Porcine sperm motility is regulated by serine phosphorylation of the glycogen synthase kinase-3α

Abstract

Sperm functions are critically controlled through the phosphorylation state of specific proteins. Glycogen synthase kinase-3 (GSK3) is a serine/threonine kinase with two different isoforms (a and b), the enzyme activity of which is inhibited by serine phosphorylation. Recent studies suggest that GSK3 is involved in the control of bovine sperm motility. Our aim was to investigate whether GSK3 is present in porcine spermatozoa and its role in the function of these cells. This work shows that both isoforms of GSK3 are present in whole cell lysates of porcine sperm and are phosphorylated on serine in spermatozoa stimulated with the cAMP analog, 8Br-cAMP. A parallel increase in serine phosphorylation of the isoform GSK3a, but not in the isoform GSK3b, is observed after treatments that also induce a significant increase in porcine sperm velocity parameters. Therefore, a significant positive correlation among straight-line velocity, circular velocity, average velocity, rapid-speed spermatozoa, and GSK3a serine phosphorylation levels exists. Inhibition of GSK3 activity by alsterpaullone leads to a significant increase in the percentage of rapid-and medium-speed spermatozoa as well as in all sperm velocity parameters and coefficients. Moreover, pretreatment of porcine spermatozoa with alsterpaullone significantly increased the percentage of capacitated porcine spermatozoa and presents no effect in the number of acrosome-reacted porcine spermatozoa. Our work suggests that the isoform GSK3a plays a negative role in the regulation of porcine sperm motility and points out the possibility that sperm motile quality might be modulated according the activity state of GSK3a. Reproduction (2007) 134 435-444

New insights into transduction pathways that regulate boar sperm function

“…The presence of GSK3 in spermatozoa was initially reported in humans [72] where only GSK3b was detected and simultaneously in bovine sperm by Somanath et al [73] where both isoforms were identified. In boar spermatozoa, both isoforms of GSK3 were identified by our group in 2007 [74]. In response to stimuli that induce the activation of the cAMP/PKA pathway in boar sperm, GSK3a and GSK3b isoforms are clearly phosphorylated in Ser21 and Ser9, respectively [74], indicating that PKA is an upstream regulator of GSK3 in boar spermatozoa.…”

“…In boar spermatozoa, both isoforms of GSK3 were identified by our group in 2007 [74]. In response to stimuli that induce the activation of the cAMP/PKA pathway in boar sperm, GSK3a and GSK3b isoforms are clearly phosphorylated in Ser21 and Ser9, respectively [74], indicating that PKA is an upstream regulator of GSK3 in boar spermatozoa. Furthermore, we have shown that GSK3 phosphorylation is totally dependent on PKA activity [66] and that is also downstream of the PKC and PI3K pathways [66].…”

“…A different signaling pathway involved in the control of GSK3 phosphorylation is PI3K, which through the regulation of cAMP levels lies upstream of PKA in boar sperm [66]. Studies aiming to elucidate the functional role of GSK3 phosphorylation in boar sperm motility reported a significant positive correlation between GSK3a inactivation and increases in the curvilinear velocity, straight linear velocity, and subsequently in the percentage of sperm showing rapid velocity [74]. Additionally, a pharmacologic approach confirmed a negative role of GSK3 on the regulation of boar spermatozoa motility as GSK3 enzymatic blockade caused a clear increase in the previously mentioned motility parameters [74].…”

“…Studies aiming to elucidate the functional role of GSK3 phosphorylation in boar sperm motility reported a significant positive correlation between GSK3a inactivation and increases in the curvilinear velocity, straight linear velocity, and subsequently in the percentage of sperm showing rapid velocity [74]. Additionally, a pharmacologic approach confirmed a negative role of GSK3 on the regulation of boar spermatozoa motility as GSK3 enzymatic blockade caused a clear increase in the previously mentioned motility parameters [74]. Besides motility, GSK3 is likely involved in the regulation of other functional processes of boar sperm such as capacitation [74].…”

Identification and regulation of glycogen synthase kinase-3 during bovine embryo development

“…Moreover, in germinal cells and in the bovine corpus luteum, an increase in the phosphorylation of GSK3 in response to agonists that elevate intracellular concentrations of cAMP has been demonstrated (Aparicio et al 2007, Roy et al 2009, showing the interaction of cAMP and GSK3 (Fang et al 2000). Lithium also interferes with another second messenger system, the inositol pathway causing selective reductions of PKC (Manji & Lenox 1999), which has been shown to phosphorylate and inactivate GSK3 mediating acentromeric spindle stabilization in mouse oocytes (Baluch & Capco 2008).…”