The Temporal Sequence of G-Protein Expression in Intimal Hyperplasia

Abstract

The universal response of a blood vessel to intimal injury is the development of intimal hyperplasia. The etiology of this lesion is not fully understood but is assumed to involve stimulation of receptors on smooth muscle cells with their subsequent proliferation. Many receptor-mediated processes are coupled to G-proteins but little information exists regarding the expression of G-proteins during the development of intimal hyperplasia. This study examines the kinetics of G-protein expression in experimental vein grafts. Male New Zealand White rabbits had a right carotid interposition bypass graft using the ipsilateral external jugular vein. These were harvested on days 1, 3, 5, 7, 14, and 28 postoperatively for histology (n= 3), forin vitroisometric tension studies of potassium chloride, serotonin, bradykinin, and histamine (n= 3), or for Western blot analysis (n= 3) of the G-protein subunits (αi1, αi2, αi3, αSand β). The results show that expression of αi3developedde novo,was detectable by day 1, and continued to increase through day 7, paralleling the development of intimal hyperplasia. The expression of αS(52 kDa) increased significantly by day 1 and also continued to increase until day 7. In contrast, expression for αi2, αS(45 kDa) and β subunits increased at a much slower rate from 1 to 7 days and remained constant thereafter. No αi1was detected. The contractile response to potassium chloride was significantly reduced (36% of the response in the jugular vein) over the first 7 days and increased to 196% of the jugular vein response at 14 and 28 days. There was minimal response to serotonin, bradykinin, and histamine over the first 7 days. Contractile responses to serotonin increased while those to bradykinin and histamine decreased from 7 to 28 days. This study demonstrates that there are specific changes in αiand αSsubunits within 24 hr of grafting and that increases in all G-proteins occur in a time dependent manner up to 7 days postoperatively. Microscopic development of intimal hyperplasia occurs from days 3 to 5 and increases rapidly between 7 and 14 days. Changes in the expression of G-proteins in the vein grafts, particularly the αi3subunit, parallel this formation of intimal hyperplasia. These alterations in G-protein expression do not appear to correlate with G-protein-mediated, contractile responses in the vein grafts.