Modulation of uncoupling protein 2 and uncoupling protein 3: regulation by denervation, leptin and retinoic acid...

We recently reported that the leptin-induced increase in uncoupling protein 1 (UCP1) mRNA in brown adipose tissue (BAT) is prevented by the denervation of BAT. We also reported that retinoic acid (RA) increases UCP1 mRNA in BAT. To extend these finding to UCP2 and UCP3 in BAT, we examined UCP2 and UCP3 mRNA after unilateral denervation of BAT, as well as after leptin, beta(3)-adrenergic agonist, RA, and glucocorticoid administration to rats. UCP3 mRNA was 20% less in the denervated compared with the intact BAT, whereas UCP2 mRNA was unchanged with denervation. The beta(3)-adrenergic agonist, CGP-12177 (0.75 mg/kg), increased UPC3 mRNA by 40% in the innervated and by 85% in the denervated BAT. Leptin (0.9 mg/day for 3 days) increased both UCP2 and UCP3 mRNA by 30% in the innervated and, surprisingly, in the denervated BAT. RA (7.5 mg/kg) increased UCP1 mRNA but decreased UCP2 and UCP3 mRNA by 50%, whereas methylprednisolone (65 mg/kg, two doses 24 h apart) suppressed all three uncoupling proteins by greater than 60%. The present findings indicate that: sympathetic innervation is necessary to maintain basal levels of UCP3 mRNA; beta(3)-adrenergic agonist stimulation induces UCP3 mRNA; leptin induces UCP2 and UCP3 mRNA and this induction is not dependent on sympathetic innervation; RA increases UCP1 but decreases UCP2 and UCP3 mRNA; and methylprednisolone suppresses UCP1, UCP2, and UCP3 mRNA equally. These data suggest that there are distinct patterns of regulation between UCP1, UCP2, and UCP3, and there may be at least two modes by which leptin could modulate thermogenesis in BAT; first, by increasing sympathetic stimulation of BAT and induction of UCP1 mRNA and, secondly, by increasing UCP2 and UCP3 mRNA by a mechanism independent of sympathetic stimulation.