TNF production by the medullary thick ascending limb of Henle's loop

Abstract

Medullary thick ascending limb of Henle's loop (mTALH) tubules, isolated from kidneys of male Sprague-Dawley rats, expressed the gene for tumor necrosis factor (TNF) and released this cytokine when challenged with lipopolysaccharide (LPS). The TNF produced was biologically active, as determined by cytotoxic activity present in supernatants from LPS-stimulated mTALH, using the TNF-sensitive murine fibrosarcoma cell line, WEHI 164. The amount of TNF produced, approximately 75 nM, has previously been shown to affect ion transport in the mTALH. The TNF-mediated cytotoxicity (and ion transport effects) were completely neutralized with a polyclonal anti-TNF antisera. Further, immunoprecipitation experiments demonstrated that the 17 kDa TNF monomer was formed by de novo protein synthesis. In contrast, the mTALH did not produce the related cytokine, lymphotoxin (LT). Production of TNF was confirmed by demonstrating the accumulation of a 1.6 kb TNF mRNA by Northern blot analysis; mRNA for LT was not detected. Expression of the TNF gene in the mTALH was confirmed by the polymerase chain reaction (PCR). Southern blot analysis and ethidium bromide staining of the resultant PCR products revealed the expected 276 bp sequence of TNF DNA for the mTALH. We have demonstrated that mTALH tubules stimulated with LPS express the gene for TNF, but not LT, and release biologically active TNF. TNF is an important mediator of septic shock and may contribute to changes in renal function associated with endotoxemia. Production of TNF by the mTALH may be an important autocrine regulatory mechanism for this nephron segment.

NKCC2A and NFAT5 regulate renal TNF production induced by hypertonic NaCl intake

“…TNF is produced by the mTAL in response to a variety of stimuli including lipopolysaccharide, angiotensin II, and calcium receptor activation (12,18,41,59). This cytokine acts via an autocrine mechanism to inhibit sodium transport in mTAL cells and is an endogenous inhibitor of NKCC2A mRNA accumulation, total NKCC2 expression, and NKCC2 activity (2,12,22).…”

“…For instance, recent studies have shown that TNF exhibits natriuretic effects, exerts a tonic inhibitory effect on the Na ϩ -K ϩ -2Cl Ϫ cotransporter (NKCC2), and inhibits endothelial nitric oxide synthase expression in the TAL (2,50,53,54). The mTAL produces TNF in response to several stimuli; however, knowledge regarding the pathways that contribute to TNF production by the kidney is limited (1,12,18,22,41,59). …”

“…Since NKCC2A expression is restricted to the TAL, NKCC2A-dependent activation of NFAT5 is part of a pathway by which the TAL produces TNF in response to hypertonic NaCl intake. TNF; NFAT5; Ton/EBP; NKCC2; thick ascending limb; hypertonic stress TUMOR NECROSIS FACTOR-␣ (TNF) is produced by several cell types along the nephron including the medullary thick ascending limb of Henle's loop (mTAL), which reabsorbs ϳ25% of filtered NaCl and is the site of action for loop diuretics (12,41). TNF acts in an autocrine manner to inhibit in vitro correlates of Na ϩ reabsorption by a mechanism involving induction of cyclooxygenase-2 (COX-2), and the contribution of this cytokine to renal function is still being defined (17).…”

Acute application of TNF stimulates apical 70-pS K+channels in the thick ascending limb of rat kidney

“…Recent studies indicate that the TAL produces TNF in response to bacterial LPS, ANG II, and elevated extracellular calcium (15,21,28). Incubation of the TAL with TNF in vitro inhibited ouabain-sensitive Rb ϩ uptake (10), suggesting that TNF may inhibit transcellular sodium transport in the TAL.…”

Tumor necrosis factor-α inhibits renin gene expression

“…Although blood mononuclear cells represent the main source of TNF-␣, it is also reported to be produced in other cell types, including mesangial and proximal tubule cells of kidneys (2,38). Remarkably, TNF-␣ is also produced in the medullar thick ascending limb of Henle's loop (mTALH) under baseline conditions (20). Therefore it would not be unlikely if TNF-␣ could play an important role in the regulation of renal functions and in the control of renin production in JG cells in particular.…”