To determine the mechanism of the cardiac dilatation and reduced contractility of obese Zucker Diabetic Fatty rats, myocardial triacylglycerol (TG) was assayed chemically and morphologically. TG was high because of underexpression of fatty acid oxidative enzymes and their transcription factor, peroxisome proliferator-activated receptor-␣. Levels of ceramide, a mediator of apoptosis, were 2-3 times those of controls and inducible nitric oxide synthase levels were 4 times greater than normal. Myocardial DNA laddering, an index of apoptosis, reached 20 times the normal level. Troglitazone therapy lowered myocardial TG and ceramide and completely prevented DNA laddering and loss of cardiac function. In this paper, we conclude that cardiac dysfunction in obesity is caused by lipoapoptosis and is prevented by reducing cardiac lipids. The recent increase in juvenile-onset obesity in the United States (1) predicts that the next generation of obese Americans will have been obese longer than ever before. This portends a higher prevalence of time-dependent complications of the disease, such as insulin resistance, non-insulin-dependent diabetes mellitus, hypertension, coronary artery disease, and other cardiac disorders. The etiology of these complications, which are often grouped together under the term ''metabolic syndrome X'' (2), is not known.We have proposed that the excessive deposition of triacylglycerol (TG) in nonadipose tissues (steatosis) enlarges the intracellular pool of fatty acyl-CoA, thereby providing substrate for nonoxidative metabolic pathways, such as ceramide synthesis, that lead to cell dysfunction and death through apoptosis (3). It seemed possible that this sequence of events, established in the pancreatic islets of genetically obese Zucker Diabetic Fatty (ZDF) rats ( fa͞fa), could also take place in other tissues such as the heart. Obesity-related heart disease, the most serious complication of human obesity, generally is attributed to coexisting disorders such as coronary artery disease and hypertension. Cardiac dysfunction, arrhythmias, cardiomyopathy, and congestive heart failure are seldom ascribed to the direct consequences of obesity, i.e., fatty acid (FA) overload of cardiac myocytes, although the literature does contain clinical reports of cardiomyopathy of obesity that can be reversed by weight loss (4).This study was designed to test the possibility that the same metabolic abnormalities that cause lipotoxicity and lipoapoptosis in the pancreatic ␤ cells of obese rats (3) might also compromise the function and viability of their myocardial cells. We used rats with obesity resulting from a loss-of-function mutation in the leptin receptor (5, 6), the ZDF ( fa͞fa) rat. We observed in their fat-laden hearts evidence of lipoapoptosis accompanied by a profound loss of cardiac function. These abnormalities were completely prevented by antisteatotic therapy. The striking benefit of such therapy on cardiac function in obese rats warrants an effort to determine whether a counterpart of this disorder ...

The endoplasmic reticulum (ER) and the Golgi comprise the first two steps in protein secretion. Vesicular carriers mediate a continuous flux of proteins and lipids between these compartments, reflecting the transport of newly synthesized proteins out of the ER and the retrieval of escaped ER residents and vesicle machinery. Anterograde and retrograde transport is mediated by distinct sets of cytosolic coat proteins, the COPII and COPI coats, respectively, which act on the membrane to capture cargo proteins into nascent vesicles. We review the mechanisms that govern coat recruitment to the membrane, cargo capture into a transport vesicle, and accurate delivery to the target organelle.

Metastasis is a frequent and lethal complication of cancer. Vascular endothelial growth factor‐C (VEGF‐C) is a recently described lymphangiogenic factor. Increased expression of VEGF‐C in primary tumours correlates with dissemination of tumour cells to regional lymph nodes. However, a direct role for VEGF‐C in tumour lymphangiogenesis and subsequent metastasis has yet to be demonstrated. Here we report the establishment of transgenic mice in which VEGF‐C expression, driven by the rat insulin promoter (Rip), is targeted to β‐cells of the endocrine pancreas. In contrast to wild‐type mice, which lack peri‐insular lymphatics, RipVEGF‐C transgenics develop an extensive network of lymphatics around the islets of Langerhans. These mice were crossed with Rip1Tag2 mice, which develop pancreatic β‐cell tumours that are neither lymphangiogenic nor metastatic. Double‐transgenic mice formed tumours surrounded by well developed lymphatics, which frequently contained tumour cell masses of β‐cell origin. These mice frequently developed pancreatic lymph node metastases. Our findings demonstrate that VEGF‐C‐induced lymphangiogenesis mediates tumour cell dissemination and the formation of lymph node metastases.

The trafficking of proteins within eukaryotic cells is achieved by the capture of cargo and targeting molecules into vesicles that bud from a donor membrane and deliver their contents to a receiving department. This process is bidirectional and may involve multiple organelles within a cell. Distinct coat proteins mediate each budding event, serving both to shape the transport vesicle and to select by direct or indirect interaction the desired set of cargo molecules. Secretion, which has been viewed as a default pathway, may require sorting and packaging signals on transported molecules to ensure their rapid delivery to the cell surface.

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COPII vesicle formation requires only three coat assembly subunits: Sar1p, Sec13/31p, and Sec23/24p. PI 4-phosphate or PI 4,5-bisphosphate is required for the binding of these proteins to liposomes. The GTP-bound form of Sar1p recruits Sec23/24p to the liposomes as well as to the ER membranes, and this Sar1p-Sec23/24p complex is required for the binding of Sec13/31p. Ultrastructural analysis shows that the binding of COPII coat proteins to liposomes results in coated patches, coated buds, and coated vesicles of 50-90 nm in diameter. Budding proceeds without rupture of the donor liposome or vesicle product. These observations suggest that the assembly of the COPII coat on the ER occurs by a sequential binding of coat proteins to specific lipids and that this assembly promotes the budding of COPII-coated vesicles.

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A combination of biochemistry in animal cell-free systems and genetics in yeast is revealing the molecular machinery of the secretory pathway of eukaryotes. Transporting vesicles have a simple coat structure and employ a general mechanism for fusion that is conserved in evolution.