Tanycytes and the Control of Thyrotropin-Releasing Hormone Flux Into Portal Capillaries
Por:
Rodriguez-Rodriguez, Adair, Lazcano, Ivan, Sanchez-Jaramillo, Edith, Maria Uribe, Rosa, Jaimes-Hoy, Lorraine, Joseph-Bravo, Patricia, Charli, Jean-Louis
Publicada:
25 jun 2019
Categoría:
Endocrinology, diabetes and metabolism
Resumen:
Central and peripheral mechanisms that modulate energy intake, partition
and expenditure determine energy homeostasis. Thyroid hormones (TH)
regulate energy expenditure through the control of basal metabolic rate
and thermogenesis; they also modulate food intake. TH concentrations are
regulated by the hypothalamus-pituitary-thyroid (HPT) axis, and by
transport and metabolism in blood and target tissues. In mammals,
hypophysiotropic thyrotropin-releasing hormone (TRH) neurons of the
paraventricular nucleus of the hypothalamus integrate energy-related
information. They project to the external zone of the median eminence
(ME), a brain circumventricular organ rich in neuron terminal
varicosities and buttons, tanycytes, other glial cells and capillaries.
These capillary vessels form a portal system that links the base of the
hypothalamus with the anterior pituitary. Tanycytes of the medio-basal
hypothalamus express a repertoire of proteins involved in transport,
sensing, and metabolism of TH; among them is type 2 deiodinase, a source
of 3,3',5-triiodo-L-thyronine necessary for negative feedback on TRH
neurons. Tanycytes subtypes are distinguished by position and phenotype.
The end-feet of beta 2-tanycytes intermingle with TRH varicosities and
terminals in the external layer of the ME and terminate close to the ME
capillaries. Besides type 2 deiodinase, beta 2-tanycytes express the
TRH-degrading ectoenzyme (TRH-DE); this enzyme likely controls the
amount of TRH entering portal vessels. TRH-DE is rapidly upregulated by
TH, contributing to TH negative feedback on HPT axis. Alterations in
energy balance also regulate the expression and activity of TRH-DE in
the ME, making beta 2-tanycytes a hub for energy-related regulation of
HPT axis activity. beta 2-tanycytes also express TRH-R1, which mediates
positive effects of TRH on TRH-DE activity and the size of beta
2-tanycyte end-feet contacts with the basal lamina adjacent to ME
capillaries. These end-feet associations with ME capillaries, and TRH-DE
activity, appear to coordinately control HPT axis activity. Thus,
down-stream of neuronal control of TRH release by action potentials
arrival in the external layer of the median eminence, imbricated
intercellular processes may coordinate the flux of TRH into the portal
capillaries. In conclusion, beta 2-tanycytes appear as a critical
cellular element for the somatic and post-secretory control of TRH flux
into portal vessels, and HPT axis regulation in mammals.
Filiaciones:
Rodriguez-Rodriguez, Adair:
Univ Nacl Autonoma Mexico, Inst Biotecnol, Dept Genet Desarrollo & Fisiol Mol, Cuernavaca, Morelos, Mexico
Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
Lazcano, Ivan:
Univ Nacl Autonoma Mexico, Inst Neurobiol, Dept Neurobiol Cellar & Mol, Juriquilia, Mexico
Departamento de Neurobiología Celular y Molecular, Instituto de Neurobiología, Universidad Nacional Autónoma de México, Juriquilla, Mexico
Sanchez-Jaramillo, Edith:
Inst Nacl Psiquiatria Ramon Fuente Muniz, Direcc Invest Neurociencias, Lab Neuroendocrinol Mol, Mexico City, DF, Mexico
Laboratorio de Neuroendocrinología Molecular, Dirección de Investigaciones en Neurociencias, Instituto Nacional de Psiquiatría Ramón de la Fuente Muñiz, Mexico City, Mexico
Maria Uribe, Rosa:
Univ Nacl Autonoma Mexico, Inst Biotecnol, Dept Genet Desarrollo & Fisiol Mol, Cuernavaca, Morelos, Mexico
Jaimes-Hoy, Lorraine:
Univ Nacl Autonoma Mexico, Inst Biotecnol, Dept Genet Desarrollo & Fisiol Mol, Cuernavaca, Morelos, Mexico
Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
Joseph-Bravo, Patricia:
Univ Nacl Autonoma Mexico, Inst Biotecnol, Dept Genet Desarrollo & Fisiol Mol, Cuernavaca, Morelos, Mexico
Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
Charli, Jean-Louis:
Univ Nacl Autonoma Mexico, Inst Biotecnol, Dept Genet Desarrollo & Fisiol Mol, Cuernavaca, Morelos, Mexico
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