Retinoids and adipose tissues: metabolism, cell differentiation and gene expression

Vitamin A derivatives (retinoids) play a key role in mammalian development and cell differentiation. Isomers of retinoic acid, the main active metabol ite of vitamin A, activate retinoid receptors that act as ligand-dependent transcription factors and affect gene expression. White and brown adipose t issues are major sites of storage of vitamin A derivatives and they play an active role in whole body metabolism of retinoids. Moreover, adipose tissu es are targets for the action of retinoic acid. In most cases retinoic acid impairs adipocyte differentiation although its final effects on adipose ti ssue development depend on retinoic acid concentration, isomers availabilit y and expression of retinoid receptor subtypes in the white or brown adipoc yte. Retinoic acid (RA) has a specific effect on brown adipose tissue, beca use it activates transcription of the gene for uncoupling protein-1, respon sible for brown fat thermogenesis.