MiRNA-Mediated Mechanisms of Cardiac Protection in Ischemic and Remote Ischemic Preconditioning-A Qualitative Systematic Review.

BACKGROUND: Ischemic preconditioning (IPC) and remote ischemic preconditioning (RIPC) protect myocardial tissue against subsequent ischemia and reperfusion injury (IRI) and have a high potential to improve patient outcome. The mediators and mechanisms of protection through IPC and RIPC remain largely unknown, but micro-RNAs (miRNAs) are promising candidates. METHODS: Systematic review of Medline and Embase databases for biomedical scientific literature. RESULTS: A total of 26 relevant publications (21 full-text original articles and 5 conference abstracts) were identified, 8 describing cell culture experiments, 14 animal experiments, and 4 randomized clinical trials in humans. Most commonly reported miRNAs with differential expression between preconditioned and control groups include miR-1, miR-21, and miR-144. Experimental designs and procedures differ widely, thereby limiting the potential to compare results between studies. Two of the four RCTs did not find any differentially expressed miRNAs. CONCLUSIONS: Results from RCTs should feed back into basic research and focused studies confirming or rejecting hypotheses generated by these RCTs are needed.

Aberrant plasma IL-7 and soluble IL-7 receptor levels indicate impaired T-cell response to IL-7 in human tuberculosis.

T-cell proliferation and generation of protective memory during chronic infections depend on Interleukin-7 (IL-7) availability and receptivity. Regulation of IL-7 receptor (IL-7R) expression and signalling are key for IL-7-modulated T-cell functions. Aberrant expression of soluble (s) and membrane-associated (m) IL-7R molecules is associated with development of autoimmunity and immune failure in acquired immune deficiency syndrome (AIDS) patients. Here we investigated the role of IL-7/IL-7R on T-cell immunity in human tuberculosis. We performed two independent case-control studies comparing tuberculosis patients and healthy contacts. This was combined with follow-up examinations for a subgroup of tuberculosis patients under therapy and recovery. Blood plasma and T cells were characterised for IL-7/sIL-7R and mIL-7R expression, respectively. IL-7-dependent T-cell functions were determined by analysing STAT5 phosphorylation, antigen-specific cytokine release and by analysing markers of T-cell exhaustion and inflammation. Tuberculosis patients had lower soluble IL-7R (p < 0.001) and higher IL-7 (p < 0.001) plasma concentrations as compared to healthy contacts. Both markers were largely independent and aberrant expression normalised during therapy and recovery. Furthermore, tuberculosis patients had lower levels of mIL-7R in T cells caused by post-transcriptional mechanisms. Functional in vitro tests indicated diminished IL-7-induced STAT5 phosphorylation and impaired IL-7-promoted cytokine release of Mycobacterium tuberculosis-specific CD4+ T cells from tuberculosis patients. Finally, we determined T-cell exhaustion markers PD-1 and SOCS3 and detected increased SOCS3 expression during therapy. Only moderate correlation of PD-1 and SOCS3 with IL-7 expression was observed. We conclude that diminished soluble IL-7R and increased IL-7 plasma concentrations, as well as decreased membrane-associated IL-7R expression in T cells, reflect impaired T-cell sensitivity to IL-7 in tuberculosis patients. These findings show similarities to pathognomonic features of impaired T-cell functions and immune failure described in AIDS patients.

Effects of remote ischemic preconditioning and myocardial ischemia on microRNA-1 expression in the rat heart in vivo.

Remote ischemic preconditioning (RIPC) is an easily applicable method for protecting the heart against a subsequent ischemia and reperfusion (I/R) injury. However, the exact molecular mechanisms underlying RIPC are unknown. We examined the involvement of microRNAs (miRNAs) and in particular the expression of miRNA-1 (miR-1) in RIPC and myocardial ischemia. Remote ischemic preconditioning was conducted by four cycles of 5-min bilateral hind-limb ischemia in male Wistar rats. Cardiac ischemia was induced by ligation of the left anterior descending coronary artery for 35 min followed by 2 or 6 h of reperfusion. MicroRNA expression was analyzed by Taqman miRNA arrays and quantitative polymerase chain reaction assays. Luciferase assays were performed to validate the miR-1 target gene brain-derived neurotrophic factor (BDNF). Brain-derived neurotrophic factor mRNA and protein levels were analyzed by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay. Remote ischemic preconditioning led to a differential expression of miRNAs. The most abundant cardiac miRNA, miR-1, was downregulated by RIPC without following ischemia as well as after I/R and RIPC followed by I/R after 2 h of reperfusion. After 6 h of reperfusion, RIPC led to an upregulation of miR-1, whereas ischemia had no effect on miR-1 expression. Luciferase assays confirmed the interaction of miR-1 with BDNF, a protein that has been shown to exert cardioprotective effects. Brain-derived neurotrophic factor protein levels in rat hearts measured by enzyme-linked immunosorbent assay were not significantly altered after 2 or 6 h of reperfusion in all intervention groups. Remote ischemic preconditioning leads to changes in the expression levels of the most abundant cardiac miRNA, miR-1. MicroRNA 1 levels did not correlate with protein levels of BDNF, a known miR-1 target, in vivo. Further studies are needed to explore the biological significance of changes in miR-1 expression levels and the potential interaction with BDNF in RIPC-induced cardioprotection.

Are microRNAs suitable biomarkers of immunity to tuberculosis?

BACKGROUND: MicroRNAs (miRNAs) are crucial regulators of human immunity e.g. against Mycobacterium tuberculosis. Against the background of still alarming high mortality of tuberculosis effective biomarkers to improve diagnosis of M. tuberculosis infection and successful treatment are of major importance. CONCLUSIONS: This review summarizes recent surrogate tissue studies for identification of miRNA biomarker candidates in human tuberculosis with a special focus on reproducibility and conformance. In addition we provide assistance for the design of biomarker studies to circumvent major pitfalls.

Decreased expression of miR-21, miR-26a, miR-29a, and miR-142-3p in CD4⁺ T cells and peripheral blood from tuberculosis patients.

The vast majority of Mycobacterium tuberculosis (M. tuberculosis) infected individuals are protected from developing tuberculosis and T cells are centrally involved in this process. MicroRNAs (miRNA) regulate T-cell functions and are biomarker candidates of disease susceptibility and treatment efficacy in M. tuberculosis infection. We determined the expression profile of 29 selected miRNAs in CD4(+) T cells from tuberculosis patients and contacts with latent M. tuberculosis infection (LTBI). These analyses showed lower expression of miR-21, miR-26a, miR-29a, and miR-142-3p in CD4(+) T cells from tuberculosis patients. Whole blood miRNA candidate analyses verified decreased expression of miR-26a, miR-29a, and miR-142-3p in children with tuberculosis as compared to healthy children with LTBI. Despite marked variances between individual donor samples, trends of increased miRNA candidate expression during treatment and recovery were observed. Functional in vitro analysis identified increased miR-21 and decreased miR-26a expression after re-stimulation of T cells. In vitro polarized Interleukin-17 positive T-cell clones showed activation-dependent miR-29a up-regulation. In order to characterize the role of miR-29a (a described suppressor of Interferon-γ in tuberculosis), we analyzed M. tuberculosis specific Interferon-γ expressing T cells in children with tuberculosis and healthy contacts but detected no correlation between miR-29a and Interferon-γ expression. Suppression of miR-29a in primary human T cells by antagomirs indicated no effect on Interferon-γ expression after in vitro activation. Finally, classification of miRNA targets revealed only a moderate overlap between the candidates. This may reflect differential roles of miR-21, miR-26a, miR-29a, and miR-142-3p in T-cell immunity against M. tuberculosis infection and disease.