Uloga purinskog signalnog sistema u procesima neurodegeneracije i neuroinflamacije izazvanih trimetil-kalajem u hipokampusu ženki pacova

Abstract

Neurodegeneracija je proces koji se odlikuje progresivnim gubitkom nervnog tkiva, posebno nervnih ćelija, nervnih nastavaka i mijelina, koji se uočava kod velikog broja neuroloških bolesti, a za koji do danas nije razvijena adekvatna terapija, niti su u brojnim bolestima otkriveni uzroci. S obzirom na to da neurodegeneracija podrazumeva oštećenje tkiva, ona je nužno praćena neuroinflamatornom aktivacijom mikroglije i astrocita, što može doprineti progresiji inicijalne patologije. Predmet istraživanja ove doktorske disertacije bio je ispitivanje promena komponenti purinske signalizacije u hipokampusu ženki pacova u modelu neurodegeneracije i neuroinflamacije izazvane trimetil kalajem (TMK). TMK je neurotoksin koji dovodi do selektivne smrti neurona limbičkog sistema, naročito u hipokampusu, što rezultuje histopatološkim i bihejvioralnim promenama koje verno reprodukuju neke od glavnih karakteristika mnogih neurodegenerativnih bolesti. Prvi set rezultata dobijenih u okviru ove disertacije pokazuje da tokom prve tri nedelje nakon delovanja TMT javlja progresivno umiranje nervnih ćelija, što je praćeno snažnom i specifičnom aktivacijom astrocita i mikroglije. Aktivirani astrociti u hipokamusu ispoljavaju morfološku i funkcionalnu dihotomiju, tako što astrociti CA1 regiona hipokampusa pokazuju odlike hipertrofiranih ćelija, dok astrociti hilarnog regiona pokazuju odlike atrofije. Aktivirane mikroglijske ćelije pojačanao eksprimiraju početni enzim purinske kaskade, NTPDaza1/CD39, dok mikroglijske ćelije ameobidnog oblika, na mestima aktivne neurodegeneracije, pojačano eksprimiraju završni enzim purinske kaskade, eN/CD73. Reaktivni astrociti pojačano eksprimiraju A1R, A2AR i P2Y1R receptore kao i C3, iNOS, NF-kB, koji ukazuju na njihov proinflamacijski karakter. U mikroglijskim ćelijama, povećana ekspresija purinskih receptora P2Y12R, P2Y6R i P2X4R na genskom nivou, ukazuje na migratorni fenotip aktivirane mikroglije tokom rane faze neurodegeneracije, dok je povećana proteinska ekspresija P2X7R verovato povezana sa fagocitozom ameboidne mikroglije. Pojačana ekspresija navedenih komponenti purinske transmisije na mikrogliji (NTPDaze1/CD39, eN/CD73 kao i P2X7R) i astrocitima (A1R, A2AR, P2Y1R) u neurodegeneraciji i neuroinflamaciji izazvanoj TMK, kao i smanjena ekspresija A1R, P2Y12R, ukazuju na ulogu purinske signalizacije u neurodegeneraciji i neuroinflamaciji.

Neurodegeneration reffers to a progressive loss of neuronal tissue, specifically nerve cells, nerve endings and myelin sheet, and it is common for many neurological disorders. There is no known effective drug or therapeutic approach for virtually all neurodegenerative diseases and cause for many of them has not been discovered yet. Neurodegenerative disorders are often accompanied by neuroinflammatory activation of microglia and astrocytes which can further contribute to pathology progression. The main goal of this dissertation was to examine changes in the main components of purinergic signaling in trimethyltin-induced (TMT) neurodegeneration and neurofinflammation of hippocampus of female rats. TMT is a potent neurotoxin which causes selective neuronal death of lymbic system, especially hippocampus which results in histopathological and behavioral changes resulting in some of the main common characteristics of neurodegenerative disorders. First set of the results of this doctoral dissertation shows that the first three weeks after TMT intoxication are accompanied by extensive neuronal death in CA sectors of hippocampus, followed by reactive astro- and microgliosis. Reactive astrocytes in hippocampus showed morphological and functional dichotomy. Astrocytes of CA1 region were characterized by hypetrhophic morphology while astrocytes od hilar region had atrophy-like morphology. Activated microglial cells showed increased expression of NTPDase1/CD39, while ameboid microglia in the site of active neurodegeneration showed eN/CD73. Reactive astrocytes showed increase expression of A1R, A2AR i P2Y1R and C3, iNOS, NF-kB, which points to their proinflammatory phenotype. Increased gene expression of P2Y12R, P2Y6R i P2X4R points toward migratory phenotype of microglia during early phase of neurodegeneration, while late expression of P2X7R is probably related to phagocitic properties of amoeboid microglial cells. Increased expression of microglial (NTPDase1/CD39, eN/CD73 and P2X7R) and astrocytic (A1R, A2AR, P2Y1R) purinergic compontents in TMT-induced neurodegeneration and neuroinflammation as well as loss of homeostatic A1R, P2Y12R receptors in neurons definitely points to an active role of purinergic signaling in neurodegenerative process.