Role of ovarian hormones in thymic involution in rats : doctoral dissertation

Beograd : [M. M. Perišić]

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Biologija - Imunologija / Biology - Immunology

Timus je primarni limfoidni organ koji obezbeđuje mikrosredinu neophodnu za diferencijaciju/sazrevanje T-limfocita. Tokom ontogeneze, ovaj organ trpi značajne strukturne i funkcionalne promene koje se zbirno označavaju kao involucija timusa, i manifestuju se kao smanjena efikasnosti timopoeze i posledično, smanjen izlazak novoformiranih T-limfocita na periferiju. Involucija timusa je kod glodara najizraženija u periodu sticanja polne zrelosti. Veliki broj literaturnih podataka ukazuje na to da hormoni hipotalamo-hipofizo-gonadne (H-H-G) osovine, pre svega hormoni gonada, utiču na razvoj i involuciju timusa. Međutim, uprkos brojnim istraživanjima u proteklim decenijama, uloga hormona jajnika u inicijaciji i održavanju/progresiji involucije timusa nije do kraja rasvetljena. Cilj ove doktorske disertacije je bio da se ispita uloga hormona jajnika u inicijaciji i održavanju/progresiji involucije timusa. U tom cilju ispitivan je uticaj jednokratnog davanja testosterona u kritičnom neonatalnom uzrastu, koji dovodi do odlaganja sazrevanja H-H-G osovine i promena u obrascu sekrecije hormona jajnika kod adultnih životinja (neonatalna androgenizacija) i uklanjanja jajnika ženkama pacova u uzrastu od 10 meseci, kada su involutivne promene timusa jasno izražene, na građu timusa i timopoezu u ranom adultnom uzrastu; odnosno u uzrastu od 11 meseci. Posebno je ispitivan, mogući, indirektan uticaj promena u sekreciji hormona jajnika na aktivnost timusnog kateholaminergičkog regulatornog sistema. Neonatalna androgenizacija, delujući na različite stadijume diferencijacije/sazrevanja T-ćelija, od ulaska/diferencijacije progenitorskih ćelija do linijskog usmeravanja timocita, povećala je efikasnost timopoeze (na osnovu većeg broja svežih timusnih emigranata u perifernoj krvi i slezini), uključujući, najverovatnije, i povećano stvaranje ćelija regulatornog fenotipa (CD4+CD25+FoxP3+ i CD161+TCRαβ+ ćelije). Pored toga, kod ovih životinja je uočeno favorizovano stvaranje ćelija CD4-CD8+TCRαβ++ fenotipa (fenotipska defeminizacija/maskulinizacija procesa timopoeze). Uprkos povećanoj efikasnosti timopoeze, nepromenjena relativna zastupljenost timusnih epitelnih ćelija (TEC) kao i nivo iRNK za IL-6, a smanjen nivo iRNK za IL-7 u tkivu timusa, ukazuju, da je kod neonatalno androgenizovanih životinja, u uzrastu od 3 meseca, najverovatnije, došlo do pokretanja mehanizama negativne povratne sprege, koji ograničavaju ekspanziju TEC i timopoezu. Ovarijektomija u uzrastu od 10 meseci, nakon 30. dana, imala je za posledicu povećanje relativne zastupljenosti TEC i efikasnosti timopoeze (uključujući i povećano stvaranje ćelija regulatornog fenotipa), što se manifestovalo povećanim brojem svežih timusnih emigranata CD4+ i CD8+ fenotipa u perifernoj krvi i slezini. Međutim, uprkos regeneraciji epitelne komponente timusa i povećanoj efikasnosti timopoeze, smanjen nivo iRNK za IL-6 i IL-7 u tkivu timusa ovarijektomisani životinja sugeriše da je kod ovih životinja došlo do aktivacije intratimusnih mehanizama negativne povratne sprege koji ograničava ekspanziju TEC koje sintetišu IL-6 i efikasnost timopoeze. U zaključku, nalazi dobijeni u ovoj disertaciji ukazuju da neonatalna androgenizacija menja kinetiku postnatalnog razvoja timusa i polno specifičan obrazac diferencijacije/sazrevanja timocita i odlaže, ali vrlo verovatno ne sprečava involuciju timusa, dok uklanjanje hormona jajnika u uzrastu kada su involutivne promene timusa uznapredovale dovodi do delimične reverzije ovih promena i efikasnije timopoeze, koji su, najverovatnije, vremenski ograničenog trajanja. Pored toga, pokazano je da se uticaj hormona jajnika na ove procese odvija i indirektno, menjanjem efikasnosti modulatornog delovanja noradrenalina na timopoezu.

The thymus is a primary lymphoid organ that provides the microenvironment necessary for the differentiation/maturation of T-lymphocytes. During ontogeny, thymus undergoes significant structural and functional changes leading to reduced efficiency of thymopoiesis and, consequently, reduced output of newly generated Tlymphocytes. These changes are collectively referred to as thymic involution. The most profound thymic changes in rodents, occur around puberty. There is an accumulating body of evidence indicating that hormones of the hypothalamic-pituitary-gonadal (H-PG) axis, particularly gonadal hormones, influence thymic development and involution. However, despite extensive research in the past decades, the role of ovarian hormones in the initiation and maintenance/progression of thymic involution is not fully understood. Bearing all aforementioned in mind, this dissertation was aimed to elucidate the role of ovarian hormones in initiation and maintenance/progression of thymic involution. To this end the effects of single injection of testosterone in critical postnatal period, which postpones H-P-G axis maturation and affects the gender-specific pattern of gonadal hormone secretion in adult animals (neonatal androgenization), and ovarian hormone removal in rats with advanced thymic involutive changes (10-month-old), on thymic structure and function, were examined in 3-month-old and 11-month-old female rats, respectively. In addition, the putative indirect, catecholamine-mediated effects of the neonatal androgenization and ovariectomy on thymopoiesis were explored. Neonatal androgenization, affecting distinct stages of thymocyte differentiation/maturation (from progenitor cell entry and differentiation to thymocyte lineage commitment), increased the efficiency of thymopoiesis and consequently thymic output (as evidenced by the increased number of recent thymic emigrants in peripheral blood and spleen), including, most likely, increased output of the cells with regulatory phenotype (CD4+CD25+FoxP3+ and CD161+TCRαβ+ cells). In addition, neonatal treatment with testosterone skewed thymocyte lineage commitment towards CD4-CD8+TCRαβ++ cells (phenotypic defeminization/masculinization of thymopoiesis). Despite the increased efficiency of thymopoiesis, unaltered relative abundance of thymic epithelial cells (TEC) and the thymic level of IL-6 mRNA, and reduced thymic level of IL-7 mRNA, indicated, most likely, activation of intrathymic negative feedback mechanisms limiting TEC proliferation and thymopoiesis in 3- month-old neonatally androgenized rats. Ovariectomy at the age of 10 months led to the expansion of TECs and greater efficiency of thymopoiesis (including generation of cells with regulatory phenotype), increasing the number of both CD4+ and CD8+ recent thymic emigrants in peripheral blood and spleen of 11-month-old rats, compared with age-matched controls. However, despite the regeneration of the thymic epithelial component and increased efficiency of thymopoiesis, reduced thymic levels of mRNA for IL-6 and IL-7 in ovariectomized rats indicated activation of intrathymic negative feedback mechanisms limiting the expansion of IL-6-synthesizing TECs and thymopoietic efficiency in these animals. In conclusion, the data obtained in this dissertation indicate that neonatal androgenization alters the kinetics of postnatal thymic development and sex-specific pattern of thymocyte differentiation/maturation and postpones thymic involution, but, most likely, does not prevent it completely. The removal of ovarian hormones in female rats with advanced thymic involutive changes leads to partial reversion of these changes, and an increase in thymopoietic efficiency of, most likely, limited duration. In addition, these data indicate that ovarian hormones might affect thymic development/involution not only directly, but also indirectly by diminishing the efficiency of noradrenaline-mediated modulation of thymopoiesis.

involucija timusa; hormoni jajnika; timusne epitelne ćelije; timopoeza; IL-6; IL-7; noradrenalin; adrenergički receptori; sveži timusni emigranti; regulatorne T ćelije

thymic involution; ovarian hormones; thymic epithelial cells; thymopoiesis; IL-6; IL-7; noradrenaline; adrenergic receptors; recent thymic emigrants; regulatory T-cells

591.465.3::577.6]:591.443]:599.45 (043.3)

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