Effects of cholera toxin on gene expression in brown preadipocytes differentiating in culture

To investigate the cellular control of the recruitment process in brown adipose tissue, the ability of cholera toxin to influence the differentiation of brown preadipocytes developing in culture was investigated. Stromalvascular cells obtained from the brown adipose tissue of 3-wk-old rats were grown in culture for 6-7 days in the presence or absence of cholera toxin. It was found that cholera toxin treatment decreased the expression of the actin gene (indicating an increased degree of differentiation), while at the same time promoting the expression of the genes coding for the mitochondriogenesis marker cytochrome-c oxidase and for the adipocyte conversion marker lipoprotein lipase (all followed at the mRNA level). Chronic cholera toxin treatment also increased the total amount of protein per cell in culture, and a specific cholera toxin-induced 35-kDa protein was identified. It was concluded that (in contrast to the case suggested for white preadipocytes) cholera toxin treatment of brown preadipocytes may not only affect the activity of catabolic enzymes but may also directly promote the differentiation process, indicating that this process is under beta-adrenergic control in the adapting animal.