KAP Degradation by Calpain Is Associated with CK2 Phosphorylation and Provides a Novel Mechanism for Cyclosporine A-Induced Proximal Tubule Injury

The use of cyclosporine A (CsA) is limited by its severe nephrotoxicity that includes reversible vasoconstrictor effects and proximal tubule cell injury, the latter associated whith chronic kidney disease progression. The mechanisms of CsA-induced tubular injury, mainly on the S3 segment, have not been completely elucidated. Kidney androgen-regulated protein (KAP) is exclusively expressed in kidney proximal tubule cells, interacts with the CsA-binding protein cyclophilin B and its expression diminishes in kidneys of CsA-treated mice. Since we reported that KAP protects against CsA toxicity in cultured proximal tubule cells, we hypothesized that low KAP levels found in kidneys of CsA-treated mice might correlate with proximal tubule cell injury. To test this hypothesis, we used KAP Tg mice developed in our laboratory and showed that these mice are more resistant to CsA-induced tubular injury than control littermates. Furthermore, we found that calpain, which was activated by CsA in cell cultures and kidney, is involved in KAP degradation and observed that phosphorylation of serine and threonine residues found in KAP PEST sequences by protein kinase CK2 enhances KAP degradation by calpain. Moreover, we also observed that CK2 inhibition protected against CsA-induced cytotoxicity. These findings point to a novel mechanism for CsA-induced kidney toxicity that might be useful in developing therapeutic strategies aimed at preventing tubular cell damage while maintaining the immunosuppressive effects of CsA

Tight junctions: from simple barriers to multifunctional molecular gates

Epithelia and endothelia separate different tissue compartments and protect multicellular organisms from the outside world. This requires the formation of tight junctions, selective gates that control paracellular diffusion of ions and solutes. Tight junctions also form the border between the apical and basolateral plasma-membrane domains and are linked to the machinery that controls apicobasal polarization. Additionally, signalling networks that guide diverse cell behaviours and functions are connected to tight junctions, transmitting information to and from the cytoskeleton, nucleus and different cell adhesion complexes. Recent advances have broadened our understanding of the molecular architecture and cellular functions of tight junctions

Kidney Androgen-Regulated Protein Transgenic Mice Show Hypertension and Renal Alterations Mediated by Oxidative Stress

[EN]Kidney androgen-regulated protein (KAP), a proximal tubule androgen-regulated gene, codes for a protein of unknown function. To investigate the consequences of KAP overexpression in kidney, we produced KAP transgenic mice and performed microarray expression analyses in kidneys of control and transgenic males. Downregulation of the androgen-sensitive Cyp4A14 monooxygenase gene in KAP transgenic mice prompted us to analyze blood pressure levels, and we observed that transgenic mice were hypertensive. Inhibition of 20-hydroxyeicosatetraenoic acid synthesis by N-hydroxy-N'-(4-n-butyl-2-methylphenyl) formamidine (HET0016) reduced the increased 20-hydroxyeicosatetraenoic acid levels in urine and normalized arterial pressure in transgenic mice, as did the NADPH oxidase inhibitor apocynin. Increased oxidative stress in transgenic mice was demonstrated by (1) enhanced excretion of urinary markers of oxidative stress, 8-iso-prostaglandin F2alpha, 8-hydroxydeoxyguanosine, and thiobarbituric acid-reacting substances; (2) augmented mitochondrial DNA damage and malondialdehyde levels in kidneys; and (3) diminished catalase and glutathione peroxidase activity in transgenic kidneys. Mice exhibited renal defects that included focal segmental glomerulosclerosis, proteinuria, glycosuria, and fibrosis. Taken together, these results indicate that KAP expression is critical for cardiovascular-renal homeostasis maintenance and that hypertension is associated with increased oxidative stress. This is the first report showing that overexpression of an androgen-regulated, proximal tubule-specific gene induces hypertension. These observations may shed light on the molecular pathophysiology of gender differences in the prevalence and severity of hypertension and chronic renal disease.Instituto de Salud Carlos III; Ministerio de Educación y Ciencia; RedinRen; Fundació La Marató de TV3; Fundación Renal Íñigo Álvarez de Toledo; Fundació Institut deRecerca Vall d’Hebrón; European Regional Development Fund (FEDER

Kidney androgen-regulated protein transgenic mice show hypertension and renal alterations mediated by oxidative stress

[EN]Kidney androgen-regulated protein (KAP), a proximal tubule androgen-regulated gene, codes for a protein of unknown function. To investigate the consequences of KAP overexpression in kidney, we produced KAP transgenic mice and performed microarray expression analyses in kidneys of control and transgenic males. Downregulation of the androgen-sensitive Cyp4A14 monooxygenase gene in KAP transgenic mice prompted us to analyze blood pressure levels, and we observed that transgenic mice were hypertensive. Inhibition of 20-hydroxyeicosatetraenoic acid synthesis by N-hydroxy-N'-(4-n-butyl-2-methylphenyl) formamidine (HET0016) reduced the increased 20-hydroxyeicosatetraenoic acid levels in urine and normalized arterial pressure in transgenic mice, as did the NADPH oxidase inhibitor apocynin. Increased oxidative stress in transgenic mice was demonstrated by (1) enhanced excretion of urinary markers of oxidative stress, 8-iso-prostaglandin F2alpha, 8-hydroxydeoxyguanosine, and thiobarbituric acid-reacting substances; (2) augmented mitochondrial DNA damage and malondialdehyde levels in kidneys; and (3) diminished catalase and glutathione peroxidase activity in transgenic kidneys. Mice exhibited renal defects that included focal segmental glomerulosclerosis, proteinuria, glycosuria, and fibrosis. Taken together, these results indicate that KAP expression is critical for cardiovascular-renal homeostasis maintenance and that hypertension is associated with increased oxidative stress. This is the first report showing that overexpression of an androgen-regulated, proximal tubule-specific gene induces hypertension. These observations may shed light on the molecular pathophysiology of gender differences in the prevalence and severity of hypertension and chronic renal disease.Instituto de Salud Carlos III; Ministerio de Educación y Ciencia; RedinRen; Fundació La Marató de TV3; Fundación Renal Íñigo Álvarez de Toledo; Fundació Institut deRecerca Vall d’Hebrón; European Regional Development Fund (FEDER

Kidney Androgen-Regulated Protein (KAP) Transgenic Mice Are Protected Against High-Fat Diet Induced Metabolic Syndrome

Abstract Metabolic Syndrome (MS) is reaching epidemic proportions with significant social and economical burden worldwide. Since the molecular basis of MS remains poorly defined, we investigated the impact of KAP, a kidney specific androgen-regulated gene, in the development of high fat-diet (hfd)-induced MS. Tg mice overexpressing KAP specifically in proximal tubule cells of the kidney exhibited reduced body weight and lower liver and adipose tissue weight compared to control littermates when fed a hfd. KAP Tg mice showed diminished adipocyte hypertrophy and reduced hepatic steatosis, significantly correlating with expression of relevant molecular markers and lower lipid content in liver. KAP transgenic were protected from hfd-induced insulin resistance, increased blood pressure and exhibited lower IL-6 serum levels and diminished expression of inflammatory markers in the adipose. Moreover, KAP was localized in the secretory pathway of proximal tubule cells and it is released to the extracellular media, preventing IL-6 induction and STAT-3 activation upon TNFα stimulation. We conclude that KAP, which might act as a hormone-like product in extra-renal tissues, protects Tg mice against hfd-induced MS by preventing inflammatory related events that are mediated, in part, through the IL-6 pathway