Sperm Lipid Markers of Male Fertility in Mammals

Abstract

Sperm plasma membrane lipids are essential for the function and integrity of mammalian spermatozoa. Various lipid types are involved in each key step within the fertilization process in their own yet coordinated way. The balance between lipid metabolism is tightly regulated to ensure physiological cellular processes, especially referring to crucial steps such as sperm motility, capacitation, acrosome reaction or fusion. At the same time, it has been shown that male reproductive function depends on the homeostasis of sperm lipids. Here, we review the effects of phospholipid, neutral lipid and glycolipid homeostasis on sperm fertilization function and male fertility in mammals.

Keywords: lipid markers; male fertility; mammals; sperm membrane.

Figure 1

Chemical structure of lipids. The pink shading in phosphatidylcholine (PC) shows the glycerol backbone. The pink shading in sphingomyelin (SM) shows the sphingoid backbone. The blue line boxes show the main parts of PC, the hydrophobic tail and the polar head, respectively. The distinction of PC and plasmalogen is whether the linkage at sn-1 is through an ether bond or ester bond. PC can be hydrolyzed by phospholipase A₂ (PLA₂) to LPC and fatty acid. Phospholipase C (PLC) and phospholipase D (PLD) act on the phosphate group and headgroup of phospholipids to break down phospholipids into DAG and PA, respectively. Phospholipases are shown in green and blue straight arrows indicate positions of catalysis.

Figure 2

Phospholipid asymmetry of sperm plasma membrane. Sphingomyelin (SM) and phosphatidylcholine (PC) are mainly present in the outer leaflet, while phosphatidylethanolamine (PE) and especially phosphatidylserine (PS) are located in the inner leaflet. Glycolipids are usually found in the outer leaflets of plasma membranes and are mainly used to maintain membrane stability and facilitate intercellular communication. Cholesterol molecules are randomly distributed over the phospholipid bilayer, binding the phospholipids together and limiting the fluidity of the membrane. During capacitation, the sperm plasma membrane first undergoes a substantial loss of cholesterol, accompanied by a decrease in phospholipids and loss of asymmetric distribution of phospholipids.