Platelet-derived growth factor-A mRNA expression in fetal, normal adult, and atherosclerotic human aortas. Analysis by competitive polymerase chain reaction

Inflammatory angiogenesis in atherogenesis--a double-edged sword

The adventitia and the outer layers of media of an atherosclerosis-prone arterial wall are vascularized by vasa vasorum. Upon growth of an atherosclerotic lesion in the intima, neovascular sprouts originating from the adventitial vasa vasorum enter the lesion, the local proangiogenic micromilieu in the lesion being created by intramural hypoxia, by increased intramural oxidant stress, and by inflammatory cell infiltration (macrophages, T cells and mast cells). The angiogenic factors present in the lesions include various growth factors, chemokines, cytokines, proteinases, and several other factors possessing direct or indirect angiogenic activities, while the current list of antiangiogenic factors is smaller. An imbalance between endogenous inducers and inhibitors of angiogenesis, with a predominance of the former ones, is essential for the development of neovessels during the progression of the lesion. By providing oxygen and nutrients to the cells of atherosclerotic lesions, neovascularization initially tends to prevent cellular death and so contributes to plaque growth and stabilization. However, the inflammatory cells may induce rupture of the fragile neovessels, and so cause intraplaque hemorrhage and ensuing plaque destabilization. Pharmacological inhibition of angiogenesis in atherosclerotic plaques with ensuing inhibition of lesion progression has been achieved in animal models, but clinical studies aiming at regulation of angiogenesis in the atherosclerotic arterial wall can be designed only after we have reached a firm conclusion about the role of angiogenesis at various stages of lesion development--good or bad.

Decreased capacity of immune cells to cause tissue injury mediates kidney ischemic preconditioning

Ischemic preconditioning (IP) is a well-established phenomenon, and the underlying mechanisms of IP are thought to involve adaptive changes within the injured tissue. Because one of the main functions of immune cells is to harbor memory, we hypothesized that circulating immune cells could mediate IP by responding to an initial ischemia reperfusion injury (IRI) and then mediate decreased injury after a second IRI event. C57BL/6 mice underwent 30 min of bilateral renal clamping or sham operation. At 5 days after ischemia, purified leukocytes from spleen were adoptively transferred into T cell-deficient (nu/nu) mice. After 1 wk, these mice underwent 30 min of renal IRI. The nu/nu mice receiving leukocytes from ischemic wild-type mice had significantly reduced renal injury compared with nu/nu mice receiving leukocytes from sham-operated, wild-type mice. Infiltration of neutrophil and macrophage in postischemic kidney did not correlate with the protection. No difference in kidney C3d or IgG deposition was detected between groups. Given that inducible NO synthase (iNOS) has been implicated in IP, leukocytes from ischemic or sham-operated, iNOS-deficient mice were transferred into nu/nu mice. Effects similar to those of wild-type transfer of ischemic leukocytes were demonstrated; thus, iNOS was not mediating the IP effect of leukocytes. This is the first evidence that immune cells are primed after renal IRI and thereby lose the capacity to cause kidney injury during a second episode of IRI. This finding may also be relevant for elucidating the mechanisms underlying cross-talk between injured kidney and distant organs.

Immunohistochemical study of apparently intact coronary artery in a child after Kawasaki disease

BACKGROUND

Coronary arterial lesions (CAL) due to Kawasaki disease (KD) often show progressive intimal hyperplasia even many years after the disease. However, most patients have no CAL after the acute phase, and it is an important issue whether or not coronary arteries without CAL have significant intimal hyperplasia, and whether or not there is the potential for this to progress to stenosis and/or atherosclerosis.

METHODS

The authors examined formalin-fixed specimens of the coronary arteries immunohistochemically, using antibodies against vascular growth factors (GFs), the receptors of transforming growth factor-beta (TbetaRs) and inducible nitric oxid synthesis (iNOS) in a KD patient without CAL, and also in four control patients: two with CAL due to KD and two without a history of KD.

RESULTS

Vascular endothelial GFs, Platelet-derived growth factor-A (PDGF-A) and TbetaRs were expressed in the vascular smooth muscle cells of all patients. PDGF-A, transforming Gfbeta1 and iNOS were expressed in the intimal smooth muscle cells of the KD but not the normal coronary artery without a history of KD. The number of TbetaR-II-positive cells were fewer than TbetaR-I-positive cells in the intima of CAL due to KD, but the number was of both almost same in the intima of coronary artery without CAL after KD and in the normal coronary.

CONCLUSION

The intact coronary artery 13 months after KD still showed the influence of the inflammation of KD. Although the authors speculate that the intimal proliferation will not continue beyond the acute phase, those patients may have a risk factor for atherosclerosis.

Platelet-derived growth factor inhibits basic fibroblast growth factor angiogenic properties in vitro and in vivo through its alpha receptor

Basic fibroblast growth factor (bFGF) and platelet-derived growth factor-BB (PDGF-BB) modulate vascular wall cell function in vitro and angiogenesis in vivo. The aim of the current study was to determine how bovine aorta endothelial cells (BAECs) respond to the simultaneous exposure to PDGF-BB and bFGF. It was found that bFGF-dependent BAEC migration, proliferation, and differentiation into tubelike structures on reconstituted extracellular matrix (Matrigel) were inhibited by PDGF-BB. The role played by PDGF receptor alpha (PDGF-Ralpha) was investigated by selective stimulation with PDGF-AA, by blocking PDGF-BB-binding to PDGF-Ralpha with neomycin, or by transfecting cells with dominant-negative forms of the receptors to selectively impair either PDGF-Ralpha or PDGF-Rbeta function. In all cases, PDGF-Ralpha impairment abolished the inhibitory effect of PDGF-BB on bFGF-directed BAEC migration. In addition, PDGF-Ralpha phosphorylation was increased in the presence of bFGF and PDGF, as compared to PDGF alone, whereas mitogen-activated protein kinase phosphorylation was decreased in the presence of PDGF-BB and bFGF compared with bFGF alone. In vivo experiments showed that PDGF-BB and PDGF-AA inhibited bFGF-induced angiogenesis in vivo in the chick embryo chorioallantoic membrane assay and that PDGF-BB inhibited bFGF-induced angiogenesis in Matrigel plugs injected subcutaneously in CD1 mice. Taken together these results show that PDGF inhibits the angiogenic properties of bFGF in vitro and in vivo, likely through PDGF-Ralpha stimulation.

Expression of platelet-derived growth factor and its receptors in the developing and adult mouse kidney

BACKGROUND

Experimental analysis of gene function is increasingly being accomplished using mouse models. Glomerular malformations occur in mice in which the platelet-derived growth factor (PDGF) B-chain gene or the PDGF receptor beta-subunit gene have been deleted. To understand potential PDGF signaling pathways in the kidney, we determined the expression pattern of PDGF ligand and receptor genes in mouse kidney during development and in the mature adult kidney.

METHODS

We used in situ hybridization to map the expression of transcripts encoding the PDGF ligands (A-chain and B-chain) and PDGF receptors (PDGFRalpha and PDGFRbeta) in the developing and mature kidney of the mouse.

RESULTS

PDGF A-chain transcripts are expressed by epithelial cells (especially in what appear to be the loop of Henle) and possibly in vascular smooth muscle cells. Its receptor, PDGFRalpha, is expressed by interstitial cells. PDGF B-chain transcripts are most highly expressed by vascular endothelial cells of developing and adult kidney and minimally by visceral epithelia of immature glomeruli. PDGFRbeta transcripts are expressed by fetal blastemal cells, interstitial cells, mesangial cells, and vascular smooth muscle cells and by adult mesangial and interstitial cells. PDGFRalpha and PDGFRbeta expression is especially prominent in lipid-laden interstitial cells in the adult kidney.

CONCLUSIONS

These patterns of expression are similar, but not identical, to those observed in rat and human and suggest that paracrine interactions mediated by the PDGF/PDGF receptor system may coordinate the development of the tubular, vascular, and interstitial components during kidney development and disease.