Extracellular vesicle mediated embryo-maternal communication – a tool for evaluating functional competency of pre-implantation embryos

Abstract

Viljatus on ülemaailmne probleem, mis vaevab hinnanguliselt 15% paaridest. Viljatuse raviks kasutatakse kunstliku viljastamist, mis aitab mitmetel paaridel rasestuda. Abistatud reprodiuktiivtehnoloogia metoodikate valik on mitmekesine, kuid kõige kasutatavam on in vitro viljastamine (IVF). Alates 1970-ndatest on abistatud reproduktsioonitehnoloogia märgatavalt arenenud ja aidanud ilmale tuua miljoneid lapsi. Sellest hoolimata on IVF-i edukus alla 40%. Edutu implantatsioon on ebaõnnestunud embrüo siirdamise peamine põhjus 2/3 juhtudest. Nidatsioon on inimese paljunemise üks olulisemaid etappe, kus embrüo kinnitub endomeetriumi. Selleks peab aga endomeetriumis toimuma mitmed muutused. Üheks endomeetriumi muutuste vallandajaks peetakse embrüo ja endomeetriumi vahelist suhtlust. Mitmete rakkudevaheliste suhtluste meetodite hulgas on rakuvälised ehk ekstratsellulaarsed vesiikulid (EV) üks olulisim transportmehhanism. EV on nanoosakesed, mis sisaldavad mitmeid bioloogiliselt aktiivseid molekule. Neid molekule viivad EV ühest rakust teise. Doktoritöös uuriti inimese ja veise embrüonaalse RNA, peamiselt mittekodeeriva RNA, ülekandumist endomeetriumi rakkudelt eralduvatest EV-dest. Embrüo RNA märgistamisega kinnitati, et embrüonaalne RNA kandub endomeetriumi rakkudesse. Selline rakkudevaheline suhtlus muutis endomeetriumi rakkude vastuvõtlikkust embrüo implantatsiooniks, millega tõestati et embrüo EV võivad märkimisväärselt muuta endomeetriumi rakkude talitlust nii inimesel kui ka veisel. Kunstlikus viljastamises on üha populaarsem siirata vaid üks parima kvaliteediga embrüo, kuid hindamismeetodid embrüo valimiseks on puudulikud. Antud doktoritöös leiti, et endomeetriumi rakkudes (eriti endomeetriumi transkriptoomis) toimunud muutused olid seoses embrüo kvaliteediga. Seda tulemust embrüo-emaka suhtluses saab teoreetiliselt kvantifitseerida ja kasutada mitteinvasiivse meetodina hindamaks embrüo kvaliteedi, mis parendaks viljatuse ravi edukust ja vähendaks patsientide kannatusi.

Subfertility is a global condition with estimated 15% of couples worldwide have trouble conceiving. In many of these cases, the most effective remedy is assisted reproduction. Assisted reproduction can take many forms. In vitro fertilization or IVF being the one with which the most people are familiar. Since its conception in the 1970s, assisted reproduction has developed significantly producing millions of successful pregnancies. However, the rate of success of IVF remains below 40% even in ideal candidates. Failure of implantation has been identified as the main cause of failed embryo transfers in 2/3 of the cases. Implantation is one of the most critical steps in human reproduction. The embryo attaches itself to the endometrial epithelium. The endometrium changes drastically in anticipation of the incoming embryo. One trigger that brings about this change is thought to be the communication between embryo and the endometrium. Among many available methods of intercellular communication, extracellular vesicles stand out because of its remarkable utility as a cargo carrier. Extracellular vesicles or EV are nanometre sized sacs that contain biologically active molecules. They can transfer these molecules in between cells as cellular messengers. In this project, we have investigated the phenomenon of embryonic RNA, especially non-coding RNA, transfer to endometrial cells using EVs as a transport mechanism. By labelling embryo RNA, we were able to confirm that Embryonic RNA is in fact transferred to the endometrium. This intercellular communication changes the physiology of the endometrium in such a way that endometrial cells were transformed into a higher level of receptivity for the incoming embryo. We also observed that only embryo EVs can induce this remarkable change on the endometrial cells. The embryonic EV based communication was also observed in bovine embryo-maternal interactions. Interestingly, the changes induced in the endometrial cells, especially in the endometrial transcriptome, correlated with the quality of the embryo that produced the EVs leading us to theorize that this method of quantifying the embryo-maternal communication can be used as a non-invasive method of embryo grading. In the ever-popular practise of elective single embryo transfer in assisted reproduction, selecting the best embryo is hugely advantages. Quantified embryo maternal communication could therefore be an invaluable tool in the field of assisted reproduction to reduce patient suffering and to increase the rate of successful pregnancies.