The low-density lipoprotein (LDL) receptor plays a crucial role in cholesterol metabolism. A related protein, designated the very low density lipoprotein (VLDL) receptor, that specifically binds apolipoprotein (apo) E has recently been characterized and shown to be expressed in heart, muscle and adipose tissue and the human monocyte-macrophage cell line THP-1. The VLDL receptor binds and internalizes VLDL and intermediate density lipoprotein from Watanabe heritable hyperlipidemic (WHHL) rabbits as well as beta-migrating VLDL from cholesterol-fed rabbits but not LDL from WHHL rabbits. Chinese hamster ovary (CHO) cells transfected with the rabbit VLDL receptor cDNA have now been shown to bind or internalize VLDL (d < 1.006 g/ml) isolated from fasted normolipidemic human subjects with lower affinity than WHHL-VLDL or rabbit beta-VLDL. However, binding and internalization were markedly enhanced when fasted human VLDL was preincubated with either recombinant human apoE (3/3) or lipoprotein lipase (LPL) in CHO cells overexpressing the rabbit or human VLDL receptor. CHO cells transfected with both the rabbit VLDL receptor cDNA and the human LPL cDNA effectively bound, internalized, and degraded fasted human VLDL without pretreatment. Treatment of heparinase reduced the effect of LPL-mediated binding at 4 degrees C, but the inhibitory effect was lower at 37 degrees C. Pseudomonas LPL also enhanced the binding of human fasted VLDL to the VLDL receptor at 37 degrees C in CHO cells overexpressing the human VLDL receptor. Taken together, LPL causes the enhancement of triglyceride-rich lipoproteins binding to the VLDL receptor via both the formation of bridge between lipoproteins and heparan sulfate proteoglycans and its lipolytic effect. Ligand blot analysis showed that the apparent molecular mass of the VLDL receptor is 118 kDa, which is smaller than that of the LDL receptor. These results indicate that the VLDL receptor recognizes both triglyceride-rich lipoproteins that are also relatively rich in apoE, as well as the remnants of triglyceride-rich lipoproteins after catabolism and the interaction with heparan sulfate proteoglycans by LPL. The VLDL receptor may thus function as a receptor for remnants of triglyceride-rich lipoproteins in extrahepatic tissues.

The very low-density lipoprotein (VLDL) receptor is a member of the low-density lipoprotein (LDL) receptor family. In vitro and in vivo studies

Objective-3-Hydroxyl-3-methyl coenzyme A reductase inhibitors (statins) can function to protect the vasculature in a manner that is independent of their lipid-lowering activity. The main feature of the antithrombotic properties of endothelial cells is an increase in the expression of thrombomodulin (TM) without induction of tissue factor (TF) expression. We investigated the effect of statins on the expression of TM and TF by endothelial cells. Methods and Results-The incubation of endothelial cells with pitavastatin led to a concentration-and time-dependent increase in cellular TM antigen and mRNA levels. In contrast, the expression of TF mRNA was not induced under the same conditions. A nuclear run-on study revealed that pitavastatin accelerates TM transcription rate. Key Words: endothelium Ⅲ thrombomodulin Ⅲ statins Ⅲ small GTPase V ascular endothelial cells play an active role in the regulation of blood coagulation and fibrinolysis. The main feature of the antithrombotic properties of endothelial cells is an increase in the expression of thrombomodulin (TM) without induction of tissue factor (TF) expression. TM is a high-affinity receptor for thrombin that is present on endothelial cell surfaces. By forming a complex with thrombin, TM alters the procoagulant activity of thrombin and acts as a cofactor for the thrombin-catalyzed activation of circulating protein C. Activated protein C functions as an anticoagulant via the proteolytic degradation of the coagulation factors Va and VIIIa, thereby limiting the generation of thrombin. Thus, the TM-protein C pathway is a major antithrombotic mechanism present in endothelial cells, and TM is important in regulating the fluidity of circulating blood.Tissue factor (TF), a membrane glycoprotein receptor that specifically binds factors VII or VIIa, functions as a cellular trigger of the coagulation cascade via activation of factors X and IX. Under normal circumstances, endothelial cells do not display TF activity. Thus, the normal vascular endothelium is relatively inert with respect to initiation of coagulation. A procedure to enhance upregulation of TM without induction of TF expression in cells provides an important clue toward the therapy and prevention of vascular thrombosis. 1 Activated protein C also functions as an important modulator of inflammation associated with severe sepsis. 2 In vitro data indicate that activated protein C exerts an anti-inflammatory effect by both inhibiting the production of inflammatory cytokines (tumor necrosis factor-␣, interleukin-1, and interleukin-6) by monocytes and limiting the rolling of monocytes and neutrophils on injured endothelium via selectin binding. 3 Activated protein C indirectly increases the fibrinolytic response by inhibiting plasminogen activator inhibitor. Recently, it has been shown that treatment with activated protein C significantly reduced mortality in patients with severe sepsis. 4 Inhibitors of 3-hydroxyl-3-methyl coenzyme A (HMGCoA) reductase (statins) are widely used in the treatment of hypercholesterolem...

Intracellular lipid accumulation (steatosis) and resultant lipotoxicity are key features of diabetic cardiomyopathy. Since cardiac hormone-sensitive lipase (HSL) is activated in diabetic mice, we sought to explore a pathophysiological function of cardiac HSL in the development of diabetic cardiomyopathy. Transgenic (Tg) mice with heart-specific HSL overexpression were generated, and cardiac histology, function, lipid profile, and gene expressions were analyzed after induction of diabetes by streptozotocin. Electron microscopy showed numerous lipid droplets in wild-type (Wt) hearts after 3 wk of diabetes, whereas Tg mice showed no lipid droplet accumulation. Cardiac content of acylglycerides was increased ∼50% with diabetes in Wt mice, whereas this was blunted in Tg hearts. Cardiac lipid peroxide content was twofold lower in Tg hearts than in Wt hearts. The mRNA expressions for peroxisome proliferator-activated receptor-α, genes for triacylglycerol synthesis, and lipoprotein lipase were increased with diabetes in Wt hearts, whereas this induction was absent in Tg hearts. Expression of genes associated with lipoapoptosis was decreased, whereas antioxidant protein metallothioneins were increased in diabetic Tg hearts. Diabetic Wt hearts showed interstitial fibrosis and increased collagen content. However, Tg hearts displayed no overt fibrosis, concomitant with decreased expression of collagens, transforming growth factor-β, and matrix metalloproteinase 2. Notably, mortality during the experimental period was approximately twofold lower in diabetic Tg mice compared with Wt mice. In conclusion, since HSL overexpression inhibits cardiac steatosis and fibrosis by apparently hydrolyzing toxic lipid metabolites, cardiac HSL could be a therapeutic target for regulating diabetic cardiomyopathy.

Incretin hormones exert pleiotropic metabolic actions beyond the pancreas. Although the heart expresses both incretin receptors, the cardiac biology of GIP receptor (GIPR) action remains incompletely understood. Here we show that GIPR agonism did not impair the response to cardiac ischemia. In contrast, genetic elimination of the Gipr reduced myocardial infarction (MI)-induced ventricular injury and enhanced survival associated with reduced hormone sensitive lipase (HSL) phosphorylation; it also increased myocardial triacylglycerol (TAG) stores. Conversely, direct GIPR agonism in the isolated heart reduced myocardial TAG stores and increased fatty acid oxidation. The cardioprotective phenotype in Gipr mice was partially reversed by pharmacological activation or genetic overexpression of HSL. Selective Gipr inactivation in cardiomyocytes phenocopied Gipr mice, resulting in improved survival and reduced adverse remodeling following experimental MI. Hence, the cardiomyocyte GIPR regulates fatty acid metabolism and the adaptive response to ischemic cardiac injury. These findings have translational relevance for developing GIPR-based therapeutics.