mGluR5 inhibits microglial activation and neuronal cell death after TBI

 描述(申请人提供)：创伤性脑损伤(TBI)触发延迟的生化变化，包括慢性神经炎，导致组织丢失和神经功能缺陷。与临床脑损伤相似，我们已经证明，在实验性脑损伤后，M1(神经毒性)小胶质细胞数月到数年地慢性活跃，导致进行性神经变性。我们小组是第一个证明传统的正构体mGluR5代谢型谷氨酸受体5(MGluR5)激动剂能够减弱miR-155的能力，miR-155是一种关键的M1诱导microRNA(MiR)，负面调节M1表型，限制慢性小胶质细胞激活和减少进行性神经元丢失，即使在脑损伤后一个月中央给药时也是如此。重要的是，mGluR5阳性变构调节剂(PAM)不仅减弱了M1，而且促进了脑损伤后M2(神经保护性)小胶质细胞的表型。这是通过联合作用于神经炎症的关键microRNA调节器，下调miR-155和上调M2诱导的miR-124来实现的。迫切需要确定选择性靶向治疗以限制创伤后炎症性神经变性，这一需求尚未得到满足。我们的中心假设是，选择性mGluR5 PAM通过同时减弱脑损伤诱导的慢性M1反应和促进神经保护性M2反应，在神经炎症/神经变性方面具有比正构体激动剂更好的治疗效果；针对潜在机制并使miR-155/miR-124平衡有利于miR-124的分子干预具有神经保护作用。这些假说得到了强有力的初步研究的支持，这些研究表明，mGluR5 PAM降低了miR-155，增加了miR-124，逆转了M1/M2失衡，并减轻了脑损伤后的神经元丢失和神经损伤。拟议的具体目标是：1)确定负责下调M1和上调M2小胶质细胞的特定mGluR5 PAM(VU0360172)信号中介；2)确定mGluR5 PAM延迟全身治疗对脑损伤所致慢性神经炎、进行性神经变性及相关神经损伤的神经保护作用；以及3)确定针对miR-155/-124的延迟分子干预对脑损伤所致慢性神经炎、进行性神经变性及相关神经损伤的神经保护作用。这些目标应支持以下预期结果：脑损伤后mGluR5 PAM的神经保护作用部分逆转了创伤后miR-155/miR-124的变化；即使延迟全身给药，mGluR5 PAM仍具有强大的神经保护作用；脑损伤后miR-155(下调)和miR-124(上调)的联合分子调控具有相加的神经保护作用。我们期望通过阐明脑外伤后进行性神经变性的病理生理机制，并为改变M1/M2平衡的晚期治疗干预提供实验支持，从而产生重要的积极影响。

 DESCRIPTION (provided by applicant): Traumatic brain injury (TBI) triggers delayed biochemical changes, including chronic neuroinflammation, that contribute to tissue loss and neurological deficits. Similar to clinical TBI, we have shown that M1 (neurotoxic) microglia are chronically active for months-to-years following experimental TBI, contributing to progressive neurodegeneration. Our group was the first to demonstrate the ability of conventional orthosteric mGluR5 metabotropic glutamate receptor 5 (mGluR5) agonists to attenuate miR-155, a key M1-inducing microRNA (miR), negatively regulate the M1 phenotype, limit chronic microglial activation and reduce progressive neuronal loss, even when administered centrally at one month after TBI. Importantly, mGluR5 positive allosteric modulators (PAMs) not only attenuate M1 but also promote M2 (neuroprotective) microglia phenotypes after TBI. This is accomplished by combined action on key microRNA modulators of neuroinflammation, down-regulating miR-155 and up-regulating the M2-inducing miR-124. There is an urgent unmet need to identify selective targeted therapies to limit posttraumatic inflammatory neurodegeneration. Our central hypothesis is that selective mGluR5 PAMs have superior therapeutic effects than orthosteric agonists on neuroinflammation/neurodegeneration by concurrently attenuating both TBI-induced chronic M1 responses and promoting neuroprotective M2 responses; molecular interventions that target the underlying mechanisms and tip the miR-155/miR-124 balance in favor of miR-124 are neuroprotective. These hypotheses are supported by strong preliminary studies showing that mGluR5 PAMs lower miR-155, increase miR-124, reverse M1/M2 imbalance, as well as attenuate neuronal loss and neurological impairments following TBI. The proposed specific aims are: 1) Define the specific mGluR5 PAM (VU0360172) signaling intermediaries that are responsible for down-regulating M1 and up-regulating M2 microglia; 2) Determine the neuroprotective effects of delayed systemic treatment with mGluR5 PAMs on TBI-induced chronic neuroinflammation, progressive neurodegeneration and associated neurological impairments; and 3) Determine the neuroprotective effects of delayed molecular interventions targeting miR-155/-124 on TBI-induced chronic neuroinflammation, progressive neurodegeneration and associated neurological impairments. These aims should support the following expected outcomes: neuroprotective effects of mGluR5 PAMs after TBI reflect, in part, reversing posttraumatic miR-155/miR-124 changes; that mGluR5 PAMs have robust neuroprotective effects even with delayed systemic administration; and that combined molecular modulation of miR-155 (down-regulation) and miR-124 (up-regulation) after TBI have additive neuroprotective effects. We expect to have an important positive impact by demonstrating the pathophysiological mechanisms underlying progressive neurodegeneration after TBI, and providing experimental support for late therapeutic interventions that alter M1/M2 balance.