Fas and Bcl-2 protein expression in thyrocytes of patients with nodular goiter

The relative expression of the apoptotic protein Fas and the anti-apoptotic protein Bcl-2 were investigated in thyrocytes from patients with non-toxic nodular goiter (NTG, n=20) and Hashimoto's thyroiditis (HT, n=5), who underwent fine-needle aspiration biopsy for diagnostic reasons. On the basis of the clinical and cytological findings, the patients with NTG were sub-classified into the group of those with colloid nodules (n=9), degenerative nodules (n=6) and adenomatous nodules (n=5).

Fine-needle biopsy aspirates were examined by immunocytochemistry for Fas and Bcl-2 expression, using specific monoclonal antibodies. For the evaluation of Fas and Bcl-2 immuno-reactivity, an expression index, based on the number of cells with positive staining, was used: grade 1 included samples with positive staining in <20% of cells; grade 2 included samples with 20-50% positive cells; and grade 3 included samples with >50% positive cells.

Fas protein expression was generally low (grade 1) in patients with nodular goiter, in contrast to patients with HT, in whom high expression was detected (grade 3). Only in aspirates from degenerative nodules (four out of six), and in which lymphocytes were also present, was Fas expressed at an intermediate level (grade 2). On the other hand, Bcl-2 protein was differentially expressed among the nodule subtypes. It was low in colloid and degenerative nodules (grade 1) but high in adenomatous ones (grades 2 and 3). Bcl-2 expression was also low in patients with HT (grade 1).

It is concluded that in comparison to HT, where there is up-regulation of Fas and down-regulation of Bcl-2 protein, Fas expression is low in human goiter, indicating low apoptotic activity. The regulation of Bcl-2 protein differs between adenomatous and colloid nodules, suggesting that this protein may play a role in the differentiation of thyroid nodules.