John Saltis

Transforming growth factor-beta 1 gene activation and growth of smooth muscle from hypertensive rats.

Cultured vascular smooth muscle cells derived from the spontaneously hypertensive rat (SHR) are known to replicate more rapidly than cells from the normotensive Wistar-Kyoto (WKY) rat. In this study we compared the responses of vascular smooth muscle cells from the two strains to transforming growth factor-beta 1 (TGF-beta 1) and evaluated its potential to account for the different growth properties of these cells in response to a number of vascular-derived growth factors. TGF-beta 1 potentiated the proliferative effects of epidermal growth factor, basic fibroblast growth factor, or the different isoforms of platelet-derived growth factor on vascular smooth muscle cells from SHR but inhibited growth factor-stimulated proliferation of vascular smooth muscle cells from WKY rats. These differential effects of TGF-beta 1 on proliferation could not be attributed to alterations in the expression of the type I, II, or III TGF-beta receptors but appeared more related to the ability of cells to autoinduce the TGF-beta 1 gene. TGF-beta 1 caused a time-dependent increase in its own mRNA levels in vascular smooth muscle cells of WKY rats but attenuated levels in vascular smooth muscle cells of SHR. This effect was specific to TGF-beta 1 autoinduction since similar elevations in TGF-beta 1 mRNA levels were observed when vascular smooth muscle cells from the two rat strains were exposed to phorbol myristate acetate, basic fibroblast growth factor, or platelet-derived growth factor-BB.(ABSTRACT TRUNCATED AT 250 WORDS)

REGULATION AND INTERACTIONS OF TRANSFORMING GROWTH FACTOR-BETA WITH CARDIOVASCULAR CELLS : IMPLICATIONS FOR DEVELOPMENT AND DISEASE

1. Transforming growth factors‐β (TGF‐β) are multifunctional proteins that regulate cell growth, differentiation, migration and extracellular matrix production and have an important role in embryonic development and tissue remodelling.

Differences in growth characteristics of vascular smooth muscle from spontaneously hypertensive and Wistar-Kyoto rats are growth factor dependent.

Objective: To investigate whether the differences in the growth properties between vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats depend on the type and nature of the growth factor. Design: The growth characteristics of VSMC from SHR and WKY rats were compared in the presence of different growth factors. These were related to growth factor receptor expression on the VSMC. Methods: Growth rates, cell densities at which VSMC become quiescent and [3H]-thymidine incorporation into DNA were examined in VSMC from SHR and WKY rats following exposure to epidermal growth factor (EGF), basic fibroblast growth factor (bFGF) or the three isoforms of platelet-derived growth factor (PDGF-AA, PDGF-AB and PDGF-BB). Receptor expression (receptor binding and Northern analysis) for these growth factors was also examined on VSMC from the two strains. Results: VSMC from SHR exposed to the individual growth factors exhibited growth rates higher than those from WKY rats. For EGF, bFGF, PDGF-AB and PDGF-BB there was no difference in the sensitivity of VSMC to stimulation of [3H]-thymidine incorporation between the strains. In contrast, VSMC from SHR exhibited significantly increased sensitivity to the mitogenic effects of PDGF-AA. VSMC from SHR exposed to PDGF-BB or EGF proliferated and then became quiescent at densities approximately 50 and 200% higher, respectively, than those from WKY rats. In contrast, in the presence of bFGF, proliferating VSMC from WKY rats became quiescent at densities approximately 20% higher than those from SHR. Scatchard analysis of [125l]-labelled growth factor binding to VSMC from the two strains revealed similar receptor numbers and dissociation constants for all growth factors. Steady-state messenger RNA levels for the different receptors were also similar and could not account for the enhanced growth rates of VSMC from SHR. Conclusion: The rate and magnitude of the proliferative response elicited in VSMC cultures from SHR and WKY rats is critically dependent on the nature of the growth factor stimulus.

Vascular smooth muscle growth in genetic hypertension: evidence for multiple abnormalities in growth regulatory pathways.

Objective: To gain insight into the mechanisms which contribute to the development of vascular hypertrophy in the spontaneously hypertensive rat (SHR). Design: These experiments were performed under conditions which most closely mimic the growth of smooth muscle in blood vessels, i.e. once cell-cell contact has been achieved. Methods: A comparison of the growth characteristics (growth rates and cell density at quiescence) of vascular smooth muscle cells (VSMC) from SHR and normotensive Wistar-Kyoto (WKY) rats. Results: In the presence of foetal calf serum (1, 2.5, 5 and 10%), early passaged VSMC from SHR exhibited higher growth rates and reached higher densities at quiescence than VSMC from WKY rats. Accelerated growth rates could not be attributed to differences in cell-cell interactions. Also, growth rates and cell density at quiescence appear to be regulated by distinct mechanisms. Transforming growth factor-β1 (TGF-β1) caused an inhibition of serum-stimulated proliferation of confluent VSMC from WKY rats. In contrast, TGF-β1 had little, if any, inhibitory action upon the growth of VSMC from SHR. Scatchard analysis of 125l-TGF-β1 binding to VSMC from both strains yielded a single class of high affinity binding sites. Conclusions: VSMC from SHR exhibit enhanced proliferation, attain a higher cell density at quiescence and are less susceptible to growth inhibition by TGF-β1 than VSMC from WKY rats. All these characteristics of SHR VSMC may contribute to the development of vascular hypertrophy in this strain.

Vascular smooth muscle cell proliferation in SHR and wky rats : evidence for specific differences in growth inhibitory regulatory mechanisms

1. This study examined and compared the actions of transforming growth factor‐β1 (TGF‐β1), heparin, dexamethasone and interferon‐γ on platelet‐derived growth factor‐BB (PDGF‐BB)‐stimulated proliferation of vascular smooth muscle cells (VSMC) from normotensive, Wistar‐Kyoto (WKY) rats and spontaneously hypertensive rats (SHR).

REGULATION BY PROTEIN KINASE C OF TRANSFORMING GROWTH FACTOR-β1 ACTION ON THE PROLIFERATION OF VASCULAR SMOOTH MUSCLE CELLS FROM SPONTANEOUSLY HYPERTENSIVE RATS

1. This study examined the role of protein kinase C (PKC) on the action of transforming growth factor‐β1 (TGF‐β1) to regulate the proliferation of vascular smooth muscle cells (VSMC) isolated from the aorta of the spontaneously hypertensive rat (SHR).

Effect of transforming growth factor-β1 on platelet-derived growth factor receptor binding and gene expression in vascular smooth muscle cells from SHR and WKY rats

1. This study examined the effects of transforming growth factor‐βl (TGF‐β1) on platelet‐derived growth factor‐BB (PDGF‐BB)‐stimulated DNA synthesis, [125I]‐PDGF‐BB receptor binding and PDGF‐β receptor mRNA expression in vascular smooth muscle cells (VSMC) isolated from Wistar‐Kyoto (WKY) rats and spontaneously hypertensive rats (SHR).

Dihydropyridine Ca2+ channel antagonists inhibit the salvage pathway for DNA synthesis in human vascular smooth muscle cells.

We examined the mechanisms by which Ca2+ channel antagonists inhibit the growth of smooth muscle cells by determining their effect on epidermal growth factor (EGF)-stimulated (i) induction of the early signalling gene, c-fos, (ii) incorporation of [3H]thymidine into cells as a measure of DNA synthesis, and (iii) increase in cell number. Verapamil, diltiazem, and the dihydropyridines felodipine, MDL 72892 A-15 (MDL) and nisoldipine had no effect on EGF-stimulated c-fos mRNA induction. Furthermore, only small inhibitory effects were observed on EGF-stimulated increases in cell number; felodipine, MDL, and nisoldipine at 0.3 microM inhibited EGF-stimulated cell proliferation by 9, 11, and 15%, respectively. In contrast, the dihydropyridine Ca2+ channel antagonists were found to be potent inhibitors of [3H]thymidine incorporation suggesting that they inhibit DNA synthesis. However, further examination revealed that the potent effects of dihydropyridine Ca2+ channel antagonists on [3H]thymidine incorporation were due not to an effect on incorporation of [3H]thymidine into DNA, but to a marked inhibitory effect on the cellular uptake of [3H]thymidine. Thus, we conclude that the small antiproliferative effects of the dihydropyridine antagonists are predominantly due to their ability to inhibit the activity of the salvage pathway for thymidylate synthesis in human vascular smooth muscle cells.

Differential regulation by transforming growth factor-β1 of platelet-derived growth factor-stimulated proliferation of vascular smooth muscle cells from SHR and WKY rats

1. This study has examined and compared the time‐course of action of transforming growth factor‐β1 (TGF‐β1) on platelet‐derived growth factor‐BB‐stimulated proliferation of vascular smooth muscle cells isolated from normotensive Wistar‐Kyoto (WKY) rats and spontaneously hypertensive rats (SHR).

DEVELOPMENTALLY REGULATED TRANSFORMING GROWTH FACTOR‐β1 ACTION ON VASCULAR SMOOTH MUSCLE GROWTH IN THE SHR

1. This study examined the effects of transforming growth factor‐β11 (TGF‐β1) on platelet‐derived growth factor‐BB (PDGF‐BB)‐stimulated proliferation of vascular smooth muscle cells (VSMC) isolated from aortic tissue of I, 4 and 12 week old spontaneously hypertensive rats (SHR).