Understanding Epithelial Plasticity in Renal Repair after Acute Kidney Injury

对急性肾损伤后肾修复中上皮可塑性的认识 急性肾损伤（阿基）后，存活的肾小管上皮细胞（TEC）增殖并再生肾小管上皮细胞。 损伤的上皮导致肾功能恢复。然而，直到最近， 上皮再生仍然难以捉摸。为此，我们最近确定SOX 9为分子驱动因子， 使受损的上皮细胞再生。将遗传谱系策略与组织特异性条件敲除相结合 方法，我们确定SOX 9作为修复和形成之间的直接，内在的分子联系， 肾单位管状上皮。在损伤后上皮成功再生后，SOX 9达到基线水平， 水平然而，在缺血性阿基进展为慢性肾病（CKD）期间， 持续性损伤的TEC安装了具有细胞增殖特征的强持续性SOX 9（sSOX 9+），从而 划分“未解决的损伤/修复细胞类型”。这些发现提出了一些尚未回答的关键问题，包括： (1)人肾脏在阿基后激活SOX 9，（2）受损上皮细胞如何快速装载SOX 9前体， 复制反应，（3）SOX 9如何驱动上皮再生以及激活后是否去分化 损伤的TEC到其胚胎祖细胞样状态以驱动修复，以及（4）sSOX 9+是否有助于 阿基进展为CKD。为此，在此我们进一步鉴定了（a）人阿基后的SOX 9活化，（B）a 原代小鼠和人近端TEC中的核磷酸EGFR：SOX 9复制前轴，和（c） sSOX 9+细胞与αSMA+肌成纤维细胞的密切、稳健的关联。该研究将测试（目的 1)损伤通过核磷酸化EGFR激活Sox 9诱导EGFR信号传导的假说， 发挥Sox 9依赖性促修复作用，Sox 9本身足以驱动增殖;（目的2） 将揭示Sox 9协调修复作用的分子基础，同时确定损伤是否 激活的Sox 9使受损的PTEC去分化为祖细胞样状态;（目的3）检验以下假设： 持续的Sox 9+亚群划分“未解决的损伤/修复”细胞类型有助于阿基的进展， CKD。拟议的研究是创新的，因为使用最先进的方法，我们将批判性地 研究肾修复中上述迄今未研究的分子和细胞途径。拟议 研究是重要的和有影响力的，因为（A）我们的发现类似于我们的小鼠研究强调SOX 9 人缺血性阿基后PTEC内的激活和人中基于SOX 9的促复制应答 原代近端肾小管上皮细胞;和（B）损伤诱导的上皮可塑性是一个知之甚少 过程，以及拟议的研究工作所获得的深刻的批判性见解不仅将推动肾脏领域， 将直接应用于对其他基于上皮的组织重塑的机制理解， 器官系统。更好地理解这些过程对于开发旨在 利用和增强内源性修复过程，同时阻断促纤维化反应。

Understanding Epithelial Plasticity in Renal Repair after Acute Kidney Injury Following acute kidney injury (AKI), surviving tubular epithelial cells (TECs) proliferate and regenerate the injured epithelium leading to kidney function recovery. However, until recently, the intrinsic molecular driver of epithelial regeneration remained elusive. To this end, we recently identified SOX9 as the molecular driver that regenerates the injured epithelium. Coupling genetic lineage strategy to tissue-specific, conditional knock-out methodology, we identified SOX9 as a direct, intrinsic molecular link between repair and formation of the nephron tubular epithelia. Upon successful regeneration of the epithelia after injury, SOX9 attained baseline level. However, during progression of ischemic AKI to chronic kidney disease (CKD), distinct, sporadic persistently injured TECs mounted a strong sustained SOX9 (sSOX9+) with cell proliferation signature thereby demarcating “unresolved injury/repair cell-type”. These findings raise crucial unanswered questions, including: (1) does human kidneys activate SOX9 after AKI, (2) how an injured epithelium rapidly mounts a SOX9 pro- replicative response, (3) how SOX9 drive epithelial regeneration and whether upon activation it dedifferentiates the injured TECs to its embryonic progenitor-like state to drive repair, and (4) whether sSOX9+ contributes to the progression of AKI to CKD. To this end, here we further identify (a) SOX9 activation after human AKI, (b) a nuclear phosphoEGFR:SOX9 pro-replicative axis in both primary mice and human proximal TECs, and (c) intimate, robust association of sSOX9+ cells with αSMA+ myofibroblasts. The proposed research will test (Aim 1) the hypothesis that injury induced EGFR signaling via nuclear phosphorylated EGFR activates Sox9 and exerts Sox9-dependent pro-reparative effects, with Sox9 per se being sufficient to drive proliferation; (Aim 2) will reveal molecular underpinnings of Sox9-orchestrated reparative action whilst determining whether injury- activated Sox9 dedifferentiates the injured PTECs to a progenitor-like state; (Aim 3) test the hypothesis that sustained Sox9+ subset demarcating “unresolved injury/repair” cell-type contribute to progression of AKI to CKD. The proposed research is innovative because using state-of-the-art approaches we will critically investigate the above heretofore-unexamined molecular and cellular pathways in renal repair. The proposed research is significant and impactful because (A) our findings akin to our mice studies highlight SOX9 activation within the PTECs after human ischemic AKI and SOX9-based pro-replicative responses in human primary proximal tubular epithelial cells; and (B) injury-induced epithelial plasticity is a poorly understood process, and deep, critical insights gained by the proposed research work will advance not only kidney field but will have direct application to the mechanistic understanding of tissue remodeling in other epithelial-based organ systems. Better understanding of such processes is crucial in the development of therapies aimed to harness and augment endogenous reparative processes while simultaneously blocking pro-fibrotic responses.