Fig. 1.

Retinoid metabolism. Retinoid receptors are specifically associated to those genes which have a retinoid acid response element (RARE). This element is usually located at the promoter region. Normally retinoid receptors are inactivated, since they are associated to a group of molecules which act as transcription repressors. Once in the cell, retinoids through the action of different cellular retinoid acid binding proteins (CRABPs) can be stored or delivered to the nucleus activating the retinoid pathways. In the presence of ligand the dimeric nuclear receptor activates and changes its structural conformation, thus liberating from the inhibitor complex and promoting the transcription of its target genes. Many genes are modulated by retinoids. Among them there are genes involved in proteostasis, the antioxidant response, the intracellular signaling, the synaptic homeostasis and the inflammation.