Sperm preparedness and adaptation to osmotic and pH stressors relate to functional competence of sperm in Bos taurus

Maharajan Lavanya,Divakar Swathi,Laxman Ramya,Harendra Kumar,Santhanahalli Siddalingappa Archana,Sellappan Selvaraju,Arunachalam Arangasamy,Arindam Dhali,Sanjay Kumar Singh,Narayanan Krishnaswamy,Muniandy Sivaram,Balakrishnan Binsila

doi:10.1038/s41598-021-01928-6

Abstract

The adaptive ability of sperm in the female reproductive tract micromilieu signifies the successful fertilization process. The study aimed to analyze the preparedness of sperm to the prevailing osmotic and pH stressors in the female reproductive tract. Fresh bovine sperm were incubated in 290 (isosmotic-control), 355 (hyperosmotic-uterus and oviduct), and 420 (hyperosmotic-control) mOsm/kg and each with pH of 6.8 (uterus) and 7.4 (oviduct). During incubation, the changes in sperm functional attributes were studied. Sperm kinematics and head area decreased significantly (p < 0.05) immediately upon exposure to hyperosmotic stress at both pH. Proportion of sperm capacitated (%) in 355 mOsm/kg at 1 and 2 h of incubation were significantly (p < 0.05) higher than those in 290 mOsm media. The magnitude and duration of recovery of sperm progressive motility in 355 mOsm with pH 7.4 was correlated with the ejaculate rejection rate (R2 = 0.7). Using this information, the bulls were divided into good (n = 5) and poor (n = 5) osmo-adapters. The osmo-responsive genes such as NFAT5, HSP90AB1, SLC9C1, ADAM1B and GAPDH were upregulated (p < 0.05) in the sperm of good osmo-adapters. The study suggests that sperm are prepared for the osmotic and pH challenges in the female reproductive tract and the osmoadaptive ability is associated with ejaculate quality in bulls.

Highlights

In mammals, sperm are exposed to gradients of osmolality and pH while traveling in the male and female reproductive tracts
The osmotic stress is well known to induce mitogen-activated kinases (MAPK) which are intimately associated with the sperm capacitation p rocess[6]
Studying the expression levels of the genes associated with other stress responses including chaperone regulating signaling events (HSP90AB1), transcriptional regulation of osmo-protective and inflammatory genes (NFAT5), sperm-specific intracellular pH regulator (SLC9C1), and a sperm egg fusion disintegrin and metalloprotease (ADAM1B)[20,21,22,23] in sperm may provide information on the osmo-adaptation ability of an ejaculate

Summary

Introduction

Sperm are exposed to gradients of osmolality and pH while traveling in the male and female reproductive tracts. The osmolality of the epididymis is 350 mOsm/kg and seminal plasma is 280–300 mOsm/kg[1], whereas the uterine and oviduct osmolality is hyperosmotic (350–355 mOsm/kg)[2] These physiological stressors necessitate the sperm to undergo maturation in the epididymis and desirable functional changes in-terms of capacitation and subsequently the acrosome reaction before they come in contact with oocyte. Despite the existence of osmotic stress in the tightly regulated reproductive tract micromilieu, the information on the osmoadaptive ability of sperm and the possible impact on their functional competence have not been studied in detail. The osmo-responsive genes that are involved in various functions such as oxidative phosphorylation (MT-ND2 and COX1), glycolysis (ENO1 and GAPDH), and calcium ion and hyperosmotic sensor (EFHD1/mitocalcin) activities[24] regulate sperm function and fertilization. Studying the expression levels of the genes associated with other stress responses including chaperone regulating signaling events (HSP90AB1), transcriptional regulation of osmo-protective and inflammatory genes (NFAT5), sperm-specific intracellular pH regulator (SLC9C1), and a sperm egg fusion disintegrin and metalloprotease (ADAM1B)[20,21,22,23] in sperm may provide information on the osmo-adaptation ability of an ejaculate

Methods

Results

Conclusion