Selective activation of cannabinoid receptor-2 reduces white matter injury via ﻿PERK signaling ﻿in a rat model of traumatic brain injury
Authors: jiang li , Li Lin , Luo Qing , Shang Bin , Yang Xiaomin , Zhou Jiru , Pan Qiuling , Wu Na , Tang Wei , Du Donglin , Sun Xiaochuan 
Published: April 2021

Abstract
Background and Purpose: Traumatic brain injury (TBI) destroys white matter, and this destruction is aggravated by secondary neuroinflammatory reactions. Although white matter injury (WMI) is strongly correlated with poor neurological function, understanding of white matter integrity maintenance is limited, and no available therapies can effectively protect white matter. One candidate approach that may fulfill this goal is cannabinoid receptor 2 (CB2) agonist treatment. Here, we confirmed that a selective CB2 agonist, JWH133, protected white matter after TBI.﻿Methods: ﻿The controlled cortical impact (CCI) was used to establish a moderate TBI model in adult male Sprague-Dawley rats (﻿8–10 weeks, 250–300g). The motor evoked potentials (MEPs), open field test, and Morris water maze test were used to assess neurobehavioral outcomes. Brain tissue loss, WM damage, Endoplasmic reticulum stress (ER stress), and microglia responses were evaluated after TBI. The functional integrity of WM was measured by diffusion tensor imaging (DTI) and transmission electron microscopy (TEM). Primary microglia and oligodendrocyte cocultures were used for additional mechanistic studies.Results: JWH133 increased myelin basic protein (MBP) and neurofilament heavy chain (NF200) levels and anatomic preservation of myelinated axons revealed by DTI and TEM. JWH133 also increased the numbers of oligodendrocyte precursor cells and mature oligodendrocytes. Furthermore, JWH133 drove microglial polarization toward the protective M2 phenotype and modulated the redistribution of microglia in the striatum. Further investigation of the underlying mechanism revealed that JWH133 downregulated phosphorylation of the ﻿protein kinase R (PKR)-like endoplasmic reticulum (ER) kinase (PERK) signaling pathway and its downstream signals eukaryotic translation initiation factor 2 α (eIF2α), activating transcription factor 4 (ATF4) and Growth arrest and DNA damage-inducible protein (GADD34); this downregulation was followed by p-Protein kinase B(p-Akt) upregulation. In primary cocultures of microglia and oligodendrocytes, JWH133 decreased phosphorylated PERK expression in microglia stimulated with tunicamycin and ﻿facilitated oligodendrocyte survival. ﻿These data reveal that JWH133ultimately alleviates WMI and improves neurological behavior following TBI. However, these effects were ﻿were prevented by SR144528(i.p. injection 3 min before receiving JWH133 intraperitoneally), a selective CB2 antagonist.Conclusions: This work illustrates the PERK-mediated interaction between microglia and oligodendrocytes. In addition, the results are consistent with recent findings that microglial polarization switching accelerates WMI, highlighting a previously unexplored role for CB2 agonists. Thus, CB2 agonists are potential therapeutic agents for TBI and other neurological conditions involving white matter destruction.