Department of Nephrology, Osaka University Graduate School of Medicine, Osaka, Japan.
Transdimensional Life Imaging Division, Institute for Open and Transdisciplinary Research Initiatives, Osaka University, Osaka, Japan.
Am J Physiol Renal Physiol. 2024 Aug 1;327(2):F208-F223. doi: 10.1152/ajprenal.00046.2024. Epub 2024 Jun 13.
Increased dietary phosphate consumption intensifies renal phosphate burden. Several mechanisms for phosphate-induced renal tubulointerstitial fibrosis have been reported. Considering the dual nature of phosphate as both a potential renal toxin and an essential nutrient for the body, kidneys may possess inherent protective mechanisms against phosphate overload, rather than succumbing solely to injury. However, there is limited understanding of such mechanisms. To identify these mechanisms, we conducted single-cell RNA sequencing (scRNA-seq) analysis of the kidneys of control and dietary phosphate-loaded (Phos) mice at a time point when the Phos group had not yet developed tubulointerstitial fibrosis. scRNA-seq analysis identified the highest number of differentially expressed genes in the clusters belonging to proximal tubular epithelial cells (PTECs). Based on these differentially expressed genes, in silico analyses suggested that the Phos group activated peroxisome proliferator-activated receptor-α (PPAR-α) and fatty acid β-oxidation (FAO) in the PTECs. This activation was further substantiated through various experiments, including the use of an FAO activity visualization probe. Compared with wild-type mice, knockout mice exhibited exacerbated tubulointerstitial fibrosis in response to phosphate overload. Experiments conducted with cultured PTECs demonstrated that activation of the PPAR-α/FAO pathway leads to improved cellular viability under high-phosphate conditions. The Phos group mice showed a decreased serum concentration of free fatty acids, which are endogenous PPAR-α agonists. Instead, experiments using cultured PTECs revealed that phosphate directly activates the PPAR-α/FAO pathway. These findings indicate that noncanonical metabolic reprogramming via endogenous activation of the PPAR-α/FAO pathway in PTECs is essential to counteract phosphate toxicity. This study revealed the activation of peroxisome proliferator-activated receptor-α and fatty acid β-oxidation in proximal tubular epithelial cells as an endogenous mechanism to protect the kidney from phosphate toxicity. These findings highlight noncanonical metabolic reprogramming as a potential target for suppressing phosphate toxicity in the kidneys.
增加膳食磷酸盐的摄入会加剧肾脏的磷酸盐负担。已经报道了几种磷酸盐诱导肾小管间质纤维化的机制。考虑到磷酸盐既是一种潜在的肾毒素，又是身体必需的营养物质，因此肾脏可能具有内在的保护机制来防止磷酸盐过载，而不仅仅是屈服于损伤。然而，人们对这些机制的了解有限。为了确定这些机制，我们对对照组和膳食磷酸盐负荷（Phos）组小鼠的肾脏进行了单细胞 RNA 测序（scRNA-seq）分析，此时 Phos 组尚未发生肾小管间质纤维化。scRNA-seq 分析鉴定出属于近端肾小管上皮细胞（PTEC）的簇中差异表达基因数量最多。基于这些差异表达基因，通过计算机分析表明 Phos 组激活了 PTEC 中的过氧化物酶体增殖物激活受体-α（PPAR-α）和脂肪酸 β-氧化（FAO）。通过各种实验进一步证实了这一点，包括使用 FAO 活性可视化探针。与野生型小鼠相比，在磷酸盐过载时， knockout 小鼠的肾小管间质纤维化加剧。用培养的 PTEC 进行的实验表明，PPAR-α/FAO 通路的激活可在高磷酸盐条件下提高细胞活力。Phos 组小鼠的血清游离脂肪酸浓度降低，而游离脂肪酸是内源性的 PPAR-α 激动剂。相反，用培养的 PTEC 进行的实验表明，磷酸盐直接激活了 PPAR-α/FAO 通路。这些发现表明，PTEC 中通过内源性激活 PPAR-α/FAO 通路的非典型代谢重编程对于抵抗磷酸盐毒性至关重要。本研究揭示了近端肾小管上皮细胞中过氧化物酶体增殖物激活受体-α和脂肪酸 β-氧化的激活是保护肾脏免受磷酸盐毒性的内在机制。这些发现强调了非典型代谢重编程作为抑制肾脏磷酸盐毒性的潜在靶点。
