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J. Biol. Chem., Vol. 282, Issue 25, 18151-18161, June 22, 2007

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Very Long-chain Polyunsaturated Fatty Acids Are the Major Acyl Groups of Sphingomyelins and Ceramides in the Head of Mammalian Spermatozoa^*

Natalia E. Furland, Gerardo M. Oresti, Silvia S. Antollini, Andrés Venturino, Eduardo N. Maldonado, and Marta I. Aveldaño¹

From the Instituto de Investigaciones Bioquímicas de Bahía Blanca, Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad Nacional del Sur, 8000-Bahía Blanca, Argentina and the Laboratorio de Teriogenología, Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad Nacional del Comahue, 8300-Neuquén, Argentina

Very long-chain (C24 to C34) polyunsaturated fatty acids (VLCPUFA) are important constituents of sphingomyelin (SM) and ceramide (Cer) in testicular germ cells. In the present paper we focused on the SM and Cer and their fatty acids in spermatozoa and their main regions, heads and tails. In bull and ram spermatozoa, SM was the third most abundant phospholipid and VLCPUFA were the major acyl groups (70%) of SM and Cer. In rat epididymal spermatozoa the SM/Cer ratio was low in the absence of and could be maintained high in the presence of the cation chelator EDTA, added to the medium used for sperm isolation. This fact points to the occurrence of an active divalent cation-dependent sphingomyelinase. Bull and rat sperm had an uneven head-tail distribution of phospholipid, with virtually all the VLCPUFA-rich SM located at the head, the lower SM content in the rat being determined by the lower sperm head/tail size ratio. Most of the SM from bull sperm heads was readily solubilized with 1% Triton X-100 at 4 °C. The detergent-soluble SM fraction was richer in VLCPUFA than the nonsoluble fraction and richer in saturated fatty acids. Cer was produced at the expense of SM, thus decreasing severalfold the SM/Cer ratio in rat spermatozoa incubated for 2 h in presence of the sperm-capacitating agents, calcium, bicarbonate, and albumin. The generation of Cer from SM in the sperm head surface may be an early step among the biochemical and biophysical changes known to take place in the spermatozoon in the physiological events preceding fertilization.

Received for publication, January 25, 2007 , and in revised form, March 28, 2007.

^* This work was supported by Consejo Nacional de Investigaciones Científicasy Técnicas, Secretaría General de Ciencia y Tecnología Universidad Nacional del Sur, and Agencia Nacional de Promoción de la Ciencia y la Tecnología, Argentina. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: INIBIBB, Centro Regional de Investigaciones Básicas y Aplicadas de Bahía Blanca, CONICET, CC 857, 8000, Bahía Blanca, Argentina. Tel.: 54-291-4861666, Ext. 138; Fax: 54-291-4861200; E-mail: avelda{at}criba.edu.ar.

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