Excessive Accumulation of Intracellular Ca2+ After Acute Exercise Potentiated Impairment of T-cell Function.

Renyi Liu,Yu Xiao,Michael Seimetz,Karsten Krüger,Wei Fan,Christian Pilat,Klaus Eder,Norbert Weissmann,Eveline Baumgart-Vogt,Frank Christoph Mooren,Robert Ringseis

doi:10.3389/fphys.2021.728625

Abstract

Ca2+ is an important intracellular second messenger known to regulate several cellular functions. This research aimed to investigate the mechanisms of exercise-induced immunosuppression by measuring intracellular calcium levels, Ca2+-regulating gene expression, and agonist-evoked proliferation of murine splenic T lymphocytes. Mice were randomly assigned to the control, sedentary group (C), and three experimental groups, which performed a single bout of intensive and exhaustive treadmill exercise. Murine splenic lymphocytes were separated by density-gradient centrifugation immediately (E0), 3h (E3), and 24h after exercise (E24). Fura-2/AM was used to monitor cytoplasmic free Ca2+ concentration in living cells. The combined method of carboxyfluorescein diacetate succinimidyl ester (CFSE) labeling and flow cytometry was used for the detection of T cell proliferation. The transcriptional level of Ca2+-regulating genes was quantified by using qPCR. Both basal intracellular Ca2+ levels and agonist (ConA, OKT3, or thapsigargin)-induced Ca2+ transients were significantly elevated at E3 group (p<0.05 vs. control). However, mitogen-induced cell proliferation was significantly decreased at E3 group (p<0.05 vs. control). In parallel, the transcriptional level of plasma membrane Ca2+-ATPases (PMCA), sarco/endoplasmic reticulum Ca2+-ATPases (SERCA), TRPC1, and P2X7 was significantly downregulated, and the transcriptional level of IP3R2 and RyR2 was significantly upregulated in E3 (p<0.01 vs. control). In summary, this study demonstrated that acute exercise affected intracellular calcium homeostasis, most likely by enhancing transmembrane Ca2+ influx into cells and by reducing expression of Ca2+-ATPases such as PMCA and SERCA. However, altered Ca2+ signals were not transduced into an enhanced T cell proliferation suggesting other pathways to be responsible for the transient exercise-associated immunosuppression.

Highlights

Exercise can enhance marked transient physiological changes and has a profound influence on the human immune function
The major findings of this study were that a single bout of intensive exercise caused reversible increases of both basal and regulating genes was normalized to the housekeeping gene, β-actin mRNA
Agonist-induced intracellular Ca2+ concentrations during the early post-exercise recovery period. These changes could be related to an enhanced transmembrane Ca2+ influx but not to an altered load of intracellular calcium stores

Summary

Introduction

Exercise can enhance marked transient physiological changes and has a profound influence on the human immune function. There is evidence that the transient “open-window” of immunosuppression might exist in the recovery from strenuous exercise as indicated by an impaired immunity around 3–72 h after exercise when athletes seem to be more susceptible to infections. This consensus meaning has been disagreed recently due to novel findings demonstrating that exercise stimulates T cell redistribution within organs and tissues, enhances mobilization of hematopoietic stem cells as a result of apoptotic T cells, and reverses T cell immunosenescence (Simpson et al, 2020). In order to test this hypothesis, this research examined the effects of acute exercise on intracellular free calcium ion concentrations under basal and agonist-stimulated conditions, the expression of Ca2+-handling factors, and changes of T cell function

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