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 systemic sclerosis (SSc) and often precede the appearance of clinically detectable fibrosis. The mechanism leading to selective microvascular injury in SSc is not known; however, microvascular endothelial cell (EC) activation has been demonstrated in SSc skin and is considered to be an early event in the pathogenesis of SSc.

EXPERIMENTAL DESIGN

The expression of genes encoding extracellular matrix (ECM) proteins was examined in adult human dermal microvascular EC (HDMVEC), human iliac vein EC (HIVEC), and human umbilical vein EC (HUVEC) using indirect immunofluorescence (IIF) and Northern hybridization analysis. The effects of heparin and the endothelial cell mitogens, endothelial cell growth factor (ECGF) supplement and acidic and basic fibroblast growth factors (aFGF 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, III, and VI collagens and marked down-regulation (more than twofold) of mRNA levels for collagen type IV and FN were observed. These results were confirmed at the protein level by IIF staining. In contrast to HDMVEC, 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 expression 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 factors, 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 caused by bFGF were 37, 41, and 36%, respectively. Heparin alone decreased the mRNA levels for these genes by 60, 77, and 65%, respectively; however, FGF potentiated the negative effect of heparin on ECM gene expression.

CONCLUSIONS

These results demonstrate that HDMVEC display a unique pattern of expression of ECM genes that is different from that displayed by EC from medium and large vessels. The data also demonstrate that heparin, ECGF supplement, aFGF, and bFGF regulate ECM gene expression in HDMVEC in vitro and suggest that these growth factors may modulate the expression of matrix genes in vivo. Altered expression of ECM genes by HDMVEC may play an important role in diseases affecting the microvasculature, such as SSc.