Different cell cycle regulation of vascular smooth muscle in genetic hypertension

Vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) proliferate faster than those from Wistar-Kyoto rats (WKY). Therefore regulation of cell cycle progression was examined in VSMC from both strains. Analysis of G1 progression was performed in VSMC synchronized by serum starvation. Double staining for propidium iodide and bromodeoxyuridine revealed that G1 progression was faster in SHR as compared with WKY. Indeed, 59+/-6% of VSMC from SHR but only 14+/-10% of those from WKY had left G1 phase after 24 hours of mitogenic stimulation. Moreover, 15+/-2% of SHR cells had already completed the cycle at this time point. Western blot analysis demonstrated that the level of cyclin D, cyclin E, and cyclin A was higher in SHR cells progressing through G1 phase, whereas expression of cyclin-dependent kinase 2 as well as the cyclin-dependent kinase inhibitors p21 and p27 were similar in the two groups. Consistent with a higher level of cyclins, the activity of cyclin-dependent kinase 2 was more pronounced in SHR cells. Analysis of G2 progression was performed in VSMC synchronized by treatment with aphidicolin and revealed an additional difference in cell cycle regulation between SHR and WKY. Indeed, the level of cell division cycle kinase 2 was higher in cells from SHR, whereas that of its catalytic partner cyclin B was similar. Consistent with this pattern of expression, the activity of cell division cycle kinase 2 was more pronounced in VSMC from SHR as compared with WKY. Thus, these data demonstrate that the different proliferation of VSMC from SHR and WKY is related to a different progression in G1 phase as the result of the expression of cyclin D, cyclin A, and cyclin E as well as a different progression in G2 phase caused by expression of cell division cycle kinase 2.