Department of Nephrology, The First Hospital of Jilin University, Changchun, China.
Department of Internal Medicine, College of Medicine, Institute of Kidney Disease Research, Yonsei University, Seoul, South Korea.
Diabetologia. 2024 Sep;67(9):1980-1997. doi: 10.1007/s00125-024-06191-8. Epub 2024 Jun 15.
AIMS/HYPOTHESIS: Glomerular lipid accumulation is a defining feature of diabetic kidney disease (DKD); however, the precise underlying mechanism requires further elucidation. Recent evidence suggests a role for proprotein convertase subtilisin/kexin type 9 (PCSK9) in intracellular lipid homeostasis. Although PCSK9 is present in kidneys, its role within kidney cells and relevance to renal diseases remain largely unexplored. Therefore, we investigated the role of intracellular PCSK9 in regulating lipid accumulation and homeostasis in the glomeruli and podocytes under diabetic conditions. Furthermore, we aimed to identify the pathophysiological mechanisms responsible for the podocyte injury that is associated with intracellular PCSK9-induced lipid accumulation in DKD.
In this study, glomeruli were isolated from human kidney biopsy tissues, and glomerular gene-expression analysis was performed. Also, db/db and db/m mice were used to perform glomerular gene-expression profiling. We generated DKD models using a high-fat diet and low-dose intraperitoneal streptozocin injection in C57BL/6 and Pcsk9 knockout (KO) mice. We analysed cholesterol and triacylglycerol levels within the kidney cortex. Lipid droplets were evaluated using BODIPY staining. We induced upregulation and downregulation of PCSK9 expression in conditionally immortalised mouse podocytes using lentivirus and siRNA transfection techniques, respectively, under diabetic conditions.
A significant reduction in transcription level of PCSK9 was observed in glomeruli of individuals with DKD. PCSK9 expression was also reduced in podocytes of animals under diabetic conditions. We observed significantly higher lipid accumulation in kidney tissues of Pcsk9 KO DKD mice compared with wild-type (WT) DKD mice. Additionally, Pcsk9 KO mouse models of DKD exhibited a significant reduction in mitochondria number vs WT models, coupled with a significant increase in mitochondrial size. Moreover, albuminuria and podocyte foot process effacement were observed in WT and Pcsk9 KO DKD mice, with KO DKD mice displaying more pronounced manifestations. Immortalised mouse podocytes exposed to diabetic stimuli exhibited heightened intracellular lipid accumulation, mitochondrial injury and apoptosis, which were ameliorated by Pcsk9 overexpression and aggravated by Pcsk9 knockdown in mouse podocytes.
CONCLUSIONS/INTERPRETATION: The downregulation of PCSK9 in podocytes is associated with lipid accumulation, which leads to mitochondrial dysfunction, cell apoptosis and renal injury. This study sheds new light on the potential involvement of PCSK9 in the pathophysiology of glomerular lipid accumulation and podocyte injury in DKD.
目的/假设：肾小球脂质积累是糖尿病肾病（DKD）的一个特征；然而，其确切的潜在机制仍需要进一步阐明。最近的证据表明，前蛋白转化酶枯草溶菌素/柯萨奇蛋白酶 9（PCSK9）在细胞内脂质稳态中发挥作用。尽管 PCSK9 存在于肾脏中，但它在肾脏细胞中的作用及其与肾脏疾病的关系在很大程度上仍未得到探索。因此，我们研究了细胞内 PCSK9 在调节糖尿病条件下肾小球和足细胞中脂质积累和稳态中的作用。此外，我们旨在确定与细胞内 PCSK9 诱导的 DKD 脂质积累相关的足细胞损伤的病理生理机制。
在这项研究中，从人肾活检组织中分离出肾小球，并进行肾小球基因表达分析。此外，还使用 db/db 和 db/m 小鼠进行肾小球基因表达谱分析。我们使用高脂肪饮食和低剂量腹腔链脲佐菌素注射在 C57BL/6 和 Pcsk9 敲除（KO）小鼠中建立 DKD 模型。我们分析了肾脏皮质中的胆固醇和三酰甘油水平。使用 BODIPY 染色评估脂滴。我们使用慢病毒和 siRNA 转染技术分别在条件性永生化小鼠足细胞中上调和下调 PCSK9 表达，在糖尿病条件下进行实验。
在 DKD 患者的肾小球中观察到 PCSK9 的转录水平显著降低。在糖尿病动物的足细胞中，PCSK9 的表达也减少了。与野生型（WT）DKD 小鼠相比，Pcsk9 KO DKD 小鼠的肾脏组织中脂质积累明显更高。此外，Pcsk9 KO 小鼠的 DKD 模型与 WT 模型相比，线粒体数量显著减少，而线粒体大小显著增加。此外，在 WT 和 Pcsk9 KO DKD 小鼠中观察到白蛋白尿和足细胞足突融合，KO DKD 小鼠的表现更为明显。暴露于糖尿病刺激的永生化小鼠足细胞表现出细胞内脂质积累、线粒体损伤和细胞凋亡增加，而 PCSK9 的过表达可改善这种情况，而 PCSK9 的敲低则会加剧这种情况。
结论/解释：足细胞中 PCSK9 的下调与脂质积累有关，这导致线粒体功能障碍、细胞凋亡和肾脏损伤。这项研究揭示了 PCSK9 可能参与 DKD 肾小球脂质积累和足细胞损伤的病理生理学机制。
