The Mechanism Of PDGFR-α/JAK2/STAT3 In Myofascial Pain Trigger Point And Depression

BackgroundMyofascial Pain Syndrome(MPS)is a group of clinical chronic pain disorders associated with painful and non-painful disorders characterized by the presence of myofascial trigger points(MTrPs).MTrPs are described as localized,hypersensitive lesions that cause spontaneous pain and discomfort with radiating pain,hyperalgesia and/or local twitch responses(LTRs)to palpation,and are thought to be caused by localized areas of tension consisting of skeletal muscles and fascia.Taut bands(TBs)were palpable at the corresponding sites.MPS has a lifetime prevalence of up to 85%in the general population and is the main type causing chronic pain.Current treatments include local injections,massage and physiotherapy measures,and the treatment results are still generally not promising.Since the mechanism of pain and its formation by pressure in MTrPs is still unclear,it is of great importance to elucidate the mechanism of its development for the prevention and treatment of such diseases.Chronic pain may induce depression,and people with depression may also show abnormal pain perception.It is estimated that 85%of patients with chronic pain have severe depression,and the prevalence of pain in patients with depression is 59.1%.It is called Depression-pain syndrome.Depression-pain syndrome has not been reported in myofascial pain,and exploring its comorbidity mechanism is beneficial to the prevention and treatment of this disease.Receptor tyrosine kinases(RTKs)are the largest family of enzyme-linked receptors,which can phosphorylate tyrosine residues of target proteins with specific kinase activity and receptor characteristics to transmit signals downstream and perform biological functions.Our previous study found that MTrPs were composed of one or more abnormally contracting sarcomeres.The RTKs family,including EphB receptor and Fibroblast growth factor receptor(FGFR),are involved in the pathophysiological process of MTrPs.Platelet-derived growth factor receptor(PDGFR)belongs to the RTKs family.PDGFR was divided into two subtypes,PDGFR-α and PDGFR-β.Previous literature has suggested that PDGFR is involved in peripheral and central pain sensitization,and inhibition of PDGFR expression can alleviate hyperalgesia.In addition,PDGFR is involved in the contractile process of smooth muscle cells.However,whether PDGFR is involved in peripheral sensitization of MTrPs and abnormal contraction of sarcomeres at MTrPs is still unknown.The rat model used in this study is a widely used animal model for studying MTrPs,but it is unknown whether it has a depressive phenotype,and the role of PDGFR-α in it is also unknown.Therefore,we posed questions:Is the rat model of myofascial pain associated with a depressive phenotype?Is PDGFR-α involved in regulating the depressive phenotype in a rat model of myofascial pain?No results were found in the relevant literatures.MethodsIn this study,we performed PDGFR-α and PDGFR-β phosphorylation antibody microarray analysis and histological staining on human MTrPs obtained by needle biopsy technique.Correlation analysis was used to analyze the correlation between the expression level of MTrPs and pain intensity.Enzyme linked immunosorbent assay(ELISA)was used to measure the serum level of PDGF-AA in MPS patients.The rat model of chronic myofascial pain was established by blunt percussion of unilateral gastrocnemius muscle for 8 weeks combined with eccentric exercise and rest recovery for 4 weeks.Histological staining was used to compare the histomorphology of human MTrPs.The function of PDGFR-α agonist was studied by local injection of PDGFR-αinto gastrocnemius of normal rats.Local injection of PDGFR-α and Janus kinase(JAK)/signal transducer and activator of transcription(STAT)signaling pathway inhibitor AZD1480 into gastrocnemius MTrPs of model rats to investigate its mechanism of action.Dexmedetomidine(Dex)was injected locally into gastrocnemius muscle of model rats to study its regulatory relationship with p-PDGFR-α and the change of mechanical pressure pain threshold.Recombinant IL-1β,IL-6 and TNF-αwere injected locally into gastrocnemius muscle of normal rats to study its regulatory relationship with p-PDGFR-α.Tail suspension test,forced swimming test and sucrose preference test were used to evaluate the depression-like behaviors such as hopelessness and anhedonia of the model rats.Histological staining and Western blot were used to determine the expression of p-PDGFR-α,the activation of glial cells and the occurrence of neuroinflammation in the hippocampus.Continuous intraperitoneal injection of PDGFR-α and JAK2/STAT3 signaling pathway inhibitors was used to study the mechanism of central depression.Results1.P-PDGFR-α was highly expressed in MTrPs(P<0.001)and positively correlated with the visual analogue scale(VAS)score of pain intensity in MPS patients(r=0.711,n=11,P<0.05),while the phosphorylation level of PDGFR-β was not increased(P>0.05),2.Histological staining showed that the tissue muscle fibers at the MTrPs were round and bulging,accompanied by a central nucleus phenomenon,which proved that the MTrPs were formed by abnormally contracting sarcomere.ELISA results showed that the serum level of PDGF-AA in MPS patients was increased(P<0.001),and immunohistochemistry showed that PDGF-AA was highly expressed in MTrPs(P<0.001).3.The chronic MTrPs model can be established by local strike combined with eccentric exercise,which can well simulate the three most significant characteristics:TBs,pressing pain,and LTRs.The histological morphology is highly similar to human MTrPs,which is the most suitable animal model for studying MPS and MTrPs at present.4.Western blot results showed that p-PDGFR-α was highly expressed in MTrPs of model rats(P<0.001),and histological staining showed that p-PDGFR-α was mainly expressed on the muscle cell membrane.In normal rats,injection of p-PDGFR-αagonist can up-regulate the expression of p-PDGFR-α,induce the decrease of mechanical pain threshold(P<0.001),upregulate the expression of inflammatory factors,and upregulate the expression of muscle contraction-related markers.5.The injection of p-PDGFR-α and JAK2/STAT3 signaling pathway inhibitors alleviated the pain-like behavior and reduced the expression of inflammatory factors,muscle fiber cross-sectional area and the expression of contractile markers in the model rats(P<0.001).Inhibition of JAK2/STAT3 signaling pathway partially rescued the reduction of mechanical tenderness threshold induced by activation of p-PDGFR-α(P<0.001).6.The expression of p-PDGFR-α was up-regulated only by injection of recombinant TNF-α(P<0.05).Dex can inhibit the expression of p-PDGFR-α and reduce peripheral hyperalgesia in MTrPs rats(P<0.001).7.The rat model of myofascial pain has increased immobility time and decreased sucrose preference index in tail suspension test and forced swimming test(P<0.01,P<0.001).At the same time,the expression of Brain-derived neurotrophic factor(BDNF)and 5-Hydroxytryptamine Receptor 1 A(5HT1AR)in hippocampus decreased compared with the control group.This indicates that the myofascial pain rat model is combined with depression.8.The results of histological staining showed that p-PDGFR-α was widely highly expressed in all areas of the hippocampus in the model group,and microglia and astrocytes were activated and inflammatory factors were highly expressed,indicating that neuroinflammation may be an important mechanism.9.The results of Nissl staining showed that hippocampal Nissl bodies in the MTrPs group were solidified,reduced in number,disorganized and irregularly arranged.Meanwhile,some Nissl bodies were fragmented and deeply stained.10.Continuous intraperitoneal injection of p-PDGFR-α and JAK2/STAT3 signaling pathway inhibitors reduced the expression of inflammatory factors in the hippocampus of rats in the MTrPs group,and the number of Nissl bodies increased significantly,the distribution gap was significantly narrowed,the arrangement was more clear,the fragmentation and shrinkage phenomenon was improved,and the depression-like behavior was improved(P<0.05,P<0.01,P<0.001).These results indicated that pPDGFR-α may mediate neuroinflammation and depression-like behaviors via JAK2/STAT3 signaling pathway.ConclusionsP-PDGFR-α mediates myofascial pain,abnormal contraction and inflammatory response at MTrPs in rats by activating JAK2/STAT3 signaling pathway.The positive feedback loop between p-PDGFR-α and TNF-α may be one of the chronic mechanisms.Dex can reduce the expression of p-PDGFR-α and relieve myofascial pain in rats,which has a clinical application prospect.It is the first time that p-PDGFR-α is related to depression-like behavior and may mediate neuroinflammation and depression-like behavior through JAK2/STAT3 signaling pathway in the rat model of myofascial pain,which is an important target for the pathogenesis of depression-pain syndrome.