Role of Cell Cycle Pathways in Traumatic Brain Injury

创伤性脑损伤（TBI）导致神经元细胞死亡，并伴有星形胶质细胞增殖和炎症 与小胶质细胞的激活有关。细胞周期蛋白的上调发生在CMS创伤后， 以促进有丝分裂后细胞如神经元的凋亡性细胞死亡。这也可能导致创伤后 胶质增生和小胶质细胞活化。我们实验室最近的研究表明， 啮齿类动物TBI或脊髓损伤后许多细胞周期蛋白，这些蛋白在神经元中共表达 显示半胱天冬酶-3活化和凋亡的形态学特征。此外，在几个经典模型中， 在原代神经元细胞培养物中，损伤与许多caspase-3依赖性细胞凋亡的上调有关。 这些相同的细胞周期蛋白。此外，初步研究表明，抑制关键的细胞周期调控， 在体外和体内，这些信号通路减少损伤诱导的细胞死亡。因此，用细胞周期抑制剂治疗 TBI后，大鼠的损伤体积和周围的胶质瘢痕明显减少;它也显着改善 脑损伤后的运动和认知功能 本研究主要针对以下假设：（1）TBI上调细胞周期调控 在神经元、星形胶质细胞和小胶质细胞中的mRNA和蛋白质水平上的组分;（2）这种上调 促进神经元凋亡和星形胶质细胞增殖;（3）细胞周期蛋白的上调有助于 小胶质细胞活化和随后相关炎症因子的释放;和（4）用细胞治疗 周期抑制剂是神经保护性的，其机制包括抑制内源性半胱天冬酶途径， 神经元，以及减少的胶质细胞活化和减少的小胶质细胞介导的炎症因子的释放。 具体目标是证明：（1）a。TBI导致许多关键细胞周期的表达增加 相关基因/蛋白，包括神经元和神经胶质中的细胞周期蛋白D1、CDK 4、CDK 5和Rb; B.增加的蛋白质 表达与神经元中半胱天冬酶依赖性凋亡、星形胶质细胞增殖、 小胶质细胞和促进小胶质细胞相关炎症因子的释放; c.细胞周期蛋白D1基因敲除小鼠 强烈损伤诱导的病理生物学包括神经元凋亡、脑损伤、星形胶质细胞瘢痕形成、 小胶质细胞相关的炎症因子和创伤后神经功能缺损;（2）a.结构不同细胞 周期抑制剂以剂量依赖性方式减少病变体积并改善认知和运动功能 在大鼠和小鼠的两种病理生物学上不同的TBI模型中; B.细胞周期抑制剂降低细胞周期 TBI后的活化，从而减少随后的神经元细胞死亡、反应性神经胶质增生和小神经胶质活化; c. 细胞周期抑制剂的延迟全身给药是一种更临床相关的范例，具有神经保护作用。

Traumatic brain injury (TBI) causes neuronal cell death combined with astroglial proliferation and inflammation associated with activation of microglia. Upregulation of cell cycle proteins occurs after CMS trauma, and appears to contribute to apoptotic cell death of post-mitotic cells such as neurons. It also likely contributes to posttraumatic gliosis and microglial activation. Recent studies in our laboratory have shown significantly increased expression of many cell cycle proteins after TBI or spinal cord injury in rodents, with the proteins co-expressed in neurons showing caspase-3 activation and morphological features of apoptosis. Moreover, in several classical models of caspase-3 dependent apoptosis in primary neuronal cell cultures, injury is associated with up-regulation of many of these same cell cycle proteins. In addition, pilot studies have indicated that inhibition of key cell cycle regulatory pathways reduces injury-induced cell death both in vitro and in vivo. Thus, treatment with a cell cycle inhibitor after TBI in rats markedly reduces lesion volumes and the surrounding glial scar; it also significantly improves motor and cognitive functions following brain injury. The proposed studies are intended to address the following hypotheses: (1) TBI up-regulates key cell cycle constituents at both the mRNA and protein levels in neurons, astrocytes, and microglia; (2) such an up-regulation promotes apoptosis in neurons and proliferation of astrocytes; (3) up-regulation of cell cycle proteins contributes to microglial activation and subsequent release of associated inflammatory factors; and (4) treatment with cell cycle inhibitors is neuroprotective, through mechanisms that include inhibition of the intrinsic caspase pathway in neurons, as well as reduced glial activation and diminished release of microglial mediated inflammatory factors. Specific aims are to demonstrate that: (1) a. TBI causes increased expression of a number of critical cell cycle related genes/proteins, including cyclin D1, CDK4, CDK5 and Rb in both neurons and glia; b. increased protein expression is associated with caspase-dependent apoptosis in neurons, proliferation of astroglia, activation of microglia and facilitated release of microglia-related inflammatory factors; c. cyclin D1 knockout mice show less intense injury-induced pathobiology including neuronal apoptosis, brain lesion, astroglial scar formation, release of microglial associated inflammatory factors, and post-traumatic neurological deficits; (2) a. structurally different cell cycle inhibitors in dose-dependent manner reduce lesion volumes and improve cognitive as well as motor function in two pathobiologically different TBI models in the rat and mouse; b. cell cycle inhibitors decrease cell cycle activation after TBI, thereby reducing subsequent neuronal cell death, reactive gliosis and microglial activation; c. delayed systemic administration of a cell cycle inhibitor, a more clinically relevant paradigm, is neuroprotective.