Thiazolidinediones inhibit the expression of β3-adrenergic receptors at transcriptional level

The effect of the thiazolidinediones (TZDs) darglitazone and troglitazone on beta (3)-adrenergic receptor (AR) expression was studied in cultured cell lines representing several tissues, After 24 h of exposing HIB-1B brown adipocytes to 30 mu mol/l darglitazone or 20 mu mol/l troglitazone, beta (3)-AR mRNA levels mere reduced by 75%. This effect was significant within 1 h of exposure to a maximal dose of these drugs, with the full effect obtained within 10 h. The darglitazone ID50 was similar to 10 nmol/l, similar to the K-d of TZDs binding to peroxisome proliferator-activated receptor-gamma (PPAR-gamma). These drugs also decreased beta (3)-AR mRNA in 3T3-F442A white adipocytes, but not in SK-N-MC cells, which lack PPAR-gamma2. A luciferase reporter gene containing 1.4 kb of 5' flanking sequence of the mouse beta (3)-AR was transiently transfected, with or without PPAR-gamma2, in SK-N-MC cells. The vigorous expression of luciferase driven by the beta (3)-AR gene sequence was inhibited by nos in a PPAR-gamma2-dependent manner. The half-lives of beta (3)-AR precursor RNA and mRNA were short, similar to 40 and similar to 100 min, respectively, and remained unaffected by TZD treatment. Exposure of HIB-1B cells to 30 mu mol/l darglitazone was associated with reduced beta (3)-AR mRNA levels, as well as decreased response of uncoupling; protein I to norepinephrine + propranolol (a beta (1), beta (2)-AR antagonist) or the specific beta (3)-AR agonist CL 316, 243. Both the beta (3)-AR mRNA level and response to these stimuli fully recovered by 24 h of removing the drug, indicating that the beta (3)-AR protein and its coupling to adenylyl cyclase rapidly followed the changes in mRNA. Thus, TZDs can rapidly reduce beta (3)-AR expression at the transcriptional level, acting through PPAR-gamma2. The rapid turnover and responses of beta (3)-AR to perturbations, along with numerous other factors reported to regulate its expression, suggest a tight control of beta (3)-AR and function. Lastly, leptin being the only other known gene suppressed by TZDs, the present studies support a concerted Lipogenic effect of these drugs.