Leptospira outer membrane protein activates NF-κB and downstream genes expressed in medullary thick ascending limb cells

Tubulointerstitial nephritis is the main manifestation of acute renal damage caused by leptospirosis, but the mechanism remains unexplored. Patients infected with Leptospira shermani in Taiwan disclosed tubular dysfunction particularly in the medullary thick ascending limb of loop of Henle (mTAL), and the related renal damage seems to be underestimated. To elucidate the mechanism of tubular damage, outer membrane protein extract from Leptospira was administered to a model of cultured mTAL cells derived from normal mice. The addition of outer membrane protein extract from L. shermani to cultured mTAL cells induced a significant nuclear DNA binding of the NF-κ B transcription factor by electrophoresis mobility shift assay. Forty-eight h after adding the outer membrane protein extract (0.2 μg/ml) to the cultured cells, the expression of inducible nitric oxide mRNA increased by 4.2-fold, monocyte chemoattractant protein-1 by 3-fold, and tumor necrosis factor-α by 2.4-fold when compared with untreated cells examined by reverse transcription competitive-PCR. Supernatant nitrite, monocyte chemoattractant protein-1, and tumor necrosis factor-α protein levels also increased by 1.8-, 7.1-, and 5-fold, respectively. An antiserum raised against L. shermani largely prevented these effects. Outer membrane protein extract from L. bratislava induced fewer effects than L. shermani, and the avirulent nonpathogenic L. biflexa serovar patoc did not induce significant effects in the mTAL cells. In conclusion, L. shermani infection may cause mTAL cell damage and inflammation through the NF-κ B-associated pathway. Findings of this study may be important in understanding the pathogenesis of tubulointerstitial nephritis caused by these organisms.