酪氨酸酶途径的多巴胺能系统功能紊乱是近视早发及高发原因的机制研究

Increasingly early-onset myopia is approaching, but the pathogenesis is still unclear, so that no effective prevention and control measures. Dopamine is known to be one of neurotransmitters which are closely related to the myopia occurrence and development. Most of studies focused on the tyrosine hydroxylase dependent dopaminergic system in the retina; however, tyrosinase dependent dopaminergic system has not been clearly demonstrated. Our recent studies have found that the albino guinea pigs have a high incidence of early-onset of myopia, and the intervention effects of dopaminergic reagent for these spontaneous myopia is different from that for the experimental myopia in pigmented guinea pigs: there are biphasic effects on the myopia development in albino ones. We also found that the tyrosinase dependent dopaminergic systems is involved in the ocular refractive development, but the action site and its mechanism are unclear. In the current study, we are using myopic albino guinea pigs and hyperopic pigmented guinea pigs as animal models, by comparing the electroretinotelegram before and after the dopaminergic reagents intervention, and jointing the changes of the thickness of the choroid from lens-induced defocus, and finally validating by the intervention of the activity of tyrosinase in hyperopic pigmented guinea pigs. We will further clarify the signaling pathways related to the dopaminergic system, and we are expecting to find the molecular mechanism related to the refractive development and myopia occurrence of tyrosinase dependent dopaminergic system in the surrounding tissue development. The effects of enhancement of dopaminergic system in surrounding tissues on myopia prevention will be discussed. When accomplished, this project would have high impact and therapeutic potential in preventing, postponing children from myopia.

近视日趋早发与高发，但发病机制仍不明确，致无有效防治措施。多巴胺是已知与近视发生发展密切相关的神经递质之一，多数研究聚焦于视网膜的酪氨酸羟化酶途径的多巴胺能系统，而酪氨酸酶途径的多巴胺能系统的作用还未明确。我们近期的研究发现白化豚鼠近视早发并高发，多巴胺能试剂对该自发近视的干预效果不同于对有色豚鼠实验性近视的干预效果，呈双向调控；同时发现酪氨酸酶途径的多巴胺能系统也参与了眼屈光的发育，但是作用部位和机制还不明确。本研究利用近视的白化豚鼠和远视的有色豚鼠为动物模型，通过比较多巴胺能试剂干预前后视网膜电生理反应的变化，以及联合镜片离焦诱导脉络膜厚度的变化，然后通过干预有色豚鼠的酪氨酸酶活性进行验证，并在此基础上对多巴胺能系统有关的信号通路进行探索，期望能够发现周围组织的多巴胺能系统在正视化发育过程及近视形成中的分子机理，进而探讨增强周围组织的多巴胺能系统的效应在近视防治中的作用。

目的：多巴胺是参与眼球生长发育调控的神经递质之一。眼内多巴胺主要来源于视网膜神经层的酪氨酸羟化酶源性的多巴胺和视网膜RPE及脉络膜复合体中的酪氨酸酶源性的多巴胺。既往对视网膜酪氨酸羟化酶源性的多巴胺研究较多，结论在不同实验动物相互矛盾。对酪氨酸酶源性的多巴胺在眼发育以及正视化中存在作用的研究将是多巴胺能系统在眼发育研究的重要补充。.方法：本研究使用自发近视高发和近视可诱导两种豚鼠进行研究，通过药物干预，观察其屈光发育、视网膜电生理反应、脉络膜对镜片离焦的形态学反应，对多巴胺能系统在眼部的作用部位及作用机制进行了实质性的研究。.结果：自发近视的白化豚鼠视网膜的多巴胺水平及其代谢产物与有色豚鼠比较没有统计学差异；脉络膜中酪氨酸酶途径的多巴胺能活性在白化豚鼠显著低于有色豚鼠，但是显著高于阴性对照视网膜，提示白化豚鼠脉络膜组织中的多巴胺能系统存在异常。半球后注射酪氨酸酶抑制剂曲酸两周后有色豚鼠的屈光发育向近视方向偏移（溶剂组vs 62.5ng vs 625ng vs 6250ng：实验眼与对侧眼的屈光度差值， -0.38±0.17D vs -1.61±0.23D vs -2.17±0.28D vs -1.92±0.44D，p<0.01；玻璃体腔的差值，0.009±0.007mm vs 0.022±0.01mm vs 0.033±0.012mm vs 0.043±0.011mm，p<0.05，单因素方差分析）；.脉络膜厚度在不同种鼠间存在差异，其对离焦镜片的补偿作用也存在差异，自发近视豚鼠脉络膜最薄，可诱导及抵制近视进展的豚鼠脉络膜厚度依次增加，且脉络膜补偿镜片离焦的能力也依次增强。在暗适应情况下的视网膜电生理反应， 白化和有色豚鼠之间没有统计学差异；在明适应情况下， 自发近视的白化豚鼠高于有色豚鼠(p<0.01,单因素方差分析)。提示白化豚鼠的光感受器细胞层的电反应处于高敏感性。酪氨酸酶抑制剂使视网膜闪光ERG呈高反应性；多巴胺D2受体激动剂quinpirole可以提高有色豚鼠视网膜外层的闪光ERG反应（打药组vs溶剂组：22.8±22.6µV vs 1.1±2.4µV），而多巴胺D1受体激动剂SKF38393作用不显著。.结论：视网膜色素上皮层及脉络膜复合体中的酪氨酸酶途径的多巴胺能系统参与了眼屈光发育及近视的发生和发展。