Non-coding RNAs in exercise immunology: A systematic review

Abstract

Regular physical exercise has been recognized as a potent modulator of immune function, with its effects including enhanced immune surveillance, reduced inflammation, and improved overall health. While strong evidence exists that physical exercise affects the specific expression and activity of non-coding RNAs (ncRNAs) also involved in immune system regulation, heterogeneity in individual study designs and analyzed exercise protocols exists, and a condensed list of functional, exercise-dependent ncRNAs with known targets in the immune system is missing from the literature. A systematic review and qualitative analysis was used to identify and categorize ncRNAs participating in immune modulation by physical exercise. Two combined approaches were used: (a) a systematic literature search for "ncRNA and exercise immunology", (b) and a database search for microRNAs (miRNAs) (miRTarBase and DIANA-Tarbase v8) aligned with known target genes in the immune system based on the Reactome database, combined with a systematic literature search for "ncRNA and exercise". Literature searches were based on PubMed, Web of Science, and SPORTDiscus; and miRNA databases were filtered for targets validated by in vitro experimental data. Studies were eligible if they reported on exercise-based interventions in healthy humans. After duplicate removal, 95 studies were included reporting on 164 miRNAs, which were used for the qualitative synthesis. Six studies reporting on long-noncoding RNAs (lncRNAs) or circular RNAs were also identified. Results were analyzed using ordering tables that included exercise modality (endurance/resistance exercise), acute or chronic interventions, as well as the consistency in reported change between studies. Evaluation criteria were defined as "validated" with 100% of ≥3 independent studies showing identical direction of regulation, "plausible" (≥80%), or "suggestive" (≥70%). For resistance exercise, upregulation of miR-206 was validated while downregulation of miR-133a appeared plausible. For endurance exercise, 15 miRNAs were categorized as validated, with 12 miRNAs being consistently elevated and 3 miRNAs being downregulated, most of them after acute exercise training. In conclusion, our approach provides evidence that miRNAs play a major role in exercise-induced effects on the innate and adaptive immune system by targeting different pathways affecting immune cell distribution, function, and trafficking as well as production of (anti-)inflammatory cytokines. miRNAs miR-15, miR-29c, miR-30a, miR-142/3, miR-181a, and miR-338 emerged as key players in mediating the immunomodulatory effects of exercise predominantly after acute bouts of endurance exercise.

Keywords: Immune system; Inflammation; MicroRNA; Physical exercise; ncRNA.

Graphical abstract

Fig. 1

Flow chart of ncRNA identification. Two different approaches were applied to identify relevant ncRNAs in exercise immunology. (A) A systematic literature search was conducted (utilizing PubMed, SPORTDiscus, and Web of Science databases) for “ncRNAs in exercise immunology”. (B) Out of 1547 identified records, 20 studies were included with 87 miRNAs identified as being regulated by physical activity. To broaden the approach, a combined investigation (i.e., literature and database search) was conducted. Targets within the immune system were identified using the Reactome database. Target lists were cross-referenced with experimentally validated miRNA-target databases miRTarBase and Tarbase v8 to identify associated miRNAs. Only miRNAs validated by 3 methods (reporter gene assay, Western blot, and qPCR) were selected, and duplicates were removed subsequently. Findings were aligned with results from a second independent literature search on “physical exercise and ncRNAs” using PubMed, SPORTDiscus, and Web of Science. The search identified 95 eligible studies and reported miRNAs were filtered by miRNAs with immune targets obtained from the database search, revealing 164 specific miRNAs. Subsequently, findings from searches A and B were combined and duplicates were removed. Of note, all studies (n = 20) included after search A were also detected by Search B. Identified non-redundant miRNAs were categorized using evaluation criteria defined as: validated (100% of ≥3 independent studies showed identical direction of regulation), plausible (≥80%), or suggestive (≥70%). The literature search also identified 20 lncRNAs and 1 circRNA as potential regulators in exercise immunology. ^a Only miRNAs regulated by endurance exercise reached at least the category “suggestive”, no miRNA described in resistance exercise fulfilled the criterion. circRNA = circular RNA; lncRNAs = long non-coding RNAs; miRNAs = microRNAs; ncRNA = non-coding RNA; NCBI = National Center for Biotechnology Information; qPCR = quantitative polymerase chain reaction.

Fig. 2

Risk of bias analysis of included studies. The PEDro scale was used to assess risk of bias, and all items were scored irrespective of the individual study design. Overall risk of bias was rated as “high”.

Fig. 3

TLR cascades are main targets of validated exercise-dependent miRNAs. Visualization of overrepresented pathways (yellow) was performed using the Reactome online analysis tool (Version 85, human targets). Identified targets of validated miRNAs were submitted to determine pathway enrichment. Darker shades indicate lower p values. Inlet shows image magnification of TLR cascades within the immune system cluster. Overall image has been cropped for visualization. Details are given in Table 3. ADAM = a disintegrin and metalloproteinase; BCR = breakpoint cluster region; BMAL = basic helix–loop–helix arnt like; BMP = bone morphogenetic protein; BTN = butyrophilin; CD22 = cluster of differentiation 22; CD95L = tumor necrosis factor ligand superfamily member 6; CSF3 = colony-stimulating factor 3; CTLA= cytotoxic T-lymphocyte associated protein; DAP = death-associated protein; ER = estrogen receptor; ERBA = avian erythroblastosis virus; FLT3 = FMS-like tyrosine kinase 3; G-CSF = granulocyte colony-stimulating factor; GPCR = G protein-coupled receptor; HLH = hemophagocytic lymphohistiocytosis; IGF = insulin like growth factor; IRAK2 = interleukin 1 receptor associated kinase 2; LGI = leucine-rich glioma inactivated; LPS = lipopolysaccharide; M-CSF = macrophage colony-stimulating facto; MAPK = mitogen-activated protein kinase; MHC = major histocompatibility complex; miRNAs = microRNAs; NR1D1 = nuclear receptor subfamily 1 group D member 1; NPAS2 = neuronal PAS domain protein 2; PD = programmed cell death protein; PECAM1 = platelet and endothelial cell adhesion molecule 1; RAP = member of RAS oncogene family; RNA = ribonucleic acid; RORA = RAR related orphan receptor A; TAZ = Tafazzin family protein; TCR = T cell receptor; TLR = Toll-like receptor; VENTX = VENT Homeobox; WNT = wingless/Int-1; WWTR1 = WW domain-containing transcription regulator 1; YAP1 = Yes1-associated transcriptional regulator 1.