Insulin-like growth factor-1 and insulin-like growth factor receptor in thyroid tissues of patients with Graves' disease

Growth factors are frequently involved in the regulation of mitosis and differentiation of several cell types and insulin-like growth factor-1 (IGF-I) is actively involved in the thyroid stimulating hormone-mediated proliferation of thyrocytes. In view of the pivotal role of IGF-1 in thyrocyte proliferation and of the still unsettled role of this growth factor in the pathogenesis of hyperplastic thyroid lesions, we investigated the expression of IGF-I and of its corresponding receptor, by means of immunohistochemistry, in the surgical specimens obtained from six patients with Graves' disease. Moreover, IGF-1 mRNA expression was analysed in one such case by means of Northern hybridisation. All samples showed consistent intracytoplasmic immunoreactivity for both IGF-1 and IGF-I receptor; the vast majority of hyperplastic thyrocytes were strongly decorated by the two antibodies used in this study whereas stromal cells displayed IGF-1 immunoreactivity only. IGF-1 mRNA was markedly overexpressed in Graves' disease in comparison with normal thyroid tissues. The results of this study suggest that IGF-1 and IGF-1 receptor may be actively involved in the pathogenesis of Graves' disease; furthermore, IGF-1 and IGF-I receptor apparently act by different mechanisms (paracrine vs. autocrine) as suggested by their differential expression in epithelial and stromal cells.