In vivo regulation of human skeletal muscle gene expression by thyroid hormone

Effect of Empagliflozin on Serum Levels of Thyroid Hormones Among Prediabetic and Diabetic Patients

Objectives: Thyroid dysfunction (TD) and diabetes mellitus (DM) are the most prevalent chronic endocrine disorders that often coexist. Thyroid hormone affects glucose homeostasis through different mechanisms. SGLT2 inhibitors are a drug class used to treat diabetes. However, the effect of this drug class on thyroid tests has not been investigated among diabetic patients. Therefore, the current study aims to assess the effect of empagliflozin on thyroid tests. Materials and Methods: This quasi-experimental study was conducted on 44 prediabetic and type 2 diabetic patients aged 18-65, directed to the clinic affiliated to Kerman Medical Sciences University in 2022-2023. Diabetic patients with HbA1c level of 0.5%-1% higher than the therapeutic target, who did not take blood sugar control drugs, were included in the study. All the patients received 10 mg of empagliflozin once daily for 3 months. Before and 3 months after taking empagliflozin, changes in TSH, total T4, and total T3 serum levels were measured. Results: The mean patients' age was 54.77 years old. The mean FBS and HbA1c levels decreased 3 months after taking empagliflozin (p < 0.05). After taking empagliflozin, T3 level as well as T3/T4 ratio increased (p=0.001). However, no significant change was observed in T4 and TSH levels (p > 0.05). Also, level of T3 significantly changed with changes in weight and triglyceride level after taking empagliflozin. Conclusion: The results showed taking empagliflozin could increase T3 level as well as T3/T4 ratio. However, it had no effect on total T4 and TSH levels. Trial Registration: Iranian Registry of Clinical Trials (IRCT): IRCT20090317001774N10.

The association between thyroid function and insulin resistance as measured by the metabolic score for insulin resistance (METS-IR): insights from NHANES 2007-2012

BACKGROUND

Altered thyroid function has been linked to insulin resistance (IR), but its relationship with the Metabolic Score for Insulin Resistance (METS-IR), a novel non-insulin-based index of IR, remains unclear. This study aimed to investigate the association between thyroid function status and METS-IR in a U.S.

POPULATION

METHODS

This cross-sectional study utilized data from 6,507 adults (aged ≥ 20 years) participating in the National Health and Nutrition Examination Survey from 2007 to 2012. Thyroid function status was categorized into five groups based on thyroid-stimulating hormone and free thyroxine levels. METS-IR was calculated from measures of fasting glucose, triglycerides, high-density lipoprotein cholesterol (HDL-C), and body mass index (BMI). Multivariate regression analyzed the relationship between thyroid status and METS-IR after adjusting for potential confounders.

RESULTS

Higher thyroid-stimulating hormone levels were positively associated with METS-IR (β = 0.003, 95% CI 0.001-0.004, p = 0.021). Subclinical hypothyroidism in males and subclinical hyperthyroidism in females showed significant correlations with higher METS-IR. Thyroid peroxidase antibodies (TPO Ab) positivity strengthened the association between overt hypothyroidism and METS-IR.

CONCLUSIONS

This study demonstrates significant associations between thyroid function status, particularly subclinical thyroid dysfunction, and insulin resistance as measured by METS-IR in a U.S.

POPULATION

Thyroid status may serve as an early marker of insulin resistance risk.

Exploring the association between triglyceride-glucose index and thyroid function

BACKGROUND

Thyroid dysfunction is associated with abnormal glucose-insulin homeostasis, and the triglyceride-glucose (TyG) index has been recommended as a convenient surrogate of insulin resistance (IR). This study aimed to investigate the relationship between TyG and thyroid function in the US population.

METHODS

 We analyzed data from the National Health and Nutrition Examination Survey (NHANES) conducted from 2007 to 2012 in a cross-sectional manner. Aside from conventional thyroid parameters, our study evaluated the central sensitivity to thyroid hormones (THs) using the thyroid feedback quantile-based index (TFQI), thyrotropin resistance index (TT4RI), and thyrotropin index (TSHI). To evaluate peripheral sensitivity to THs, we calculated the ratio of free triiodothyronine (FT3) to free thyroxine (FT4) and the sum activity of peripheral deiodinases (SPINA-GD). In the 1848 adults, multivariable linear regression, subgroup, and interaction analyses were employed to estimate the association between TyG and thyroid parameters. The nonlinear relationship was addressed by smooth curve fittings and generalized additive models.

RESULTS

After adjusting covariates, we demonstrated a significant negative association between TyG and FT4 (β = - 0.57, p < 0.001), and a positive relationship between TyG and thyroid-stimulating hormone (β = 0.34, p = 0.037), as well as TgAb (β = 17.06, p = 0.005). Subgroup analysis indicated that the association between TyG and TgAb was more pronounced in the female subjects (β = 32.39, p < 0.001, p for interaction = 0.021). We also confirmed an inverse correlation between TyG and central sensitivity to THs, as assessed by TSHI and TT4RI (βTSHI = 0.12, p < 0.001; βTT4RI = 2.54, p = 0.023). In terms of peripheral sensitivity to THs, we found a significant positive correlation between TyG and FT3/FT4 (β = 0.03, p = 0.004), and SPINA-GD (β = 2.93, p = 0.004).

CONCLUSION

The present study established a noteworthy association between TyG and thyroid parameters, indicating a strong link between IR and thyroid dysfunction. Further investigations are warranted to validate these results.

Levothyroxine use and longitudinal changes in thigh muscles in at-risk participants for knee osteoarthritis: preliminary analysis from Osteoarthritis Initiative cohort

BACKGROUND

We examined the association between levothyroxine use and longitudinal MRI biomarkers for thigh muscle mass and composition in at-risk participants for knee osteoarthritis (KOA) and their mediatory role in subsequent KOA incidence.

METHODS

Using the Osteoarthritis Initiative (OAI) data, we included the thighs and corresponding knees of participants at risk but without established radiographic KOA (baseline Kellgren-Lawrence grade (KL) < 2). Levothyroxine users were defined as self-reported use at all annual follow-up visits until the 4th year and were matched with levothyroxine non-users for potential confounders (KOA risk factors, comorbidities, and relevant medications covariates) using 1:2/3 propensity score (PS) matching. Using a previously developed and validated deep learning method for thigh segmentation, we assessed the association between levothyroxine use and 4-year longitudinal changes in muscle mass, including cross-sectional area (CSA) and muscle composition biomarkers including intra-MAT (within-muscle fat), contractile percentage (non-fat muscle CSA/total muscle CSA), and specific force (force per CSA). We further assessed whether levothyroxine use is associated with an 8-year risk of standard KOA radiographic (KL ≥ 2) and symptomatic incidence (incidence of radiographic KOA and pain on most of the days in the past 12 months). Finally, using a mediation analysis, we assessed whether the association between levothyroxine use and KOA incidence is mediated via muscle changes.

RESULTS

We included 1043 matched thighs/knees (266:777 levothyroxine users:non-users; average ± SD age: 61 ± 9 years, female/male: 4). Levothyroxine use was associated with decreased quadriceps CSAs (mean difference, 95%CI: - 16.06 mm2/year, - 26.70 to - 5.41) but not thigh muscles' composition (e.g., intra-MAT). Levothyroxine use was also associated with an increased 8-year risk of radiographic (hazard ratio (HR), 95%CI: 1.78, 1.15-2.75) and symptomatic KOA incidence (HR, 95%CI: 1.93, 1.19-3.13). Mediation analysis showed that a decrease in quadriceps mass (i.e., CSA) partially mediated the increased risk of KOA incidence associated with levothyroxine use.

CONCLUSIONS

Our exploratory analyses suggest that levothyroxine use may be associated with loss of quadriceps muscle mass, which may also partially mediate the increased risk of subsequent KOA incidence. Study interpretation should consider underlying thyroid function as a potential confounder or effect modifier. Therefore, future studies are warranted to investigate the underlying thyroid function biomarkers for longitudinal changes in the thigh muscles.

Association between sitting/lying down, standing, walking time and number of steps per day with the hormonal profile and resting energy expenditure of women with obesity living in a low-income region

Reducing sedentary behaviour (SB) and increasing physical activity (PA) by sitting less and standing/walking more is advised to prevent chronic diseases. However, the mechanisms underlying this recommendation are not well established, especially in individuals with obesity living in low-income regions. The present study evaluated whether there are associations between PA indicators (PAI - standing time, walking time and the number of steps/d) and SB indicators (SBI - sitting/lying down time) with the hormonal profile and resting energy expenditure (REE) of adult women living in a low-income region. This is a cross-sectional study. We collected data on hormones (insulin resistance, leptin and thyroid axis), body composition (tetrapolar bioimpedance), REE (indirect calorimetry), and PAI and SBI (triaxial accelerometers, ActivPAL). Multivariable linear models adjusting for age and fat-free mass were performed. Fifty-eight women (mean age of 31 years and BMI of 33 kg/m²) were included. The mean sitting/lying down time and standing time were 16·08 and 5·52 h/d, respectively. Sitting/lying down time showed a direct association with free thyroxine (FT₄) (β = 0·56 ng/dl; 95 % CI = -1·10, -0·02). Standing time showed a direct association with FT₄ (β = 0·75 ng/dl; 95 % CI = 0·01; 1·48) and inverse association with free triiodothyronine (β = -2·83 pg/ml 95 % CI = -5·56, -0·10). There were no associations between PAI and SBI with the REE, insulin resistance, leptin and thyroid-stimulating hormone. Thus, decreased SB is associated with thyroid hormones levels but not with REE, insulin resistance or leptin in women with obesity living in low-income regions.

Targeting skeletal muscle mitochondrial health in obesity

Metabolic demands of skeletal muscle are substantial and are characterized normally as highly flexible and with a large dynamic range. Skeletal muscle composition (e.g., fiber type and mitochondrial content) and metabolism (e.g., capacity to switch between fatty acid and glucose substrates) are altered in obesity, with some changes proceeding and some following the development of the disease. Nonetheless, there are marked interindividual differences in skeletal muscle composition and metabolism in obesity, some of which have been associated with obesity risk and weight loss capacity. In this review, we discuss related molecular mechanisms and how current and novel treatment strategies may enhance weight loss capacity, particularly in diet-resistant obesity.

Association between thyroid hormones and insulin resistance indices based on the Korean National Health and Nutrition Examination Survey

Thyroid dysfunction has been implicated as a potential pathophysiological factor in glucose homeostasis and insulin resistance (IR). This study aimed to identify the correlation between thyroid dysfunction and IR. We used data from the sixth Korean National Health and Nutrition Examination Survey to evaluate a total of 5727 participants. The triglyceride glucose (TyG) index and homeostasis model assessment of insulin resistance (HOMA-IR) were calculated to represent IR. Correlation analysis was performed between thyroid dysfunction and IR. The log-transformed TSH (LnTSH) and free T4 were significantly correlated with the TyG index (TSH, beta coefficient 0.025, 95% confidence interval [CI] 0.014–0.036, p < 0.001; free T4, − 0.110 (− 0.166 to − 0.054), p < 0.001) but not HOMA-IR. Overt hypothyroidism is correlated with increased TyG index in pre-menopausal females (0.215 (0.122–0.309) p < 0.001). On the other hand, overt hyperthyroidism is correlated with increased HOMA-IR in males (0.304 (0.193–0.416), p < 0.001) and post-menopausal females (1.812 (1.717–1.907), p < 0.001). In euthyroid subjects, LnTSH and TyG index were significantly correlated in females. In conclusion, both hyperthyroidism and hypothyroidism might be associated with IR but by different mechanisms. It might be helpful to assess IR with appropriate indexes in patients with thyroid dysfunction.

Smoothelin-Like Protein 1 Regulates Development and Metabolic Transformation of Skeletal Muscle in Hyperthyroidism

Hyperthyroidism triggers a glycolytic shift in skeletal muscle (SKM) by altering the expression of metabolic proteins, which is often accompanied by peripheral insulin resistance. Our previous results show that smoothelin-like protein 1 (SMTNL1), a transcriptional co-regulator, promotes insulin sensitivity in SKM. Our aim was to elucidate the role of SMTNL1 in SKM under physiological and pathological 3,3',5-Triiodo-L-thyronine (T3) concentrations. Human hyper- and euthyroid SKM biopsies were used for microarray analysis and proteome profiler arrays. Expression of genes related to energy production, nucleic acid- and lipid metabolism was changed significantly in hyperthyroid samples. The phosphorylation levels and activity of AMPKα2 and JNK were increased by 15% and 23%, respectively, in the hyperthyroid samples compared to control. Moreover, SMTNL1 expression showed a 6-fold decrease in the hyperthyroid samples and in T3-treated C2C12 cells. Physiological and supraphysiological concentrations of T3 were applied on differentiated C2C12 cells upon SMTNL1 overexpression to assess the activity and expression level of the elements of thyroid hormone signaling, insulin signaling and glucose metabolism. Our results demonstrate that SMTNL1 selectively regulated TRα expression. Overexpression of SMTNL1 induced insulin sensitivity through the inhibition of JNK activity by 40% and hampered the non-genomic effects of T3 by decreasing the activity of ERK1/2 through PKCδ. SMTNL1 overexpression reduced IRS1 Ser307 and Ser612 phosphorylation by 52% and 53%, respectively, in hyperthyroid model to restore the normal responsiveness of glucose transport to insulin. SMTNL1 regulated glucose phosphorylation and balances glycolysis and glycogen synthesis via the downregulation of hexokinase II by 1.3-fold. Additionally, mitochondrial respiration and glycolysis were measured by SeaHorse analysis to determine cellular metabolic function/phenotype of our model system in real-time. T3 overload strongly increased the rate of acidification and a shift to glycolysis, while SMTNL1 overexpression antagonizes the T3 effects. These lines of evidence suggest that SMTNL1 potentially prevents hyperthyroidism-induced changes in SKM, and it holds great promise as a novel therapeutic target in insulin resistance.

A prolonged hiatus in postmenopausal HRT, does not nullify the therapy's positive impact on ageing related sarcopenia

Background

Previous work suggest a positive skeletal muscle effect of hormone replacement therapy (HRT) on skeletal muscle characteristics This study aimed to quantify any continued positive effect of HRT even after a sustained hiatus in treatment, controlling for two key muscle modulation hormones: Estradiol (E2) and Tri-iodo-thyronine (T3).

Method and findings

In 61 untrained women (18-78yrs) stratified as pre-menopausal, post-menopausal without (No_HRT) and post-menopausal with (Used_HRT) HRT history, body composition, physical activity, serum E2 and T3 were assessed by dual energy x-ray absorptiometry, Baecke questionnaire and ELISA. Gastrocnemius medialis (GM) and tibialis anterior (TA) electromyographic profiles (mean power frequency (mPowerF)), isometric plantar-flexion (PF) and dorsi-flexion (DF) maximum voluntary contraction (MVC), rate of torque development (RTD), isokinetic MVC and muscle volume, were assessed using surface electromyography, dynamometry and ultrasonography. Muscle quality was quantified as MVC per unit muscle size. E2 and E2:T3 ratio were significantly lower in postmenopausal participants, and were positively correlated with RTD even after controlling for adiposity and/or age. Pre-menopausal females had greater MVC in 8/8 PF and 2/5 DF (23.7–98.1%; P<0.001–0.049) strength measures compared to No_HRT, but only 6/8 PF (17.4–42.3%; P<0.001–0.046) strength measures compared to Used_HRT. Notably, Used_HRT had significant higher MVC in 7 PF MVC (30.0%-37.7%; P = 0.006–0.031) measures than No_HRT, while premenopausal and Used_HRT had similar uncorrected muscle size or quality. In addition, this cross-sectional data suggest an annual reduction in GM muscle volume corrected for intra-muscular fat by 1.3% in No_HRT and only 0.5% in Used_HRT.

Conclusion

Even years after cessation of the therapy, a history of HRT is positively associated with negating the expected post-menopausal drop in muscle quantity and quality. Whilst mPowerF did not differ between groups, our work highlights positive associations between RTD against E2 and E2:T3. Notwithstanding our study limitation of single time point for blood sampling, our work is the first to illustrate an HRT attenuation of ageing-related decline in RTD. We infer from these data that high E2, even in the absence of high T3, may help maintain muscle contractile speed and quality. Thus our work is the first to points to markedly larger physiological reserves in women with a past history of HRT.

Interactions between Growth of Muscle and Stature: Mechanisms Involved and Their Nutritional Sensitivity to Dietary Protein: The Protein-Stat Revisited

Childhood growth and its sensitivity to dietary protein is reviewed within a Protein-Stat model of growth regulation. The coordination of growth of muscle and stature is a combination of genetic programming, and of two-way mechanical interactions involving the mechanotransduction of muscle growth through stretching by bone length growth, the core Protein-Stat feature, and the strengthening of bone through muscle contraction via the mechanostat. Thus, growth in bone length is the initiating event and this is always observed. Endocrine and cellular mechanisms of growth in stature are reviewed in terms of the growth hormone-insulin like growth factor-1 (GH-IGF-1) and thyroid axes and the sex hormones, which together mediate endochondral ossification in the growth plate and bone lengthening. Cellular mechanisms of muscle growth during development are then reviewed identifying (a) the difficulties posed by the need to maintain its ultrastructure during myofibre hypertrophy within the extracellular matrix and the concept of muscle as concentric "bags" allowing growth to be conceived as bag enlargement and filling, (b) the cellular and molecular mechanisms involved in the mechanotransduction of satellite and mesenchymal stromal cells, to enable both connective tissue remodelling and provision of new myonuclei to aid myofibre hypertrophy and (c) the implications of myofibre hypertrophy for protein turnover within the myonuclear domain. Experimental data from rodent and avian animal models illustrate likely changes in DNA domain size and protein turnover during developmental and stretch-induced muscle growth and between different muscle fibre types. Growth of muscle in male rats during adulthood suggests that "bag enlargement" is achieved mainly through the action of mesenchymal stromal cells. Current understanding of the nutritional regulation of protein deposition in muscle, deriving from experimental studies in animals and human adults, is reviewed, identifying regulation by amino acids, insulin and myofibre volume changes acting to increase both ribosomal capacity and efficiency of muscle protein synthesis via the mechanistic target of rapamycin complex 1 (mTORC1) and the phenomenon of a "bag-full" inhibitory signal has been identified in human skeletal muscle. The final section deals with the nutritional sensitivity of growth of muscle and stature to dietary protein in children. Growth in length/height as a function of dietary protein intake is described in the context of the breastfed child as the normative growth model, and the "Early Protein Hypothesis" linking high protein intakes in infancy to later adiposity. The extensive paediatric studies on serum IGF-1 and child growth are reviewed but their clinical relevance is of limited value for understanding growth regulation; a role in energy metabolism and homeostasis, acting with insulin to mediate adiposity, is probably more important. Information on the influence of dietary protein on muscle mass per se as opposed to lean body mass is limited but suggests that increased protein intake in children is unable to promote muscle growth in excess of that linked to genotypic growth in length/height. One possible exception is milk protein intake, which cohort and cross-cultural studies suggest can increase height and associated muscle growth, although such effects have yet to be demonstrated by randomised controlled trials.

μ-Crystallin in Mouse Skeletal Muscle Promotes a Shift from Glycolytic toward Oxidative Metabolism

μ-Crystallin, encoded by the CRYM gene, binds the thyroid hormones, T3 and T4. Because T3 and T4 are potent regulators of metabolism and gene expression, and CRYM levels in human skeletal muscle can vary widely, we investigated the effects of overexpression of Crym. We generated transgenic mice, Crym tg, that expressed Crym protein specifically in skeletal muscle at levels 2.6-147.5 fold higher than in controls. Muscular functions, Ca2+ transients, contractile force, fatigue, running on treadmills or wheels, were not significantly altered, although T3 levels in tibialis anterior (TA) muscle were elevated ~190-fold and serum T4 was decreased 1.2-fold. Serum T3 and thyroid stimulating hormone (TSH) levels were unaffected. Crym transgenic mice studied in metabolic chambers showed a significant decrease in the respiratory exchange ratio (RER) corresponding to a 13.7% increase in fat utilization as an energy source compared to controls. Female but not male Crym tg mice gained weight more rapidly than controls when fed high fat or high simple carbohydrate diets. Although labeling for myosin heavy chains showed no fiber type differences in TA or soleus muscles, application of machine learning algorithms revealed small but significant morphological differences between Crym tg and control soleus fibers. RNA-seq and gene ontology enrichment analysis showed a significant shift towards genes associated with slower muscle function and its metabolic correlate, β-oxidation. Protein expression showed a similar shift, though with little overlap. Our study shows that μ-crystallin plays an important role in determining substrate utilization in mammalian muscle and that high levels of μ-crystallin are associated with a shift toward greater fat metabolism.

Monosomy X in Female Mice Influences the Regional Formation and Augments the Severity of Angiotensin II-Induced Aortopathies

OBJECTIVE

Turner syndrome women (monosomy X) have high risk of aortopathies consistent with a role for sex chromosomes in disease development. We demonstrated that sex chromosomes influence regional development of Ang II (angiotensin II)-induced aortopathies in mice. In this study, we determined if the number of X chromosomes regulates regional development of Ang II-induced aortopathies. Approach and Results: We used females with varying numbers of X chromosomes (XX female mice [XXF] or XO female mice [XOF]) on an C57BL/6J (ascending aortopathies) or low-density lipoprotein receptor deficient (Ldlr-/-) background (descending and abdominal aortopathies) compared with XY males (XYM). To induce aortopathies, mice were infused with Ang II. XOF (C57BL/6J) exhibited larger percent increases in ascending aortic lumen diameters than Ang II-infused XXF or XYM. Ang II-infused XOF (Ldlr-/-) exhibited similar incidences of thoracic (XOF, 50%; XYM, 71%) and abdominal aortopathies (XOF, 83%; XYM, 71%) as XYM, which were greater than XXF (XXF, 0%). Abdominal aortic lumen diameters and maximal external diameters were similar between XOF and XYM but greater than XXF, and these effects persisted with extended Ang II infusions. Larger aortic lumen diameters, abdominal aortopathy incidence (XXF, 20%; XOF, 75%), and maximal aneurysm diameters (XXF, 1.02±0.17; XOF, 1.96±0.32 mm; P=0.027) persisted in ovariectomized Ang II-infused XOF mice. Data from RNA-seq demonstrated that X chromosome genes that escape X-inactivation (histone lysine demethylases Kdm5c and Kdm6a) exhibited lower mRNA abundance in aortas of XOF than XXF (P=0.033 and 0.024, respectively). Conversely, DNA methylation was higher in aortas of XOF than XXF (P=0.038).

CONCLUSIONS

The absence of a second X chromosome promotes diffuse Ang II-induced aortopathies in females.

Insulin resistance and pancreatic β cell dysfunction are associated with thyroid hormone functions: A cross-sectional hospital-based study in Turkey

BACKGROUND AND AIMS

The prevalence of thyroid disease in diabetic patients is significantly higher than the general population. This indicates a possible interaction between thyroid functions and insulin sensitivity. This study aimed to investigate the relationship between insulin resistance (IR), pancreatic β cell function, and thyroid function tests.

METHODS

This cross-sectional study was conducted with adults who applied to Eskişehir Osmangazi University Hospital for general control. Fasting insulin, glucose, TSH, fT3, and fT4 levels in the serum of 1340 adult (18-60 aged) patients without any chronic diseases were examined retrospectively. The fT3/fT4 ratio, Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), and HOMA-β values were calculated. The correlation between HOMA-IR and HOMA-β values with thyroid function tests and differences between hormone levels of patients with and without IR were evaluated.

RESULTS

There was a positive correlation between HOMA-IR and TSH, negative with fT4. Also, a positive correlation between HOMA-β and fT3, negative correlation with fT4 were observed. In the IR group, fT3 levels were found significantly higher and fT4 levels were significantly lower. TSH levels were higher in the IR group but not statistically significant. The fT3/fT4 ratio was found significantly higher in the IR group and was correlated positively with both HOMA-IR and HOMA-β.

CONCLUSION

Our results revealed that thyroid dysfunction prevalence is quite high in adults who have not yet been diagnosed with diabetes but have insulin resistance and the onset of pancreatic β cell dysfunction.

Athlete's Passport: Prevention of Infections, Inflammations, Injuries and Cardiovascular Diseases

Laboratory medicine in sports medicine is taking on an ever-greater role in the assessment and monitoring of an athlete's health condition. The acute or intense exercise practiced by elite athletes can lead to the appearance of infections, inflammations, muscle injuries or cardiovascular disorders, whose diagnosis is not always rapid and efficient, as there is no continuous monitoring of the athlete. The absence of such monitoring can have serious consequences in terms of recovery of the professional athlete. These imbalances can induce metabolic adaptations which translate into alterations of specific parameters in terms of concentration and activity. The aim of this study was to follow the variation of specific biochemical biomarkers in a basketball team participating to the maximum championship during different phases of the agonistic season. The evaluation of serum biomarkers can help doctors to safeguard the athlete's health and sports trainers to adapt workouts, thus avoiding the appearance of diseases and injuries that in some cases can be underestimated by becoming irreversible ailments that do not allow the athlete to return to a healthy state. This information can be useful to create athlete biologic passports.

Effects of Breastfeeding and Formula Feeding on the Expression Level of FTO, CPT1A and PPAR-α Genes in Healthy Infants

PURPOSE

The study aimed to investigate the effect of breastfeeding, formula feeding and mix feeding (breastfed plus formula-fed) on the expression level of obesity-predisposing genes including fat mass and obesity-associated (FTO), carnitine palmitoyltransferase 1A (CPT1A), and peroxisome proliferator-activated receptor-α (PPAR-α) in 5- to 6-month-old infants.

PATIENTS AND METHODS

A total of 150 infants participated in this case-control study. All subjects were healthy infants aged 5-6 months that divided into 3 groups: breastfed, formula-fed, and mix-fed. The expression level of FTO, CPT1A, and PPAR-α genes in peripheral blood mononuclear cells (PBMC) was evaluated in each group using reverse transcription-polymerase chain reaction (RT-PCR) method.

RESULTS

Our findings showed that the current weight, height, and head circumference of infants in the formula feeding and mix feeding groups were significantly higher than those in the exclusive breastfeeding group. The expression level of FTO and CPT1A genes in formula-fed and mix-fed infants was significantly higher (p<0.001) than that in breastfed infants, while the expression level of PPAR-α gene was significantly lower (p<0.05).

CONCLUSION

Breastfeeding showed modulatory effects on the expression level of obesity-predisposing genes and can protect against obesity and subsequent non-communicable diseases. However, more investigations are required to explain the epigenetic effects of breast milk.

Screening for New Markers to Assess Thyroid Hormone Action by OMICs Analysis of Human Samples

Determination of the levels of thyroid-stimulating hormone (TSH) and free thyroid hormones (fTHs) is crucial for assessing thyroid function. However, as a result of inter-individual genetic variability and different environmental factors individual set points exist for TSH and fTHs and display considerable variation. Furthermore, under specific pathophysiological conditions like central hypothyroidism, TSH secreting pituitary tumors, or thyroid hormone resistance the established markers TSH and fTH fail to reliably predict thyroid function and adequate supply of TH to peripheral organs. Even in case of overt hyper- and hypothyroidism circulating fTH concentrations do not correlate with clinical symptoms. Therefore, there is a clear need for novel, more specific biomarkers to diagnose and monitor thyroid function. OMICs screening approaches allow parallel profiling of hundreds to thousands of molecules and thus comprehensive monitoring of molecular alterations in tissues and body fluids that might be associated with changes in thyroid function. These techniques thus constitute promising tools for the identification of urgently needed novel biomarkers. This mini review summarizes the findings of OMICs studies in thyroid research with a particular focus on population-based and patient studies as well as interventional approaches investigating the effects of thyroid hormone administration.

A Significant Association of Upper Limb Muscle Strength with Thyroid Function in Overweight and Obese Population: A Study of the Sixth Korea National Health and Nutrition Examination Survey (KNHANES 2014-2015)

Background. As skeletal muscle is one of main targets of thyroid hormone signalling, an association of thyroid function and muscle strength could be expected. The aim of study is to evaluate the association of free thyroxine (FT4) and thyrotropin (TSH) with upper limb muscle strength, measured by hand grip strength, in subjects with normal FT4 from national representative data. The study utilized the sixth edition of the Korea National Health and Nutrition Examination Survey. After exclusion of subjects with FT4 level out of normal range, a history of thyroid disease or cerebral disease, restricted activity, and incomplete data, a total of 3503 were recruited (age range 19-80 years, 51% male). FT4 positively correlated with upper limb muscle strength (β coefficient = -12.84, p < 0.001), while TSH did negatively (β coefficient = -0.37, p=0.002). After adjusting for confounding factors, statistical significance disappeared. However, among subjects with BMI above 23 kg/m², a negative correlation of TSH with upper limb muscle strength was found in a younger age group (19-39 years old) (β coefficient = -0.56, p=0.021), while FT4 positively correlated with upper limb muscle strength (β coefficient = 3.24, p=0.019) in an older group (above 40 years old). In overweight and obese subjects, a significant association of thyroid function with upper limb muscle strength was observed in nation-wide representative data. High TSH in a younger group and low FT4 in an older group could be risk factors for decreased upper limb muscle strength in obese population.

Bipolar limbic expression of auto-immune thyroid targets: thyroglobulin and thyroid-stimulating hormone receptor

The associations between thyroid auto-immunity and neuro-psychiatric disorders are well-documented. However, there exists limited literature specifically linking auto-immune thyroid disease (AITD) to bipolar disorder (BD). Thus, we investigated the likely association between Hashimoto's disease and BD through the extra-thyroidal localisation of thyroid-stimulating hormone receptor (TSH-R) and thyroglobulin (TG) in limbic regions of normal and bipolar human adult brain. Further, we hypothesised that changes in thyroid expression in bipolar limbic cortex may contribute to mood dysregulation associated with BD. Immuno-chemistry and in-situ PCR were used to localise TSH-R/TG within the amygdala, cingulate gyrus and frontal cortex of normal (n = 5) and bipolar (n = 5) brains. Reverse-transcriptase qPCR provided fold-change differences in TSH-R gene expression. The results demonstrated reduced thyroid protein expression in bipolar limbic regions; these novel results correlate with other neuro-imaging reports that describe reduced cortico-limbic tissue volumes and neuro-physiological activity during BD. We also demonstrated TG-like proteins exclusive to bipolar amygdala neurons, and which relates to previous neuro-imaging studies of amygdala hyperactivity and enhanced emotional sensitivity in BD. Indeed, reduced TSH-R/TG in limbic regions may predispose to, or bear relevance in the pathophysiology of mood dysregulation and symptoms of BD. Further, we attribute mood dysregulation in BD to limbic-derived TSH-R, which probably provides potential targets for thyroid auto-immune factors during Hashimoto's disease. Consequently, this may lead to inactivated and/or damaged neurons. The neuro-pathology of diminished neuronal functioning or neuronal atrophy suggests a novel neuro-degeneration mechanism in BD.

Insulin resistance and diabetes in hyperthyroidism: a possible role for oxygen and nitrogen reactive species

In addition to insulin, glycemic control involves thyroid hormones. However, an excess of thyroid hormone can disturb the blood glucose equilibrium, leading to alterations of carbohydrate metabolism and, eventually, diabetes. Indeed, experimental and clinical hyperthyroidism is often accompanied by abnormal glucose tolerance. A common characteristic of hyperthyroidism and type 2 diabetes is the altered mitochondrial efficiency caused by the enhanced production of reactive oxygen and nitrogen species. It is known that an excess of thyroid hormone leads to increased oxidant production and mitochondrial oxidative damage. It can be hypothesised that these species represent the link between hyperthyroidism and development of insulin resistance and diabetes, even though direct evidence of this relationship is lacking. In this review, we examine the literature concerning the effects of insulin and thyroid hormones on glucose metabolism and discuss alterations of glucose metabolism in hyperthyroid conditions and the cellular and molecular mechanisms that may underline them.

Empowering thyroid hormone research in human subjects using OMICs technologies

OMICs subsume different physiological layers including the genome, transcriptome, proteome and metabolome. Recent advances in analytical techniques allow for the exhaustive determination of biomolecules in all OMICs levels from less invasive human specimens such as blood and urine. Investigating OMICs in deeply characterized population-based or experimental studies has led to seminal improvement of our understanding of genetic determinants of thyroid function, identified putative thyroid hormone target genes and thyroid hormone-induced shifts in the plasma protein and metabolite content. Consequently, plasma biomolecules have been suggested as surrogates of tissue-specific action of thyroid hormones. This review provides a brief introduction to OMICs in thyroid research with a particular focus on metabolomics studies in humans elucidating the important role of thyroid hormones for whole body metabolism in adults.

Expression of thyroid-stimulating hormone receptors and thyroglobulin in limbic regions in the adult human brain

Expression of the human thyroid-specific proteins, thyroid-stimulating hormone receptor (TSH-R) and thyroglobulin (TG) in non-thyroid tissue is well-documented. TSH-R has been identified in the heart, kidney, bone, pituitary, adipose tissue, skin and astrocyte cultures. TG has been identified in the skin, thymus and kidney. However, none of those previous studies had identified TSH-R or TG in specific human brain regions. Previously, a pilot study conducted by our group on normal adult human brain demonstrated TSH-R and TG in cortical neurons and cerebral vasculature, respectively, within various brain areas. In the present study, we extend this investigation of thyroid proteins specifically in limbic regions of normal human brain. Forensic human samples of amygdalae, cingulate gyrii, frontal cortices, hippocampii, hypothalamii, and thalamii were obtained from five individuals who had died of causes unrelated to head injury and had no evidence of brain disease or psychological abnormality. Tissues were probed with commercial polyclonal antibodies against human TSH-R and TG which resulted in the significant demonstration of neuronal TSH-R in all limbic regions examined. Other novel results demonstrated TG in vascular smooth muscle of all limbic regions and in some neurons. Finding thyroid proteins in limbic areas of the human brain is unique, and this study demonstrates that cerebro-limbic localisation of thyroid proteins may have potential roles in neuro-psycho-pharmacology.

Thyroid hormone upregulates MDM2 in rat type I fibre: Implications for skeletal muscle mass regulation

AIM

Based upon a microarray assay, we have identified that triiodothyronine (T3) upregulates MDM2 gene expression in the rat skeletal muscle. As MDM2 protein is an E3 ligase, we hypothesized that this enzyme could play a role in T3 effects on skeletal muscle mass control.

METHODS

To test our hypothesis, male rats (2 months old) were randomly assigned into the following groups: intact controls, treated with 20 physiological doses of T3 for 0.5, 1 and 7 days, or with 5, 20 and 50 physiological doses of T3 for 7 days. For in vitro experiments, myotubes and C2C12 cells were treated with T3 for 3 days.

RESULTS

After validation of the microarray finding throughout RT-PCR and confirmation that T3 induces increases in MDM2 protein expression in a dose-dependent manner, we observed that MDM2 was upregulated by T3 exclusively in fibre type I. Moreover, detailed histological evaluation showed that MDM2 overexpression distributes punctiformily along the cross section of the fibre and also inside nuclei. MDM2 colocalizes with PAX7 in control muscle and T3 downregulates this myogenic factor. Pharmacological inhibition of MDM2 in cultured myotubes caused a severe decrease in their diameter (~35%, P < .001 vs Control), enhancing the effect of T3 (from ~12% to ~35%, P < .001) alone upon myotube diameter and mRNA levels of atrogenes. Finally, we observed that FOXO3 (MDM2 target) is kept outside the nucleus under T3 stimulation.

CONCLUSION

Our results indicate that MDM2 might be involved in the pro-trophic effects of T3 in skeletal muscle.

Retinal S-opsin dominance in Ansell's mole-rats (Fukomys anselli) is a consequence of naturally low serum thyroxine

Mammals usually possess a majority of medium-wavelength sensitive (M-) and a minority of short-wavelength sensitive (S-) opsins in the retina, enabling dichromatic vision. Unexpectedly, subterranean rodents from the genus Fukomys exhibit an S-opsin majority, which is exceptional among mammals, albeit with no apparent adaptive value. Because thyroid hormones (THs) are pivotal for M-opsin expression and metabolic rate regulation, we have, for the first time, manipulated TH levels in the Ansell's mole-rat (Fukomys anselli) using osmotic pumps. In Ansell's mole-rats, the TH thyroxine (T4) is naturally low, likely as an adaptation to the harsh subterranean ecological conditions by keeping resting metabolic rate (RMR) low. We measured gene expression levels in the eye, RMR, and body mass (BM) in TH-treated animals. T4 treatment increased both, S- and M-opsin expression, albeit M-opsin expression at a higher degree. However, this plasticity was only given in animals up to approximately 2.5 years. Mass-specific RMR was not affected following T4 treatment, although BM decreased. Furthermore, the T4 inactivation rate is naturally higher in F. anselli compared to laboratory rodents. This is the first experimental evidence that the S-opsin majority in Ansell's mole-rats is a side effect of low T4, which is downregulated to keep RMR low.

Identification and characterization of long non-coding RNA in prenatal and postnatal skeletal muscle of sheep

lncRNAs are a class of transcriptional RNA molecules of >200 nucleotides in length. However, the overall expression pattern and function of lncRNAs in sheep muscle is not clear. Here, we identified 1566 lncRNAs and 404 differentially expressed lncRNAs in sheep muscle from prenatal (110 days of fetus) and postnatal (2 to 3 years old of adult sheep) developmental stages by using RNA-seq technology. Several lncRNAs were identified by using RT-PCR and DNA sequencing. The expression levels of several lncRNAs were confirmed by qRT-PCR. We analyzed the effect of lncRNAs that act cis to the target genes. lncRNA targeting genes were involved in signaling pathways associated with growth and development of muscle by GO and KEGG enrichment analysis. Through our study, we provide a comprehensive expression profile of muscle lncRNAs in sheep, which provides valuable resources for further understanding genetic regulation of muscle growth and development from the perspective of lncRNA.

Thyroid State Regulates Gene Expression in Human Whole Blood

CONTEXT

Despite the well-recognized clinical features resulting from insufficient or excessive thyroid hormone (TH) levels in humans, it is largely unknown which genes are regulated by TH in human tissues.

OBJECTIVE

To study the effect of TH on human gene expression profiles in whole blood, mainly consisting of T3 receptor (TR) α-expressing cells.

METHODS

We performed next-generation RNA sequencing on whole blood samples from eight athyroid patients (four females) on and after 4 weeks off levothyroxine replacement. Gene expression changes were analyzed through paired differential expression analysis and confirmed in a validation cohort. Weighted gene coexpression network analysis (WGCNA) was applied to identify thyroid state-related networks.

RESULTS

We detected 486 differentially expressed genes (fold-change >1.5; multiple testing corrected P value < 0.05), of which 76% were positively and 24% were negatively regulated. Gene ontology (GO) enrichment analysis revealed that three biological processes were significantly overrepresented, of which the process translational elongation showed the highest fold enrichment (7.3-fold, P = 1.8 × 10-6). WGCNA analysis independently identified various gene clusters that correlated with thyroid state. Further GO analysis suggested that thyroid state affects platelet function.

CONCLUSIONS

Changes in thyroid state regulate numerous genes in human whole blood, predominantly TRα-expressing leukocytes. In addition, TH may regulate gene transcripts in platelets.

Thyroid hormone signaling and deiodinase actions in muscle stem/progenitor cells

Thyroid hormone (TH) regulates such crucial biological functions as normal growth, development and metabolism of nearly all vertebrate tissues. In skeletal muscle, TH plays a critical role in regulating the function of satellite cells, the bona fide skeletal muscle stem cells. Deiodinases (D2 and D3) have been found to modulate the expression of various TH target genes in satellite cells. Regulation of the expression and activity of the deiodinases constitutes a cell-autonomous, pre-receptor mechanism that controls crucial steps during the various phases of myogenesis. Here, we review the roles of deiodinases in skeletal muscle stem cells, particularly in muscle homeostasis and upon regeneration. We focus on the role of T3 in stem cell functions and in commitment towards lineage progression. We also discuss how deiodinases might be therapeutically exploited to improve satellite-cell-mediated muscle repair in skeletal muscle disorders or injury.

Treatment of Swedish Patients with Graves' Hyperthyroidism Is Associated with Changes in Acylcarnitine Levels

BACKGROUND

Hyperthyroidism is associated with alterations in metabolism that are currently only partially understood. The objective of the study was to investigate changes in metabolism associated with reinstatement of euthyroidism in Swedish patients.

METHODS

Eighty metabolites in plasma were profiled from 10 subjects with Graves' disease (GD) at baseline and after 9 and 15 months of treatment to reinstate euthyroidism. Thyroid parameters, thyrotropin (TSH), TSH receptor antibodies, free triiodothyronine, and free thyroxine were followed. Main findings were validated in plasma from 20 subjects with GD at baseline and at three, six, and nine months. The study was conducted at the endocrinology clinic in Malmö, Sweden.

RESULTS

Euthyroidism was reinstated at three months, and thyroid status did not change further during the 15-month follow-up. This was paralleled by altered levels of 9/19 detected acylcarnitines (p < 0.05 after adjustment for multiple testing). Levels of short-chain acylcarnitines were decreased, intermediate-chain acylcarnitines elevated, and long-chain acylcarnitines unaltered.

CONCLUSIONS

GD and treatment of the disease is associated with pronounced acyl chain length-dependent alterations in acylcarnitine levels. These changes may be impacted by ethnicity and or dietary differences.

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.

Content of selected amino acids in the gastrocnemius muscle during experimental hypothyroidism in rats

Introduction: Thyroid hormones affect protein turnover, and in the case of hypothyroidism a decrease in protein synthesis and reduced release of certain amino acids from skeletal muscles are observed. Changes in the amino acid system of skeletal muscles may be responsible for the occurrence of muscle disorders. Material and Methods: The study measured the content of selected amino acids in the gastrocnemius muscle of Wistar rats during experimental hypothyroidism induced by oral administration of methimazole at a concentration of 0.05% in drinking water for 90 d. The rats were divided into four groups: E1 (n = 6) - experimental males, E2 (n = 6) - experimental females, C1 (n = 6) - control males, and C2 (n = 6) control females. Results: A statistically significant reduction occurred in leucine, isoleucine, and 1-methylhistidine levels in males, and 1-methylhistidine in females, in comparison to the control groups. Conclusion: The hypothyroidism-induced changes in amino acid content may be responsible for the occurrence of skeletal muscle function disorders.

Hypothyroid myopathy: A peculiar clinical presentation of thyroid failure. Review of the literature

Abnormalities in thyroid function are common endocrine disorders that affect 5-10 % of the general population, with hypothyroidism occurring more frequently than hyperthyroidism. Clinical symptoms and signs are often nonspecific, particularly in hypothyroidism. Muscular symptoms (stiffness, myalgias, cramps, easy fatigability) are mentioned by the majority of patients with frank hypothyroidism. Often underestimated is the fact that muscle symptoms may represent the predominant or the only clinical manifestation of hypothyroidism, raising the issue of a differential diagnosis with other causes of myopathy, which sometimes can be difficult. Elevated serum creatine kinase, which not necessarily correlates with the severity of the myopathic symptoms, is certainly suggestive of muscle impairment, though it does not explain the cause. Rare muscular manifestations, associated with hypothyroidism, are rhabdomyolysis, acute compartment syndrome, Hoffman's syndrome and Kocher-Debré-Sémélaigne syndrome. Though the pathogenesis of hypothyroid myopathy is not entirely known, proposed mechanisms include altered glycogenolytic and oxidative metabolism, altered expression of contractile proteins, and neuro-mediated damage. Correlation studies of haplotype, muscle gene expression and protein characterization, could help understanding the pathophysiological mechanisms of this myopathic presentation of hypothyroidism.

Proteomics of Breast Muscle Tissue Associated with the Phenotypic Expression of Feed Efficiency within a Pedigree Male Broiler Line: I. Highlight on Mitochondria

As feed represents 60 to 70% of the cost of raising an animal to market weight, feed efficiency (the amount of dry weight intake to amount of wet weight gain) remains an important genetic trait in animal agriculture. To gain greater understanding of cellular mechanisms of feed efficiency (FE), shotgun proteomics was conducted using in-gel trypsin digestion and tandem mass spectrometry on breast muscle samples obtained from pedigree male (PedM) broilers exhibiting high feed efficiency (FE) or low FE phenotypes (n = 4 per group). The high FE group had greater body weight gain (P = 0.004) but consumed the same amount of feed (P = 0.30) from 6 to 7 wk resulting in higher FE (P < 0.001). Over 1800 proteins were identified, of which 152 were different (P < 0.05) by at least 1.3 fold and ≤ 15 fold between the high and low FE phenotypes. Data were analyzed for a modified differential expression (DE) metric (Phenotypic Impact Factors or PIF) and interpretation of protein expression data facilitated using the Ingenuity Pathway Analysis (IPA) program. In the entire data set, 228 mitochondrial proteins were identified whose collective expression indicates a higher mitochondrial expression in the high FE phenotype (binomial probability P < 0.00001). Within the top up and down 5% PIF molecules in the dataset, there were 15 mitoproteome proteins up-regulated and only 5 down-regulated in the high FE phenotype. Pathway enrichment analysis also identified mitochondrial dysfunction and oxidative phosphorylation as the number 1 and 5 differentially expressed canonical pathways (up-regulated in high FE) in the proteomic dataset. Upstream analysis (based on DE of downstream molecules) predicted that insulin receptor, insulin like growth receptor 1, nuclear factor, erythroid 2-like 2, AMP activated protein kinase (α subunit), progesterone and triiodothyronine would be activated in the high FE phenotype whereas rapamycin independent companion of target of rapamycin, mitogen activated protein kinase 4, and serum response factor would be inhibited in the high FE phenotype. The results provide additional insight into the fundamental molecular landscape of feed efficiency in breast muscle of broilers as well as further support for a role of mitochondria in the phenotypic expression of FE.

Funding provided by USDA-NIFA (#2013–01953), Arkansas Biosciences Institute (Little Rock, AR), McMaster Fellowship (AUS to WB) and the Agricultural Experiment Station (Univ. of Arkansas, Fayetteville).

Thyroid Hormone Stimulation of Autophagy Is Essential for Mitochondrial Biogenesis and Activity in Skeletal Muscle

Thyroid hormone (TH) and autophagy share similar functions in regulating skeletal muscle growth, regeneration, and differentiation. Although TH recently has been shown to increase autophagy in liver, the regulation and role of autophagy by this hormone in skeletal muscle is not known. Here, using both in vitro and in vivo models, we demonstrated that TH induces autophagy in a dose- and time-dependent manner in skeletal muscle. TH induction of autophagy involved reactive oxygen species (ROS) stimulation of 5'adenosine monophosphate-activated protein kinase (AMPK)-Mammalian target of rapamycin (mTOR)-Unc-51-like kinase 1 (Ulk1) signaling. TH also increased mRNA and protein expression of key autophagy genes, microtubule-associated protein light chain 3 (LC3), Sequestosome 1 (p62), and Ulk1, as well as genes that modulated autophagy and Forkhead box O (FOXO) 1/3a. TH increased mitochondrial protein synthesis and number as well as basal mitochondrial O2 consumption, ATP turnover, and maximal respiratory capacity. Surprisingly, mitochondrial activity and biogenesis were blunted when autophagy was blocked in muscle cells by Autophagy-related gene (Atg)5 short hairpin RNA (shRNA). Induction of ROS and 5'adenosine monophosphate-activated protein kinase (AMPK) by TH played a significant role in the up-regulation of Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PPARGC1A), the key regulator of mitochondrial synthesis. In summary, our findings showed that TH-mediated autophagy was essential for stimulation of mitochondrial biogenesis and activity in skeletal muscle. Moreover, autophagy and mitochondrial biogenesis were coupled in skeletal muscle via TH induction of mitochondrial activity and ROS generation.

Thyroid Hormone Receptor α Plays an Essential Role in Male Skeletal Muscle Myoblast Proliferation, Differentiation, and Response to Injury

Thyroid hormone plays an essential role in myogenesis, the process required for skeletal muscle development and repair, although the mechanisms have not been established. Skeletal muscle develops from the fusion of precursor myoblasts into myofibers. We have used the C2C12 skeletal muscle myoblast cell line, primary myoblasts, and mouse models of resistance to thyroid hormone (RTH) α and β, to determine the role of thyroid hormone in the regulation of myoblast differentiation. T3, which activates thyroid hormone receptor (TR) α and β, increased myoblast differentiation whereas GC1, a selective TRβ agonist, was minimally effective. Genetic approaches confirmed that TRα plays an important role in normal myoblast proliferation and differentiation and acts through the Wnt/β-catenin signaling pathway. Myoblasts with TRα knockdown, or derived from RTH-TRα PV (a frame-shift mutation) mice, displayed reduced proliferation and myogenic differentiation. Moreover, skeletal muscle from the TRα1PV mutant mouse had impaired in vivo regeneration after injury. RTH-TRβ PV mutant mouse model skeletal muscle and derived primary myoblasts did not have altered proliferation, myogenic differentiation, or response to injury when compared with control. In conclusion, TRα plays an essential role in myoblast homeostasis and provides a potential therapeutic target to enhance skeletal muscle regeneration.

A Review of the Phenomenon of Hysteresis in the Hypothalamus-Pituitary-Thyroid Axis

The existence of a phase of prolonged suppression of TSH despite normalization of serum thyroid hormones over a variable period of time during the recovery of thyrotoxicosis has been documented in literature. Conversely, a temporary elevation of TSH despite attainment of euthyroid levels of serum thyroid hormones following extreme hypothyroidism has also been observed. This rate-independent lag time in TSH recovery is an evidence of a "persistent memory" of the history of dysthyroid states the hypothalamus-pituitary-thyroid (HPT) axis has encountered after the thyroid hormone perturbations have faded out, a phenomenon termed "hysteresis." Notwithstanding its perplexing nature, hysteresis impacts upon the interpretation of thyroid function tests with sufficient regularity that clinicians risk misdiagnosing and implementing erroneous treatment out of ignorance of this aspect of thyrotropic biology. Mathematical modeling of this phenomenon is complicated but may allow the euthyroid set point to be predicted from thyroid function data exhibiting strong hysteresis effects. Such model predictions are potentially useful for clinical management. Although the molecular mechanisms mediating hysteresis remain elusive, epigenetics, such as histone modifications, are probably involved. However, attempts to reverse the process to hasten the resolution of the hysteretic process may not necessarily translate into improved physiology or optimal health benefits. This is not unexpected from teleological considerations, since hysteresis probably represents an adaptive endocrinological response with survival advantages evolutionarily conserved among vertebrates with a HPT system.

μ-Crystallin controls muscle function through thyroid hormone action

μ-Crystallin (Crym), a thyroid hormone-binding protein, is abnormally up-regulated in the muscles of patients with facioscapulohumeral muscular dystrophy, a dominantly inherited progressive myopathy. However, the physiologic function of Crym in skeletal muscle remains to be elucidated. In this study, Crym was preferentially expressed in skeletal muscle throughout the body. Crym-knockout mice exhibited a significant hypertrophy of fast-twitch glycolytic type IIb fibers, causing an increase in grip strength and high intensity running ability in Crym-null mice. Genetic inactivation of Crym or blockade of Crym by siRNA-mediated knockdown up-regulated the gene expression of fast-glycolytic contractile fibers in satellite cell-derived myotubes in vitro These alterations in Crym-inactivated muscle were rescued by inhibition of thyroid hormone, even though Crym is a positive regulator of thyroid hormone action in nonmuscle cells. The results demonstrated that Crym is a crucial regulator of muscle plasticity, controlling metabolic and contractile properties of myofibers, and thus the selective inactivation of Crym may be a potential therapeutic target for muscle-wasting diseases, such as muscular dystrophies and age-related sarcopenia.-Seko, D., Ogawa, S., Li, T.-S., Taimura, A., Ono, Y. μ-Crystallin controls muscle function through thyroid hormone action.

Thyroid Hormone at Near Physiologic Concentrations Acutely Increases Oxygen Consumption and Extracellular Acidification in LH86 Hepatoma Cells

Thyroid hormone (T3) has been known to regulate the basal metabolic rate for more than a century, but mechanistic understanding is lacking both at the level of the intact organism and in terms of how T3 alters energy expenditure in individual tissues. The current studies investigate the question of which metabolically relevant genes respond acutely as T3 concentrations increase through the physiologic range in liver cells. Because this has been technically unfeasible historically, we developed a modified protocol for extracellular flux analysis using a 96-well Extracellular Flux Analyzer (Seahorse Bioscience). Using a modified extracellular flux protocol and LH86 human hepatoma cells, we established an experimental system where small but significant changes in O2 consumption could be reproducibly quantified as hypothyroid cells were exposed to near-physiologic final concentrations of T3 approximately 2 orders of magnitude lower than most studies (0.04 nM free T3), in only 6-7 hours. Taking advantage of the nondestructive nature of 96-well Extracellular Flux Analyzer measurements, the acute, direct, transcriptional changes that occur were measured in the exact same cells demonstrating increased O2 consumption. An unbiased, genome-wide microarray analysis identified potential candidate genes related to fatty acid oxidation, angiogenesis, nucleotide metabolism, immune signaling, mitochondrial respiration, and cell proliferation. The identified transcriptome is likely enriched in the genes most important for mediating the energetic effects of T3 in hepatoma cells.

Regulation of skeletal muscle mitochondrial activity by thyroid hormones: focus on the "old" triiodothyronine and the "emerging" 3,5-diiodothyronine

3,5,3′-Triiodo-L-thyronine (T3) plays a crucial role in regulating metabolic rate and fuel oxidation; however, the mechanisms by which it affects whole-body energy metabolism are still not completely understood. Skeletal muscle (SKM) plays a relevant role in energy metabolism and responds to thyroid state by remodeling the metabolic characteristics and cytoarchitecture of myocytes. These processes are coordinated with changes in mitochondrial content, bioenergetics, substrate oxidation rate, and oxidative phosphorylation efficiency. Recent data indicate that “emerging” iodothyronines have biological activity. Among these, 3,5-diiodo-L-thyronine (T2) affects energy metabolism, SKM substrate utilization, and mitochondrial functionality. The effects it exerts on SKM mitochondria involve more aspects of mitochondrial bioenergetics; among these, respiratory chain activity, mitochondrial thermogenesis, and lipid-handling are stimulated rapidly. This mini review focuses on signaling and biochemical pathways activated by T3 and T2 in SKM that influence the above processes. These novel aspects of thyroid physiology could reveal new perspectives for understanding the involvement of SKM mitochondria in hypo- and hyper-thyroidism.

Guidelines for the treatment of hypothyroidism: prepared by the american thyroid association task force on thyroid hormone replacement

BACKGROUND

A number of recent advances in our understanding of thyroid physiology may shed light on why some patients feel unwell while taking levothyroxine monotherapy. The purpose of this task force was to review the goals of levothyroxine therapy, the optimal prescription of conventional levothyroxine therapy, the sources of dissatisfaction with levothyroxine therapy, the evidence on treatment alternatives, and the relevant knowledge gaps. We wished to determine whether there are sufficient new data generated by well-designed studies to provide reason to pursue such therapies and change the current standard of care. This document is intended to inform clinical decision-making on thyroid hormone replacement therapy; it is not a replacement for individualized clinical judgment.

METHODS

Task force members identified 24 questions relevant to the treatment of hypothyroidism. The clinical literature relating to each question was then reviewed. Clinical reviews were supplemented, when relevant, with related mechanistic and bench research literature reviews, performed by our team of translational scientists. Ethics reviews were provided, when relevant, by a bioethicist. The responses to questions were formatted, when possible, in the form of a formal clinical recommendation statement. When responses were not suitable for a formal clinical recommendation, a summary response statement without a formal clinical recommendation was developed. For clinical recommendations, the supporting evidence was appraised, and the strength of each clinical recommendation was assessed, using the American College of Physicians system. The final document was organized so that each topic is introduced with a question, followed by a formal clinical recommendation. Stakeholder input was received at a national meeting, with some subsequent refinement of the clinical questions addressed in the document. Consensus was achieved for all recommendations by the task force.

RESULTS

We reviewed the following therapeutic categories: (i) levothyroxine therapy, (ii) non-levothyroxine-based thyroid hormone therapies, and (iii) use of thyroid hormone analogs. The second category included thyroid extracts, synthetic combination therapy, triiodothyronine therapy, and compounded thyroid hormones.

CONCLUSIONS

We concluded that levothyroxine should remain the standard of care for treating hypothyroidism. We found no consistently strong evidence for the superiority of alternative preparations (e.g., levothyroxine-liothyronine combination therapy, or thyroid extract therapy, or others) over monotherapy with levothyroxine, in improving health outcomes. Some examples of future research needs include the development of superior biomarkers of euthyroidism to supplement thyrotropin measurements, mechanistic research on serum triiodothyronine levels (including effects of age and disease status, relationship with tissue concentrations, as well as potential therapeutic targeting), and long-term outcome clinical trials testing combination therapy or thyroid extracts (including subgroup effects). Additional research is also needed to develop thyroid hormone analogs with a favorable benefit to risk profile.

Mechanisms modulating skeletal muscle phenotype

Mammalian skeletal muscles are composed of a variety of highly specialized fibers whose selective recruitment allows muscles to fulfill their diverse functional tasks. In addition, skeletal muscle fibers can change their structural and functional properties to perform new tasks or respond to new conditions. The adaptive changes of muscle fibers can occur in response to variations in the pattern of neural stimulation, loading conditions, availability of substrates, and hormonal signals. The new conditions can be detected by multiple sensors, from membrane receptors for hormones and cytokines, to metabolic sensors, which detect high-energy phosphate concentration, oxygen and oxygen free radicals, to calcium binding proteins, which sense variations in intracellular calcium induced by nerve activity, to load sensors located in the sarcomeric and sarcolemmal cytoskeleton. These sensors trigger cascades of signaling pathways which may ultimately lead to changes in fiber size and fiber type. Changes in fiber size reflect an imbalance in protein turnover with either protein accumulation, leading to muscle hypertrophy, or protein loss, with consequent muscle atrophy. Changes in fiber type reflect a reprogramming of gene transcription leading to a remodeling of fiber contractile properties (slow-fast transitions) or metabolic profile (glycolytic-oxidative transitions). While myonuclei are in postmitotic state, satellite cells represent a reserve of new nuclei and can be involved in the adaptive response.

Maternal endocrine adaptation throughout pregnancy to nutrient manipulation: consequences for sexually dimorphic programming of thyroid hormones and development of their progeny

Maternal nutrient restriction during critical windows of fetal development alters postnatal growth, often in a sexually dimorphic manner. Intrauterine growth restriction is frequently characterized by accelerated growth and increased adiposity in later life. Thyroid hormones are implicated as part of the mechanism involved in this scenario via their actions within the hypothalamic-pituitary-thyroid axis. We fed high (H = 240%) and low (L = 70%) levels of recommended daily crude protein intake during the first and second trimesters of gestation to beef heifers to investigate effects to their progeny's plasma concentrations of free and total triiodothyronine (FT3 and TT3) and thyroxine (FT4 and TT4) from birth until weaning at 191 days of age (n = 68). The study design was a two-by-two factorial. For male progeny, exposure to maternal diets low in protein during the first trimester of gestation resulted in greater FT4 at birth (P < 0.05) which was subsequent to lower concentrations of leptin in maternal plasma at 271 days of gestation compared with their high-protein-exposed counterparts. These same animals went on to have greater milk intake during the latter half of the lactation period (P < 0.05) and exhibited faster rates of average daily gain (ADG) relative to birth weight during this time (P < 0.05). For all progeny, independent of sex, exposure to low-protein maternal diets during the second trimester of gestation resulted in greater FT3 relative to TT3 at birth. Because FT3 at birth and 29 days was positively associated with ADG (P < 0.05) and ADG relative to birth weight (P < 0.05), it is proposed that FT3 plays an integral role in catch-up growth in the bovine as per other species. Protein intake during the first and second trimesters of gestation has a sexually dimorphic effect on progeny plasma thyroid hormone concentrations, and these changes are associated with altered milk intake and postnatal growth pathway.

Thyroid Hormone Signaling in Muscle Development, Repair and Metabolism

Skeletal muscle is a plastic organ made by highly specialize fibers with specific and different structure, function and metabolism. Skeletal muscle fibers can adapt, change, recover/regenerate after injury in response to various stimulators including hormones. Thyroid hormones are important players in the homeostasis of several tissue including skeletal muscle and their genomic action mostly depend on the tissue T3 bioavailability and on the distribution of the thyroid receptor isoforms which act as transcription factors and are modulated by T3. Changing in contractile and metabolic proprieties of the muscle fibers has been described in experimental models of hyper and hypothyroidism. Animal models with disruption of thyroid hormone signaling showed different and specific skeletal muscle phenotypes. By focusing on thyroid hormone signaling in skeletal muscle homeostasis, we review T3 specific action on skeletal muscle development, postnatal growth, function and metabolism.

Different levels of thyroid hormones between impaired fasting glucose and impaired glucose tolerance: free T3 affects the prevalence of impaired fasting glucose and impaired glucose tolerance in opposite ways

CONTEXT

There is an association between thyroid disorders and diabetes mellitus.

OBJECTIVE

To investigate thyroid hormone levels in different glucose metabolic statuses, analyse relationships between thyroid hormone levels and different categories of prediabetes and metabolic parameters within a large euthyroid nondiabetic population.

METHODS

A total of 3328 subjects without diabetes or thyroid dysfunction were included in this cross-sectional study. Subjects were divided in to four groups [normal glucose tolerance (NGR), impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and combined glucose intolerance (CGI)] according to the results of oral glucose tolerance test. Participants were then divided into four groups according to the quartile of free T3 (FT3) in their blood.

RESULTS

Subjects with IFG had higher levels of FT3 and ratio of FT3 to FT4 (FT3/FT4), but lower level of free T4 (FT4) than subjects with IGT. FT3/FT4 was negatively associated with postprandial plasma glucose (PPG) [standardized β (β) = -0·087; P < 0·001]. The prevalence of IFG and CGI was increased with the level of FT3, while the prevalence of IGT was decreased with the level of FT3 (P for trend: <0·001, 0·003 and <0·001, respectively). FT3 was negatively associated with the risk of IGT (OR = 0·409, 95% CI 0·179-0·935), whereas FT4 was positively associated with the risk of IGT (OR = 1·296, 95% CI 1·004-1·673).

CONCLUSIONS

Free thyroid hormone levels were different between subjects with IFG and IGT. FT3 affects the prevalence of IFG and IGT in opposite ways. The difference in thyroid hormone levels may play an important role in the different pathological mechanisms of IFG and IGT.

Thyroid hormones and skeletal muscle--new insights and potential implications

Thyroid hormone signalling regulates crucial biological functions, including energy expenditure, thermogenesis, development and growth. The skeletal muscle is a major target of thyroid hormone signalling. The type 2 and 3 iodothyronine deiodinases (DIO2 and DIO3, respectively) have been identified in skeletal muscle. DIO2 expression is tightly regulated and catalyses outer-ring monodeiodination of the secreted prohormone tetraiodothyronine (T4) to generate the active hormone tri-iodothyronine (T3). T3 can remain in the myocyte to signal through nuclear receptors or exit the cell to mix with the extracellular pool. By contrast, DIO3 inactivates T3 through removal of an inner-ring iodine. Regulation of the expression and activity of deiodinases constitutes a cell-autonomous, pre-receptor mechanism for controlling the intracellular concentration of T3. This local control of T3 activity is crucial during the various phases of myogenesis. Here, we review the roles of T3 in skeletal muscle development and homeostasis, with a focus on the emerging local deiodinase-mediated control of T3 signalling. Moreover, we discuss these novel findings in the context of both muscle homeostasis and pathology, and examine how skeletal muscle deiodinase activity might be therapeutically harnessed to improve satellite-cell-mediated muscle repair in patients with skeletal muscle disorders, muscle atrophy or injury.

Distinct disease phenotypes linked to different combinations of GAA mutations in a large late-onset GSDII sibship

Background

Glycogenosis type II (GSDII or Pompe disease) is an autosomal recessive disease, often characterized by a progressive accumulation of glycogen within lysosomes caused by a deficiency of α-1,4-glucosidase (GAA; acid maltase), a key enzyme of the glycogen degradation pathway. To date, more than 326 different mutations in the GAA gene have been identified in patients with GSDII but the course of the disease is difficult to be predicted on the basis of molecular genetic changes. Studies on large informative families are advisable to better define how genetics and non genetics factors like exercise and diet may influence the clinical phenotype.

Methods and results

In this study, we report on clinical, instrumental, and pathological features as well as on molecular analysis of a family with 10 out of 13 siblings affected by late-onset Pompe disease. Three mutations segregated in the family, two of which are novel mutations. Siblings showing a more severe phenotype were compound heterozygous for c.118C > T [p.R40X] and c.2647-7G > A [p.N882fs] on GAA, whereas, two patients showing a mild phenotype were compound heterozygous c.2647-7G > A [p.N882fs] and c.2276G > C [p.G759A] mutations. Quantitative expression analysis showed, in the patients carrying p.R40X/ p.N882fs, a significant (p 0.01) correlation between the levels of expression of the mutated allele and the age at onset of the disease.

Conclusions

As far as we know, this is the largest informative family with late-onset Pompe disease described in the literature showing a peculiar complex set of mutations of GAA gene that may partially elucidate the clinical heterogeneity of this family.

High correlations in gene expression between paired umbilical cord blood and neonatal blood of healthy newborns on Guthrie cards

OBJECTIVE

To examine the correlation in genes expressed in paired umbilical cord blood (UCB) and newborn blood (NB).

METHOD

Total mRNA and mRNA of three gene sets (inflammatory, hypoxia, and thyroidal response) was assessed using microarray in UCB and NB spotted on Guthrie cards from 7 mother/infant pairs.

RESULTS

The average gene expression correlation between paired UCB and NB samples was 0.941 when all expressed genes were considered, and 0.949 for three selected gene sets.

CONCLUSION

The high correlation of UCB and NB gene expression suggest that either source may be useful for examining gene expression in the perinatal period.

Associations between thyroid hormones and serum metabolite profiles in an euthyroid population

The aim was to characterise associations between circulating thyroid hormones-free thyroxine (FT4) and thyrotropin (TSH)-and the metabolite profiles in serum samples from participants of the German population-based KORA F4 study. Analyses were based on the metabolite profile of 1463 euthyroid subjects. In serum samples, obtained after overnight fasting (≥8), 151 different metabolites were quantified in a targeted approach including amino acids, acylcarnitines (ACs), and phosphatidylcholines (PCs). Associations between metabolites and thyroid hormone concentrations were analysed using adjusted linear regression models. To draw conclusions on thyroid hormone related pathways, intra-class metabolite ratios were additionally explored. We discovered 154 significant associations (Bonferroni p < 1.75 × 10-04) between FT4 and various metabolites and metabolite ratios belonging to AC and PC groups. Significant associations with TSH were lacking. High FT4 levels were associated with increased concentrations of many ACs and various sums of ACs of different chain length, and the ratio of C2 by C0. The inverse associations observed between FT4 and many serum PCs reflected the general decrease in PC concentrations. Similar results were found in subgroup analyses, e.g., in weight-stable subjects or in obese subjects. Further, results were independent of different parameters for liver or kidney function, or inflammation, which supports the notion of an independent FT4 effect. In fasting euthyroid adults, higher serum FT4 levels are associated with increased serum AC concentrations and an increased ratio of C2 by C0 which is indicative of an overall enhanced fatty acyl mitochondrial transport and β-oxidation of fatty acids.

Gene expression in archived newborn blood spots distinguishes infants who will later develop cerebral palsy from matched controls

BACKGROUND

Gene expression in archived newborn blood spots remaining from newborn screening may reflect pathophysiological disturbances useful in understanding the etiology of cerebral palsy (CP).

METHODS

We quantified the expression of gene sets representing four physiological pathways hypothesized to contribute to CP in archived unfrozen residual newborn blood spot specimens from 53 children with CP and 53 age-, gender-, and gestational age-matched controls. We selected four empirical and three canonical gene sets representing the inflammatory, hypoxic, coagulative, and thyroidal pathways and examined mRNA expression using an 8 × 60,000 oligonucleotide microarray. The log2 fold change of gene expression between matched cases and controls was analyzed using the generally applicable gene set enrichment method.

RESULTS

The empirical inflammatory and empirical hypoxic gene sets were significantly downregulated in term-born CP cases (n = 33) as compared with matched controls (P = 0.0007 and 0.0009, respectively), whereas both gene sets were significantly upregulated (P =0.0055 and 0.0223, respectively) in preterm-born CP cases (n = 20). The empirical thyroidal gene set was significantly upregulated in preterm-born CP cases (P = 0.0023).

CONCLUSION

The newborn blood spot transcriptome can serve as a platform for investigating distinctive gene expression patterns in children who later develop CP.

Skeletal muscle mitochondrial energetics in obesity and type 2 diabetes mellitus: endocrine aspects

During the development of type 2 diabetes mellitus, skeletal muscle is a major site of insulin resistance. The latter has been linked to mitochondrial dysfunction and impaired fatty acid oxidation. Some hormones like insulin, thyroid hormones and adipokines (e.g., leptin, adiponectin) have positive effects on muscle mitochondrial bioenergetics through their direct or indirect effects on mitochondrial biogenesis, mitochondrial protein expression, mitochondrial enzyme activities and/or AMPK pathway activation--all of which can improve fatty acid oxidation. It is therefore not surprising that treatment with these hormones has been proposed to improve muscle and whole body insulin sensitivity. However, treatment of diabetic patients with leptin and adiponectin has no effect on muscle mitochondrial bioenergetics showing resistance to these hormones during type 2 diabetes. Furthermore, treatment with most thyroid hormones has unexpectedly revealed negative effects on muscle insulin sensitivity. Future research should focus on development of agents that improve metabolic dysfunction downstream of hormone receptors.