Thyroid Hormone and the Neuroglia: Both Source and Target

Thyroid hormone plays a crucial role in the development and function of the nervous system. In order to bind to its nuclear receptor and regulate gene transcription thyroxine needs to be activated in the brain. This activation occurs via conversion of thyroxine to T3, which is catalyzed by the type 2 iodothyronine deiodinase (D2) in glial cells, in astrocytes, and tanycytes in the mediobasal hypothalamus. We discuss how thyroid hormone affects glial cell function followed by an overview on the fine-tuned regulation of T3 generation by D2 in different glial subtypes. Recent evidence on the direct paracrine impact of glial D2 on neuronal gene expression underlines the importance of glial-neuronal interaction in thyroid hormone regulation as a major regulatory pathway in the brain in health and disease

A központi idegrendszeri pajzsmirigyhormon aktiváció szabályozásának molekuláris biológiája = Molecular biology of the regulation of thyroid hormone activation in the central nervous system

A pajzsmirigyhormonok számos biológiai folyamat, így a fejlődés, a növekedés és az anyagcsere alapvető fontosságú tényezői. A tiroxin (T4) pro-hormon, melynek a pajzsmirigyhormon aktiváció során dejodációval T3-á kell alakulnia ahhoz, hogy a pajzsmirigyhormon magreceptorhoz kötődve biológiai hatásait kifejthesse. A T4 aktivációt az agyban a kettes-típusú dejodáz enzim (D2) katalizálja. A pályázat célkitűzései a központi idegrendszeri pajzsmirigyhormon aktiváció celluláris és molekuláris vonatkozásainak vizsgálatához kapcsolódtak. Az alacsony T3 szindróma molekuláris pathogenezisének vizsgálata során feltártuk az emberi dio2 gén NF-kB érzékenységét és leírtuk annak molekuláris hátterét. Jellemeztük a D2 fehérje ubikvitinációjában kulcsszerepet játszó fehérjék idegrendszeri eloszlását, továbbá a D2 enzim poszt-transzlációs szabályozásának szubcelluláris és konformációs feltételeit. Vizsgálataink során tanulmányoztuk a T3 képződés mechanizmusát a fejlődő idegrendszerben és kimutattuk a D2 expresszió megjelenését a fejlődő hipotalamusz tanicitáiban. Munkánk az idegrendszeri T3 függő génexpressziós profilok kialakulásért felelős szabályozó mechanizmusok feltérképezése révén járul hozzá a fejlődő és kifejlett agy működését befolyásoló tényezők jobb megértéséhez. | Thyroid hormone is a crucial factor of development, growth and metabolism. The pro-hormone thyroxine (T4) has to be converted to T3 via thyroid hormone activation in order to bind the thyroid hormone receptor to modulate thyroid hormone dependent pathways. Local T3 generation in the adult and developing brain is catalyzed by the type 2 deiodinase selenoenzyme (D2). The aim of the project was to better understand the cellular and molecular events underlying thyroid hormone activation in the central nervous system. We studied the molecular pathogenesis of the low T3 syndrome and described the molecular components ensuring NF-kB mediated induction of the human dio2 gene. We characterized the distribution of key proteins of D2 ubiquitination in the brain and determined the subcellular and conformational requirements of post-translational regulation of the D2 enzyme. We studied the mechanisms of T3 generation in the developing brain and determined the developmental expression of D2 in hypothalamic tanycytes. Our data contribute to the better understanding of factors regulating the function of the developing and adult brain via providing a deeper insight into mechanisms generating T3 dependent gene expression profiles

Myofiber integrity depends on desmin network targeting to Z-disks and costameres via distinct plectin isoforms

Dysfunction of plectin, a 500-kD cytolinker protein, leads to skin blistering and muscular dystrophy. Using conditional gene targeting in mice, we show that plectin deficiency results in progressive degenerative alterations in striated muscle, including aggregation and partial loss of intermediate filament (IF) networks, detachment of the contractile apparatus from the sarcolemma, profound changes in myofiber costameric cytoarchitecture, and decreased mitochondrial number and function. Analysis of newly generated plectin isoform–specific knockout mouse models revealed that IF aggregates accumulate in distinct cytoplasmic compartments, depending on which isoform is missing. Our data show that two major plectin isoforms expressed in muscle, plectin 1d and 1f, integrate fibers by specifically targeting and linking desmin IFs to Z-disks and costameres, whereas plectin 1b establishes a linkage to mitochondria. Furthermore, disruption of Z-disk and costamere linkages leads to the pathological condition of epidermolysis bullosa with muscular dystrophy. Our findings establish plectin as the major organizer of desmin IFs in myofibers and provide new insights into plectin- and desmin-related muscular dystrophies

Extracellular vesicles transmit epithelial growth factor activity in the intestinal stem cell niche.

Extracellular vesicles (EV) are membrane-surrounded vesicles that represent a novel way of intercellular communication by carrying biologically important molecules in a concentrated and protected form. The intestinal epithelium is continuously renewed by a small proliferating intestinal stem cell population (ISC), residing at the bottom of the intestinal crypts in a specific microenvironment, the stem cell niche. By using 3D mouse and human intestinal organoids, we show that intestinal fibroblast-derived EVs are involved in forming the ISC niche by transmitting Wnt and epidermal growth factor (EGF) activity. With a mouse model that expresses EGFP in the Lgr5+ ISCs we prove that loss in ISC number in the absence of EGF is prevented by fibroblast-derived EVs. Furthermore, we demonstrate that intestinal fibroblast-derived EVs carry EGF family members, such as amphiregulin. Mechanistically, blocking EV-bound amphiregulin inhibited the EV-induced survival of organoids. In contrast, EVs have no role in transporting R-Spondin, a critical niche factor amplifying Wnt signalling. Collectively, we prove the important role of fibroblast-derived EVs as a novel transmission mechanism of factors in the normal ISC niche. © AlphaMed Press 2019 SIGNIFICANCE STATEMENT: Intestinal stem cells (ISC) reside in a specific microenvironment in the intestinal epithelium, the ISC niche. Although they are critical in maintaining tissue integrity, the transmission of ISC niche factors is still not well known. Extracellular vesicles (EV) carry biologically active molecules in a membrane-surrounded form, thus, representing a novel way of intercellular communication. Here we provide evidence that fibroblast-derived EVs transport epidermal growth factor activity, one of the critical niche factors, by carrying amphiregulin, thus, they represent a novel way of intercellular signal transmission mechanism for normal ISCs

A Novel Pathway Regulates Thyroid Hormone Availability in Rat and Human Hypothalamic Neurosecretory Neurons

Hypothalamic neurosecretory systems are fundamental regulatory circuits influenced by thyroid hormone. Monocarboxylate-transporter-8 (MCT8)-mediated uptake of thyroid hormone followed by type 3 deiodinase (D3)-catalyzed inactivation represent limiting regulatory factors of neuronal T3 availability. In the present study we addressed the localization and subcellular distribution of D3 and MCT8 in neurosecretory neurons and addressed D3 function in their axons. Intense D3-immunoreactivity was observed in axon varicosities in the external zone of the rat median eminence and the neurohaemal zone of the human infundibulum containing axon terminals of hypophysiotropic parvocellular neurons. Immuno-electronmicroscopy localized D3 to dense-core vesicles in hypophysiotropic axon varicosities. N-STORM-superresolution-microscopy detected the active center containing C-terminus of D3 at the outer surface of these organelles. Double-labeling immunofluorescent confocal microscopy revealed that D3 is present in the majority of GnRH, CRH and GHRH axons but only in a minority of TRH axons, while absent from somatostatin-containing neurons. Bimolecular-Fluorescence-Complementation identified D3 homodimers, a prerequisite for D3 activity, in processes of GT1-7 cells. Furthermore, T3-inducible D3 catalytic activity was detected in the rat median eminence. Triple-labeling immunofluorescence and immuno-electronmicroscopy revealed the presence of MCT8 on the surface of the vast majority of all types of hypophysiotropic terminals. The presence of MCT8 was also demonstrated on the axon terminals in the neurohaemal zone of the human infundibulum. The unexpected role of hypophysiotropic axons in fine-tuned regulation of T3 availability in these cells via MCT8-mediated transport and D3-catalyzed inactivation may represent a novel regulatory core mechanism for metabolism, growth, stress and reproduction in rodents and humans

MiR-200b categorizes patients into pancreas cystic lesion subgroups with different malignant potential

Extracellular vesicles (EV) carry their cargo in a membrane protected form, however, their value in early diagnostics is not well known. Although pancreatic cysts are heterogeneous, they can be clustered into the larger groups of pseudocysts (PC), and serous and mucinous pancreatic cystic neoplasms (S-PCN and M-PCN, respectively). In contrast to PCs and S-PCNs, M-PCNs may progress to malignant pancreatic cancers. Since current diagnostic tools do not meet the criteria of high sensitivity and specificity, novel methods are urgently needed to differentiate M-PCNs from other cysts. We show that cyst fluid is a rich source of EVs that are positive and negative for the EV markers CD63 and CD81, respectively. Whereas we found no difference in the EV number when comparing M-PCN with other pancreatic cysts, our EV-based biomarker identification showed that EVs from M-PCNs had a higher level of miR-200b. We also prove that not only EV-derived, but also total cyst fluid miR-200b discriminates patients with M-PCN from other pancreatic cysts with a higher sensitivity and specificity compared to other diagnostic methods, providing the possibility for clinical applications. Our results show that measuring miR-200b in cyst fluid-derived EVs or from cyst fluid may be clinically important in categorizing patients