Photoreceptor Rescue By Inhibition of Dopamine Signaling

描述(申请人提供)：由于cGMP-磷酸二酯酶基因的β亚基缺陷，Rd1小鼠的杆状光感受器在体内或器官培养中一个月大时退化。与大多数视网膜色素变性模型一样，退化的潜在机制仍然知之甚少。多巴胺是一种神经调节剂，影响脊椎动物视网膜中大多数(如果不是全部)细胞类型。我们发现，在RD1视网膜器官培养模型中，来自D_1或D_2受体家族的多巴胺拮抗剂完全阻断光感受器的退化。目前的理论模型和对多巴胺能功能的观察都无法解释这一令人惊讶的结果。例如，在小鼠的光感受器中，只有D4受体亚型被清楚地识别出来；而D1-家族 对抗者同样具有保护性。此外，D1族和D2族受体通常通过相反的途径发挥作用，以调节另一种途径的影响；在这里，它们给出了相同的结果。最后，多巴胺在视网膜中通常具有微妙的调节作用；在这里，对细胞存活的影响是戏剧性的和完全的-4周后，野生型和处理的RDL器官培养物之间没有检测到形态上的差异，而在未经处理的RD1培养物中，几乎所有的视杆都退化了。我们建议进行实验来解决这些差异，并在体内测试我们的发现的意义。首先，我们将确定缺乏多巴胺受体是否可以增加Rd1小鼠体内视网膜的光感受器存活和功能。其次，我们将解决潜在机制的两个方面，首先测试一个关于多巴胺受体的新假设，多巴胺受体是更大的G蛋白偶联受体家族的一个亚型。在最近的一次范式转变中，以前被认为只能作为单体发挥作用的G蛋白偶联受体，现在被认为有时会与非典型的 药理和功能。最近，阿片类药物、GABA和其他GPCRs已经证明了这种新的特征。由不同多巴胺受体亚型组成的异源二聚体的形成可以解释许多感知到的不一致。我们还将确定在RD1光感受器中是否存在D1族多巴胺受体。拟议的实验将产生两个重要的结果。首先，我们将在体内确定多巴胺信号在光感受器退化中的重要性，这可能导致视网膜退化的全新治疗方法。其次，我们将研究潜在的机制，包括测试多巴胺受体异二聚体诱导的退行性变模型，这可能导致一个新的区域。 视网膜细胞生物学的研究。

DESCRIPTION (provided by applicant): The rod photoreceptors of the rd1 mouse degenerate in vivo or in organ culture by one month of age as a result of a defect in the beta-subunit of the cGMP-phosphodiesterase gene. As with most models of retinitis pigmentosa, the underlying mechanism of degeneration remains poorly understood. Dopamine is a neuromodulator affecting most, if not all, cell types in the vertebrate retina. We have discovered that dopamine antagonists from either the D1- or D2-receptor families completely block the degeneration of photoreceptors in the rd1 retinal organ culture model. Current theoretical models and observations of dopaminergic function fail to explain this surprising result. For example, only the D4 receptor subtype has been clearly identified in mouse photoreceptors; yet a D1-family antagonist is equally protective. Also, D1- and D2-family receptors generally act through opposing pathways to modulate the effects of the other; here they give the same result. Finally, dopamine generally has subtle, modulatory effects in the retina; here the effect on cell survival is dramatic and complete - no morphological difference can be detected between wild type and treated rdl organ cultures after 4 weeks, when nearly all of the rods have degenerated in the untreated rd1 culture. We propose experiments to address these differences and to test the significance of our findings in vivo. First, we will determine whether the absence of dopamine receptors can increase photoreceptor survival and function in the rd1 mouse retina in vivo. Secondly, we will address two aspects of the underlying mechanism, first testing a novel hypothesis concerning dopamine receptors, a subtype of the larger G-protein-coupled receptor family. In a recent paradigm shift, G-protein-coupled receptors, previously thought to function only as monomers, are now recognized to sometimes form heterodimers with atypical pharmacology and function. Such novel characteristics have recently been demonstrated with opioid, GABA, and other GPCRs. The formation of heterodimers comprised of different dopamine receptor subtypes could explain many of the perceived incongruities. We will also determine if D1-family dopamine receptors are present in rd1 photoreceptors. The proposed experiments will generate two important results. First, we will determine the importance of dopamine signaling in photoreceptor degeneration in vivo, which could lead to entirely new therapeutic approaches for retinal degeneration. Secondly, we will investigate the underlying mechanism including testing a dopamine receptor heterodimer-induced model of degeneration which could lead to a new area of investigation in retinal cell biology.