Vascular smooth muscle cell differentiation in human cerebral vascular malformations

OBJECTIVE: The pathogenesis of central nervous system vascular malformation s likely involves the abnormal assembly, differentiation of vascular smooth muscle cells (VSMC), or both in association with dysmorphic vessel wall. W e hypothesize that intracranial arteriovenous malformations (AVMs) and cere bral cavernous malformations (CCMs) exhibit distinct patterns of expression of molecular markers of differentiation and maturity of VSMCs. We further speculate that the unique VSMC phenotype in the different lesions is not ne cessarily maintained in cell culture. METHODS: Paraffin-embedded sections of five AVMs, CCMs, and control brain t issues were stained immunohistochemically with antibodies to alpha -smooth muscle actin (alpha -SMA), myosin heavy chain, and smoothelin, a novel mark er for contractile VSMC phenotype. Large (greater than or equal to 100 mum) and small (<100 <mu>m) vessels were counted and assessed for immunoexpress ion of each protein, then categorized according to expression of one or mor e of these markers. Cultured nonendothelial cells isolated from four other excised AVM and CCM lesions were assessed for immunoexpression of the same antibodies. RESULTS: alpha -SMA was universally expressed in all vessels in AVMs and in control brains. It was expressed in the subendothelial layer of 97% of lar ge caverns and 85% of small caverns and in scattered intercavernous connect ive tissue fibrocytes in CCMs. Myosin heavy chain was expressed in the majo rity of brain and AVM vessels, except for normal veins, and in the subendot helial layer of more than half of the caverns in CCMs. Smoothelin expressio n was less prevalent in large vessels in AVMs than in control brains and wa s not found in any caverns in CCMs (large vessels in control brains, 40.9%; AVMs, 21.9%; CCMs, 0%; P < 0.0001). Cultured AVM and CCM nonendothelial ce lls expressed <alpha>-SMA, but myosin heavy chain was expressed weakly in c ells from only one CCM. Smoothelin was negative in all cells. CONCLUSION: We describe vessels with various stages of VSMC differentiation in AVMs and CCMs. The subendothelial layer of CCMs commonly expresses alph a -SMA and less commonly expresses myosin heavy chain. Expression of smooth elin was less prevalent in large AVM vessels than in normal brain, which ma y reflect the loss of contractile property associated with hemodynamic stre ss. It is difficult to evaluate VSMC differentiation in culture because of phenotypic change.