The role of cyclin G1 in chronic kidney disease

急性肾损伤(AKI)不仅是住院患者死亡率增加的独立危险因素，它 极大地增加了在以后的生活中患上慢性肾脏疾病(CKD)的可能性。治疗 预防AKI向CKD转变以及CKD进展为终末期肾病的选择仍然存在 非常有限。已知细胞周期停滞于G2/M期有助于进行性肾纤维化； 然而，潜在的机制尚不清楚。我们的初步数据已经确定了细胞周期蛋白G1，一种非典型的 细胞周期蛋白作为一种新的肾脏G2/M期停滞调节因子。细胞周期蛋白G1在未损伤的肾脏中不表达， 不是细胞周期进程所必需的。细胞周期蛋白G1在慢性阻塞性肺疾病小鼠模型中显著上调 肾脏疾病。Cyclin G1基因缺失可抑制CKD模型的G2/M期停滞和纤维化进展。我们有 细胞周期蛋白G1‘S细胞周期蛋白依赖性激酶是慢性肾脏病G2/M期停滞和纤维化的主要驱动因素。 我们的假设是Cyclin G1通过激活CDK5诱导促纤维化的G2/M期停滞，有助于 促进病理性线粒体碎裂和衰老样分泌的纤维化 表型。该应用的目的是(1)确定周期蛋白G1诱导G2/M的机制 停滞；(2)确定细胞周期依赖的线粒体变化在纤维化进展中的作用；以及(3) 明确G2/M期停滞如何驱动促纤维化因子的分泌。在目标1中，我们将测试慢性损伤对 缺乏CDK5的小鼠肾脏减少，并确定细胞周期蛋白G1/CDK5如何调节G2/M期停滞、纤维化 细胞因子的产生与器官纤维化。对于目标2，我们将利用体外细胞培养基因敲除模型， 抑制剂和分子生物学方法来评估线粒体网络是否发生破坏 在细胞周期的G2和M期，在延长线粒体的过程中导致前纤维化表型 G2/M期阻滞细胞出现片段化。我们还将量化线粒体形态的变化 活体使用我们实验室开发的一种新的超分辨率成像技术。在目标3中，我们将研究 CDK5诱导的衰老样表型可促进近端肾小管细胞分泌细胞因子。 这些目标的成功完成将确立细胞周期蛋白G1在器官纤维化中的作用，并确定 G2/M期停滞调节纤维化反应的机制，提示潜在的治疗潜力 细胞周期蛋白G1的抑制作用。抗细胞周期蛋白G1基因疗法已被批准进行3期临床试验，并用于 实体瘤患者，最长随访9年。因此，靶向细胞周期蛋白G1代表了一种很有希望的 治疗纤维化的方法。

Acute kidney injury (AKI) is not only an independent risk factor for increased mortality in hospitalized patients, it dramatically increases the likelihood of developing chronic kidney disease (CKD) later in life. Treatment options to prevent the AKI to CKD transition, as well as CKD progression to end-stage kidney disease, remain very limited. It is known that cell cycle arrest at the G2/M phase contributes to progressive kidney fibrosis; however, the underlying mechanism is unclear. Our preliminary data have identified cyclin G1, an atypical cyclin, as a novel regulator of G2/M arrest in the kidney. Cyclin G1 is not expressed in uninjured kidney and is not required for cell cycle progression. Cyclin G1 is dramatically upregulated in mouse models of chronic kidney disease. Deletion of cyclin G1 inhibits G2/M arrest and fibrosis progression in models of CKD. We have identified cyclin G1’s cyclin dependent kinase (CDK5) as the main driver of G2/M arrest and fibrosis in CKD. Our hypothesis is cyclin G1 induces a pro-fibrotic G2/M arrest via activation of CDK5, contributing to fibrosis by promoting a pathological mitochondrial fragmentation and senescence-like secretory phenotype. The aims of the application are to (1) Define the mechanism by which cyclin G1 induces G2/M arrest; (2) Determine the role of cell cycle-dependent changes to mitochondria in fibrosis progression; and (3) Define how G2/M arrest drives secretion of profibrotic factors. In Aim 1, we will test if chronic injury to the kidneys is reduced in mice lacking CDK5 and define how cyclin G1/CDK5 regulates G2/M arrest, profibrotic cytokine production and organ fibrosis. For Aim 2, we will utilize in vitro cell culture knockout models, specific inhibitors and molecular biology approaches to assess if disruption of the mitochondrial network, which occurs during the G2 and M phases of the cell cycle, leads to profibrotic phenotypes during prolonged mitochondrial fragmentation observed in G2/M arrested cells. We will also quantify changes in mitochondrial morphology in vivo using a novel super-resolution imaging technique developed in our lab. In Aim 3 we will examine whether the CDK5 induce senescence-like phenotypes can promote cytokine secretion from proximal tubular cells. Successful completion of the aims will establish the role of cyclin G1 in organ fibrosis as well as determine the mechanism by which G2/M arrest regulates fibrotic responses, informing the potential therapeutic potential of inhibition of cyclin G1. Anti-cyclin G1 gene therapy has been approved for phase 3 clinical trials and used in patients with solid tumors, with up to 9-year follow-up. Thus, targeting of cyclin G1 represents a promising approach to treat fibrosis.