Extracellular matrix components and integrins in the control of arterial smooth muscle cell structure and function

Atherosclerosis and Matrix Dystrophy

Atherosclerosis is characterized by inflammatory metabolic change with lipid accumulation in the artery. Atherosclerotic plaque occurs at discrete locations in the arterial system and involves the proliferation of smooth muscle cells (SMCs) together with imbalance of the extracellular matrix elements, elastic fiber in particular. The role of elastin in arterial development and disease was confirmed by generating mice that lack elastin. Thus, elastin is a critical regulatory molecule that regulates the phenotypic modulation, proliferation and migration of SMCs. We estimated that elastin expression and SMC proliferation are coupled inversely: potent stimulators of cell proliferation may potentially inhibit elastin expression and potent inhibitors of cell proliferation can stimulate elastin expression. Moreover, elastin was found to be expressed maximally at the G(0) and minimally at the G(2)/M phase during the cell cycle, suggesting that its expression is regulated by the cell growth state. The elastin peptide VPGVG enhanced SMC proliferation, resulting in the reduction of elastin expression. The inhibition of elastin expression by elastin fragments may be reflected in the negative feedback regulatory mechanism. The relationship between cell proliferation and elastin expression may be changed in atherosclerosis. Areas of atherosclerotic plaque show abnormality of elasticity and permeability from the viewpoint of the physiological function of the arterial wall. The etiology was estimated to be that cholesterol and calcium are deposited on the elastic fiber, resulting in decreased elastin synthesis and cross-linking formation. In addition, these dysfunctions of elastin fiber are also associated, in that the down-regulation of elastin and its related components (fibrillin-1 and lysyl oxidase) are directly related to calcification in SMCs. The denatured arterial elastin by cholesterol and calcium accumulation was also susceptible to proteolytic enzymes such as elastase and matrix metalloproteinase (MMP). Therefore, metabolic change in elastic fiber induces decreased elasticity and is associated with essential hypertension. Vitamin K(2) is used in drug therapy against atherosclerosis, or calcification in diabetes mellitus or dialysis, due to its promotion of the carboxylation of the matrix Gla protein.

Paxillin-associated focal adhesion involvement in perinatal pulmonary arterial remodelling

Birth is followed by remodelling of the actin cytoskeleton of pulmonary arterial smooth muscle cells, then by extracellular matrix deposition. Hypothesising that the cell/matrix adhesions would also be remodelled, we investigated the expression, localisation and biochemical characteristics of the focal adhesion protein paxillin in vivo, in vessels from normal and pulmonary hypertensive neonatal piglets. Initially we showed that in intact porcine pulmonary arteries exposed to cytochalasin D there was a reduction filamentous actin accompanied by a reduction in paxillin-associated focal adhesions, similar to that seen in cultured pulmonary arterial smooth muscle cells. Vessels from normal and hypoxic animals were found to have two isoforms of paxillin, of 60 and 66 kDa with pI values of 6.7-4.2. Transient changes occurred during the first 14 days of life. Between birth and 6 days there was a reduction in the amount of both paxillin isoforms, a shift to more acidic pI values and an increase in paxillin phosphorylation. Simultaneously, immunostaining showed a transient reduction in paxillin expression, a change temporally and spatially associated with a previously demonstrated reduction in actin. Findings are consistent with an immediate postnatal spatial reorganisation of paxillin-associated focal adhesions. Paxillin content and remodelling was abnormal in pulmonary hypertensive arteries, the response varying according to postnatal age.