Novelty of the Pyruvate Metabolic Enzyme Dihydrolipoamide Dehydrogenasein Spermatozoa

Abstract

Spermatozoa are cells distinctly different from other somatic cells of the body, capacitation being one of the unique phenomena manifested by this gamete. We have shown earlier that dihydrolipoamide dehydrogenase, a post-pyruvate metabolic enzyme, undergoes capacitation-dependent tyrosine phosphorylation, and the functioning of the enzyme is required for hyperactivation (enhanced motility) and acrosome reaction of hamster spermatozoa (Mitra, K., and Shivaji, S. (2004) Biol. Reprod. 70, 887-899). In this report we have investigated the localization of this mitochondrial enzyme in spermatozoa revealing non-canonical extra-mitochondrial localization of the enzyme in mammalian spermatozoa. In hamster spermatozoa, dihydrolipoamide dehydrogenase along with its host complex, the pyruvate dehydrogenase complex, are localized in the acrosome and in the principal piece of the sperm flagella. The localization of dihydrolipoamide dehydrogenase, however, appears to be in the mitochondria in the spermatocytes, but in spermatids it appears to show a juxtanuclear localization (like Golgi). The capacitation-dependent time course of tyrosine phosphorylation of dihydrolipoamide dehydrogenase appears to be different in the principal piece of the flagella and the acrosome in hamster spermatozoa. Activity assays of this bi-directional enzyme suggest a strong correlation between the tyrosine phosphorylation and the bi-directional enzyme activity. This is the first report of a direct correlation of the localization, tyrosine phosphorylation, and activity of the important metabolic enzyme, dihydrolipoamide dehydrogenase, implicating dual involvement and regulation of the enzyme during sperm capacitation.Spermatozoa, the haploid cells, are unique compared with other cells with respect to their morphology and functionality; needless to say the underlying signaling mechanisms in a functional spermatozoon are also unique. The metabolic pathways in a mature spermatozoon are compartmentalized (1-3), which probably enables them to survive in two different kinds of milieu, the male and the female reproductive tract. The residence time in the female reproductive tract is an obligatory event in the life cycle of a spermatozoon and has been termed "capacitation" (4, 5). During capacitation spermatozoa undergo multifaceted changes in aspects like metabolism, intracellular ion concentrations, plasma membrane fluidity, and thus membrane reorganization, intracellular pH, intracellular cAMP concentration, and generation of reactive oxygen species (6 -8). These cellular alterations during capacitation bring about three physiological changes: (a) hyperactivation (enhanced motility), (b) tyrosine phosphorylation in an array of proteins, and (c) acrosome reaction (release of the acrosomal contents); the first two events show a temporal correlation with capacitation, whereas acrosome reaction is taken to be the end point of capacitation (9).Protein tyrosine phosphorylation is considered to be a hallmark of sperm capacitation (10 -15), but only a few of thes...

Identification and validation of mouse sperm proteins correlated with epididymal maturation

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Nuclear Localization of Mitochondrial TCA Cycle Enzymes as a Critical Step in Mammalian Zygotic Genome Activation

“…Published literature provides precedence for extra-mitochondrial localization of PDH (Chueh et al, 2011; Mitra et al, 2005; Sutendra et al, 2014). Similar to our results in the pre-implantation embryo, all three subunits of PDH can be detected during the S phase of the cell cycle in the nucleus of lung cancer cell lines (Sutendra et al, 2014).…”

Identification of novel immunodominant epididymal sperm proteins using combinatorial approach

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