Department of Nephrology and Hypertension, Friedrich-Alexander University Erlangen-Nürnberg and University Hospital Erlangen, Loschgestrasse 8, 91054, Erlangen, Germany.
Cell Tissue Res. 2020 Jul;381(1):125-140. doi: 10.1007/s00441-020-03186-w. Epub 2020 Mar 18.
The role of the hypoxia-inducible transcription factor (HIF) pathway in renal lipid metabolism is largely unknown. As HIF stabilizing prolyl hydroxylase (PHD) inhibitors are currently investigated in clinical trials for the treatment of renal anemia, we studied the effects of genetic deletion and pharmacological inhibition of PHDs on renal lipid metabolism in transgenic mice and human primary tubular epithelial cells (hPTEC). Tubular cell-specific deletion of HIF prolyl hydroxylase 2 (Phd2) increased the size of Oil Red-stained lipid droplets in mice. In hPTEC, the PHD inhibitors (PHDi) DMOG and ICA augmented lipid accumulation, which was visualized by Oil Red staining and assessed by microscopy and an infrared imaging system. PHDi-induced lipid accumulation required the exogenous availability of fatty acids and was observed in both proximal and distal hPTEC. PHDi treatment was not associated with structural features of cytotoxicity in contrast to treatment with the immunosuppressant cyclosporine A (CsA). PHDi and CsA differentially upregulated the expression of the lipid droplet-associated genes PLIN2, PLIN4 and HILPDA. Both PHDi and CsA activated AMP-activated protein kinase (AMPK) indicating the initiation of a metabolic stress response. However, only CsA triggered endoplasmic reticulum (ER) stress as determined by the increased mRNA expression of multiple ER stress markers but CsA-induced ER stress was not linked to lipid accumulation. Our data raise the possibility that PHD inhibition may protect tubular cells from toxic free fatty acids by trapping them as triacylglycerides in lipid droplets. This mechanism might contribute to the renoprotective effects of PHDi in experimental kidney diseases.
缺氧诱导因子（HIF）通路在肾脏脂质代谢中的作用在很大程度上尚不清楚。由于 HIF 稳定脯氨酰羟化酶（PHD）抑制剂目前正在临床试验中用于治疗肾性贫血，因此我们研究了基因敲除和 PHD 抑制剂对转基因小鼠和人原代肾小管上皮细胞（hPTEC）中肾脏脂质代谢的影响。HIF 脯氨酰羟化酶 2（Phd2）的肾小管细胞特异性缺失增加了小鼠油红染色脂质滴的大小。在 hPTEC 中，PHD 抑制剂（PHDi）DMOG 和 ICA 增强了脂质积累，这可以通过油红染色和显微镜观察以及红外成像系统进行评估。PHDi 诱导的脂质积累需要外源性脂肪酸的可用性，并且在近端和远端 hPTEC 中都观察到。与免疫抑制剂环孢素 A（CsA）的治疗不同，PHDi 治疗与细胞毒性的结构特征无关。与 CsA 处理相比，PHDi 和 CsA 分别上调了与脂滴相关的基因 PLIN2、PLIN4 和 HILPDA 的表达。PHDi 和 CsA 均激活了 AMP 激活的蛋白激酶（AMPK），表明代谢应激反应的开始。然而，只有 CsA 通过多个 ER 应激标志物的 mRNA 表达增加来触发内质网（ER）应激，但 CsA 诱导的 ER 应激与脂质积累无关。我们的数据提出了一种可能性，即 PHD 抑制可能通过将游离脂肪酸捕获在脂滴中作为三酰基甘油来保护肾小管细胞免受毒性游离脂肪酸的侵害。这种机制可能有助于 PHDi 在实验性肾脏疾病中的肾脏保护作用。
