Fuel/Energy Sources of Spermatozoa

Abstract

Spermatozoa consume energy in the form of intracellular adenosine triphosphate (ATP) generated by its fuel machinery. Energy is required to facilitate sperm functions, from sperm motility and hyperactivation to capacitation and acrosome reaction, all of which are crucial for the success of fertilization. Glycolysis and oxidative phosphorylation are the two metabolic pathways known to generate energy in spermatozoa. However, the cellular mechanism and signaling pathways that spermatozoa predominantly utilize to generate the energy it requires to achieve successful fertilization are not fully elucidated. Oxidative phosphorylation occurs in the mitochondria and is a more efficient pathway for ATP production compared to glycolysis. Mitochondrial respiration is reported to be the primary source of energy for sperm motility, yet the diffusion potential of ATP from the mitochondria downwards of the entire flagellar length is inadequate to support sperm motility. On the other hand, glycolysis, which takes place in the sperm head and tail, is the main source of ATP along the flagellum. Although inhibition of the glycolysis process does not appear to disrupt sperm function and motility, it is uncertain whether such motility is sustainable over an extended time period or if it is vigorous enough for fertilization to occur effectively. This chapter provides an overview of sperm energy metabolism, which is supported by the unique anatomical and physiological characteristics in spermatozoa as well as the coordination between the Sertoli cells and spermatogonial cells during energy production in spermatozoa. Energy utilization during each sperm process and the consequence of fuel depletion on sperm function are also described. Understanding the intricacies of sperm energy metabolism would help improve the in vitro sperm storage media and contribute toward the development of non-hormonal contraceptives.