Characterization of Myofibroblast Phenotype in Fibrovascular Tissues of Primary and Recurrent Pterygia

Abstract

Abstract: : Purpose: To determine if myofibroblasts are present in pterygia and their cell origin. Methods: A total of 87 pterygium specimens including head, body, and surrounding fibrovascular tissue from 46 primary and 28 recurrent pterygia were stained with Hematoxylin-eosin, immunohistochemically stained with antibodies against alpha-smooth muscle actin (αSMA), desmin (Des), vimentin (Vim) and caldesmon (h-CD), and studied with transmission electron microscopy (TEM). Five exenterated specimens without pterygia were used to search for the origin of myofibroblasts. Fibroblasts subcultured from pterygium fibrovascular tissue were also examined for their phenotype using the above antibodies. Results: Bundles of dense fibrous tissues were noted in 86% of the specimens evaluated. Cells within these bundles were characterized as myofibroblasts based on positive staining to α -SMA, but negative to Des and h-CD - markers for smooth muscle cells. Interestingly, positive α -SMA staining was also found in the periorbital fibroadipose tissue posterior to Tenon’s capsule near the nasal conjunctiva in all exenteration specimens. All subcultured fibroblasts expressed Vim and some were positive to α -SMA, but all were negative to Des or h-CD. TEM revealed ultrastructural features consistent with myofibroblastic differentiation including intracytoplasmic bundles of microfilaments with fusiform densities in the pteryium fibrovascular tissue. Conclusions: This study clearly demonstrates the presence of contractile myofibroblasts in pterygia. We speculate that these cells might have been derived from the periorbital tissue and attracted by pterygial insults including actinic exposure to the ocular surface with subsequent upregulation of α -SMA expression.

Keywords: Pterygium • pathology: human • degenerations/dystrophies