Affiliations: Division of Applied Life Sciences, Graduate School of
Agriculture, Kyoto University, Kyoto 606-8502, Japan | Bio-oriented Technology Research Advancement
Institution (BRAIN), Tokyo 105-0001, Japan | School of Human Culture, University of Shiga
Prefecture, Hikone, Shiga 522-0057, Japan
Note: [] Division of Applied Life Sciences, Graduate School of
Agriculture, Kyoto University, Kyoto 606-8502, Japan. Fax: +81 75 753 6264;
E-mail: fat@kais.kyoto-u.ac.jp
Abstract: The adipocyte differentiation program is regulated by the sequential
expression of transcriptional activators, mainly peroxisome proliferator
activated receptor (PPAR) families. In the present study, we have decided to
systematically examine the effects of vitamin A and its precursors, carotenoids
and retinoids, on terminal differentiation from preadipocytes to adipocytes on
the cellular and molecular aspects. The effects of active form of vitamin A,
retinoic acid (RA), are believed to be mediated by specific nuclear receptor
proteins [retinoic acid receptor (RAR)] which are members of the steroid and
thyroid/retinoid receptor superfamily of ligand dependent transcriptional
regulators. RAR\alpha, RAR\gamma,
RXR\alpha, and RXR\beta mRNA were
abundant in adipose tissue and 3T3-L1 adipose cells. The autoregulated
amplification of RAR\gamma mRNA was observed by these own
ligands in 3T3-L1 cells. And, RA inhibited PPAR\gamma2
expression more effectively and caused concomitantly a greater inhibition of
adipocyte differentiation. These results suggest that the inhibitory action of
adipocyte differentiation by carotenoids and retinoids are exhibited through
the RAR up-regulation and the suppression of PPAR\gamma2.
The nature of the cross talk of vitamin A actions between the RARs, RXRs and
PPARs via co-activator in adipose tissue will likely prove to be important for
understanding the process of adipogenesis.
