Irisin, Exercise, and COVID-19

Abstract

Muscle and adipose tissue produce irisin during exercise. Irisin is thermogenic adipomyokine, improves glucose and lipid metabolism, and ameliorates the effects of obesity-driven inflammation, metabolic syndrome, and diabetes. In addition, exercise-induced irisin activates anti-inflammatory pathways and may play an essential role in improving the outcomes of inflammatory conditions, such as coronavirus disease (COVID-19). COVID-19 infection can activate different intracellular receptors and modulate various pathways during the course of the disease. The cytokine release storm (CRS) produced is significant because it promotes the context for systemic inflammation, which increases the risk of mortality in patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV2). In addition, viral infection and the resulting organ damage may stimulate the mitogen-activated protein kinase(MAPK) and toll-like receptor 4 (TLR4)/toll interleukin receptor (TIR)-domain-containing adaptor (MyD88) pathways while negatively modulating the AMP-activated protein kinase (AMPK) pathway, leading to increased inflammatory cytokine production. Exercise-induced irisin may counteract this inflammatory modulation by decreasing cytokine production. Consequently, increased irisin levels, as found in healthy patients, may favor a better prognosis in patients with SARS-CoV2. This review aims to explore the molecular mechanisms underlying the anti-inflammatory properties of irisin in mitigating CRS and preventing severe outcomes due to infection with SARS-CoV2.

Keywords: COVID-19; adipomyokine; exercise; inflammation; irisin.

Figure 1

Macrophage inflammatory pathways modulated by irisin during different SARS-CoV2 infection stages and lifestyle contexts. (A) The first stage of SARS-CoV2 infection activates innate immune responses through the recognition of PAMPs by TLR3 and TLR4, which are downregulated by irisin. (B) The second stage of SARS-CoV2 infection causes cellular damage and induces a cytokine release storm, which activates the MAPK/p38/NF-kB pathway through TKR. CRS results in further organ damage, leading to DAMP release and MyD88/NF-kB pathway activation. Irisin can downregulate both these pathways, decreasing inflammatory cytokine production. In addition, the TLR4 and MyD88/NF-kB pathways can be stimulated by LPS, which can be released due to potential bacterial coinfection. (C) Although sedentarism and aging lead to AMPK downregulation and consequent mTOR activation, exercise produces the opposite effect. Exercise-derived AMP and irisin can stimulate AMPK, inhibiting mTOR and downregulating the NF-kB pathway while decreasing cytokine production (#) Cytokine transcription modulation by inflammatory pathways. (*) Cytokine transcription modulation by irisin.