Sphingosine-1-Phosphate in Inhibition of Male Germ Cell Apoptosis in the Human Testis

Abstract

It has been suggested that apoptosis is controlled by two intracellular sphingolipids, ceramide and sphingosine-1-phosphate (S1P), which are widely distributed in mammalian tissues. In the ovary, S1P was found to effectively block apoptosis caused by cancer therapies. Its role in male germ cell death, however, was unknown. In this study, we investigated the effects of ceramide and S1P on human male germ cell apoptosis. Germ cell death was induced by incubation of segments of seminiferous tubules in vitro. During apoptosis, ceramide levels increased rapidly before appearance of caspase 3 activation and DNA laddering, suggesting a role for ceramide in the induction of germ cell death. Ceramide appeared to regulate an early step of apoptosis because n-acetyl-L-cysteine and blockade of mitochondrial respiration inhibited apoptosis but had no effect on ceramide levels. Moreover, fumonisin B1 (ceramide synthetase inhibitor) did not significantly affect testicular apoptosis. Therefore, elevated ceramide levels are likely to result from breakdown of sphingomyelin rather than from de novo synthesis. Finally, we found that S1P at 1 and 10 micromol/liter suppressed germ cell apoptosis by 30% (P < 0.001). Taken together, sphingolipids appear to play a role in male germ cell apoptosis and can partly be inhibited by S1P.

Ceramides and Sphingomyelins with High Proportions of Very Long-chain Polyunsaturated Fatty acids in Mammalian Germ Cells

“…SM-derived Cer has been proposed to participate in the apoptosis-mediated control of the number of germ cells in the seminiferous tubule (11,12), and exogenously added Cer has been shown to act as a pro-apoptotic second messenger in seminiferous tubules (13). Using the present approach, we observed a small (20 -40%), transient Cer increase in whole testis at time points close to those specified by the respective authors as accumulating the largest number of apoptotic cells per testis (e.g.…”

“…Given the relationship between Cer and apoptosis, this physiological "background" of apoptosis was a second reason for our interest in investigating testicular Cer and its fatty acids in relation to those of SM. Tilly and Kolesnick (12) predicted that SM-derived Cer and sphingosine 1-phosphate could have a potential impact on gonadal physiology by mediating apoptosis and its control in normal and pathological conditions, a concept that received confirmation in experiments measuring these metabolites in sections of human seminiferous tubules (13). The balance between cell growth stimulation and arrest in the mature testis involves a delicate equilibrium between biosynthesis, remodeling, catabolism and recycling of lipids, including sphingolipids and their fatty acids.…”

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 4: Intercellular bridges, mitochondria, nuclear envelope, apoptosis, ubiquitination, membrane/voltage‐gated channels, methylation/acetylation, and transcription factors

“…During human germ cell apoptosis, ceramide increases before the appearance of caspase-3 activation and DNA laddering, suggesting a role in the induction of germ cell death. On the other hand, SIP suppresses germ cell apoptosis (Suomalainen et al, 2003). -504] is a small peptide of 8.5 kDa, which can covalently attach to proteins through a series of enzymatic reactions that begin with the ATP-dependent activation of ubiquitin by one of many ubiquitin E1 activating enzymes (e.g.…”

Docosahexaenoic acid down-regulates phenobarbital-induced cytochrome P450 2B1 gene expression in rat primary hepatocytes via the sphingomyelinase/ceramide pathway

“…Extracted lipids were dried under nitrogen and resuspended in 1 ml of 100:100:1 (vol/vol/vol) CHCl 3 /MeOH/HCl. Lipids were resolved on a Silica-60 TLC plate (Merck, Darmstadt, Germany) with 100:5:2 (vol/ vol/vol) CH 3 Cl/MeOH/CH 3 COOH as a mobile phase by a modification of the method described previously [41]. Individual lipid classes were visualized by dipping each plate into CuSO 4 (3%)-H 3 PO 4 (8%) for 30 s, drying the thin-layer chromatography (TLC) plate and charring the plate on a hot plate.…”