Human sperm ion channel (dys)function:implications for fertilization

BACKGROUND: Intensive research on sperm ion channels has identified members of several ion channel families in both mouse and human sperm. Gene knock-out studies have unequivocally demonstrated the importance of the calcium and potassium conductances in sperm for fertility. In both species, the calcium current is carried by the highly complex cation channel of sperm (CatSper). In mouse sperm, the potassium current has been conclusively shown to be carried by a channel consisting of the pore forming subunit SLO3 and auxiliary subunit leucine-rich repeat-containing 52 (LRRC52). However, in human sperm it is controversial whether the pore forming subunit of the channel is composed of SLO3 and/or SLO1. Deciphering the role of the proton-specific Hv1 channel is more challenging as it is only expressed in human sperm. However, definitive evidence for a role in, and importance for, human fertility can only be determined through studies using clinical samples.OBJECTIVE AND RATIONALE: This review aims to provide insight into the role of sperm ion channels in human fertilization as evidenced from recent studies of sperm from infertile men. We also summarize the key discoveries from mouse ion channel knock-out models and contrast the properties of mouse and human CatSper and potassium currents. We detail the evidence for, and consequences of, defective ion channels in human sperm and discuss hypotheses to explain how defects arise and why affected sperm have impaired fertilization potential.SEARCH METHODS: Relevant studies were identified using PubMed and were limited to ion channels that have been characterized in mouse and human sperm. Additional notable examples from other species are included as appropriate.OUTCOMES: There are now well-documented fundamental differences between the properties of CatSper and potassium channel currents in mouse and human sperm. However, in both species, sperm lacking either channel cannot fertilize in vivo and CatSper-null sperm also fail to fertilize at IVF. Sperm-lacking potassium currents are capable of fertilizing at IVF, albeit at a much lower rate. However, additional complex and heterogeneous ion channel dysfunction has been reported in sperm from infertile men, the causes of which are unknown. Similarly, the nature of the functional impairment of affected patient sperm remains elusive. There are no reports of studies of Hv1 in human sperm from infertile men.WIDER IMPLICATIONS: Recent studies using sperm from infertile men have given new insight and critical evidence supporting the supposition that calcium and potassium conductances are essential for human fertility. However, it should be highlighted that many fundamental questions remain regarding the nature of molecular and functional defects in sperm with dysfunctional ion channels. The development and application of advanced technologies remains a necessity to progress basic and clinical research in this area, with the aim of providing effective screening methodologies to identify and develop treatments for affected men in order to help prevent failed ART cycles. Conversely, development of drugs that block calcium and/or potassium conductances in sperm is a plausible strategy for producing sperm-specific contraceptives.</p

Research Funding for Male Reproductive Health and Infertility in the UK and USA [2016 – 2019]

There is a paucity of data on research funding levels for male reproductive health (MRH). We investigated the research funding for MRH and infertility by examining publicly accessible web-databases from the UK and USA government funding agencies. Information on the funding was collected from the UKRI-GTR, the NIHR’s Open Data Summary, and the USA’s NIH RePORT web-databases. Funded projects between January 2016 and December 2019 were recorded and funding support was divided into three research categories: (i) male-based; (ii) female-based; and (iii) not-specified. Between January 2016 and December 2019, UK agencies awarded a total of £11,767,190 to 18 projects for male-based research and £29,850,945 to 40 projects for female-based research. There was no statistically significant difference in the median funding grant awarded within the male-based and female-based categories (p = 0.56, W = 392). The USA NIH funded 76 projects totalling $59,257,746 for male-based research and 99 projects totalling$83,272,898 for female-based research Again, there was no statistically significant difference in the median funding grant awarded between the two research categories (p = 0.83, W = 3834). This is the first study examining funding granted by main government research agencies from the UK and USA for MRH. This results should stimulate further discussion of the challenges of tackling male infertility and reproductive health disorders and formulating appropriate investment strategies.</p

Biodiversity patterns and conservation of the coastal forests of Eastern Africa

The earth is in the midst of a sixth major extinction crisis with biodiversity highly threatened by climate change at global scales. Biodiversity is crucial to humans due to the ecosystem functioning and services it provides, and therefore the conservation of biodiversity is paramount to human prosperity in in the future. This PhD thesis uses amphibians to examine biodiversity patterns across the Coastal Forests of Eastern Africa (CFEA), a global biodiversity hotspot. The CFEA comprises of a network of tiny fragmented forest patches thought to be the remnants of a once widespread tropical forest that spanned across tropical Africa from West to East prior to major tectonic activity in the Miocene. The gradual aridification of the African continent since then, combined with significant climate and sea level oscillations during the Pliocene and Pleistocene contributed to the natural fragmentation of the CFEA, but human impacts have severely accelerated the pace of forest loss. The work in this thesis integrates field work, taxonomy, morphology, molecular techniques and spatial data to measure biodiversity across the CFEA, explain its distribution and provide a conceptual framework in which this data can be usefully applied for future conservation efforts. A broad scale DNA barcoding project forms the basis of all work in the thesis, assimilating museum specimens and archived spatial records with newly collected data from recent fieldwork to create the most thorough inventory of the CFEA amphibians currently known. Chapter 1 focuses on the use of Next Generation Sequencing (NGS) data for five widespread species clades to estimate phylogeny and population structure, genetic distances between populations, and explain these patterns using long-term environmental data. Chapter 2 maps the spatial distribution of evolutionary history measured from phylogenetic branch lengths for multiple intraspecific lineages within species, highlighting places which appear to be refugia and examining their environmental correlates and conservation. Chapter 3 uses close to the full assemblage of Tanzania and Kenya (55 species) to categorize the types of endemism present, distinguishing areas that are ‘museums’ supporting ancient diversity (paleo-endemism) from ‘cradles’ that support recently evolved diversity (neo-endemism). Chapter 4 combines morphological, genetic and spatial data to describe a new endemic species of treefrog, Hyperolius ruvuensis, from a highly threatened reserve in coastal Tanzania. A synthesis chapter summarises the work in the thesis and outlines new directions for CFEA conservation

Sperm function and the diagnosis of male infertility

This D.Sc. presents a selected series of publications, focusing on the understanding and diagnosis of male infertility. Twenty five articles are presented from work spanning 1990-2018. Experiments assessing the predictive/diagnostic potential of a basic semen analysis and kinematic parameters of sperm motility in the context on in vivo conception are described as are studies aimed at improving the understanding of sperm function. This knowledge has been used to potentially develop new diagnostic tests for use at home and in the laboratory. A consistent theme has been involvement with national and international authorities to use evidence based information for making recommendations for both the diagnosis and treatment of the sub fertile male

Complex CatSper-dependent and independent [Ca2⁺]i signalling in human spermatozoa induced by follicular fluid

STUDY QUESTION: Does progesterone in human follicular fluid (hFF) activate CatSper and do other components of hFF modulate this effect and/or contribute separately to hFF-induced Ca2+ signaling?SUMMARY ANSWER: hFF potently stimulates CatSper and increases [Ca2+]i, primarily due to high concentrations of progesterone, however,other components of hFF also contribute to [Ca2+]i signaling, including modulation of CatSper channel activity and inhibition of [Ca2+]i oscillations.WHAT IS KNOWN ALREADY: CatSper, the principal Ca2+ channel in spermatozoa, is progesterone-sensitive and essential for fertility. Both hFF and progesterone, which is present in hFF, influence sperm function and increase their [Ca2+]i.STUDY DESIGN, SIZE, DURATION: This basic medical research study used semen samples from &gt;40 donors and hFF from &gt;50 patients who were undergoing surgical oocyte retrieval for IVF/ICSI.PARTICIPANTS/MATERIALS, SETTING, METHODS: Semen donors and patients were recruited in accordance with local ethics approval (13/ES/0091) from the East of Scotland Research Ethics Service REC1. Activities of CatSper and KSper were assessed by patch clamp electrophysiology. Sperm [Ca2+]i responses were examined in sperm populations and single cells. Computer-assisted sperm analysis (CASA) parameters and penetration into viscous media were used to assess functional effects.MAIN RESULTS AND THE ROLE OF CHANCE: hFF and progesterone significantly potentiated CatSper currents. Under quasiphysiologicalconditions, hFF (up to 50%) failed to alter membrane K+ conductance or current reversal potential. hFF and progesterone (at an equivalent concentration) stimulated similar biphasic [Ca2+]i signals both in sperm populations and single cells. At a high hFF concentration (10%), the sustained (plateau) component of the [Ca2+]i signal was consistently greater than that induced by progesterone alone. In single cell recordings, 1% hFF-induced [Ca2+]i oscillations similarly to progesterone but with 10% hFF generation of [Ca2+]i oscillations was suppressed. After treatment to ‘strip’ lipid-derived mediators, hFF failed to significantly stimulate CatSper currents but induced small [Ca2+]i responsesthat were greater than those induced by the equivalent concentration of progesterone after stripping. Similar [Ca2+]i responses were observed when sperm pretreated with 3 μM progesterone (to desensitize progesterone responses) were stimulated with hFF or stripped hFF. hFF stimulated viscous media penetration and was more effective than the equivalent does of progesterone.LARGE SCALE DATA: N/A.LIMITATIONS, REASONS FOR CAUTION: This was an in vitro study. Caution must be taken when extrapolating these results in vivo.WIDER IMPLICATIONS OF THE FINDINGS: This study directly demonstrates that hFF activates CatSper and establishes that the biologically important effects of hFF reflect, at least in part, action on this channel, primarily via progesterone. However, these experiments also demonstrate that other components of hFF both contribute to the [Ca2+]i signal and modulate the activation of CatSper. Simple in vitro experiments performed out of the context of the complex in vivo environment need to be interpreted with caution

Behavioural switching during oscillations of intracellular Ca²⁺ concentration in free-swimming human sperm

A human sperm must swim to the egg to fertilise it. To do this the sperm uses different types of swimming (behaviours) as they are needed. When we watch sperm swimming we see that they regularly change behaviour, sometimes repeatedly switching between two different types. Calcium ions inside cells are crucial in controlling many cell functions and in sperm they play a key role in regulating their behaviour. Here we have measured the concentration of calcium ions inside swimming human sperm. We found that in 12/35 (34%) of the cells we assessed, the concentration of calcium changed repeatedly, averaging more than one cycle of rise and fall per minute. These changes in the concentration of calcium ions occurred as the sperm switched swimming stroke, suggesting that oscillation of calcium concentration is involved in controlling the switching of sperm behaviour. Impaired sperm motility is an important cause of subfertility in men. Understanding how sperm behaviour is controlled will allow the development of treatments that can rescue the fertility of sperm with impaired motility.Fil: Torrezan Nitao, Elis. University of Birmingham; Reino UnidoFil: Guidobaldi, Héctor Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Centro de Biología Celular y Molecular; ArgentinaFil: Giojalas, Laura Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Centro de Biología Celular y Molecular; ArgentinaFil: Barratt, Christopher. University of Dundee; Reino UnidoFil: Publicover, Stephen. University of Birmingham; Reino Unid