Sex-Linked Skeletal Phenotype of Lysyl Oxidase Like-1 Mutant Mice

Abstract

Lysyl oxidases are required for collagen and elastin cross-linking and extracellular matrix maturation including in bone. The lysyl oxidase family consists of lysyl oxidase (LOX) and 4 isoforms (LOXL1-4). Here we investigate whether deletion of LOXL1, which has been linked primarily to elastin maturation, leads to skeletal abnormalities. Left femurs (n = 8), L5 vertebrae (n = 8), and tibiae (n = 8) were analyzed by micro-computed tomography in 13-week-old wild-type (WT) and LOXL1-/- male and female mice. Right femurs (n = 8) were subjected to immunohistochemistry for LOXL1, and histochemical/histology analyses of osteoclasts and growth plates. Sera from all mice were analyzed for bone turnover markers. Results indicate strong expression of LOXL1 in wild-type growth plates in femurs. Significant deterioration of trabecular bone structure in long bones and vertebrae from female was observed but not from male, mutant mice compared with WT. Decreases in BV/TV, Conn.D, trabecular thickness, and number in the femoral distal metaphysis were observed in female, but not in male, mutant mice. Trabecular spacing was increased significantly in femurs of female mutant mice. Findings were similar in trabeculae of L5 vertebrae from female mutant mice. The number of TRAP positive osteoclasts at the trabecular bone surface was increased in female mutant mice compared with WT females, consistent with increased serum RANKL and decreased OPG levels. Analysis of bone turnover markers confirmed increased bone resorption as indicated by significantly elevated CTX-1 in the serum of female LOXL1-/- mice compared to their wild-type counterparts, as well as decreased bone formation as measured by decreased serum levels of PINP. Picrosirius red staining revealed a loss of heterogeneity in collagen organization in female LOXL1-/- mice only, with little to no yellow and orange birefringence. Organization was also impaired in chondrocyte columns in both female and male LOXL1-/- mice, but to a greater extent in females. Data indicate that LOXL1-/- mutant mice develop appendicular and axial skeletal phenotypes characterized by decreased bone volume fraction and compromised trabecular microstructure, predominantly in females.

Intraductal xenografts show lobular carcinoma cells rely on their own extracellular matrix and LOXL1

“…BAPN inhibits the activity of all LOX family members, some of which are widely expressed, and has severe side effects precluding clinical use (Alsofi et al , 2016). LOXL1, on the other hand, is expressed in only a few tissues, like the eye (Thorleifsson et al , 2007), making this family member an attractive drug target.…”

Precocious chondrocyte differentiation disrupts skeletal growth in Kabuki syndrome mice

“…Three genes were identified as being involved in chondrocyte development and/or endochondral ossification and potentially connected with Sox9 in the literature. Loxl1 encodes lysyl oxidase-like protein 1 (LOXL1) involved in extracellular matrix metabolism and endochondral ossification; however, Loxl1 -/mice exhibit decreased rather than increased cellularity at growth plates and do not exhibit long bone shortening, as in Kmt2d +/βGeo mice (22). Ccnd1 encodes cyclin D1, a cell cycle regulator expressed in and required for chondrocyte proliferation (23); expression of this gene has been shown to directly correlate with that of Sox9 (and Col2a1) in an osteoarthritis model, disfavoring a role for Ccnd1 in Sox9 inhibition (24).…”

Sexual Dimorphism in Osteoclasts

“…A variety of gene deleted mice have also been shown to have sexually dimorphic bone mass or osteoclast phenotypes. Mice with deletion of lysyl oxidases, which is an enzyme that cross-links collagen, demonstrated enhanced osteoclastogenesis and bone loss in females compared to males [ 41 ]. Male mice with deletion of transient receptor potential vanilloid 4 (TRPV4) have decreased osteoclasts in their bones and in bone marrow cell cultures relative to females [ 42 ].…”