Studies on the metabolism of essential fatty acids in isolated human testicular cells

The essential fatty acid 22:6(n-3) is a minor component of the Western diet , but a major fatty acid in human testis and semen. In mature spermatozoa, the physical and fusogenic properties of the plasma membrane are probably i nfluenced by its particular fatty acid composition. In this study, the synt hesis of 22:6(n-3) and 22:5(n-6) was investigated in isolated human testicu lar cells. [1-C-14]20:4(n-6), [1-C-14]20:5(n-3), [1-C-14]22:4(n-6) and [1-C -14]22:5(n-3) were incubated in a 'crude' cell suspension (consisting of a mixture of the cells in the seminiferous tubule), and in fractionated pachy tene spermatocytes and round spermatids. The esterification of fatty acids in lipid and phospholipid classes and the fatty acid chain elongation and d esaturation were measured. The crude cell suspension metabolized the fatty acids more actively than did the fractionated germ cell suspension, indicat ing that types of cell other than the germ cells are important for fatty ac id elongation and desaturation and thus the production of 22:6(n-3). This f inding is in agreement with previous results in rats that indicated that th e Sertoli cells are the most important type of cell for the metabolism of e ssential fatty acids in the testis. Some [1-C-14]20:5(n-3) was elongated to [C-14]22:5(n-3) in the fractionated germ cells, but very little was elonga ted further to [C-14]24:5(n-3), possibly restricting the formation of [C-14 ]22:6(n-3). In the fractionated germ cells, the fatty acid substrates were recovered primarily in the phospholipid fraction, indicating an incorporati on in the membranes, whereas in the crude cells, more substrates were ester ified in the triacylglycerol fraction. In the phospholipids, more radioacti vity was recovered in phosphatidylcholine than in phosphatidylethanolamine and more radioactivity was recovered in phosphatidylethanolamine than in ph osphatidylinositol or phosphatidylserine.