Abstract：
After acute kidney injury (AKI), renal tubular epithelial cells (RTECs) are pathologically characterized by intracellular lipid droplet (LD) accumulation, which are involved in RTEC injury and kidney fibrosis. However, its pathogenesis remains incompletely understood. The protein, αKlotho, primarily expressed in RTECs, is well known as an anti-aging hormone wielding versatile functions, and its membrane form predominantly acts as a co-receptor for fibroblast growth factor 23. Here, we discovered a connection between membrane αKlotho and intracellular LDs in RTECs. Fluorescent fatty acid (FA) pulse-chase assays showed that membrane αKlotho deficiency in RTECs, as seen in αKlotho homozygous mutated (kl/kl) mice or in mice with ischemia-reperfusion injury (IRI)-induced AKI, inhibited FA mobilization from LDs by impairing adipose triglyceride lipase (ATGL)-mediated lipolysis and lipophagy. This resulted in LD accumulation and FA underutilization. IRI-induced alterations were more striking in αKlotho deficiency. Mechanistically, membrane αKlotho deficiency promoted E3 ligase peroxin2 binding to ubiquitin-conjugating enzyme E2 D2, resulting in ubiquitin-mediated degradation of ATGL which is a common molecular basis for lipolysis and lipophagy. Overexpression of αKlotho rescued FA mobilization by preventing ATGL ubiquitination, thereby lessening LD accumulation and fibrosis after AKI. This suggests that membrane αKlotho is indispensable for the maintenance of lipid homeostasis in RTECs. Thus, our study identified αKlotho as a critical regulator of lipid turnover and homeostasis in AKI, providing a viable strategy for preventing tubular injury and the AKI-to-chronic kidney disease transition.
摘要：
急性肾损伤（AKI）后，肾小管上皮细胞（RTEC）的病理特征是细胞内脂滴（LD）积累，参与RTEC损伤和肾纤维化。然而,其发病机制尚不完全清楚。蛋白质,αKlotho,主要以RTEC表示，是众所周知的抗衰老激素，具有多种功能，其膜形式主要充当成纤维细胞生长因子23的共受体。这里,我们发现了膜αKlotho与RTEC细胞内LD之间的联系。荧光脂肪酸（FA）脉冲追踪试验表明，RTEC中膜αKlotho缺乏，如在αKlotho纯合突变（kl/kl）小鼠或缺血再灌注损伤（IRI）诱导的AKI小鼠中所见，通过损害脂肪甘油三酯脂肪酶（ATGL）介导的脂解和吞噬来抑制FA从LD动员。这导致LD积累和FA利用不足。IRI诱导的改变在αKlotho缺乏症中更为明显。机械上,膜αKlotho缺乏促进E3连接酶过氧化物酶2与泛素缀合酶E2D2结合，导致泛素介导的ATGL降解，这是脂解和吞噬的共同分子基础。αKlotho的过表达通过阻止ATGL泛素化来拯救FA动员，从而减少AKI后的LD积累和纤维化。这表明膜αKlotho对于维持RTEC中脂质稳态是必不可少的。因此，我们的研究确定αKlotho是AKI中脂质周转和稳态的关键调节因子，为预防肾小管损伤和AKI向慢性肾脏疾病过渡提供可行的策略。
