The Effects of Intra-Articular Triamcinolone and Autologous Protein Solution on Metabolic Parameters in Horses.

Intra-articular corticosteroids are a popular treatment choice for joint-associated pain and inflammation in horses despite recent work on the metabolic effects of these drugs. The goal of this project was to compare metabolic effects between intra-articular (IA) triamcinolone acetonide (TA) and an autologous protein solution (APS). Five mixed-breed geldings (4-9 years) were utilized for this project. Three identical and consecutive 28-day treatment blocks were used, with metacarpophalangeal IA treatments consisting of equal volumes of saline, a commercially available APS, or 9 mg of TA. Regular plasma and serum samples were collected for ACTH, cortisol, glucose, insulin, and thyroid hormone analysis, in addition to thyrotropin-releasing hormone (TRH) and oral sugar tests (OSTs). Significant treatment effects of IA TA were present at 48 h post-injection in both the TRH and the OST. There was also significant suppression by IA TA of baseline ACTH and cortisol between 2 h and 96 h post-treatment, hyperglycemia between 12 h and 48 h, and hyperinsulinemia at 32 h post-treatment. There were no treatment effects with respect to any measured thyroid hormones, nor were there any significant treatment effects of APS noted. Results suggest at least 2 days and up to 7 days should elapse between a single 9 mg IA TA treatment and OST and/or TRH testing. This study found that TA exhibits significant effects on ACTH, cortisol, glucose, and insulin, while the APS does not.

Novel Leptin-Cardiac TRH pathway responsible for the cardiac alterations in the Hyperleptinemic obesity.

The association between hypertension and obesity-induced cardiac damage is usually accepted. However, no studies have been focused on cardiac alterations in obesity, independently of blood pressure increase. It is well known that Cardiac TRH induces Left Ventricular Hypertrophy (LVH) and fibrosis, and its inhibition prevents the development of hypertrophy. Also, it has been described that the adiponectin leptin induces TRH expression. Thus, we hypothesized that in obesity, the increase in TRH induced by hyperleptinemia is responsible for LVH, until now mostly attributed to pressure load. We studied obese Agouti mice suffering from hypertension with hyperleptinemia and found a significant LVH development with increased TRH gene expression. Consequently, we found higher fibrotic (collagens and TGF-ß) and hypertrophic markers (BNP and ß-MHC) expression vs lean black controls. As pressure could explain these results, we treated obese mice with diuretic (hydrochlorothiazide 20 mg/kg/day) since weaning. Diuretic treatment was successful as the diuretic group was normotensive in contrast to control obese mice. Nevertheless, both groups showed LVH development, higher cardiac precursor TRH gene and peptide expressions and elevated fibrotic and hypertrophic markers expression, pointing out that obesity-induced LVH is not due to hypertension. In addition, we performed Cardiac TRH inhibition by specific siRNA injection compared to control siRNA treatment and evaluated cardiac damage. As expected, expressions and protein increase in hypertrophic and fibrotic markers observed in the AG mouse with the native cTRH system were not seen in the AG mouse with the cTRH silencing. Indeed, the AG + TRH-siRNA group showed hypertrophic markers expression and fibrosis measurements similar to the lean BL mice. On the whole, these results point out that the novel Leptin-Cardiac TRH pathway is responsible for the cardiac alterations present in hyperleptinemic obesity, independent of blood pressure, and cTRH long-term silencing since early stages totally prevent LVH development and cardiac fibrosis.

Novel DNA methylation biomarkers for early diagnosis of oral tongue squamous cell carcinoma (OTSCC).

Oral tongue squamous cell carcinoma (OTSCC) is the most common malignancy type among males across the world. However, analysis of molecular markers could be useful in detecting the early-stage OTSCC, which would allow optimal clinical treatments and prolong the survival rate of patients consequently. The study has the objective of detecting the role of salivary biomarkers based on gene promoter hypermethylation. Sample data from 45 OTSCC and normal groups were analyzed to exhibit the methylation levels of salivary biomarkers (TRH, FHIT, MGMT, p16, and RASSF1A). The specificity and sensitivity analysis of methylation biomarkers was conducted in addition to the receiver operating characteristic (ROC) curve for both early-stage and advanced OTSCC stages. Quantitative data findings showed the perfect sensitivity and specificity for TRH, MGMT, p16, and RASSF1A with 100%, and > 90%, respectively. In addition, the results indicated an inefficient area under curves (> 0.7) for these biomarkers to detect the OTSCC. There were no significant differences observed between TRH and FHIT and p16 and MGMT based on the Wilcoxon signed-rank test. The methylation statuses of genes TRH, RASSF1A, p16, and MGMT might become utilized as predictive biomarkers for clinical application in early diagnosis of OTSCC and noninvasive oral cancer screening.

Regulation of phosphosignaling pathways involved in transcription of cell cycle target genes by TRH receptor activation in GH1 cells.

Thyrotropin-releasing hormone (TRH) is known to activate several cellular signaling pathway, but the activation of the TRH receptor (TRH-R) has not been reported to regulate gene transcription. The aim of this study was to identify phosphosignaling pathways and phosphoprotein complexes associated with gene transcription in GH1 pituitary cells treated with TRH or its analog, taltirelin (TAL), using label-free bottom-up mass spectrometry-based proteomics. Our detailed analysis provided insight into the mechanism through which TRH-R activation may regulate the transcription of genes related to the cell cycle and proliferation. It involves control of the signaling pathways for ß-catenin/Tcf, Notch/RBPJ, p53/p21/Rbl2/E2F, Myc, and YY1/Rb1/E2F through phosphorylation and dephosphorylation of their key components. In many instances, the phosphorylation patterns of differentially phosphorylated phosphoproteins in TRH- or TAL-treated cells were identical or displayed a similar trend in phosphorylation. However, some phosphoproteins, especially components of the Wnt/ß-catenin/Tcf and YY1/Rb1/E2F pathways, exhibited different phosphorylation patterns in TRH- and TAL-treated cells. This supports the notion that TRH and TAL may act, at least in part, as biased agonists. Additionally, the deficiency of ß-arrestin2 resulted in a reduced number of alterations in phosphorylation, highlighting the critical role of ß-arrestin2 in the signal transduction from TRH-R in the plasma membrane to transcription factors in the nucleus.

The TRH test provides valuable information in the diagnosis of central hypothyroidism in patients with known pituitary disease and low T4 levels.

Objective: To evaluate the value of the thyrotropin-releasing hormone (TRH) test in the diagnosis of central hypothyroidism (CH) in patients with pituitary disease. Methods: Systematic evaluation of 359 TRH tests in patients with pituitary disease including measurements of thyroxine (T4), TBG-corrected T4 (T4corr), baseline TSH (TSH0) and relative or absolute TSH increase (TSHfold, TSHabsolute). Results: Patients diagnosed with CH (n=39) show comparable TSH0 (p-value 0.824) but lower T4corr (p-value <0.001) and lower TSH increase (p-value <0.001) compared to patients without CH. In 54% (42 of 78 cases) of patients with low T4corr, the CH diagnosis was rejected based on a high TSHfold. In these cases, a spontaneous increase and mean normalization in T4corr (from 62 to 73 nmol/L, p-value <0.001) was observed during the follow-up period (7.6 ± 5.0 years). Three of the 42 patients (7%) were started on replacement therapy due to spontaneous deterioration of thyroid function after 2.8 years. Patients diagnosed with CH reported significantly more symptoms of hypothyroidism (p-value 0.005), although, symptoms were reported in most patients with pituitary disease. The TRH test did not provide clinical relevant information in patients with normal T4 or patients awaiting pituitary surgery (78%, 281 of 359). There were only mild and reversible adverse effects related to the TRH test except for possibly one case (0.3%) experiencing a pituitary apoplexy. Conclusion: The TRH test could be reserved to patients with pituitary disease, low T4 levels without convincing signs of CH. Approximately 50% of patients with a slightly decreased T4 were considered to have normal pituitary thyroid function based on the TRH test results.

Efficiency of CIN2+ Detection by Thyrotropin-Releasing Hormone (TRH) Site-Specific Methylation.

Cervical cancer screening typically involves a Pap smear combined with high-risk human papillomavirus (hr-HPV) detection. Women with hr-HPV positivity but normal cytology, as well as those with precancerous abnormal cytology, such as low-grade squamous intraepithelial lesions (LSIL) and high-grade SIL (HSIL), are referred for colposcopy and histology examination to identify abnormal lesions, such as cervical intraepithelial neoplasia (CIN) and cervical cancer. However, in order to enhance the accuracy of detection, bioinformatics analysis of a microarray database was performed, which identified cg01009664, a methylation marker of the thyrotropin-releasing hormone (TRH). Consequently, a real-time PCR assay was developed to distinguish CIN2+ (CIN2, CIN3, and cervical cancer) from CIN2- (CIN1 and normal cervical epithelia). The real-time PCR assay utilized specific primers targeting methylated cg01009664 sites, whereas an unmethylated reaction was used to check the DNA quality. A cut-off value for the methylated reaction of Ct < 33 was established, resulting in improved precision in identifying CIN2+. In the first cohort group, the assay demonstrated a sensitivity of 93.7% and a specificity of 98.6%. In the cytology samples identified as atypical squamous cells of undetermined significance (ASC-US) and LSIL, the sensitivity and specificity for detecting CIN2+ were 95.0% and 98.9%, respectively. However, when self-collected samples from women with confirmed histology were tested, the sensitivity for CIN2+ detection dropped to 49.15%, while maintaining a specificity of 100%. Notably, the use of clinician-collected samples increased the sensitivity of TRH methylation testing. TRH methylation analysis can effectively identify women who require referral for colposcopy examinations, aiding in the detection of CIN2+.

New Efforts to Demonstrate the Successful Use of TRH as a Therapeutic Agent.

Thyrotropin-releasing hormone (TRH) is a tripeptide that regulates the neuroendocrine thyroid axis. Moreover, its widespread brain distribution has indicated that it is a relevant neuromodulator of behaviors such as feeding, arousal, anxiety, and locomotion. Importantly, it is also a neurotrophic peptide, and thus may halt the development of neurodegenerative diseases and improve mood-related disorders. Its neuroprotective actions on those pathologies and behaviors have been limited due to its poor intestinal and blood-brain barrier permeability, and because it is rapidly degraded by a serum enzyme. As new strategies such as TRH intranasal delivery emerge, a renewed interest in the peptide has arisen. TRH analogs have proven to be safe in animals and humans, while not inducing alterations in thyroid hormones' levels. In this review, we integrate research from different approaches, aiming to demonstrate the therapeutic effects of TRH, and to summarize new efforts to prolong and facilitate the peptide's actions to improve symptoms and the progression of several pathologies.

Thyrotropin-releasing hormone stimulates NR4A3 expression in the pituitary thyrotrophs of proestrus rats.

The secretion of several hypothalamic peptide hormones is activated during the preovulatory period. Hypothalamic thyrotropin-releasing hormone (TRH) is one such hormone with reproductive and/or metabolic significance. However, it remains unclear whether thyroid-stimulating hormone (TSH)-producing thyrotrophs are produced during the preovulatory period. We previously found a transient increase in the expression of the nuclear receptor NR4A3, a well-known immediate early gene, in the proestrus afternoon in the anterior pituitary glands of rats. To investigate the relationship between TRH secretion and pituitary NR4A3 expression during proestrus, we used proestrus and thyroidectomized rats to identify NR4A3-expressing cells and examined the regulation of Nr4a3 gene expression via the hypothalamus-pituitary-thyroid (HPT) axis. The percentage of NR4A3-expressing cells increased in thyrotrophs at 14:00 h of proestrus. Incubation of rat primary pituitary cells with TRH transiently stimulated Nr4a3 expression. Thyroidectomy to attenuate the negative feedback effects led to increased serum TSH levels and Nr4a3 gene expression in the anterior pituitary, whereas thyroxine (T4) administration conversely suppressed Nr4a3 expression. Additionally, the administration of T4 or TRH antibodies significantly suppressed the increase in Nr4a3 expression at 14:00 h of proestrus. These results demonstrate that pituitary NR4A3 expression is regulated by the HPT axis, and that TRH stimulates thyrotrophs and induces NR4A3 expression during the proestrus afternoon. This suggests the potential involvement of NR4A3 in the regulation of the HPT axis during pre- and post-ovulatory periods.

Hypothyroidism-associated immunosuppression involves induction of galectin-1-producing regulatory T cells.

Hypothyroidism exerts deleterious effects on immunity, but the precise role of the hypothalamic-pituitary-thyroid (HPT) axis in immunoregulatory and tolerogenic programs is barely understood. Here, we investigated the mechanisms underlying hypothyroid-related immunosuppression by examining the regulatory role of components of the HPT axis. We first analyzed lymphocyte activity in mice overexpressing the TRH gene (Tg-Trh). T cells from Tg-Trh showed increased proliferation than wild-type (WT) euthyroid mice in response to polyclonal activation. The release of Th1 pro-inflammatory cytokines was also increased in Tg-Trh and TSH levels correlated with T-cell proliferation. To gain further mechanistic insights into hypothyroidism-related immunosuppression, we evaluated T-cell subpopulations in lymphoid tissues of hypothyroid and control mice. No differences were observed in CD3/CD19 or CD4/CD8 ratios between these strains. However, the frequency of regulatory T cells (Tregs) was significantly increased in hypothyroid mice, and not in Tg-Trh mice. Accordingly, in vitro Tregs differentiation was more pronounced in naïve T cells isolated from hypothyroid mice. Since Tregs overexpress galectin-1 (Gal-1) and mice lacking this lectin (Lgals1-/- ) show reduced Treg function, we investigated the involvement of this immunoregulatory lectin in the control of Tregs in settings of hypothyroidism. Increased T lymphocyte reactivity and reduced frequency of Tregs were found in hypothyroid Lgals1-/- mice when compared to hypothyroid WT animals. This effect was rescued by the addition of recombinant Gal-1. Finally, increased expression of Gal-1 was found in Tregs purified from hypothyroid WT mice compared with their euthyroid counterpart. Thus, a substantial increase in the frequency and activity of Gal-1-expressing Tregs underlies immunosuppression associated with hypothyroid conditions, with critical implications in immunopathology, metabolic disorders, and cancer.

Hypothalamic-prolactin axis regulation in major depressed patients with suicidal behavior.

BACKGROUND: So far, little is known about the control of hypothalamic-prolactin axis activity by dopamine (DA) and thyrotropin-releasing hormone (TRH) in depressed patients with suicidal behavior disorder (SBD). METHODS: We evaluated prolactin (PRL) responses to apomorphine (APO; a DA direct receptor agonist) and 0800 h and 2300 h protirelin (TRH) tests in 50 medication-free euthyroid DSM-5 major depressed inpatients with SBD (either current [n = 22], or in early remission [n = 28]); and 18 healthy hospitalized controls (HCs). RESULTS: Baseline (BL) PRL levels were comparable across the three diagnostic groups. SBDs in early remission did not differ from HCs regarding PRL suppression to APO (PRLs), PRL stimulation to 0800 h and 2300 h TRH tests (∆PRL), and ∆∆PRL values (difference between 2300 h-∆PRL and 0800 h-∆PRL values). Current SBDs showed lower PRLs and ∆∆PRL values than HCs and SBDs in early remission. Further analyses revealed that current SBDs with a history of violent and high-lethality suicide attempts were more likely to exhibit co-occurrence of low ∆∆PRL and PRLS values. CONCLUSIONS: Our results suggest that regulation of the hypothalamic-PRL axis is impaired in some depressed patients with current SBD, particularly those who have made serious suicide attempts. Considering the limitations of our study, our findings support the hypothesis that decreased pituitary D2 receptor functionality (possibly adaptive to increased tuberoinfundibular DAergic neuronal activity) together with decreased hypothalamic TRH drive might be a biosignature for high-lethality violent suicide attempts.

Role of Thyrotropin-Releasing Hormone in Regulating Fibroblast Growth Factor 21 in Mouse Pancreatic ß Cells.

Background: Thyrotropin-releasing hormone (TRH) is primarily produced in the hypothalamus and regulates the thyrotropin secretion from the pituitary. TRH is distributed ubiquitously in the extrahypothalamic region, especially in pancreatic islets, while its physiological role remains nebulous. We have previously established a TRH-deficient mouse model, and showed impaired glucose tolerance and downregulated expression of fibroblast growth factor 21 (FGF21) in islets. Recent studies have demonstrated the physiological roles of pancreatic FGF21. Therefore, in this study, we elucidate the direct functions of TRH in pancreatic islets via the regulation of FGF21. Methods: To explore the functions of TRH in pancreatic islets, a microarray analysis using isolated islets from TRH-knockout mice was conducted. The regulatory mechanism of TRH in pancreatic FGF21 was investigated using islet cell lines; reverse transcription-quantitative polymerase chain reaction and Western blotting were used to determine the mRNA and protein expression levels of FGF21 in pancreatic islets and islet cell lines. Induction of FGF21 expression by TRH treatment was examined in vitro. To identify the transcription factors binding to the region responsible for TRH-induced stimulation of the FGF21 promoter, electromobility shift assays were conducted. Results: Among the detected and considerably changed genes in microarray, FGF21 was the most consistently downregulated in TRH-deficient mice islets. FGF21 was strongly co-expressed with insulin in mouse islets, and TRH stimulated endogenous Fgf21 mRNA expression in the islet cell line ßHC9. The E-box site in the FGF21 promoter was responsible for TRH-induced stimulation via the extracellular signal-regulated kinase (ERK)1/2 signaling pathway. The transcription factor upstream stimulatory factor 1 (USF1) could specifically bind to the E-box site. Overexpression of USF1 increased FGF21 promoter activity. Conclusion: FGF21 was transcriptionally upregulated by TRH through the ERK1/2 and USF1 pathways in pancreatic ß cells.

TRH and NPY Interact to Regulate Dynamic Changes in Energy Balance in the Male Zebra Finch.

In contrast to mammals, birds have a higher basal metabolic rate and undertake wide range of energy-demanding activities. As a consequence, food deprivation for birds, even for a short period, poses major energy challenge. The energy-regulating hypothalamic homeostatic mechanisms, although extensively studied in mammals, are far from clear in the case of birds. We focus on the interplay between neuropeptide Y (NPY) and thyrotropin-releasing hormone (TRH), 2 of the most important hypothalamic signaling agents, in modulating the energy balance in a bird model, the zebra finch, Taeniopygia guttata. TRH neurons were confined to a few nuclei in the preoptic area and hypothalamus, and fibers widely distributed. The majority of TRH neurons in the hypothalamic paraventricular nucleus (PVN) whose axons terminate in median eminence were contacted by NPY-containing axons. Compared to fed animals, fasting significantly reduced body weight, PVN pro-TRH messenger RNA (mRNA) and TRH immunoreactivity, but increased NPY mRNA and NPY immunoreactivity in the infundibular nucleus (IN, avian homologue of mammalian arcuate nucleus) and PVN. Refeeding for a short duration restored PVN pro-TRH and IN NPY mRNA, and PVN NPY innervation to fed levels. Compared to control tissues, treatment of the hypothalamic superfused slices with NPY or an NPY-Y1 receptor agonist significantly reduced TRH immunoreactivity, a response blocked by treatment with a Y1-receptor antagonist. We describe a detailed neuroanatomical map of TRH-equipped elements, identify new TRH-producing neuronal groups in the avian brain, and demonstrate rapid restoration of the fasting-induced suppression of PVN TRH following refeeding. We further show that NPY via Y1 receptors may regulate PVN TRH neurons to control energy balance in T. guttata.

Current Review of the Function and Regulation of Tuberoinfundibular Dopamine Neurons.

Tuberoinfundibular dopamine (TIDA) neurons have cell bodies located in the arcuate nucleus of the mediobasal hypothalamus. They project to the external zone of the median eminence, and the dopamine (DA) released there is carried by the hypophysial portal vasculature to the anterior pituitary. The DA then activates D2 receptors to inhibit prolactin (PRL) secretion from lactotrophs. The TIDA neuronal population is the principal regulatory factor controlling PRL secretion. The neuroendocrine role subserved by TIDA neurons sets them apart from other dopaminergic populations like the nigrostriatal and mesolimbic DA neurons. TIDA neurons exhibit intrinsic oscillatory fluctuations in their membrane potential that give rise to phasic firing and bursting activity. TIDA neuronal activity is sexually differentiated and modulated by gonadal hormones and PRL, as well as an array of small molecule and peptide neurotransmitters. This review covers these characteristics.

TRH Regulates the Synthesis and Secretion of Prolactin in Rats with Adenohypophysis through the Differential Expression of miR-126a-5p.

Prolactin (PRL) is an important hormone that is secreted by the pituitary gland and plays an important role in the growth, development and reproduction of organisms. Thyrotropin-releasing hormone (TRH) is a common prolactin-releasing factor that regulates the synthesis and secretion of prolactin. In recent studies, microRNAs (miRNAs) have been found to play a key role in the regulation of pituitary hormones. However, there is a lack of systematic studies on the regulatory role that TRH plays on the pituitary transcriptome, and the role of miRNAs in the regulation of PRL synthesis and secretion by TRH lacks experimental evidence. In this study, we first investigated the changes in PRL synthesis and secretion in the rat pituitary gland after TRH administration. The results of transcriptomic analysis after TRH treatment showed that 102 genes, including those that encode Nppc, Fgf1, PRL, Cd63, Npw, and Il23a, were upregulated, and 488 genes, including those that encode Lats1, Cacna2d1, Top2a, and Tfap2a, were downregulated. These genes are all involved in the regulation of prolactin expression. The gene expression of miR-126a-5p, which regulates the level of PRL in the pituitary gland, was screened by analysis prediction software and by a dual luciferase reporter system. The data presented in this study demonstrate that TRH can regulate prolactin synthesis and secretion through miR-126a-5p, thereby improving our understanding of the molecular mechanism of TRH-mediated PRL secretion and providing a theoretical basis for the role of miRNAs in regulating the secretion of pituitary hormones.

The Hypothalamic-Pituitary-Thyroid Axis Equivalent in Normal and Cancerous Oral Tissues: A Scoping Review.

The hypothalamic-pituitary-thyroid (HPT) axis is crucial in regulating thyroid hormone levels that contribute to the development and homeostasis of the human body. Current literature supports the presence of a local HPT axis equivalent within keratinocytes of the skin, with thyroid hormones playing a potential role in cancer progression. However, this remains to be seen within oral tissue cells. An electronic search of Scopus and PubMed/Medline databases was conducted to identify all original publications that reported data on the production or effects of HPT axis components in normal or malignant cells of the oral cavity. The search identified 221 studies, of which 14 were eligible. Eight studies were retrospective analyses of clinical samples, one study involved both in vivo and in vitro experiments, and the remaining five studies were conducted in vitro using cell lines. The search identified evidence of effects of HPT components on oral cancer cells. However, there were limited data for the production of HPT axis components by oral tissues. We conclude that a possible role of the local HPT axis equivalent in the oral mucosa may not be established at present. The gaps in knowledge identified in this scoping review, particularly regarding the production of HPT components by oral tissues, warrant further investigation.

Prospective Case Series of Clinical Signs and Adrenocorticotrophin (ACTH) Concentrations in Seven Horses Transitioning to Pituitary Pars Intermedia Dysfunction (PPID).

Poor recognition of subtle clinical abnormalities and equivocal ACTH concentrations make early diagnosis of PPID difficult. Progressive clinical findings and corresponding ACTH concentrations in horses transitioning to PPID over time have not been documented. Seven horses with ACTH concentrations equivocal for PPID (utilizing locally derived, seasonally adjusted diagnostic-cut off values (DCOV)) and no clinical signs of PPID were selected. Sequential measurement of basal and thyrotropin-releasing hormone (TRH)-stimulated ACTH concentrations and recording of clinical findings occurred from October 2017 to November 2021 in a prospective case series. In two horses, marked hypertrichosis developed. Although 1/11 basal ACTH concentrations were below DCOV in 2018, subsequently all basal ACTH concentrations in these two horses without treatment were greater than DCOV. One horse was treated with pergolide which normalized basal ACTH concentrations. Four horses developed intermittent, mild hypertrichosis, and one horse never developed hypertrichosis. Basal ACTH concentrations in these five horses were greater than DCOV in 63/133 (47.4%) of testing points. TRH-stimulated ACTH concentrations in these five horses were greater than DCOV in 77/133 (57.9%) of testing points, sometimes markedly increased and greater than the assay upper limit of detection (LoD) of 1250pg/mL. TRH-stimulated ACTH concentrations were most frequently positive in late summer and early autumn, with 24/37 (64.9%) of TRH-stimulated ACTH concentrations greater than the DCOV in February and March. Horses transitioning to PPID can have subtle clinical signs and equivocal ACTH concentrations. However, TRH-stimulated ACTH concentrations can be markedly greater than DCOV, especially in late summer and early autumn (February and March) allowing for identification of subclinical and transitional cases.

Biochemical and physiological insights into TRH receptor-mediated signaling.

Thyrotropin-releasing hormone (TRH) is an important endocrine agent that regulates the function of cells in the anterior pituitary and the central and peripheral nervous systems. By controlling the synthesis and release of thyroid hormones, TRH affects many physiological functions, including energy homeostasis. This hormone exerts its effects through G protein-coupled TRH receptors, which signal primarily through Gq/11 but may also utilize other G protein classes under certain conditions. Because of the potential therapeutic benefit, considerable attention has been devoted to the synthesis of new TRH analogs that may have some advantageous properties compared with TRH. In this context, it may be interesting to consider the phenomenon of biased agonism and signaling at the TRH receptor. This possibility is supported by some recent findings. Although knowledge about the mechanisms of TRH receptor-mediated signaling has increased steadily over the past decades, there are still many unanswered questions, particularly about the molecular details of post-receptor signaling. In this review, we summarize what has been learned to date about TRH receptor-mediated signaling, including some previously undiscussed information, and point to future directions in TRH research that may offer new insights into the molecular mechanisms of TRH receptor-triggered actions and possible ways to modulate TRH receptor-mediated signaling.

Thyrotropin-releasing hormone analog as a stable upper airway-preferring respiratory stimulant with arousal properties.

Taltirelin is a stable, brain-penetrating thyrotropin-releasing hormone (TRH) analog with minimal endocrine activity and potential respiratory stimulant properties. Taltirelin's receptor target shows high differential expression at the hypoglossal motor nucleus, and local taltirelin microperfusion into the hypoglossal motor nucleus causes sustained tongue motor activation compared with the transient activating effects of TRH itself. Here, we performed a randomized, within-subject, repeated-measures design over six separate study days (separated by at least 72 h) in chronically instrumented male (n = 10) and female (n = 9) rats to identify effects on sleep and breathing. Vehicle controls or taltirelin (0.1 and 1 mg/kg) with and without trazodone (30 mg/kg) were administered by intraperitoneal injection. Trazodone was included due to clinical interest in the context of sleep apnea pharmacotherapy as it can suppress arousal without compromising pharyngeal muscle activity. Systemically administered taltirelin (1 but not 0.1 mg/kg) increased tonic and within-breath phasic tonic muscle activity compared with vehicle controls (P ≤ 0.007), with little or no changes in diaphragm amplitude or respiratory rate. Taltirelin also suppressed nonrapid eye movement (non-REM) sleep and increased wakefulness (P ≤ 0.037). Other indices of taltirelin-induced central nervous system arousal included increased trapezius muscle tone in non-REM sleep and decreased total electroencephalogram power and δ (0.5-4 Hz) power (P ≤ 0.046). These effects were especially apparent in non-REM sleep and not prevented by trazodone. These preclinical findings identify taltirelin as a stable upper airway-preferring respiratory stimulant with arousal properties, traits that have potential favorable relevance to some respiratory disorders but not others.NEW & NOTEWORTHY One of the major goals for translational sleep science and medicine is to identify viable and tractable pharmacological targets for obstructive sleep apnea and other respiratory disorders of sleep or sedation. In the present preclinical study in rats, we performed a randomized, within-subject, repeated-measures design over six intervention study days in chronically instrumented male and female rats with systemic peripheral administration of vehicle controls, the thyrotropin-releasing hormone analog taltirelin at two doses, all with and without coadministered trazodone. Trazodone was included due to clinical interest in the context of sleep apnea pharmacotherapy as it can suppress arousal without compromising pharyngeal muscle activity. These preclinical findings newly identify taltirelin as a stable upper airway-preferring respiratory stimulant with arousal properties. These traits have potential favorable relevance to some respiratory disorders but not others, as identified and discussed.

Thyrotropin-releasing hormone induces Ca2+ increase in a subset of vagal nodose ganglion neurons.

Thyrotropin-releasing hormone (TRH) plays a central role in metabolic homeostasis, and single-cell sequencing has recently demonstrated that vagal sensory neurons in the nodose ganglion express thyrotropin-releasing hormone receptor 1 (TRHR1). Here, in situ hybridization validated the presence of TRHR1 in nodose ganglion (NG) neurons and immunohistochemistry showed that the receptor is expressed at the protein level. However, it has yet to be demonstrated whether TRHR1 is functionally active in NG neurons. Using NG explants transduced with a genetically encoded Ca2+ indicator (GECI), we show that TRH increases Ca2+ in a subset of NG neurons. TRH-induced Ca2+ transients were briefer compared to those induced by CCK-8, 2-Me-5-HT and ATP. Blocking Na+ channels with TTX or Na+ substitution did not affect the TRH-induced Ca2+ increase, but blocking Gq signaling with YM-254890 abolished the TRH-induced response. Field potential recordings from the vagus nerve in vitro showed an increase in response to TRH, suggesting that TRH signaling produces action potentials in NG neurons. These observations indicate that TRH activates a small group of NG neurons, involving Gq pathways, and we hypothesize that these neurons may play a role in gut-brain signaling.

Integrative RNA profiling of TBEV-infected neurons and astrocytes reveals potential pathogenic effectors.

Tick-borne encephalitis virus (TBEV), the most medically relevant tick-transmitted flavivirus in Eurasia, targets the host central nervous system and frequently causes severe encephalitis. The severity of TBEV-induced neuropathogenesis is highly cell-type specific and the exact mechanism responsible for such differences has not been fully described yet. Thus, we performed a comprehensive analysis of alterations in host poly-(A)/miRNA/lncRNA expression upon TBEV infection in vitro in human primary neurons (high cytopathic effect) and astrocytes (low cytopathic effect). Infection with severe but not mild TBEV strain resulted in a high neuronal death rate. In comparison, infection with either of TBEV strains in human astrocytes did not. Differential expression and splicing analyses with an in silico prediction of miRNA/mRNA/lncRNA/vd-sRNA networks found significant changes in inflammatory and immune response pathways, nervous system development and regulation of mitosis in TBEV Hypr-infected neurons. Candidate mechanisms responsible for the aforementioned phenomena include specific regulation of host mRNA levels via differentially expressed miRNAs/lncRNAs or vd-sRNAs mimicking endogenous miRNAs and virus-driven modulation of host pre-mRNA splicing. We suggest that these factors are responsible for the observed differences in the virulence manifestation of both TBEV strains in different cell lines. This work brings the first complex overview of alterations in the transcriptome of human astrocytes and neurons during the infection by two TBEV strains of different virulence. The resulting data could serve as a starting point for further studies dealing with the mechanism of TBEV-host interactions and the related processes of TBEV pathogenesis.