Purpose: In resistance to thyroid hormone due to mutations in thyroid hormone receptor beta, peripheral tissues are variably refractory to the action of circulating thyroid hormones. We evaluated parameters contributing to atherosclerotic risk in this disorder. Methods: We measured low-density lipoprotein cholesterol (LDL-C), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), nonesterified fatty acids (NEFA), intrahepatic lipid (IHL) and intramyocellular lipid (IMCL), Homeostasis-model assessment of insulin resistance (HOMA-IR), augmentation index (AIx) and pulse wave velocity (PWV), flow-mediated dilatation, and carotid intima-media thickness (cIMT) in an unselected, genetically confirmed cohort of adult RTH beta patients (n = 27-77) and compared these with measurements in healthy subjects (up to n = 100) and thyrotoxic patients (n = 40). Results: Resistance to thyroid hormone beta (RTH beta) patients exhibited higher LDL-C (P = 0.008) and TG (P = 0.002) and lower HDL-C concentrations (P = 0.015 x 10(-2)) than control subjects, with LDL-C being higher than in thyrotoxic patients with comparable hyperthyroxinemia. Proprotein convertase subtilisin/kexin 9 (P = 0.002) and apolipoprotein B (P = 0.0009) levels were reduced in thyrotoxic patients but not lower in RTH beta patients or control subjects. Intrahepatic lipid (P = 0.02 x 10(-4)), IMCL (P = 0.002), HOMA-IR (P = 0.01 x 10(-2)), and NEFA (P = 0.04 x 10(-6)) were significantly higher in RTH beta patients than control subjects. Flow-mediated dilatation was increased (P = 0.04) but cIMT (P = 0.71), PWV P = 0.81), and AIx (P = 0.95) were unaltered in RTH beta patients. Conclusions: We have documented mixed dyslipidemia with hepatic and IMCL accumulation in RTH beta, suggesting that surveillance for these metabolic abnormalities is warranted. How they combine with enhanced endothelial function and unaltered vessel wall thickness and compliance to determine overall cardiometabolic risk in this disorder remains to be defined.

Dopamine (DA) transmission plays a critical role in processing rewarding and pleasurable stimuli. Increased synaptic DA release in the nucleus accumbens (NAc) is a central component of the physiological effects of drugs of abuse. The essential trace element selenium mitigates methamphetamine-induced neurotoxicity. Selenium can also alter DA production and turnover. However, studies have not directly addressed the role of selenium in DA neurotransmission. Selenoprotein P (SELENOP1) requires selenium for synthesis and transports selenium to the brain, in addition to performing other functions. We investigated whether SELENOP1 directly impacts (1) DA signaling and (2) the dopaminergic response to methamphetamine. We used fast-scan cyclic voltammetry to investigate DA transmission and the response to methamphetamine in NAc slices from C57/BL6J SELENOP1 KO mice. Recordings from SELENOP1 KO mouse slices revealed reduced levels of evoked DA release and slower DA uptake rates. Methamphetamine caused a dramatic increase in vesicular DA release in SELENOP1 KO mice not observed in wild-type controls. This elevated response was attenuated by SELENOP1 application through a selenium-independent mechanism involving SELENOP1-apolipoprotein E receptor 2 (ApoER2) interaction to promote dopamine D2 receptor (D2R) function. In wild-type mice, increased vesicular DA release in response to methamphetamine was revealed by blocking D2R activation, indicating that the receptor suppresses the methamphetamine-induced vesicular increase. Our data provide evidence of a direct physiological role for SELENOP1 in the dopaminergic response to methamphetamine and suggest a signaling role for the protein in DA transmission.

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Mitochondrial dysfunction is associated with insulin resistance and type 2 diabetes. It has thus been suggested that primary and/or genetic abnormalities in mitochondrial function may lead to accumulation of toxic lipid species in muscle and elsewhere, impairing insulin action on glucose metabolism. Alternatively, however, defects in insulin signaling may be primary events that result in mitochondrial dysfunction, or there may be a bidirectional relationship between these phenomena. To investigate this, we examined mitochondrial function in patients with genetic defects in insulin receptor (INSR) signaling. We found that phosphocreatine recovery after exercise, a measure of skeletal muscle mitochondrial function in vivo, was significantly slowed in patients with INSR mutations compared with that in healthy age-, fitness-, and BMI-matched controls. These findings suggest that defective insulin,signaling may promote mitochondrial dysfunction. Furthermore, consistent with previous studies of mouse models of mitochondrial dysfunction, basal and sleeping metabolic rates were both significantly increased in genetically insulin-resistant patients, perhaps because mitochondrial dysfunction necessitates increased nutrient oxidation in order to maintain cellular energy levels.

Resistance to thyroid hormone (RTH), a dominantly inherited disorder usually associated with mutations in thyroid hormone receptor beta (THRB), is characterized by elevated levels of circulating thyroid hormones (including thyroxine), failure of feedback suppression of thyrotropin, and variable tissue refractoriness to thyroid hormone action. Raised energy expenditure and hyperphagia are recognized features of hyperthyroidism, but the effects of comparable hyperthyroxinemia in RTH patients are unknown. Here, we show that resting energy expenditure (REE) was substantially increased in adults and children with THRB mutations. Energy intake in RTH subjects was increased by 40%, with marked hyperphagia particularly evident in children. Rates of muscle TCA cycle flux were increased by 75% in adults with RTH, whereas rates of ATP synthesis were unchanged, as determined by 13C/31P magnetic resonance spectroscopy. Mitochondrial coupling index between ATP synthesis and mitochondrial rates of oxidation (as estimated by the ratio of ATP synthesis to TCA cycle flux) was significantly decreased in RTH patients. These data demonstrate that basal mitochondrial substrate oxidation is increased and energy production in the form of ATP synthesis is decreased in the muscle of RTH patients and that resting oxidative phosphorylation is uncoupled in this disorder. Furthermore, these observations suggest that mitochondrial uncoupling in skeletal muscle is a major contributor to increased REE in patients with RTH, due to tissue selective retention of thyroid hormone receptor alpha sensitivity to elevated thyroid hormone levels.

Selenium, a trace element that is fundamental to human health, is incorporated into some proteins as selenocysteine (Sec), generating a family of selenoproteins. Sec incorporation is mediated by a multiprotein complex that includes Sec insertion sequence-binding protein 2 (SECISBP2; also known as SBP2). Here, we describe subjects with compound heterozygous defects in the SECISBP2 gene. These individuals have reduced synthesis of most of the 25 known human selenoproteins, resulting in a complex phenotype. Azoospermia, with failure of the latter stages of spermatogenesis, was associated with a lack of testis-enriched selenoproteins. An axial muscular dystrophy was also present, with features similar to myopathies caused by mutations in selenoprotein N (SEPN1). Cutaneous deficiencies of antioxidant selenoenzymes, increased cellular ROS, and susceptibility to ultraviolet radiation-induced oxidative damage may mediate the observed photosensitivity. Reduced levels of selenoproteins in peripheral blood cells were associated with impaired T lymphocyte proliferation, abnormal mononuclear cell cytokine secretion, and telomere shortening. Paradoxically, raised ROS in affected subjects was associated with enhanced systemic and cellular insulin sensitivity, similar to findings in mice lacking the antioxidant selenoenzyme glutathione peroxidase 1 (GPx1). Thus, mutation of SECISBP2 is associated with a multisystem disorder with defective biosynthesis of many selenoproteins, highlighting their role in diverse biological processes.

CONTEXTHomozygous loss-of-function mutations in forkhead box E1/thyroid transcription factor 2 (FOXE1/TTF-2) cause syndromic congenital hypothyroidism, with thyroid dysgenesis, cleft palate, spiky hair, and variable choanal atresia and bifid epiglottis in three cases reported hitherto. We have elucidated the molecular basis of the disorder in a female with a similar clinical phenotype, born to nonconsanguineous parents.OBJECTIVE AND DESIGNThe FOXE1 gene, located on chromosome 9q22, was sequenced in the proband and family members. Microsatellite marker and multiplex ligation probe amplification analyses determined chromosomal inheritance patterns and FOXE1 copy number. Mutant FOXE1 function was predicted by structural modeling and tested in transfection assays.RESULTSThe proband was homozygous for a novel missense (c.412T-->C; F137S) FOXE1 mutation, but her mother showed heterozygous and father wild-type alleles for this gene sequence. However, the proband was also homozygous for 10 microsatellite markers spanning chromosome 9 with exclusively maternal inheritance. Multiplex ligation probe amplification assays showed two copies of FOXE1 in the proband, indicating maternal isodisomy for chromosome 9. Consistent with structural modeling, the F137S mutant FOXE1 protein failed to bind DNA and showed negligible transcriptional activity.CONCLUSIONWe have described the first case of uniparental disomy causing homozygosity for a novel, loss-of-function FOXE1/TTF-2 mutation in dysgenetic congenital hypothyroidism.

Diabetes is one of the most serious health issues facing developed countries today. In the UK it accounts for around 5% of all National Health Service (NHS) spending (similar to 10 pound million/day) and is a leading cause of heart disease, stroke, blindness, amputation and kidney failure. The majority (similar to 90%) of these cases are type 2 in origin, reflecting a trend towards obesity and more sedentary lifestyles as the 'norm' rather than exception in western society. The development of insulin resistance is a critical step in the evolution of this disorder and, accordingly, improving insulin sensitivity, and thereby ameliorating excess vascular risk, is a primary goal for those concerned with its treatment. Recent interest has focussed on a novel class of antidiabetic agent, the thiazolidinediones which act as insulin sensitizers, thus targeting the underlying metabolic disturbance. These compounds are high affinity ligands for the nuclear receptor peroxisome proliferator-activated receptor gamma (PPAR gamma), and a significant body of in vitro and in vivo data exists to support their increasing therapeutic use. Importantly, clinical and laboratory observations made in human subjects harbouring genetic variations in PPAR gamma have confirmed its pivotal role in the regulation of adipogenesis and glucose homeostasis, with evidence also emerging to indicate important contributions to lipid metabolism and control of blood pressure. It is not surprising then that this receptor has emerged as a key therapeutic target in the context of the metabolic syndrome. Indeed the 'race is on' to identify the next generation of PPAR gamma modulators, agents that will promote maximal therapeutic benefit by targeting specific facets of the metabolic syndrome (glucose intolerance/diabetes, dyslipidaemia and hypertension), while simultaneously avoiding undesirable side effects of PPAR gamma activation (e.g. weight gain and fluid retention).

Diabetes is one of the most serious health issues facing developed countries today. In the UK it accounts for around 5% of all National Health Service (NHS) spending (∼£10 million/day) and is a leading cause of heart disease, stroke, blindness, amputation and kidney failure. The majority (∼90%) of these cases are type 2 in origin, reflecting a trend towards obesity and more sedentary lifestyles as the ‘norm’ rather than exception in western society. The development of insulin resistance is a critical step in the evolution of this disorder and, accordingly, improving insulin sensitivity, and thereby ameliorating excess vascular risk, is a primary goal for those concerned with its treatment. Recent interest has focussed on a novel class of antidiabetic agent, the thiazolidinediones which act as insulin sensitizers, thus targeting the underlying metabolic disturbance. These compounds are high affinity ligands for the nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ), and a significant body of in vitro and in vivo data exists to support their increasing therapeutic use. Importantly, clinical and laboratory observations made in human subjects harbouring genetic variations in PPARγ have confirmed its pivotal role in the regulation of adipogenesis and glucose homeostasis, with evidence also emerging to indicate important contributions to lipid metabolism and control of blood pressure. It is not surprising then that this receptor has emerged as a key therapeutic target in the context of the metabolic syndrome. Indeed the ‘race is on’ to identify the next generation of PPARγ modulators, agents that will promote maximal therapeutic benefit by targeting specific facets of the metabolic syndrome (glucose intolerance/diabetes, dyslipidaemia and hypertension), while simultaneously avoiding undesirable side effects of PPARγ activation (e.g. weight gain and fluid retention).

Context: Adiponectin has been suggested to play a role in the etiopathogenesis of at least some forms of insulin resistance, in part based on a strong correlation between plasma levels of adiponectin and measures of insulin sensitivity.Objective: The objective of the study was to establish whether this relationship is maintained at extreme levels of insulin resistance.Design/Setting: This was a cross-sectional study in a university teaching hospital of subjects recruited from the United Kingdom and the United States.Participants: Participants included 75 subjects with a range of syndromes of severe insulin resistance and 872 nondiabetic controls.Outcome Measures: Fasting plasma insulin, adiponectin, and leptin were measured.Results: Unexpectedly, subjects with mutations in the insulin receptor, despite having the most severe degree of insulin resistance, had elevated plasma adiponectin [median 24.4 mg/liter; range 6.6-36.6 (normal adult range for body mass index 20 kg/m(2) = 3-19 mg/liter)], whereas all other subjects had low adiponectin levels (median 2.0 mg/liter; range 0.12-11.2). Plasma leptin in all but one subject with an insulin receptoropathy was low or undetectable [median 0.5 ng/ml; range 0-16: normal adult range for body mass index of < 25 kg/m(2) = 2.4-24.4 (female) and 0.4-8.3 ng/ml (male)].Conclusions: We conclude that the relationship between plasma adiponectin and insulin sensitivity is complex and dependent on the precise etiology of defective insulin action and that the combination of high plasma adiponectin with low leptin may have clinical utility in patients with severe insulin resistance as a marker of the presence of a genetic defect in the insulin receptor.

PPAR gamma is essential for adipogenesis and metabolic homeostasis. We describe mutations in the DNA and ligand binding domains of human PPAR gamma in lipodystrophic, severe insulin resistance. These receptor mutants lack DNA binding and transcriptional activity but can translocate to the nucleus, interact with PPAR gamma coactivators and inhibit coexpressed wild-type receptor. Expression of PPAR gamma target genes is markedly attenuated in mutation-containing versus receptor haploinsufficent primary cells, indicating that such dominant-negative inhibition operates in vivo. Our observations suggest that these mutants restrict wild-type PPAR gamma action via a non-DNA binding, transcriptional interference mechanism, which may involve sequestration of functionally limiting coactivators.