Activated Satellite Cells in Medial Rectus Muscles of Patients with Strabismus

Autor: Linda K. McLoon, Rosalia Antunes-Foschini, Denise Miyashita, Harley E. A. Bicas
Rok vydání: 2008
Předmět:
Zdroj: Investigative Opthalmology & Visual Science. 49:215
ISSN: 1552-5783
DOI: 10.1167/iovs.07-0507
Popis: Strabismus is a disorder of ocular alignment of unknown etiology.1,2 The lack of knowledge about its cause may explain, in part, why surgical correction of strabismus and the maintenance of adequate alignment and binocularity are so difficult.3,4 Although recent genetic analyses of incomitant strabismus disorders demonstrated that the genetic causes that underlie specific congenital cranial dysinnervation disorders, such as CFEOM1 and -2, are due to mutations in genes critical to development of ocular motor neurons and their axonal connections,5,6 we are still a long way from understanding the possible genetic factors that underlie the various forms of complex strabismus that occur in the absence of known structural brain anomalies. Recent evidence suggests that comitant horizontal strabismus, such as congenital or infantile esotropias and exotropias, can be found in distantly related members of the same family.7 The exotropias are oculomotor disorders in which there is an imbalance between an underactive medial rectus (MR) muscle and an overactive lateral rectus (LR) muscle. The surgical treatment can be achieved by a recession–resection procedure: the LR is recessed while the MR is resected. Congenital or infantile esotropias are convergent deviations, which usually need surgical procedures if angles of deviation are greater than 30 prism diopters. The realignment is obtained by weakening an “overactive” MR (recess procedure) associated or not with strengthening of an “underactive” LR (resection procedure), depending on the size of the deviation. In some cases, when the deviation is very big, even big recess procedures are not enough to realign the eyes. In these situations, resections or marginal tenotomies are alternative techniques.8 The difficulty in producing a successful surgical outcome supports the idea that changes in the muscles themselves before, during, and after strabismus surgical corrections are performed are not well understood. Adult mammalian extraocular muscles (EOMs) express several characteristics that are not normally expressed in adult nonocular skeletal muscles. For example, myofibers of adult EOMs continue to express molecules such as the neonatal and developmental myosin heavy-chain isoforms,9 neural cell adhesion molecule,10 and a variety of muscle mitogens and growth factors.11,12 These molecules are normally downregulated in mature limb skeletal muscle, where they are usually associated only with skeletal muscle development or regeneration. Normal adult EOMs, unlike limb skeletal muscle, continuously remodel individual myofibers throughout life.13,14 In the unperturbed EOMs of adult humans, there is also a small percentage of activated satellite cells, the regenerative cell population found in skeletal muscle, positive for the myogenic lineage-specific marker MyoD.15 This suggests that this process of myofiber remodeling occurs in human EOMs as well. MyoD is expressed in both activated satellite cells and myoblasts but not in myotubes, mature myofibers,16,17 or quiescent satellite cells.18 Based on these data, our objectives were to determine whether the MR muscles of patients with a history of MR underaction or overaction show alterations in the process of satellite cell activation when compared to normal age-matched control muscles.
Databáze: OpenAIRE
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