PARENT SESSION
Capacitation & Acrosome Reaction

CHOLESTEROL AND PHOSPHOLIPID CONTENTS AND MOLAR DISTRIBUTION OF PHOSPHOLIPID SATURATED/ MONO-UNSATURATED AND POLYUNSATURATED FATTY ACYL CHAINS OF NON-CAPACITATED AND CAPACITATED MOUSE SPERM.

Furimsky, Anna¹, Kates, Morris¹, Tanphaichitr, Nongnuj^1,2,3, ^{1 2 3}

ABSTRACT- Cell membrane fluidity is greatly affected by lipid composition, such as cholesterol (chol) and phospholipids (PLs) containing poly- and mono-unsaturated fatty acids (PUFA and MUFA). Since sperm membranes become more fluid during capacitation, we were interested in comparing lipid composition of washed non-capacitated (washed) mouse sperm and in vitro capacitated mouse sperm from both the whole sperm population (cap) and those having normal morphology and high motility, as selected by Percoll gradient centrifugation (PGC). Albumin-containing KRB medium was used to capacitate sperm. Fluorometric and colorometric assays of chol and PLs revealed reduced levels of both lipids in PGC sperm (chol:0.120 nmole/g DNA, PL:0.419 nmole/g DNA), as compared to those of the other two samples (chol:0.338 and 0.430 nmole/g DNA, PL:0.986 and 0.987 nmole/g DNA for wash and cap sperm, respectively). The three major PLs:phosphatidylcholine (PC), phosphatidylethanolamine (PE) and sphingomyelin (SM) separated on HPTLC showed the ratio of 60:35:5 in all three sperm samples. Gas chromatography revealed that 16:0 and 18:0 were the main saturated fatty acids (SFA), 18:1n9 was the only MUFA, and 20:4n6, 22:5n6 and 22:6n3 were the three PUFAs of PC and PE. For PC, SFA molar distribution was the same in all three sperm samples (~45%), whereas MUFA was increased in PGC sperm (13% vs 8% in the other two sperm samples). The molar percentage of 20:4n6 in PC was greatly reduced in PGC sperm (3.5% vs 27 and 21% in wash and cap sperm), while that of 22:5n6 + 22:6n3 was increased to 37% (~ 2x that in wash and cap sperm). For PE, significant reduction of 20:4n6 mol% in both cap and PGC sperm was observed (0 and 8%, respectively, vs 33% in wash sperm). The distribution of 22:5n6 + 22:6n3 was low in wash (5%) and cap (1%) sperm but was at 9% in PGC sperm. SFA was predominant in both cap and PGC sperm (97 and 59%, respectively, vs 39% in wash sperm). PGC sperm also contained significant molar distribution of 18:1n9 (24%), the value higher than that of wash (13%) and cap (5%) sperm. All of these results suggest that a decrease in chol:PL ratio and in molar distribution of 20:4n6 PC and PE, and an increase in molar percentages of 22:5n6 and 22:6n3 may be important for sperm to achieve capacitation and fertilizing ability. Supported by NSERC grant 183958 to NT and OGS to AF.

KEY WORDS: sperm lipids, sperm capacitation, fertilization, phospholipids