Enhancement of mouse sperm motility by the PI3-kinase inhibitor LY294002 does not result in toxic effects on preimplantation embryo development

Breakthroughs in the Use of Inositols for Assisted Reproductive Treatment (ART)

It is well known that myo-inositol (MI) and D-chiro-inositol (DCI) are insulin-sensitizing agents, and MI is of proven utility in polycystic ovary syndrome (PCOS). In addition, MI plays a pivotal role in the physiology of reproduction, and has beneficial effects on the development of oocytes, spermatozoa, and embryos. By contrast, DCI has little effect on spermatozoa, but high concentrations in the ovary can negatively affect the quality of oocytes and the blastocyst. Overall, the evidence in the literature supports the beneficial effects of MI in both female and male reproduction, warranting clinical use of MI in assisted reproductive treatment (ART).

The TCL1 function revisited focusing on metabolic requirements of stemness

The oncogenic ability of the T-cell leukemia/lymphoma 1 gene, TCL1, has captured the attention in the field of prolymphocytic T-cell and B-cell chronic leukemias for more than two decades. However, the finding that TCL1 is also expressed in totipotent cells of the mouse preimplantation embryos and that it is among the 10 genes, including the transcription factors Nanog, Oct4, Sox2, Tbx3, and Esrrb, that are required for maintaining the mitotic self-renewal state of embryonic stem cells, raises a great interest. In this review, we highlight newly acquired evidence pinpointing TCL1 as a crucial regulator of metabolic pathways that dictate somatic cell reprogramming toward pluripotency. In our opinion, this feature provides a relevant hint for reframing the role that this factor plays at early stages of mammalian embryo development and in tumorigenesis. Hence, the TCL1-dependent enhancement of serine/threonine AKT/PKB kinase activity favoring cell proliferation appears to be associated to the promotion of glucose transport and activation of glycolytic pathways. This is also consistent with the TCL1 ability to suppress mitochondrial biogenesis and oxygen consumption, downplaying the contribution of oxidative phosphorylation to energy metabolism. It thus appears that TCL1 masters the direction of energy metabolism toward the glycolytic pathway to meet a critical metabolic requirement that goes beyond the mere ATP production. For instance, the synthesis of glycolytic intermediates that are required for DNA synthesis likely represents the most pressing cellular need for both cleavage-stage embryos and rapidly proliferating tumor cells.

Protein kinase Akt2/PKBβ is involved in blastomere proliferation of preimplantation mouse embryos

Activation of Akt/Protein Kinase B (PKB) by phosphatidylinositol-3-kinase (PI3K) controls several cellular functions largely studied in mammalian cells, including preimplantation embryos. We previously showed that early mouse embryos inherit active Akt from oocytes and that the intracellular localization of this enzyme at the two-cell stage depends on the T-cell leukemia/lymphoma 1 oncogenic protein, Tcl1. We have now investigated whether Akt isoforms, namely Akt1, Akt2 and Akt3, exert a specific role in blastomere proliferation during preimplantation embryo development. We show that, in contrast to other Akt family members, Akt2 enters male and female pronuclei of mouse preimplantation embryos at the late one-cell stage and thereafter maintains a nuclear localization during later embryo cleavage stages. Depleting one-cell embryos of single Akt family members by microinjecting Akt isoform-specific antibodies into wild-type zygotes, we observed that: (a) Akt2 is necessary for normal embryo progression through cleavage stages; and (b) the specific nuclear targeting of Akt2 in two-cell embryos depends on Tcl1. Our results indicate that preimplantation mouse embryos have a peculiar regulation of blastomere proliferation based on the activity of the Akt/PKB family member Akt2, which is mediated by the oncogenic protein Tcl1. Both Akt2 and Tcl1 are essential for early blastomere proliferation and embryo development.

Myo-inositol and D-chiro-inositol (40:1) reverse histological and functional features of polycystic ovary syndrome in a mouse model

Mice exposed to continuous light undergo functional and histological changes that mimic those of human Polycystic Ovary Syndrome (PCOS). We herein induced the syndrome by exposing 30-day-old females to 10 weeks of permanent light. Ovarian morphology and histology, as well as reproductive parameters (time of observed pregnancy/delivery) were investigated. Ovaries of PCOS-modeled mice showed lack of tertiary follicles and corpora lutea, altered ovarian architecture, and increased thickness of the theca layer. When mice were returned to a normal light-dark regimen for 10 days, a slight, spontaneous improvement occurred, whereas a quick and almost complete recovery from PCOS signs and symptoms was obtained by treating animals with a daily supplementation of 420 mg/kg myo-inositol and D-chiro-inositol (MyoIns/DCIns) in a 40:1 molar ratio. Namely, ovaries from mice treated by this protocol recovered normal histological features and a proper ratio of theca/granulosa cell layer thickness (TGR), suggesting that the androgenic phenotype was efficiently reversed. Indeed, we identified TGR as a useful index of PCOS, as its increase in PCOS-modeled mice correlated linearly with reduced reproductive capability ( r = 0.75, p < 0.0001). Mice treated with a 40:1 formula regained low TGR values and faster recovery of their fertility, with a physiological delivery time after mating. On the other hand, a higher D-chiro-inositol treatment formula, such as MyoIns versus DCIns 5:1, was ineffective or even had a negative effect on clinical-pathological outcomes.

Technologies for the Production of Fertilizable Mammalian Oocytes

Women affected by ovarian pathologies or with cancer can usually preserve fertility by egg/embryo freezing. When oocyte retrieval is not feasible, the only option available is ovarian tissue cryopreservation and transplantation. The culture of follicles isolated from fresh or cryopreserved ovaries is considered still experimental, although this procedure is considered safer, because the risk of unintentional spreading of cancer cells eventually present in cryopreserved tissue is avoided. Animal and human small follicles can be cultured in vitro, but standardized protocols able to produce in vitro grown oocytes with the same developmental capacity of in vivo grown oocytes are not available yet. In fact, the different sizes of follicles and oocytes, the hormonal differences existing between mono- (e.g., human, goat, cow, and sheep) and poly-ovulatory (rodents and pig) species, and the incomplete identification of the mechanisms regulating the oocyte–follicle and follicle–ovary interrelationships affect the outcome of in vitro culture. From all these attempts, however, new ideas arise, and the goal of assuring the preservation of female reproductive potential appears a more realistic possibility. This review surveys and discusses advances and challenges of these technologies that, starting from a simple attempt, are now approaching the biosynthesis of a functional engineered ovary.

TLR signalling affects sperm mitochondrial function and motility via phosphatidylinositol 3-kinase and glycogen synthase kinase-3α

Infection in male and female genital tracts can lead to infertility. The underlying mechanisms of this process remain unclear. Toll-like receptors (TLRs) recognize conserved structures and respond to pathogens by initiating signals that activate inflammatory gene transcription. Here, we demonstrate that TLR activation in sperm reduces sperm motility via signalling through myeloid differentiation factor 88 (MyD88), phosphatidylinositol 3-kinase (PI3K), and glycogen synthase kinase (GSK)-3α. Upon TLR activation, phosphorylated forms of PI3K and GSK3α were detected in the mitochondria, and the mitochondrial membrane potential was impaired in sperm. In addition, mitochondrial ATP levels were decreased after TLR agonist stimulation. Furthermore, blocking PI3K or GSK3α activation abrogated these effects and reversed the TLR-induced reduction in sperm motility. These results identify a previously unrecognized TLR signalling pathway that leads to dysfunctional sperm mitochondria, which reduce sperm motility. Our study reveals a novel mechanism by which pathogenic infection affects sperm motility and possibly leads to infertility.

Phosphorylated AKT preserves stallion sperm viability and motility by inhibiting caspases 3 and 7

AKT, also referred to as protein kinase B (PKB or RAC), plays a critical role in controlling cell survival and apoptosis. To gain insights into the mechanisms regulating sperm survival after ejaculation, the role of AKT was investigated in stallion spermatozoa using a specific inhibitor and a phosphoflow approach. Stallion spermatozoa were washed and incubated in Biggers–Whitten–Whittingham medium, supplemented with 1% polyvinyl alcohol (PVA) in the presence of 0 (vehicle), 10, 20 or 30 μM SH5, an AKT inhibitor. SH5 treatment reduced the percentage of sperm displaying AKT phosphorylation, with inhibition reaching a maximum after 1 h of incubation. This decrease in phosphorylation was attributable to either dephosphorylation or suppression of the active phosphorylation pathway. Stallion spermatozoa spontaneously dephosphorylated during in vitro incubation, resulting in a lack of a difference in AKT phosphorylation between the SH5-treated sperm and the control after 4 h of incubation. AKT inhibition decreased the proportion of motile spermatozoa (total and progressive) and the sperm velocity. Similarly, AKT inhibition reduced membrane integrity, leading to increased membrane permeability and reduced the mitochondrial membrane potential concomitantly with activation of caspases 3 and 7. However, the percentage of spermatozoa exhibiting oxidative stress, the production of mitochondrial superoxide radicals, DNA oxidation and DNA fragmentation were not affected by AKT inhibition. It is concluded that AKT maintains the membrane integrity of ejaculated stallion spermatozoa, presumably by inhibiting caspases 3 and 7, which prevents the progression of spermatozoa to an incomplete form of apoptosis.

Free Spanish abstract

A Spanish translation of this abstract is freely available at http://www.reproduction-online.org/content/148/2/221/suppl/DC1.

Mammalian Fused is essential for sperm head shaping and periaxonemal structure formation during spermatogenesis

During mammalian spermatogenesis, the diploid spermatogonia mature into haploid spermatozoa through a highly controlled process of mitosis, meiosis and post-meiotic morphological remodeling (spermiogenesis). Despite important progress made in this area, the molecular mechanisms underpinning this transformation are poorly understood. Our analysis of the expression and function of the putative serine-threonine kinase Fused (Fu) provides critical insight into key steps in spermatogenesis. In this report, we demonstrate that conditional inactivation of Fu in male germ cells results in infertility due to diminished sperm count, abnormal head shaping, decapitation and motility defects of the sperm. Interestingly, mutant flagellar axonemes are intact but exhibit altered periaxonemal structures that affect motility. These data suggest that Fu plays a central role in shaping the sperm head and controlling the organization of the periaxonemal structures in the flagellum. We show that Fu localizes to multiple tubulin-containing or microtubule-organizing structures, including the manchette and the acrosome-acroplaxome complex that are involved in spermatid head shaping. In addition, Fu interacts with the outer dense fiber protein Odf1, a major component of the periaxonemal structures in the sperm flagellum, and Kif27, which is detected in the manchette. We propose that disrupted Fu function in these structures underlies the head and flagellar defects in Fu-deficient sperm. Since a majority of human male infertility syndromes stem from reduced sperm motility and structural defects, uncovering Fu׳s role in spermiogenesis provides new insight into the causes of sterility and the biology of reproduction.

Glimepiride induces proliferation and differentiation of rat osteoblasts via the PI3-kinase/Akt pathway

Glimepiride is a third-generation sulfonylurea agent and is widely used in the treatment of type 2 diabetes mellitus. In addition to the stimulatory effects on pancreatic insulin secretion, glimepiride has also been reported to have extrapancreatic functions including activation of PI3 kinase (PI3K) and Akt in rat adipocytes and skeletal muscle. PI3-kinase and Akt are important signaling molecules in the regulation of proliferation and differentiation in various cells. This study investigated the actions of glimepiride in rat osteoblasts and the role of PI3K/Akt pathway. Cell proliferation was determined by measuring absorbance at 550 nm. Supernatant assay was used for measuring alkaline phosphatase activity. Western blot analysis was used for determining collagen I, insulin receptor substrate-1/2, PI3K/Akt, and endothelial nitric oxide synthase expression. We found that glimepiride significantly enhanced proliferation and differentiation of osteoblasts and led to activation of several key signaling molecules including insulin receptor substrate-1/2, PI3K/Akt, and endothelial nitric oxide synthase. Furthermore, a specific inhibitor of PI3K abolished the stimulatory effects of glimepiride on proliferation and differentiation. Taken together, these observations provide concrete evidence that glimepiride activates the PI3K/Akt pathway; and this activation is likely required for glimepiride to stimulate proliferation and differentiation of rat osteoblasts.

Role and regulation of PI3K in sperm capacitation and the acrosome reaction

Mammalian spermatozoa undergo several signaling and biochemical transformations in the female genital tract, collectively called capacitation. The capacitated spermatozoon binds to the egg zona pellucida, where it undergoes the acrosome reaction (AR), a process enabling it to penetrate and fertilize the egg. Actin polymerization occurs in sperm capacitation and depolymerization prior to the AR. In this review we describe the possible role and regulation of PI3K in sperm capacitation and the acrosome reaction. We claim that PI3K is activated by protein kinase A and suppressed by protein kinase C. Only partial activation of PI3K is seen during the capacitation time, however towards the end of incubation, full activation is observed. Actin polymerization during capacitation is independent on PI3K activity, suggesting that the enzyme is not involved in sperm capacitation. However, the full activation of PI3K towards the end of the capacitation suggests that it might mediate the AR, as indeed was found.

Phosphatidylinositol 3-kinase pathway regulates sperm viability but not capacitation on boar spermatozoa

Phosphatidylinositol 3-kinase (PI3-K) plays an important role in cell survival in somatic cells and recent data pointed out a role for this kinase in sperm capacitation and acrosome reaction (AR). This study was undertaken to evaluate the role of PI3-K pathway on porcine spermatozoa capacitation, AR, and viability using two unrelated PI3-K inhibitors, LY294002 and wortmannin. In boar spermatozoa, we have identified the presence of PDK1, PKB/Akt, and PTEN, three of the main key components of the PI3-K pathway. Incubation of boar sperm in a capacitating medium (TCM) caused a significant increase in the percentage of capacitated (25 +/- 2 to 34 +/- 1% P < 0.05, n = 6) and acrosome reacted (1 +/- 1 to 11 +/- 1% P < 0.01, n = 6) spermatozoa compared with sperm in basal medium (TBM). Inhibition of PI3-K did affect neither the capacitation status nor AR nor protein p32 tyrosine phosphorylation of boar spermatozoa incubated in TBM or TCM. Boar sperm viability in TBM was significantly decreased by 40 and 20% after pretreatment with LY294002 or wortmannin, respectively. Similar results were observed after incubation of boar spermatozoa in TCM. Treatment of boar spermatozoa with the analog of cAMP, 8Br-cAMP significantly prevented the reduction on sperm viability. Our results provide evidence for an important role of the PI3-K pathway in the regulation of boar sperm viability and suggests that other signaling pathways different from PI3-K must be activated downstream of cAMP to contribute to regulation of sperm viability. Finally, in our conditions the PI3-K pathway seems not related with boar sperm capacitation or AR.