Integrated Expression Profiles of mRNA and miRNA in Polarized Primary Murine Microglia

Massachusetts General Hospital and Harvard Medical School, United States of America
PLoS ONE (Impact Factor: 3.23). 11/2013; 8(11):e79416. DOI: 10.1371/journal.pone.0079416
Source: PubMed


Neuroinflammation contributes to many neurologic disorders including Alzheimer's disease, multiple sclerosis, and stroke. Microglia is brain resident myeloid cells and have emerged as a key driver of the neuroinflammatory responses. MicroRNAs (miRNAs) provide a novel layer of gene regulation and play a critical role in regulating the inflammatory response of peripheral macrophages. However, little is known about the miRNA in inflammatory activation of microglia. To elucidate the role that miRNAs have on microglial phenotypes under classical (M1) or alternative (M2) activation under lipopolysaccharide ('M1'-skewing) and interleukin-4 ('M2a'-skewing) stimulation conditions, we performed microarray expression profiling and bioinformatics analysis of both mRNA and miRNA using primary cultured murine microglia. miR-689, miR-124, and miR-155 were the most strongly associated miRNAs predicted to mediate pro-inflammatory pathways and M1-like activation phenotype. miR-155, the most strongly up-regulated miRNA, regulates the signal transducer and activator of transcription 3 signaling pathway enabling the late phase response to M1-skewing stimulation. Reduced expression in miR-689 and miR-124 are associated with dis-inhibition of many canonical inflammatory pathways. miR-124, miR-711, miR-145 are the strongly associated miRNAs predicted to mediate anti-inflammatory pathways and M2-like activation phenotype. Reductions in miR-711 and miR-124 may regulate inflammatory signaling pathways and peroxisome proliferator-activated receptor-gamma pathway. miR-145 potentially regulate peripheral monocyte/macrophage differentiation and faciliate the M2-skewing phenotype. Overall, through combined miRNA and mRNA expression profiling and bioinformatics analysis we have identified six miRNAs and their putative roles in M1 and M2-skewing of microglial activation through different signaling pathways.

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Available from: Tsuneya Ikezu, Aug 14, 2014
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    • "MiR-23a expression was found to inversely correlate with CCR2 mRNA levels (Fig. 5F) and directly correlate with the percentage of cells negative for CCR2 (Fig. 5G). Because no differences in miRNA expression were found between controls and MCI patients, we can anticipate that all five miRNAs have potential, as conversion biomarkers, to distinguish MCI from AD. Evaluation of the expression of three miRNAs, miR- 155, miR-145, and miR-124, which serve as signature markers for the M1, M2a, and M0 activation phenotypes, respectively (Fig. 5L)[36], did not reveal differences in miR-124 and miR-145 expression profiles (Fig. 5Jand K) but showcased an increase in miR-155 levels in AD patients with respect to both controls and MCI (Fig. 5I), suggesting a tendency toward the M1 phenotype. "
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    • "Exposure of microglia cell cultures to bacterial lipopolysaccharides (LPS) (Bhat et al., 1998; Chao et al., 1992), tumor necrosis factor-alpha (TNF-α) (Takeuchi et al., 2006), interferon-gamma (IFN-γ) (Meda et al., 1995), or oligomers of amyloid beta (Aβ) (Maezawa et al., 2011) induces the M1 phenotype. On the other hand, the alternative, M2 phenotype is neuroprotective (Hjorth et al., 2013; Koenigsknecht-Talboo and Landreth, 2005; Mandrekar- Colucci et al., 2012) and can be induced in primary microglial cells by interleukins (IL)-4 and IL-13 (Freilich et al., 2013). IL-4 was found to decrease inducible nitric oxide synthase (iNOS) activity, and superoxide and TNF-α production in LPS-activated microglia (Chao et al., 1993; Zhao et al., 2006). "
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    • "Moreover, decreased miR-124 and miR-155 that revealed a negative correlation with age (Fichtlscherer et al., 2010; Noren Hooten et al., 2010; Smith-Vikos and Slack, 2012), parallelled by the enhanced miR-146a expression, further reinforce that 16 DIV microglia mainly represent aged-like microglia. In addition the reduced miR-124 obtained in these cells, indicated as being associated to the M2a-alternatively activated state (Freilich et al., 2013) and to inhibit inflammation (Prinz and Priller, 2014), strengthen their dormant/senescent phenotype. In contrast, the predominant amoeboid morphology together with increased NF-κB activation, cell migration, phagocytosis and the higher levels of miR-155 expression in 2 DIV microglia, as compared with aged cells, are indicative of a major representation of cells with a stressed/reactive phenotype. "
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