Thyroid hormone receptor β mediates acute illness-induced alterations in central thyroid hormone metabolism

Analysis of genes differentially expressed in the cortex of mice with the Tbl1xr1Y446C/Y446C variant

Transducin β-like 1 X-linked receptor 1 (mouse Tbl1xr1) or TBL1X/Y related 1 (human TBL1XR1), part of the NCoR/SMRT corepressor complex, is involved in nuclear receptor signaling. Variants in TBL1XR1 cause a variety of neurodevelopmental disorders including Pierpont syndrome caused by the p.Tyr446Cys variant. We recently reported a mouse model carrying the Tbl1xr1Y446C/Y446C variant as a model for Pierpont syndrome. To obtain insight into mechanisms involved in altered brain development we studied gene expression patterns in the cortex of mutant and wild type (WT) mice, using RNA-sequencing, differentially expressed gene (DEG) analysis, gene set enrichment analysis (GSEA), weighted gene correlation network analysis (WGCNA) and hub gene analysis. We validated results in mutated mouse cortex, as well as in BV2 and SK-N-AS cell lines, in both of which Tbl1xr1 was knocked down by siRNA. Two DEGs (adj.P. Val < 0.05) were found in the cortex, Mpeg1 (downregulated in mutant mice) and 2900052N01Rik (upregulated in mutant mice). GSEA, WGCNA and hub gene analysis demonstrated changes in genes involved in ion channel function and neuroinflammation in the cortex of the Tbl1xr1Y446C/Y446C mice. The lowered expression of ion channel genes Kcnh3 and Kcnj4 mRNA was validated in the mutant mouse cortex, and increased expression of TRIM9, associated with neuroinflammation, was confirmed in the SK-N-AS cell line. Conclusively, our results show altered expression of genes involved in ion channel function and neuroinflammation in the cortex of the Tbl1xr1Y446C/Y446C mice. These may partly explain the impaired neurodevelopment observed in individuals with Pierpont syndrome and related TBL1XR1-related disorders.

Investigating the Predictive Value of Thyroid Hormone Levels for Stroke Prognosis

Given the expansion of life expectancy, the aging of the population, and the anticipated rise in the number of stroke survivors in Europe with severe neurological consequences in the coming decades, stroke is becoming the most prevalent cause of functional disability. Therefore, the prognosis for a stroke must be timely and precise. Two databases (MEDLINE and Scopus) were searched to identify all relevant studies published between 1 January 2005 and 31 December 2022 that investigated the relationship between thyroid hormone levels and acute stroke severity, mortality, and post-hospital prognosis. Only full-text English-language articles were included. This review includes Thirty articles that were traced and incorporated into the present review. Emerging data regarding the potential predictive value of thyroid hormone levels suggests there may be a correlation between low T3 syndrome, subclinical hypothyroidism, and poor stroke outcome, especially in certain age groups. These findings may prove useful for rehabilitation and therapy planning in clinical practice. Serum thyroid hormone concentration measurement is a non-invasive, relatively harmless, and secure screening test that may be useful for this purpose.

An update on non-thyroidal illness syndrome

The non-thyroidal illness syndrome (NTIS) was first reported in the 1970s as a remarkable ensemble of changes in serum TH (TH) concentrations occurring in probably any severe illness. Ever since, NTIS has remained an intriguing phenomenon not only because of the robustness of the decrease in serum triiodothyronine (T3), but also by its clear correlation with morbidity and mortality. In recent years, it has become clear that (parenteral) feeding in patients with critical illness should be taken into account as a major determinant not only of NTIS but also of clinical outcome. Moreover, both experimental animal and clinical studies have shown that tissue TH concentrations during NTIS do not necessarily reflect serum low TH concentrations and may decrease, remain unaltered, or even increase according to the organ and type of illness studied. These differential changes now have a solid basis in molecular studies on organ-specific TH transporters, receptors and deiodinases. Finally, the role of inflammatory pathways in these non-systemic changes has begun to be clarified. A fascinating role for TH metabolism in innate immune cells, including neutrophils and monocytes/macrophages, was reported in recent years, but there is no evidence at this early stage that this may be a determinant of susceptibility to infections. Although endocrinologists have been tempted to correct NTIS by TH supplementation, there is at present insufficient evidence that this is beneficial. Thus, there is a clear need for adequately powered randomized clinical trials (RCT) with clinically relevant endpoints to fill this knowledge gap.

Dynamics and prognostic value of the hypothalamus-pituitary-adrenal axis responses to pediatric critical illness and association with corticosteroid treatment: a prospective observational study

PURPOSE

Increased systemic cortisol availability during adult critical illness is determined by reduced binding-proteins and suppressed breakdown rather than elevated ACTH. Dynamics, drivers and prognostic value of hypercortisolism during pediatric critical illness remain scarcely investigated.

METHODS

This preplanned secondary analysis of the PEPaNIC-RCT (N = 1440), after excluding 420 children treated with corticosteroids before PICU-admission, documented (a) plasma ACTH, (free)cortisol and cortisol-metabolism at PICU-admission, day-3 and last PICU-day, their prognostic value, and impact of withholding early parenteral nutrition (PN), (b) the association between corticosteroid-treatment and these hormones, and (c) the association between corticosteroid-treatment and outcome.

RESULTS

ACTH was normal upon PICU-admission and low thereafter (p ≤ 0.0004). Total and free cortisol were only elevated upon PICU-admission (p ≤ 0.0003) and thereafter became normal despite low binding-proteins (p < 0.0001) and persistently suppressed cortisol-metabolism (p ≤ 0.03). Withholding early-PN did not affect this phenotype. On PICU-day-3, high free cortisol and low ACTH independently predicted worse outcome (p ≤ 0.003). Also, corticosteroid-treatment initiated in PICU, which further suppressed ACTH (p < 0.0001), was independently associated with poor outcomes (earlier live PICU-discharge: p < 0.0001, 90-day mortality: p = 0.02).

CONCLUSION

In critically ill children, systemic cortisol availability is elevated only transiently, much lower than in adults, and not driven by elevated ACTH. Further ACTH lowering by corticosteroid-treatment indicates active feedback inhibition at pituitary level. Beyond PICU-admission-day, low ACTH and high cortisol, and corticosteroid-treatment, predicted poor outcome. This suggests that exogenously increasing cortisol availability during acute critical illness in children may be inappropriate. Future studies on corticosteroid-treatment in critically ill children should plan safety analyses, as harm may be possible.

Nonthyroidal illness in critically ill children

PURPOSE OF REVIEW

This review summarizes recent literature on nonthyroidal illness syndrome (NTI) and outcome of pediatric critical illness, to provide insight in pathophysiology and therapeutic implications.

RECENT FINDINGS

NTI is typically characterized by lowered triiodothyronine levels without compensatory TSH rise. Although NTI severity is associated with poor outcome of pediatric critical illness, it remains unclear whether this association reflects an adaptive protective response or contributes to poor outcome. Recently, two metabolic interventions that improved outcome also altered NTI in critically ill children. These studies shed new light on the topic, as the results suggested that the peripheral NTI component, with inactivation of thyroid hormone, may represent a beneficial adaptation, whereas the central component, with suppressed TSH-driven thyroid hormone secretion, may be maladaptive. There is currently insufficient evidence for treatment of NTI in children. However, the recent findings raised the hypothesis that reactivation of the central NTI component could offer benefit, which should be tested in RCTs.

SUMMARY

NTI in critically ill children can be modified by metabolic interventions. The peripheral, but not the central, component of NTI may be a beneficial adaptive response. These findings open perspectives for the development of novel strategies to improve outcome of critical illness in children.

Downregulation of Type 3 Deiodinase in the Hypothalamus During Inflammation

Background: Inflammation is associated with marked changes in cellular thyroid hormone (TH) metabolism in triiodothyronine (T3) target organs. In the hypothalamus, type 2 deiodinase (D2), the main T3 producing enzyme, increases upon inflammation, leading to an increase in local T3 availability, which in turn decreases thyrotropin releasing hormone expression in the paraventricular nucleus. Type 3 deiodinase (D3), the T3 inactivating enzyme, decreases during inflammation, which might also contribute to the increased T3 availability in the hypothalamus. While it is known that D2 is regulated by nuclear factor κB (NF-κB) during inflammation, the underlying mechanisms of D3 regulation are unknown. Therefore, the aim of the present study was to investigate inflammation-induced D3 regulation using in vivo and in vitro models. Methods: Mice were injected with a sublethal dose of bacterial endotoxin (lipopolysaccharide [LPS]) to induce a systemic acute-phase response. A human neuroblastoma (SK-N-AS) cell line was used to test the involvement of the thyroid hormone receptor alpha 1 (TRα1) as well as the activator protein-1 (AP-1) and NF-κB inflammatory pathways in the inflammation-induced decrease of D3. Results: D3 expression in the hypothalamus was decreased 24 hours after LPS injection in mice. This decrease was similar in mice lacking the TRα. Incubation of SK-N-AS cells with LPS robustly decreased both D3 mRNA expression and activity. This led to increased intracellular T3 concentrations. The D3 decrease was prevented when NF-κB or AP-1 was inhibited. TRα1 mRNA expression decreased in SK-N-AS cells incubated with LPS, but knockdown of the TRα in SK-N-AS cells did not prevent the LPS-induced D3 decrease. Conclusions: We conclude that the inflammation-induced D3 decrease in the hypothalamus is mediated by the inflammatory pathways NF-κB and AP-1, but not TRα1. Furthermore, the observed decrease modulates intracellular T3 concentrations. Our results suggest a concerted action of inflammatory modulators to regulate both hypothalamic D2 and D3 activities to increase the local TH concentrations.

Low-normal free triiodothyronine and high leukocyte levels in relation to stroke severity and poor outcome in acute ischemic stroke with intracranial atherosclerotic stenosis

BACKGROUND

It is uncertain that the effect of free triiodothyronine (FT3) within normal ranges on initial severity and early functional outcomes in acute ischemic stroke (AIS) patients with Intracranial Atherosclerotic Stenosis (ICAS). The predictive values of white blood cell (WBC) and FT3 are also unclear in symptomatic ICAS (sICAS) patients.

METHODS

We consecutively reviewed 848 ischemic stroke patients admitted into Xiangya Hospital within 72 h after symptom onset. sICAS was defined as AIS patient with degree of ICAS ≥50% proved by magnetic resonance angiography, computed tomography angiography or digital subtraction angiography. WBC and FT3 were assessed within 24 h after admission. Neurological severity was evaluated on admission using the National Institutes of Health Stroke Scale (NIHSS). Stroke outcomes were defined by the modified Rankin Scale (mRS) on the 14th day after admission.

RESULTS

Logistic regression analysis showed that hypertension, lower FT3 and higher WBC concentrations independently associated with severe stroke [FT3 (odds ratio(OR) = 0.543, 95% confidence interval(95% CI): 0.383-0.769); hypertension (OR = 0.436, 95% CI: 0.238-0.800); WBC (OR = 1.17; 95% CI:1.041-1.316]. Besides, lower FT3, higher FT4, higher WBC and higher plasma glucose concentrations independently associated with unfavorable outcomes [FT3 (OR = 0.460; 95% CI: 0.306-0.690); FT4 (OR = 1.151; 95% CI: 1.055-1.255); WBC (OR = 1.178; 95% CI: 1.039-1.334); Plasma glucose (OR = 1.160; 95% CI: 1.002-1.342)].

CONCLUSIONS

Lower FT3 levels within normal ranges and higher WBC count are independently associated with the severity and early poor prognosis of sICAS simultaneously, FT3 and WBC count might be important biomarkers for sICAS patients.

The Mechanism of Negative Transcriptional Regulation by Thyroid Hormone: Lessons From the Thyrotropin β Subunit Gene

Thyroid hormone (T3) activates (positive regulation) or represses (negative regulation) target genes at the transcriptional level. The molecular mechanism of the former has been elucidated in detail; however, the mechanism for negative regulation has not been established. The best example of the gene that is negatively regulated by T3 is the thyrotropin (thyroid-stimulating hormone) β subunit (TSHβ) gene. Analogous to the T3-responsive element (TRE) in positive regulation, a negative TRE (nTRE) has been postulated in the TSHβ gene. However, TSHβ promoter analysis, performed in the presence of transcription factors Pit1 and GATA2, which are determinants of thyrotroph differentiation in the pituitary, revealed that the nTRE is dispensable for inhibition by T3. We propose a tethering model in which the T3 receptor is tethered to GATA2 via protein-protein interaction and inhibits GATA2-dependent transactivation of the TSHβ gene in a T3-dependent manner.

Dissecting thyroid hormone transport and metabolism in dendritic cells

We reported thyroid hormone (TH) receptor expression in murine dendritic cells (DCs) and 3,5,3'-triiodothyronine (T₃)-dependent stimulation of DC maturation and ability to develop a Th1-type adaptive response. Moreover, an increased DC capacity to promote antigen-specific cytotoxic T-cell activity, exploited in a DC-based antitumor vaccination protocol, was revealed. However, putative effects of the main circulating TH, l-thyroxine (T₄) and the mechanisms of TH transport and metabolism at DC level, crucial events for TH action at target cell level, were not known. Herein, we show that T₄ did not reproduce those registered T₃-dependent effects, finding that may reflect a homoeostatic control to prevent unspecific systemic activation of DCs. Besides, DCs express MCT10 and LAT2 TH transporters, and these cells mainly transport T₃ with a favored involvement of MCT10 as its inhibition almost prevented T₃ saturable uptake mechanism and reduced T₃-induced IL-12 production. In turn, DCs express iodothyronine deiodonases type 2 and 3 (D2, D3) and exhibit both enzymatic activities with a prevalence towards TH inactivation. Moreover, T₃ increased MCT10 and LAT2 expression and T₃ efflux from DCs but not T₃ uptake, whereas it induced a robust induction of D3 with a parallel slight reduction in D2. These findings disclose pivotal events involved in the mechanism of action of THs on DCs, providing valuable tools for manipulating the immunogenic potential of these cells. Furthermore, they broaden the knowledge of the TH mechanism of action at the immune system network.

The Role of Hypothalamic NF-κB Signaling in the Response of the HPT-Axis to Acute Inflammation in Female Mice

A large proportion of critically ill patients have alterations in the hypothalamus-pituitary-thyroid (HPT) axis, collectively known as the nonthyroidal illness syndrome. Nonthyroidal illness syndrome is characterized by low serum thyroid hormone (TH) concentrations accompanied by a suppressed central component of the HPT axis and persistent low serum TSH. In hypothalamic tanycytes, the expression of type 2 deiodinase (D2) is increased in several animal models of inflammation. Because D2 is a major source of T3 in the brain, this response is thought to suppress TRH expression in the paraventricular nucleus via increased local bioavailability of T3. The inflammatory pathway component RelA (the p65 subunit of nuclear factor-κB) can bind the Dio2 promoter and increases D2 expression after lipopolysaccharide (LPS) stimulation in vitro. We aimed to determine whether RelA signaling in tanycytes is essential for the LPS-induced D2 increase in vivo by conditional elimination of RelA in tanycytes of mice (RelA(ASTKO)). Dio2 and Trh mRNA expression were assessed by quantitative in situ hybridization 8 or 24 hours after saline or LPS injection. At the same time points, we measured pituitary Tshβ mRNA expression and serum T3 and T4 concentrations. In RelA(ASTKO) mice the LPS-induced increase in Dio2 and decrease in Trh mRNA levels in the hypothalamus were reduced compared with the wild-type littermates, whereas the drop in pituitary Tshβ expression and in serum TH concentrations persisted. In conclusion, RelA is essential for the LPS-induced hypothalamic D2 increase and TRH decrease. The central changes in the HPT axis are, however, not required for the down-regulation of Tshβ expression and serum TH concentrations.

Alteration of Thyroid-Related Hormones within Normal Ranges and Early Functional Outcomes in Patients with Acute Ischemic Stroke

This study evaluated the prognostic value of thyroid-related hormones within normal ranges after acute ischemic stroke. This was a retrospective study and we reviewed 1072 ischemic stroke patients consecutively admitted within 72 h after symptom onset. Total triiodothyronine (T3), total thyroxine (T4), free T3, free T4, and thyroid-stimulating hormone (TSH) were assessed to determine their values for predicting functional outcome at the first follow-up clinic visits, which usually occurred 2 to 4 weeks after discharge from the hospital. 722 patients were finally included. On univariate analysis, poor functional outcome was associated with presence of atrial fibrillation as the index event. Furthermore, score of National Institutes of Health Stroke Scale (NIHSS), total T4, free T4, and C-reactive protein at admission were significantly higher in patients with poor functional outcome, whereas free T3 and total T3 were significantly lower. On multiple logistic regression analysis, lower total T3 concentrations remained independently associated with poor functional outcome [odds ratio (OR), 0.10; 95% confidence interval (CI), 0.01-0.84; P = 0.035]. The only other variables independently associated with poor functional outcome were NIHSS scores. In sum, lower total T3 concentrations that were within the normal ranges were independently associated with poor short-term outcomes.

The molecular basis of the non-thyroidal illness syndrome

The 'sick euthyroid syndrome' or 'non-thyroidal illness syndrome' (NTIS) occurs in a large proportion of hospitalized patients and comprises a variety of alterations in the hypothalamus-pituitary-thyroid (HPT) axis that are observed during illness. One of the hallmarks of NTIS is decreased thyroid hormone (TH) serum concentrations, often viewed as an adaptive mechanism to save energy. Downregulation of hypophysiotropic TRH neurons in the paraventricular nucleus of the hypothalamus and of TSH production in the pituitary gland points to disturbed negative feedback regulation during illness. In addition to these alterations in the central component of the HPT axis, changes in TH metabolism occur in a variety of TH target tissues during NTIS, dependent on the timing, nature and severity of the illness. Cytokines, released during illness, are known to affect a variety of genes involved in TH metabolism and are therefore considered a major determinant of NTIS. The availability of in vivo and in vitro models for NTIS has elucidated part of the mechanisms involved in the sometimes paradoxical changes in the HPT axis and TH responsive tissues. However, the pathogenesis of NTIS is still incompletely understood. This review focusses on the molecular mechanisms involved in the tissue changes in TH metabolism and discusses the gaps that still require further research.

Parallel regulation of thyroid hormone transporters OATP1c1 and MCT8 during and after endotoxemia at the blood-brain barrier of male rodents

There is increasing evidence that local thyroid hormone (TH) availability changes profoundly in inflammatory conditions due to altered expression of deiodinases that metabolize TH. It is largely unknown, however, how inflammation affects TH availability via the expression of TH transporters. In this study we examined the effect of bacterial lipopolysaccharide (LPS) administration on two TH transporters that are critically important for brain TH homeostasis, organic anion-transporting polypeptide 1c1 (OATP1c1), and monocarboxylate transporter 8 (MCT8). MRNA levels were studied by in situ hybridization and qPCR as well as protein levels by immunofluorescence in both the rat and mouse forebrain. The mRNA of both transporters decreased robustly in the first 9 hours after LPS injection, specifically in brain blood vessels; OATP1c1 mRNA in astrocytes and MCT8 mRNA in neurons remained unchanged. At 24 and/or 48 hours after LPS administration, OATP1c1 and MCT8 mRNAs increased markedly above control levels in brain vessels. OATP1c1 protein decreased markedly in vessels by 24 hours whereas MCT8 protein levels did not decrease significantly. These changes were highly similar in mice and rats. The data demonstrate that OATP1c1 and MCT8 expression are regulated in a parallel manner during inflammation at the blood-brain barrier of rodents. Given the indispensable role of both transporters in allowing TH access to the brain, the results suggest reduced brain TH uptake during systemic inflammation.

A novel role for the thyroid hormone-activating enzyme type 2 deiodinase in the inflammatory response of macrophages

Deiodinase type 2 (D2) is a thyroid hormone-activating enzyme converting the prohormone T4 into the active hormone T3. In the present study, we show for the first time that D2 is up-regulated in the mouse liver during acute and chronic inflammation, in close correlation with the proinflammatory cytokine IL-1β and independently of serum T3. Inflammation-induced D2 expression was confirmed in macrophages, in conjunction with selective thyroid hormone transporter (monocarboxylate transporter 10) and thyroid hormone receptor (TR)α1 stimulation, and was absent in hepatocytes. Moreover, D2 knockdown in macrophages resulted in a clear attenuation of the lipopolysaccharide (LPS)-induced IL-1β and GM-CSF expression, in addition to aberrant phagocytosis. Locally produced T3, acting via the TRα, may be instrumental in this novel inflammatory response, because LPS-treated TRα(0/0) mice showed a markedly decreased LPS-induced GM-CSF mRNA expression. We now propose that hepatic D2 favors the innate immune response by specifically regulating cellular thyroid hormone levels in macrophages.

Inflammation-inducible type 2 deiodinase expression in the leptomeninges, choroid plexus, and at brain blood vessels in male rodents

Thyroid hormone regulates immune functions and has antiinflammatory effects. In promoter assays, the thyroid hormone-activating enzyme, type 2 deiodinase (D2), is highly inducible by the inflammatory transcription factor nuclear factor-κ B (NF-κB), but it is unknown whether D2 is induced in a similar fashion in vivo during inflammation. We first reexamined the effect of bacterial lipopolysaccharide (LPS) on D2 expression and NF-κB activation in the rat and mouse brain using in situ hybridization. In rats, LPS induced very robust D2 expression in normally non-D2-expressing cells in the leptomeninges, adjacent brain blood vessels, and the choroid plexus. These cells were vimentin-positive fibroblasts and expressed the NF-κB activation marker, inhibitor κ B-α mRNA, at 2 hours after injection, before the increase in D2 mRNA. In mice, LPS induced intense D2 expression in the choroid plexus but not in leptomeninges, with an early expression peak at 2 hours. Moderate D2 expression along numerous brain blood vessels appeared later. D2 and NF-κB activation was induced in tanycytes in both species but with a different time course. Enzymatic assays from leptomeningeal and choroid plexus samples revealed exceptionally high D2 activity in LPS-treated rats and Syrian hamsters and moderate but significant increases in mice. These data demonstrate the cell type-specific, highly inducible nature of D2 expression by inflammation, and NF-κB as a possible initiating factor, but also warrant attention for species differences. The results suggest that D2-mediated T₃ production by fibroblasts regulate local inflammatory actions in the leptomeninges, choroid plexus and brain blood vessels, and perhaps also in other organs.

NFκB signaling is essential for the lipopolysaccharide-induced increase of type 2 deiodinase in tanycytes

The enzyme type 2 deiodinase (D2) is a major determinant of T₃ production in the central nervous system. It is highly expressed in tanycytes, a specialized cell type lining the wall of the third ventricle. During acute inflammation, the expression of D2 in tanycytes is up-regulated by a mechanism that is poorly understood at present, but we hypothesized that cJun N-terminal kinase 1 (JNK1) and v-rel avian reticuloendotheliosis viral oncogene homolog A (RelA) (the 65 kD subunit of NFκB) inflammatory signal transduction pathways are involved. In a mouse model for acute inflammation, we studied the effects of lipopolysaccharide (LPS) on mRNA expression of D2, JNK1, and RelA in the periventricular area (PE) and the arcuate nucleus-median eminence of the hypothalamus. We next investigated LPS-induced D2 expression in primary tanycyte cell cultures. In the PE, the expression of D2 was increased by LPS. In the arcuate nucleus, but not in the PE, we found increased RelA mRNA expression. Likewise, LPS increased D2 and RelA mRNA expression in primary tanycyte cell cultures, whereas JNK1 mRNA expression did not change. Phosphorylation of RelA and JNK1 was increased in tanycyte cell cultures 15-60 minutes after LPS stimulation, confirming activation of these pathways. Finally, inhibition of RelA with the chemical inhibitors sulfasalazine and 4-Methyl-N¹-(3-phenylpropyl)benzene-1,2-diamine (JSH-23) in tanycyte cell cultures prevented the LPS-induced D2 increase. We conclude that NFκB signaling is essential for the up-regulation of D2 in tanycytes during inflammation.

Ischemic stroke functional outcomes are independently associated with C-reactive protein concentrations and cognitive outcomes with triiodothyronine concentrations: a pilot study

Elevated concentrations of C-reactive protein (CRP) and decreased concentrations of triiodothyronine (T3) were shown to predict poor outcomes in patients with stroke. However, the prognostic value of CRP and T3 has not been studied simultaneously in relation to stroke functional and cognitive outcomes despite of close interaction between inflammatory markers and thyroid function. We evaluated the association of thyroid hormone and CRP concentrations with immediate outcomes after ischemic stroke. Eighty-eight ischemic stroke patients on admission to the stroke unit were evaluated for clinical stroke severity (Scandinavian stroke scale or SSS) and concentrations of thyroid-stimulating hormone, free thyroxin, free T3, and CRP. Functional outcome (modified Rankin scale) and cognitive outcome (Mini mental state examination) were evaluated at discharge. Greater ln CRP concentrations (r = -0.35, p = 0.001), but not thyroid hormone concentrations, correlated with score on the SSS. In univariate analyses lower free T3 concentrations and higher CRP concentrations were associated with poor functional and poor cognitive outcomes. After adjustment for clinical stroke severity, higher CRP concentrations (β = 0.18, p = 0.04) remained associated with worse functional outcome and lower free T3 concentrations with worse cognitive outcome (β = 0.23, p = 0.03). In sum, clinical stroke severity is associated with elevated CRP concentration. Higher CRP concentration is independently associated with worse functional outcomes and lower free T3 concentration with worse cognitive outcomes at discharge. T3 and CRP can be important biomarkers in patients with acute ischemic stroke.

Septic shock non-thyroidal illness syndrome causes hypothyroidism and conditions for reduced sensitivity to thyroid hormone

Non-thyroidal illness syndrome (NTIS) is part of the neuroendocrine response to stress, but the significance of this syndrome remains uncertain. The aim of this study was to investigate the effect of lipopolysaccharide (LPS)-induced NTIS on thyroid hormone (TH) levels and TH molecular targets, as well as the relationship between septic shock nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) activation and TH receptor β (THRB) gene expression at a multi-tissue level in a pig model. Prepubertal domestic pigs were given i.v. saline or LPS for 48 h. Serum and tissue TH was measured by chemiluminescence and RIA. Expression of THRs and cofactors was measured by real-time PCR, and deiodinase (DIO) activity was measured by enzyme assays. Tissue NF-kB nuclear binding activity was evaluated by EMSA. LPS-treated pigs had decreased TH levels in serum and most tissues. DIO1 expression in liver and kidney and DIO1 activity in kidney decreased after LPS. No changes in DIO2 activity were observed between groups. LPS induced an increase in hypothalamus, thyroid, and liver DIO3 activity. Among the other studied genes, monocarboxylate transporter 8 and THRB were the most commonly repressed in endotoxemic pigs. LPS-induced NF-kB activation was associated with a decrease in THRB gene expression only in frontal lobe, adrenal gland, and kidney cortex. We conclude that LPS-induced NTIS in pigs is characterized by hypothyroidism and tissue-specific reduced TH sensitivity. The role of NF-kB in regulating THRB expression during endotoxemia, if any, is restricted to a limited number of tissues.

Action of specific thyroid hormone receptor α(1) and β(1) antagonists in the central and peripheral regulation of thyroid hormone metabolism in the rat

BACKGROUND

The iodine-containing drug amiodarone (Amio) and its noniodine containing analogue dronedarone (Dron) are potent antiarrhythmic drugs. Previous in vivo and in vitro studies have shown that the major metabolite of Amio, desethylamiodarone, acts as a thyroid hormone receptor (TR) α(1) and β(1) antagonist, whereas the major metabolite of Dron debutyldronedarone acts as a selective TRα(1) antagonist. In the present study, Amio and Dron were used as tools to discriminate between TRα(1) or TRβ(1) regulated genes in central and peripheral thyroid hormone metabolism.

METHODS

Three groups of male rats received either Amio, Dron, or vehicle by daily intragastric administration for 2 weeks. We assessed the effects of treatment on triiodothyronine (T(3)) and thyroxine (T(4)) plasma and tissue concentrations, deiodinase type 1, 2, and 3 mRNA expressions and activities, and thyroid hormone transporters monocarboxylate transporter 8 (MCT8), monocarboxylate transporter 10 (MCT10), and organic anion transporter 1C1 (OATP1C1).

RESULTS

Amio treatment decreased serum T(3), while serum T(4) and thyrotropin (TSH) increased compared to Dron-treated and control rats. At the central level of the hypothalamus-pituitary-thyroid axis, Amio treatment decreased hypothalamic thyrotropin releasing hormone (TRH) expression, while increasing pituitary TSHβ and MCT10 mRNA expression. Amio decreased the pituitary D2 activity. By contrast, Dron treatment resulted in decreased hypothalamic TRH mRNA expression only. Upon Amio treatment, liver T(3) concentration decreased substantially compared to Dron and control rats (50%, p<0.01), but liver T(4) concentration was unaffected. In addition, liver D1, mRNA, and activity decreased, while the D3 activity and mRNA increased. Liver MCT8, MCT10, and OATP1C1 mRNA expression were similar between groups.

CONCLUSION

Our results suggest an important role for TRα1 in the regulation of hypothalamic TRH mRNA expression, whereas TRβ plays a dominant role in pituitary and liver thyroid hormone metabolism.

Leptin administration restores the fasting-induced increase of hepatic type 3 deiodinase expression in mice

BACKGROUND

Decreased serum leptin has been proposed as a critical signal initiating the neuroendocrine response to fasting. Leptin administration partially reverses the fasting-induced suppression of the hypothalamus-pituitary-thyroid axis at the central level. It is, however, unknown to what extent leptin affects peripheral thyroid hormone metabolism. The aim of this study was to evaluate the effect of leptin administration on starvation-induced alterations of peripheral thyroid hormone metabolism in mice.

METHODS

Three types of experiments were performed: (i) mice were fasted for 24 hours while leptin was administered twice (at 0 and 8 hours, 1 μg/g body weight [BW]), (ii) mice were fasted for 24 hours and, subsequently, leptin was given once at 24 hours (killed at 28 and 32 hours), and (iii) mice were fasted for 48 hours. All groups had appropriate controls. Serum triiodothyronine and thyroxine, liver type 1 deiodinase (D1), type 3 deiodinase (D3), thyroid hormone receptor (TR)β1, TRα1 and α2 mRNA expression, and liver D1 and D3 activity were measured.

RESULTS

Twenty-four hours of fasting decreased liver TRβ1 mRNA expression, while liver TRα1, TRα2, and D1 mRNA expression and activity did not change. In contrast, 24 hours of fasting increased liver D3 mRNA. Leptin administration after fasting restored liver D3 expression, while serum thyroid hormone levels and liver TRβ1 expression remained low.

CONCLUSION

Leptin administration selectively restores starvation-induced increased hepatic D3 expression independently of serum thyroid hormone concentrations. The present study shows that fasting-induced changes in mRNA expression of genes involved in hepatic hormone metabolism are influenced not only by decreased serum thyroid hormone levels but also by serum leptin.

Beyond low plasma T3: local thyroid hormone metabolism during inflammation and infection

Decreased serum thyroid hormone concentrations in severely ill patients were first reported in the 1970s, but the functional meaning of the observed changes in thyroid hormone levels, together known as nonthyroidal illness syndrome (NTIS), remains enigmatic. Although the common view was that NTIS results in overall down-regulation of metabolism in order to save energy, recent work has shown a more complex picture. NTIS comprises marked variation in transcriptional and translational activity of genes involved in thyroid hormone metabolism, ranging from inhibition to activation, dependent on the organ or tissue studied. Illness-induced changes in each of these organs appear to be very different during acute or chronic inflammation, adding an additional level of complexity. Organ- and timing-specific changes in the activity of thyroid hormone deiodinating enzymes (deiodinase types 1, 2, and 3) highlight deiodinases as proactive players in the response to illness, whereas the granulocyte is a novel and potentially important cell type involved in NTIS during bacterial infection. Although acute NTIS can be seen as an adaptive response to support the immune response, NTIS may turn disadvantageous when critical illness enters a chronic phase necessitating prolonged life support. For instance, changes in thyroid hormone metabolism in muscle during critical illness may be relevant for the pathogenesis of myopathy associated with prolonged ventilator dependence. This review focuses on NTIS as a timing-related and organ-specific response to illness, occurring independently from the decrease in serum thyroid hormone levels and potentially relevant for disease progression.

Acute restraint stress increases intrahypothalamic oestradiol concentrations in conjunction with increased hypothalamic oestrogen receptor β and aromatase mRNA expression in female rats

Activation of the hypothalamic-pituitary-adrenal axis is considered to be one of the key physiological responses to stress and, interestingly, shows a marked sex difference. Oestradiol plays an important role in this sex difference. The present study investigated the systemic and intrahypothalamic oestradiol response to physical restraint stress in female rats. We used jugular catheterisation and intrahypothalamic microdialysis to simultaneously measure plasma oestradiol and local oestradiol concentrations in the paraventricular nucleus (PVN) of the hypothalamus. We also assessed corticotrophin-releasing hormone (CRH), aromatase, and oestrogen receptor (ER) α and β mRNA expression in the PVN by quantitative polymerase chain reaction immediately after the acute stress period. As expected, PVN CRH mRNA and plasma corticosterone were significantly increased after acute stress. Interestingly, the local oestradiol concentration in the PVN also increased during the 1-h stress period in pro-oestrus and in ovariectomised (OVX) animals. Aromatase mRNA expression in the PVN was increased markedly in pro-oestrus but only modestly in oestrus. PVN ERβ but not ERα mRNA expression was significantly elevated in pro-oestrous animals. In addition, plasma oestradiol levels increased 10 min after stress, both during pro-oestrus and oestrus but not in OVX animals. To conclude, we report an intra-hypothalamic oestradiol response to restraint stress. The rising hypothalamic oestradiol concentration together with increased ERβ gene expression indicates a positive feedback of hypothalamic oestradiol signalling during acute stress in rats.

Acute inflammation increases pituitary and hypothalamic glycoprotein hormone subunit B5 mRNA expression in association with decreased thyrotrophin receptor mRNA expression in mice

The biological function of thyrostimulin, consisting of the GPA2 and GPB5 subunit, is currently poorly understood. The recent observation that pro-inflammatory cytokines up-regulate the transcription of GPB5 in vitro suggested a role for thyrostimulin in the nonthyroidal illness syndrome, a state of altered thyroid hormone metabolism occurring during illness. In the present study, we used GPB5 knockout (GPB5(-/-) ) and wild-type (WT) mice to evaluate the role of GPB5 in the pituitary and hypothalamus during acute inflammation induced by lipopolysaccharide (LPS, bacterial endotoxin) administration. We evaluated serum thyroid hormones and mRNA expression of genes involved in thyroid hormone metabolism in the pituitary and in two hypothalamic regions; the periventricular region (PE) and the arcuate nucleus/median eminence region. As expected, LPS administration increased deiodinase type 2 mRNA in the PE, at the same time as decreasing pituitary thyrotrophin (TSH)β mRNA and serum thyroxine and triiodothyronine both in GPB5(-/-) and WT mice. GPB5 mRNA, but not GPA2 mRNA, markedly increased after LPS in the pituitary (200-fold) and hypothalamus of WT mice. In addition, we found large (>50%) suppression of TSH receptor (TSHR) mRNA in the pituitary and hypothalamus of WT mice but not in GPB5(-/-) mice. In conclusion, our results demonstrate in vivo regulation of central GPB5 transcription during acute illness. The observed differences between GPB5(-/-) and WT mice point to a distinct role for GPB5 in pituitary and hypothalamic TSHR suppression during acute illness.

Transient hypothyroxinemia in juvenile glycoprotein hormone subunit B5 knock-out mice

The heterodimer thyrostimulin, comprised of two novel glycoprotein hormone subunits GPA2 and GPB5, activates the TSH receptor. To understand its role in the regulation of the hypothalamus-pituitary-thyroid (HPT-) axis, we evaluated juvenile and adult GPB5 knock-out (GPB5(-/-)) and wild type mice (WT) during euthyroidism, hypothyroidism and thyrotoxicosis. Surprisingly, juvenile euthyroid GPB5(-/-) mice displayed marked hypothyroxinemia (25% lower serum T(4), unchanged TSH) and also during thyrotoxicosis juvenile GPB5(-/-) mice had 25% lower serum T(4), compared to WT. During hypothyroidism, despite similar serum T(4), pituitary TSHbeta mRNA was 2-fold lower in GPB5(-/-) mice compared to WT. Adult mice displayed increased pituitary deiodinase type 2 during euthyroidism and decreased serum T(4) during hypothyroidism in GPB5(-/-). Thus, lacking GPB5 results in moderate deviations of the HPT-axis. The more pronounced differences observed in juvenile mice compared to adult mice are in agreement with the notion that GPB5 has a role during development.

Central and peripheral effects of thyroid hormone signalling in the control of energy metabolism

Increasing evidence points towards a role for thyroid hormone signalling in the central nervous system with respect to the development of symptoms of thyroid disease, in addition to the well-known peripheral effects of thyroid hormone. Thyroid hormone affects target tissues directly via thyroid hormone receptors, but also indirectly through effects on the integration of the sympathetic signal in target tissues. The present review discusses these pathways and the evidence for a third pathway, that is effects of thyroid hormone on the pre-autonomic neurones in the central nervous system. The pre-autonomic neurones reside in the hypothalamus in brain nuclei such as the paraventricular nucleus of the hypothalamus where thyroid hormone receptor isoforms are expressed. Recent data from studies in transgenic mice implicate a role for thyroid hormone receptor alpha 1 in the modulation of sympathetic signalling to target tissues, thereby affecting both glucose and lipid metabolism. Focal stimulation of hypothalamic nuclei expressing thyroid hormone receptors and selective liver denervation experiments in rats have provided further evidence indicating that the metabolic changes observed during hyperthyroidism are not only a result of increased thyroid hormone signalling in the periphery, but also, at least in part, result from altered signalling in thyroid hormone sensitive neurones.