Retinal progenitor cells (RPCs) remain in the eye throughout life and can be characterized by their ability for self-renewal as well as their specialization into different cell types. A recent study has suggested that metabotropic glutamate receptors (mGluRs) participate in the processes of multiple types of stem cells. Therefore, clarifying the functions of different subtypes of mGluRs in RPCs may provide a novel treatment strategy for regulating the proliferation and differentiation of endogenous RPCs after retinal degeneration. In this study, we observed that mGluR4 was functionally expressed in RPCs, with an effect on cell viability and intracellular cAMP concentration. The activation of mGluR4 by VU0155041 (VU, mGluR4 positive allosteric selective modulator) reduced the number of BrdU⁺/Pax6⁺ double-positive cells and Cyclin D1 expression levels while increasing the number of neuron-specific class III beta-tubulin (Tuj1)- and Doublecortin (DCX)-positive cells. The knockdown of mGluR4 by target-specific siRNA abolished the effects of VU on RPC proliferation and neuronal differentiation. Further investigation demonstrated that mGluR4 activation inhibited AKT phosphorylation and up-regulated PTEN protein expression. Moreover, the VU0155041-induced inhibition of proliferation and enhancement of neuronal differentiation in RPCs were significantly hampered by Forskolin (adenylyl cyclase activator) and VO-OHpic trihydrate (PTEN inhibitor). In contrast, the effect of LY294002 (a highly selective Akt inhibitor) on proliferation and differentiation was similar to that of VU. These results indicate that mGluR4 activation can suppress proliferation and promote the neural differentiation of cultured rat RPCs through the cAMP/PTEN/AKT pathway. Our research lays the foundation for further pharmacological work exploring a novel potential therapy for several retinal diseases.

视网膜祖细胞（RPCs）终生保留在眼中，其特征在于它们的自我更新能力以及它们对不同细胞类型的专长。最近的一项研究表明，代谢型谷氨酸受体（mGluRs）参与多种类型的干细胞的过程。因此，阐明RPC中mGluRs不同亚型的功能可能为调节视网膜变性后内源RPC的增殖和分化提供一种新的治疗策略。在这项研究中，我们观察到mGluR4在RPC中功能性表达，对细胞活力和细胞内cAMP浓度有影响。VU0155041（VU，mGluR4正构构选择性调节剂）激活mGluR4减少了BrdU ⁺ / Pax6 ^+的数量双阳性细胞和Cyclin D1表达水平，同时增加神经元特异性III类β-微管蛋白（Tuj1）和Doublecortin（DCX）阳性细胞的数量。靶标特异性siRNA抑制mGluR4消除了VU对RPC增殖和神经元分化的影响。进一步的研究表明，mGluR4激活抑制AKT磷酸化并上调PTEN蛋白表达。此外，Forskolin（腺苷酸环化酶激活剂）和VO-OHpic trihydrate（PTEN抑制剂）显着阻碍了VU0155041诱导的RPC增殖抑制和神经元分化增强。相反，LY294002（一种高度选择性的Akt抑制剂）对增殖和分化的作用与VU相似。这些结果表明，mGluR4激活可以抑制增殖，并通过cAMP / PTEN / AKT途径促进培养的大鼠RPC的神经分化。我们的研究为进一步的药理工作奠定了基础，以探索针对几种视网膜疾病的新型潜在疗法。