Thyroid Hormone Plays an Important Role in Cardiac Function: From Bench to Bedside

Thyroid hormones (THs) are synthesized in the thyroid gland, and they circulate in the blood to regulate cells, tissues, and organs in the body. In particular, they exert several effects on the cardiovascular system. It is well known that THs raise the heart rate and cardiac contractility, improve the systolic and diastolic function of the heart, and decrease systemic vascular resistance. In the past 30 years, some researchers have studied the molecular pathways that mediate the role of TH in the cardiovascular system, to better understand its mechanisms of action. Two types of mechanisms, which are genomic and non-genomic pathways, underlie the effects of THs on cardiomyocytes. In this review, we summarize the current knowledge of the action of THs in the cardiac function, the clinical manifestation and parameters of their hemodynamics, and treatment principles for patients with hyperthyroid- or hypothyroid-associated heart disease. We also describe the cardiovascular drugs that induce thyroid dysfunction and explain the mechanism underlying the thyroid toxicity of amiodarone, which is considered the most effective antiarrhythmic agent. Finally, we discuss the recent reports on the involvement of thyroid hormones in the regulation of myocardial regeneration and metabolism in the adult heart.

[New therapeutic avenues for neurosteroids in psychiatric diseases]

Discovered in the eighties by Pr Baulieu and colleagues, neurosteroids are a class of neuroactive brain-born steroids, which comprises the steroid hormones, their biosynthesis precursors and their metabolites. They can act through genomic as well as non-genomic pathways. Genomic pathways, only triggered by the neurosteroid hormones, are, in the brain, the same as those largely described in the periphery: the binding of these steroid hormones to nuclear receptors leads to transcription regulations. On the other hand, their precursors and metabolites, such as pregnenolone (PREG), dehydroepiandrosterone (DHEA), their respective sulfate esters, pregnenolone sulfate (PREG-S) and DHEA sulfate (DHEA-S) and allopregnanolone (ALLOP), are defined as neurosteroids, but no corresponding nuclear receptors have been identified so far. In fact, they trigger non-genomic pathways which consist in (i) inhibitory ionotropic receptors, (ii) excitatory ionotropic receptors and (iii) the microtubular system. Hence, inhibitory neurosteroids, whose mostly studied representative is ALLOP, positively modulate, or directly activate, the ionotropic GABA-A receptors. In contrast, excitatory neurosteroids, represented by PREG-S, DHEA-S and DHEA, inhibit the GABA-A receptors, and activate, directly or indirectly, through the sigma-1 receptors, the NMDA glutamate receptors. Neurosteroids of the third group, the microtubular neurosteroids, are able to bind microtubule associated proteins, in particular MAP2, to promote microtubule assembly, neurite outgrowth and in fine structural neuroplasticity. So far, PREG, DHEA and progesterone are the three identified microtubular neurosteroids. The pharmacological properties of neurosteroids have led to specific investigations for assessing their therapeutic potentialities in psychiatric diseases, using validated animal models. In some cases, clinical trials were also performed. These studies showed that ALLOP, the main inhibitory neurosteroid, displayed clear-cut anxiolytic-like and antidepressant-like efficacy in animals. It has been subsequently developed as Brexanolone and tested with success in phase III of clinical trials for the treatment of post-partum depression. Although showing pro-cognitive properties in animals, the sulfated neurosteroids, PREG-S and DHEA-S, were, in contrast, never tested in clinical trials, probably due to their poor stability and proconvulsivant side effects. Their respective non-sulfated forms, PREG and DHEA, showed antidepressant and antipsychotic efficacies in clinical trials, but these drugs never reached the phase III of clinical development because their therapeutic uses would have led to an overproduction of active metabolites responsible for intolerable side effects. The alternative strategy which has been selected consists of the development of non-metabolizable synthetic derivatives of these natural steroids, which keep the same neuroactive properties as their parent molecules, but are devoid of any hormonal side effects. An example of such innovative drugs is MAP4343, a synthetic derivative of PREG, which exhibits potent antidepressant-like efficacy in validated animal models. It is currently tested in depressed patients.

Progesterone-Mediated Non-Classical Signaling

Progesterone is essential for pregnancy maintenance and menstrual cycle regulation. Hormone action has been primarily ascribed to the well-characterized classical signaling pathway involving ligand binding, activation of nuclear progesterone receptors (PRs), and subsequent activation of genes containing progesterone response elements (PREs). Recent studies have revealed progesterone actions via non-classical signaling pathways, often mediated by non-genomic signaling. Progesterone signaling, in conjunction with growth factor signaling, impacts on the function of growth factors and regulates important physiological actions such as cell growth and remodeling, as well as apoptosis. This review focuses on non-classical progesterone signaling pathways, both including and excluding PR, and highlights how research in this area will provide a better understanding of progesterone actions and may inform novel therapeutic strategies.