miR-124 disinhibits neurite outgrowth in an inflammatory environment

Abstract

Lesions of the central nervous system elicit inflammatory responses that counteract the regeneration of neurites. Microglia and infiltrating macrophages that were activated by trauma have been identified as cellular sources of inhibitory factors. We examine cultured macrophage (RAW264.7) and neuronal (PC12) cell lines to ascertain the potential modulators of the inflammatory impact on neurons. By exposing quiescent macrophages to lipopolysaccharide (LPS) and interferon γ (IFN-γ), cells can be transformed into an activated M1 phenotype. Neurite extension was induced in PC12 cells by culturing them in the presence of nerve growth factor. Neurite outgrowth was quantified by analyzing immunofluorescence and phase contrast microscopy images. Activated macrophages significantly reduced neurite extension. Macrophage activation by LPS/IFN-γ induced a 1000-fold increase in tumor necrosis factor alpha (TNF-α) secretion, as quantified by enzyme-linked immunosorbent assays (ELISA). Recombinant TNF-α inhibited neurite formation at concentrations as low as 0.016 ng/ml. In contrast, the masking of TNF-α with specific functional antibodies abrogated neurite growth inhibition by activated macrophages. Taken together, these results indicated that TNF-α is a key component of inhibitory macrophage action. The transfection of PC12 neurons with microRNA-124 (miR-124) counteracted the inhibition of neurites mediated by both recombinant TNF-α and macrophages. miR-124 did not stimulate neurite formation per se, nor was cell viability affected. These data suggest that miR-124 might be a valuable tool for desensitizing neurons to a repulsive inflammatory environment.

Increased miR‐124‐3p in microglial exosomes following traumatic brain injury inhibits neuronal inflammation and contributes to neurite outgrowthviatheir transfer into neurons

“…We also found that applying exosomal miR-124-3p to injured neurons, or direct transfection of miR-124-3p into the cells both promoted neurite outgrowth characterized by an increase on the number of neurite branches and total neurite length. These results indicate that microglial exosomal miR-124-3p can promote neurite outgrowth, at least partly by inhibiting neuronal inflammation, which is consistent with the results of a previous report that miR-124-3p disinhibits neurite outgrowth in an inflammatory environment (62). In addition, increased miR-124-3p in microglial exosomes improved the neurologic outcome and inhibited neuroinflammation in rTBI mice.…”

D-4F increases microRNA-124a and reduces neuroinflammation in diabetic stroke rats

“…In vitro , miR-124 expression is down-regulated by activated microglia, and in the CNS, miR-124 levels correlate inversely with the state of microglial activation and macrophages [ 11 ]. MiR-124 also promotes neuron-microglia interaction and desensitizes neurons in an inflammatory environment [ 51 ]. Increasing miR-124by injection significantly increases neuronal survival and increases number of M2-like polarized microglia/macrophages [ 52 ], and suppresses experimental autoimmune encephalomyelitis symptoms and leukocyte infiltration in the CNS [ 11 ].…”

Sustained release of collagen VI potentiates sciatic nerve regeneration by modulating macrophage phenotype

“…Macrophages play a vital role in the inflammatory response, but they have also been regarded as a ‘double‐edged sword’ (Okabe & Medzhitov, ). Macrophages can not only promote injured nerve regeneration by clearing debris and inhibiting pro‐inflammatory factors but also provoke excessive inflammatory tissue damage and retard nerve regeneration (Chen et al ., ; Doring et al ., ; Hartmann et al ., ; Kwon et al ., ).…”