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Home / Equine Research Bank / Front Cell Dev Biol / Bicarbonate-Stimulated Membrane Reorganization in Stallion S...
Frontiers in cell and developmental biology2021; 9; 772254; doi: 10.3389/fcell.2021.772254

Bicarbonate-Stimulated Membrane Reorganization in Stallion Spermatozoa.

Abstract: Classical in vitro fertilization (IVF) is still poorly successful in horses. This lack of success is thought to be due primarily to inadequate capacitation of stallion spermatozoa under in vitro conditions. In species in which IVF is successful, bicarbonate, calcium, and albumin are considered the key components that enable a gradual reorganization of the sperm plasma membrane that allows the spermatozoa to undergo an acrosome reaction and fertilize the oocyte. The aim of this work was to comprehensively examine contributors to stallion sperm capacitation by investigating bicarbonate-induced membrane remodelling steps, and elucidating the contribution of cAMP signalling to these events. In the presence of capacitating media containing bicarbonate, a significant increase in plasma membrane fluidity was readily detected using merocyanine 540 staining in the majority of viable spermatozoa within 15 min of bicarbonate exposure. Specific inhibition of soluble adenylyl cyclase (sAC) in the presence of bicarbonate by LRE1 significantly reduced the number of viable sperm with high membrane fluidity. This suggests a vital role for sAC-mediated cAMP production in the regulation of membrane fluidity. Cryo-electron tomography of viable cells with high membrane fluidity revealed a range of membrane remodelling intermediates, including destabilized membranes and zones with close apposition of the plasma membrane and the outer acrosomal membrane. However, lipidomic analysis of equivalent viable spermatozoa with high membrane fluidity demonstrated that this phenomenon was neither accompanied by a gross change in the phospholipid composition of stallion sperm membranes nor detectable sterol efflux (p > 0.05). After an early increase in membrane fluidity, a significant and cAMP-dependent increase in viable sperm with phosphatidylserine (PS), but not phosphatidylethanolamine (PE) exposure was noted. While the events observed partly resemble findings from the in vitro capacitation of sperm from other mammalian species, the lack of cholesterol removal appears to be an equine-specific phenomenon. This research will assist in the development of a defined medium for the capacitation of stallion sperm and will facilitate progress toward a functional IVF protocol for horse gametes.
Copyright © 2021 Maitan, Bromfield, Hoogendijk, Leung, Zeev-Ben-Mordehai, van de Lest, Jansen, Leemans, Guimarães, Stout, Gadella and Henning.
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Publication Date: 2021-11-17 PubMed ID: 34869370PubMed Central: PMC8635755DOI: 10.3389/fcell.2021.772254Google Scholar: Lookup
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  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research article discusses a study focused on improving success rates of in vitro fertilization (IVF) in horses, specifically by investigating the role of bicarbonate in enhancing the capacitation of stallion spermatozoa. The authors observed that bicarbonate, along with a compound known as cAMP, could increase the fluidity of the sperm membrane, a vital step to facilitate sperm’s ability to fertilize the egg (oocyte).

Objective and Methodology

  • Species that have higher rates of successful IVF often involve conditions that facilitate a reorganization of the sperm plasma membrane. This change, which involves bicarbonate, calcium and albumin, enables sperm to undergo an acrosome reaction (a necessary process for fertilization).
  • The researchers in this study aimed to identify factors that contribute to stallion sperm capacitation. Specifically, they were investigating the role of bicarbonate in inducing membrane remodelling and the associated role of cAMP signalling.
  • To do so, the researchers observed the effects on spermatozoa when bicarbonate was added to capacitating media (a mix intended to mimic the environment found in female’s reproductive tract). They tracked changes in plasma membrane fluidity using a specific dye (merocyanine 540) and also targeted the inhibition of soluble adenylyl cyclase (sAC), an enzyme linked to cAMP production.

Critical Findings

  • A significant increase in plasma membrane fluidity was observed in the majority of viable spermatozoa within 15 minutes of bicarbonate exposure.
  • The inhibition of sAC in the presence of bicarbonate resulted in a significant reduction of viable sperm with high membrane fluidity. This indicated that sAC-mediated cAMP production plays a critical role in regulating membrane fluidity.
  • Cryo-electron tomography, a form of 3D imaging, revealed various states of membrane remodeling, including destabilized membranes and areas where the plasma membrane and outer acrosomal membrane were closely located.
  • However, lipidomic analysis (the study of lipids in biological samples) showed that bicarbonate exposure and its resultant increase in membrane fluidity did not significantly change the composition of the sperm’s phospholipid membrane.
  • Following an initial increase in membrane fluidity, a significant cAMP-dependent increase in viable sperm with exposure to a certain type of lipid (phosphatidylserine or PS) was noted.

Summary and Implications

  • Though some of the events mirror findings from sperm capacitation in other mammalian species, the lack of observable cholesterol removal from the sperm membrane under these conditions appears to be distinct to horses.
  • The findings suggest the essential role of bicarbonate and cAMP in achieving successful capacitation of stallion spermatozoa. This research could help in refining the medium used for the capacitation of stallion sperm and thus improving the success rate of equine IVF.

Cite This Article

APA
Maitan PP, Bromfield EG, Hoogendijk R, Leung MR, Zeev-Ben-Mordehai T, van de Lest CH, Jansen JWA, Leemans B, Guimarães JD, Stout TAE, Gadella BM, Henning H. (2021). Bicarbonate-Stimulated Membrane Reorganization in Stallion Spermatozoa. Front Cell Dev Biol, 9, 772254. https://doi.org/10.3389/fcell.2021.772254

Publication

Frontiers in cell and developmental biology
ISSN: 2296-634X
NlmUniqueID: 101630250
Country: Switzerland
Language: English
Volume: 9
Pages: 772254

Researcher Affiliations

Maitan, Paula Piccolo
  • Department of Clinical Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, Netherlands.
  • Department of Veterinary Medicine, Universidade Federal de Viçosa, Viçosa, Brazil.
Bromfield, Elizabeth G
  • Department of Biomolecular Health Science, Faculty of Veterinary Medicine, Utrecht University, Utrecht, Netherlands.
  • Priority Research Centre for Reproductive Science, The University of Newcastle, Callaghan, NSW, Australia.
Hoogendijk, Romy
  • Department of Clinical Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, Netherlands.
Leung, Miguel Ricardo
  • Cryo-Electron Microscopy, Bijvoet Centre for Biomolecular Research, Utrecht University, Utrecht, Netherlands.
Zeev-Ben-Mordehai, Tzviya
  • Cryo-Electron Microscopy, Bijvoet Centre for Biomolecular Research, Utrecht University, Utrecht, Netherlands.
van de Lest, Chris H
  • Department of Biomolecular Health Science, Faculty of Veterinary Medicine, Utrecht University, Utrecht, Netherlands.
Jansen, Jeroen W A
  • Department of Biomolecular Health Science, Faculty of Veterinary Medicine, Utrecht University, Utrecht, Netherlands.
Leemans, Bart
  • Department of Clinical Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, Netherlands.
Guimarães, José Domingos
  • Department of Veterinary Medicine, Universidade Federal de Viçosa, Viçosa, Brazil.
Stout, Tom A E
  • Department of Clinical Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, Netherlands.
Gadella, Bart M
  • Department of Biomolecular Health Science, Faculty of Veterinary Medicine, Utrecht University, Utrecht, Netherlands.
  • Department of Population Health Science, Faculty of Veterinary Medicine, Utrecht University, Utrecht, Netherlands.
Henning, Heiko
  • Department of Clinical Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, Netherlands.

Conflict of Interest Statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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