Effects Of Highly Selective Sensory/motor Nerve Injury On Bone Metabolism And Its Mechanism In Rats

BACKGROUNDBone metabolic system is one of the important metabolic organs in human body.It constantly carries out the metabolism of osteogenesis and bone breaking.This metabolism can adjust the dynamic balance of blood calcium and phosphorus in normal human body.It is found that bone tissue reconstruction and bone metabolism are regulated by hormones of nervous system and endocrine system.Osteoclasts and osteoblasts are regulated through relevant signal pathways,and bone metabolism and bone remodeling are carried out continuously.With the deepening of the research on the nervous system and bone metabolism,there have been many studies on the effect of nerve injury on bone metabolism,but the mechanism of different components of nerves on bone metabolism and bone reconstruction is still unclear.In 2013,Japanese scholars knocked out the growth inducing factor semaphorin3a in the nervous system of mice.They found that there was obvious osteoporosis in the vertebrae and femur of mice.Based on the above research results,they put forward the new concept of sensory nerve regulating bone metabolism for the first time.PURPOSEBased on previous studies,we realize the importance of exploring the mechanism of different nerve components regulating bone remodeling and bone metabolism.However,the effects of simple motor nerve injury or simple sensory nerve injury on bone metabolism and the differences between the two effects have not been reported at home and abroad.This study used the method of highly selective transection of rat sensory/motor nerve to analyze and explore the effects of simple motor nerve injury and simple sensory nerve injury on bone metabolism and its mechanism by detecting relevant indexes and signal pathways.METHODS(1)Experimental animals and modeling:40 SD clean healthy(SPF)rats were randomly divided into 4 groups(n=10)and dorsal root transection group(PRG);Ventral rhizotomy group(ARG);Control group(SOG);Dorsal root and abdominal root(sensory and motor)transection group(APRG),the above operations were completed under the operating microscope.Tests of successful modeling:①osmic acid staining:resection of the ventral root of the anterior horn of the spinal cord can degenerate the motor nerve fiber axon at the distal end of the sciatic nerve,but there is no significant change in the sensory nerve axon in the sciatic nerve;Resection of the dorsal root ganglion of the posterior horn of the spinal cord can degenerate the sensory nerve axons in the distal end of the sciatic nerve,but there is no significant change in the motor nerve axons.② NeuN immunohistochemical staining of L4-6 segments of spinal cord:after resection of dorsal root sensory nerve,sensory neurons in the dorsal horn of spinal cord decreased or partially disappeared;After resection of the ventral root motor nerve,the motor neurons in the anterior horn of the spinal cord decreased or partially disappeared..(2)Evaluation of bone morphology:Micro-CT software was used for three-dimensional reconstruction of bone trabecula in the scanning area,and then the structural parameters of cancellous phase were analyzed.(3)Histological evaluation of bone:HE staining of tibia was used to observe the arrangement of osteocytes and bone trabeculae;The number and activity of osteoclasts were observed by trap staining;The positive expressions of neuropeptides CGRP,OPG,rank and OCN were observed by immunohistochemical staining.(4)Detection of signal pathways related to bone remodeling:The mRNA expression of related factors in bone tissue was detected that Wnt/β-catenin、PPAR-γ and NF-κB signal pathway(OCN,PPAR-γ、Runx2、AP2、LPL、OPG、RANKL、Wnts5a、Wnts1、LRP5、Lef1、β-catenin、Ctnnb1、β-actin、NF-κB TRAF6)RESULTS(1)Osteoporosis after motor neurotomy:PPAR-γ Signaling pathways and NF-κB signaling pathways are activated,Wnt/β-catenin pathway was inhibited.Wntsl,LRP5,Runx2,OPG and β-catenin down regulation,PPAR-γ、Ap2,LPL,RANKL,TRAF6 and NF-κB is up-regulated,bone resorption is enhanced,bone formation is reduced,and the dynamic balance of osteogenesis and osteoclast is biased towards the direction of osteoclast,which is characterized by high conversion bone metabolism..(2)Osteoporosis after sensory nerve transection:NF-κB pathway is activated,Wnt/β-catenin pathway and PPAR-y that was no change in the pathway.OPG expression was down regulated,RANKL,TRAF6 and NF-κB up regulation,wnts1,LRP5,PPAR-γ、AP2、LPL、β-catenin was no significant change in catenin and Runx2,the OPG/RANKL ratio decreased,osteoclasts were activated,bone formation decreased and bone resorption increased,and the activity of osteoblasts was inhibited,showing the characteristics of low conversion bone metabolism.In addition,CGRP can directly act on osteoblasts and increase their activity.After sensory nerve transection,less CGRP secreted by neuropeptides is released,resulting in the obstacle of osteoblast maturation(3)Osteoporosis after sensory and motor neurotomy:PPAR-y pathway,NF-κB pathway is activated,Wnt/β-catenin pathway was inhibited.Appears,PPAR-γ、Ap2，LPL,RANKL,TRAF6 and NF-κB up regulation,OPG,wntsl,LRP5,Runx2 and β-catenin the expression was down regulated.At the same time,the decrease of neuropeptide secretion leads to the decrease of cAMP content,the weakening of Runx2 activity and bone formation,which is characterized by high conversion bone metabolism.CONCLUSION(1)Sensory nerve transection or motor nerve transection can lead to bone loss,and bone mineral density decreases,and the bone loss caused by motor nerve transection occurs faster and to a greater extent than sensory nerve transection..(2)The signal pathways leading to bone remodeling after nerve transection of different components are different:①Motor neurotomy:PPAR-y Signal pathway,NF-κB signal pathways are activated,Wnt/β-catenin pathway was inhibited and showed the characteristics of high conversion bone metabolism.②Sensory nerve transection:NF-κB pathway is activated,Wnt/β-catenin pathway and PPAR-y was no change in the pathway,showing the characteristics of low conversion bone metabolism.③Sensory and motor neurotomy:PPAR-y Pathways and NF-κB pathway is activated,Wnt/β-catenin pathway was inhibited and showed the characteristics of high conversion bone metabolism...