We conclude that insulin sensitivity is reduced to a similar extent in acromegalic patients with normal glucose tolerance and those with impaired glucose tolerance or diabetes. Compensatory hyperfunction of beta-cells appears to counterbalance the reduced insulin sensitivity in the acromegalic patients with normal glucose tolerance but not in those with impaired glucose tolerance or diabetes.

Insulin stimulates glucose transport in muscle and fat cells by inducing translocation of GLUT4 glucose transporters from a storage site to the cell surface. The mechanism of this translocation and the identity of the storage site are unknown, but it has been hypothesized that transporters recycle between an insulin-sensitive pool, endosomes, and the cell surface. Upon cell homogenization and fractionation, the storage site migrates with light microsomes (LDM) separate from the plasma membrane fraction (PM). Cellubrevin is a recently identified endosomal protein that may be involved in the reexocytosis of recycling endosomes. Here we describe that cellubrevin is expressed in 3T3-L1 adipocytes and is more abundant in the LDM than in the PM. Cellubrevin was markedly induced during differentiation of 3T3-L1 fibroblasts into adipocytes, in parallel with GLUT4, and the development of insulin regulated traffic. In response to insulin, the cellubrevin content decreased in the LDM and increased in the PM, suggesting translocation akin to that of the GLUT4 glucose transporter. Vesicle-associated membrane protein 2 (VAMP-2)/synaptobrevin-II, a protein associated with regulated exocytosis in secretory cells, also redistributed in response to insulin. Both cellubrevin and VAMP-2 were susceptible to cleavage by tetanus toxin. Immunopurified GLUT4-containing vesicles contained cellubrevin and VAMP-2, and immunopurified cellubrevin-containing vesicles contained GLUT4 protein, but undiscernible amounts of VAMP-2. These observations suggest that cellubrevin and VAMP-2 are constituents of the insulin-regulated pathway of membrane traffic. These results are the first demonstration that cellubrevin is present in a regulated intracellular compartment. We hypothesize that cellubrevin and VAMP-2 may be present in different subsets of GLUT4-containing vesicles.

Objective-There has been accumulating evidence demonstrating that activators for peroxisome proliferator-activated receptor ␣ (PPAR␣) have antiinflammatory, antiatherogenic, and vasodilatory effects. We hypothesized that PPAR␣ activators can modulate endothelial nitric oxide synthase (eNOS) expression and its activity in cultured vascular endothelial cells. Methods and Results-Bovine aortic endothelial cells were treated with the PPAR␣ activator fenofibrate. The amount of eNOS activity and the expression of eNOS protein and its mRNA were determined. Our data show that treatment with fenofibrate for 48 hours resulted in an increase in eNOS activity. Fenofibrate failed to increase eNOS activity within 1 hour. Fenofibrate also increased eNOS protein as well as its mRNA levels. RU486, which has been shown to antagonize PPAR␣ action, inhibited the fenofibrate-induced upregulation of eNOS protein expression. WY14643 and bezafibrate also increased eNOS protein levels, whereas rosiglitazone did not. Transient transfection experiments using human eNOS promoter construct showed that fenofibrate failed to enhance eNOS promoter activity. Actinomycin D studies demonstrated that the half-life of eNOS mRNA increased with fenofibrate treatment. Conclusions-PPAR␣ activators upregulate eNOS expression, mainly through mechanisms of stabilizing eNOS mRNA. This is a new observation to explain one of the mechanisms of PPAR␣-mediated cardiovascular protection. Key Words: atherosclerosis Ⅲ endothelium Ⅲ nitric oxide Ⅲ vascular biology Ⅲ vasodilatation H ypolipidemic fibrates are pharmacological compounds that activate peroxisome proliferator-activated receptor ␣ (PPAR␣), a member of the nuclear hormone receptor superfamily. 1 These fibrates have been widely used as effective drugs lowering serum triglycerides and low-density lipoprotein cholesterol and raising high-density lipoprotein cholesterol. 2 There has been accumulating evidence showing that fibrates have favorable effects of slowing the progression of atherosclerosis and reducing the number of events of coronary heart diseases in high-risk patients. 3-5 PPAR␣ is known to be expressed in the liver, which is mainly involved in lipid and lipoprotein metabolism exerted by fibrates. 1 In addition, recent studies have shown that PPAR␣ is also expressed in the cardiovascular system, including heart and vascular wall component cells such as vascular endothelial, vascular smooth muscle, and monocyte cells, and performs a direct antiatherogenic and antiinflammatory action. 6 Staels et al have shown that PPAR␣ ligands inhibit interleukin (IL)-1-induced expression of IL-6, prostaglandin, and cyclooxygenase 2 in aortic smooth muscle cells. 7 These authors further showed that patients receiving fenofibrate, a potent fibrate, had lower plasma C-reactive protein, fibrinogen, and IL-6 concentrations. 7 Furthermore, it has been demonstrated that PPAR␣ activators inhibit cytokine-induced vascular cell adhesion molecule-1 (VCAM-1), 8,9 and thrombin-induced endothelin-1 expression 10 in vascular en...

Runx2 (runt-related transcription factor 2) is an important transcription factor for chondrocyte differentiation as well as for osteoblast differentiation. To investigate the function of Runx2 in chondrocytes, we isolated chondrocytes from the rib cartilage of Runx2-deficient (Runx2–/–) mice and examined the effect of Runx2 deficiency on chondrocyte function and behavior in culture for up to 12 days. At the beginning of the culture, Runx2–/– chondrocytes actively proliferated, had a polygonal shape and expressed type II collagen; these are all characteristics of chondrocytes. However, they gradually accumulated lipid droplets that stained with oil red O and resembled adipocytes. Northern blot analysis revealed that the expression of adipocyte-related differentiation marker genes including PPARγ (peroxisome proliferator-activated receptor γ), aP2 and Glut4 increased over time in culture, whereas expression of type II collagen decreased. Furthermore, the expression of Pref-1, an important inhibitory gene of adipogenesis, was remarkably decreased. Adenoviral introduction of Runx2 or treatment with transforming growth factor-β, retinoic acid, interleukin-1β, basic fibroblast growth factor, platelet-derived growth factor or parathyroid hormone inhibited the adipogenic changes in Runx2–/– chondrocytes. Runx2 and transforming growth factor-β synergistically upregulated interleukin-11 expression, and the addition of interleukin-11 to the culture medium reduced adipogenesis in Runx2–/– chondrocytes. These findings indicate that depletion of Runx2 resulted in the loss of the differentiated phenotype in chondrocytes and induced adipogenic differentiation in vitro, and show that Runx2 plays important roles in maintaining the chondrocyte phenotype and in inhibiting adipogenesis. Our findings suggest that these Runx2-dependent functions are mediated, at least in part, by interleukin-11.

The extent of carotid atherosclerosis in the acromegalic patients was not higher than that in non-acromegalic subjects, considering their atherosclerotic risk factors. Increased concentration of IGF-I might be involved in the lack of susceptibility to atherosclerosis in some acromegalic patients.