THE EFFECT OF ADIPOCYTE DIFFERENTIATION ON THE CAPACITY OF 3T3-L1 CELLS TO UNDERGO APOPTOSIS IN RESPONSE TO GROWTH-FACTOR DEPRIVATION

OBJECTIVE: Little is known about the regulation of apoptosis in the ad ipocyte. Using the 3T3-L1 cell model of adipogenesis, we investigated whether induction of apoptosis by serum-starvation is differentiation- specific. METHODS: Apoptosis was assessed by phase-contrast microscopy , Hoechst staining and DNA fragmentation. Protein expression levels we re evaluated by immunoblot analysis, RESULTS: Following serum deprivat ion, Hoechst staining revealed chromatin condensation and formation of apoptotic bodies in 3T3-L1 preadipocytes, but not in differentiated a dipocytes. Similarly, although cell cultures of serum-starved 3T3-L1 p readipocytes displayed extensive apoptotic DNA fragmentation, this was barely detectable for cell cultures subjected to differentiation medi um, in which 70-90% of the cells had assumed the mature phenotype. Con sistent with the ability of the adipocytes to resist apoptosis, immuno blot analysis revealed that differentiated cell cultures expressed Bcl -2 and the endonuclease DNase I at higher and lower levels, respective ly. CONCLUSION: Expression of cell survival genes is modulated during 3T3-L1 adipocyte differentiation, potentially contributing to the stat e of resistance to apoptosis observed for mature 3T3-L1 adipocytes upo n growth factor deprivation.