Studies on aryl hydrocarbon receptor in murine granulosa cells and human embryonic stem cells

Abstract

Arüülsüsivesinike retseptor (AHR) on ligand-aktiveeritav transkriptsioonifaktor. AHR avastati esialgu kui erinevate mürgiste keskkonnakemikaalide toime vahendaja. Levinuimad viimaste seast on polütsüklilised halogeenitud arüülsüsivesinikud, kaasa arvatud AHR-ile kõige suuremat afiinsust omav TCDD. Uuemad teadmised on näidanud, et lisaks keskkonnas levinud mürgiste kemikaalide toime vahendamisele on AHR-il organismis täita hulgaliselt muid ülesandeid. Sellele on viidanud katsed Ahr nokaut loommudelitega, aga ka saadud teadmised AHR-i endogeensete ligandide kohta. AHR-i füsioloogilist tähtsust on näidatud mitmetes organites ja kudedes, kõige enam immuunsüsteemis, maksas, kopsus, rasvkoes, ajus ja vähkkoes. Ühtlasi on näidatud selle valgu tähtsust reproduktiivsüsteemis ning tüvirakkudes. Uuringud AHR-i ülesannete ning geeni avaldumise teemal on viitanud võimalusele kasutada AHR-i terapeutilise märklauana. Praegused uuringud keskenduvad paljuski sellele, kuidas kasutada AHR-i avaldumist indikaatorina mitmete haiguste tuvastamisel, aga ka ravi tõhususe tõstmisele läbi AHR-i aktiivsuse mõjutamise. Siiski, teadmised AHR-i avaldumise ja aktiivsuse kohta erinevates kudedes on puudulikud. Samuti on näidatud, et AHR-il on koe- ning rakuspetsiifilised ülesanded, mistõttu on vajalik uurida AHR-i bioloogilisi ülesandeid erinevates rakkudes. Käesolevas dissertatsioonis keskenduti AHR-i uurimisele hiire munasarja granuloosarakkudes ja inimese embrüonaalsetes tüvirakkudes. Täpsemalt keskenduti töö käigus AHR-i avaldumise kontrollmehhanismide selgitamisele. Lisaks avardati teadmisi AHR-i füsioloogilisest tähtsusest, tehes kindlaks, milliste geenide avaldumist uuritav transkriptsioonifaktor otseselt mõjutab.

Aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor. It was initially discovered as a mediator of toxic effects of various environmental pollutants, secreted into the environment as organic waste. These include a wide range of polycyclic and halogenated aryl hydrocarbons, including the highest affinity AHR ligand TCDD. However, research over the past few decades has revealed that AHR has a broad range of functions other than being a sensor to toxic substances. Evidence for this has derived from studies using Ahr knockout animal models as well as the gained knowledge about the vast number of endogenous ligands for AHR. The role of AHR in regulating cellular homeostasis has been shown in various organs and tissues, most prominently in the immune system, liver, lung, fat tissue, brain and cancer. Additionally, AHR has been discovered to be important in reproductive system and in stem cells. Clinical sampling of AHR expression as well as basic research studying the role of AHR has paved way to the prospect of using this protein as a therapeutic target. Today’s research is widely focused on of its potential to serve as a marker in various diseases, but also as being a cellular target in modulation of treatment outcomes. However, the knowledge about the exact functions of this protein is far from complete. In addition, studies have implied AHR to have cell- and tissue-specific functions. The complex nature of this protein has urged to study its expression and functions in different cells. The current thesis focused on characterising the expression of Ahr gene in murine granulosa cells and human embryonic stem cells. A particular focus was placed on elucidating the regulatory mechanisms controlling Ahr expression. In addition, this thesis aimed to expand the knowledge on the roles of AHR in cellular homeostasis by identification of novel AHR target genes.