Dietary salt intake modulates differential splicing of the Na-K-2Cl cotransporter NKCC2

Abstract

Schie␤l IM, Rosenauer A, Kattler V, Minuth WW, Oppermann M, Castrop H. Dietary salt intake modulates differential splicing of the Na-K-2Cl cotransporter NKCC2. Am J Physiol Renal Physiol 305: F1139 -F1148, 2013. First published August 14, 2013 doi:10.1152/ajprenal.00259.2013.-Both sodium reabsorption in the thick ascending limb of the loop of Henle (TAL) and macula densa salt sensing crucially depend on the function of the Na/K/2Cl cotransporter NKCC2. The NKCC2 gene gives rise to at least three different full-length NKCC2 isoforms derived from differential splicing. In the present study, we addressed the influence of dietary salt intake on the differential splicing of NKCC2. Mice were subjected to diets with low-salt, standard salt, and high-salt content for 7 days, and NKCC2 isoform mRNA abundance was determined. With decreasing salt intake, we found a reduced abundance of the low-affinity isoform NKCC2A and an increase in the high-affinity isoform NKCC2B in the renal cortex and the outer stripe of the outer medulla. This shift from NKCC2A to NKCC2B during a low-salt diet could be mimicked by furosemide in vivo and in cultured kidney slices. Furthermore, the changes in NKCC2 isoform abundance during a salt-restricted diet were partly mediated by the actions of angiotensin II on AT 1 receptors, as determined using chronic angiotensin II infusion. In contrast to changes in oral salt intake, water restriction (48 h) and water loading (8% sucrose solution) increased and suppressed the expression of all NKCC2 isoforms, without changing the distribution pattern of the single isoforms. In summary, the differential splicing of NKCC2 pre-mRNA is modulated by dietary salt intake, which may be mediated by changes in intracellular ion composition. Differential splicing of NKCC2 appears to contribute to the adaptive capacity of the kidney to cope with changes in reabsorptive needs. differential spacing; NKCC2; salt transport THE THICK ASCENDING LIMB OF the loop of Henle (TAL) contributes to 25-30% of total renal Na ϩ reabsorption. Apical Na uptake in cells of the TAL is primarily mediated by the bumetanide-sensitive Na-K-2Cl cotransporter NKCC2 (5). In addition to its function in TAL salt retrieval, the NKCC2-dependent transport activity of macula densa cells constitutes the initial step in the tubulovascular signaling pathways between the TAL in the juxtaglomerular region and the afferent arteriole (20,33). By detecting changes in luminal NaCl concentration, macula densa cells modulate the tone of the afferent arteriole and subsequently control the single-nephron glomerular filtration rate. This negative feedback loop is known as tubuloglomerular feedback (TGF; Ref. 38). Macula densa cells also control the secretion of renin from granular cells of the afferent arteriole (4).NKCC2 is encoded by the gene Slc12a1 (8, 16). In humans and all other examined mammalian species, differential splicing of Slc12a1 gives rise to at least three different full-length isoforms of NKCC2, known as NKCC2B, NKCC2A, and NKCC2F (3,16,28,40). ...

Everything we always wanted to know about furosemide but were afraid to ask

“…Each isoform is expressed differently along the thick ascending limb of Henle. Although the functional significance of these three isoforms is uncertain (117,136), and factors affecting the level of expression are not fully understood, differential splicing of NKCC2 seems to be modulated by dietary salt intake. Dietary sodium restriction enhanced the expression of the high-affinity NKCC2B isoform and reduced the low-affinity NKCC2A isoform (136).…”

“…Although the functional significance of these three isoforms is uncertain (117,136), and factors affecting the level of expression are not fully understood, differential splicing of NKCC2 seems to be modulated by dietary salt intake. Dietary sodium restriction enhanced the expression of the high-affinity NKCC2B isoform and reduced the low-affinity NKCC2A isoform (136). Reports regarding selectivity between NKCC1/2 of furosemide are limited, yet indicate that furosemide has no selectivity for the two isoforms when NKCC1 is measured in the active state (60).…”

Expression of three isoforms of Na-K-2Cl cotransporter (NKCC2) in the kidney and regulation by dehydration

“…Our data show that hyperosmolality increased NKCC2 mRNA expression in MAL. Salt intake has been reported to influence the activity of isoforms [20]. These data suggest that dehydration should increase NKCC2 expression in MAL via increased plasma AVP level and/or hyperosmolality of plasma and urine.…”

Physiological role of SLC12 family members in the kidney

“…Interestingly, the splicing machinery that produces these isoforms can be modulated by the dietary salt content. A low-salt diet promotes upregulation of the high-affinity variant NKCC2B in the cortical TAL, and its appearance in the outer medullary TAL (124). The molecular mechanisms by which dietary salt variation alters the spliceosome to preferentially generate one variant over another are completely unknown.…”