Germinal matrix hemorrhage (GMH) is the most common neurological disease of premature newborns leading to detrimental neurological sequelae. Minocycline has been reported to play a key role in neurological inflammatory diseases by controlling some mechanisms that involve cannabinoid receptor 2 (CB2R). The current study investigated whether minocycline reduces neuroinflammation and protects the brain from injury in a rat model of collagenase-induced GMH by regulating CB2R activity. To test this hypothesis, the effects of minocycline and a CB2R antagonist (AM630) were evaluated in male rat pups that were post-natal day 7 (P7) after GMH. We found that minocycline can lead to increased CB2R mRNA expression and protein expression in microglia. Minocycline significantly reduced GMH-induced brain edema, microglial activation, and lateral ventricular volume. Additionally, minocycline enhanced cortical thickness after injury. All of these neuroprotective effects of minocycline were prevented by AM630. A cannabinoid CB2 agonist (JWH133) was used to strengthen the hypothesis, which showed the identical neuroprotective effects of minocycline. Our study demonstrates, for the first time, that minocycline attenuates neuroinflammation and brain injury in a rat model of GMH, and activation of CBR2 was partially involved in these processes.
Microglia play dual roles after germinal matrix hemorrhage, and the neurotrophic phenotype maybe neuroprotective. However, the phenotype transformation and the way by which neuron-microglia dialogue remain unclear. We raise the hypothesis that a cannabinoid receptor2 agonist (JWH133) accelerates the CX3CR1 microglia secreting neurotrophic factors and restores damaged neuronal circuit. Here, we report a novel function of JWH133 in transforming the microglia CX3CR1 positive that secrete brain-derived neurotrophic factor (BDNF), which triggers neuron proliferation and neuronal restoration. Using a collagen VII-induced GMH model in rat pups postnatal day 7 (P7), we found that the drug showed robust activity in neuronal precursors. Moreover, the FA value of DTI in the internal zone revealed the positive effects of JWH133 on neural restoration. CX3CR1, a critical modulating molecule expressed in microglia, was upregulated after treatment with JWH133 and the corresponding shRNA (NM_133534.1) was used to silence the expression of CX3CR1. 3 days after treatment with JWH133, we detected reduced expression of biomarkers for neural progenitor cells (NPCs) in pups pre-injected in the lateral ventricular tissue with CX3CR1 shRNA, but not in pups injected with control shRNA. Overall, this study provides evidence that JWH133 promoted a neurotrophic phenotype of microglia (CX3CR1 microglia), beyond merely alleviating microglial proliferation and inflammation. Moreover, JWH133 restored impaired neuronal circuit, which represent a novel therapeutic strategy following GMH in clinic.
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