Capacitation status of activated bovine sperm cultured in media containing methyl-β-cyclodextrin affects the acrosome reaction and fertility

Effect of cholesterol-loaded cyclodextrin treatment of bovine sperm on capacitation timing

Pre-loading bovine sperm with cholesterol prior to freezing is known to increase cryosurvival, though the timing of capacitation in these sperm has not been evaluated. The objective of this study was to determine if there is a potential delay in capacitation timing in these sperm due to the increased cholesterol content. Flow cytometric evaluation was utilized to assess viability, and stain technology to assess acrosome intactness (Propidium Iodide/FITC-PNA), intracellular calcium levels (Propidium Iodide/FLUO 3-AM) and membrane fluidity (Merocyanine 540/YO-PRO-1). Cholesterol-loaded cyclodextrin (CLC) (2 mg/mL) improved post-thaw viability to 61% from 45% in control sperm (p < .05). The addition of ionomycin (0.05 mM) induced capacitation in sperm by 1 h, resulting in increased intracellular calcium and increased acrosome reaction, and consequently viability loss by 3 h. Treatment with CLC significantly decreased membrane fluidity in sperm (p < .05). In conclusion, CLC-treated sperm required 1 h more to capacitate when compared with non-treated sperm based on percentage of live cells with high membrane disorder (p < .05). Increased cryosurvival and viability over time was observed, but longer time to capacitate may hinder fertilization capacity and/or require adjustments to timing of in vitro fertilization.

Sperm capacitation pretreatment positively impacts bovine intracytoplasmic sperm injection

The efficiency of intracytoplasmic sperm injection (ICSI) in bovines is low compared to other species due in part to inadequate egg activation and sperm nucleus decondensation after injection. We hypothesized that this low efficiency is due to the lack of complete sperm capacitation, so we evaluated the effects of isobutylmethylxanthine (IBMX) and methyl-β-cyclodextrin (MβCD) on bovine sperm capacitation and on the preimplantation developmental potential of bovine embryos generated by ICSI. Treatment with IBMX and MβCD decreased sperm viability (between 13-30%); nevertheless, 0.4 mM IBMX and 1 mM MβCD increased (p < 0.05) capacitation metrics-that is, acrosome exocytosis, intracellular calcium level, plasma membrane fluidity, and tyrosine phosphorylation-compared to the control. After ICSI, embryos injected with IBMX- and MβCD-treated sperm showed similar cleavage to the untreated group (range 82-88%). Pronucleus formation rate was higher with MβCD-pretreatment (54%) compared to the control group (25%), and blastocyst rate was significantly improved with MβCD-pretreatment (24%) compared to the IBMX (18%) and control (17%) groups. Importantly, embryo quality-as assessed by the total number of cells, cell allocation, and apoptotic cell index-was not affected by the sperm treatments. In conclusion, MβCD pretreatment of sperm improved the efficiency of blastocyst production in bovine ICSI.

Changes in Sperm Motility and Capacitation Induce Chromosomal Aberration of the Bovine Embryo following Intracytoplasmic Sperm Injection

Intracytoplasmic sperm injection (ICSI) has become the method of choice to treat human male infertility. One of the outstanding problems associated with this technique is our current lack of knowledge concerning the effect of sperm capacitation and motility upon the subsequent development of oocytes following ICSI. In the present study, we first examined the capacitation state of sperm exhibiting normal motility, along with sperm that had been activated, and examined the effect of reactive oxygen species (ROS) produced by these sperm types upon embryogenesis following bovine in vitro fertilization (IVF) and ICSI. Data showed that activated sperm reduced the chromosomal integrity of IVF/ICSI embryos at the blastocyst stage, while capacitated sperm produced ROS in capacitation media. Secondly, we treated sperm with carbonyl cyanide m-chlorophenyl hydrazine (CCCP), a chemical known to uncouple cell respiration within the mitochondria, and investigated the effect of this treatment upon blastocyst formation and chromosomal integrity at the blastocyst stage. Activated sperm in which the mitochondria had been treated with CCCP reduced levels of chromosomal aberration at the blastocyst stage following ICSI, by reducing mitochondrial activity in activated sperm. In conclusion, these findings suggest that capacitated sperm exhibiting activated motility induced chromosomal aberration during development to the blastocyst stage following ICSI. The injection of sperm exhibiting normal motility, or activated sperm in which mitochondrial activity had been reduced, improved the quality of ICSI-derived embryos. Therefore, the selection of sperm exhibiting progressive motility may not always be better for early embryo development and fetal growth following human ICSI, and that the use of a bovine model may contribute to a deeper understanding of sperm selection for human ICSI embryo development.

Lipid rafts: keys to sperm maturation, fertilization, and early embryogenesis

Cell membranes are composed of many different lipids and protein receptors, which are important for regulating intracellular functions and cell signaling. To orchestrate these activities, the cell membrane is compartmentalized into microdomains that are stably or transiently formed. These compartments are called "lipid rafts". In gamete cells that lack gene transcription, distribution of lipids and proteins on these lipid rafts is focused during changes in their structure and functions such as starting flagella movement and membrane fusion. In this paper, we describe the role of lipid rafts in gamete maturation, fertilization, and early embryogenesis.