Expression And Role Of Rho GTPases In Sarcomeres Of Myofascial Trigger Points

Background and objective:Myofascial trigger points?MTrPs?is the key target of myofascial pain syndrome?MPS?.Located on the palpable taut bands?TBs?or nodules,MTrPs has been proved abnormally contracted sarcomeres.The pathophysiology of these abnormally contracted sarcomeres remains unclear.Rho GTPases?Rho,Racl,Cdc42,etc.?and the downstream kinase ROCK play significant roles in the maintainance of smooth muscle contraction via Ca2+ sensitization mechanism and the regulation of skeletal muscle may be similar with that of smooth muscle.Therefore,we hypothesize that Rho GTPases and ROCK may play vital roles in the pathophysiology of the persistent abnormal contraction of sarcomeres in MTrPs.The aim of the present study was to detect the expression of Rho,Racl,Cdc42 and ROCK2 in the abnormally contracted sarcomeres of MTrPs.Methods:Twenty MPS patients with MTrPs in their upper trapezius muscle were assigned into group M?n=20?,while ten volunteers to receive cervical vertebral surgery without any MTrP in trapezius muscle were assigned into group C?n=10?.Microbiopsy samples were obtained via SuperCore microbiopsy needle.HE and Masson trichrome staining were used to observe the morphology changes of MTrPs.Immunohistochemistry staining was used to detect the expression of Rho?A-C?.Rac1,Cdc42 and ROCK2.Results:HE staining:In longitudinal section,sacomeres in group C were almost identically organized and the sarcomere length of group C was 1.91?0.19?um.For group M,the sarcomeres in region a abnormally contracted[sarcomere length was 0.71?0.32?um?p<0.05 vs.group C?],while the sarcomeres in the adjacent region?region b?were extended[sarcomere length was 2.33?0.31?um?p<0.05 vs.group C;p<0.01 vs.region a of group M?].In cross section,average diameter of group C and group M were 37.37± 3.72 um and 82.61 ± 19.48 um respectively?p<0₀1?.Masson trichrome staining:Muscle fibers from two groups were all red staining and connective tissue around muscle fibers was slightly blue staining.Immunohistochemisty:? Rho and ROCK:Rho?A-C?and ROCK2 were moderately and homogeneously expressed in cytoplasm of group C.In region a of group M,the expression decreased significantly?p<0.01 vs.group C?.In region b of group M,the expression was relatively increased?p<0.05 vs.region a of group M;p>0.05 vs.group C.however?.?Racl:The expression of Racl was moderate and homogeneous in group C.In region a of group M,the expression decreased significantly?p<0.01 vs.group C?.In region b of group M,the expression was significantly increased?p<0.01 vs.region a of group M and p>0.05 vs.group C?.?Cdc42:There has no significant difference among group C and the two regions of group M?p>0.05.respectively?for Cdc42 expression.Conclusion:Rho/ROCK and Racl?not Cdc42?may be involved in the regulation of abnormal sarcomere contraction in MTrPs via Ca2+ sensitization mechanism.Further researches are needed to clarify the exact pathophysiology.