Cinematographic analysis of vascular smooth muscle cell interactions with extracellular matrix

Summary The interactions of vascular smooth muscle cells with growth modulators and extracellular matrix molecules may play a role in the proliferation and migration of these cells after vascular injury and during the development of atherosclerosis. Time-lapse cinematographic techniques have been used to study cell division and migration of bovine carotid artery smooth muscle cells in response to matrix molecules consisting of solubilized basement membrane (Matrigel) and type I collagen. When cells were grown adjacent to Matrigel, both migration and cell proliferation were increased and interdivision time was shortened. Cells grown in Matrigel or in type I collagen had markedly reduced migration rates but interdivision time was not altered. Further, diffusible components of the Matrigel were found to stimulate proliferation of the smooth muscle cells. This work was supported by grants HL35684 and SCOR HL14212 from the National Institutes of Health, Bethesda, MD.     

Aging effects on the elastin composition in the extracellular matrix of cultured rat aortic smooth muscle cells

Summary Elastin accumulation in the extracellular matrix of cultured rat aortic smooth muscle cells was monitored as a function of age. The effect of the animal donor age and time in culture in single or consecutive passages on the cells’ ability to accumulate total protein as well as elastin was evaluated. Smooth muscle cells were obtained from animals ranging in age from 2 d to 36 mo. Protein accumulation by the cells based on DNA content was similar regardless of which of the above aging parameters was examined. Although there were significant amounts of elastin present in the extracellular matrix of those cells originating from the younger animals (2 d and 6 wk old), little or none was detected in cell cultures derived from the oldest animals. A soluble elastin-like fraction which was isolated from the cultures of the 2-d-old rats seemed to be lacking in the cultures of cells from the 36-mo-old animals. This observation may, in part, explain the absence of insoluble elastin in the matrix of some cultures obtained from older animals. The data strongly suggest that the age of the donor animal from which the cells originate has the greatest influence on in vitro elastin accumulation. This study was supported by National Institutes of Health Grants HL 19717 and HL 13262.     

Ascorbate-induced changes in gangliosides of calf aortic smooth muscle cells in culture: Possible influence of extracellular matrix

Summary The ganglioside composition of calf aortic smooth muscle cells, cultured in the presence and absence of ascorbate, was analyzed. Previous work has shown that ascorbate supplementation leads to the formation of an extracellular matrix consisting primarily of collagen and that this matrix influences the biosynthetic capabilities of the cell. Cell cultures were supplemented with ascorbate for 3 wk and labeled with [¹⁴C]glucosamine for 3 d before harvesting. Ascorbate supplementation resulted in increased ganglioside sialic acid levels and a change in chromatographic profile involving both absolute and relative increases in GD1a. The latter, along with polysialo species, showed increased incorporation of [¹⁴C]glucosamine. These findings are interpreted in relation to the proposed role of gangliosides as mediators in the interaction of various cells with extracellular matrix. This work was supported by grants 1-P01-AG05554 and 2-R01-NS-04834 from the Public Health Service, Washington, DC, as well as a Presidential Junior Faculty Development Award (JAS) from the Purchase College Foundation.     

Stimulation of human arterial smooth muscle cell chondroitin sulfate proteoglycan synthesis by transforming growth factor-beta

Summary Human platelet-derived transforming growth factor-beta (TGF-beta) is a cell-type specific promotor of proteoglycan synthesis in human adult arterial cells. Cultured human adult arterial smooth muscle cells synthesized chondroitin sulfate, dermatan sulfate, and heparan sulfate proteoglycans, and the percent composition of these three proteoglycan subclasses varied to some extent from cell strain to cell strain. However, TGF-beta consistently stimulated the synthesis of chondroitin sulfate proteoglycan. Both chondroitin 4- and chondroitin 6-sulfate were stimulated by TGF-beta to the same extent. TGF-beta had no stimulatory effect on either class of [³⁵S]sulfate-labeled proteoglycans which appeared in an approximately 1:1 and 2:1 ratio of heparan sulfate to dermatan sulfate of the medium and cell layers, respectively, of arterial endothelial cells. Human adult arterial endothelial cells synthesized little or no chondroitin sulfate proteoglycan. Pulse-chase labeling revealed that the appearance of smooth muscle cell proteoglycans into the medium over a 36-h period equaled the disappearance of labeled proteoglycans from the cell layer, independent of TGF-beta. Inhibitors of RNA synthesis blocked TGF-beta-stimulated proteoglycan synthesis in the smooth muscle cells. The incorporation of [³⁵S]methionine into chondroitin sulfate proteoglycan core proteins was stimulated by TGF-beta. Taken together, the results presented indicate that TGF-beta stimulates chondroitin sulfate proteoglycan synthesis in human adult arterial smooth muscle cells by promoting the core protein synthesis. Supported in part by grants from the Public Health Service, U.S. Department of Health and Human Services, Washington, DC (CA 37589 and HL 33842), RJR Nabisco, Inc., and Chang Gung Biomedical Research Foundation (CMRP 291).     

Fibronectin promotes cell cycle entry in smooth muscle cells in primary culture

Smooth muscle cell proliferation after arterial injury is regulated by growth factors and components of the extracellular matrix. We have previously demonstrated that fibronectin promotes a phenotypic modulation of freshly isolated rat smooth muscle cells from a contractile to a synthetic phenotype in primary culture and supports the ability of the cells to respond to growth factors. Here, we analyzed if fibronectin promotes cell cycle entry in freshly isolated rat aortic smooth muscle cells during primary culture. Cell cycle analysis showed that cells seeded on fibronectin remained in the G(0)/G(1) phase of the cell cycle during the first 6 days of culture. During this period, there was an increased expression of cyclin D1 and p27(KIP1) in the absence of exogenous growth factors. Addition of serum was followed by enhanced cyclin D1 expression, decreased p27(KIP1) levels, hyperphosphorylation of Rb protein, induction of cyclin A and cyclin D3 expression, and cell cycle progression into S phase. The results indicate that fibronectin initiates cell cycle entry in freshly isolated smooth muscle cells by promoting the induction of cyclin D1 and thereby facilitates further cell cycle progression together with growth factors.     

Intracellular lysyl oxidase: Effect of a specific inhibitor on nuclear mass in proliferating cells

LOX, the principal enzyme involved in crosslinking of collagen, was the first of several lysyl oxidase isotypes to be characterized. Its active form was believed to be exclusively extracellular. Active LOX was later reported to be present in cell nuclei; its function there is unknown. LOX expression opposes the effect of mutationally activated Ras, which is present in about 30% of human cancers. The mechanism of LOX in countering the action of Ras is also unknown. In the present work, assessment of nuclear protein for possible effects of lysyl oxidase activity led to the discovery that proliferating cells dramatically increase their nuclear protein content when exposed to BAPN (β-aminopropionitrile), a highly specific lysyl oxidase inhibitor that reportedly blocks LOX inhibition of Ras-induced oocyte maturation. In three cell types (PC12 cells, A7r5 smooth muscle cells, and NIH 3T3 fibroblasts), BAPN caused a 1.8-, 1.7-, and 2.1-fold increase in total nuclear protein per cell, respectively, affecting all major components in both nuclear matrix and chromatin fractions. Since nuclear size is correlated with proliferative status, enzyme activity restricting nuclear growth may be involved in the lysyl oxidase tumor suppressive effect. Evidence is also presented for the presence of apparent lysyl oxidase isotype(s) containing a highly conserved LOX active site sequence in the nuclei of PC12 cells, which do not manufacture extracellular lysyl oxidase substrates. Results reported here support the hypothesis that nuclear lysyl oxidase regulates nuclear growth, and thereby modulates cell proliferation.     

Elastin in a neonatal rat smooth muscle cell culture has greatly decreased susceptibility to proteolysis by human neutrophil elastase. An in vitro model of elastolytic injury

Summary A neonatal rat aorta smooth muscle cell culture system with a unique elastin-rich extracellular matrix was used as a model substrate for elastases. To study the susceptibility to solubilization of insoluble elastin, cultures were incubated in the presence of human neutrophil elastase (HNE) or porcine pancreatic elastase (PPE) and in the absence of serum for periods up to 45 min. Both the incubation media and cell layers were then assessed for elastin and collagen markers, total protein, and lactate dehydrogenase (LDH). Although HNE and PPE exhibited comparable activity against elastin purified from the cell layer, HNE exhibited a 6.7- to 25-fold reduction in its elastin solubilizing activity using intact cell layers as compared with the purified elastin, whereas PPE exhibited only a 1.5- to 2.5-fold reduction. This effect could not satisfactorily be explained as preferential inhibition of HNE activity in the culture system, because the amount of protein solubilized by HNE was 59% that of PPE. The mean elastin content of PPE-solubilized protein was 110% that of the elastin content of the corresponding cell layer; the value for HNE-solubilized protein was only 16%. Thus, the amount of elastin per microgram of solubilized protein for HNE was 15% that for PPE. Possible explanations for the greatly diminished elastolytic activity of HNE in the culture system include the preference of HNE for other substrates in the cell layer, the inability of HNE to penetrate sufficiently into the cell layer, and the presence of sulfated glycosaminoglycans in the vicinity of the elastin that act in an inhibitory fashion. Although there was extensive proteolytic damage to the extracellular matrix, LDH and DNA measurements indicated that little loss of cells or cell viability occurred. The observed differences in elastolytic activity of HNE and PPE in the culture system parallel the relative emphysema-inducing potency of the elastases in the hamster model of elastase-induced emphysema. Supported by National Heart, Lung and Blood Institute, Bethesda, MD, grants NIH-HL-25229, HL-19717, and HL-33522. Presented in part at the April 1985 meeting of the Federation of American Societies for Experimental Biology.     

改良组织块消化法建立大鼠气道平滑肌细胞模型

目的：建立改进大鼠气道平滑肌细胞（ASMC）的体外培养方法,为相关研究提供实验材料。方法：将组织块连续贴壁进行细胞原代培养,胰酶消化传代培养,差速贴壁进行细胞纯化,形态学及免疫细胞化学染色法进行细胞鉴定。MTT法检测PDGF-BB诱导的ASMC增殖。结果：成功培养大鼠ASMC,以改良组织块消化法最为理想。第四代平滑肌细胞纯度可达95％以上。相差显微镜下培养细胞呈典型“峰谷状”生长。免疫荧光化学染色显示特异性平滑肌肌动蛋白阳性表达。随着PDGF浓度的升高（2-80ng／ml）,MTT比色A490值呈上升趋势。与对照组相比较,80ng／ml、20ng／ml PDGF—BB组有统计学意义（P〈0．01）。结论：改良组织块消化法可缩短培养周期,在充分利用标本的基础上获得大量气道平滑肌细胞。     

The extracellular matrix and the control of proliferation of vascular endothelial and vascular smooth muscle cells

In this short review we describe the observations which have led us to conclude that one of the most important components involved in modulating cell proliferation in vitro, and probably in vivo as well, may be the extrac-cellular matrix upon which cells rest.     

大鼠肺细小动脉平滑肌细胞培养新方法的建立及血小板衍生因子对其增殖迁移的影响

目的：建立一种操作简单、实验仪器要求低的大鼠肺细小动脉平滑肌细胞（PASMCs）分离和培养的方法,并且探索血小板衍生因子（PDGF）介导的增殖、迁移的情况。方法：向右心注射铁及琼脂糖,利用琼脂糖能同时粘附血管内皮细胞、平滑肌细胞及铁粉,再结合胶原酶I的消化,通过磁力架吸引铁,特异性地分选出带血管的肺组织,经过3~4周左右的培养及纯化,得到肺细小动脉平滑肌细胞。用倒置相差显微镜观察细胞形态,免疫细胞化学法和免疫荧光染色法进行α-平滑肌肌动蛋白鉴定。MTT实验和划痕实验检测PDGF诱导的肺动脉细小平滑肌细胞的增殖和迁移。结果：分离后第14天、第21天及传代后进行鉴定,均表明分离培养的细胞为PASMCs。MTT结果表明,与不加PDGF组相比,PDGF增殖明显增加（P<0.05）。划痕实验结果显示PDGF刺激组比不刺激组迁移显著增多。结论：本方法分离培养大鼠的PASMCs,操作方便,实验仪器要求低。PDGF能够促进肺细小动脉平滑肌细胞的增殖、迁移。     

大鼠细小肺动脉平滑肌细胞原代培养和鉴定方法的研究

目的：建立一种重复性好、培养周期短及传代次数多的大鼠细小肺动脉平滑肌细胞（PASMCs）培养方法。方法：在无菌条件下,分离雄性SD大鼠肺细小动脉,剥离外膜和剔除内皮细胞,经胶原酶I消化,培养PASMCs。0.4%台盼蓝染色测定细胞活力;倒置相差显微镜观察;免疫细胞化学法和免疫荧光染色法,进行平滑肌α-肌动蛋白（α-SMactin）鉴定。结果：形态学观察、免疫细胞化学法及免疫荧光染色法鉴定表明培养细胞为PASMCs;细胞存活率在96.5%以上;原代培养后4～7d即可传代,并且生长特点、细胞形态不易发生改变。结论：采用胶原酶I消化法培养PASMCs,方法简单、酶消化时间易控制、培养周期短、重复性好,培养的原代PASMCs具有数量多和生长迅速的特点。