Abstract
Before a mature spermatozoon is able to fertilise the oocyte, it must first traverse the female reproductive tract, through obstacles such as highly viscous mucus. As the sperm is thought to be transcriptionally and translationally inactive, it must rely on cues from its external environment in order to alter its function. Membrane-localised ion channels are fundamental in this process, where activation/inhibition of the channel results in modification of intracellular ion concentrations, resulting in change in behaviour of the sperm, in particular sperm motility. The sperm-specific calciumpermeable cation channel CatSper is necessary for initiation of hyperactive motility in murine spermatozoa, and was previously identified to be disrupted in sperm from an infertile patient. However, little is known about the incidence of CatSper defects in the IVF (in-vitro fertilisation) patient population.In the present study two groups of patients, 1) IVF patients and 2) IVF or ICSI (intracytoplasmic sperm injection) patients who had experienced a cycle of low/failed fertilisation were screened for defects in calcium regulation and particularly CatSper function. In a novel finding, one patient from each of these groups were found to have normal semen analysis, yet sperm were found to have a complete absence of calcium response to progesterone, thus indicating CatSper dysfunction.
This study also investigated the effect of cryopreservation on human sperm function, with particular reference to calcium regulation. Cryopreservation was able to significantly diminish the calcium response to progesterone, basal hyperactivation and penetration into viscous media. The assay identified a subset of donors who were particularly susceptible to cryodamage, which may be of significant clinical relevance, due to the common use of cryopreservation of semen in ART. The present study also describes the novel use of single cell calcium imaging as a sensitive screening tool for calcium defects in healthy volunteer donors, IVF and ICSI patients, thus enabling study of sperm samples of low concentration, particularly relevant for male infertility patients exhibiting oligozoospermia.
| Date of Award | 2016 |
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| Original language | English |
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| Supervisor | Christopher Barratt (Supervisor) & Sarah Martins Da Silva (Supervisor) |