P-058 Defects in phospholipase C zeta cause polyspermy and low fertilization after conventional IVF: not just ICSI failure
Authors: Dai C , Che J , Zeng S , Wu H , Wu Y , Dai J , Cheng D , Wen Q , Gong F , Lu G , Lin G 
Published: June 2023

Abstract

Study question
How does sperm phospholipase C zeta (PLCζ) affect fertilization in conventional in vitro fertilization (cIVF)?

Summary answer
Absence of PLCζ causes polyspermy, and a decline in the proportion of sperm expressing PLCζ is correlated with a low fertilization rate (FR) after cIVF.

What is known already
PLCζ is a key sperm-borne factor that triggers Ca2+ oscillations and the subsequent oocyte activation following gamete fusion. Mutations in PLCZ1, the gene encoding PLCζ, cause male infertility and intra-cytoplasmic sperm injection (ICSI) fertilization failure; and PLCζ expression and localization patterns are significantly correlated with ICSI FR. However, few studies have been published on the relationship between PLCζ and cIVF, an insemination procedure involving several key events that are bypassed in ICSI, e.g., sperm-zona binding and penetration, as well as polyspermy blocking. It is possible that sperm PLCζ may affect fertilization in a different manner from that in ICSI.

Study design, size, duration
Sixty couples who underwent cIVF treatments were recruited from the Reproductive and Genetic Hospital of CITIC-Xiangya between February 2019 and January 2022.

Participants/materials, setting, methods
We performed whole-exome sequencing in two unrelated males who exhibited infertility and polyspermy in cIVF. Immunofluorescence staining and oocyte-activation testing were employed to evaluate the effects of the candidate variants on PLCζ protein. Subsequent PLCζ analysis was performed in additional 58 males who underwent cIVF. The Pearson correlation coefficient was performed to evaluate the relationships between PLCζ and FRs. The receiver operating characteristic curve and Youden’s index analysis were used to indicate the cutoff value.

Main results and the role of chance
We identified one previously reported and two novel PLCZ1 variants in two males that were associated with male infertility and polyspermy characterized by excessive sperm–zona binding and a delay in pronuclear (PN) formation. In vitro functional analyses revealed that virtually all sperm from patients lacked functional PLCζ and were thus unable to evoke the physiologic pattern of Ca2+ oscillations. ICSI with an artificial oocyte-activation treatment successfully rescued the polyspermic phenotype and resulted in a live birth. Subsequent PLCζ analysis were performed in additional 58 males, who were allocated to three groups according to fertilization outcomes: a multiple pronuclear (MPN) group (no. of PN ≥ 3, MPN rate ≥ 50%, n = 9) and low fertilization (LF, total FR ≤ 30%, n = 18) and normal fertilization groups (NF, 2PN ≥ 50%, 1PN + MPN &lt; 30%, n = 31). We found that the proportion of sperm that expressed PLCζ was positively correlated with both 2PN rate (P = 0.0005) and total FR (P = 0.0008) after cIVF, and that the optimal cutoff value below which males were likely to experience low FR (total FR ≤ 30%) after cIVF was 56.7% (area under the ROC curve, 0.705; P = 0.0176).

Limitations, reasons for caution
Precise mechanisms that underly the roles of PLCζ in cIVF outcomes are still uncovered. Follow-up studies with larger numbers of patients are required to validate the sensitivity, specificity, and accuracy of PLCζ as a diagnostic biomarker in cIVF outcomes.

Wider implications of the findings
Our study identified PLCZ1 as a novel causative gene of polyspermy in humans,highlighting the potential value of PLCζ as a fertility marker for cIVF outcomes.

Trial registration number
nor applicable