Age-related accumulation of lysosomes and other cytological features in active thyroid follicles of the CBA mouse

Abstract

This study attempts to elucidate the mechanism through which lysosomal accumulation occurs with age in the epithelial cells of the thyroid gland and especially in the "active" follicles of the aging mouse thyroid. Thyroid morphology and function in old CBA (at least 24 months of age) male mice were compared with those in young (2 months of age) animals. The effects of different intake of iodine were tested and compared in both cohorts, each of which was divided into three groups: (i) low iodine group, (ii) moderate iodine group, and (iii) high iodine group. As expected, the present work confirmed the well-known accumulation with age of "cold" follicles coexisting with "active" follicles in the old mouse thyroid. Attention has been focused on the active follicles whose follicular cells contained in their cytoplasm a large number of pleomorphic dense bodies. The lysosomal nature of these bodies, referred to as secondary lysosomes, was confirmed by histochemistry; however, they displayed variability in acid phosphatase staining. In old animals, regardless of the type of iodine regimen, the ratio between relative follicular volume and relative colloid volume as determined by morphometry remained unchanged. Ultrastructurally, the relative volume occupied by secondary lysosomes in "active" follicles was always higher than in the young groups. Autoradiographic studies with 125I revealed that a large part of the radioactivity was located in secondary lysosomes of thyroid cells in "active" follicles of old mice when radioiodine was injected 3 weeks before death. Two different types of vacuoles were present in a non-negligible number of thyrocytes of the "active" follicles in aged cohorts. The first type was made up of grossly dilated rough endoplasmic cisternae, the second corresponded to intracytoplasmic microfollicular vacuoles. Both aspects have been described in conditions of chronic stimulation. It is concluded (1) that different intake of iodine for 6 weeks does not modulate the thyroid morphology in old mice; (2) that in the thyrocytes of the "active" follicles in old mice accumulation of secondary lysosomes occurs due to a slowdown of turnover; and (3) that the follicular cells of "active" follicles feature morphological aspects suggesting a hyperactive state compensating the lack of hormone production in the "cold" follicles.

Orchidectomy of middle-aged rats decreases liver deiodinase 1 and pituitary deiodinase 2 activity

“…At the ultrastructural level, both in SO and in Orx middleaged rats, besides numerous follicular cells with typical organization of cell organelles, quite a few thyrocytes were characterized by dilated and distended RER cisternae. Similar ultrastructural changes were previously reported in thyrocytes of aged mouse thyroid (Tamura & Fujita 1981, Nève & Rondeaux 1991. Tamura & Fujita (1981) described such ultrastructural changes in thyrocytes of 'active' follicles as degenerative.…”

Ultrastructural Changes in Thyroid Follicular Cells During Normal Postnatal Development and After Infrared Laser Radiation

“…The morphological changes found in the thyroid cells suggest that IR radiation has a stimulating e#ect on secretory activity, although the significant dilation of the RER leads us to consider an asynchronicity between the synthesis of the thyroglobulin protein and its glycosylation and transportation by the Golgi apparatus to the colloid [39]. This hypothesis is supported by the decrease in the Fig.…”

“…Another type of morphological alteration, a consequence of the application of IR laser to follicular cells, is the intracellular accumulation of large vacuoles, whose morphological aspect leads us to believe they are colloid droplets, and polymorphic dense bodies, presumably lysosomes. Similar morphological changes have been attributed to the slowdown in turnover of the iodised components in the lysosomes [39,40]. This could be due to the lack of interaction between the colloid droplets and the lysosomes.…”

Histologic and ultrastructural observations on the thyroid gland of the White Fulani (Zebu) cattle in Northern Nigeria

“…An increase in size and number of lysosomes with developmental age was observed in this study, such that in very old pubertal cattle, the flattened (squamous) follicular cells that surrounded highly eosinophilic colloid were seen with large number of lysosome-like bodies, including multivesicular bodies. This indicate thyroid involution at this advanced age of cattle corresponding to-the so called 'cold' follicles of mouse thyroid (Nẻve and Rondeux, 1991). A large number of lysosomes in the cytoplasm of follicular cells possibly represent a common feature in the aging thyroid.…”