Differential Expression of Lysyl Oxidases LOXL1 and LOX During Growth and Aging Suggests Specific Roles in Elastin and Collagen Fiber Remodeling in Rat Aorta

The extracellular matrix (ECM) plays an important role in vascular tissue structure, maintenance, and function. Lysyl oxidases catalyze a key step in the posttranslational cross-linking of elastin and collagens in the ECM. Gene knockout studies in mice suggested a role for lysyl oxidase-like (LOXL1) in adult elastin synthesis and a role for its isoform, lysyl oxidase (LOX), in the synthesis of both collagens and elastin during development. However, the relative expression of both isoforms as a function of age is not known and was therefore investigated here. LOX and LOXL1 immunohistochemistry and real-time RT-PCR were performed during development, growth and aging in the aorta of LOU and Brown-Norway (BN) rats, two inbred strains with different susceptibilities to arterial fragility. In addition, expression of genes encoding for elastic fiber proteins and type I collagen, together with elastin and collagen contents, was measured in adult and old rat aortas. High aortic LOX expression was observed early in the development (embryonic day 15), followed by a drastic reduction in adulthood, whereas LOXL1 was mainly detectable in the intima and media; its expression was maintained throughout life in the LOU rat. Expression of tropoelastin, type-I collagen, and LOXL1 genes was reduced in the aorta of 6-week-old BN rats. Aging is characterized by a decreased elastin/collagen ratio and a greatly decreased expression of LOX, tropoelastin, and type-I collagen. These findings indicate a different spatial and temporal expression of LOX and LOXL1 during growth and aging in the rat aorta and suggest specific roles for LOX and LOXL1 in the synthesis and remodeling of elastic and collagen fibers.