Inferior Alveolar Nerve Transection Disturbs Innate Immune Responses And Bone Healing After Tooth Extraction

PURPOSE:The effects of innate immune response in sensory nerve regulation have become a research hotspot in recent years.Coordination between the nervous and innate immune systems to maintain bone homeostasis is largely uncharacterized.A large number of sensory nerve fibers and innate immune cells are distributed in alveolar bone and the lining mucosa.Sensory nerve fibers can release neuropeptides such as calcitonin gene-related peptide(CGRP).Vitro experiments have proved that CGRP has various anti-inflammatory effects and can regulate the recruitment of innate immune cells.The present study investigated the sensory–immune interaction in resting alveolar bone and healing socket to provide a certain theoretical and experimental basis for the treatment of bone-related diseases.METHODS: 1.Animal model of unilateral inferior alveolar nerve transection was established,Calcein-alizarin red fluorescent double labeling,HE staining and TRAP staining were used to observe new bone formation.2.Surgical tooth extraction was performed,the changes of the innate immune system and bone tissue remodeling in the healing socket after tooth extraction were analyzed by means of bone histological measurement,immunohistochemical staining and flow cytometry.3.CGRP was added to the healing socket after tooth extraction,and the variations of bone reconstruction and innate immune system after sensory nerve innervation were analyzed using bone histomorphology,immunohistochemical staining,and Masson staining.RESULTS: 1.The results of double fluorescent labeling showed that the bony cortex of the first mandibular molar was significantly reduced after sensory denervation,and the difference was statistically significant.Bone histomorphometry and immunohistochemistry showed that sensory denervation resulted in moderate suppression of bone remodeling,with a proinflammatory milieu manifested by increased neutrophil recruitment and possible alternations in macrophage phenotypes along the resting bone surface.2.The denervation effect intensified when bone remodeling was triggered by tooth extraction,as revealed by disrupted temporospatial variations in macrophage subpopulations at 8 weeks and neutrophil infiltration at 1 week,which were closely associated with a dramatic decline in socket bone filling and residual ridge height showed by Micro-CT,and the difference was statistically significant.3.Antagonism of calcitonin generelated peptide(CGRP)brought about similar antianabolic and proinflammatory effects as sensory denervation,suggesting that sensory nerves may monitor the bony milieu by CGRP.Depletion of macrophages,rather than neutrophils,ruled out CGRP effects,illustrating that macrophages were the primary immune mechanism that linked sensory innervation,innate immunity,and bone.CONCLUSION: Sensory innervation is required for control of innate immune responses and maintenance of bone homeostasis.Sensory neuropeptides,such as CGRP,are a possible target for the development of proanabolic treatments in bone disease by modulating innate immune responses.