FEMALE GONADAL HORMONES ARE A RISK FACTOR FOR DEVELOPING ATHEROSCLEROTIC CHANGES IN C57BL/6J MICE ON ATHEROGENIC DIET

Abstract

In humans, estrogens are considered protective factor against atherosclerosis because the risk increases in postmenopausal women. However, it is not clear whether estrogens are the only factor, whether sex chromosomes also have an influence, and whether estrogens play the same role in all mammals. The mouse line C57BL/6J is prone to develop atherosclerotic changes in the largest arteries after prolonged feeding of a high-fat diet containing cholesterol and cholate (Paigen diet). We aimed to examine effect of sex hormones and sex chromosome complement on the development of atherosclerotic plaques using agonadal SF-1 knockout mouse on C57BL/6J background. Gonadally intact and prepubertally gonadectomized WT and agonadal SF-1 knockout C57BL/6J mice of both sexes were exposed to a Paigen diet and a control diet for 20 weeks. We monitored their body weight, food intake, and serum lipid profile. The aortas were examined by the en face method, and the cross sections of the aortic bulbs were stained for lipid content. In all groups of mice, atherosclerotic changes were small and confined to the aortic bulb. The formation of atherosclerotic plaques was sex- and hormone-dependent, as female animals with functioning ovaries developed the most prominent atherosclerotic plaques. Gonadally intact females were also the only group that gained weight comparably on control or atherogenic diet. Diet affected blood biochemistry, but there were almost no significant differences between groups in serum lipid levels. Results indicated main mechanism causing sex-dependent differences in atherosclerosis depends on sex hormones rather than sex chromosomes. Our results also suggest that a mouse model of dietary induced atherosclerosis is of limited use to study the mechanisms of atherosclerosis in humans because the presence of estrogens impairs lipid metabolism and contributes to the formation of atherosclerotic plaques. ŽENSKI SPOLNI HORMONI PREDSTAVLJAJO DEJAVNIK TVEGANJA ZA NASTANEK ATEROSKLEROZNIH SPREMEMB PRI MIŠIH LINIJE C57BL/6J NA ATEROGENI DIETI Izvleček: Pri ženskah se v postmenopavznem obdobju poveča tveganje za razvoj ateroskleroze, zato je splošno sprejeto, da estrogeni hormoni varujejo ožilje pred razvojem tega žilnega obolenja. Ni pa še popolnoma raziskano, ali so estrogeni poglavitni dejavnik, ali imajo vpliv tudi spolni kromosomi in ali je vpliv spolnih hormonov enak med sesalci. Živalski modeli za proučevanje ateroskleroznega obolenja so redki, eden izmed njih so miši linije C57BL/6J, ki lahko spontano razvijejo aterosklerotične spremembe v večjih telesnih arterijah, če se jih dlje časa hrani s hrano z visoko vsebnostjo maščob, z dodatkom holesterola in holata - s t.i. aterogeno dieto po Paigenu. V raziskavi smo želeli proučiti vpliv spolnih hormonov in spolnih kromosomov na razvoj aterosklerotičnih plakov v žilah s pomočjo modela miši z izbitim genom SF-1, ki se razvijejo brez spolnih organov. 20 tednov smo mišim dajali hrano po receptu Paigen oziroma kontrolno hrano z nižjo vsebnostjo maščob. Miši obeh spolov so bile bodisi brez spolnih organov zaradi izbitega gena SF-1 (na ozadju C57BL/6J), bodisi smo jim gonade operativno odstranili pred puberteto. Tretjino samcev in samic smo pustili intaktne z gonadami. Spremljali smo telesno težo živali, povprečno porabo hrane in opravili analizo serumskih lipidov. Pregledali smo preparirane aorte po metodi en-face ter ocenili obseg plakov in maščob na prečnih rezih aortnega korena na nivoju aortnih zaklopk s histološkim barvanjem in analizo mikroskopske slike. Pri vseh skupinah miši, ki so bile hranjene z aterogeno dieto, so bile aterosklerotične spremembe relativno majhne in omejene na aortni koren. Obseg plakov je bil odvisen od kromosomskega spola in prisotnosti hormonov, plaki so bili najbolj očitni pri samicah z jajčniki. Istočasno so bile intaktne samice edina skupina živali, ki so podobno pridobivale na teži tako na aterogeni kot kontrolni hrani, pri ostalih skupinah so živali na aterogeni dieti priraščale bistveno manj. Vrsta hrane je imela vpliv na serumski lipidni profil, vendar praktično ni bilo statistično značilnih razlik med različnimi skupinami živali in analize krvnega seruma nismo mogli povezati z drugimi ugotovljenimi odstopanji pri samicah. Rezultati raziskave kažejo, da so glavni povod za spolne razlike pri razvoju aterosklerotičnih sprememb spolni hormoni in ne spolni kromosom. Hkrati pa rezultati postavljajo pod vprašaj uporabnost mišjih modelov za proučevanje ateroskleroze, ki jo induciramo s prehrano, saj prisotnost estrogenov – obratno kot pri ljudeh - pri miših negativno vpliva na presnovo lipidov in doprinese k izoblikovanju aterosklerotičnih plakov. Ključne besede: ateroskleroza; dieta po Paigenu; spol; spolni hormoni; miš, lipidi in holesterol