Functional relationships between capacitation-dependent cell signaling andcompartmentalized metabolic pathways in murine spermatozoa

Spermatozoa are highly polarized cells with specific metabolic pathways com partmentalized in different regions. Previously, we hypothesized that glyco lysis is organized in the fibrous sheath of the flagellum to provide ATP to dynein ATPases that generate motility and to protein kinases that regulate motility. Although a recent report suggested that glucose is not essential for murine sperm capacitation, we demonstrated that glucose (but not lacta te or pyruvate) was necessary and sufficient to support the protein tyrosin e phosphorylation events associated with capacitation. The effect of glucos e on this signaling pathway was downstream of cAMP, and appeared to arise i ndirectly as a consequence of metabolism as opposed to a direct signaling e ffect Moreover, the phosphorylation events were not affected by uncouplers of oxidative respiration, inhibitors of electron transfer, or by a lack of substrates for oxidative respiration in the medium. Further experiments aim ed,at identifying potential regulators of sperm,glycolysis focused on a ger m cell-specific isoform of hexokinase, HK1-SC, which localizes to the fibro us sheath. HK1-SC: activity and biochemical localization did not change dur ing sperm capacitation, suggesting that glycolysis in sperm is regulated ei ther at the level of substrate availability or by downstream enzymes. These data Support the hypothesis that ATP specifically produced by a compartmen talized glycolytic pathway in the principal piece of the flagellum, as oppo sed to ATP generated by mitochondria in the mid-piece, is strictly required for protein tyrosine phosphorylation events that take place during sperm c apacitation. The relationship between these pathways suggests that spermato zoa offer a model system for the study of integration of compartmentalized metabolic and signaling pathways.