The adipocyte-derived hormone adiponectin regulates glucose and lipid metabolism and influences the risk for developing obesity, type 2 diabetes, and cardiovascular disease. Adiponectin binds to two different seven-transmembrane domain receptors termed AdipoR1 and AdipoR2. To study the physiological importance of these receptors, AdipoR1 gene knockout mice (AdipoR1 Ϫ/Ϫ ) and AdipoR2 gene knockout mice (AdipoR2 Ϫ/Ϫ ) were generated. AdipoR1 Ϫ/Ϫ mice showed increased adiposity associated with decreased glucose tolerance, spontaneous locomotor activity, and energy expenditure. However, AdipoR2Ϫ/Ϫ mice were lean and resistant to high-fat diet-induced obesity associated with improved glucose tolerance and higher spontaneous locomotor activity and energy expenditure and reduced plasma cholesterol levels. Thus, AdipoR1 and AdipoR2 are clearly involved in energy metabolism but have opposing effects. Diabetes 56:583-593, 2007

Glycerol-3-phosphate acyltransferase (GPAT) catalyses the first committed step in glycerolipid biosynthesis. The mitochondrial isoform (mtGPAT) is mainly expressed in liver, where it is highly regulated, indicating that mtGPAT may have a unique role in hepatic fatty acid metabolism. Because both mtGPAT and carnitine palmitoyl transferase-1 are located on the outer mitochondrial membrane, we hypothesized that mtGPAT directs fatty acyl-CoA away from ␤ -oxidation and toward glycerolipid synthesis. Adenoviralmediated overexpression of murine mtGPAT in primary cultures of rat hepatocytes increased mtGPAT activity 2.7-fold with no compensatory effect on microsomal GPAT activity. MtGPAT overexpression resulted in a dramatic 80% reduction in fatty acid oxidation and a significant increase in hepatic diacylglycerol and phospholipid biosynthesis. Following lipid loading of the cells, intracellular triacylglycerol biosynthesis was also induced by mtGPAT overexpression. Changing an invariant aspartic acid residue to a glycine [D235G] in mtGPAT resulted in an inactive enzyme, which helps define the active site required for mammalian mtGPAT function. To determine if obesity increases hepatic mtGPAT activity, two models of rodent obesity were examined and shown to have Ͼ 2-fold increased enzyme activity.Overall, these results support the concept that increased hepatic mtGPAT activity associated with obesity positively contributes to lipid disorders by reducing oxidative processes and promoting de novo glycerolipid synthesis. -Lindén, D., L. William-Olsson, M. Rhedin, A-K. Asztély, J. C. Clapham, and S. Schreyer. Overexpression of mitochondrial GPAT in rat hepatocytes leads to decreased fatty acid oxidation and increased glycerolipid biosynthesis.

Glycerol-3-phosphate acyltransferase (GPAT) catalyzes the first committed step in triacylglycerol (TAG) and phospholipid biosynthesis. GPAT activity has been identified in both ER and mitochondrial subcellular fractions. The ER activity dominates in most tissues except in liver, where the mitochondrial isoform (mtGPAT) can constitute up to 50% of the total activity. To study the in vivo effects of hepatic mtGPAT overexpression, mice were transduced with adenoviruses expressing either murine mtGPAT or a catalytically inactive variant of the enzyme. Overexpressing mtGPAT resulted in massive 12- and 7-fold accumulation of liver TAG and diacylglycerol, respectively but had no effect on phospholipid or cholesterol ester content. Histological analysis showed extensive lipid accumulation in hepatocytes. Furthermore, mtGPAT transduction markedly increased adipocyte differentiation-related protein and stearoyl-CoA desaturase-1 (SCD-1) in the liver. In line with increased SCD-1 expression, 18:1 and 16:1 in the hepatic TAG fraction increased. In addition, mtGPAT overexpression decreased ex vivo fatty acid oxidation, increased liver TAG secretion rate 2-fold, and increased plasma TAG and cholesterol levels. These results support the hypothesis that increased hepatic mtGPAT activity associated with obesity and insulin resistance contributes to increased TAG biosynthesis and inhibition of fatty acid oxidation, responses that would promote hepatic steatosis and dyslipidemia.

Excess mineralocorticoid receptor (MR) activation promotes target organ dysfunction, vascular injury and fibrosis. MR antagonists like eplerenone are used for treating heart failure, but their use is limited due to the compound class-inherent hyperkalemia risk. Here we present evidence that AZD9977, a first-in-class MR modulator shows cardio-renal protection despite a mechanism-based reduced liability to cause hyperkalemia. AZD9977 in vitro potency and binding mode to MR were characterized using reporter gene, binding, cofactor recruitment assays and X-ray crystallopgraphy. Organ protection was studied in uni-nephrectomised db/db mice and uni-nephrectomised rats administered aldosterone and high salt. Acute effects of single compound doses on urinary electrolyte excretion were tested in rats on a low salt diet. AZD9977 and eplerenone showed similar human MR in vitro potencies. Unlike eplerenone, AZD9977 is a partial MR antagonist due to its unique interaction pattern with MR, which results in a distinct recruitment of co-factor peptides when compared to eplerenone. AZD9977 dose dependently reduced albuminuria and improved kidney histopathology similar to eplerenone in db/db uni-nephrectomised mice and uni-nephrectomised rats. In acute testing, AZD9977 did not affect urinary Na+/K+ ratio, while eplerenone increased the Na+/K+ ratio dose dependently. AZD9977 is a selective MR modulator, retaining organ protection without acute effect on urinary electrolyte excretion. This predicts a reduced hyperkalemia risk and AZD9977 therefore has the potential to deliver a safe, efficacious treatment to patients prone to hyperkalemia.

Adipose differentiation-related protein (ADRP) is a lipid droplet-associated protein that is expressed in various tissues. In mice treated with the peroxisome proliferatoractivated receptor a (PPARa) agonist Wy14,643 (Wy), hepatic mRNA and protein levels of ADRP as well as hepatic triglyceride content increased. Also in primary mouse hepatocytes, Wy increased ADRP expression and intracellular triglyceride mass. The triglyceride mass increased in spite of unchanged triglyceride biosynthesis and increased palmitic acid oxidation. However, Wy incubation decreased the secretion of newly synthesized triglycerides, whereas apolipoprotein B secretion increased. Thus, decreased availability of triglycerides for VLDL assembly could help to explain the cellular accumulation of triglycerides after Wy treatment. We hypothesized that this effect could be mediated by increased ADRP expression. Similar to PPARa activation, adenovirusmediated ADRP overexpression in mouse hepatocytes enhanced cellular triglyceride mass and decreased the secretion of newly synthesized triglycerides. In ADRP-overexpressing cells, Wy incubation resulted in a further decrease in triglyceride secretion. This effect of Wy was not attributable to decreased cellular triglycerides after increased fatty acid oxidation because the triglyceride mass in Wy-treated ADRPoverexpressing cells was unchanged. In summary, PPARa activation prevents the availability of triglycerides for VLDL assembly and increases hepatic triglyceride content in part by increasing the expression of ADRP. Peroxisome proliferator-activated receptor a (PPARa) is a ligand-activated transcription factor that plays a key role in the regulation of genes involved in carbohydrate, lipid, and lipoprotein metabolism (for review, see 1).PPARa is highly expressed in tissues with high mitochondrial and peroxisomal b-oxidation activities, such as liver, heart, kidney, and skeletal muscle (2-5). In humans, treatment with PPARa agonists (i.e., fibrates) results in decreased plasma levels of triglycerides and increased plasma HDL cholesterol levels (6, 7). The triglyceride-lowering effect of fibrates is partly explained by increased lipoprotein lipase expression (8) and downregulation of hepatic apolipoprotein C-III expression (9, 10), which results in increased turnover of VLDL. In addition, fibrates have been shown to decrease the plasma concentration of atherogenic small dense LDL particles (11, 12), indicating decreased hepatic triglyceride secretion, because small dense LDLs are products of triglyceride-rich VLDL (VLDL 1 ) particles (13). Indeed, fibrates have been shown to decrease VLDL triglyceride secretion in both humans and rats (14,15). In primary rat hepatocytes, fibrates reduced triglyceride secretion and decreased the size of the secreted apolipoprotein B (apoB)-containing lipoproteins (16). The reduced triglyceride secretion may be explained by decreased triglyceride biosynthesis in rat hepatocytes (16,17). However, in vivo in rats, incorporation of palmitate into liver triglyc...