RESUMO
Cathepsin K deficiency in male mice (Ctsk-/-) results in decreased numbers of hippocampal astrocytes and altered neuronal patterning as well as learning and memory deficits. Additionally, cathepsin K carries essential roles in the thyroid gland where it contributes to the liberation of thyroid hormones (TH). Because TH are essential for brain development, in particular for the cerebellum, we investigated whether cathepsin K's function in the thyroid is directly linked to the brain phenotype of Ctsk-/- mice. Serum levels of thyroid stimulating hormone, brain concentrations of free TH, and deiodinase 2 (Dio2) activity in brain parenchyma as well as cerebellar development were comparable in Ctsk-/- and WT animals, suggesting regular thyroid states and TH metabolism. Despite unaltered transcript levels, protein expression of two TH transporters was enhanced in specific brain regions in Ctsk-/- mice, suggesting altered TH supply to these regions. Thyrotropin releasing hormone (Trh) mRNA levels were enhanced threefold in the hippocampus of Ctsk-/- mice. In the striatum of Ctsk-/- mice the mRNA for Dio2 and hairless were approximately 1.3-fold enhanced, while mRNA levels for monocarboxylate transporter 8 and Trh were reduced to 60% and 40%, respectively, pointing to altered striatal physiology. We conclude that the role of cathepsin K in the thyroid gland is not directly associated with its function in the central nervous system (CNS) of mice. Future studies will show whether the brain region-specific alterations in Trh mRNA may eventually result in altered neuroprotection that could explain the neurobehavioral defects of Ctsk-/- mice.
Assuntos
Catepsina K/fisiologia , Sistema Nervoso Central/enzimologia , Glândula Tireoide/enzimologia , Animais , Catepsina K/genética , Cerebelo/enzimologia , Cerebelo/crescimento & desenvolvimento , Masculino , Camundongos , Camundongos Knockout , RNA Mensageiro/análise , Tireotropina/sangue , Tiroxina/sangue , Tri-Iodotironina/sangueRESUMO
Thyroid hormone (TH) and TH receptors (TRs) α and ß act by binding to TH response elements (TREs) in regulatory regions of target genes. This nuclear signaling is established as the canonical or type 1 pathway for TH action. Nevertheless, TRs also rapidly activate intracellular second-messenger signaling pathways independently of gene expression (noncanonical or type 3 TR signaling). To test the physiological relevance of noncanonical TR signaling, we generated knockin mice with a mutation in the TR DNA-binding domain that abrogates binding to DNA and leads to complete loss of canonical TH action. We show that several important physiological TH effects are preserved despite the disruption of DNA binding of TRα and TRß, most notably heart rate, body temperature, blood glucose, and triglyceride concentration, all of which were regulated by noncanonical TR signaling. Additionally, we confirm that TRE-binding-defective TRß leads to disruption of the hypothalamic-pituitary-thyroid axis with resistance to TH, while mutation of TRα causes a severe delay in skeletal development, thus demonstrating tissue- and TR isoform-specific canonical signaling. These findings provide in vivo evidence that noncanonical TR signaling exerts physiologically important cardiometabolic effects that are distinct from canonical actions. These data challenge the current paradigm that in vivo physiological TH action is mediated exclusively via regulation of gene transcription at the nuclear level.
Assuntos
Sistema Hipotálamo-Hipofisário/metabolismo , Miocárdio/metabolismo , Sistema Hipófise-Suprarrenal/metabolismo , Receptores dos Hormônios Tireóideos/metabolismo , Transdução de Sinais , Hormônios Tireóideos/metabolismo , Animais , Técnicas de Introdução de Genes , Camundongos , Camundongos Knockout , Receptores dos Hormônios Tireóideos/genética , Hormônios Tireóideos/genéticaRESUMO
Clinical manifestation of hyperthyroidism and hypothyroidism vary with age, with an attenuated, oligosymptomatic presentation of thyroid dysfunction (TD) in older patients. We asked, whether in rodents TD phenotypes are influenced by age and whether this involves changes in systemic and/or organ thyroid hormone (TH) signaling. Chronic hyper- or hypothyroidism was induced in male mice at different life stages (5, 12, and 20 months). TH excess resulted in pronounced age-specific body weight changes (increase in youngest and decrease in old mice), neither explained by changes in food intake (similar increase at all ages), nor by thermogenic gene expression in brown adipose tissue (BAT) or TH serum concentrations. Relative increase in body temperature and activity were more pronounced in old compared to young hyperthyroid mice. An attenuated hypothyroid state was found in old mice for locomotor activity and in heart and BAT on functional (less bradycardia) and gene expression level (heart and BAT). In contrast, decrease in body weight was pronounced in old hypothyroid mice. Thus, age has divergent impact on features of TD in mice, whereby effects on highly complex systems, such as energy homeostasis are not proportional to serum TH state, in contrast to organ-specific responses in heart and BAT.
Assuntos
Envelhecimento/fisiologia , Hipertireoidismo/fisiopatologia , Hipotireoidismo/fisiopatologia , Hormônios Tireóideos/sangue , Tecido Adiposo/metabolismo , Animais , Temperatura Corporal/fisiologia , Expressão Gênica , Coração/fisiopatologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Atividade Motora/fisiologia , FenótipoRESUMO
Background: Serum thyroid state in older adults correlates with extended longevity. We hypothesized that age impacts not only systemic but also organ-specific thyroid state and response to thyroxine (T4). Methods: Young (3 months) and old (23 months) male mice were analyzed at baseline and after acute T4 challenge. Age effects on circulating thyrotropin (TSH) and thyroid hormone (TH) concentrations, transcript expression in the pituitary and thyroid were compared with organ-specific responses characterized by hepatic and cardiac content of TH and TH metabolites and expression of TH-target genes, as well as hepatic deiodinase 1 activity. Results: Circulating TH concentrations and hepatic and cardiac TH content were lower in old versus young mice. After injection with T4, conversion of T4 to triiodothyronine was decreased in old mice while TH transport in liver and heart was not affected. Organ-specific TH response was augmented in old mice in liver but not heart, indicating age- and tissue-specific sensitivity to TH. A compensatory increase of thyroid stimulating hormone subunit beta expression in the pituitary and increased serum TSH concentrations, but reduced expression of thyroid differentiation markers were found in old mice. Conclusions: We suggest that a reduced activity of the aged thyroid is responsible for the systemic low TH state in old mice. Further, divergent TH metabolism and tissue response in liver and heart occur after T4 treatment in an aged organism. These rodent data are in agreement with a much narrower window for T4 substitution in the older adults to avoid overtreatment.
Assuntos
Envelhecimento/metabolismo , Envelhecimento/patologia , Glândula Tireoide/crescimento & desenvolvimento , Glândula Tireoide/metabolismo , Tiroxina/metabolismo , Tiroxina/farmacologia , Animais , Proteínas de Ligação a DNA/biossíntese , Proteínas de Ligação a DNA/genética , Sistema Hipotálamo-Hipofisário , Fígado/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Miocárdio/metabolismo , Hipófise/crescimento & desenvolvimento , Hipófise/metabolismo , Glândula Tireoide/patologia , Hormônios Tireóideos/sangue , Tireotropina/sangue , Fatores de Transcrição/biossíntese , Fatores de Transcrição/genéticaRESUMO
BACKGROUND: Sex and age play a role in the prevalence of thyroid dysfunction (TD), but their interrelationship for manifestation of hyper- and hypothyroidism is still not well understood. Using a murine model, we asked whether sex impacts the phenotypes of hyper- and hypothyroidism at two life stages. METHODS: Hyper- and hypothyroidism were induced by i.p. T4 or MMI/ClO4-/LoI treatment over 7 weeks in 12- and 20-months-old female and male C57BL/6N mice. Control animals underwent PBS treatment (n = 7-11 animals/sex/treatment). Animals were investigated for impact of sex on body weight, food and water intake, body temperature, heart rate, behaviour (locomotor activity, motor coordination and strength) and serum thyroid hormone (TH) status. RESULTS: Distinct sex impact was found in eu- and hyperthyroid mice, while phenotypic traits of hypothyroidism were similar in male and female mice. No sex difference was found in TH status of euthyroid mice; however, T4 treatment resulted in twofold higher TT4, FT4 and FT3 serum concentrations in adult and old females compared to male animals. Hyperthyroid females consistently showed higher locomotor activity and better coordination but more impairment of muscle function by TH excess at adult age. Importantly and in contrast to male mice, adult and old hyperthyroid female mice showed increased body weight. Higher body temperature in female mice was confirmed in all age groups. No sex impact was found on heart rate irrespective of TH status in adult and old mice. CONCLUSIONS: By comparison of male and female mice with TD at two life stages, we found that sex modulates TH action in an organ- and function-specific manner. Sex differences were more pronounced under hyperthyroid conditions. Importantly, sex-specific differences in features of TD in adult and old mice were not conclusively explained by serum TH status in mice.
Assuntos
Hipertireoidismo/fisiopatologia , Hipotireoidismo/fisiopatologia , Caracteres Sexuais , Envelhecimento/fisiologia , Animais , Temperatura Corporal/fisiologia , Peso Corporal/fisiologia , Ingestão de Líquidos/fisiologia , Ingestão de Alimentos/fisiologia , Feminino , Frequência Cardíaca/fisiologia , Masculino , Camundongos Endogâmicos C57BL , Atividade Motora/fisiologia , Hormônios Tireóideos/sangueRESUMO
BACKGROUND: Thyroid dysfunction is more common in the female population, however, the impact of sex on disease characteristics has rarely been addressed. Using a murine model, we asked whether sex has an influence on phenotypes, thyroid hormone status, and thyroid hormone tissue response in hyper- and hypothyroidism. METHODS: Hypo- and hyperthyroidism were induced in 5-month-old female and male wildtype C57BL/6N mice, by LoI/MMI/ClO4 (-) or T4 i.p. treatment over 7 weeks, and control animals underwent sham treatment (N = 8 animals/sex/treatment). Animals were investigated for impact of sex on body weight, food and water intake, body temperature, heart rate, behaviour (locomotor activity, motor coordination, and strength), liver function, serum thyroid hormone status, and cellular TH effects on gene expression in brown adipose tissue, heart, and liver. RESULTS: Male and female mice showed significant differences in behavioural, functional, metabolic, biochemical, and molecular traits of hyper- and hypothyroidism. Hyperthyroidism resulted in increased locomotor activity in female mice but decreased muscle strength and motor coordination preferably in male animals. Hypothyroidism led to increased water intake in male but not female mice and significantly higher serum cholesterol in male mice. Natural sex differences in body temperature, body weight gain, food and water intake were preserved under hyperthyroid conditions. In contrast, natural sex differences in heart rate disappeared with TH excess and deprivation. The variations of hyper- or hypothyroid traits of male and female mice were not explained by classical T3/T4 serum state. TH serum concentrations were significantly increased in female mice under hyperthyroidism, but no sex differences were found under eu- or hypothyroid conditions. Interestingly, analysis of expression of TH target genes and TH transporters revealed little sex dependency in heart, while sex differences in target genes were present in liver and brown adipose tissue in line with altered functional and metabolic traits of hyper- and hypothyroidism. CONCLUSIONS: These data demonstrate that the phenotypes of hypo- and hyperthyroidism differ between male and female mice and indicate that sex is an important modifier of phenotypic manifestations.
RESUMO
Protocols for induction of hyperthyroidism in mice are highly variable and mostly involve short-term thyroid hormone (TH) treatment. In addition, little is known about a possible influence of sex on experimental TH manipulation. Here we analyzed the efficacy of intraperitoneal vs. oral levothyroxine (T4) administration to induce chronic hyperthyroidism in male and female mice and asked which T4 dosing intervals are required to achieve stable organ thyrotoxicosis. T4 was administered intraperitoneally or orally over a period of 6/7 weeks. Assessment included monitoring of body weight, TH serum concentrations, and serial quantitative TH target gene expression analysis in liver and heart. Our results show that both intraperitoneal and oral T4 treatment are reliable methods for induction of chronic hyperthyroidism in mice. Thereby T4 injection intervals should not exceed 48 h and oral levothyroxine should be administered continuously during experiments and up to sacrifice to ensure a hyperthyroid organ state. Furthermore, we found a sex-dependent variation in levothyroxine-induced TH serum state, with significantly higher T4 concentrations in female mice, while expression of investigated classical TH responsive genes in liver and heart did not vary with animal's sex. In summary, our study shows that common approaches for rendering rodents thyrotoxic can also be used for induction of chronic hyperthyroidism in male and female mice. Thereby T4 dosing intervals are critical as are read-out parameters to verify a chronic thyrotoxic organ state.
Assuntos
Modelos Animais de Doenças , Hipertireoidismo/induzido quimicamente , Tiroxina , Animais , Feminino , Hipertireoidismo/sangue , Masculino , Camundongos , Fatores SexuaisRESUMO
BACKGROUND: In the liver the tight junction protein claudin-1 plays an important role in bile secretion by maintaining the paracellular barrier of bile canaliculi and the bile duct. A diminished bile excretion has been found in hypothyroid patients, and the prevalence of gallstones is increased in hypothyroidism. This association, however, only applies for men and is in contrast to the well-established female preponderance of biliary disease in the general population. OBJECTIVES: We hypothesized that hypothyroidism could lead to altered claudin-1 expression in the liver, and that this effect may be sex specific. METHODS: We characterized claudin-1 expression and localization in livers of euthyroid and hypothyroid male and female C57BL/6NTac mice by real-time PCR, Western blot and immunofluorescence. RESULTS: Claudin-1 is expressed in canalicular regions and the bile ducts of the murine liver. Livers of female mice showed lower claudin-1 expression than male livers. In hypothyroid livers, female animals showed an elevated claudin-1 expression, whereas reduced claudin-1 expression was found in male animals compared to the euthyroid controls. CONCLUSION: We demonstrate a correlation between claudin-1 expression and hypothyroidism in the murine liver. Furthermore, a sex-dependent alteration of claudin-1 expression was found.
RESUMO
BACKGROUND: Clinical features of thyroid dysfunction vary with age, and an oligosymptomatic presentation of hyperthyroidism is frequently observed in the elderly. This suggests age modulation of thyroid hormone (TH) action, which may occur, for example, by alterations in TH production, metabolism and/or TH action in target organs. OBJECTIVES: In this paper, we address possible changes in TH transporter expression in liver tissues as a mechanism of age-dependent variation in TH action. METHODS: Chronic hyperthyroidism was induced in 4- and 20-month-old C57BL6/NTac male mice (n = 8-10) by intraperitoneal injections of 1 µg/g body weight L-thyroxine (T4) every 48 h over 7 weeks. Control animals were injected with PBS. Total RNA was isolated from liver samples for analysis of the TH transporter and TH-responsive gene expression. TH concentrations were determined in mice sera. RESULTS: Baseline serum free T4 (fT4) concentrations were significantly higher in euthyroid young compared to old mice. T4 treatment increased total T4, fT4 and free triiodothyronine to comparable concentrations in young and old mice. In the euthyroid state, TH transporter expression was significantly higher in old than in young mice, except for Mct8 and Oatp1a1 expression levels. Hyperthyroidism resulted in upregulation of Mct10, Lat1 and Lat2 in liver tissue, while Oatp1a1, Oatp1b2 and Oatp1a4 expression was downregulated. This effect was preserved in old animals. CONCLUSION: Here, we show age-dependent differences in TH transporter mRNA expression in the euthyroid and hyperthyroid state of mice focusing on the liver as a classical TH target organ.