A key enzyme upregulating collagen production by scleroderma fibroblasts

Context

Systemic sclerosis (SSc) is a fibroproliferative autoimmune disease characterized by the excessive production and deposition of collagen in skin and internal organs. Acting through specific transmembrane receptors, transforming growth factor-? (TGF-?) is known to play a crucial role in the development of tissue fibrosis. The authors had previously identified several signaling molecules other than Smad proteins including protein kinase C-d (PKC-d) as candidates downstream of TGF-? receptors. The aim of the present study was to examine the possible role of PKC-d in the upregulation collagen gene expression in SSc dermal fibroblasts.

Significant findings

Compared to normal fibroblasts, SSc dermal fibroblasts had increased type I and III collagen mRNA and protein as well as upregulation of PKC-d protein. Rottlerin, a specific inhibitor of PKC-d, inhibited collagen gene expression in both normal and SSc fibroblasts. Moreover, this study identified a 129-bp promoter region of the type I collagen gene encompassing nucleotides -804 to -675 which was responsive to the transcriptional inhibition by rottlerin and dominant-negative PKC-d expression.

Comments

These results indicate that PKC-d is a key molecule in the upregulation of type I collagen expression. However, the number of samples obtained from normal and SSc skins was too small to show a significant difference in the amounts of collagen and PKC-d expressed. In addition, most of the results presented in this paper relied on a single "selective" inhibitor of PKC-d, rottlerin. The following points should be addressed in future studies: 1) identification of transcription factors downstream of PKC-d that interact with a promoter segment encompassing nucleotides -804 -675; 2) comparison of PKC-d activity between SSc and normal fibroblasts; 3) possible differences in collagen and PKC-d expression among subgroups of SSc (e.g., diffuse cutaneous SSc and limited cutaneous SSc).

Methods

ELISA, collagenase digestion assay, northern blotting, in vitro nuclear transcription assay, chloramphenicol acetyl transferase gene assay, high-resolution fluorescence immunomicroscopy, western blotting