Molecular and tissue alterations of collagens in fibrosis.

The collagen network is altered in fibrotic diseases associated with extracellular matrix (ECM) biosynthesis and remodeling. This mini-review focuses on the quantitative and qualitative modifications of collagens occurring at the molecular and tissue levels in fibrosis. They result from changes in collagen expression, biosynthesis, enzymatic cross-linking and degradation by several protease families. These molecular modifications, which are mostly regulated by TGF-β, are associated with altered collagen organization at the tissue level, leading to a fibrotic signature that can be analyzed by Second Harmonic Generation (SHG) microscopy.