Association of endometrosis in horses with differentiation of periglandular myofibroblasts and changes of extracellular matrix proteins

Periglandular fibrosis and cystic dilation of uterine glands are associated with equine endometrosis. The presence of extracellular matrix proteins (c ollagen type I, III and IV, laminin and fibronectin) in healthy and endomet rotic specimens was demonstrated by immunohistochemistry. The distribution of collagen I, but not collagen III, was dependent on the stage of the oest rous cycle. The arrangement of collagen I and collagen III in endometrotic specimens was similar to that in normal endometrium. In periglandular fibro sis, collagen IV, laminin and fibronectin deposition outside the basement m embrane was observed. In these regions, stromal cells were characterized im muno-histochemically as myofibroblasts because of their expression of a-smo oth muscle actin, and occasionally tropomyosin and desmin. Periglandular di fferentiation of contractile cells could be interpreted as a reaction to su pport the extrusion of secretions in cystic dilated glands. Moreover, the c hanges of extracellular matrix proteins are characteristic for neoplastic l esions, although further development of endometrosis to benign or malignant tumours is not known in horses. Knowledge of the factors responsible for t hese fibroblastic modulations may be the key to explaining the pathogenesis of endometrosis.