Study On Muscular Pathology And Expression Of MyoD And Myogenin In Concomitant Exotropia

Objective:To probe the number of the MyoD-and myogenin-positiveactivated satellite cells,mRNA expression of MyoD and myogenin gene,which are the members of MRFs,and pathological changes.in patients withconcomitant extropia.To investigate the relationship of these factors and therole of MyoD and myogenin in the etiology of concomitant extropia.Methods:In part 1:to collect 24 cases with concomitant extropia and thendivide them into 4 groups which are the group of children with congenitalextropia,the group of children with intermittent extropia,the group of adultswith concomitant extropia and adults control group.Medial rectus muscles wereobtained with consent from patients undergoing surgical resection and were preparedfor histologic examination by fixation and paraffin embedding.Control muscles wereobtained from patients undergoing ophthalmectomy who had no history of strabismusor neuromuscular disease.Cross sections were obtained and stained by HE methodfor observing the pathological changes and measuring the cross-sectional area ofmyofibers.Cross sections were stained simmunohistochemically for the presence ofactivated satellite cells,as identified by MyoD and myogenin immunoreactivity.Thepercentages of MyoD-and myogenin-positive satellite cells per 100 myofibers incross section were calculated.In part 2:to collect 27 cases with concomitantextropia and then divide them into the same groups as that in part 1 and obtainthe muscles Using semiquantitative real-time PCR with SYBR Green,mRNA expression of MyoD and myogenin gene were calculated.To compareall the quantified data in different groups.Results:The medial rectus muscles from the patients with extropia showedthe remarkable pathological changes,the decreased cross-sectional area ofmyofibers (288.5±65.3μm~2) and the decreased numbers of MyoD-(2.2%±1.2%) and myogenin-positive (2.4±2.3%) satellite cells comparingwith control group (820.0±42.7μm~2,4.0%±0.5%,4.4±0.38%,respectively)(P＜0.05).The cross-sectional area of myofibers and the number of MyoD-satellite cells were decreased in the group of children with congenital extropia (241.0±28.9μm~2,2.0%±0.1%,respectively),comparing with the group ofchildren with intermittent extropia (310.0±95.3μm~2,3.0%±1.5%,respectively).However,there was no significant differences between twogroups.The number of myogenin-positive satellite cells (0.6±0.1%) weredecreased in the former comparing with that (4.0±2.3%) in the latter(P＜0.05) The group of adults with extropia had decreased thecross-sectional area of myofibers (303.5±35.6μm~2) and the numbers ofMyoD-(1.6±1.1%) and myogenin-positive (2.5±1.6%) satellitecells,comparing with the group of children with intermittent extropia,however,there is no significant difference.The group of adults with extropiahad significantly decreased the cross-sectional area of myofibers and thenumbers of MyoD-and myogenin-positive satellite cells,comparing withadults control group(P＜0.05).There were significant differences (P＜0.05)in mRNA expression of MyoD gene between the group of children withcongenital extropia (0.52±0.19) and the group of children with intermittentextropia (0.96±0.55),the group of adults with extropia (0.20±0.19) and thegroup of children with intermittent extropia,and between the group of adultswith extropia and control group (0.42±0.10).The formers had lower levelthan the latters.There were negative correlation between mRNA expressionof MyoD gene and prism diopter of deviation and between mRNA expressionofMyoD gene and patients' age (r=-0.528,P=0.014;r=-0.467,P=0.033,respectively).There was no difference in mRNA expression of myogenin geneamong the groups.Conclusions:There were muscular artrophy with decreased the numberof myofibers and cross-sectional area of that,accompanied with sarcomeredamaging and hyperplastic collagen tissue.MyoD has the role of masterswitch in the processing of myoblastic specific gene regulation.Thedecreased level of mRNA expression of MyoD gene may cause the decreasedthe numbers of MyoD-and myogenin-positive satellite cells,whichsuppressed the self-renewal and repairing process in extraocular muscle.Weconsidered it may be the muscular eitiology of concomitant exotropia with deteriorating process.Although it was not defined as the first cause forcongenital exotropia,the decreased level of mRNA expression of MyoD genemay affect the muscular development after birth.So we considered it shouldbe one of the factors which cause early onset and large deviation in congenitalexotropia.Unchanged mRNA expression level of myogenin gene mayberelate with sustaining existing MHC-I in the media rectus,or may becaused by mRNA not being translated to functional protein.