Lipids with very long chain fatty acids (VLCPUFA) in germ cells and residual bodies

Abstract

In seminiferous tubules, Sertoli cells and spermatogenic cells at different stages of differentiation coexist. In this work pachytene spermatocytes (PS) and round spermatids (RS) were isolated to study how ceramides (Cer) and sphingomyelin (SM) with VLCPUFA are formed in the testis. Although the concentration of phospholipids including SM was similar in both cell types, there were many differences in their polyenoic fatty acids (FA). In glycerophopholipids, the 20:4n-6/22:5n-6 ratio was significantly higher in PS than in RS. In SM (and Cer), 28:4n-6, 30:5n-6, 32:5n-6 were the main FA in PS, whereas 28:4n-6 predominated in RS. By contrast, in the latter, an important proportion of SM (and Cer) FA were recovered as a-hydroxylated versions of VLCPUFA (2-OH 28:4 to 32:5). The residual bodies (RB) contain materials –including lipids– that are discarded from late spermatids (elongated forms) as they differentiate to spermatozoa, to be phagocytized and “recycled” in Sertoli cells. The RB were very rich in glycerophopholipids and triglycerides with 22:5n-6. The SM of RB contained virtually no VLCPUFA but was extremely rich in 2-OH VLCPUFA. The results point to fatty acid desaturase, elongase and hydroxylase activities that are highly specific for long-chain and very long-chain polyenoic fatty acids encoded by genes that are expressed sequentially as cell- differentiation proceeds