Faculty Bibliography

BACKGROUND:The mechanism of action of transmyocardial laser revascularization (TMR) is poorly understood. TMR has been shown to stimulate angiogenesis in porcine and canine myocardium. METHODS AND RESULTS/RESULTS:We examined the possibility that angiogenesis also occurs in ovine myocardium and that it is a nonspecific tissue injury response. Five Dorset sheep underwent creation of transmyocardial channels of equal diameter in both the apical and basal regions of the left ventricle through the use of both CO2 laser in 1 region and a power drill in the alternate region of the same heart. All channels were closed at 4 weeks. Histology showed channel remnants composed of granulation tissue, fibrosis, and new vessels (NV). These changes were not distinguishable on the basis of the method of channel creation. The average diameter of the channels was similar (laser, 630 +/- 180 microns; drill, 750 +/- 280 microns) (P = NS). NV with smooth muscle media were seen within the channel remnant and immediately surrounding this region using Verhoeff-Van Gieson (elastic) stain. The densities of the NV within the channel remnants were similar (laser, 1.87 +/- 1.05 NV/high-power field [hpf]; drill, 1.92 +/- 1.09 NV/hpf; P = NS), and both were significantly greater than the density of vessels in remote regions, > 5 mm from the channel center (remote laser area, 0.09 +/- 0.28 NV/hpf; remote drill area, 0.04 +/- 0.21 NV/hpf; P = NS for remote areas, P < 0.001 for laser versus remote laser, P < 0.001 for drill versus remote drill area). CONCLUSIONS:These findings demonstrate that the CO2 laser stimulates angiogenesis in normal ovine myocardium and suggest that this response represents a nonspecific reaction to tissue injury.

Golgi-associated cytoplasmic proteins, such as the coatomer protein complex, are required for vesicle budding and trafficking. We have previously described a cytoplasmic phosphoprotein, p200, which binds dynamically and specifically to Golgi membranes. The p200 protein is dissociated from Golgi membranes in the presence of brefeldin A and it is induced to bind to Golgi membranes by activation of guanine nucleotide binding proteins (G proteins) with guanosine 5'-[gamma-thio]triphosphate or aluminum fluoride. To establish the role of p200 in vesicle budding, we localized membrane-bound p200 in intact cells and on isolated Golgi membranes. We show that p200 is preferentially associated with vesicles in the trans-Golgi network (TGN). Activation of G proteins induced budding and accumulation of small, coated vesicles from Golgi membranes and p200 was localized on the cytoplasmic surface of some of these vesicles. Using immunogold labeling we further demonstrate that p200 and beta-COP are localized on different populations of Golgi-derived vesicles. These data establish that p200 is involved in the budding and coating of a class of Goli vesicles that are likely to be derived from the TGN. The data also show that there are distinct populations of non-clathrin-coated vesicles budded from Golgi membranes, and vesicles labeled for either beta-COP or p200 may represent transport vesicles for separate steps of protein transport.

A new mAb, designated anti-KCA-3, was developed against rat Kupffer cells. The reactivity of anti-KCA-3 was restricted to macrophages with preferential binding to Kupffer cells; only a few macrophages in the spleen, lymph nodes, lungs, and intestine stained with the antibody. A very small number of peritoneal resident and exudate macrophages reacted with the antibody and no reactivity was seen within the thymus, skin, heart, kidneys, brain, peripheral blood, and bone marrow. KCA-3 was expressed predominantly by the Kupffer cells in the periportal region rather than in the centrilobular region of the hepatic lobules. The cells in the portal tract did not stain with the antibody. The staining of the cytosmears and FACS analysis of the Kupffer cell fraction isolated from hepatic sinusoidal cells by centrifugal elutriation revealed that as many as 62% and 49% of the cells were stained with anti-KCA-3, respectively. Immunoelectron microscopic study of the liver indicated that expression of KCA-3 on Kupffer cells was limited to the plasma membrane facing the sinusoid rather than the space of Disse. Immunoprecipitation and SDS-PAGE analysis demonstrated KCA-3 to have a m.w. of approximately 50 kDa under both reducing and nonreducing conditions. After treatment of KCA-3 with N-glycanase, there was no significant change in the m.w., indicating KCA-3 was not highly glycosylated. C3b- and iC3b-mediated rosette formation between Kupffer cells and sensitized SRBC was inhibited by the antibody, implying that KCA-3 functioned as a complement C3 receptor or complement receptor-associated molecule. Furthermore, KCA-3 was eluted from C3b-Sepharose but not HSA-Sepharose after incubation with Kupffer cell lysate, indicating that KCA-3 directly binds C3b. The cell distribution, ligand-binding specificity, and biochemical properties of the protein were found to be different from the complement C3 receptors previously described. Because OX42 (antibody reactive with the rat CR3 receptor) inhibited complement C3-mediated rosette formation with peritoneal resident macrophages but not with Kupffer cells, the findings suggest that C3-mediated binding to Kupffer cells and to peritoneal macrophages is mediated by two different receptors. We conclude that anti-KCA-3 recognizes a novel type of complement C3 receptor preferentially expressed on Kupffer cells.

A mAb AD7, raised against canine liver Golgi membranes, recognizes a novel, 200-kD protein (p200) which is found in a wide variety of cultured cell lines. Immunofluorescence staining of cultured cells with the AD7 antibody produced intense staining of p200 in the juxtanuclear Golgi complex and more diffuse staining of p200 in the cytoplasm. The p200 protein in the Golgi complex was colocalized with other Golgi proteins, including mannosidase II and beta-COP, a coatomer protein. Localization of p200 by immunoperoxidase staining at the electron microscopic level revealed concentrations of p200 at the dilated rims of Golgi cisternae. Biochemical studies showed that p200 is a peripheral membrane protein which partitions to the aqueous phase of Triton X-114 solutions and is phosphorylated. The p200 protein is located on the cytoplasmic face of membranes, since it was accessible to trypsin digestion in microsomal preparations, and is recovered in approximately equal amounts in membrane pellets and in the cytosol of homogenized cells. Immunofluorescence staining of normal rat kidney cells exposed to the toxin brefeldin A (BFA), showed that there was very rapid redistribution of p200, which was dissociated from Golgi membranes in the presence of this drug. The effect of BFA was reversible, since upon removal of the toxin, AD7 rapidly reassociated with the Golgi complex. In the BFA-resistant cell line PtK1, BFA failed to cause redistribution of p200 from Golgi membranes. Taken together, these results indicate that the p200 Golgi membrane-associated protein has many properties in common with the coatomer protein, beta-COP.

A heterotrimeric G alpha i subunit, alpha i-3, is localized on Golgi membranes in LLC-PK1 and NRK epithelial cells where it colocalizes with mannosidase II by immunofluorescence. The alpha i-3 was found to be localized on the cytoplasmic face of Golgi cisternae and it was distributed across the whole Golgi stack. The alpha i-3 subunit is found on isolated rat liver Golgi membranes by Western blotting and G alpha i-3 on the Golgi apparatus is ADP ribosylated by pertussis toxin. LLC-PK1 cells were stably transfected with G alpha i-3 on an MT-1, inducible promoter in order to overexpress alpha i-3 on Golgi membranes. The intracellular processing and constitutive secretion of the basement membrane heparan sulfate proteoglycan (HSPG) was measured in LLC-PK1 cells. Overexpression of alpha i-3 on Golgi membranes in transfected cells retarded the secretion of HSPG and accumulated precursors in the medial-trans-Golgi. This effect was reversed by treatment of cells with pertussis toxin which results in ADP-ribosylation and functional uncoupling of G alpha i-3 on Golgi membranes. These results provide evidence for a novel role for the pertussis toxin sensitive G alpha i-3 protein in Golgi trafficking of a constitutively secreted protein in epithelial cells.