1. ¹Department of medicine, Rheumatology Section, Boston University School of Medicine, Arthritis Center, Boston, Massachusetts, USA
2. ²Department of Orthopaedics Surgery, Boston University Medical Center, Boston, Massachusetts, USA
3. ³Nephrology Research Unit, Department of Medicine, Mayo Proteomics Research Center, Rochester, Minnesota, USA

Correspondence: Dr Raphael Lemaire, Rheumatology Section, Boston University School of Medicine, Arthritis Center, Building. E-5, 715 Albany Street, Boston, Massachusetts 02118, USA. E-mail: rlemaire@bu.edu

Received 23 April 2007; Revised 16 July 2007; Accepted 15 August 2007; Published online 18 October 2007.

Abstract

Systemic sclerosis (SSc) is a complex human disorder characterized by progressive skin fibrosis. To better understand the molecular basis of dermal fibrosis in SSc, we analyzed microarray gene expression in skin of the Tight-skin (Tsk) mouse, an animal model where skin fibrosis is caused by an in-frame duplication in fibrillin-1 (Fbn-1). Tsk skin showed increased mRNA levels of several genes involved in Wnt signaling, including Wnt2, Wnt9a, Wnt10b and Wnt11; Dapper homolog antagonist of -catenin (DACT1) and DACT2; Wnt-induced secreted protein 2; and secreted frizzled-related protein (SFRP)2 and SFRP4. RNase protection and northern blot confirmed microarray results. Furthermore, Wnt3a markedly stimulated matrix assembly of microfibrillar proteins, including Fbn-1, by cultured fibroblasts, suggesting that Wnts contribute to increased microfibrillar matrices in Tsk skin. Further analysis showed that SFRP4 expression is specifically increased in tissues expressing Tsk-Fbn-1, such as skeletal muscle and skin. The increase in SFRP4 mRNA in Tsk skin started 2 weeks after birth, following the increase in Wnt2 mRNA that occurred at birth. This suggests that SFRP4 may modulate Wnt functions in Tsk skin fibrosis. Lesional skin from SSc patients also showed large increases in SFRP4 mRNA and protein levels in the deep dermis compared to healthy skin, suggesting that the Wnt pathway might regulate skin fibrosis in SSc.