n signature and tissue beta hydroxybutyrate levels that were clearly indicative of fatty acid oxidation. Although we did not measure malonyl CoA levels, we predict that they were reduced with fasting, but not insulin neutralization, based on reduced expression of ACACA. Malonyl CoA allosteri cally binds FK228 and inhibits CPT1A, minimizing fatty acid transport and subsequent oxidation in mitochondria. With insulin neutralization, increased PDK4 may thus be more aligned with the demand for glycerol needed to re esterify fatty acids liberated by lipolysis. Additional experiments are needed to confirm that manipulation of PDK4 alters fatty acid oxidation in chicken adipose tissue and to delineate its relative contributions to fatty acid oxi dation and glyceroneogenesis under varying metabolic states.

If manipulation of PDK4 does alter fatty acid oxida tion, our results highlight this pathway as a potential tar get for reducing fatness, which has relevance for both poultry and humans. Microarray data indicate that the effects of fasting in chicken adipose tissue extend beyond metabolism. GO analysis highlighted pathways such as cell cycle and cytokine cytokine receptor interaction that are most likely related to changes in the stromal vascular fraction, which contains proliferating preadipocytes and cells of the immune system. In particular, a number of genes that regulate multiple steps in adipogenesis were signifi cantly altered by fasting. Chickens rapidly accumulate abdominal fat after hatch, and until approximately 7 weeks of age this is due more to formation of new adi pocytes than to adipocyte hypertrophy.

Adipocytes arise from mesenchymal stem cells in a two stage process of lineage commitment to an adipocyte fate, fol lowed by differentiation of fibroblast like preadipocytes into mature fat storing cells. Members of both the Wnt and TGFB BMP sig naling pathways were significantly regulated by fasting. Fasting down regulated expression of CEBP and PPAR��, two transcription factors that orchestrate the cascade of gene expression changes that lead to terminal adipocyte differentiation. Expression of other adipo genic mediators including fibroblast growth factor 2, fibroblast growth factor receptor 1, and nuclear receptor corepressor 1 were also significantly regulated by fasting.

Collectively, Drug_discovery these changes suggest that adipocyte number in chickens is dynamically tied to energy status, at least in young chicks that are rap idly forming new adipocytes. An elegant study by Arner et al. concluded that adipocyte number in humans is a major determinant of adult fat mass and is determined during early childhood. Less is known about this process in humans due to the limitations of sampling adipose tissue, particularly during development and from different abdominal depots. In light of what appears to be sensitive regulation of adipogenesis by nu tritional state, chickens may inhibitor purchase thus be particularly valu able models in which to elucidate mechanisms of adipocyte