Altered hepatic mRNA expression of apoptotic genes during dimethylnitrosamine exposure.

The role of TNFalpha in regulating apoptotic signaling was investigated during subacute, low-dose (5.0 mg/kg) dimethylnitrosamine (DMN)-induced hepatotoxicity. In TNFalpha receptor (TNFR) intact (wild-type, WT) mice following 4 and 7 DMN exposures, hepatic transcripts for TNFalpha and TNFR-1 were elevated as compared to vehicle controls. DMN hepatotoxicity in WT and TNFR-1/TNFR-2 double knockout (DKO) mice were then compared over a 7-d exposure period. Liver RNA was isolated to measure hepatic expression of TNFalpha/Fas-related genes and the Bcl-2 family of genes that impact apoptosis. Hepatic mRNA levels for Fas, the apoptosis-promoting gene Bax, and the anti-apoptotic gene, Bcl-X(L), were up regulated following 4 and 7 DMN exposures in both WT and TNFR DKO mice as compared to vehicle controls. Notably, hepatic transcript levels for Bax were higher in TNFR DKO mice treated with DMN compared to identically treated WT mice. However, we detected approximately equal DMN-induced apoptotic degradation of liver DNA following 1, 4, and 7 exposures in WT and TNFR DKO mice. Taken together, these data show DMN-induced hepatic TNFalpha expression and suggest that TNFR-1 signaling may be up regulated following 4 and 7 daily DMN exposures. However, TNFalpha is not required for apoptotic signaling at the mRNA transcript level within the liver and instead may actually decrease Bax production.