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

Abstract

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 O2 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 ∼40% of total O2 consumption, whereas, in medullary thick ascending limb tubules from TNF−/− mice, it was 5.6 ± 0.3 nmol·min−1·mg−1, representing ∼60% of total O2 consumption. Administration of hTNF to TNF−/− mice restored the bumetanide-sensitive component to ∼30% of total O2 consumption. Ambient urine osmolality was higher in TNF−/− compared with WT mice (2,072 ± 104 vs. 1,696 ± 153 mosmol/kgH2O, 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/kgH2O, respectively, P < 0.01). Collectively, these findings suggest that TNF plays a role as an endogenous inhibitor of NKCC2 expression and function.