Lysyl Oxidase-like-2 (LOXL2) Is a Major Isoform in Chondrocytes and Is Critically Required for Differentiation

Abstract

The lysyl oxidase family is made up of five members: lysyl oxidase (LOX) and lysyl oxidase-like 1-4 (LOXL1-LOXL4). All members share conserved C-terminal catalytic domains that provide for lysyl oxidase or lysyl oxidase-like enzyme activity; and more divergent propeptide regions. LOX family enzyme activities catalyze the final enzymatic conversion required for the formation of normal biosynthetic collagen and elastin cross-links. The importance of lysyl oxidase enzyme activity to normal bone development has long been appreciated, but regulation and roles for specific LOX isoforms in bone formation in vivo is largely unexplored. Fracture healing recapitulates aspects of endochondral bone development. The present study first investigated the expression of all LOX isoforms in fracture healing. A remarkable coincidence of LOXL2 expression with the chondrogenic phase of fracture healing was found, prompting more detailed analyses of LOXL2 expression in normal growth plates, and LOXL2 expression and function in developing ATDC5 chondrogenic cells. Data show that LOXL2 is expressed by pre-hypertrophic and hypertrophic chondrocytes in vivo, and that LOXL2 expression is regulated in vitro as a function of chondrocyte differentiation. Moreover, LOXL2 knockdown studies in vitro show that LOXL2 expression is required for ATDC5 chondrocyte cell line differentiation through regulation of SNAIL and SOX9, important transcription factors that control chondrocyte differentiation. Taken together, data provide evidence that LOXL2, like LOX, is a multifunctional protein. LOXL2 promotes chondrocyte differentiation by mechanisms that are likely to include roles as both a regulator and an effector of chondrocyte differentiation.The lysyl oxidase family is made up of five members: lysyl oxidase (LOX) 3 and lysyl oxidase-like 1-4 (LOXL1-LOXL4)(1). All five members share a conserved C-terminal catalytic domain that provides for lysyl oxidase or lysyl oxidase-like enzyme activity, and more divergent propeptide regions. LOX family enzyme activities catalyze the final enzymatic conversion required for the subsequent formation of normal lysinederived biosynthetic cross-links found in collagens and elastin (2). The importance of lysyl oxidase enzyme activity to normal bone development has long been known, and is based in part on studies in which enzyme activities are inhibited by lathyrogens in vivo (3), including ␤-aminopropionitrile, a potent inhibitor of LOX and LOX isoform activity (4). The LOX family can be subdivided into two subgroups. Although all members have similarities in the catalytic C-terminal region, LOX and LOXL1 are more closely related to each other than they are to LOXL2-LOXL4. Moreover, the pro-peptide regions of LOX and LOXL1 have very little similarity to each other and no similarity to LOXL2-LOXL4. The pro-regions of LOXL2-LOXL4 each contain four scavenger receptor cysteine-rich (SRCR) domains whose functions are likely to depend on interactions with other proteins (1). The pro-regions of all LOX family members may have...

Lysine-Specific Histone Demethylases Contribute to Cellular Differentiation and Carcinogenesis

“…Consistently, the inhibition of LOXL2 activity promotes hDPSC differentiation to odontoblasts [173]. In contrast, LOXL2 expression increases significantly during chondrocyte differentiation, and its depletion abolishes chondrocyte differentiation [174].…”

LOXL2 in Epithelial Cell Plasticity and Tumor Progression

“…In fact, LOXL2 mRNA is markedly decreased in differentiated keratinocytes [63], and it has recently been shown that LOXL2 catalytic activity is dispensable for LOXL2-induced inhibition of keratinocyte differentiation, being the fourth scavenger receptor cysteine-rich domain in LOXL2 reportedly responsible for this function [64]. On the other hand, LOXL2 seems to be critically required for chondrocyte differentiation even though the detailed role of LOXL2 in chondrogenesis is not completely understood [65].…”

Enhanced in vitro biological activity generated by surface characteristics of anodically oxidized titanium – the contribution of the oxidation effect

“…Thus, the oxidative stress of the surface •OH of Ao-Ti could enhance the mineralization of adherent cells to a greater extent than in the other samples. Despite the estimated oxidative stress on Ao-Ti, a previous study reported a great reduction in the oxidative stress on Ao-Ti as a consequence of oxygen diffusion into the culture medium by the invariable reaction between surface •OH and water (Iwai-Yoshida et al, 2012).…”

“…Because bone is a natural biocomposite consisting of mineralized collagen fibers (Dvir et al, 2011;Gower, 2008), a cross-linked collagenous matrix is therefore essential, together with the expression of specific genes that induce ossification to ensure the hardness and elastic modulus of mineralized tissues (Paschalis et al, 2003;Wang et al, 2002). A recent study reports the expression of Loxl2 by prehypertrophic and hypertrophic chondrocytes during the chondrogenic phase of bone fracture healing (Iftikhar et al, 2011). Although the biological functions of the LOX family members in bone formation have not been fully elucidated, the cooperative interaction between osteogenic differentiation and oxidation of the collagen matrix is capable of mediating harder and stiffer in vitro mineralized tissue.…”