Prevention of apoptosis averts glomerular tubular disconnection and podocyte loss in proteinuric kidney disease

Abstract

There is a great need for treatment that arrests progression of chronic kidney disease. Increased albumin in primary urine leads to apoptosis and fibrosis of podocytes and tubular cells and is a major cause of functional deterioration. There have been many attempts to target fibrosis but few to target apoptosis, because of lack of appropriate agents. Our group has described an ouabain activated Na,K-ATPase/IP3R signalosome, which protects from apoptosis. Here we show that albumin uptake in primary rat renal epithelial cells is accompanied by a time and dose dependent mitochondrial accumulation of the apoptotic factor Bax, down-regulation of the anti-apoptotic factor Bcl-xL and mitochondrial membrane depolarization. Ouabain opposes these effects and protects from apoptoss in albumin-exposed proximal tubule cells and podocytes. The efficacy of ouabain as an anti-apoptotic and kidney-protective therapeutic tool is tested in rats with passive Heymann nephritis, a model of proteinuric chronic kidney disease. Chronic ouabain treatment preserves renal function, protects from renal cortical apoptosis, up-regulation of Bax, down-regulation of Bcl-xL and rescues from glomerular tubular disconnection and podocyte loss. Thus we have identified a novel clinically feasible therapeutic tool, which has the potential to protect from apoptosis and rescue from loss of functional tissue in chronic proteinuric kidney disease.

Renal disease pathophysiology and treatment: contributions from the rat

“…Recently, ouabain, which is a cardiotonic steroid, has been found to have anti-apoptotic actions. Chronic ouabain treatment of rats with passive Heymann nephritis [PHN; a model of human membranous nephropathy, a slow progressive proteinuric kidney disease (Salant et al, 1979)] prevented the loss of podocytes, reduced the level of apoptotic proximal tubule cells and reduced renal fibrosis (Burlaka et al, 2016). Ouabain might represent a novel therapy that could potentially protect against apoptosis and prevent the loss of functional tissue in chronic proteinuric kidney disease.…”

Ouabain‐regulated phosphoproteome reveals molecular mechanisms for Na + , K + ‐ATPase control of cell adhesion, proliferation, and survival

“…CAMK2G has been reported to specifically phosphorylate the proapoptotic Bcl-2–family protein BAD at a site that blocks its proapoptotic effect (22). Because ouabain protects primary rat proximal tubule cells from apoptosis caused by serum deprivation (10), Shiga toxin (12), excessive concentration of albumin (13), or glucose (ongoing study), we tested whether CAMK2G down-regulation abolishes the antiapoptotic effect of ouabain. Primary rat proximal tubule cells, transfected with siRNA targeting CAMK2G mRNA or with nontargeting control siRNA (Supplemental Fig.…”

“…Protection from apoptosis is a well-documented downstream effect of ouabain treatment (10, 12, 13). Apoptosis is a major contributor to the progressive loss of functional renal tissue in kidney disease (60).…”

“…CAMK2G is reported to have an antiapoptotic effect by deactivating the proapoptotic protein BCL2 associated agonist of cell death (BAD), a member of the Bcl-2 family (22). Subsaturating concentration of ouabain protects primary kidney epithelial cells from apoptosis caused by a variety of stimuli that activate proapoptotic Bcl-2–family proteins (10, 12, 13). To verify the functional significance of CAMK2G phosphorylation, we examined whether CAMK2G down-regulation in primary renal epithelial cells might prohibit the ouabain antiapoptotic effect.…”

“…Ouabain is commonly used to study the NKA function. High concentration of ouabain inhibits the NKA pumping function and will eventually cause cell death, whereas subsaturating concentration stimulates cell proliferation (5)(6)(7), modulates cell-to-cell contacts (8,9), and protects from apoptosis (10)(11)(12)(13). Subsaturating concentration of ouabain triggers low-frequency oscillations of intracellular calcium concentration ([Ca 2+ ] i ) and phosphorylation of several signaling molecules, including mitogen-activated protein kinases, protein kinase B, and SRC, in primary and immortalized mammalian cells (14,15).…”