Decaying kidney function during cirrhosis correlates with remodeling of distal colon aldosterone target gene expression.

Liver cirrhosis is associated to circulatory abnormalities leading to hypovolemia and stimulation of the renin-angiotensin-aldosterone system (RAAS). Advanced stages of the disease cause renal failure, impairing K+ and Na+ homeostasis. It has been proposed that the distal colon undergoes functional remodeling during renal failure, in particular by aldosterone-driven increased K+ excretion. In this study, we compared the transcriptional response of aldosterone target genes in the rat distal colon under two models of increased circulating aldosterone (one with concomitant RAAS activation) and in a model of secondary hyperaldosteronism induced by cirrhosis. The expression of a subset of these genes was also tested in distal colon biopsies from control subjects or patients with cirrhosis with varying levels of disease progression and treated or not with mineralocorticoid receptor inhibitor spironolactone. We examined known aldosterone-regulated transcripts involved in corticosteroid signaling and transepithelial ion transport. In addition, we included aldosterone-regulated genes related to cell proliferation. Our comparison revealed multiple aldosterone target genes upregulated in the rat distal colon during decompensated cirrhosis. Epithelial Na+ channel ß and γ subunit expression correlated positively with plasma aldosterone concentration and negatively with glomerular filtration rate. Patients with cirrhosis showed increased expression of 11-ß-hydroxysteroid-dehydrogenase 2 (11ßHSD2), which was reverted by spironolactone treatment, suggesting a sensitization of the distal colon to aldosterone action. In summary, our data show that decaying kidney function during cirrhosis progression toward a decompensated state with hypovolemia correlates with remodeling of distal colon ion transporter expression, supporting a role for aldosterone in the process.NEW & NOTEWORTHY Liver cirrhosis progression significantly alters ion transporter subunit expression in the rat distal colon, a change that correlated well with declining kidney function and the severity of the disease. Our data suggest that the steroid hormone aldosterone participates in this homeostatic response to maintain electrolyte balance.

Increased SGK1 activity potentiates mineralocorticoid/NaCl-induced kidney injury.

Serum and glucocorticoid-regulated kinase 1 (SGK1) stimulates aldosterone-dependent renal Na+ reabsorption and modulates blood pressure. In addition, genetic ablation or pharmacological inhibition of SGK1 limits the development of kidney inflammation and fibrosis in response to excess mineralocorticoid signaling. In this work, we tested the hypothesis that a systemic increase in SGK1 activity would potentiate mineralocorticoid/salt-induced hypertension and kidney injury. To that end, we used a transgenic mouse model with increased SGK1 activity. Mineralocorticoid/salt-induced hypertension and kidney damage was induced by unilateral nephrectomy and treatment with deoxycorticosterone acetate and NaCl in the drinking water for 6 wk. Our results show that although SGK1 activation did not induce significantly higher blood pressure, it produced a mild increase in glomerular filtration rate, increased albuminuria, and exacerbated glomerular hypertrophy and fibrosis. Transcriptomic analysis showed that extracellular matrix- and immune response-related terms were enriched in the downregulated and upregulated genes, respectively, in transgenic mice. In conclusion, we propose that systemically increased SGK1 activity is a risk factor for the development of mineralocorticoid-dependent kidney injury in the context of low renal mass and independently of blood pressure.NEW & NOTEWORTHY Increased activity of the protein kinase serum and glucocorticoid-regulated kinase 1 may be a risk factor for accelerated renal damage. Serum and glucocorticoid-regulated kinase 1 expression could be a marker for the rapid progression toward chronic kidney disease and a potential therapeutic target to slow down the process.

SGK1 activation exacerbates diet-induced obesity, metabolic syndrome and hypertension.

The serum- and glucocorticoid-induced kinase 1 (SGK1) is a transcriptional target of steroid hormones including glucocorticoids or aldosterone in addition to other stimuli such as glucose. SGK1 is activated via phosphoinositide 3-kinase, placing it downstream of insulin signaling. SGK1 participates in the upregulation of kidney Na+ reabsorption by aldosterone and has been linked to obesity-related hypertension in humans. We hypothesized that a systemic increase in SGK1 activity may trigger a multiplicity of mechanisms leading to simultaneous development of the main conditions that characterize the metabolic syndrome (MetS), including hypertension. We used a transgenic mouse model made with a bacterial artificial chromosome containing the whole mouse Sgk1 gene modified to introduce an activating point mutation. Wild type or transgenic 14-week-old male mice were fed with standard chow diet or high-fat diet for up to 18 weeks. Development of the main features of MetS and hepatic steatosis were monitored, and in vitro adipocyte differentiation was studied. Our results show that transgenic animals under high-fat diet rapidly and markedly develop MetS characterized by obesity, glucose intolerance, insulin resistance, dyslipidemia and hypertension. In addition, SGK1 gain-of-function accelerates the development of hepatic steatosis. Our study suggests that inappropriate SGK1 activity represents a risk factor in developing MetS with hypertension and related end-organ damage. Our data support SGK1 as a possible therapeutic target in MetS and related complications and provides a useful gain-of-function model for pre-clinical drug testing.