Variations in LOXL1 associated with exfoliation glaucoma do not affect amine oxidase activity

Lysyl oxidase-like 1 (LOXL1) is a copper-dependant amine oxidase that plays an essential role in elastogenesis. Two non-synonymous single-nucleotide polymorphisms of LOXL1, R141L (rs1048661) and G153D (rs3825942), have been reported to significantly increase susceptibility to exfoliation glaucoma (XFG). To evaluate the impact of the R141L and G153D variations on the amine oxidase activity of LOXL1, we generated four different haplotypes of LOXL1 with R141L and G153D and assessed the amine oxidase activity of the LOXL1 variant proteins.

The four different haplotype variants of LOXL1 were created by oligonucleotide-directed mutagenesis in an LOXL1 expression vector. Recombinant LOXL1 variant proteins were purified by nickel-affinity chromatography. The amine oxidase activities of the LOXL1 variant proteins were assessed using peroxidase-coupled fluorometric assays.

All of the haplotype variants of LOXL1 (141R-153G, 141R-153D, 141L-153G, and 141L-153D) showed β-aminopropionitrile-inhibitable amine oxidase activity toward elastin, type I collagen, and cadaverine, indicating that each LOXL1 variant functions as an amine oxidase. However, there were no significant differences in amine oxidase activity between the LOXL1 haplotype variants toward the tested substrates.

The R141L and G153D variations in the NH(2)-terminal region of LOXL1 do not affect the amine oxidase activity of LOXL1. This is consistent with recent genetic findings on the reversal of risk alleles of R141L and G153D in different ethnic backgrounds. Our results suggest that other unknown genetic factors or molecular mechanisms may be more relevant to the development of XFG.