RESUMO
C3H/HeJ (C3H) mice are deficient of type I deiodinase (D1), an enzyme that activates thyroid hormone (TH), converting thyroxine (T4) to triiodothyronine (T3). Nevertheless, C3H mice present normal serum T3 and a gross euthyroid phenotype. To investigate if a global D1 deficiency interferes in the TH effects on bone, we compared bone growth, bone mass accrual and bone strength of C3H and C57BL/6J (B6) mice under abnormal TH status. Four-week-old female mice of both strains were grouped as Euthyroid, Hypothyroid (pharmacologically-induced), 1xT4 and 10xT4 (hypothyroid animals receiving 1- or 10-fold the physiological dose of T4 /day/16 weeks). Hypothyroidism and TH excess similarly impaired body weight (BW) gain and body growth in both mice strains. In contrast, whereas hypothyroidism only slightly impaired bone mineral density (BMD) accrual in B6 mice, it severely impaired BMD accrual in C3H mice. No differences were observed in serum and bone concentrations of T3 between hypothyroid animals of both strains. Interestingly, treatment with 10xT4 was less deleterious to BMD accrual in C3H than in B6 mice and resulted in less elevated T3 serum levels in B6 than in C3H mice, which is probably explained by the lower D1 activity in C3H mice. In addition, hypothyroidism decreased bone strength only in C3H but not in B6 mice, while TH excess decreased this parameter in both strains. These findings indicate that D1 deficiency contributes to the TH excess-induced differences in bone mass accrual in C3H vs. B6 mice and suggest that deiodinase-unrelated genetic factors might account for the different skeleton responses to hypothyroidism between strains.
RESUMO
Em 2007 a cidade de Cajazeiras-PB recebeu a implantação do curso de Medicina pela Universidade Federal de Campina Grande. Neste processo, os docentes se depararam com várias dificuldades. Para propor melhoras e até, suplementação da carga de conceitos em Anatomia Humana, foi criada uma atividade didática chamada Desafio Anatômico, no qual os discentes eram instruídos a confeccionar modelos anatômicos que fossem didáticos a ponto de serem usados nas aulas, auxiliando o conteúdoda disciplina. Após a apresentação dos trabalhos, os discentes mostraram-se satisfeitos com os resultados, sobretudo sob o ponto de vista de transmissão de conhecimento e absorção de conteúdo. Desta maneira, esta experiência mostrou-se positiva e singular para o processo de ensino-aprendizagem da anatomia no curso médico, pois a mesma estimulou de diversas formas a criatividade, memória etrabalho em grupo dos participantes.
In 2007 the city of Cajazeiras-PB received the implantation of the School of Medicine from Federal University of Campina Grande. In this process professors were faced with several difficulties. To propose improvements and even supplementation in Anatomy concepts, they created a didactic activity calledAnatomical Challenge in which the students were instructed to fabricate didactical anatomical models to be used in classrooms, helping the content of the discipline. After work, the students were satisfied with the results, especially from the point of view of knowledge transmission and absorption of content.Thus, this experience was positive and unique to the process of teaching and learning of anatomy inmedical school, because it stimulated creativity in many ways, memory and group working by the participants.
Assuntos
Anatomia , Educação Médica , Modelos AnatômicosRESUMO
Evidence demonstrates that sympathetic nervous system (SNS) activation causes osteopenia via ß(2)-adrenoceptor (ß2-AR) signaling. Here we show that female mice with chronic sympathetic hyperactivity owing to double knockout of adrenoceptors that negatively regulate norepinephrine release, α(2A)-AR and α(2C)-AR (α(2A) /α(2C)-ARKO), present an unexpected and generalized phenotype of high bone mass with decreased bone resorption and increased formation. In α(2A) /α(2C)-ARKO versus wild-type (WT) mice, micro-computed tomographic (µCT) analysis showed increased, better connected, and more plate-shaped trabeculae in the femur and vertebra and increased cortical thickness in the vertebra, whereas biomechanical analysis showed increased tibial and femoral strength. Tibial mRNA expression of tartrate-resistant acid phosphatase (TRACP) and receptor activator of NF-κB (RANK), which are osteoclast-related factors, was lower in knockout (KO) mice. Plasma leptin and brain mRNA levels of cocaine amphetamine-regulated transcript (CART), which are factors that centrally affect bone turnover, and serum levels of estradiol were similar between mice strains. Tibial ß(2)-AR mRNA expression also was similar in KO and WT littermates, whereas α(2A)-, α(2B)- and α(2C)-AR mRNAs were detected in the tibia of WT mice and in osteoblast-like MC3T3-E1 cells. By immunohistochemistry, we detected α(2A)-, α(2B)-, α(2C)- and ß(2)-ARs in osteoblasts, osteoclasts, and chondrocytes of 18.5-day-old mouse fetuses and 35-day-old mice. Finally, we showed that isolated osteoclasts in culture are responsive to the selective α(2)-AR agonist clonidine and to the nonspecific α-AR antagonist phentolamine. These findings suggest that ß(2)-AR is not the single adrenoceptor involved in bone turnover regulation and show that α(2)-AR signaling also may mediate the SNS actions in the skeleton.
Assuntos
Osso e Ossos/patologia , Deleção de Genes , Hipercinese/patologia , Receptores Adrenérgicos alfa 2/metabolismo , Sistema Nervoso Simpático/patologia , Agonistas de Receptores Adrenérgicos alfa 2/farmacologia , Animais , Reabsorção Óssea/sangue , Reabsorção Óssea/complicações , Reabsorção Óssea/genética , Osso e Ossos/efeitos dos fármacos , Osso e Ossos/metabolismo , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Estradiol/sangue , Feminino , Regulação da Expressão Gênica/efeitos dos fármacos , Hipercinese/sangue , Hipercinese/complicações , Leptina/sangue , Camundongos , Camundongos Knockout , Miocárdio/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Norepinefrina/sangue , Tamanho do Órgão/efeitos dos fármacos , Osteoclastos/efeitos dos fármacos , Osteoclastos/patologia , Osteogênese/efeitos dos fármacos , Fenótipo , Sistema Nervoso Simpático/efeitos dos fármacosRESUMO
Previous studies showed anabolic effects of GC-1, a triiodothyronine (T3) analogue that is selective for both binding and activation functions of thyroid hormone receptor (TR) beta1 over TRalpha1, on bone tissue in vivo. The aim of this study was to investigate the responsiveness of rat (ROS17/2.8) and mouse (MC3T3-E1) osteoblast-like cells to GC-1. As expected, T3 inhibited cellular proliferation and stimulated mRNA expression of osteocalcin or alkaline phosphatase in both cell lineages. Whereas equimolar doses of T3 and GC-1 equally affected these parameters in ROS17/2.8 cells, the effects of GC-1 were more modest compared to those of T3 in MC3T3-E1 cells. Interestingly, we showed that there is higher expression of TRalpha1 than TRbeta1 mRNA in rat (approximately 20-90%) and mouse (approximately 90-98%) cell lineages and that this difference is even higher in mouse cells, which highlights the importance of TRalpha1 to bone physiology and may partially explain the modest effects of GC-1 in comparison with T3 in MC3T3-E1 cells. Nevertheless, we showed that TRbeta1 mRNA expression increases (approximately 2.8- to 4.3-fold) as osteoblastic cells undergo maturation, suggesting a key role of TRbeta1 in mediating T3 effects in the bone forming cells, especially in mature osteoblasts. It is noteworthy that T3 and GC-1 induced TRbeta1 mRNA expression to a similar extent in both cell lineages (approximately 2- to 4-fold), indicating that both ligands may modulate the responsiveness of osteoblasts to T3. Taken together, these data show that TRbeta selective T3 analogues have the potential to directly induce the differentiation and activity of osteoblasts.
Assuntos
Acetatos/farmacologia , Diferenciação Celular , Proliferação de Células/efeitos dos fármacos , Osteoblastos/efeitos dos fármacos , Fenóis/farmacologia , Receptores beta dos Hormônios Tireóideos/agonistas , Fosfatase Alcalina/genética , Fosfatase Alcalina/metabolismo , Animais , Linhagem Celular , Expressão Gênica , Camundongos , Osteoblastos/citologia , Osteoblastos/fisiologia , Osteocalcina/genética , Osteocalcina/metabolismo , Reação em Cadeia da Polimerase , RNA Mensageiro/antagonistas & inibidores , RNA Mensageiro/genética , Ratos , Receptores beta dos Hormônios Tireóideos/genética , Tri-Iodotironina/farmacologiaRESUMO
BACKGROUND: Several plasma membrane transporters have been shown to mediate the cellular influx and/or efflux of iodothyronines, including the sodium-independent organic anion co-transporting polypeptide 1 (OATP1), the sodium taurocholate co-transporting polypeptide (NTCP), the L-type amino acid transporter 1 (LAT1) and 2 (LAT2), and the monocarboxylate transporter 8 (MCT8). The aim of this study was to investigate if the mRNAs of these transporters were expressed and regulated by thyroid hormone (TH) in mouse calvaria-derived osteoblastic MC3T3-E1 cells and in the fetal and postnatal bones of mice. METHODS: The mRNA expression of the iodothyronine transporters was investigated with real-time polymerase chain reaction analysis in euthyroid and hypothyroid fetuses and litters of mice and in MC3T3-E1 cells treated with increasing doses of triiodothyronine (T(3); 10(-10) to 10(-6) M) or with 10(-8) M T(3) for 1-9 days. RESULTS: MCT8, LAT1, and LAT2 mRNAs were detected in fetal and postnatal femurs and in MC3T3-E1 cells, while OATP1 and NTCP mRNAs were not. LAT1 and LAT2 mRNAs were not affected by TH status in vivo or in vitro or by the stage of bone development or osteoblast maturation (analyzed by the expression of osteocalcin and alkaline phosphatase, which are key markers of osteoblastic differentiation). In contrast, the femoral mRNA expression of MCT8 decreased significantly during post-natal development, whereas MCT8 mRNA expression increased as MC3T3-E1 cells differentiated. We also showed that MCT8 mRNA was up-regulated in the femur of hypothyroid animals, and that it was down-regulated by treatment with T(3) in MC3T3-E1 cells. CONCLUSIONS: This is the first study to demonstrate the mRNA expression of LAT1, LAT2, and MCT8 in the bone tissue of mice and in osteoblast-like cells. In addition, the pattern of MCT8 expression observed in vivo and in vitro suggests that MCT8 may be important to modulate TH effects on osteoblast differentiation and on bone development and metabolism.
Assuntos
Sistema y+ de Transporte de Aminoácidos/biossíntese , Osso e Ossos/metabolismo , Cadeias Leves da Proteína-1 Reguladora de Fusão/biossíntese , Proteínas de Membrana Transportadoras/biossíntese , Osteoblastos/metabolismo , Sistema y+L de Transporte de Aminoácidos , Animais , Osso e Ossos/embriologia , Diferenciação Celular/efeitos dos fármacos , Regulação para Baixo , Fêmur/metabolismo , Feto/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Hipotireoidismo/metabolismo , Camundongos , Transportadores de Ácidos Monocarboxílicos , RNA Mensageiro/metabolismo , Simportadores , Tiroxina/sangue , Tri-Iodotironina/sangue , Tri-Iodotironina/farmacologia , Regulação para CimaRESUMO
Thyroid hormone (TH) plays a key role on post-natal bone development and metabolism, while its relevance during fetal bone development is uncertain. To study this, pregnant mice were made hypothyroid and fetuses harvested at embryonic days (E) 12.5, 14.5, 16.5 and 18.5. Despite a marked reduction in fetal tissue concentration of both T4 and T3, bone development, as assessed at the distal epiphyseal growth plate of the femur and vertebra, was largely preserved up to E16.5. Only at E18.5, the hypothyroid fetuses exhibited a reduction in femoral type I and type X collagen and osteocalcin mRNA levels, in the length and area of the proliferative and hypertrophic zones, in the number of chondrocytes per proliferative column, and in the number of hypertrophic chondrocytes, in addition to a slight delay in endochondral and intramembranous ossification. This suggests that up to E16.5, thyroid hormone signaling in bone is kept to a minimum. In fact, measuring the expression level of the activating and inactivating iodothyronine deiodinases (D2 and D3) helped understand how this is achieved. D3 mRNA was readily detected as early as E14.5 and its expression decreased markedly ( approximately 10-fold) at E18.5, and even more at 14 days after birth (P14). In contrast, D2 mRNA expression increased significantly by E18.5 and markedly ( approximately 2.5-fold) by P14. The reciprocal expression levels of D2 and D3 genes during early bone development along with the absence of a hypothyroidism-induced bone phenotype at this time suggest that coordinated reciprocal deiodinase expression keeps thyroid hormone signaling in bone to very low levels at this early stage of bone development.