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Review
. 2023 Jun 15:10:1154872.
doi: 10.3389/fmolb.2023.1154872. eCollection 2023.

Running from stress: a perspective on the potential benefits of exercise-induced small extracellular vesicles for individuals with major depressive disorder

Affiliations
Review

Running from stress: a perspective on the potential benefits of exercise-induced small extracellular vesicles for individuals with major depressive disorder

Reine Khoury et al. Front Mol Biosci. .

Abstract

Aerobic exercise promotes beneficial effects in the brain including increased synaptic plasticity and neurogenesis and regulates neuroinflammation and stress response via the hypothalamic-pituitary-adrenal axis. Exercise can have therapeutic effects for numerous brain-related pathologies, including major depressive disorder (MDD). Beneficial effects of aerobic exercise are thought to be mediated through the release of "exerkines" including metabolites, proteins, nucleic acids, and hormones that communicate between the brain and periphery. While the specific mechanisms underlying the positive effects of aerobic exercise on MDD have not been fully elucidated, the evidence suggests that exercise may exert a direct or indirect influence on the brain via small extracellular vesicles which have been shown to transport signaling molecules including "exerkines" between cells and across the blood-brain barrier (BBB). sEVs are released by most cell types, found in numerous biofluids, and capable of crossing the BBB. sEVs have been associated with numerous brain-related functions including neuronal stress response, cell-cell communication, as well as those affected by exercise like synaptic plasticity and neurogenesis. In addition to known exerkines, they are loaded with other modulatory cargo such as microRNA (miRNA), an epigenetic regulator that regulates gene expression levels. How exercise-induced sEVs mediate exercise dependent improvements in MDD is unknown. Here, we perform a thorough survey of the current literature to elucidate the potential role of sEVs in the context of neurobiological changes seen with exercise and depression by summarizing studies on exercise and MDD, exercise and sEVs, and finally, sEVs as they relate to MDD. Moreover, we describe the links between peripheral sEV levels and their potential for infiltration into the brain. While literature suggests that aerobic exercise is protective against the development of mood disorders, there remains a scarcity of data on the therapeutic effects of exercise. Recent studies have shown that aerobic exercise does not appear to influence sEV size, but rather influence their concentration and cargo. These molecules have been independently implicated in numerous neuropsychiatric disorders. Taken together, these studies suggest that concentration of sEVs are increased post exercise, and they may contain specifically packaged protective cargo representing a novel therapeutic for MDD.

Keywords: aerobic exercise; blood-brain barrier; epigenetics; major depressive disorder; miRNA; sex differences; small extracellular vesicles.

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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.

Figures

FIGURE 1
FIGURE 1
The systemic release of exerkines and their effect on the brain. Aerobic exercise stimulates different peripheral tissues to release exerkines into the bloodstream such as microRNAs, metabolites, cytokines, neurotrophic factors, and myokines. They can cross the blood-brain barrier, increase neurogenesis, improve synaptic plasticity, and neural differentiation.
FIGURE 2
FIGURE 2
The possible effects of exercise on EV size, concentration, and cargo. During or after physical exercise, skeletal muscles release sEVs into the bloodstream. Evidence to date suggests that exercise is more likely to affect cargo and concentration and not size.
FIGURE 3
FIGURE 3
sEVs as intercellular mediators between the periphery and the brain. Although the molecular mechanism is not fully understood, an increasing number of studies suggest that exogenous sEVs from peripheral tissues cross BBB, and act as intercellular communicators, along with endogenous sEVs to regulate physiological processes in the brain such as neurogenesis, synaptic plasticity, stress tolerance, and neuronal protection. Changes in these physiological processes have been associated in MDD. A leaky and inflamed BBB is linked with MDD pathology in the brain (Adapted from Saeedi et al., 2019).
FIGURE 4
FIGURE 4
Aerobic exercise causes skeletal muscles to release exercise-induced sEVs into blood circulation. These sEVs contain important exerkines (cytokines, microRNAs) and are taken up by other tissues such as the brain. Exercise-induced sEVs cross the BBB via different putative mechanisms (transcytosis, micropinocytosis, and clathrin-dependent endocytosis), and influence neural pathways associated with the etiopathogenesis of major depression, such as neurogenesis, neural plasticity and neuroinflammation, hence mediating the beneficial effects of exercise on MDD.

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Grants and funding

CN is supported by grants from the Canadian Institute of Health Research CIHR (PJT-183904) and the Natural Sciences and Engineering Research Council of Canada NSERC (RGPIN-2022-03979).

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