Characterization of an L-amino acid oxidase in equine spermatozoa.
This study demonstrates for the first time the presence of an L-amino acid oxidase (LAAO) enzyme in equine spermatozoa that is able to generate significant amounts of reactive oxygen species (ROS) and create a state of oxidative stress. RT-PCR analysis revealed that the mRNA for this enzyme was present in the equine testis and spermatozoa, while immunocytochemical studies demonstrated that the mature LAAO protein was located in the sperm head, particularly in the acrosomal and postacrosomal domains. Experimental studies demonstrated that the aromatic amino acids (L-phenylalanine > L-tryptophan > L-tyrosine) were substrates for this enzyme, eliciting the dose- and time-dependent generation of ROS via mechanisms that were enhanced by cell death. This unexpected result was confirmed by analyses of ROS generation in subcellular sperm fractions, which again located a majority of LAAO activity to the sperm head. Equine cryopreservation medium was shown to contain sufficient quantities of aromatic amino acids to activate the LAAO system and generate ROS. The biological significance of this activity was established in an experiment in which physiological concentrations of aromatic amino acids were found to suppress sperm motility but only if dead spermatozoa were present in the same suspension. The combination of aromatic amino acids and nonviable cells was also found to enhance the levels of lipid peroxidation in live spermatozoa. These results suggest the potential significance of LAAO activity in generating the oxidative stress associated with the cryopreservation of equine spermatozoa. It is possible that inhibitors of this enzyme system may facilitate the development of modified cryostorage regimes for clinical validation in vivo.
Faculty of Veterinary Science, University of Sydney, Camperdown, New South Wales, Australia.
Joanna B
JB
Aitken
Priority Research Centre for Reproductive Science, Discipline of Biological Sciences, Faculty of Science and IT, University of Newcastle, Callaghan, New South Wales, Australia.
Nenad
N
Naumovski
Priority Research Centre for Reproductive Science, Discipline of Biological Sciences, Faculty of Science and IT, University of Newcastle, Callaghan, New South Wales, Australia.
Ben
B
Curry
Faculty of Veterinary Science, University of Sydney, Camperdown, New South Wales, Australia.
Christopher G
CG
Grupen
Priority Research Centre for Reproductive Science, Discipline of Biological Sciences, Faculty of Science and IT, University of Newcastle, Callaghan, New South Wales, Australia.
Zamira
Z
Gibb
Priority Research Centre for Reproductive Science, Discipline of Biological Sciences, Faculty of Science and IT, University of Newcastle, Callaghan, New South Wales, Australia john.aitken@newcastle.edu.au.
R John
RJ
Aitken
D000818:Animals; D015925:Cryopreservation / Q000662:veterinary; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D006736:Horses / Q000502:physiology*; D006861:Hydrogen Peroxide; D050830:L-Amino Acid Oxidase / Q000235:genetics / Q000378:metabolism*; D008297:Male; D013094:Spermatozoa / Q000201:enzymology*
D006861:Hydrogen Peroxide; D050830:L-Amino Acid Oxidase
cryopreservation; gamete biology; oxidative stress; sperm; sperm motility and transport