Adipocytes secrete a variety of bioactive molecules that affect the insulin sensitivity of other tissues. We now show that the abundance of monocyte chemoattractant protein-1 (MCP-1) mRNA in adipose tissue and the plasma concentration of MCP-1 were increased both in genetically obese diabetic (db/db) mice and in WT mice with obesity induced by a high-fat diet. Mice engineered to express an MCP-1 transgene in adipose tissue under the control of the aP2 gene promoter exhibited insulin resistance, macrophage infiltration into adipose tissue, and increased hepatic triglyceride content. Furthermore, insulin resistance, hepatic steatosis, and macrophage accumulation in adipose tissue induced by a high-fat diet were reduced extensively in MCP-1 homozygous KO mice compared with WT animals. Finally, acute expression of a dominant-negative mutant of MCP-1 ameliorated insulin resistance in db/db mice and in WT mice fed a high-fat diet. These findings suggest that an increase in MCP-1 expression in adipose tissue contributes to the macrophage infiltration into this tissue, insulin resistance, and hepatic steatosis associated with obesity in mice.

Editorial, see p 225Mitochondria are dynamic organelles that constantly undergo fusion and fission 5 to adapt to changes in the cellular environment. Although mitochondrial fusion allows mitochondria to maintain membrane potential by fusing depolarized mitochondria to intact ones, fission allows the segregation of unrecoverable mitochondria so that they can be eliminated by autophagy or mitophagy, a specialized form of autophagy.6 Mitochondrial fusion is critically

Background-Excessive myocardial fibrosis impairs cardiac function in hypertensive hearts. Roles of transforming growth factor (TGF)-␤ in myocardial remodeling and cardiac dysfunction were examined in pressure-overloaded rats. Methods and Results-Pressure overload was induced by a suprarenal aortic constriction in Wistar rats. Fibroblast activation (proliferation and phenotype transition to myofibroblasts) was observed after day 3 and peaked at days 3 to 7. Thereafter, myocyte hypertrophy and myocardial fibrosis developed by day 28. At day 28, echocardiography showed normal left ventricular fractional shortening, but the decreased ratio of early to late filling velocity of the transmitral Doppler velocity and hemodynamic measurement revealed left ventricular end-diastolic pressure elevation, indicating normal systolic but abnormal diastolic function. Myocardial TGF-␤ mRNA expression was induced after day 3, peaked at day 7, and remained modestly increased at day 28. An anti-TGF-␤ neutralizing antibody, which was administered intraperitoneally daily from 1 day before operation, inhibited fibroblast activation and subsequently prevented collagen mRNA induction and myocardial fibrosis, but not myocyte hypertrophy. Neutralizing antibody reversed diastolic dysfunction without affecting blood pressure and systolic function. Conclusions-TGF-␤ plays a causal role in myocardial fibrosis and diastolic dysfunction through fibroblast activation in pressure-overloaded hearts. Our findings may provide an insight into a new therapeutic strategy to prevent myocardial fibrosis and diastolic dysfunction in pressure-overloaded hearts.

Endothelium-dependent relaxations are achieved by a combination of endothelium-derived prostacyclin (PGI2), nitric oxide (NO), and endothelium-derived hyperpolarizing factor (EDHF). However, it remains to be fully clarified whether the relative contribution of these three mechanisms to endothelium-dependent relaxations varies as a function of the vessel size. This study was designed to clarify this point. Acetylcholine (ACh)-induced endothelium-dependent relaxations were examined in isolated blood vessels taken from the aorta and the proximal and distal mesenteric arteries of the rat. The contributions of PGI2, NO, and EDHF were evaluated by the inhibitory effects of indomethacin, N omega-nitro-L-arginine methyl ester (L-NAME) in the presence of indomethacin, and KCl in the presence of indomethacin and L-NAME, respectively. The membrane potentials were recorded with microelectrodes. The expression of endothelial No synthase (eNOS) was examined by both immunostaining and immunoblotting. The contribution of PGI2 was negligible in three different-sized blood vessels. The contribution of NO was most prominent in the aorta, whereas that of EDHF was most prominent in the distal mesenteric arteries. The resting membrane potential was significantly deeper and the ACh-induced hyperpolarization was greater in the distal mesenteric arteries than those in the aorta. The expression of eNOS was the highest in the aorta and the lowest in the distal mesenteric arteries. These results indicate that the importance of EDHF increases as the vessel size decreases in endothelium-dependent relaxations in the rat mesenteric circulation.