Effects of valproate and liraglutide in rodent models of Wolfram syndrome: emphasis on transcriptomic changes in the renin–angiotensin–aldosterone system

Abstract

Wolframi sündroom (WS) on harvikhaigus, mis on põhjustatud mutatsioonidest WFS1 geenis, mis kodeerib valku wolframiin. Haigust iseloomustavad insuliinsõltuv diabeet, süvenev nägemisnärvi kahjustus, magediabeet ja kuulmislangus. Lisaks võivad kaasuda mitmed psühhiaatrilised ning neuroloogilised häired. WS korral täna tõhus ravi puudub, kuid haiguse kulu pidurdamiseks on uurimisel mitmed juba kliinilises kasutuses olevad ravimid. Sealhulgas epilepsiavastane valproaat ja diabeedivastane ravim liraglutiid, mida peetakse potentsiaalseteks WS-i leevendavateks ravimiteks. Käesoleva väitekirja esimene pool keskendus valproaadi toime iseloomustamisele WS hiire mudelis. Leiti, et valproaat mõjutas WS hiirte maksakoes enim geene, mis on seotud oksüdatiivsete reaktsioonide, rasvade ainevahetuse ning ööpäevarütmi reguleerimisega. Enim oli mõjutatud Ppar𝛽/𝛿, millel on oluline roll ka glükoosi ainevahetuses. Testides valproaadi mõju WS hiirte veresuhkrule, leiti, et ravimi ühekordne manustamine parandas veresuhkru ainevahetust samal ajal kui pikaajalisel ravil toime puudus. Väitekirja teises pooles uuriti WFS1 olulisust ning valproaadi ja liraglutiidi toimet reniin-angiotensiin-aldosterooni süsteemis (RAAS) WS rotimudeli kudedes, kus on olulisel hulgal ka WFS1. RAAS süsteemi on sarnaselt WFS1-ga seostatud struktuuridega, mis seovad mitokondreid ja endoplasmaatilist retiikulumi ja on olulised närvirakkude elulemuses. Leiti, et RAAS-i võtmeretseptorite angiotensiin II tüüp 2 retseptori ja bradükiniini retseptori B1 geenide avaldumine on WS rottides märkimisväärselt alla reguleeritud. Lisaks täheldati madalamat aldosterooni ja kõrgemat bradükiniini taset. Vähenenud aldosterooni taset on hiljuti otseselt seostatud WFS1 puudulikkusega. Valproaat ja liraglutiid ei suutnud nende geenide avaldumise tasemeid normaliseerida, kuid tõstsid aldosterooni ja vähendasid bradükiniini taset. Kuigi WS rottidel ei esine RAAS-i häiretele viitavaid füsioloogilisi ilminguid, on see süsteem geenide avaldumise tasemel häirunud. Sealjuures tundub, et selle toimimist mõjutab tugevalt stress. Häirunud RAAS võib võimendada põletikulisi protsesse ja oksüdatiivset stressi, seeläbi kiirendades haiguse kulgu, mistõttu on oluline neid uusi teadmisi edaspidi arvestada.

Wolfram syndrome (WS) is a rare disease caused by mutations in the WFS1 gene, which encodes the protein Wolframin. The disease is characterized by insulin-dependent diabetes, progressive optic nerve atrophy, diabetes mellitus and hearing loss, which develop on average during the first twenty years of life. In addition, psychiatric disorders and several other neurological complications may accompany it. There is currently no effective treatment for WS, but several drugs already in clinical use are being investigated to slow the course of WS. These include the antiepileptic valproate and the antidiabetic liraglutide. The first half of this thesis focused on characterizing the effects of valproate in a mouse model of WS. It was found that valproate affected genes mainly related to oxidative reactions, fat metabolism and circadian rhythm in the liver tissue of WS mice. The most affected was Ppar𝛽/𝛿, which also plays an important role in glucose metabolism. When testing the effect of valproate on blood sugar in WS mice, it was found that a single administration of the drug improved blood sugar metabolism, while long-term treatment had no effect. In the second half of the thesis, the importance of WFS1 and the effects of valproate and liraglutide on the renin-angiotensin-aldosterone system (RAAS) were investigated in a rat model of WS. The RAAS, like WFS1, has been linked to structures associating mitochondria and endoplasmic reticulum that are important for neuron survival. Gene expression of the key RAAS receptors angiotensin II type 2 and bradykinin B1 was significantly decreased in WS rats. In addition, lower aldosterone and higher bradykinin levels were observed. Low aldosterone levels have recently been directly linked to WFS1 deficiency. Valproate and liraglutide failed to normalize the gene expression levels, but increased aldosterone and decreased bradykinin levels in those rats. Although physiological manifestations suggestive of RAAS disturbance are not apparent in WS rats, the RAAS is evidently dysregulated at the transcriptional level. At the same time, it seems that its functioning is strongly affected by stress. Disturbed RAAS can exacerbate inflammatory processes and oxidative stress, thereby accelerating the course of the disease, so it’s importance in WS cannot be underestimated.