Biomedical subjects

M A Perrella

Publications and source records attributed to M A Perrella.

At least 55 records · Page 3Linked to original sources

PubMed1997

Inhibition of growth and p21ras methylation in vascular endothelial cells by homocysteine but not cysteine.

Although hyperhomocysteinemia has been recognized recently as a prevalent risk factor for myocardial infarction and stroke, the mechanisms by which it accelerates arteriosclerosis have not been elucidated, mostly because the biological effects of homocysteine can only be demonstrated at very high concentrations and can be mimicked by cysteine, which indicates a lack of specificity. We found that 10-50 microM of homocysteine (a range that overlaps levels observed clinically) but not cysteine inhibited DNA synthesis in vascular endothelial cells (VEC) and arrested their growth at the G1 phase of the cell cycle. Homocysteine in this same range had no effect on the growth of vascular smooth muscle cells (VSMC) or fibroblasts. Homocysteine decreased carboxyl methylation of p21(ras) (a G1 regulator whose activity is regulated by prenylation and methylation in addition to GTP-GDP exchange) by 50% in VEC but not VSMC, a difference that may be explained by the ability of homocysteine to dramatically increase levels of S-adenosylhomocysteine, a potent inhibitor of methyltransferase, in VEC but not VSMC. Moreover, homocysteine-induced hypomethylation in VEC was associated with a 66% reduction in membrane-associated p21(ras) and a 67% reduction in extracellular signal-regulated kinase 1/2, which is a member of the mitogen-activated protein (MAP) kinase family. Because the MAP kinases have been implicated in cell growth, the p21(ras)-MAP kinase pathway may represent one of the mechanisms that mediates homocysteine's effect on VEC growth. VEC damage is a hallmark of arteriosclerosis. Homocysteine-induced inhibition of VEC growth may play an important role in this disease process.

Calcium-Calmodulin-Dependent Protein Kinases↗

PubMed1997

Down-regulation of the cyclin A promoter by transforming growth factor-beta1 is associated with a reduction in phosphorylated activating transcription factor-1 and cyclic AMP-responsive element-binding protein.

Transforming growth factor (TGF)-beta1 prevents cell cycle progression by inhibiting several regulators, including cyclin A. To study the mechanisms by which TGF-beta1 down-regulates cyclin A gene expression, we transfected reporter plasmids driven by the cyclin A promoter into mink lung epithelial cells in the absence and presence of TGF-beta1. The TGF-beta1-induced down-regulation of cyclin A promoter activity appeared to be mediated via the activating transcription factor (ATF) site, because mutation of this site abolished down-regulation. Surprisingly, although TGF-beta1 treatment for 24 h markedly decreased cyclin A promoter activity, it did not decrease the abundance of the ATF-binding proteins ATF-1 and cyclic AMP-responsive binding protein (CREB). However, we detected 90 and 78% reductions (by Western analysis) in phosphorylated CREB and ATF-1, respectively, in mink lung epithelial cells treated with TGF-beta1. TGF-beta1-induced down-regulation of cyclin A promoter activity was reversed by okadaic acid (a phosphatase inhibitor) and by cotransfection with plasmids expressing the cAMP-dependent protein kinase catalytic subunit or the simian virus small tumor antigen (Sm-t, an inhibitor of PP2A). These data indicate that TGF-beta1 may down-regulate cyclin A promoter activity by decreasing phosphorylation of CREB and ATF-1.

Activating Transcription Factor 1↗

PubMed1997

Induction of heme oxygenase-1 expression in vascular smooth muscle cells. A link to endotoxic shock.

Endotoxic shock is a life-threatening consequence of severe Gram-negative infection characterized by vascular smooth muscle cell relaxation and severe hypotension. The production of nitric oxide (NO), through the inducible NO synthase pathway, has been implicated as a major contributor in this process. We now demonstrate that heme oxygenase (HO), an enzyme that generates carbon monoxide (CO) in the course of heme metabolism, may also be involved in the hemodynamic compromise of endotoxic shock. Inducible HO (HO-1) mRNA levels are dramatically increased in aortic tissue from rats receiving endotoxin, and this increase in vascular HO-1 message is associated with an 8.9-fold increase in HO enzyme activity in vivo. Immunocytochemical staining localizes an increase in HO-1 protein within smooth muscle cells of both large (aorta) and small (arterioles) blood vessels. Furthermore, zinc protoporphyrin IX, an inhibitor of HO activity, abrogates endotoxin-induced hypotension in rats. Studies performed in rat vascular smooth muscle cells in vitro show that the induction of HO-1 mRNA is regulated at the level of gene transcription, and this induction is independent of NO production. Taken together, these studies suggest that the up-regulation of HO-1, and the subsequent production of CO, contributes to the reduction in vascular tone during endotoxic shock.

Animals↗

PubMed1997

Collagen VIII is expressed by vascular smooth muscle cells in response to vascular injury.

To identify genes involved in vascular remodeling, we applied differential mRNA display analysis to the rat carotid artery balloon injury model. One polymerase chain reaction product showing increased expression at days 2 to 14 after vascular injury was nearly identical to the mouse alpha 1 chain of type VIII collagen, a heterotrimeric short-chain collagen of uncertain function expressed by a limited number of cell types. By Northern analysis, expression of both chains of the type VIII collagen heterotrimer increased: collagen alpha 1 (VIII) mRNA expression was almost 4-fold higher than control by 7 days after vascular injury, and collagen alpha 2 (VIII) mRNA expression reached a maximum of almost 6-fold above baseline by 3 days after injury. By immunohistochemical analysis, type VIII collagen expression increased in the media and neointima in a localized pattern consistent with the distribution of activated dedifferentiated vascular smooth muscle cells (VSMCs). Cultured VSMCs expressed higher levels of type VIII collagen in response to serum and growth factors, notably platelet-derived growth factor (PDGF)-BB. VSMCs adhered significantly less to type VIII collagen than to type I collagen substrata and showed greater PDGF-BB-stimulated migration (by 2.2-fold) on type VIII collagen than on type I collagen. We hypothesize that increased expression of type VIII collagen by VSMCs after arterial injury may contribute to vascular remodeling through the promotion of VSMC migration.

Angioplasty, Balloon↗

PubMed1996

APEG-1, a novel gene preferentially expressed in aortic smooth muscle cells, is down-regulated by vascular injury.

Despite the importance of phenotypic alterations in arterial smooth muscle cells (ASMC) during the pathogenesis of arteriosclerosis, little is known about genes that define differentiated ASMC. Using differential mRNA display, we isolated a novel gene preferentially expressed in the rat aorta and termed this gene APEG-1. The cDNA of rat APEG-1 contained an open reading frame encoding 113 amino acids, which would predict a basic protein of 12.7 kDa. The amino acid sequence of rat APEG-1 was highly conserved among human and mouse homologues (97 and 98%, respectively). Using an APEG-1 fusion protein containing an N-terminal c-Myc tag, we identified APEG-1 as a nuclear protein. By in situ hybridization, APEG-1 mRNA was expressed in rat ASMC. Although APEG-1 was expressed highly in differentiated ASMC in vivo, its expression was quickly down-regulated and disappeared in dedifferentiated ASMC in culture. In vivo, APEG-1 mRNA levels decreased by more than 80% in response to vascular injury as ASMC changed from a quiescent to a proliferative phenotype. Taken together, these data indicate that APEG-1 is a novel marker for differentiated ASMC and may have a role in regulating growth and differentiation of this cell type.

Amino Acid Sequence↗

PubMed1996

Downregulation of vascular endothelial growth factor receptors by tumor necrosis factor-alpha in cultured human vascular endothelial cells.

Vascular endothelial growth factor (VEGF) potently stimulates angiogenesis, whereas TNF-alpha has both pro- and anti-angiogenic activity. By measuring thymidine uptake, we found that TNF-alpha blocked a 2.3-fold increase in DNA synthesis induced by VEGF in human endothelial cells. To explore the possibility that the two interact to regulate endothelial cell proliferation, we examined the effect of TNF-alpha on VEGF receptor expression. In venous and arterial endothelial cells, TNF-alpha potently reduced mRNA transcripts of the two VEGF receptors (KDR/flk-1 and flt-1) in a dose- and time-dependent fashion. TNF-alpha at 1 ng/ml induced maximal inhibition of mRNA expression, which fell by approximately 70% after 24 h. TNF-alpha treatment did not significantly affect the KDR/flk-1 half-life but did decrease its rate of transcription to 40% of control. The decrease in KDR/flk-1 mRNA depended partially on new protein synthesis and was abolished by phorbol ester pretreatment. TNF-alpha decreased the amount of 35S-labeled KDR/flk-1 immunoprecipitated by an antibody specific for KDR/flk-1 to 18% of control. We conclude that TNF-alpha downregulates expression of both VEGF receptors in human endothelial cells and that this effect is transcriptional (at least for KDR/flk-1). These data support the hypothesis that TNF-alpha exerts its antiangiogenic effect in part by modulating the VEGF-specific angiogenic pathway.

Anisomycin↗

PubMed1996

Suppression of interleukin-1beta-induced nitric-oxide synthase promoter/enhancer activity by transforming growth factor-beta1 in vascular smooth muscle cells. Evidence for mechanisms other than NF-kappaB.

Nitric-oxide synthases (NOS) utilize L-arginine to produce NO, a potent vasodilator that contributes to the regulation of vascular tone. We demonstrated previously that transforming growth factor (TGF)-beta1 down-regulates inducible NOS after its induction by interleukin (IL)-1beta by decreasing the rate of inducible NOS gene transcription. In the present study we transfected reporter plasmids containing various lengths of the inducible NOS 5'-flanking region into primary cultured rat aortic smooth muscle cells and stimulated the cells with IL-1beta or vehicle. IL-1beta increased the activity of the plasmid containing -1485 to +31 of the inducible NOS gene by more than 10-fold, indicating the presence of IL-1beta-responsive elements. Further deletion analysis revealed that a construct containing -234 to +31 of the inducible NOS gene contained the majority of promoter/enhancer activity after IL-1beta stimulation. Mutation of the NF-kappaB site within this region partially reduced IL-1beta-inducible activity; however, a large portion of activity remained independent of the NF-kappaB site. TGF-beta1 suppressed promoter/enhancer activity after IL-1beta stimulation, and this suppression was complete in the construct with a mutated NF-kappaB site. In addition, TGF-beta1 did not decrease the binding of nuclear proteins to the NF-kappaB site. These data suggest that the ability of TGF-beta1 to suppress inducible NOS promoter/enhancer activity occurs through a site(s) other than the NF-kappaB motif in vascular smooth muscle cells.

Animals↗

PubMed1996

Molecular cloning and characterization of SmLIM, a developmentally regulated LIM protein preferentially expressed in aortic smooth muscle cells.

Differentiated, quiescent vascular smooth muscle cells assume a dedifferentiated, proliferative phenotype in response to injury, one of the hallmarks of arteriosclerosis. Members of the LIM family of zinc-finger proteins are important in the differentiation of various cells including striated muscle. We describe here the molecular cloning and characterization of a developmentally regulated smooth muscle LIM protein, SmLIM, that is expressed preferentially in the rat aorta. This 194-amino acid protein has two LIM domains, and comparisons of rat SmLIM with its mouse and human homologues reveal high levels of amino acid sequence conservation (100 and 99%, respectively). SmLIM is a nuclear protein and maps to human chromosome 3. SmLIM mRNA expression was high in aorta but not in striated muscle and low in other smooth muscle tissues such as intestine and uterus. In contrast with arterial tissue, SmLIM mRNA was barely detectable in venous tissue. The presence of SmLIM expression within aortic smooth muscle cells was confirmed by in situ hybridization. In vitro, SmLIM mRNA levels decreased by 80% in response to platelet-derived growth factor-BB in rat aortic smooth muscle cells. In vivo, SmLIM mRNA decreased by 60% in response to vessel wall injury during periods of maximal smooth muscle cell proliferation. The down-regulation of SmLIM by phenotypic change in vascular smooth muscle cells suggests that it may be involved in their growth and differentiation.

Amino Acid Sequence↗

PubMed1996

Arrest of endotoxin-induced hypotension by transforming growth factor beta1.

Septic shock is a cytokine-mediated process typically caused by a severe underlying infection. Toxins generated by the infecting organism trigger a cascade of events leading to hypotension, to multiple organ system failure, and frequently to death. Beyond supportive care, no effective therapy is available for the treatment of septic shock. Nitric oxide (NO) is a potent vasodilator generated late in the sepsis pathway leading to hypotension; therefore, NO represents a potential target for therapy. We have previously demonstrated that transforming growth factor (TGF) beta1 inhibits inducible NO synthase (iNOS) mRNA and NO production in vascular smooth muscle cells after its induction by cytokines critical in the sepsis cascade. Thus, we hypothesized that TGF-beta1 may inhibit iNOS gene expression in vivo and be beneficial in the treatment of septic shock. In a conscious rat model of septic shock produced by Salmonella typhosa lipopolysaccharide (LPS), TGF-beta1 markedly reduced iNOS mRNA and protein levels in several organs. In contrast, TGF-beta1 did not decrease endothelium-derived constitutive NOS mRNA in organs of rats receiving LPS. We also performed studies in anesthetized rats to evaluate the effect of TGF-beta1 on the hemodynamic compromise of septic shock; after an initial 25% decrease in mean arterial pressure, TGF-beta1 arrested LPS-induced hypotension and decreased mortality. A decrease in iNOS mRNA and protein levels in vascular smooth muscle cells was demonstrated by in situ hybridization and NADPH diaphorase staining in rats treated with TGF-beta1. Thus these studies suggest that TGF-beta1 inhibits iNOS in vivo and that TGF-beta1 may be of future benefit in the therapy of septic shock.

Animals↗

PubMed1996

Induction of apoptosis by pyrrolidinedithiocarbamate and N-acetylcysteine in vascular smooth muscle cells.

Pyrrolidinedithiocarbamate (PDTC) and N-acetylcysteine (NAC) have been used as antioxidants to prevent apoptosis in lymphocytes, neurons, and vascular endothelial cells. We report here that PDTC and NAC induce apoptosis in rat and human smooth muscle cells. In rat aortic smooth muscle cells, PDTC induced cell shrinkage, chromatin condensation, and DNA strand breaks consistent with apoptosis. In addition, overexpression of Bcl-2 suppressed vascular smooth muscle cell death caused by PDTC and NAC. The viability of rat aortic smooth muscle cells decreased within 3 h of treatment with PDTC and was reduced to 30% at 12 h. The effect of PDTC and NAC on smooth muscle cells was not species specific because PDTC and NAC both caused dose-dependent reductions in viability in rat and human aortic smooth muscle cells. In contrast, neither PDTC nor NAC reduced viability in human aortic endothelial cells. The use of antioxidants to induce apoptosis in vascular smooth muscle cells may help prevent their proliferation in arteriosclerotic lesions.

Acetylcysteine↗

PubMed1996

Induction of cyclin A gene expression by homocysteine in vascular smooth muscle cells.

Homocysteine is an important and independent risk factor for arteriosclerosis. We showed previously that homocysteine stimulates vascular smooth muscle cell proliferation, a hallmark of arteriosclerosis. We show here that homocysteine and serum increased DNA synthesis synergistically in both human and rat aortic smooth muscle cells (RASMCs). Treatment of quiescent RASMCs with 1 mM homocysteine or 2% calf serum for 36 h increased cyclin A mRNA levels by 8- and 14-fold, respectively, whereas homocysteine plus serum increased cyclin A mRNA levels by 40-fold, indicating a synergistic induction of cyclin A mRNA. Homocysteine did not increase the half-life of cyclin A mRNA (2.9 h), but it did increase the transcriptional rate of the cyclin A gene in nuclear run-on experiments. The positive effect of homocysteine on cyclin A gene transcription was confirmed by our finding that homocysteine increased cyclin A promoter activity and ATF-binding protein levels in RASMCs. Finally, 1 mM homocysteine increased cyclin A protein levels and cyclin A-associated kinase activity by threefold. This homocysteine-induced expression lesions by promoting proliferation of vascular smooth muscle cells.

Activating Transcription Factors↗

PubMed1995

Cloning and functional analysis of the promoter for KDR/flk-1, a receptor for vascular endothelial growth factor.

KDR/flk-1 is one of two receptors for vascular endothelial growth factor, a potent angiogenic peptide. KDR/flk-1 is an early marker for endothelial cell progenitors, and its expression is restricted to endothelial cells in vivo. To investigate the molecular mechanisms regulating expression of KDR/flk-1, we cloned and characterized the promoter of the human KDR/flk-1 gene. The transcription start site was localized by primer extension and ribonuclease protection to a nucleotide 303 base pairs (bp) 5' of the initiation methionine codon. The 5'-flanking sequence is rich in G and C residues and contains five Sp1 elements but no TATA consensus sequence. By reporter gene transfection experiments, we found that approximately 4 kilobases of KDR/flk-1 5'-flanking sequence directed high level luciferase activity in bovine aortic endothelial cells; further deletion analysis revealed positive regulatory elements between bp -225 to -164, -95 to -77, -77 to -60, and +105 to +127. Mutation of an atypical GATA sequence between bp +105 and +127 did not affect promoter activity, suggesting that GATA elements are not essential for the high level promoter activity of this gene. Consistent with endothelial cell-restricted expression of KDR/flk-1 mRNA, we found that the 4-kilobase flanking sequence directed high level promoter activity in endothelial cells but not in other cell types. To our knowledge this is the first report characterizing the KDR/flk-1 promoter. Understanding the KDR/flk-1 promoter will allow us to investigate endothelial cell-specific gene regulation and to uncover methods for targeting gene delivery specifically to endothelial cells.

Animals↗

PubMed1995

Smooth muscle cell-derived carbon monoxide is a regulator of vascular cGMP.

Carbon monoxide (CO) is a product of the enzyme heme oxygenase (HO; EC 1.14.99.3). In vascular smooth muscle cells, exogenously administered CO increases cyclic guanosine 3',5'-monophosphate (cGMP), which is an important regulator of vessel tone. We report here that smooth muscle cells produce CO via HO and that it regulates cGMP levels in these cells. Hypoxia, which has profound effects on vessel tone, significantly increased the transcriptional rate of the HO-1 gene resulting in corresponding increases of its mRNA and HO enzymatic activity. In addition, under the same conditions, rat aortic and pulmonary artery smooth muscle cells accumulated high levels of cGMP following a similar time course to that of HO-1 production. The increased accumulation of cGMP in smooth muscle cells required the enzymatic activity of HO, since it was abolished by a specific HO inhibitor, tin protoporphyrin. In contrast, N omega-nitro-L-arginine, a potent inhibitor of nitric oxide (NO) synthesis, had no effect on cGMP produced by smooth muscle cells, indicating that NO is not responsible for the activation of guanylyl cyclase in this setting. Furthermore, conditioned medium from hypoxic smooth muscle cells stimulated cGMP production in recipient cells and this stimulation was completely inhibited by tin protoporphyrin or hemoglobin, an inhibitor of CO production and a scavenger of CO, respectively. This report shows that HO-1 is expressed by vascular smooth muscle cells and that its product, CO, may regulate vascular tone under physiologic and pathophysiologic (such as hypoxic) conditions.

Animals↗

PubMed1995

Induction of vascular endothelial growth factor gene expression by interleukin-1 beta in rat aortic smooth muscle cells.

Vascular endothelial growth factor (VEGF) is a potent and specific mitogen for vascular endothelial cells and promotes neovascularization in vivo. To determine whether interleukin-1 beta (IL-1 beta), which is present in atherosclerotic lesions, induces VEGF gene expression in vascular smooth muscle cells, we performed RNA blot analysis on rat aortic smooth muscle cells (RASMC) with a rat VEGF cDNA probe. IL-1 beta increased VEGF mRNA levels in RASMC in a time- and dose-dependent manner. As little as 0.1 ng/ml IL-1 beta increased VEGF mRNA levels by 2-fold and 10 ng/ml IL-1 beta increased VEGF mRNA by 4-fold. We also measured the half-life of VEGF mRNA and performed nuclear run-on experiments before and after addition of IL-1 beta to see if IL-1 beta increased VEGF mRNA levels by stabilizing the mRNA or by increasing its rate of transcription. The normal, 2-h half-life of VEGF mRNA in RASMC was lengthened to 3.2 h (60%) by IL-1 beta, and IL-1 beta increased the rate of VEGF gene transcription by 2.1-fold. In immunoblot experiments with an antibody specific for VEGF, we found that IL-1 beta increased VEGF protein levels in RASMC by 3.3-fold. Together these data indicate that IL-1 beta induces VEGF gene expression in smooth muscle cells. This IL-1 beta-induced expression of VEGF may accelerate the progression of atherosclerotic lesions by promoting the development of new blood vessels.

Animals↗

PubMed1995

The ATF site mediates downregulation of the cyclin A gene during contact inhibition in vascular endothelial cells.

Contact inhibition mediates monolayer formation and withdrawal from the cell cycle in vascular endothelial cells. In studying the cyclins--key regulators of the cell cycle--in bovine aortic endothelial cells (BAEC), we found that levels of cyclin A mRNA decreased in confluent BAEC despite the presence of 10% fetal calf serum. We then transfected into BAEC a series of plasmids containing various lengths of the human cyclin A 5' flanking sequence and the luciferase gene. Plasmids containing 3,200, 516, 406, 266, or 133 bp of the human cyclin A promoter directed high luciferase activity in growing but not confluent BAEC. In contrast, a plasmid containing 23 bp of the cyclin A promoter was associated with a 65-fold reduction in activity in growing BAEC, and the promoter activities of this plasmid were identical in both growing and confluent BAEC. Mutation of the activating transcription factor (ATF) consensus sequence at bp -80 to -73 of the cyclin A promoter decreased its activity, indicating the critical role of the ATF site. We identified by gel mobility shift analysis protein complexes that bound to the ATF site in nuclear extracts from growing but not confluent BAEC and identified (with antibodies) ATF-1 as a binding protein in nuclear extracts from growing cells. Also, ATF-1 mRNA levels decreased in confluent BAEC. Taken together, these data suggest that the ATF site and its cognate binding proteins play an important role in the downregulation of cyclin A gene expression during contact inhibition.

Activating Transcription Factor 1↗

PubMed1995

Disappearance of cyclin A correlates with permanent withdrawal of cardiomyocytes from the cell cycle in human and rat hearts.

The regulated expression of cyclins controls the cell cycle. Because cardiomyocytes in adult mammals withdraw permanently from the cell cycle and thus cannot regenerate after injury, we examined cyclin expression during development by comparing cyclin A-E mRNA levels in fetal and adult human hearts. Cyclin B mRNA was detectable in adult hearts, although at a level markedly lower than that in fetal hearts. Levels of cyclin C, D1, D2, D3, and E mRNA were essentially identical in the two groups. In contrast, cyclin A mRNA was undetectable in adult hearts whereas cyclin A mRNA and protein were readily detectable in fetal hearts and cardiomyocytes, respectively. We then measured cyclin A mRNA and protein levels in rat hearts at four stages of development (fetal and 2, 14, and 28 d). Cyclin A mRNA and protein levels decreased quickly after birth (to 37% at day 2) and became undetectable within 14 d, an observation consistent with reports that cardiomyocytes stop replicating in rats by the second to third postnatal week. This disappearance of cyclin A gene expression in human and rat hearts at the time cardiomyocytes become terminally differentiated suggests that cyclin A downregulation is important in the permanent withdrawal of cardiomyocytes from the cell cycle.

Adult↗

PubMed1994

Regulation of heparin-binding epidermal growth factor-like growth factor mRNA levels by hypertrophic stimuli in neonatal and adult rat cardiac myocytes.

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a recently characterized member of the EGF family of peptide signaling factors that acts as an early response gene to growth stimuli in vascular smooth muscle cells, as well as being a potent mitogen for these cells. As many of these growth stimuli also induce a hypertrophic response in heart muscle, we examined the regulation of HB-EGF mRNA abundance and function in primary cultures of neonatal rat ventricular myocytes and adult rat ventricular myocytes (ARVM). HB-EGF mRNA levels increased 40- and 6-fold in neonatal rat ventricular myocytes and ARVM, respectively, following a 2-4-h exposure to the alpha-adrenergic agonist phenylephrine, a known hypertrophic stimulus for these cells. Phenylephrine had no effect on HB-EGF mRNA stability, and induction of HB-EGF could be blocked completely by actinomycin D. HB-EGF mRNA abundance was also increased 15-fold in ARVM maintained in defined medium that had been induced to contract at 3 Hz by continual uniform electric field stimulation, a mechanical stimulus that we have shown preserves contractile function and induces cell growth in vitro. To determine whether cardiac myocytes would respond to exogenous HB-EGF, quiescent ARVM were exposed to defined medium conditioned by transfected COS MT cells overexpressing HB-EGF. These myocytes exhibited nearly a 2-fold increase in protein content at 24 h compared with unstimulated control ARVM exposed to medium conditioned by COS cells transfected with the plasmid vector alone. Thus, neonatal and adult cardiac muscle cells respond to both neurohumoral and mechanical growth stimuli with a marked increase in HB-EGF mRNA, which may act as an early response gene to facilitate hypertrophic growth in these cells.

Age Factors↗

PubMed1994

Promotion of vascular smooth muscle cell growth by homocysteine: a link to atherosclerosis.

Plasma homocysteine levels are elevated in 20-30% of all patients with premature atherosclerosis. Although elevated homocysteine levels have been recognized as an independent risk factor for myocardial infarction and stroke, the mechanism by which these elevated levels cause atherosclerosis is unknown. To understand the role of homocysteine in the pathogenesis of atherosclerosis, we examined the effect of homocysteine on the growth of both vascular smooth muscle cells and endothelial cells at concentrations similar to those observed in clinical studies. As little as 0.1 mM homocysteine caused a 25% increase in DNA synthesis, and homocysteine at 1 mM increased DNA synthesis by 4.5-fold in rat aortic smooth muscle cells (RASMC). In contrast, homocysteine caused a dose-dependent decrease in DNA synthesis in human umbilical vein endothelial cells. Homocysteine increased mRNA levels of cyclin D1 and cyclin A in RASMC by 3- and 15-fold, respectively, indicating that homocysteine induced the mRNA of cyclins important for the reentry of quiescent RASMC into the cell cycle. Furthermore, homocysteine promoted proliferation of quiescent RASMC, an effect markedly amplified by 2% serum. The growth-promoting effect of homocysteine on vascular smooth muscle cells, together with its inhibitory effect on endothelial cell growth, represents an important mechanism to explain homocysteine-induced atherosclerosis.

Animals↗