Expression of lysyl oxidase family of proteins during cartilage formation -- a role for lysyl oxidase like-2 in chondrogenesis

Abstract

The organic matrix of cartilaginous tissues is composed of collagen type I; and the correct composition and organization of this collagen network is important for the mechanical properties of cartilage. The lysyl oxidase family of enzymes is required for the cross-linking of collagen and elastin molecules in various tissues, including cartilaginous tissues. We studied the expression pattern of lysyl oxidase and the lysyl oxidase like proteins in the context of cartilage formation. To investigate this, tissues samples derived from fracture healing models and growth plates were subjected to real-time PCR analysis for mRNA expression and immunohistochemistry. Data shows that the expression of lysyl oxidase and the LOX-like proteins is regulated during the cartilaginous phase of fracture healing. Amongst these, the expression pattern of LOXL2 is unique, in that it is abundantly expressed in cartilage cells and is regulated in a temporal manner during fracture repair, peaking during the phase of chondrogenesis. In vitro differentiation of chondrogenic ADTC5 cells shows that LOXL2 has an expression pattern that mirrors the expression of collagen type II, a marker for chondrogenesis. Most importantly, lentivirus mediated knockdown of LOXL2 resulted in a simultaneous inhibition of collagen type II expression. Together, our data indicates that LOXL2 may play an essential role during chondrogenesis.