Makoto Tagaya1, Shinji Kume2, Mako Yasuda-Yamahara1, Shogo Kuwagata1, Kosuke Yamahara1, Naoko Takeda1, Yuki Tanaka1, Masami Chin-Kanasaki1, Yuki Nakae3, Hideki Yokoi4, Masashi Mukoyama5, Naotada Ishihara6, Masatoshi Nomura7, Shin-Ichi Araki8, Hiroshi Maegawa1. 1. Department of Medicine, Shiga University of Medical Science, Tsukinowa-cho, Otsu, Shiga 520-2192, Japan. 2. Department of Medicine, Shiga University of Medical Science, Tsukinowa-cho, Otsu, Shiga 520-2192, Japan. Electronic address: skume@belle.shiga-med.ac.jp. 3. Departments of Stem Cell Biology and Regenerative Medicine, Shiga University of Medical Science, Tsukinowa-cho, Otsu, Shiga 520-2192, Japan. 4. Department of Nephrology, Graduate School of Medicine, Kyoto University, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan. 5. Department of Nephrology, Graduate School of Medical Sciences, Kumamoto University, 1-1-1 Honjo, Chuo-ku, Kumamoto, Kumamoto 860-8556, Japan. 6. Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka 560-0043, Japan. 7. Department of Endocrinology and Metabolism, Kurume University School of Medicine, 67 Asahi-machi, Kurume 830-0011, Japan. 8. Department of Medicine, Shiga University of Medical Science, Tsukinowa-cho, Otsu, Shiga 520-2192, Japan. Electronic address: araki@belle.shiga-med.ac.jp.
Abstract
AIMS: Identifying the mechanisms that underlie progression from endothelial damage to podocyte damage, which leads to massive proteinuria, is an urgent issue that must be clarified to improve renal outcome in diabetic kidney disease (DKD). We aimed to examine the role of dynamin-related protein 1 (Drp1)-mediated regulation of mitochondrial fission in podocytes in the pathogenesis of massive proteinuria in DKD. METHODS: Diabetes- or albuminuria-associated changes in mitochondrial morphology in podocytes were examined by electron microscopy. The effects of albumin and other diabetes-related stimuli, including high glucose (HG), on mitochondrial morphology were examined in cultured podocytes. The role of Drp1 in podocyte damage was examined using diabetic podocyte-specific Drp1-deficient mice treated with neuraminidase, which removes endothelial glycocalyx. RESULTS: Neuraminidase-induced removal of glomerular endothelial glycocalyx in nondiabetic mice led to microalbuminuria without podocyte damage, accompanied by reduced Drp1 expression and mitochondrial elongation in podocytes. In contrast, streptozotocin-induced diabetes significantly exacerbated neuraminidase-induced podocyte damage and albuminuria, and was accompanied by increased Drp1 expression and enhanced mitochondrial fission in podocytes. Cell culture experiments showed that albumin stimulation decreased Drp1 expression and elongated mitochondria, although HG inhibited albumin-associated changes in mitochondrial dynamics, resulting in apoptosis. Podocyte-specific Drp1-deficiency in mice prevented diabetes-related exacerbation of podocyte damage and neuraminidase-induced development of albuminuria. Endothelial dysfunction-induced albumin exposure is cytotoxic to podocytes. Inhibition of mitochondrial fission in podocytes is a cytoprotective mechanism against albumin stimulation, which is impaired under diabetic condition. Inhibition of mitochondrial fission in podocytes may represent a new therapeutic strategy for massive proteinuria in DKD.
AIMS: Identifying the mechanisms that underlie progression from endothelial damage to podocyte damage, which leads to massive proteinuria, is an urgent issue that must be clarified to improve renal outcome in diabetic kidney disease (DKD). We aimed to examine the role of dynamin-related protein 1 (Drp1)-mediated regulation of mitochondrial fission in podocytes in the pathogenesis of massive proteinuria in DKD. METHODS: Diabetes- or albuminuria-associated changes in mitochondrial morphology in podocytes were examined by electron microscopy. The effects of albumin and other diabetes-related stimuli, including high glucose (HG), on mitochondrial morphology were examined in cultured podocytes. The role of Drp1 in podocyte damage was examined using diabetic podocyte-specific Drp1-deficient mice treated with neuraminidase, which removes endothelial glycocalyx. RESULTS: Neuraminidase-induced removal of glomerular endothelial glycocalyx in nondiabetic mice led to microalbuminuria without podocyte damage, accompanied by reduced Drp1 expression and mitochondrial elongation in podocytes. In contrast, streptozotocin-induced diabetes significantly exacerbated neuraminidase-induced podocyte damage and albuminuria, and was accompanied by increased Drp1 expression and enhanced mitochondrial fission in podocytes. Cell culture experiments showed that albumin stimulation decreased Drp1 expression and elongated mitochondria, although HG inhibited albumin-associated changes in mitochondrial dynamics, resulting in apoptosis. Podocyte-specific Drp1-deficiency in mice prevented diabetes-related exacerbation of podocyte damage and neuraminidase-induced development of albuminuria. Endothelial dysfunction-induced albumin exposure is cytotoxic to podocytes. Inhibition of mitochondrial fission in podocytes is a cytoprotective mechanism against albumin stimulation, which is impaired under diabetic condition. Inhibition of mitochondrial fission in podocytes may represent a new therapeutic strategy for massive proteinuria in DKD.