Role of the small heat shock proteins in regulating vascular smooth muscle tone

Vasospasm occurs in conduits used for vascular reconstructions. The small heat shock proteins, HSP20 and HSP27, coordinately regulate vascular smooth muscle tone. Phosphorylated HSP20 is associated with vasorelaxation, and phosphorylated HSP27 inhibits the phosphorylation of HSP20 and relaxation. We hypothesized that the relationship between the phosphorylated states of these two proteins might dictate the tone of a vessel and may contribute to vasospasm.

Sodium nitroprusside relaxation of vascular smooth muscle was recorded using pig coronary artery and human saphenous vein. Segments were frozen and homogenized, and extracted proteins were separated by one- and two-dimensional gel electrophoresis, transferred to Immobilon (Millipore), and probed with anti-cGMP-dependent protein kinase (anti-PKG), -HSP20, -HSP27, and -phosphoHSP27 antibodies. Band intensity was estimated using densitometry.

Pig coronary artery completely relaxed (100%) with SNP (10(-7)M), but human saphenous vein only partially relaxed (20%). The levels of cGMP-dependent protein kinase and HSP20 were similar in the two tissue types. Human saphenous vein had significantly higher levels of HSP27 versus pig coronary artery (30.14 +/- 0.8 versus 6.62 +/- 0.2 pixels/mg; p < or = 0.001) and phosphoHSP27 (8.29 +/- 3.43 versus 0.012 +/- 0.008 pixels/mg; p < or = 0.001).

Human saphenous vein contained significantly higher levels of HSP27 and pHSP27. Increased levels of phosphorylated HSP27 might contribute to vasospasm in human saphenous vein.