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Calciprotein particle-induced cytotoxicity via lysosomal dysfunction and altered cholesterol distribution in renal epithelial HK-2 cells.

ABSTRACT: Dietary phosphate overload induces chronic kidney disease (CKD), and calciprotein particles (CPPs), a form of nanoparticle comprising calcium phosphate and serum proteins, has been proposed to cause renal toxicity. However, the mechanism of CPP cytotoxicity in renal tubular cells is unknown. Here we show that in renal proximal tubular epithelial HK-2 cells, endocytosed CPPs accumulate in late endosomes/lysosomes (LELs) and increase their luminal pH by ~ 1.0 unit. This results in a decrease in lysosomal hydrolase activity and autophagic flux blockage without lysosomal rupture and reactive oxygen species generation. CPP treatment led to vulnerability to H₂O₂-induced oxidative stress and plasma membrane injury, probably because of autophagic flux blockage and decreased plasma membrane cholesterol, respectively. CPP-induced disruption of lysosomal homeostasis, autophagy flux and plasma membrane integrity might trigger a vicious cycle, leading to progressive nephron loss.

SUBMITTER: Kunishige R

PROVIDER: S-EPMC7676272 | biostudies-literature | 2020 Nov

REPOSITORIES: biostudies-literature

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Calciprotein particle-induced cytotoxicity via lysosomal dysfunction and altered cholesterol distribution in renal epithelial HK-2 cells.

Kunishige Rina R Mizoguchi Mai M Tsubouchi Asako A Hanaoka Kenjiro K Miura Yutaka Y Kurosu Hiroshi H Urano Yasuteru Y Kuro-O Makoto M Murata Masayuki M

Scientific reports 20201118 1

Dietary phosphate overload induces chronic kidney disease (CKD), and calciprotein particles (CPPs), a form of nanoparticle comprising calcium phosphate and serum proteins, has been proposed to cause renal toxicity. However, the mechanism of CPP cytotoxicity in renal tubular cells is unknown. Here we show that in renal proximal tubular epithelial HK-2 cells, endocytosed CPPs accumulate in late endosomes/lysosomes (LELs) and increase their luminal pH by ~ 1.0 unit. This results in a decrease in ly ...[more]

PMID: 33208865

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Project description:BackgroundThe liver-derived plasma protein fetuin A is a systemic inhibitor of ectopic calcification. Fetuin-A stabilizes calcium phosphate mineral initially as ion clusters to form calciprotein monomers (CPM), and then as larger multimeric consolidations containing amorphous calcium phosphate (primary CPP, CPP 1) or more crystalline phases (secondary CPP, CPP 2). CPM and CPP mediate excess mineral stabilization, transport and clearance from circulation.MethodsWe injected i.v. synthetic fluorescent CPM and studied their clearance by live two-photon microscopy. We analyzed organ sections by fluorescence microscopy to assess CPM distribution. We studied cellular clearance and cytotoxicity by flow cytometry and live/dead staining, respectively, in cultured macrophages, liver sinusoidal endothelial cells (LSEC), and human proximal tubule epithelial HK-2 cells. Inflammasome activation was scored in macrophages. Fetuin A monomer and CPM charge were analyzed by ion exchange chromatography.ResultsLive mice cleared CPP in the liver as published previously. In contrast, CPM were filtered by kidney glomeruli into the Bowman space and the proximal tubules, suggesting tubular excretion of CPM-bound calcium phosphate and reabsorption of fetuin A. Fetuin-A monomer clearance was negligible in liver and low in kidney. Anion exchange chromatography revealed that fetuin A monomer was negatively charged, whereas CPM appeared neutral, suggesting electrochemical selectivity of CPM versus fetuin A. CPM were non-toxic in any of the investigated cell types, whereas CPP 1 were cytotoxic. Unlike CPP, CPM also did not activate the inflammasome.ConclusionsFetuin-A prevents calcium phosphate precipitation by forming CPM, which transform into CPP. Unlike CPP, CPM do not trigger inflammation. CPM are readily cleared in the kidneys, suggesting CPM as a physiological transporter of excess calcium and phosphate. Upon prolonged circulation, e.g., in chronic kidney disease, CPM will coalesce and form CPP, which cannot be cleared by the kidney, but will be endocytosed by liver sinusoidal endothelial cells and macrophages. Large amounts of CPP trigger inflammation. Chronic CPM and CPP clearance deficiency thus cause calcification by CPP deposition in blood vessels and soft tissues, as well as inflammation.

Project description:AimsCalciprotein particles (CPPs) are circulating calcium and phosphate nanoparticles associated with the development of vascular calcification (VC) in chronic kidney disease (CKD). Although recent studies have been focusing on associations of CPPs with the presence of VC in CKD, insights in the underlying processes and mechanisms by which CPPs might aggravate VC and vascular dysfunction in vivo are currently lacking. Here, we assessed the overall burden of abdominal VC in healthy kidney donors and CKD patients and subsequently performed transcriptome profiling in the vascular tissue obtained from these subjects, linking outcome to CPP counts and calcification propensity.Methods and resultsCalcification scores were quantified in renal arteries, iliac arteries, and abdominal aorta using computed tomography (CT) scans of kidney donors and CKD patients. The vascular tissue was collected from kidney donors (renal artery) and CKD patients (iliac artery), after which bulk RNA sequencing and gene set enrichment analysis (GSEA) were performed on a subset of patients. Calcification propensity (crystallization time, T50) was measured using nephelometry and CPP counts with microparticle flow cytometric analysis. Increased calcification scores (based on CT) were found in CKD patients compared to kidney donors. Transcriptome profiling revealed enrichment for processes related to endothelial activation, inflammation, extracellular matrix (ECM) remodelling, and ossification in CKD vascular biopsies compared to kidney donors. Calcification propensity was increased in CKD, as well as CPP counts, with the latter being significantly associated with markers of vascular remodelling.ConclusionOur findings reveal that CKD is characterized by systemic VC with increased calcification propensity and CPP counts. Transcriptome profiling showed altered vascular gene expression with enrichment for endothelial activation, inflammation, ECM remodelling, and ossification. Moreover, we demonstrate, for the first time, that vascular remodelling processes are associated with increased circulating CPP counts. Interventions targeting CPPs are promising avenues for alleviating vascular remodelling and VC in CKD.

Dataset Information

Calciprotein particle-induced cytotoxicity via lysosomal dysfunction and altered cholesterol distribution in renal epithelial HK-2 cells.

Publications

Calciprotein particle-induced cytotoxicity via lysosomal dysfunction and altered cholesterol distribution in renal epithelial HK-2 cells.

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