽家族是一种神经多肽物质，研究表明，其与受体广泛分布于包括视网膜视神经在内的中枢神经系统，结合激活第二信使cGMP，产生生物活性，尤其是C-型利钠肽（CNP）对中枢神经系统神经细胞凋亡相关退行性病变有重要保护作用，但作用机制不清。前期工作表明，CNP不仅可降低眼内压，还对兴奋性氨基酸所致大鼠视网膜神经兴奋性毒性有明显抑制的神经保护作用。.本课题在前期工作基础上，成功建立SD大鼠视网膜神经节细胞的原代培养和压力诱导培养系统，成功建立SD大鼠巩膜上静脉水下电凝的慢性高眼压模型，进一步从体外到体内，从病理形态学和分子生物学角度，成功证实CNP不仅对巩膜上静脉水下电凝所造成的中度慢性高眼压有高达近50%的降压作用，还对其所致的RGCs细胞损伤有神经保护作用，其可能是通过假设信号链“ CNP→结合NPRB→cGMP↑→PKGs→L-Ca2+通道↓→[Ca2+]i↓→μ-Calpain↓→BAX↓/ BcL-xL↑→线粒体膜通透性↓→细胞色素C↓和Caspase-9/3↓ ”通路，来抑制细胞凋亡产生神经保护作用。为CNP乃至利钠肽家族，成为既降眼压又保护视神经的抗青光眼治疗新途径打下基础，以期在青光眼的治疗上有所突破。