The Glial Plasticity And Changes In Histone H3 Acetylation Induced By TREZ Chronic Compression Injury

ObjectiveThe trigeminal root entry zone（TREZ）is the transitional zone of central and peripheral tissue compartments in the trigeminal root.Microvascular compression on the TREZ is the main etiology of most idiopathic trigeminal neuralgia（TN）patients.However,the pathogenesis of TN is still uncertain.This study was designed to investigate the glial plasticity in oligodendrocytes,Schwann cells,astrocytes and microglias in the TREZ in TN,and explore the epigenetic regulation of histone H3acetylation in the TREZ in a rat model of TN.Methods1.An animal model of TN was established,and adult male Sprague-Dawley rats were randomly assigned to a TN group with trigeminal nerve root compression,sham operation group,TN+HDACi group（TN plus selective histone deacetylase inhibitor injection into the TREZ）,or TN+Veh group（TN plus vehicle injection into the TREZ）.2.The orofacial mechanical stimulation threshold of rats were test before operation for baseline and after operation for mechanical allodynia by Von Frey filaments.3.To measure the length of the central portion of the TREZ from the junction of the trigeminal nerve root entering the pons to the interface of the dome-shaped CNS-PNS transitional zone,immunofluorescent staining of glia and glial nuclei was performed using glial fbrillary acidic protein（GFAP）antibody and DAPI,respectively.4.The MBP,P75^NTR,GFAP and Iba1 proteins expression of TREZ tissues from rats with TN induced by compression injury were detected with immunohistochemical staining and Western blot methods.5.To investigate the acetylation of histone H3 within the TREZ in a TN animal model group,sham operation group,TN+HDACi group and TN+Veh group,localization of histone H3K9,H3K18,and H3K27 acetylation was examined via immunohistochemical staining methods.Results1.Rats in the TN group showed signifcant mechanical hypersensitivity compared to that in the sham operation group from POD 14 to POD 28（p<0.05）.The threshold of orofacial mechanical allodynia in the TN+HDACi group with SAHA administration increased on postoperative days 7 and 14,compared with that in the TN+Veh group（p<0.05）.2.The average length from the junction of the trigeminal nerve root connecting the pons to the glial fringe of the TREZ in the TN group was longer than that in the sham operation group（p<0.05）and that the interface gradually migrated distally.3.GFAP-immunoreactive astrocyte processes significantly proliferated and extended distally from the central region to the peripheral side of the TREZ after nerve compression injury in the TN group.Moreover,the expression of P75^NTR in Schwann cells was upregulated on the peripheral side of the TREZ,and activated Iba1-immunoreactive microglia/mononuclear macrophages were observed on both sides of the TREZ.A significantly higher levels of P75^NTR,GFAP and Iba1 proteins were found in the TN group than in the sham operation group.（p<0.05）.4.Oligodendrocytes are located at the central side of the TREZ.There was a significantly lower level of MBP protein detected with Western blot method in the TN animal model from POD 7 to POD 21 than in the sham group（p<0.05）,and then it was upregulated and restored to a similar level as the sham group on POD 28.5.Cells that stained positive for acetylated histone H3K9,H3K18,and H3K27were distributed around both sides of the border of the CNS-PNS junction in the TREZ.The ratio of immunoreactive H3K9-,H3K18-and H3K27-positive cells in the TN group was obviously higher than that in the sham operation group on postoperative days 7,14,21,and 28（p<0.05）.6.Compared with the results of histone acetylation in the TN+Veh group,the immunoreactive acetylated cells of the TN+HDACi group with SAHA administration signifcantly increased on postoperative day 7 and 14.Conclusions1.After the establishment of TN rat models induced by chronic compression of the trigeminal nerve root,there was no significant change in the glial cell boundary formed by oligodendrocytes in the TREZ and surrounding schwann cells at the CNS-PNS junction,but the glial cell boundary area at the central end was significantly changed and migrated to the surrounding end.2.After chronic compression injury in the TREZ,oligodendrocytes,astrocytes,schwann cells,microglia/mononuclear macrophages undergo different degrees of activation and plasticity changes,and histones H3K9,H3K18 and H3K27 also undergo different degrees of acetylation changes.3.The glial plasticity and changes in histone H3 acetylation induced by TREZ chronic compression injury may be involved in the pathogenesis of TN rat models.