15-Lipoxygenase is a component of the mammalian sperm cytoplasmic droplet

Abstract

Lipoxygenases (LOXs) are a family of enzymes capable of peroxidizing phospholipids. A member of the LOX family of enzymes, 15-LOX, participates in the degradation of mitochondria and other organelles within differentiating red blood cells, the reticulocytes. The present study provides biochemical and immunocytochemical evidence for the presence of 15-LOX in the sperm cytoplasmic droplet (CD). Testicular, epididymal and ejaculated spermatozoa were evaluated for the presence of 15-LOX using an affinity-purified immune serum raised against a synthetic peptide corresponding to the C-terminal sequence of rabbit reticulocyte 15-LOX. Western blotting revealed an appropriate single band of ,81 kDa in boar spermatozoa but not in boar seminal plasma. When ejaculated boar spermatozoa were subjected to separation on a 45/90% Percoll gradient, 15-LOX co-migrated with the immotile sperm and cellular debris/CD fractions, but not with the motile sperm fraction containing morphologically normal spermatozoa without CDs. Varied levels of 15-LOX were expressed in ejaculated sperm samples from boars with varied semen quality. By immunofluorescence, prominent 15-LOX immunoreactivity was found within the residual body in the testis and within the CDs from caput, corpus and cauda epididymal and ejaculated spermatozoa. Components of the ubiquitin-dependent proteolytic pathway, which is thought to facilitate both spermiogenesis and reticulocyte organelle degradation, were also detected in the sperm CD. These included ubiquitin, the ubiquitin-conjugating enzyme E2, the ubiquitin C-terminal hydrolase PGP 9.5, and various 20S proteasomal core subunits of the a-and b-type. The 15-LOX and various components of the ubiquitin-proteasome pathway were also detected in sperm CDs of other mammalian species, including the human, mouse, stallion and wild babirusa boar. We conclude that 15-LOX is prominently present in the mammalian sperm CD and thus may contribute to spermiogenesis, CD function or CD removal. Reproduction (2005) 130 213-222

Group III secreted phospholipase A2 regulates epididymal sperm maturation and fertility in mice

“…cells (e.g., testicular Sertoli and Leydig cells as well as epididymal epithelial cells) (62,63) could be regarded as further evidence for the action of sPLA 2 -III on the sperm membrane, where the arachidonate/linoleate released by sPLA 2 -III would be more readily accessible to proximal 12/15-lipoxygenase than to distant cyclooxygenases. Although the role of 12/15-lipoxygenase in male fertility has not yet been fully established, expression of this enzyme in spermatogenic cells has led to the suggestion that it may participate in sperm maturation (62).…”

The Relationship between Sperm Morphology and In Vitro Fertilization Ability in Mice

“…The shape of the CD is related to infertility in some human patients [10] and is thus thought to affect fertilizability in vivo and in vitro. Although the shedding system and function of the CD are still unclear, the protein 15-LOX [19] and molecules recognized by anti-ubiquitin antibody [20] have been reported to be involved in CD function and removal. Further analyses are needed to determine whether the distribution of these molecules is strain-dependent, as is the presence of a CD.…”

The RNA-binding protein Mex3b regulates the spatial organization of the Rap1 pathway

“…To test the hypothesis of a Sertoli cell phagocytic dysfunction in the absence of Mex3b, we immunolabeled 15-lipoxygenase (15-LOX; also known as Alox15), an enzyme that peroxidizes lipids and is known to concentrate within residual bodies (Fischer et al, 2005). As depicted in Fig.…”