Increased plasminogen activator inhibitor 1 (PAI-1) has been linked to not only thrombosis and fibrosis but also to obesity and insulin resistance. Increased PAI-1 levels have been presumed to be consequent to obesity. We investigated the interrelationships of PAI-1, obesity, and insulin resistance in a high-fat/high-carbohydrate (HF) diet-induced obesity model in wild-type (WT) and PAI-1-deficient mice (PAI-1 ؊/؊ ). Obesity and insulin resistance developing in WT mice on an HF diet were completely prevented in mice lacking PAI-1. PAI-1 ؊/؊ mice on an HF diet had increased resting metabolic rates and total energy expenditure compared with WT mice, along with a marked increase in uncoupling protein 3 mRNA expression in skeletal muscle, likely mechanisms contributing to the prevention of obesity. In addition, insulin sensitivity was enhanced significantly in PAI-1 ؊/؊ mice on an HF diet, as shown by euglycemichyperinsulinemic clamp studies. Peroxisome proliferator-activated receptor (PPAR)-␥ and adiponectin mRNA, key control molecules in lipid metabolism and insulin sensitivity, were maintained in response to an HF diet in white adipose tissue in PAI-1 ؊/؊ mice, contrasting with downregulation in WT mice. This maintenance of PPAR-␥ and adiponectin may also contribute to the observed maintenance of body weight and insulin sensitivity in PAI-1 ؊/؊ mice. Treatment in WT mice on an HF diet with the angiotensin type 1 receptor antagonist to downregulate PAI-1 indeed inhibited PAI-1 increases and ameliorated diet-induced obesity, hyperglycemia, and hyperinsulinemia. PAI-1 deficiency also enhanced basal and insulin-stimulated glucose uptake in adipose cells in vitro. Our data suggest that PAI-1 may not merely increase in response to obesity and insulin resistance, but may have a direct causal role in obesity and insulin resistance. Inhibition of PAI-1 might provide a novel anti-obesity and anti-insulin resistance treatment. Diabetes 53: 336 -346, 2004

The present study examined the expression and role of the thiazolidinedione (TZD)-activated transcription factor, peroxisome proliferator-activated receptor gamma (PPARgamma), in human bladder cancers. In situ hybridization shows that PPARgamma mRNA is highly expressed in all human transitional epithelial cell cancers (TCCa's) studied (n=11). PPARgamma was also expressed in five TCCa cell lines as determined by RNase protection assays and immunoblot. Retinoid X receptor alpha (RXRalpha), a 9-cis-retinoic acid stimulated (9-cis-RA) heterodimeric partner of PPARgamma, was also co-expressed in all TCCa tissues and cell lines. Treatment of the T24 bladder cancer cells with the TZD PPARgamma agonist troglitazone, dramatically inhibited 3H-thymidine incorporation and induced cell death. Addition of the RXRalpha ligands, 9-cis-RA or LG100268, sensitized T24 bladder cancer cells to the lethal effect of troglitazone and two other PPAR- activators, ciglitazone and 15-deoxy-delta(12,14)-PGJ2 (15dPGJ(2)). Troglitazone treatment increased expression of two cyclin-dependent kinase inhibitors, p21(WAF1/CIP1) and p16(INK4), and reduced cyclin D1 expression, consistent with G1 arrest. Troglitazone also induced an endogenous PPARgamma target gene in T24 cells, adipocyte-type fatty acid binding protein (A-FABP), the expression of which correlates with bladder cancer differentiation. In situ hybridization shows that A-FABP expression is localized to normal uroepithelial cells as well as some TCCa's. Taken together, these results demonstrate that PPARgamma is expressed in human TCCa where it may play a role in regulating TCCa differentiation and survival, thereby providing a potential target for therapy of uroepithelial cancers.

PGE 2 exerts potent diuretic and natriuretic effects on the kidney. This action is mediated in part by direct inhibition of collecting duct Na ϩ absorption via a Ca ϩϩ -coupled mechanism. These studies examine the role the Ca ϩϩ -coupled PGE-E EP 1 receptor plays in mediating these effects of PGE 2 on Na ϩ transport. Rabbit EP 1 receptor cDNA was amplified from rabbit kidney RNA. Nuclease protection assays demonstrated highest expression of EP 1 mRNA in kidney, followed by stomach, adrenal, and ileum. In situ hybridization, demonstrated renal expression of EP 1 mRNA was exclusively over the collecting duct. In fura-2-loaded microperfused rabbit cortical collecting duct, EP 1 active PGE analogs were 10-1,000-fold more potent in raising intracellular Ca ϩϩ than EP 2 , EP 3 , or EP 4 -selective compounds. Two different EP 1 antagonists, AH6809 and SC19220, completely blocked the PGE 2 -stimulated intracellular calcium increase. AH6809 also completely blocked the inhibitory effect of PGE 2 on Na ϩ absorption in microperfused rabbit cortical collecting ducts. These studies suggest that EP 1 receptor activation mediates PGE 2 -dependent inhibition of Na ϩ absorption in the collecting duct, thereby contributing to its natriuretic effects. ( J. Clin. Invest . 1998. 102:194-201.)

Regulation of renal function by prostaglandin E receptors. Prostaglandin E 2 is the major cyclooxygenase product of arachidonic acid metabolism produced along the nephron. This autacoid interacts with four distinct, G-protein-coupled E-prostanoid receptors designated EP 1 -EP 4 . The intrarenal distribution of each receptor has been mapped and the consequences of receptor activation examined. EP 3 receptor mRNA is expressed highly in the medullary thick ascending limb (mTAL) and collecting duct (CD). EP 3 receptor activation inhibits cAMP generation via G i , thus inhibiting vasopressin-stimulated water reabsorption in the CD. EP 3 receptor activation also may contribute to PGE 2mediated inhibition of NaCl absorption in the mTAL. The EP 1 receptor is coupled to increased cell [Ca 2ϩ ]. EP 1 mRNA expression is restricted to the CD, and receptor activation inhibits Na ϩ absorption. PGE 2 also increases cAMP generation in the cortical thick ascending limb and CD; this may be due to EP 4 receptor activation. EP 4 mRNA is readily detected in the CD with little detectable EP 2 expression. The EP 4 receptor appears to be expressed both on luminal and basolateral membranes. EP 4 receptor activation also may contribute to the regulation of renin release by the juxtaglomerular apparatus. The consequences of renal EP-receptor activation for salt and water balance may be determined by the relative renal expression of each of these receptors.