Immunohistochemical profiling of the ultimobranchial remnants in the rat postnatal thyroid gland.

Ultimobranchial (UB) remnants are a constant presence in the thyroid throughout rat postnatal life; however, the difficulty in identifying the most immature forms from the surrounding thyroid tissue prompted us to search for a specific marker. With that objective, we applied a panel of antibodies reported to be specific for their human counterpart, solid cell nests (SCNs), using double immunohistochemistry and immunofluorescence. Our results demonstrated that cytokeratin 34ßE12 and p63 are highly sensitive markers for the immunohistologic screening of UB-remnants, independently of their maturity or size. Furthermore, rat UB-follicles (UBFs) coincided with human SCNs in the immunohistochemical pattern exhibited by both antigens. In contrast, the pattern displayed for calcitonin and thyroglobulin differs considerably but confirm the hypothesis that rat UB-cells can differentiate into both types of thyroid endocrine cells. This hypothesis agrees with recent findings that thyroid C-cells share an endodermic origin with follicular cells in rodents. We suggest that the persistence of p63-positive undifferentiated cells in UB-remnants may constitute a reservoir of basal/stem cells that persist beyond embryogenesis from which, in certain unknown conditions, differentiated thyroid cells or even unusual tumors may arise.

Melatonin controls experimental autoimmune encephalomyelitis by altering the T effector/regulatory balance.

Experimental autoimmune encephalomyelitis (EAE), the experimental model for multiple sclerosis (MS), is triggered by myelin-specific Th1 and Th17 cells. The immunomodulatory activities of melatonin have been shown to be beneficial under several conditions in which the immune system is exacerbated. Here, we sought to elucidate the basis of the melatonin protective effect on EAE by characterizing the T effector/regulatory responses, particularly those of the memory cell subsets. Melatonin was tested for its effect on Th1, Th17 and T regulatory (Treg) cells in the lymph nodes and CNS of immunodominant peptide of myelin oligodendrocyte glycoprotein (pMOG)-immunized and EAE mice, respectively. The capacity of melatonin to ameliorate EAE as well as modifying both T cell response and effector/regulatory balance was surveyed. T cell memory subsets and CD44, a key activation marker involved in the EAE pathogenesis, were also examined. Melatonin protected from EAE by decreasing peripheral and central Th1/Th17 responses and enhancing both the Treg frequency and IL-10 synthesis in the CNS. Melatonin reduced the T effector memory population and its pro-inflammatory response and regulated CD44 expression, which was decreased in T effector cells and increased in Tregs. The alterations in the T cell subpopulations were associated with a reduced mononuclear infiltration (CD4 and CD11b cells) of the melatonin-treated mice CNS. For the first time, we report that melatonin protects against EAE by controlling peripheral and central T effector/regulatory responses, effects that might be partially mediated by CD44. This immunomodulatory effect on EAE suggests that melatonin may represent an effective treatment option for MS.

Expression of hypothalamic regulatory peptides in thyroid C cells of different mammals.

Besides intervening in calcium homeostasis by means of calcitonin, C cells are also implicated in the synthesis of an increasing number of regulatory peptides that could exert a paracrine regulation on the neighbouring follicular cells. Among the latest peptides reported in C cells, there are several characteristic hypothalamic peptides, such as TRH, CART, and ghrelin, which are mainly involved in the regulation of the metabolism at hypothalamic-pituitary-thyroid axis. The main aim of the present work has been to study the synthesis of the referred hypothalamic peptides by normal and neoplastic C cells of different mammals as well as in C-cell lines of both rat (CA-77, 6-23) and human (TT) origins in order to elucidate whether this is a fact in this kind of vertebrates. With that objective, we have applied the immunoperoxidase technique to analyze the presence of TRH, CART, ghrelin, and somatostatin in thyroid tissues of different species, and immunofluorescence to study those same peptides in C-cell cultures. Furthermore, we have investigated their expression at mRNA level by RT-PCR analysis. Our results demonstrate immunocolocalization of CART, ghrelin, somatostatin and TRH with calcitonin in normal C cells of different mammals, as well as in rat and human neoplastic C cells. We also confirm the expression of those peptides in rat and human C-cell lines by RT-PCR. Consequently, we can conclude that the synthesis of those peptides by C cells is a general event characteristic of the thyroid gland in mammals.

Postnatal fate of the ultimobranchial remnants in the rat thyroid gland.

The ultimobranchial follicles (UBFs) are considered embryonic remnants from the ultimobranchial body (UBB). They are follicular structures that vary in size and appearance depending on the age of the rat. The main objective of this article was to study the progressive changes in shape, size, and frequency of the UBFs in the postnatal rat, from birth to old-age. To accomplish that objective, a systematic morphometric and incidental study of the UBF has been carried out in 110 Wistar rats of different ages and both sexes, divided into three groups: 1) young rats (5-90-day-old); 2) adult rats (6-15-month-old), and 3) old rats (18-24-month-old). The glands were serially sectioned and immunostained for calcitonin at five equidistant levels. According to our results, UBFs were observed in all thyroid glands but a more exhaustive sampling was occasionally necessary in male rats. In young rats, immature UBFs predominantly appeared whereas in adult rats, mature UBFs with cystic appearance and variable luminal content prevailed. We frequently found spontaneous anomalous UBFs in old rats, which we have termed as "ultimobranchial cystadenomata." Additionally, in young rats, UBF areas significantly increased with age and they were larger when compared to that of normal thyroid follicles. Likewise, in adult rats, UBFs were significantly larger than normal thyroid follicles but only in female rats. In general, UBFs in females were also significantly larger than those found in male rats. Finally, all these differences related to UBFs together with a higher incidence in females of UB cystadenomata suggest a sexual dimorphism in regard to the destiny of these embryonic remnants during postnatal thyroid development.

Functional expression of the thyrotropin receptor in C cells: new insights into their involvement in the hypothalamic-pituitary-thyroid axis.

Thyroid C cells, or parafollicular cells, are mainly known for producing calcitonin, a hormone involved in calcium homeostasis with hypocalcemic and hypophosphatemic effects. Classically, the main endocrine activity of this cell population has been believed to be restricted to its roles in serum calcium and bone metabolism. Nonetheless, in the last few years evidence has been accumulating in the literature with regard to local regulatory peptides secreted by C cells, such as somatostatin, ghrelin, thyrotropin releasing hormone or the recently described cocaine- and amphetamine-related transcript, which could modify thyroid function. As thyrotropin is the main hormone controlling the hypothalamic-pituitary-thyroid axis and, accordingly, thyroid function, we have examined the functional expression of the thyrotropin receptor in C-cell lines and in thyroid tissues. We have found that rat and human C-cell lines express the thyrotropin receptor at both mRNA and protein levels. Furthermore, incubation of C cells with thyrotropin resulted in a 10-fold inhibition of thyrotropin-receptor expression, and a concomitant decrease of the steady-state mRNA levels for calcitonin and calcitonin gene-related peptide determined by quantitative real-time PCR was found. Finally, thyrotropin receptor expression by C cells was confirmed at protein level in both normal and pathological thyroid tissues by immunohistochemistry and immunofluorescence. These results confirm that C cells, under regulation by thyrotropin, are involved in the hypothalamic-pituitary-thyroid axis and suggest a putative role in local fine-tuning of follicular cell activity.

C cells evolve at the same rhythm as follicular cells when thyroidal status changes in rats.

C cells are primarily known for producing calcitonin, a hypocalcemic and hypophosphatemic hormone. Nevertheless, besides their role in calcium homeostasis, C cells may be involved in the intrathyroidal regulation of follicular cells, suggesting a possible interrelationship between the two endocrine populations. If this premise is true, massive changes induced by different agents in the activity of follicular cells may also affect calcitonin-producing cells. To investigate the behaviour of C cells in those circumstances, we have experimentally induced two opposite functional thyroid states. We hyperstimulated the follicular cells using a goitrogen (propylthiouracil), and we suppressed thyroid hormone synthesis by oral administration of thyroxine. In both scenarios, we measured T(4), TSH, calcitonin, and calcium serum levels. We also completely sectioned the thyroid gland, specifically immunostained the C cells, and rigorously quantified this endocrine population. In hypothyroid rats, not only follicular cells but also C cells displayed hyperplastic and hypertrophic changes as well as increased calcitonin levels. When exogenous thyroxine was administered to the rats, the opposite effect was noted as a decrease in the number and size of C cells, as well as decreased calcitonin levels. Additionally, we noted that the two cell types maintain the same numerical relation (10 +/- 2.5 follicular cells per C cell), independent of the functional activity of the thyroid gland. Considering that TSH serum levels are increased in hypothyroid rats and decreased in thyroxine-treated rats, we discuss the potential involvement of thyrotropin in the observed results.