Tumor necrosis factor-α is an endogenous inhibitor of Na+-K+-2Cl- cotransporter (NKCC2) isoform A in the thick ascending limb

Battula S, Hao S, Pedraza PL, Stier CT, Ferreri NR. Tumor necrosis factor-alpha is an endogenous inhibitor of Na+-K+-2Cl(-) cotransporter (NKCC2) isoform A in the thick ascending limb. Am J Physiol Renal Physiol 301: F94-F100, 2011. First published April 20, 2011; doi: 10.1152/ajprenal.00650.2010.-The effects of TNF gene deletion on renal Na+-K+-2Cl(-) cotransporter (NKCC2) expression and activity were determined. Outer medulla from TNF-/- mice exhibited a twofold increase in total NKCC2 protein expression compared with wild-type (WT) mice. This increase was not observed in TNF-/- mice treated with recombinant human TNF (hTNF) for 7 days. Administration of hTNF had no effect on total NKCC2 expression in WT mice. A fourfold increase in NKCC2A mRNA accumulation was observed in outer medulla from TNF-/- compared with WT mice; NKCC2F and NKCC2B mRNA accumulation was similar between genotypes. The increase in NKCC2A mRNA accumulation was attenuated when TNF-/- mice were treated with hTNF. Bumetanide- sensitive O-2 consumption, an in vitro correlate of NKCC2 activity, was 2.8 +/- 0.2 nmol.min(-1).mg(-1) in medullary thick ascending limb tubules from WT, representing similar to 40% of total O-2 consumption, whereas, in medullary thick ascending limb tubules from TNF-/- mice, it was 5.6 +/- 0.3 nmol.min(-1).mg(-1), representing similar to 60% of total O-2 consumption. Administration of hTNF to TNF-/- mice restored the bumetanide-sensitive component to similar to 30% of total O-2 consumption. Ambient urine osmolality was higher in TNF-/- compared with WT mice (2,072 +/- 104 vs. 1,696 +/- 153 mosmol/kgH(2)O, P < 0.05). The diluting ability of the kidney, assessed by measuring urine osmolality before and after 1 h of water loading also was greater in TNF-/- compared with WT mice (174 +/- 38 and 465 +/- 81 mosmol/kgH(2)O, respectively, P < 0.01). Collectively, these findings suggest that TNF plays a role as an endogenous inhibitor of NKCC2 expression and function.