Thick Ascending Limbs (TALs)-specific deletion of ALMS1 (Alstrom syndrome 1) increases surface NKCC2 expression and NaCl reabsorption in the TAL

The regulation of NKCC2 mediated NaCl reabsorption in Thick Ascending Libs (TALs) is essential to salt homeostasis and blood pressure regulation. Previously, our lab showed that NKCC2 activity is regulated by membrane traffcking and inhibiting endocytosis enhanced surface NKCC2 expression and NaCl reabsorption. We also found that ALMS1, a protein mutated in Alström syndrome, is expressed in TALs. Whole animal gene deletion of ALMS1 caused hypertension, and inhibits NKCC2 endocytosis, increasing its surface expression and renal NaCl reabsorption. Little is known about additional functions of ALMS1, however, global gene deletion of ALMS1 induces obesity, and that, in turn may affect TAL and NKCC2 function. We hypothesized that ALMS1 is a part of protein complex that binds apical NKCC2 in TALs and promotes its endocytosis. To dissect the specific role of ALMS1 in TALs, without interference of systemic effects, we studied surface NKCC2 expression and TAL mediated Na transport after inducible deletion of ALMS1 in TALs. To do this, we generated a loxP flanked exon 7 ALMS1 transgenic mouse line, that we crossed with TAL specific inducible Umod-ERT2 Cre mice (Umod-ALMS1 KO). 3 weeks after inducing Cre expression with tamoxifen, ALMS1 expression in TAL suspensions decreased by 85% (p<0.01) (n=5). In Umod-ALMS1 KO TALs the surface to total NKCC2 ratio, was increased by 37±15% compared to control floxed ALMS1 (p<0.01) (n=5). Recombinant ALMS1 (GST-Carboxyl terminus-ALMS1), or immunoprecipitation of ALMS1, pulled down NKCC2 from TAL lysates (n=3), suggesting that the mechanism by which ALMS1 regulates surface NKCC2 involves protein-protein interactions. Three weeks after inducing ALMS1 deletion, we measured bumetanide-induced natriuresis (4h) as an index of NKCC2-mediated NaCl absorption. We found that bumetanide induced UNa excretion was enhanced in Umod-ALMS1 KO, compared to control (control: 110±7 vs Umod-ALMS1 KO: 173±26 μmols Na/4h, p<0.01). We conclude that ALMS1, binds NKCC2 to regulate its surface expression. Depletion of ALMS1, specifically in the TAL enhances surface NKCC2 and TAL NaCl reabsorption. Our data indicate that regulation of the ALMS1-NKCC2 interaction in the TAL is important for renal NaCl reabsorption. Decreased ALMS1 function or expression increased TAL NaCl reabsorption and this may contribute to the hypertension and kidney disease that is associated with SNPs in the ALMS1 gene in the general population, or in patients with Alstrom Syndrome. NIH R01, Henry Ford Fund. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.