Effects of TSH on cAMP levels and thyroid hormone release in human thyroid 'autonomous' nodules: relationship with iodothyronine and iodine content in thyroglobulin

Bipolar mania and epilepsy pathophysiology and treatment may converge in purine metabolism: A new perspective on available evidence

Decreased ATPergic signaling is an increasingly recognized pathophysiology in bipolar mania disease models. In parallel, adenosine deficit is increasingly recognized in epilepsy pathophysiology. Under-recognized ATP and/or adenosine-increasing mechanisms of several antimanic and antiseizure therapies including lithium, valproate, carbamazepine, and ECT suggest a fundamental pathogenic role of adenosine deficit in bipolar mania to match the established role of adenosine deficit in epilepsy. The depletion of adenosine-derivatives within the purine cycle is expected to result in a compensatory increase in oxopurines (uric acid precursors) and secondarily increased uric acid, observed in both bipolar mania and epilepsy. Cortisol-based inhibition of purine conversion to adenosine-derivatives may be reflected in observed uric acid increases and the well-established contribution of cortisol to both bipolar mania and epilepsy pathology. Cortisol-inhibited conversion from IMP to AMP as precursor of both ATP and adenosine may represent a mechanism for treatment resistance common in both bipolar mania and epilepsy. Anti-cortisol therapies may therefore augment other treatments both in bipolar mania and epilepsy. Evidence linking (i) adenosine deficit with a decreased need for sleep, (ii) IMP/cGMP excess with compulsive hypersexuality, and (iii) guanosine excess with grandiose delusions may converge to suggest a novel theory of bipolar mania as a condition characterized by disrupted purine metabolism. The potential for disease-modification and prevention related to adenosine-mediated epigenetic changes in epilepsy may be mirrored in mania. Evaluating the purinergic effects of existing agents and validating purine dysregulation may improve diagnosis and treatment in bipolar mania and epilepsy and provide specific targets for drug development.

The role of thyroglobulin in thyroid hormonogenesis

In humans, the thyroid hormones T₃ and T₄ are synthesized in the thyroid gland in a process that crucially involves the iodoglycoprotein thyroglobulin. The overall structure of thyroglobulin is conserved in all vertebrates. Upon thyroglobulin delivery from thyrocytes to the follicular lumen of the thyroid gland via the secretory pathway, multiple tyrosine residues can become iodinated to form mono-iodotyrosine (MIT) and/or di-iodotyrosine (DIT); however, selective tyrosine residues lead to preferential formation of T₄ and T₃ at distinct sites. T₄ formation involves oxidative coupling between two DIT side chains, and de novo T₃ formation involves coupling between an MIT donor and a DIT acceptor. Thyroid hormone synthesis is stimulated by TSH activating its receptor (TSHR), which upregulates the activity of many thyroid gene products involved in hormonogenesis. Additionally, TSH regulates post-translational changes in thyroglobulin that selectively enhance its capacity for T₃ formation - this process is important in iodide deficiency and in Graves disease. 167 different mutations, many of which are newly discovered, are now known to exist in TG (encoding human thyroglobulin) that can lead to defective thyroid hormone synthesis, resulting in congenital hypothyroidism.

TSH-induced gene expression involves regulation of self-renewal and differentiation-related genes in human bone marrow-derived mesenchymal stem cells

Bone marrow-derived mesenchymal stem cells are pluripotent cells that are capable of differentiating into a variety of cell types including neuronal cells, osteoblasts, chondrocytes, myocytes, and adipocytes. Despite recent advances in stem cell biology, neuroendocrine relations, particularly TSH interactions remain elusive. In this study, we investigated expression and biological consequence of TSH receptor (TSHR) interactions in mesenchymal stem cells of cultured human bone marrow. To the best of our knowledge, we demonstrated for the first time that human bone marrow-derived mesenchymal stem cells expressed a functional thyrotropin receptor that was capable of transducing signals through cAMP. We extended this study to explore possible pathways that could be associated directly or indirectly with the TSHR function in mesenchymal stem cells. Expression of 80 genes was studied by real-time PCR array profiles. Our investigation indicated involvements of interactions between TSH and its receptor in novel regulatory pathways, which could be the important mediators of self-renewal, maintenance, development, and differentiation in bone marrow-derived mesenchymal stem cells. TSH enhanced differentiation to the chondrogenic cell lineage; however, further work is required to determine whether osteoblastic differentiation is also promoted. Our results presented in this study have opened an era of regulatory events associated with novel neuroendocrine interactions of hypothalamic-pituitary axis in mesenchymal stem cell biology and differentiation.

Cytofluorometric analysis of lymphocyte subsets in thyroid aspirates from patients with autonomously functioning nodules

A microscale method, based on two-colour dye immunolabelling and flow sorting cytofluorometry, was used to characterize lymphocyte subsets in thyroid tissue specimens obtained by fine-needle aspiration (FNA) in 21 patients with autonomously functioning thyroid nodule (AFTN) and five patients with cold thyroid nodule (CTN). Inversion of the ratio between CD4+ and CD8+ lymphocytes, due to a relative increase of CD8+ cells, was found among intrathyroidal lymphocytes in AFTN patients. The abnormal lymphocyte subset distribution was not observed in the peripheral blood of the same group of patients. In patients with CTN the lymphocyte subset distribution was normal, both in the thyroid and in the peripheral blood. In AFTN patients, a significant correlation was observed between the decrease of intrathyroidal CD4+/CD8+ ratio and the increase of plasma thyroid hormone levels. Whether the immunological abnormalities found in AFTN could play a pathogenetic role in the clinical presentation and outcome of the disease remains to be established. The FNA-applied micromethod used in this study could be extended as a routine investigation to characterize the immunogenic substrate of thyroid disorders.

Interaction of VIPergic and cholinergic receptors in human thyroid cell

The thyroid tissue is innervated by cholinergic and VIPergic nerves. The present study investigated the possible interactions of cholinergic agents with VIP-induced cAMP accumulation and thyroid hormone release in vitro. Carbamylcholine (Cch), acting through the muscarinic receptor increases cellular cGMP content in cultured human thyroid cells incubated with a phosphodiesterase inhibitor. Cch (10 microM) inhibits cellular cAMP accumulation and thyroxine (T4) release induced by vasoactive intestinal peptide (VIP), with or without a phosphodiesterase inhibitor. Cch (10 microM) inhibits 8-bromo-cAMP-induced T4 release from human thyroid slices. 8-Bromo-cGMP inhibits VIP-induced T4 release from human thyroid slices, only in cells incubated without the phosphodiesterase inhibitor. The results indicate that interactions between VIPergic and cholinergic receptors may be of importance in human thyroid cell.

Catecholamine, vasoactive intestinal peptide and thyrotrophin-dependent cAMP levels display a different sensitivity to iodothyronines in both normal and pathological human thyroid cells in culture

As the interactions of iodothyronines on adrenergic and vipergic receptors are not clear, the effect of exogenous T3 and T4 on catecholamine- and VIP-induced cAMP accumulation in human normal thyroid cells after eight days of primary culture has been investigated. To evaluate the effect of endogenous iodothyronines, the response of the adenylate cyclase system to isoprenaline, adrenaline, VIP, and TSH was studied during a 10 d period. T3 and T4 were unable to modify the catecholamine- and VIP-induced cAMP accumulation in human normal thyroid cells after 6-8 days of culture, while the response to TSH was significantly inhibited. In cells cultured from thyrotoxic tissue, the response of the adenylate cyclase system to catecholamines and VIP, during a 10 d primary culture, showed a behaviour similar to controls. TSH responsiveness was negligible up to the fourth day of culture, while in normal cells a response to all the agonists was present from the beginning. In view of the lack of effect of iodothyronines on catecholamine- and VIP-induced cAMP accumulation, and of the superimposable behaviour of the response to catecholamines and VIP in normal and hyperthyroid cells during the first days of culture, we can conclude that iodothyronines do not directly modify the response of the adenylate cyclase system to adrenergic and vipergic stimulation in human thyroid follicular cells. The lack of responsiveness to TSH of cells obtained from hyperthyroid tissue during the first 4 d of culture, associated with normal responsiveness to catecholamines and VIP, points to a possible involvement of biogenic amines and neuropeptides in sustaining such hyperthyroid states.