Esfingolípidos con ácidos grasos poliinsaturados de muy larga cadena: Una característica específica de la gametogénesis masculina

Abstract

In seminiferous tubules, sperrnatogenic cells and Sertoli cells coexist. The latter phagocytize lipid-laden residual bodies released from elongating, condensing spermatids and apoptotic bodies arising from dying germ cells. Sphingomyelins (SM) and ceramides (Cer) that contain very-long-chain (C28-C32) polyunsaturated fatty acids (VLCPUFA), in nonhydroxylated (N) and 2-hydroxylated (2-OH) versions, appeared in the testis only after the onset of spermatogenesis. The ratio 2-OH / N VLCPUFA increased as spermatocytes become spermatids. In the process, residual bodies with plenty of 2-OH VLCPUFA-rich SM were formed. N- and 2-OH VLCPUFA-rich sphingolipids disappeared from the adult rat testis, in this order, in experimental conditions that damage germ cells but spare Sertoli cells (e.g., irradiation). Germ cells were able to de novo biosynthesize their own sphingolipids, as shown by the incorporation of appropriate precursors into SM, Cer and glucosyl-Cer of pachytene spermatocytes and round spermatids in primary culture. Mature spermatozoa were endogenously rich in Cer with 2-OH VLCPUFA. Studies of lipid distribution in the gametes showed that this Cer belonged to the sperm tail, and SM to the head. Hydrolysis of head SM into Cer was highly sensitive to the presence of calcium, and was almost complete after incubations inducing the acrosomal reaction. The unique fatty acids of these sphingolipids convert them into useful biomarkers for studies on normal aspects and pathological alterations of germ cell or spermatozoal functions.