Upregulation of distinct collagen transcripts in post-surgery scar tissue: a study of conjunctival fibrosis

Abstract

Excessive accumulation of collagen is often used to assess the development of fibrosis. This study aims to identify collagen genes that define fibrosis in the conjunctiva following glaucoma filtration surgery (GFS). Using the mouse model of GFS, we have identified collagen transcripts that were upregulated in the fibrotic phase of wound healing via RNA-seq. The top three highest induced collagen transcripts belong to Col8a1, Col11a1 and Col8a2. Further validation of the Col8a1, Col11a1 and Col8a2 transcripts revealed their increase by 67-, 54- and 18-folds respectively in the fibrotic phase, compared to 12-fold for Col1a1, the most commonly evaluated collagen gene for fibrosis. However, only type I collagen was significantly upregulated at the protein level in the fibrotic phase. Type VIII and type I collagens co-localized in fibrous structures and in ACTA-2-positive pericytes, and appeared to compensate for each other in expression levels. Type XI collagen showed low co-localization with both type VIII and type I collagens but can be found in association with macrophages. Furthermore, we show that both mouse and human conjunctival fibroblasts expressed elevated levels of the top collagen genes in response to TGF-β2. Importantly, conjunctival tissues from patients whose surgeries have failed due to scarring expressed 3.60- and 2.78-folds increase in type VIII and I collagen transcripts respectively compared to those from patients with no prior surgeries. These data demonstrate that distinct collagen transcripts are highly induced in the conjunctiva after surgery and their unique expression profiles may imply differential influences on the fibrotic outcome.