Does advancing male age influence the expression levels and localisation patterns of phospholipase C zeta (PLCζ) in human sperm?

Socio-economic factors have led to an increasing trend for couples to delay parenthood. However, advancing age exerts detrimental effects upon gametes which can have serious consequences upon embryo viability. While such effects are well documented for the oocyte, relatively little is known with regard to the sperm. One fundamental role of sperm is to activate the oocyte at fertilisation, a process initiated by phospholipase C zeta (PLCζ), a sperm-specific protein. While PLCζ deficiency can lead to oocyte activation deficiency and infertility, it is currently unknown whether the expression or function of PLCζ is compromised by advancing male age. Here, we evaluate sperm motility and the proportion of sperm expressing PLCζ in 71 males (22–54 years; 44 fertile controls and 27 infertile patients), along with total levels and localisation patterns of PLCζ within the sperm head. Three different statistical approaches were deployed with male age considered both as a categorical and a continuous factor. While progressive motility was negatively correlated with male age, all three statistical models concurred that no PLCζ–related parameter was associated with male age, suggesting that advancing male age is unlikely to cause problems in terms of the sperm’s fundamental ability to activate an oocyt

Oocyte activation and fertilisation: crucial contributors from the sperm and oocyte

This chapter intends to summarise the importance of sperm- and oocyte-derived factors in the processes of sperm-oocyte binding and oocyte activation. First, we describe the initial interaction between sperm and the zona pellucida, with particular regard to acrosome exocytosis. We then describe how sperm and oocyte membranes fuse, with special reference to the discovery of the sperm protein IZUMO1 and its interaction with the oocyte membrane receptor JUNO. We then focus specifically upon oocyte activation, the fundamental process by which the oocyte is alleviated from metaphase-II arrest by a sperm-soluble factor. The identity of this sperm factor has been the source of much debate recently although mounting evidence, from several different laboratories, provides strong support for phospholipase C ζ (PLCζ), a sperm-specific phospholipase. Herein, we discuss the evidence in support of PLCζ and evaluate the potential role of other candidate proteins, such as post-acrosomal WWP-binding domain protein (PAWP/WBP2NL). Since the cascade of downstream events triggered by the sperm-borne oocyte activation factor heavily relies upon specialised cellular machinery within the oocyte, we also discuss the critical role of oocyte-borne factors, such as the inositol trisphosphate receptor (IP3R), protein kinase C (PKC), store-operated calcium entry (SOCE) and calcium/calmodulin-dependent protein kinase II (CaMKII), during the process of oocyte activation. In order to place the implications of these various factors and processes into a clinical context, we proceed to describe their potential association with oocyte activation failure and discuss how clinical techniques such as the in vitro maturation of oocytes may affect oocyte activation ability. Finally, we contemplate the role of artificial oocyte activating agents in the clinical rescue of oocyte activation deficiency and discuss options for more endogenous alternatives.</p

Phospholipase C zeta and male infertility: clinical update and topical developments

The development of a mammalian embryo is initiated by a sequence of molecular events collectively referred to as ‘oocyte activation’ and regulated by the release of intracellular calcium in the ooplasm. Over the last decade, phospholipase C zeta (PLCζ), a sperm protein introduced into the oocyte upon gamete fusion, has gained almost universal acceptance as the protein factor responsible for initiating oocyte activation. A large body of consistent and reproducible evidence, from both biochemical and clinical settings, confers support for the role of PLCζ in this fundamental biological context, which has significant ramifications for the management of human male infertility. Oocyte activation deficiency (OAD) and total fertilisation failure (TFF) are known causes of infertility and have both been linked to abnormalities in the structure, expression, and localisation pattern of PLCζ in human sperm. Assisted oocyte activators (AOAs) represent the only therapeutic option available for OAD at present, although these agents have been the source of much debate recently, particularly with regard to their potential epigenetic effects upon the embryo. Consequently, there is much interest in the deployment of sensitive PLCζ assays as prognostic/diagnostic tests and human recombinant PLCζ protein as an alternative form of therapy. Although PLCζ deficiency has been directly linked to a cohort of infertile cases, we have yet to identify the specific causal mechanisms involved. While two genetic mutations have been identified which link defective PLCζ protein to an infertile phenotype, both were observed in the same patient, and have yet to be described in other patients. Consequently, some researchers are investigating the possibility that genetic variations in the form of single nucleotide polymorphisms (SNPs) could provide some explanation, especially since &gt;6000 SNPs have been identified in the PLCζ gene. As yet, however, there is no consistent data to suggest that any of these SNPs influence the functional ability of PLCζ. Other laboratories appear to be focusing upon the PLCζ promoter, which is bi-directional and shared with the actin filament capping muscle Z-line alpha 3 gene (CAPZA3), or seeking to identify interacting proteins within the ooplasm. The aim of this review is to provide a synopsis of recent progress in the application of PLCζ in diagnostic and therapeutic medicine, to discuss our current understanding of how the functional ability of PLCζ might be controlled, and thus how PLCζ deficiency might arise, and finally, to consider the potential implications of alternative sperm protein candidates, such as post-acrosomal WW-domain binding protein (PAWP), which has caused much debate and confusion in the field over the last few years

Oocyte activation and fertilisation: crucial contributors from the sperm and oocyte

This chapter intends to summarise the importance of sperm- and oocyte-derived factors in the processes of sperm-oocyte binding and oocyte activation. First, we describe the initial interaction between sperm and the zona pellucida, with particular regard to acrosome exocytosis. We then describe how sperm and oocyte membranes fuse, with special reference to the discovery of the sperm protein IZUMO1 and its interaction with the oocyte membrane receptor JUNO. We then focus specifically upon oocyte activation, the fundamental process by which the oocyte is alleviated from metaphase-II arrest by a sperm-soluble factor. The identity of this sperm factor has been the source of much debate recently although mounting evidence, from several different laboratories, provides strong support for phospholipase C ζ (PLCζ), a sperm-specific phospholipase. Herein, we discuss the evidence in support of PLCζ and evaluate the potential role of other candidate proteins, such as post-acrosomal WWP-binding domain protein (PAWP/WBP2NL). Since the cascade of downstream events triggered by the sperm-borne oocyte activation factor heavily relies upon specialised cellular machinery within the oocyte, we also discuss the critical role of oocyte-borne factors, such as the inositol trisphosphate receptor (IP3R), protein kinase C (PKC), store-operated calcium entry (SOCE) and calcium/calmodulin-dependent protein kinase II (CaMKII), during the process of oocyte activation. In order to place the implications of these various factors and processes into a clinical context, we proceed to describe their potential association with oocyte activation failure and discuss how clinical techniques such as the in vitro maturation of oocytes may affect oocyte activation ability. Finally, we contemplate the role of artificial oocyte activating agents in the clinical rescue of oocyte activation deficiency and discuss options for more endogenous alternatives.</p

Oocyte activation deficiency: a role for an oocyte contribution?

Infertility affects between 10 and 16% of couples worldwide. Twenty to 30% of cases of infertility are due to a male factor, 20-35% to a female factor, and 25-40% are due to both male and female factors. In ∼10-25% of cases, the precise underlying cause remains unclear. IVF or ICSI followed by embryo transfer can be very appropriate treatment options in cases of female tubal damage, ovulatory failure or male-factor infertility. While the use of IVF has been reported to be suitable for many infertile couples, normal IVF cycles can fail in some cases. While ICSI can represent a powerful alternative in cases of IVF failure, complete fertilization failure can still occur in 1-5% of ICSI cycles. This can be due to a variety of factors and while commonly attributed to deficiency of sperm factors, it is very likely that abnormalities in crucial oocyte factors could also play a key role.A critical literature review using PubMed was performed between April 2014 and July 2015 targeting studies concerning sperm and oocyte factors that could account for oocyte activation deficiency, and including studies of in vitro oocyte maturation in human oocytes, and animal models.Accumulating evidence indicates that phospholipase C zeta (PLCζ) is the sperm oocyte activation factor, although recent studies claim that another sperm protein known as post-acrosomal WWP-binding domain protein could also play a significant role in the activation of oocytes. The present review discusses our current understanding of these two proteins but emphasizes that defects in the molecular machinery within the oocyte that interacts with such sperm proteins may also represent an underlying cause of fertilization failure and infertility, especially in cases where there is no obvious indication for sperm deficiency. Abnormalities in such mechanisms are highly likely to exert influence over the pulsatile release of calcium within the ooplasm, the critical signal that controls oocyte activation events. These molecular targets within the oocyte are rarely, if ever, considered clinically. We therefore recommend that future diagnostic assays should be developed to consider the inositol triphosphate receptor, protein kinase C, proteins associated with stored operated calcium entry calcium/calmodulin-dependent protein kinase II and mitogen-activated protein kinase. Development of such assays would represent a significant step forward in the diagnosis of oocyte activation deficiency and may identify a series of potential therapeutic targets.The present review provides a general overview of how a combination of sperm and oocyte factors can underlie oocyte activation deficiency, but pays particular attention to the less appreciated role of the oocyte. Enhanced research within this realm is much warranted and may establish new approaches for the diagnosis and treatment of infertility

Identification of novel mutations in PLCZ1 in two patients with fertilization failure after ICSI

Study question Are abnormalities in the phospholipase C zeta (PLCZ1) gene responsible for failed fertilization after ICSI? Study answer PLCZ1 mutational screening in patients with a history of failed or low fertilization after ICSI resulted in the identification of three mutations in two patients.</p