Protective effects of noradrenaline against tumor necrosis factor-alpha-induced apoptosis in cultured rat brown adipocytes: role of nitric oxide-induced heat shock protein 70 expression

OBJECTIVE: To elucidate the effects and molecular mechanism(s) by means of which noradrenaline (NA) protects against the tumor necrosis factor (TNF)-a lpha -incluced apoptosis of brown adipocytes. DESIGN: Brown fat precursor cells were isolated from young rats; 2.5 millio n cells were added to each 24-well culture plate and cultured in a defined culture medium. On day 8, the cultured cells were exposed to murine recombi nant TNF-alpha and/or cycloheximide (CHX; 10 mug/ml) and/or NA and/or nitri c oxide (NO) donors and/or the NO synthase inhibitor N-G-nitro-L-arginine m ethyl ester (L-NAME) and/or 10 muM heat shock protein 70 (HSP70) antisense or sense oligomers. MEASUREMENTS: Analysis of DNA fragmentation on agarose gel as a marker of a poptosis; reverse transcriptase-polymerase chain reaction analysis of mRNA levels; Western blotting analysis of protein levels. RESULTS: Pretreatment of primary cultures of rat brown fat cells with micro molar concentrations of NA or the NO-donor S-nitroso-N-acetylpenicillamine (SNAP) induced the expression of HSP70 mRNA and protein, which was associat ed with cytoprotection against TNF-alpha plus CHX-induced apoptosis. The L- NAME inhibitor of NO synthase activity inhibited both NA-stimulated HSP70 e xpression and cytoprotection. Furthermore, pretreatment of brown adipocytes with an antisense oligonucleotide to HSP70 antagonized both SNAP- and NA-i nduced cytoprotection. CONCLUSION: These findings demonstrate that the NO produced by NA stimulati on can induce resistance to the TNF-alpha -induced apoptosis of brown adipo cytes, possibly by means of the expression of HSP70.