Objective: To elucidate the effects and molecular mechanism(s) by means of which noradrenaline (NA) protects against the tumor necrosis factor (TNF)-alpha-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-alpha and/or cycloheximide (CHX; 10 microg/ml) and/or NA and/or nitric oxide (NO) donors and/or the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) and/or 10 microM 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 S-nitroso-N-acetylpenicillamine (SNAP) induced the expression of HSP70 mRNA and protein, which was associated with cytoprotection against TNF-alpha plus CHX-induced apoptosis. The L-NAME inhibitor of NO synthase activity inhibited both NA-stimulated 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-alpha-induced apoptosis of brown adipocytes, possibly by means of the expression of HSP70.