MicroRNAs in Macrophages: Regulators of Activation and Function

Macrophages are sentinels of the innate immune system that maintain tissue homeostasis and contribute to inflammatory responses. Their broad scope of action depends on both functional heterogeneity and plasticity. Small noncoding RNAs called microRNAs (miRNAs) contribute to macrophage function as post-transcriptional inhibitors of target gene networks. Genetic and pharmacologic studies have uncovered genes regulated by miRNAs that control macrophage cellular programming and macrophage-driven pathology. miRNAs control proinflammatory M1-like activation, immunoregulatory M2-like macrophage activation, and emerging macrophage functions in metabolic disease and innate immune memory. Understanding the gene networks regulated by individual miRNAs enhances our understanding of the spectrum of macrophage function at steady state and during responses to injury or pathogen invasion, with the potential to develop miRNA-based therapies. This review aims to consolidate past and current studies investigating the complexity of the miRNA interactome to provide the reader with a mechanistic view of how miRNAs shape macrophage behavior.

Association between miR-27a rs895819 polymorphism and breast cancer susceptibility: Evidence based on 6118 cases and 7042 controls

BACKGROUND

Polymorphism in miR-27a rs895819 has been associated with breast cancer (BC) risk, but studies have reported inconsistent results. This meta-analysis investigated the possible association between miR-27a rs895819 polymorphism and BC risk.

METHODS

PubMed, EMBASE, Google Scholar, and the Chinese National Knowledge Infrastructure (CNKI) databases were systematically searched to identify relevant studies in English and Chinese. Meta-analyses were performed to examine the association between miR-27a rs895819 and BC susceptibility.

RESULTS

A total of 16 case-control studies involving 6118 cases and 7042 controls were included. Analysis using five genetic models suggested no significant association between miR-27a rs895819 polymorphism and BC risk in the total population, or specifically in Asian or Chinese subpopulations. In the Caucasian subpopulation, however, the G-allele and AG genotype at rs895819 were significantly associated with decreased BC risk according to the allelic model (OR 0.90, 95% CI 0.84-0.97, P = .004) and heterozygous model (OR 0.89, 95% CI 0.81-089, P = .02), while the wild-type AA genotype was significantly associated with increased BC risk according to the dominant model (OR 1.13, 95% CI 1.03-1.24, P = .007).

CONCLUSION

These results indicate that among Caucasians, the wild-type AA genotype at rs895819 may confer increased susceptibility to BC, while the G-allele and AG genotype may be protective factors. These conclusions should be verified in large, well-designed studies.

Knockdown of miR-23, miR-27, and miR-24 Alters Fetal Liver Development and Blocks Fibrosis in Mice

MicroRNAs (miRNAs) regulate cell fate selection and cellular differentiation. miRNAs of the miR23b polycistron (miR-23b, miR-27b, and miR-24) target components of the TGF-β signaling pathway and affect murine bile ductular and hepatocyte cell fate selection in vitro. Here we show that miR-23b polycistron miRNAs directly target murine Smad4, which is required for TGF-β signaling. Injection of antagomirs against these miRNAs directly into E16.5 murine fetuses caused increased cytokeratin expression in sinusoids and primitive ductular elements throughout the parenchyma of newborn mice. Similar antagomir injection in newborn mice increased bile ductular differentiation in the liver periphery and reduced hepatocyte proliferation. Antagomir injection in newborn Alb/TGF-β1 transgenic mice that develop fibrosis inhibited the development of fibrosis, and injection of older mice caused the resolution of existing fibrosis. Furthermore, murine stellate cell activation, including ColA1 and ACTA2 expression, is regulated by miR-23b cluster miRNAs. In summary, knockdown of miR-23b cluster miRNAs in fetal and newborn liver promotes bile duct differentiation and can block or revert TGF-β-induced liver fibrosis that is dependent on stellate cell activation. These data may find practical application in the highly needed development of therapies for the treatment of fibrosis.