Long non-coding RNA Malat1 modulates CXCR4 expression to regulate the interaction between induced neural stem cells and microglia following closed head injury.

Background: Closed head injury (CHI) provokes a prominent neuroinflammation that may lead to long-term health consequences. Microglia plays pivotal and complex roles in neuroinflammation-mediated neuronal insult and repair following CHI. We previously reported that induced neural stem cells (iNSCs) can block the effects of CXCL12/CXCR4 signaling on NF-κB activation in activated microglia by CXCR4 overexpression. Here we aim to uncover the mechanism of CXCR4 upregulation in iNSCs.

Methods: We performed bioinformatic analysis to detect the differentially expressed genes in iNSCs after co-cultured with LPS-activated microglia. Subsequently, we predicted the target genes and performed gain- and loss-of-functional studies, dualluciferase reporter, RNA immunoprecipitation, biotin-coupled miRNA pulldown, fluorescence in situ hybridization and cell transplantation assays to further elucidate the mechanism underlying the immunoregulatory effects of iNSCs. Student's t-test and one-way analysis of variance (ANOVA) with Tukey's post hoc test were used to determine statistical significance.

Results: Our results indicated that Malat1 could act as a sponge of miR-139-5p to modulate the expression of CXCR4 that exerted significant influence on the immunoregulatory effects of iNSCs on the secretion of CXCL12, TNF-α and IGF-1 by activated microglia. Furthermore, Malat1 inhibition blocked the immunoregulatory effects of iNSC grafts on microglial activation as well as neuroinflammation in the injured cortices of CHI mice. Interestingly, NF-κB activation in iNSCs augmented the immunoregulatory effects of iNSCs on microglial activation by activating the axis of Malat1/miR-139-5p/Cxcr4. Notably, we found that TNF-α secreted by activated microglia could bind to TNFR1 at the surface of iNSCs to trigger NF-κB activation in iNSCs.

Conclusions: In short, our findings reveal a novel role of Malat1 in the immunomodulatory effects of iNSCs on microglial activation, suggesting that transplanted iNSCs may self-perceive the changes of the activated state of microglia and thus make prudential regulation of the neuroinflammation following CHI.