Adipocyte development is dependent upon stem cell recruitment and proliferation of preadipocytes

Objectives: The ability to acquire fat cells persists over the life spans o f animals. It is unknown whether adipocyte acquisition is the result of pre adipocyte proliferation or stem cell recruitment to become adipocytes. The purposes of these studies were 1) to characterize early differentiation of stromal vascular (S-V) cells to preadipocytes as it is influenced by insuli n, dexamethasone (DEX), and insulin-like growth factor-I (IGF-I); and 2) to determine whether new fat cells arise from stem cell recruitment or preadi pocyte proliferation. Research Methods and Procedures: Freshly isolated S-V cells from rat inguin al adipose tissues were plated for 24 hours then exposed to serum-free medi um. Results: Approximately 15% of freshly plated S-V cells were preadipocytes a s determined by a preadipocyte specific marker, AD3. Total cell number and proportion of preadipocytes were significantly greater with 100 nM insulin treatment than with 0, 0.1, or 1.0 nM, but IGF-I treatment at 10 nM resulte d in preadipocyte development similar to that with 100 nM insulin treatment . The addition of 5 nM DEX to the 100 nM insulin treatment resulted in a 20 % increase in preadipocyte number by day 2 when compared to either treatmen t alone. 5-Bromo-2'-deoxy-uridine treatment suppressed the increased propor tion of preadipocytes from days 0-2 in non-insulin treated cells and preven ted the increase typically observed with insulin. A mitosis inhibitor also significantly reduced the proportion of preadipocytes. Discussion: These results show for the first time that S-V cells are recrui ted as preadipocytes and that proliferation of these preadipocytes and earl y differentiation occur simultaneously.