A review of the peripheral levels of regulation by thyroid hormone

Bisphenol S reduces locomotor performance and modifies muscle protein levels but not mitochondrial bioenergetics in adult zebrafish

Human activity has now introduced novel chemicals into most aquatic ecosystems. Endocrine-disrupting compounds originating from plastic pollution and manufacture can have pronounced biological effects by disrupting hormone-mediated processes. Bisphenol A (BPA) is one of the most commonly produced endocrine-disrupting compounds, which interferes with signalling by a broad range of hormones. In recognition of its potentially harmful effects, BPA is being replaced by substitutes such as bisphenol S (BPS). However, toxicological studies revealed that BPS too can bind to hormone receptors and disrupt signalling, particularly of thyroid hormone. The aim of this study was to test whether BPS exposure impacts locomotor performance and muscle function in zebrafish (Danio rerio). Locomotor performance depends on thyroid hormone signalling, and it is closely related to fitness so that its disruption can have negative ecological and evolutionary consequences. BPS exposure of 15 μg l^-1 [∼60 nM] and 30 μg l^-1 (but not 60 μg l^-1) decreased sustained swimming performance (U_crit), but not sprint speed. In a fully factorial design, we show that living in flowing water increased U_crit compared to a still water control, and that BPS reduced U_crit under both conditions but did not eliminate the training effect. In a second factorial experiment, we show that BPS did not affect mitochondrial bioenergetics in skeletal muscle (state 3 and 4 rates, respiratory control ratios, ROS production), but that induced hypothyroidism decreased state 3 and 4 rates of respiration. However, both hypothyroidism and BPS exposure decreased activity of AMP-activated protein kinase (pAMPK:total AMPK) but increased protein levels of myocyte enhancer factor 2, and slow and fast myosin heavy chains. Our data indicate that BPS is not a safe alternative for BPA and that exposure to BPS can have ecological consequences, which are likely to be at least partly mediated via thyroid hormone disruption.

Endocrine disruption from plastic pollution and warming interact to increase the energetic cost of growth in a fish

Energetic cost of growth determines how much food-derived energy is needed to produce a given amount of new biomass and thereby influences energy transduction between trophic levels. Growth and development are regulated by hormones and are therefore sensitive to changes in temperature and environmental endocrine disruption. Here, we show that the endocrine disruptor bisphenol A (BPA) at an environmentally relevant concentration (10 µgl^-1) decreased fish (Danio rerio) size at 30°C water temperature. Under the same conditions, it significantly increased metabolic rates and the energetic cost of growth across development. By contrast, BPA decreased the cost of growth at cooler temperatures (24°C). BPA-mediated changes in cost of growth were not associated with mitochondrial efficiency (P/O ratios (i.e. adenosine diphosphate (ADP) used/oxygen consumed) and respiratory control ratios) although BPA did increase mitochondrial proton leak. In females, BPA decreased age at maturity at 24°C but increased it at 30°C, and it decreased the gonadosomatic index suggesting reduced investment into reproduction. Our data reveal a potentially serious emerging problem: increasing water temperatures resulting from climate warming together with endocrine disruption from plastic pollution can impact animal growth efficiency, and hence the dynamics and resilience of animal populations and the services these provide.

Thyroid hormone regulation of thermal acclimation in ectotherms: Physiological mechanisms and ecoevolutionary implications

The pathways that regulate adaptive thermal plasticity in ectothermic vertebrates have received little attention relative to those in birds and mammals. However, there is increasing evidence that thyroid hormone represents a critical regulator of thermal plasticity in both ectothermic and endothermic vertebrates. In this review, I summarize the evidence for thyroid hormone-mediated thermal compensation responses in ectothermic vertebrates, with specific focus on effects on the whole animal, skeletal muscle, and cardiac muscle. Interestingly, these effects can differ wildly between focal tissues and species. I move on to discuss what the role of thyroid hormone in ectotherm thermal plasticity can reveal about stressor interactions and central vs. peripheral levels of thyroid hormone regulation. Lastly, I focus on the conserved nature of thyroid hormone signaling in animal thermal responses, with specific reference to the ectotherm → endotherm spectrum. I use this framework to highlight research avenues that will further resolve the evolutionary trajectory of thyroid hormone actions across animals. I hope to emphasize what thyroid hormone-mediated cold acclimation in a 3 cm fish can contribute to ongoing debates surrounding the impacts of stressor interactions, the potential costs of plasticity, the evolution of endothermy, and the impacts of global change.

Thyrotrophin and thyroxine support immune homeostasis in humans

The endocrine and the immune systems interact by sharing receptors for hormones and cytokines, cross‐control and feedback mechanisms. To date, no comprehensive study has assessed the impact of thyroid hormones on immune homeostasis. By studying immune phenotype (cell populations, antibody concentrations, circulating cytokines, adipokines and acute‐phase proteins, monocyte–platelet interactions and cytokine production capacity) in two large independent cohorts of healthy volunteers of Western European descent from the Human Functional Genomics Project (500FG and 300BCG cohorts), we identified a crucial role of the thyroid hormone thyroxin (T4) and thyroid‐stimulating hormone (TSH) on the homeostasis of lymphocyte populations. TSH concentrations were strongly associated with multiple populations of both effector and regulatory T cells, whereas B‐cell populations were significantly associated with free T4 (fT4). In contrast, fT4 and TSH had little impact on myeloid cell populations and cytokine production capacity. Mendelian randomization further supported the role of fT4 for lymphocyte homeostasis. Subsequently, using a genomics approach, we identified genetic variants that influence both fT4 and TSH concentrations and immune responses, and gene set enrichment pathway analysis showed enrichment of fT4‐affected gene expression in B‐cell function pathways, including the CD40 pathway, further supporting the importance of fT4 in the regulation of B‐cell function. In conclusion, we show that thyroid function controls the homeostasis of the lymphoid cell compartment. These findings improve our understanding of the immune responses and open the door for exploring and understanding the role of thyroid hormones in the lymphocyte function during disease.

Standard hypothyroid treatment did not restore proper metabolic response to carbohydrate

PURPOSE

Hypothyroidism is associated with a lower metabolic rate, impaired glucose tolerance, and increased responsiveness of sympathetic nervous system to glucose ingestion. The Levothyroxine (LT4) monotherapy is the standard treatment for hypothyroidism; however to what extent this treatment restores the patients' metabolism has not been verified. The aim of this study was to test the hypothesis that standard LT4 therapy may not restore proper metabolic response to carbohydrate ingestion.

METHODS

Energy expenditure, glucose tolerance, and catecholamine response to glucose ingestion were compared in 18 subjects with pharmacologically compensated hypothyroidism (PCH) and controls, at baseline and during oral glucose tolerance test conditions.

RESULTS

Metabolic rate was significantly lower in PCH (P < 0.0001). Glucose tolerance was decreased in this group with no differences in insulin resistance indicators between both groups. Adrenergic activity (P < 0.05) as well as adrenergic reaction to glucose ingestion (P < 0.001) were stronger in PCH.

CONCLUSIONS

Standard treatment for hypothyroidism does not restore the normal metabolic reaction to carbohydrate which is observed in healthy people.

The effect of thyroid dysfunction and treatment on adropin, asprosin and preptin levels in rats

OBJECTIVES

Thyroid hormones have important roles in normal development and energy regulating mechanisms as well as signaling mechanisms that affect energy consumption through central and peripheral pathways. The aim of this study was to determine the effects of thyroid dysfunction on adropin, asprosin and preptin levels in rat.

METHODS

The study was performed on the 38 male Wistar-albino rats. Experiment groups were designed as follows. 1-Control, 2-Hypothyroidism; To induce hypothyroidism PTU was applied by intraperitoneal as 10 mg/kg/day for 2 weeks. 3-Hypothyroidism + Thyroxine; Previously animals were made with hypothyroidism by 1 week PTU application and then 1 week l-thyroxine was given by intraperitoneal as 1.5 mg/kg/day. 4-Hyperthyroidism; Rats were made with hyperthyroidism by 3 weeks l-thyroxine (0.3 mg/kg/day). 5-Hyperthyroidism + PTU; Animals were made hyperthyroisim by l-thyroxine as groups 4, then 1 week PTU was applied to treatment of hiperthyrodism. At the end of supplementation animals were sacrificed and blood samples were collected for FT3, FT4, adropin, asprosin, preptin analysis.

RESULTS

FT3 ve FT4 levels were reduced significantly in hypothyroidism while increased in hyperthyroidism (p<0.001). Hipothyrodism led to reduces adropin, asprosin and preptin levels. And also hyperthyroidism reduced adropin and preptin levels (p<0.001).

CONCLUSIONS

The results of study show that experimental hypothyroidism and hyperthyroidism lead to significantly change to adropin, asprosin and preptin levels. However, correction of thyroid function caused to normals levels in asprosin and preptin.

Combined approaches to reveal genes associated with litter size in Yunshang black goats

Intensive artificial selection has been imposed in Yunshang black goats, the first black specialist mutton goat breed in China, with a breeding object of improving reproductive performance, which has contributed to reshaping of the genome including the characterization of SNP, ROH and haplotype. However, variation in reproductive ability exists in the present population. A WGS was implemented in two subpopulations (polytocous group, PG, and monotocous group, MG) with evident differences of litter size. Following the mapping to reference genome, and SNP calling and pruning, three approaches - GWAS, ROH analysis and detection of signatures of selection - were employed to unveil candidate genes responsible for litter size. Consequently, 12 candidate genes containing OSBPL8 with the minimum P-value were uncovered by GWAS. Differences were observed in the pattern of ROH between two subpopulations that shared similar low inbreeding coefficients. Two ROH hotspots and 12 corresponding genes emerged from ROH pool association analysis. Based on the nS_L statistic, 15 and 61 promising genes were disclosed under selection for MG and PG respectively. Of them, some promising genes participate in ovarian function (PPP2R5C, CDC25A, ESR1, RPS26 and SERPINBs), seasonal reproduction (DIO3, BTG1 and CRYM) and metabolism (OSBPL8, SLC39A5 and SERPINBs). Our study pinpointed some novel promising genes influencing litter size, provided a comprehensive insight into genetic makeup of litter size and might facilitate selective breeding in goats.

Effects of a temperature rise on melatonin and thyroid hormones during smoltification of Atlantic salmon, Salmo salar

Smoltification prepares juvenile Atlantic salmon (Salmo salar) for downstream migration. Dramatic changes characterize this crucial event in the salmon's life cycle, including increased gill Na⁺/K⁺-ATPase activity (NKA) and plasma hormone levels. The triggering of smoltification relies on photoperiod and is modulated by temperature. Both provide reliable information, to which fish have adapted for thousands of years, that allows deciphering daily and calendar time. Here we studied the impact of different photoperiod (natural, sustained winter solstice) and temperature (natural, ~ + 4° C) combinations, on gill NKA, plasma free triiodothyronine (T3) and thyroxine (T4), and melatonin (MEL; the time-keeping hormone), throughout smoltification. We also studied the impact of temperature history on pineal gland MEL production in vitro. The spring increase in gill NKA was less pronounced in smolts kept under sustained winter photoperiod and/or elevated temperature. Plasma thyroid hormone levels displayed day-night variations, which were affected by elevated temperature, either independently from photoperiod (decrease in T3 levels) or under natural photoperiod exclusively (increase in T4 nocturnal levels). Nocturnal MEL secretion was potentiated by the elevated temperature, which also altered the MEL profile under sustained winter photoperiod. Temperature also affected pineal MEL production in vitro, a response that depended on previous environmental acclimation of the organ. The results support the view that the salmon pineal is a photoperiod and temperature sensor, highlight the complexity of the interaction of these environmental factors on the endocrine system of S. salar, and indicate that climate change might compromise salmon's time "deciphering" during smoltification, downstream migration and seawater residence.

What do warming waters mean for fish physiology and fisheries?

Environmental signals act primarily on physiological systems, which then influence higher-level functions such as movement patterns and population dynamics. Increases in average temperature and temperature variability associated with global climate change are likely to have strong effects on fish physiology and thereby on populations and fisheries. Here we review the principal mechanisms that transduce temperature signals and the physiological responses to those signals in fish. Temperature has a direct, thermodynamic effect on biochemical reaction rates. Nonetheless, plastic responses to longer-term thermal signals mean that fishes can modulate their acute thermal responses to compensate at least partially for thermodynamic effects. Energetics are particularly relevant for growth and movement, and therefore for fisheries, and temperature can have pronounced effects on energy metabolism. All energy (ATP) production is ultimately linked to mitochondria, and temperature has pronounced effects on mitochondrial efficiency and maximal capacities. Mitochondria are dependent on oxygen as the ultimate electron acceptor so that cardiovascular function and oxygen delivery link environmental inputs with energy metabolism. Growth efficiency, that is the conversion of food into tissue, changes with temperature, and there are indications that warmer water leads to decreased conversion efficiencies. Moreover, movement and migration of fish relies on muscle function, which is partially dependent on ATP production but also on intracellular calcium cycling within the myocyte. Neuroendocrine processes link environmental signals to regulated responses at the level of different tissues, including muscle. These physiological processes within individuals can scale up to population responses to climate change. A mechanistic understanding of thermal responses is essential to predict the vulnerability of species and populations to climate change.

Lamprey metamorphosis: Thyroid hormone signaling in a basal vertebrate

As one of the most basal living vertebrates, lampreys represent an excellent model system to study the evolution of thyroid hormone (TH) signaling. The lamprey hypothalamic-pituitary-thyroid and reproductive axes overlap functionally. Lampreys have 3 gonadotropin-releasing hormones and a single glycoprotein hormone from the hypothalamus and pituitary, respectively, that regulate both the reproductive and thyroid axes. TH synthesis in larval lampreys takes place in an endostyle that transforms into typical vertebrate thyroid tissue during metamorphosis; both the endostyle and follicular tissue have all the typical TH synthetic components found in other vertebrates. Furthermore, lampreys also have the vertebrate suite of peripheral regulators including TH distributor proteins (THDPs), deiodinases and TH receptors (TRs). Although at the molecular level the components of the lamprey thyroid system are ancestral to other vertebrates, their functions have been largely conserved. TH signaling as it relates to lamprey metamorphosis represents a particularly interesting phenomenon. Unlike other metamorphosing vertebrates, lamprey THs increase throughout the larval period, peak prior to metamorphosis and decline rapidly at the onset of metamorphosis; patterns of deiodinase activity are consistent with these increases and declines. Moreover, goitrogens (which suppress TH levels) initiate precocious metamorphosis, and exogenous TH treatment blocks goitrogen-induced metamorphosis and disrupts natural metamorphosis. Despite this clear physiological difference, TH action via TRs is consistent with higher vertebrates. Based on observations that TRs are upregulated in a tissue-specific fashion during morphogenesis and the finding that lamprey TRs upregulate genes via THs in a fashion similar to higher vertebrates, we propose the following hypothesis for further testing. THs have a dual role in lampreys where high TH levels promote larval feeding and growth and then at the onset of metamorphosis TH levels decrease rapidly; at this time the relatively low TH levels function via TRs in a fashion similar to that of other metamorphosing vertebrates.

Avoiding the pitfalls when quantifying thyroid hormones and their metabolites using mass spectrometric methods: The role of quality assurance

This short review aims to assess the application of basic quality assurance (QA) principles in published thyroid hormone bioanalytical methods using mass spectrometry (MS). The use of tandem MS, in particular linked to liquid chromatography has become an essential bioanalytical tool for the thyroid hormone research community. Although basic research laboratories do not usually work within the constraints of a quality management system and regulated environment, all of the reviewed publications, to a lesser or greater extent, document the application of QA principles to the MS methods described. After a brief description of the history of MS in thyroid hormone analysis, the article reviews the application of QA to published bioanalytical methods from the perspective of selectivity, accuracy, precision, recovery, instrument calibration, matrix effects, sensitivity and sample stability. During the last decade the emphasis has shifted from developing methods for the determination of L-thyroxine (T₄) and 3,3',5-triiodo-L-thyronine (T₃), present in blood serum/plasma in the 1-100 nM concentration range, to metabolites such as 3-iodo-L-thyronamine (3-T₁AM), 3,5-diiodo-L-thyronine (3,5-T₂) and 3,3'-diiodo-L-thyronine (3,3'-T₂). These metabolites seem likely to be present in the low pM concentrations; consequently, QA parameters such as selectivity and sensitivity become more critical. The authors conclude that improvements, particularly in the areas of analyte selectivity, matrix effect measurement/documentation and analyte recovery would be beneficial.

The evolution of metabolic regulation in animals

Energy metabolism is determined by a suite of regulatory mechanism, and their increasing complexity over evolutionary time provides the key to understanding the emergence of different metabolic phenotypes. Energy metabolism is at the core of biological processes because all organisms must maintain energy balance against thermodynamic gradients. Energy metabolism is regulated by a bewildering array of interacting molecular mechanisms, and much of what is known about metabolic regulation comes from the medical literature. However, ecology and evolutionary research would gain considerably by incorporating regulatory mechanisms more explicitly in research on topics such as the evolution of endothermy, metabolic plasticity, and energy balance. The purpose of this brief review is to summarise the main regulatory pathways of energy metabolism in animals and their evolutionary origins to make these complex interactions more accessible to researchers from a broad range of backgrounds. Some of the principal regulators of energy balance, such as the AMP-stimulated protein kinase, have an ancient prokaryotic origin. Most regulatory pathways (e.g. thyroid hormone, insulin, adipokines), however, are eukaryotic in origin and diversified substantially in metazoans and vertebrates. Diversification in vertebrates is at least partly due to genome duplications early in this lineage. The interaction between regulatory mechanisms permitted an increasingly sophisticated fine-tuning of energy balance and metabolism. Hence, regulatory complexity increased over evolutionary time, and taxa differ in their potential range of metabolic phenotypes. Choice of model organism therefore becomes important, and bacteria or even invertebrates are not good models for more derived vertebrates. Different metabolic phenotypes and their evolution, such as endothermy and metabolic plasticity, should be interpreted against this regulatory background.

Plasticity of Performance Curves Can Buffer Reaction Rates from Body Temperature Variation in Active Endotherms

Endotherms regulate their core body temperature by adjusting metabolic heat production and insulation. Endothermic body temperatures are therefore relatively stable compared to external temperatures. The thermal sensitivity of biochemical reaction rates is thought to have co-evolved with body temperature regulation so that optimal reaction rates occur at the regulated body temperature. However, recent data show that core body temperatures even of non-torpid endotherms fluctuate considerably. Additionally, peripheral temperatures can be considerably lower and more variable than core body temperatures. Here we discuss whether published data support the hypothesis that thermal performance curves of physiological reaction rates are plastic so that performance is maintained despite variable body temperatures within active (non-torpid) endotherms, and we explore mechanisms that confer plasticity. There is evidence that thermal performance curves in tissues that experience thermal fluctuations can be plastic, although this question remains relatively unexplored for endotherms. Mechanisms that alter thermal responses locally at the tissue level include transient potential receptor ion channels (TRPV and TRPM) and the AMP-activated protein kinase (AMPK) both of which can influence metabolism and energy expenditure. Additionally, the thermal sensitivity of processes that cause post-transcriptional RNA degradation can promote the relative expression of cold-responsive genes. Endotherms can respond to environmental fluctuations similarly to ectotherms, and thermal plasticity complements core body temperature regulation to increase whole-organism performance. Thermal plasticity is ancestral to endothermic thermoregulation, but it has not lost its selective advantage so that modern endotherms are a physiological composite of ancestral ectothermic and derived endothermic traits.

Endocrine and metabolic impacts of warming aquatic habitats: differential responses between recently isolated populations of a eurythermal desert pupfish

Temperatures of inland aquatic habitats are increasing with climate change, and understanding how fishes respond physiologically to thermal stress will be crucial for identifying species most susceptible to these changes. Desert fishes may be particularly vulnerable to rising temperatures because many species occupy only a fraction of their historical range and occur in habitats with already high temperatures. Here, we examined endocrine and metabolic responses to elevated temperature in Amargosa pupfish, Cyprinodon nevadensis amargosae. We studied C. n. amargosae from two habitats with distinct thermal conditions: the Amargosa River, which experiences diurnally and seasonally variable temperatures (0.2-40°C); and Tecopa Bore, a spring and marsh fed by hot groundwater (47.5°C) from an artesian borehole. These allopatric populations differ in morphology, and prior evidence suggests that temperature might contribute to these differences via altered thyroid hormone (TH) regulation of morphological development. Here, we document variation in hepatic iodothyronine deiodinase type 2 (dio2) and type 3 (dio3) and TH receptor β (trβ) gene transcript abundance between the Amargosa River and Tecopa Bore wild populations. Fish from these populations acclimated to 24 or 34°C retained differences in hepatic dio2, dio3 and trβ mRNAs and also varied in transcripts encoding the TH membrane transporters monocarboxylate transporter 8 (mct8) and organic anion-transporting protein 1c1 (oatp1c1). Tecopa Bore pupfish also exhibited higher dio2 and trβ mRNA levels in skeletal muscle relative to Amargosa River fish. Muscle citrate synthase activity was lower at 34°C for both populations, whereas lactate dehydrogenase activity and lactate dehydrogenase A-chain (ldhA) transcripts were both higher and 3,5,3'-triiodothryonine responsive in Tecopa Bore pupfish only. These findings reveal that local population variation and thermal experience interact to shape how pupfish respond to elevated temperatures, and point to the need to consider such interactions in management actions for desert fishes under a changing climate.