Protective effects of noradrenaline against tumor necrosis factor-α-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-induced apoptosis of brown adipocytes. DESIGN: Brown fat precursor cells were isolated from young rats; 2.5 million 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 recombinant TNF-a and=or cycloheximide (CHX; 10 mg=ml) and=or NA and=or nitric oxide (NO) donors and=or the NO synthase inhibitor NG-nitro-Larginine methyl ester (L-NAME) and=or 10 mM heat shock protein 70 (HSP70) antisense or sense oligomers. MEASUREMENTS: Analysis of DNA fragmentation on agarose gel as a marker of apoptosis; 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 micromolar concentrations of NA or the NO-donor Snitroso- N-acetylpenicillamine (SNAP) induced the expression of HSP70 mRNA and protein, which was associated with cytoprotection against TNF-a plus CHX-induced apoptosis. The L-NAME inhibitor of NO synthase activity inhibited both NAstimulated HSP70 expression and cytoprotection. Furthermore, pretreatment of brown adipocytes with an antisense oligonucleotide to HSP70 antagonized both SNAP- and NA-induced cytoprotection. CONCLUSION: These findings demonstrate that the NO produced by NA stimulation can induce resistance to the TNF-a- induced apoptosis of brown adipocytes, possibly by means of the expression of HSP70.