Sorbitol can fuel mouse sperm motility and protein tyrosine phosphorylation via sorbitol dehydrogenase

Abstract

Energy sources that can be metabolized to yield ATP are essential for normal sperm functions such as motility. Two major monosaccharides, sorbitol and fructose, are present in semen. Furthermore, sorbitol dehydrogenase (SORD) can convert sorbitol to fructose, which can then be metabolized via the glycolytic pathway in sperm to make ATP. Here we characterize Sord mRNA and SORD expression during mouse spermatogenesis and examine the ability of sorbitol to support epididymal sperm motility and tyrosine phosphorylation. Sord mRNA levels increased during the course of spermatogenic differentiation. SORD protein, however, was first detected at the condensing spermatid stage. By indirect immunofluorescence, SORD was present along the length of the flagella of caudal epididymal sperm. Furthermore, immunoelectron microscopy showed that SORD was associated with mitochondria and the plasma membranes of sperm. Sperm incubated with sorbitol maintained motility, indicating that sorbitol was utilized as an energy source. Sorbitol, as well as glucose and fructose, were not essential to induce hyperactive motility. Protein tyrosine phosphorylation increased in a similar manner when sorbitol was substituted for glucose in the incubation medium used for sperm capacitation. These results indicate that sorbitol can serve as an alternative energy source for sperm motility and protein tyrosine phosphorylation.

Metabolic Substrates Exhibit Differential Effects on Functional Parameters of Mouse Sperm Capacitation1

“…4A). However, sorbitol did not support capacitation-dependent tyrosine phosphorylation, even though sorbitol dehydrogenase present in mouse sperm flagella [27] should convert this monosaccharide to fructose.…”

“…Glucose (2.78 mM), lactate (21.4 mM), and pyruvate (0.33 mM) were initially tested at the concentrations found in HTF complete medium [42]. Other substrates were tested at concentrations shown previously to support sperm motility and other aspects of capacitation, including 5 mM mannose, 5 mM fructose, 5 mM sorbitol, 5 mM hydroxybutyrate, and 10 mM citrate [14,[25][26][27][53][54][55]. We also tested glucose, lactate, pyruvate, and citrate at 5 mM but found that changing the concentration did not have significant effects on the sperm motility parameters described below (data not shown).…”

“…Sperm capacitation is correlated with the tyrosine phosphorylation of a distinct subset of proteins [56], previously reported to occur at highest levels in the presence of glucose [27,57]. We incubated sperm from individual mice or from pools of two to three mice (to simultaneously assess the effect of all single substrates on the sperm population) for 2 h in HTF medium with single substrates and examined tyrosine phosphorylation patterns by Western blot analysis using the phosphotyrosine-specific antibody 4G10.…”

“…Human sperm also appear to obtain a significant proportion of their ATP from glycolysis [14,22]. Nevertheless, reports conflict regarding the maintenance of ATP levels and motility when mouse or human sperm are incubated in the absence of glycolysable substrates [14,15,[22][23][24][25][26][27][28].…”

Identification of a truncated kinase suppressor of Ras 2 mRNA in sperm

“…Sperm were collected as previously described [17]. Briefly, the caudal epididymis was minced and the sperm were allowed to swim out in phosphate buffered saline (PBS).…”