Rafael Medina-Navarro1, Yessica Dorin Torres-Ramos2, Alberto Martin Guzmán-Grenfell2, Margarita Díaz-Flores3, Guadalupe León-Reyes2, Juan José Hicks G4. 1. Department of Experimental Metabolism, Center for Biomedical Research, Michoacán, Mexico. Electronic address: rafael.medina@imss.gob.mx. 2. Department of Immuno-Biochemistry, National Institute of Perinatology, Ministry of Health, Mexico City, Mexico. 3. Biochemistry Medical Research Unit, National Medical Center, IMSS, México City, Mexico. 4. Health Research Policies, Coordinating Commission of National Health Institutes and Highly Specialized Hospitals, Mexico City, Mexico.
Abstract
AIMS: Increased amounts of protein, in particular albumin within renal tubular cells (TBCs), induce the expression of inflammatory and fibrogenic mediators, which are adverse prognostic factors in tubulointerstitial fibrosis and diabetic nephropathy (DN). We sought to assess the participation of the thiol-linked tertiary structure of albumin in the mechanism of protein toxicity in a model of TBCs. MATERIALS AND METHODS: Cultured human renal proximal tubular cells, HK-2, were exposed to isolated albumin from patients with and without DN (Stages 0, 1 and 4). The magnitude of change of the albumin tertiary structure, cell viability (LDH leakage), apoptosis (Annexin V), transdifferentiation and reticulum endoplasmic stress (Western blot and flow cytometry) and lysosomal enzyme activity were assessed. KEY FINDINGS: We found that albumin from Stage 4 patients presented >50% higher thiol-dependent changes of tertiary structure compared to Stages 0 and 1. Cells incubated with Stage 4 albumin displayed 5 times less viability, accompanied by an increased number of apoptotic cells; evidence of profibrogenic markers E-cadherin and vimentin and higher expression of epithelial-to-mesenchymal transition markers α-SMA and E-cadherin and of endoplasmic reticulum stress protein GRP78 were likewise observed. Moreover, we found that cathepsin B activity in isolated lysosomes showed a significant inhibitory effect on albumin from patients in advanced stages of DN and on albumin that was intentionally modified. SIGNIFICANCE: Overall, this study showed that thiol-dependent changes in albumin's tertiary structure interfere with the lysosomal proteolysis of renal TBCs, inducing molecular changes associated with interstitial fibrosis and DN progression.
AIMS: Increased amounts of protein, in particular albumin within renal tubular cells (TBCs), induce the expression of inflammatory and fibrogenic mediators, which are adverse prognostic factors in tubulointerstitial fibrosis and diabetic nephropathy (DN). We sought to assess the participation of the thiol-linked tertiary structure of albumin in the mechanism of protein toxicity in a model of TBCs. MATERIALS AND METHODS: Cultured human renal proximal tubular cells, HK-2, were exposed to isolated albumin from patients with and without DN (Stages 0, 1 and 4). The magnitude of change of the albumin tertiary structure, cell viability (LDH leakage), apoptosis (Annexin V), transdifferentiation and reticulum endoplasmic stress (Western blot and flow cytometry) and lysosomal enzyme activity were assessed. KEY FINDINGS: We found that albumin from Stage 4 patients presented >50% higher thiol-dependent changes of tertiary structure compared to Stages 0 and 1. Cells incubated with Stage 4 albumin displayed 5 times less viability, accompanied by an increased number of apoptotic cells; evidence of profibrogenic markers E-cadherin and vimentin and higher expression of epithelial-to-mesenchymal transition markers α-SMA and E-cadherin and of endoplasmic reticulum stress protein GRP78 were likewise observed. Moreover, we found that cathepsin B activity in isolated lysosomes showed a significant inhibitory effect on albumin from patients in advanced stages of DN and on albumin that was intentionally modified. SIGNIFICANCE: Overall, this study showed that thiol-dependent changes in albumin's tertiary structure interfere with the lysosomal proteolysis of renal TBCs, inducing molecular changes associated with interstitial fibrosis and DN progression.
Authors: Shiv Pratap S Yadav; Ruben M Sandoval; Jingfu Zhao; Yifan Huang; Exing Wang; Sudhanshu Kumar; Silvia B Campos-Bilderback; George Rhodes; Yehia Mechref; Bruce A Molitoris; Mark C Wagner Journal: Am J Physiol Renal Physiol Date: 2020-12-07