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Cathepsin D in Podocytes Is Important in the Pathogenesis of Proteinuria and CKD.

ABSTRACT: Studies have revealed many analogies between podocytes and neurons, and these analogies may be key to elucidating the pathogenesis of podocyte injury. Cathepsin D (CD) is a representative aspartic proteinase in lysosomes. Central nervous system neurons in CD-deficient mice exhibit a form of lysosomal storage disease with a phenotype resembling neuronal ceroid lipofuscinoses. In the kidney, the role of CD in podocytes has not been fully explored. Herein, we generated podocyte-specific CD-knockout mice that developed proteinuria at 5 months of age and ESRD by 20-22 months of age. Immunohistochemical analysis of these mice showed apoptotic podocyte death followed by proteinuria and glomerulosclerosis with aging. Using electron microscopy, we identified, in podocytes, granular osmiophilic deposits (GRODs), autophagosome/autolysosome-like bodies, and fingerprint profiles, typical hallmarks of CD-deficient neurons. CD deficiency in podocytes also led to the cessation of autolysosomal degradation and accumulation of proteins indicative of autophagy impairment and the mitochondrial ATP synthase subunit c accumulation in the GRODs, again similar to changes reported in CD-deficient neurons. Furthermore, both podocin and nephrin, two essential components of the slit diaphragm, translocated to Rab7- and lysosome-associated membrane glycoprotein 1-positive amphisomes/autolysosomes that accumulated in podocyte cell bodies in podocyte-specific CD-knockout mice. We hypothesize that defective lysosomal activity resulting in foot process effacement caused this accumulation of podocin and nephrin. Overall, our results suggest that loss of CD in podocytes causes autophagy impairment, triggering the accumulation of toxic subunit c-positive lipofuscins as well as slit diaphragm proteins followed by apoptotic cell death.

SUBMITTER: Yamamoto-Nonaka K

PROVIDER: S-EPMC5004641 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature

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Cathepsin D in Podocytes Is Important in the Pathogenesis of Proteinuria and CKD.

Yamamoto-Nonaka Kanae K Koike Masato M Asanuma Katsuhiko K Takagi Miyuki M Oliva Trejo Juan Alejandro JA Seki Takuto T Hidaka Teruo T Ichimura Koichiro K Sakai Tatsuo T Tada Norihiro N Ueno Takashi T Uchiyama Yasuo Y Tomino Yasuhiko Y

Journal of the American Society of Nephrology : JASN 20160128 9

Studies have revealed many analogies between podocytes and neurons, and these analogies may be key to elucidating the pathogenesis of podocyte injury. Cathepsin D (CD) is a representative aspartic proteinase in lysosomes. Central nervous system neurons in CD-deficient mice exhibit a form of lysosomal storage disease with a phenotype resembling neuronal ceroid lipofuscinoses. In the kidney, the role of CD in podocytes has not been fully explored. Herein, we generated podocyte-specific CD-knockout ...[more]

PMID: 26823550

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Project description:BackgroundA multidrug treatment strategy that targets urinary proteins with an angiotensin-converting enzyme (ACE) inhibitor and angiotensin receptor blocker (ARB) up-titrated to the respective maximum tolerated dose combined with intensified blood pressure (BP) control has been found to prevent renal function loss in adults with proteinuric nephropathies. Herein, we investigated the effects of this treatment protocol in the pediatric patient population.MethodsFrom May 2002 to September 2014 we included in this observational, longitudinal, cohort study 20 consecutive children with chronic nephropathies and 24-h proteinuria of >200 mg who had received ramipril and losartan up-titrated to the respective maximum approved and tolerated doses [mean (standard deviation) dose:2.48 (1.37) mg/m2 and 0.61 (0.46) mg/kg daily, respectively]. The primary efficacy endpoint was a >50 % reduction in 24-h proteinuria to <200 mg (remission). Secondary outcomes included changes in proteinuria, serum albumin, BP, and glomerular filtration rate (GFR).ResultsMean (± standard deviation) patient age at inclusion was 13.8 ± 2.8 years, and the median [interquartile range (IQR)] serum creatinine level and proteinuria were 0.7 (0.6-1.0) mg/dl and 690 (379-1270) mg/24 h or 435 (252-711) mg/m2/24 h, respectively. Proteinuria significantly decreased by month 6 of follow-up, and serum albumin levels increased over a median follow-up period of 78 (IQR 39-105) months. In the nine children who achieved remission, proteinuria reduction persisted throughout the whole follow-up without rebounds. The GFR improved in those children who achieved remission and worsened in those who did not. The mean GFR slopes differed significantly between these two groups (p < 0.05), being positive in those children with remission and negative in those without remission (+0.023 ± 0.15 vs.-0.014 ± 0.23 ml/min/1.73 m2/month, respectively), whereas BP control was similar between the two groups. Hyperkalemia was observed in two children.ConclusionsCombination therapy with maximum approved doses of ACE inhibitors and ARBs is a safe strategy which may achieve proteinuria remission with kidney function stabilization or even improvement in a substantial proportion of children with proteinuric nephropathies.

Project description:INTRODUCTION:Advanced glycation end-products (AGEs) are implicated in the pathogenesis of diabetic nephropathy (DN). Previous studies have shown that AGEs contribute to glomerulosclerosis and proteinuria. Podocytes, terminally differentiated epithelial cells of the glomerulus and the critical component of the glomerular filtration barrier, express the receptor for AGEs (RAGE). Podocytes are susceptible to severe injury during DN. In this study, we investigated the mechanism by which AGEs contribute to podocyte injury. RESEARCH DESIGN AND METHODS:Glucose-derived AGEs were prepared in vitro. Reactivation of Notch signaling was examined in AGE-treated human podocytes (in vitro) and glomeruli from AGE-injected mice (in vivo) by quantitative reverse transcription-PCR, western blot analysis, ELISA and immunohistochemical staining. Further, the effects of AGEs on epithelial to mesenchymal transition (EMT) of podocytes and expression of fibrotic markers were evaluated. RESULTS:Using human podocytes and a mouse model, we demonstrated that AGEs activate Notch1 signaling in podocytes and provoke EMT. Inhibition of RAGE and Notch1 by FPS-ZM1 (N-Benzyl-4-chloro-N-cyclohexylbenzamide) and DAPT (N-[N-(3,5-Difluorophenacetyl)-L-alanyl]-S-phenyl glycine t-butylester), respectively, abrogates AGE-induced Notch activation and EMT. Inhibition of RAGE and Notch1 prevents AGE-induced glomerular fibrosis, thickening of the glomerular basement membrane, foot process effacement, and proteinuria. Furthermore, kidney biopsy sections from people with DN revealed the accumulation of AGEs in the glomerulus with elevated RAGE expression and activated Notch signaling. CONCLUSION:The data suggest that AGEs activate Notch signaling in the glomerular podocytes. Pharmacological inhibition of Notch signaling by DAPT ameliorates AGE-induced podocytopathy and fibrosis. Our observations suggest that AGE-induced Notch reactivation in mature podocytes could be a novel mechanism in glomerular disease and thus could represent a novel therapeutic target.

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Cathepsin D in Podocytes Is Important in the Pathogenesis of Proteinuria and CKD.

Publications

Cathepsin D in Podocytes Is Important in the Pathogenesis of Proteinuria and CKD.

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