White adipose tissue is the major energy storage depot for neutral lipids and is also a key endocrine regulator of a host of homeostatic activities, including metabolism, feeding behaviors, cardiovascular functions and reproduction. Abnormal fat accretion in the setting of obesity can lead to insulin resistance and type 2 diabetes, and has been linked to some cancers and arteriosclerosis. Thus, a thorough appreciation of the intricate signaling events that must take place as quiescent adipocyte precursors are recruited into the proliferating cell population that then must 'decide' to differentiate into fully functional fat cells is critical to our understanding of diseases related to excess adipogenesis. We are beginning to gain insights into the molecular regulators of adipocyte differentiation. A significant advance would be to construct mathematical modeling tools that would assist cell biologists in predicting how environmental and/or intrinsic inputs could influence preadipocyte fate decision making. We have developed a model of how preadipocytes may use the dynamic interplay of two transcription factors, nuclear factor-kappa B (NF-kappaB) and peroxisome proliferator-activated receptor-gamma (PPAR-gamma) in early proliferation and differentiation events in vitro. Critical to the model is the feedback signaling between NF-kappaB and its inhibitor, I kappaB. The model is based on differential equations that describe the interactions of stimuli for NF-kappaB activation and mitogen concentrations and allows one to make predictions about how mouse 3T3-L1 preadipocytes choose between proliferation, differentiation or quiescence. Those predictions are supported by experiments on mouse 3T3-L1 cells.
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