Autocrine induction of DNA synthesis by mechanical injury of cultured smooth muscle cells. Potential role of FGF and PDGF

Injury-induced osteopontin gene expression in rat arterial smooth muscle cells is dependent on mitogen-activated protein kinases ERK1/ERK2

Previous work shows that osteopontin has a role during matrix reorganization after tissue injury including vascular conditions such as atherosclerosis and restenosis following angioplasty. In vitro, osteopontin promotes activities such as adhesion and migration but the mechanisms that regulate the expression of this matrix protein remain essentially unknown. This study examined if the ERK signaling pathway is involved in injury-induced osteopontin expression in cultured rat aortic smooth muscle cells. Northern and Western blotting demonstrated a marked activation of osteopontin expression in response to injury. Treating the cells with PD98059, a specific MEK1 inhibitor, prior to injury, blocked this upregulation. MEK1 phosphorylates ERK1/ERK2, which belong to the family of mitogen-activated protein kinases. We conclude that ERK1/ERK2 are involved in the regulation of osteopontin expression in cultured vascular smooth muscle cells.

Smooth muscle cell response to mechanical injury involves intracellular calcium release and ERK1/ERK2 phosphorylation

We have investigated possible signaling pathways coupled to injury-induced ERK1/2 activation and the subsequent initiation of vascular rat smooth muscle cell migration and proliferation. Aortic smooth muscle cells were cultured to confluency and subjected to in vitro injury under serum-free conditions. In fluo-4-loaded cells, injury induced a rapid wave of intracellular Ca(2+) release that propagated about 200 microm in radius from the injured zone, reached a peak in about 20 s, and subsided to the baseline within 2 min. The wave was abolished by prior treatment with the sarcoplasmic reticulum ATPase inhibitor thapsigargin, but not by omission of extracellular Ca(2+). ERK1/2 activation reached a peak at 10 min after injury and was inhibited by the MEK1 inhibitor PD98059, as well as by thapsigargin, fluphenazine, genistein, and the Src inhibitor PP2. These inhibitors also reduced [(3)H]thymidine incorporation and migration of cells into the injured area determined at 48 h after injury. These results show that mechanical injury to vascular smooth muscle cells induces a Ca(2+) wave which is dependent on intracellular Ca(2+) release. Furthermore, the injury activates ERK1/2 phosphorylation as well as cell migration and replication.

Vascular smooth muscle growth: autocrine growth mechanisms

Vascular smooth muscle cells (VSMC) exhibit several growth responses to agonists that regulate their function including proliferation (hyperplasia with an increase in cell number), hypertrophy (an increase in cell size without change in DNA content), endoreduplication (an increase in DNA content and usually size), and apoptosis. Both autocrine growth mechanisms (in which the individual cell synthesizes and/or secretes a substance that stimulates that same cell type to undergo a growth response) and paracrine growth mechanisms (in which the individual cells responding to the growth factor synthesize and/or secrete a substance that stimulates neighboring cells of another cell type) are important in VSMC growth. In this review I discuss the autocrine and paracrine growth factors important for VSMC growth in culture and in vessels. Four mechanisms by which individual agonists signal are described: direct effects of agonists on their receptors, transactivation of tyrosine kinase-coupled receptors, generation of reactive oxygen species, and induction/secretion of other growth and survival factors. Additional growth effects mediated by changes in cell matrix are discussed. The temporal and spatial coordination of these events are shown to modulate the environment in which other growth factors initiate cell cycle events. Finally, the heterogeneous nature of VSMC developmental origin provides another level of complexity in VSMC growth mechanisms.

Nuclear accumulation of exogenous DNA fragments in viable cells mediated by FGF-2 and DNA release upon cellular injury

We and others have previously shown that basic fibroblast growth factor (FGF-2 or bFGF) can be used as a targeting molecule to help carry plasmid DNA into cells when the growth factor molecule is physically coupled to the DNA molecule being delivered. Herein we report our observations on the FGF-mediated uptake of exogenous labeled DNA into cultured cells in a manner that is representative of that which may occur under physiological conditions at sites of wounded tissue. Cellular debris at such sites contains nucleic acid fragments released from dead cells, as well as growth factors such as FGF-2 that function early in the wound repair process. Using a cell culture model designed to mimic the local environment of a wound with respect to the presence of soluble FGF-2 and DNA fragments, we have shown that FGF-2 is able to direct the cellular uptake and nuclear localization of fragments of exogenous DNA via the FGF receptor into intact and healthy cells. Furthermore, we can monitor and quantitate this type of FGF-mediated DNA delivery by using indirect immunofluorescence of bromodeoxyuridine-labeled exogenous DNA. Our results suggest that this type of FGF-mediated DNA fragment uptake could allow for the transduction of viable nearest neighbor cells at sites of injury in vivo. Such a phenomenon may lead to mutational aberrations in the recipient cells and enhance the probability of wound carcinogenesis.

Immunolocalization of proliferating cells in the rabbit iliac artery after balloon angioplasty

PURPOSE

Experiments were performed to characterize the location of proliferating cells in the balloon-dilated rabbit iliac artery.

MATERIALS AND METHODS

Balloon angioplasty was performed on the external iliac arteries in each of four rabbits. The arteries were removed 3 days later, frozen, cryosectioned, and immunostained with Ki-67, an antibody that identifies proliferating cells. The sections were then examined to determine the patterns of cell proliferation within the arterial media and the ratio of proliferating to nonproliferating cells.

RESULTS

Of the 31 arterial cross-sections examined, cell proliferation was circumferential in five (16%), and focal in 26 (84%). Of the 86 foci of proliferation examined within the 31 cross-sections, proliferation was localized to the inner media in 30 (35%), to the outer media in four (5%), and was transmural in 52 (60%). The internal elastica lamina (IEL) appeared normal at 22 foci (26%), but appeared stretched or torn at 64 (74%). Proliferation was usually confined to the inner media at foci having no IEL injury (18 of 22; 82%), but was most often transmural where the IEL was stretched or torn (49 of 64; 77%). The ratio of proliferating to nonproliferating cells, which averaged 0.31 +/- .20, was greater (P < .01) in areas with IEL injury than in areas without IEL injury.

CONCLUSION

These results suggest that angioplasty-induced cell proliferation is typically focal rather than circumferential and is associated with stretching or tearing of the IEL.

Techniques for mechanical stimulation of cells in vitro: a review

A wide variety of laboratory apparatuses have been devised for mechanical stimulation of cell and tissue cultures. This article reviews the functional attributes of several dozen systems developed for that purpose, including their major advantages and disadvantages. These devices can be categorized in terms of their primary loading modality: compression (hydrostatic pressure or direct platen contact), longitudinal stretch, bending, axisymmetric substrate bulge, in-plane substrate distention, fluid shear stress, or combined substrate distention and fluid shear.

Photodynamic therapy inhibits the injury-induced fibrotic response of vascular smooth muscle cells

OBJECTIVES

excessive deposition of extracellular matrix (ECM) proteins plays a key role in the intervention-related vascular fibroproliferative response, resulting in intimal hyperplasia (IH). Cytokines, such as platelet-derived growth factor (PDGF), released after vascular injury and deposited in the ECM, are known to stimulate production of matrix proteins. Photodynamic therapy (PDT), the combination of light and a photosensitive dye to produce free radicals, is a novel approach to inhibit experimental IH by the local eradication of smooth-muscle cells (SMC) and alteration of ECM. This in vitro study examined whether PDT can inhibit the fibrotic response of vascular SMC.

MATERIALS AND METHODS

the effect of PDT on important pro-fibrotic factors was determined by performing PDT of isolated ECM, injured SMC and pure PDGF. SMC production of collagen was monitored by cellular [3H]-proline incorporation.

RESULTS

untreated SMC seeded on ECM demonstrated an increase of 50% in collagen production ( p <0.0001) as compared to SMC on an empty plate. This increase was also seen when SMC was incubated with the conditioned media of mechanically injured SMC, or pure PDGF. However, after PDT of ECM, injured SMC or PDGF, there was an inhibition of 40% ( p <0.05) in SMC-collagen production.

CONCLUSIONS

these findings indicate that PDT can interfere with factors that lead to the vascular fibrotic response. In this way, PDT, with its cytotoxic and extracellular effects, can promote healing of the vessel wall without the stimulus of fibrosis that can lead to restenosis.

Bunazosin hydrochloride inhibits exaggerated growth of vascular smooth muscle cells from spontaneously hypertensive rats by suppressing the response to growth factors

Selective alpha1-adrenoreceptor blockers were recently reported to have an in vivo antiproliferative effect on hypertensive cardiovascular organs. Cultured vascular smooth-muscle cells (VSMCs) from spontaneously hypertensive rats (SHRs) show exaggerated growth compared with cells from Wistar-Kyoto (WKY) rats. We investigated the effects of an alpha1-adrenoreceptor blocker, bunazosin hydrochloride (HCl), on the growth of VSMCs from SHRs. In the absence of serum, bunazosin HCl significantly inhibited basal DNA synthesis by VSMCs from SHRs, but not by cells from WKY rats. In the presence of serum, bunazosin HCl significantly inhibited DNA synthesis by VSMCs from both rat strains. Angiotensin (Ang) II, platelet-derived growth factor (PDGF)-AA, and epidermal growth factor (EGF) dose-dependently increased DNA synthesis by VSMCs from SHRs, but not by VSMCs from WKY rats. Bunazosin HCl significantly suppressed the response of DNA synthesis to PDGF-AA and EGF, but not to Ang II, in VSMCs from SHRs. Expression of basic fibroblast growth factor (bFGF), transforming growth factor-beta1 (TGFbeta1), and PDGF messenger RNA (mRNA) was markedly greater in VSMCs from SHRs than in cells from WKY rats. Bunazosin HCl significantly inhibited the expression of bFGF and TGFbeta1 mRNA in VSMCs from SHRs, but not in cells from WKY rats. These findings suggest that the inhibition of growth factor hyperresponsiveness and inhibition of the expression of growth factors in VSMCs from SHRs are associated with the antiproliferative effect of bunazosin.

Small mechanical strains selectively suppress matrix metalloproteinase-1 expression by human vascular smooth muscle cells

Mechanical forces and biochemical stimuli may interact to regulate cellular responses. In this study, we tested the hypothesis that very small mechanical strains interact with growth factors in the regulation of matrix metalloproteinase (MMP)-1. Human vascular smooth muscle cells (VSMCs) were cultured on a precoated silicone membrane in a device that imposes a highly uniform biaxial strain. VSMCs cultured on fibronectin were treated with cyclic 1-Hz strains of 0, 1, or 4%, and MMPs were assayed by Western analysis or gelatin zymography. Small strains did not induce MMP-1 in VSMCs, but strain was a potent inhibitor of platelet-derived growth factor (PDGF)- or tumor necrosis factor-alpha-induced synthesis of MMP-1. In contrast, MMP-2 and TIMP-2 levels were not changed by PDGF and/or mechanical strain. VSMCs strained on the 120-kDa chymotryptic fragment of fibronectin or RGD peptides suppressed PDGF-induced expression of MMP-1, indicating that this effect is not mediated by the heparin-binding domain or connecting segment-1 of fibronectin. Northern analysis of ets-1, a transcriptional activator of MMP-1 expression, showed that strain down-regulated ets-1 expression, whereas c-fos expression was augmented. Thus, small deformations can selectively suppress MMP-1 synthesis by VSMCs, demonstrating the exquisite sensitivity of the cell to mechanical stimuli.