Anna Milanesi

Thyroid Hormone Receptor Sumoylation Is Required for Preadipocyte Differentiation and Proliferation

Background: Thyroid hormone receptor (TR) sumoylation is essential for thyroid hormone regulation of gene expression. Results: TR sumoylation mutants impair differentiation though down-regulation of C/EBPs, constitutive interaction with NCoR, interference with PPARγ signaling, and disruption of the Wnt canonical signaling pathway important for preadipocyte proliferation. Conclusion: TR sumoylation site mutations impair preadipocyte proliferation and differentiation. Significance: TR sumoylation is required for adipogenesis. Thyroid hormone and thyroid hormone receptor (TR) play an essential role in metabolic regulation. However, the role of TR in adipogenesis has not been established. We reported previously that TR sumoylation is essential for TR-mediated gene regulation and that mutation of either of the two sites in TRα or any of the three sites in TRβ reduces TR sumoylation. Here, we transfected TR sumoylation site mutants into human primary preadiocytes and the mouse 3T3L1 preadipocyte cell line to determine the role of TR sumoylation in adipogenesis. Reduced sumoylation of TRα or TRβ resulted in fewer and smaller lipid droplets and reduced proliferation of preadipocytes. TR sumoylation mutations, compared with wild-type TR, results in reduced C/EBP expression and reduced PPARγ2 mRNA and protein levels. TR sumoylation mutants recruited NCoR and disrupted PPARγ-mediated perilipin1 (Plin1) gene expression, associated with impaired lipid droplet formation. Expression of NCoRΔID, a mutant NCoR lacking the TR interaction domain, partially “rescued” the delayed adipogenesis and restored Plin1 gene expression and adipogenesis. TR sumoylation site mutants impaired Wnt/β-catenin signaling pathways and the proliferation of primary human preadipocytes. Expression of the TRβ K146Q sumoylation site mutant down-regulated the essential genes required for canonical Wnt signal-mediated proliferation, including Wnt ligands, Fzds, β-catenin, LEF1, and CCND1. Additionally, the TRβ K146Q mutant enhanced the canonical Wnt signaling inhibitor Dickkopf-related protein 1 (DKK1). Our data demonstrate that TR sumoylation is required for activation of the Wnt canonical signaling pathway during preadipocyte proliferation and enhances the PPARγ signaling that promotes differentiation.

Management of hypothyroidism in pregnancy.

Purpose of reviewExamine recent studies on the assessment of thyroid status in pregnancy, approach to thyroid testing, the spectrum of hypothyroidism in pregnancy, and strategies for thyroid replacement in women with known hypothyroidism. Recent findingsTrimester-specific references range for thyroid-stimulating hormone (TSH) and free thyroxine in pregnancy must take into account iodine and thyroid autoantibody status, race, BMI, as well as other factors. Thyroid testing of only those pregnant women at increased risk for thyroid disease, case finding, will miss 30–80% of women with thyroid disease. Subclinical hypothyroidism is associated with an increasing number of adverse effects including infertility, miscarriage, preterm delivery, and breech presentation at birth. Many pregnant women with known hypothyroidism have an out-of-range TSH at the time of confirmed pregnancy. A variety of strategies are effective at keeping serum TSH normal during pregnancy including preconception increase in thyroxine, increase in thyroxine dose at the time pregnancy is confirmed, or making adjustments based on serum TSH monitoring. SummaryEvaluation of thyroid status in pregnancy requires an understanding of pregnancy-associated changes in thyroid function tests and how they vary by trimester. The spectrum of hypothyroidism in pregnancy includes isolated thyroid peroxidase antibody positivity, isolated hypothyroxinemia, subclinical and overt hypothyroidism. These patterns, in some situations, may be related to iodine status, selenium status, or underlying thyroid disease. There are a variety of approaches to management of thyroxine replacement in known hypothyroid women at the time of pregnancy that are all effective at maintaining a normal range during pregnancy.

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.

Amniotic fluid stem cells prevent β-cell injury

BACKGROUND AIMS The contribution of amniotic fluid stem cells (AFSC) to tissue protection and regeneration in models of acute and chronic kidney injuries and lung failure has been shown in recent years. In the present study, we used a chemically induced mouse model of type 1 diabetes to determine whether AFSC could play a role in modulating β-cell injury and restoring β-cell function. METHODS Streptozotocin-induced diabetic mice were given intracardial injection of AFSC; morphological and physiological parameters and gene expression profile for the insulin pathway were evaluated after cell transplantation. RESULTS AFSC injection resulted in protection from β-cell damage and increased β-cell regeneration in a subset of mice as indicated by glucose and insulin levels, increased islet mass and preservation of islet structure. Moreover, β-cell preservation/regeneration correlated with activation of the insulin receptor/Pi3K/Akt signaling pathway and vascular endothelial growth factor-A expression involved in maintaining β-cell mass and function. CONCLUSIONS Our results suggest a therapeutic role for AFSC in preserving and promoting endogenous β-cell functionality and proliferation. The protective role of AFSC is evident when stem cell transplantation is performed before severe hyperglycemia occurs, which suggests the importance of early intervention. The present study demonstrates the possible benefits of the application of a non-genetically engineered stem cell population derived from amniotic fluid for the treatment of type 1 diabetes mellitus and gives new insight on the mechanism by which the beneficial effect is achieved.

Ketosis-prone type 2 diabetes in a veteran population.

Ketosis-prone type 2 diabetes is a unique and underrecognized clinical entity characterized by new adult onset of diabetes with severe hyperglycemia and ketosis similar to type 1 diabetes, but with clinical and biological features typical of type 2 diabetes (1). Hyperglycemic crisis with ketosis in these individuals appears to be related to acute and reversible β-cell dysfunction with subsequent insulin independence and acceptable glycemic control on diet and/or oral agents during follow-up (2). In our retrospective study spanning from 1999 to 2011, we identified 62 adult veterans with new onset of diabetes presenting to the VA Greater Los Angeles Healthcare System (VAGLA) with diabetic ketoacidosis (DKA). Computerized medical records were used to identify DKA admissions. Diagnosis of DKA was established in the emergency room (3) in the absence of concomitant comorbidities that can lead …

Iodine and Thyroid Hormone Synthesis, Metabolism, and Action

Abstract Iodine is a crucial micronutrient for thyroid hormone synthesis and the only source is dietary. Iodide (I−) is absorbed in the stomach and small intestine, and is concentrated from the blood stream into the thyroid follicular cell through the action of the sodium/iodide symporter (NIS). Iodide is incorporated into thyroglobulin, a process referred to as organification. Thyroid hormone is secreted from the thyroid predominantly as the prohormone thyroxine (T4) and must be activated in tissues to the active form, triiodothyronine (T3), through the action of the 5′-deiodinase enzymes, type 1 (D1) and type 2 (D2), both of which require the trace element selenium. Thyroid hormone acts predominantly through nuclear thyroid hormone receptors (TR), α and β, and is required for normal fetal growth and maturation, and regulation of metabolism in the adult. In conditions of low iodine and resulting reduced thyroid hormone production, compensation occurs through an increase in thyroid stimulating hormone (TSH) secretion from the pituitary, increased D2 activity, and resulting increase in T4 to T3 conversion. If selenium deficiency coexists with iodine deficiency, this reduces D2 activity and impairs this mechanism to compensate for low iodine. Inadequate dietary intake of iodine in pregnancy is of special concern and can be associated with both maternal and fetal hypothyroidism, with retarded psychomotor development and irreversible mental retardation in the offspring. Iodine is essential for thyroid hormone synthesis and must be provided through dietary sources. Thyroid hormone is required for normal growth and development. The regulation of thyroid hormone production and metabolism allows for adequate thyroid hormone action in tissues, despite significant fluctuations in iodine supply. In some situations, such as pregnancy, however, these mechanisms may not be sufficient to compensate and sustain normal fetal development.