Comprehensive investigation of the expression profiles of common long noncoding RNAs during microglial activation

Microglia, similar to peripheral macrophages, are the primary immune cells of the central nervous system (CNS). Microglia exist in the resting state in the healthy CNS, but can be activated and polarized into either M1 or M2 subtypes for immune defense and the maintenance of CNS homeostasis by multiple stimuli. Several long noncoding RNAs (lncRNAs) mediate human inflammatory diseases and neuropathologies by regulating their target genes. However, the function of common lncRNAs that contribute to microglial activation remains unclear. Thus, we used bioinformatic approaches to identify common lncRNAs involved in microglial activation in vitro. Our study identified several lncRNAs as common regulators of microglial activation. We identified 283 common mRNAs and 53 common lncRNAs during mouse M1 microglial activation processes, whereas 26 common mRNAs and five common lncRNAs were identified during mouse M2 microglial activation processes. A total of 648 common mRNAs and 274 common lncRNAs were identified during the activation of human M1 microglia. In addition, we identified 1,920 common co-expressed pairs in mouse M1 activation processes and 25 common co-expressed pairs in mouse M2 activation processes. Our study provides a comprehensive understanding of common lncRNA expression profiles in microglial activation processes in vitro. The list of common lncRNAs identified in this study provides novel evidence and clues regarding the molecular mechanisms underlying microglial activation.

Mesenchymal Stem Cell-Derived Extracellular Vesicles Alleviate M1 Microglial Activation in Brain Injury of Mice With Subarachnoid Hemorrhage via microRNA-140-5p Delivery

BACKGROUND

It is documented that mesenchymal stem cells (MSCs) secrete extracellular vesicles (EVs) to modulate subarachnoid hemorrhage (SAH) development. miR-140-5p expression has been detected in MSC-derived EVs, while the mechanism of MSC-derived EVs containing miR-140-5p in SAH remains unknown. We aim to fill this void by establishing SAH mouse models and extracting MSCs and MSC-EVs.

METHODS

After ALK5 was silenced in SAH mice, neurological function was evaluated, neuron apoptosis was detected by TdT-mediated dUTP-biotin nick end labeling with NeuN staining, and expression of serum inflammatory factors (interleukin-6, interleukin-1β, and tumor necrosis factor-α) was determined by enzyme-linked immunosorbent assay. The effect of ALK5 on NOX2 expression was assessed by western-blot analysis. Targeting the relationship between miR-140-5p and ALK5 was evaluated by dual luciferase assay. Following extraction of MSCs and MSC-EVs, EVs and miR-140-5p were labeled by PKH67 and Cy3, respectively, to identify the transferring of miR-140-5p by MSC-EVs. SAH mice were treated with EVs from miR-140-5p mimic/inhibitor-transfected MSCs to detect effects of MSC-EV-miR-140-5p on brain injury and microglial polarization.

RESULTS

ALK5 silencing increased the neurological score and reduced neuron apoptosis and neuroinflammation in SAH mice. ALK5 silencing inhibited M1 microglia activation by inactivating NOX2. ALK5 was a target gene of miR-140-5p. MSC-derived EVs contained miR-140-5p and transferred miR-140-5p into microglia. MSC-EV-delivered miR-140-3p reduced ALK5 expression to contribute to repression of brain injury and M1 microglia activation in SAH mice.

CONCLUSIONS

MSC-derived EVs transferred miR-140-5p into microglia to downregulate ALK5 and NOX2, thus inhibiting M1 microglia activation in SAH mice.

STAT1 drives M1 microglia activation and neuroinflammation under hypoxia

Microglia are resident immune cells that act as the first active defence in the central nervous system. These cells constantly monitor the tissue microenvironment and rapidly react in response to hypoxia, infection and injuries. Hypoxia in the brain has been detected in several neurodegenerative disorders such as Alzheimer's disease, amyotrophic lateral sclerosis, Parkinson's disease and Huntington's disease. Hypoxic conditions activate microglia cells towards M1 phenotype resulting in oxidative stress and the release of pro-inflammatory cytokines. Recently, we have demonstrated that oxidative stress induces S-glutathionylation of the STAT1 and hyper-activates its signaling in microglia BV2 cells pointing out the importance of this transcription factor in neuroinflammation. In this paper we analyse the cellular mechanisms that drive M1 microglia activation in BV2 cells in response to hypoxia correlating it to STAT1 activation. The analysis of the molecular mechanism of STAT1 signaling reveals that hypoxia generates oxidative stress and induces both phosphorylation and S-glutathionylation of STAT1 that are responsible of its aberrant activation. The silencing of STAT1 protein expression counteracts hypoxia-M1 microglia phenotype suggesting the strong link between hypoxia-STAT1 and STAT1-microglia activation.