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Activated satellite cells in medial rectus muscles of patients with strabismus

Abstract

Purpose: The goal of this study was to determine if the medial rectus muscles of patients with a history of medial rectus underaction or overaction show alterations in the process of satellite cell activation when compared to normal age-matched control muscles.Methods: Medial rectus muscles were obtained with consent from adult patients undergoing surgical resection due to medial rectus underaction or overaction and prepared for histological examination by fixation and paraffin embedding. Control muscles were obtained from adult cornea donors who had no history of strabismus or neuromuscular disease. Cross-sections were obtained and immunohistochemically for the presence of MyoD-positive satellite cells, and the percentage of MyoD positive satellite cells per myofiber was calculated.Results: As predicted from the literature, MyoD-positive satellite cells, indicative of activation, were present in both the control and resected muscles. In the underacting medial rectus muscles, the frequency of MyoD-positive satellite cells was approximately 2.5 fold higher than the percent seen in control muscles. In the overacting medical rectus muscles, the frequency of MyoD-positive satellite cells was two-fold less than control muscles.Conclusions: The presence of increased numbers of activated satellite cells in the resected underacting medial rectus muscles and the decreased numbers of activated satellite cells in the overacting muscles was unexpected. The upregulation in the number of MyoD positive satellite cells in underacting muscles suggests that there is potential for successful upregulation of muscle size in these muscles, as the cellular machinery for muscle repair and regeneration, the satellite cells, are retained and active in patients with medial rectus underaction. The decreased numbers of activated satellite cells in overacting MR muscle suggests that factors are pushing these muscles toward a more differentiated state. These hypotheses are currently being tested. (AU)

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