Lipid remodelling during epididymal maturation of rat spermatozoa. Enrichment in plasmenylcholines containing long-chain polyenoic fatty acids of the n-9 series

Abstract

In their transit from the caput to the cauda segments of the epididymis, rat spermatozoa undergo significant modifications in lipid content and composition. The amount of lipid phosphorus per cell decreases, and most lipid classes show specific changes in their constituent fatty acids. A depletion of phosphatidylcholine and phosphatidylethanolamine, concomitant with a virtually unchanged amount of the corresponding plasmalogens, are the major alterations, plasmenylcholine thereby becoming the major phospholipid. Diphosphatidylglycerol, sphingomyelin and the phosphoinositides decrease to a lesser extent or do not change at all, also resulting in relative increases with sperm maturation. Concerning the fatty acids, the proportions of oleate (C18:1, n-9) and linoleate (C18:2, n-6) in most lipids decrease on movement of sperm from caput to cauda, augmenting in turn the proportions of longer-chain (C20 to C24) and more unsaturated fatty acids. Docosapentaenoate (C22:5, n-6) is a major acyl chain present in all lipids at both stages, but uncommon long-chain polyenoic fatty acids of the n-9 series are also present, being almost exclusively found in the choline glycerophospholipids. These fatty acids are found to undergo the most significant changes during sperm maturation. They are minor components of plasmenylcholine in immature spermatozoa, but increase severalfold on maturation, representing more than half of the acyl chains of this major lipid in cells from the cauda. The high concentration of n-9 polyenes in mature sperm plasmenylcholine raises intriguing questions on the possible role epididymal cells may play in providing spermatozoa with such an unusual phospholipid. These plasmenylcholines could contribute to the characteristic lipid domain organization of the mature spermatozoa plasma membrane.

Sterols in spermatogenesis and sperm maturation

“…The HE1 homolog has been suggested to be one of the important regulators of cholesterol content in sperm membranes at least in some species ( 65 ). During epididymal transit, the content of cholesterol in sperm membranes decreased by approximately 50% in several species ( 57,(66)(67)(68). In some species, cholesterol content increased during sperm maturation ( 69 ) or remained unchanged ( 70 ).…”

Role of Membrane Lipid Fatty Acids in Sperm Cryopreservation

“…Plasma membrane lipids of the goat [16], ram [17], and boar [18] spermatozoa have been shown to undergo marked changes during epididymal maturation. The lipid content of whole sperm decreases during epididymal maturation in boar, bull, ram, and rat [19][20][21][22][23][24][25][26], and the cholesterol content decreases in ram, rat, and hamster sperm [27][28][29]. The cholesterol : phospholipid ratio and concentration of phosphatidylserine, phosphatidylethanolamine, cardiolipin, and ethanolamine plasmalogen decrease in whole ram sperm [20,27].…”

Co‐expression and interaction of cubilin and megalin in the adult male rat reproductive system

“…The result ofthis is that the sperm plasma membrane, which already contains an unusually high proportion of polyunsaturated phospholipids from the outset, acquires and even greater degree of unsaturation as the sperm matures. The cholesterol content in the rat spermatozoon also declines by over 50% in its epididymal transit, vllith an accompanying decrease in the cholesterol:phospholipid ratio from 0.28 to 0.17 (Aveldano et al, 1992). Together, the decreasing saturated:unsaturated fatty acid and cholesterol:phospholipid ratios suggest that the plasma membrane becomes more fluid in its maturation.…”

“…In fact, there is a 54% decrease in the total membrane phospholipid content from caput to corpus epididymidis (Aveldano et al, 1992). While an phospholipids show a decrease, those found predominantly in the inner leaflet (phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol and ethanolamine plasmalogen) show a much greater decrease than those found predominantly on the outer leaflet (phosphatidylcholine, choline plasmalogen and sphingomyelin) which remain relatively stable (Aveldano et al, 1992;Parks and Hammerstedt, 1985). The result ofthis is that the sperm plasma membrane, which already contains an unusually high proportion of polyunsaturated phospholipids from the outset, acquires and even greater degree of unsaturation as the sperm matures.…”