A study of fibroblast-mediated contraction in ocular scarring : gene expression profiling and the role of small GTPases in Matrix Metalloproteinase 1 (MMP1) regulation

• Main Author: Li, He
• Other Authors: Bailly, M. ; Khaw, P.
• Published: University College London (University of London) 2017
• Subjects: 617.7
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.746924

Understanding the molecular mechanisms involved in fibroblast-mediated tissue contraction is essential for developing future therapeutics for anti-scaring and fibrosis treatment not only for eyes, but also for a wide range of fibrotic diseases. The small Rho GTPase Rac1 is a master regulator of actin dynamics, which plays an essential role in protrusive activity, tissue repair and wound healing. A genome wide microarray study was performed with/without the transient treatment of human conjunctival fibroblasts with Rac1 inhibitor NSC23766 in a collagen gel contraction model to unveil the signalling events underlying contractile activity and the contribution of Rac1 activation. Through a comprehensive analysis that combined a pilot parallel study of scarring in an in vivo model in rabbit following glaucoma filtration surgery, and previously obtained microarray data of human ocular fibrotic diseases (including trachoma and thyroid-associated orbitopathy), it was identified that the contraction process consisted of two phases: an early phase that exhibited a classic serum/wound response profile with upregulation of genes related to inflammation, matrix remodelling, and transcription activation; and a late stage when the hyperactive signal receded and the gene profile progressed to promote fibrosis. The transient treatment with NSC23766 altered gene expression, and the early inhibition of Rac1 blocked the fibroblasts from entering the contractile phenotype as a whole. Interestingly, NSC23766 did not supress the mRNA expression of Matrix Metalloproteinase (MMP) 1, 3 and 10 during contraction, but reduced their enzymatic activity. The link between the activation of the Rho GTPase and MMP expression was subsequently investigated using MMP1 as an example. The results showed Rac1, Cdc42 and RhoA differently regulated MMP1 expression and secretion in fibroblasts during contraction, suggesting that the rate-limiting step for modulating MMP is the release in the extracellular medium rather than expression levels, drawing some interesting new prospects for therapies.