Fibroblast Matrix Gene Expression and Connective Tissue Remodeling: Role of Endothelin-1

Abstract

This study examines endothelin-induced modulation of extracellular matrix synthesis and remodeling by fibroblasts, and its potential role in the pathogenesis of systemic sclerosis (scleroderma). Endothelin-1 promoted fibroblast synthesis of collagen types I and III, but not fibronectin, by a mechanism dependent upon both ETA and ETB receptors. Conversely, endothelin-1 inhibited both protein expression of matrix metalloproteinase 1 and zymographic activity exclusively via ETA receptors. A dual regulatory role for endothelin-1 in transcriptional regulation was suggested by the ability of endothelin-1 to enhance steady-state levels of collagen mRNA and activate the proalpha2(I) collagen (Col1a2) promoter, but in contrast to reduce matrix metalloproteinase 1 transcript expression and suppress transcription of a human matrix metalloproteinase 1 promoter reporter construct in transient transfection assays. Although endothelin-1 significantly enhanced remodeling of three-dimensional collagen lattices populated by normal fibroblasts, this was not observed for lattices populated by systemic sclerosis fibroblasts. Promotion of matrix remodeling was dependent upon ETA receptor expression and was blocked by specific inhibitors of tyrosine kinases or protein kinase C. Reverse transcriptase polymerase chain reaction, S1 nuclease, and functional cell surface binding studies showed that normal and systemic sclerosis fibroblasts express both ETA and ETB receptors (predominantly ETA), but that ETA receptor mRNA levels and ETA binding sites on fibroblasts cultured from systemic sclerosis skin biopsies are reduced by almost 50%. Endothelin-1 is thus able to induce a fibrogenic phenotype in normal fibroblasts that is similar to that of lesional systemic sclerosis fibroblasts. Moreover, reduced responsiveness to exogenous endothelin-1 in systemic sclerosis suggests that downstream pathways may have already been activated in vivo. These data further implicate dysregulated endothelin-receptor pathways in fibroblasts in the pathogenesis of connective tissue fibrosis.

Endothelin-1 mediated regulation of extracellular matrix collagens in cells of human lamina cribrosa

“…Both BQ610 an ET A receptor antagonist and BQ788 an ET B receptor antagonist were able to each partially inhibit collagen type I and collagen type VI deposition suggesting the involvement of both receptor subtypes in ET-1 mediated collagen deposition in LC cells. Similar results have been reported previously where dual ET A and ET B receptor antagonists effectively inhibit ET-1 mediated collagen synthesis (Shi-wen et al, 2001;Morgera et al, 2003;Clozel and Salloukh 2005).…”

“…We were therefore interested in studying the role ET-1 in regulation of collagens type I and VI in LC cells. The dose and time point selected for ET-1 in the present study are consistent with previous studies (Shi-wen et al, 2001;Hafizi et al, 2004;Horstmeyer et al, 2005;He et al, 2007).…”

“…In cardiovascular and pulmonary tissues ET-1 mediated collagen synthesis and ECM deposition have been primarily attributed to stimulation of ET A receptors (Hafizi et al, 2004;Rodriguez-Vita et al, 2005). In dermal and hepatic tissues however, ET B receptors, contribute to ET-1 mediated collagen synthesis and ECM deposition (Gandhi et al, 2000;Shi-wen et al, 2001). ET A receptor serve as regulators of collagen homeostasis by inducing both its synthesis and degradation while it has been shown that ET B receptor mediates only collagen synthesis (Guarda et al, 1993;Shi-wen et al, 2001Tostes et al, 2002.…”

“…In dermal and hepatic tissues however, ET B receptors, contribute to ET-1 mediated collagen synthesis and ECM deposition (Gandhi et al, 2000;Shi-wen et al, 2001). ET A receptor serve as regulators of collagen homeostasis by inducing both its synthesis and degradation while it has been shown that ET B receptor mediates only collagen synthesis (Guarda et al, 1993;Shi-wen et al, 2001Tostes et al, 2002. Chronic exposure of ET-1 in cultured fibroblasts also resulted in a switch of receptor subtype from ET A to ET B , resulting in an ET B mediated increase in collagen synthesis (Shi-wen et al, 2001;Horstmeyer et al, 2005;).…”

“…ET A receptor serve as regulators of collagen homeostasis by inducing both its synthesis and degradation while it has been shown that ET B receptor mediates only collagen synthesis (Guarda et al, 1993;Shi-wen et al, 2001Tostes et al, 2002. Chronic exposure of ET-1 in cultured fibroblasts also resulted in a switch of receptor subtype from ET A to ET B , resulting in an ET B mediated increase in collagen synthesis (Shi-wen et al, 2001;Horstmeyer et al, 2005;). An upregulation of ET B receptors results in autoinduction of ET-1 synthesis and further enhances ET-1 effects through ET B receptors (Iwasaki et al, 1995).…”