Role of RARRES1 in diabetic kidney disease

项目总结 糖尿病肾病(DKD)是美国终末期肾病(ESRD)的最常见原因， 足细胞损伤是DKD和原发肾小球疾病的关键事件。体外和体内研究 维甲酸(RA)对小鼠足细胞损伤的保护作用 肾小球疾病，但这些发现尚未在人体研究中得到证实。利用肾小球 从肾病综合征研究中获得的人类原发性肾小球疾病的转录数据集 我们最近发现了维甲酸受体反应蛋白1(RARRES1) 作为一个基因，其表达与估计的肾小球滤过率(EGFR)下降呈负相关 并与原发性肾小球疾病患者的肾脏预后恶化有关，这表明 RARRES1是人类肾小球疾病的危险基因。由于RA信号已被证明在很大程度上 在实验性CKD模型中对足细胞损伤的肾脏保护作用，这些结果表明RA信号在 事实上，活体可能赋予二分性细胞保护(RARRES1非依赖性)和细胞病变(RARRES1- 依赖)在足细胞稳态调节中的作用。事实上，我们的体外和体内研究结果表明 足细胞RARRES1表达增加导致小鼠足细胞病变，而RARRES1表达降低 减轻实验性FSGS小鼠模型的足细胞损伤和疾病进展。从机械上讲， 膜结合RARRES1胞外区的裂解为可溶性形式(SRARRES1)及其 RARRES1介导的足细胞凋亡需要随后的内吞摄取。这些结果表明， RARRES1介导的足细胞损伤在肾小球疾病中的关键作用，最近发表在JCI上 [Chen et al.2020年，PMID：32634130]。在这些结果的基础上，我们进一步假设RARRES1是一个关键 足细胞丢失和DKD进展的致病诱因。由于RARRES1裂解对足细胞至关重要 体内细胞凋亡，对RARRES1裂解机制的更好理解可以转化为治疗 减少DKD的足细胞丢失，以及ii)由于DKD患者的血浆和尿液中sRARRES1水平增加， 血浆和尿sRARRES1可作为DKD进展的预后生物标志物。因此，在这个 应用1)研究RARRES1裂解的机制及其在肾细胞损伤中的作用 2)检测RARRES1在体内DKD发病机制中的作用；3)检测RARRES1在DKD发病机制中的作用 SRARRES1检测可用作DKD未来发病或进展的预后生物标志物， 利用两个群体(ISMMS BIOME BIOBANK和ACCORD)。此外，这项提案将解决当前的 关于RA在足细胞动态平衡中的二分性作用的知识缺口。

PROJECT SUMMARY Diabetic kidney disease (DKD) is the most common cause of end-stage renal disease (ESRD) in the US, and podocyte injury is a key event in DKD and primary glomerular diseases. In vitro and in vivo studies with experimental mouse models demonstrated a protective role of retinoic acid (RA) against podocyte injury in glomerular diseases, but these findings had not been validated in human studies. Leveraging the glomerular transcriptomic datasets of human primary glomerular disease available from the Nephrotic Syndrome Study Network Consortium (NEPTUNE), we recently identified retinoic acid receptor responder protein 1 (RARRES1) as a gene whose expression was negatively correlated with estimated glomerular filtration rate (eGFR) decline and associated with worsened renal outcomes in patients with primary glomerular disease, suggesting that RARRES1 is a risk gene for human glomerular disease. Since RA signaling had been shown to be largely renoprotective against podocyte injury in experimental CKD models, these results suggested that RA signaling in vivo may in fact confer dichotomous cytoprotective (RARRES1-independent) and cytopathic (RARRES1- dependent) effects in the regulation of podocyte homeostasis. Indeed, our in vitro and in vivo findings show that increased podocyte RARRES1 expression leads to podocytopathy in mice, whereas decreased RARRES1 mitigates podocyte injury and disease progression in experimental mouse model of FSGS. Mechanistically, the cleavage of membrane-bound RARRES1 in its extracellular domain into a soluble form (sRARRES1) and its subsequent endocytic uptake is required for RARRES1-mediated podocyte apoptosis. These results indicate a critical role of RARRES1-mediated podocyte injury in glomerular disease, which were recently published in JCI [Chen et al. 2020, PMID: 32634130]. Expanding on these results, we further posit that RARRES1 is a key pathogenic inducer of podocyte loss and DKD progression. Since RARRES1 cleavage is critical for the podocyte apoptosis in vivo, a better understanding of RARRES1 cleavage mechanism can be translated therapeutically to attenuate podocyte loss in DKD, and ii) since sRARRES1 levels increase in the plasma and urine of DKD patients, plasma and urinary sRARRES1 may serve as a prognostic biomarker of DKD progression. Therefore, in this application we propose to 1) examine the mechanism of RARRES1 cleavage and its role in kidney cell injury in vitro; 2) Examine the contribution of RARRES1 in DKD pathogenesis in vivo; and 3) Examine whether the sRARRES1 detection can be utilized as a prognostic biomarker for future incidence or progression of DKD, leveraging two cohorts (ISMMS BioMe biobank and ACCORD). Moreover, this proposal will address the current knowledge gap on the dichotomous role of RA in podocyte homeostasis.