EXPRESSION OF EXTRACELLULAR-MATRIX GENES IN ADULT HUMAN DERMAL MICROVASCULAR ENDOTHELIAL-CELLS AND THEIR REGULATION BY HEPARIN AND ENDOTHELIAL-CELL MITOGENS

BACKGROUND: Microvascular alterations are prominent features of system ic sclerosis (SSc) and often precede the appearance of clinically dete ctable fibrosis. The mechanism leading to selective microvascular inju ry in SSc is not known; however, microvascular endothelial cell (EC) a ctivation has been demonstrated in SSc skin and is considered to be an early event in the pathogenesis of SSc.EXPERIMENTAL DESIGN: The expre ssion of genes encoding extracellular matrix (ECM) proteins was examin ed in adult human dermal microvascular EC (HDMVEC), human iliac vein E C (HUVEC), and human umbilical vein EC (HUVEC) using indirect immunofl uorescence (IIF) and Northern hybridization analysis, The effects of h eparin and the endothelial cell mitogens, endothelial cell growth fact or (ECGF) supplement and acidic and basic fibroblast growth factors (a fGF and bFGF), on the expression of ECM genes by these cells were also studied. RESULTS: Abundant transcripts for collagen types I, IV, VI, and fibronectin (FN) and weak expression of the type III collagen gene were detected in HDMVEC cultures in the absence of ECGF and heparin. In contrast, in the presence of these factors, no mRNA for types I, II I, and VI collagens and marked down-regulation (more than twofold) of mRNA levels for collagen type IV and FN were observed. These results w ere confirmed at the protein level by IIF staining. In contrast to HDM VEC, HIVEC and HUVEC did not show expression of genes encoding types I , III, and VI collagens under any culture conditions examined. Next we studied the separate effect of heparin and aFGF or bFGF on the expres sion of ECM genes in HDMVEC. In contrast to the maximal expression of types I and VI collagens and FN detected in the absence of growth fact ors, aFGF decreased mRNA levels by 43% for type I collagen, by 52% for type VI collagen, and by 47% for FN. The decreases in mRNA levels cau sed by bFGF were 37, 41, and 36%, respectively. Heparin alone decrease d the mRNA levels for these genes by 60, 77, and 65%, respectively; ho wever, FGF potentiated the negative effect of heparin on ECM gene expr ession. CONCLUSIONS: These results demonstrate that HDMVEC display a u nique pattern of expression of ECM genes that is different from that d isplayed by EC from medium and large vessels. The data also demonstrat e that heparin, ECGF supplement, aFGF, and bFGF regulate ECM gene expr ession in HDMVEC in vitro and suggest that these growth factors may mo dulate the expression of matrix genes in vivo. Altered expression of E CM genes by HDMVEC may play an important role in diseases affecting th e microvasculature, such as SSc.