ATP-Citrate Lyase down-regulation negatively affects sheep preimplantation embryo development

Recently it was reported that around 60% of in vitro fertilized (IVF) human embryos undergo irreversibly arrest before compaction owing to metabolic and epigenetic dysfunctions. De novo lipogenesis (DNL), the process whereby cells generate fatty acids from excess carbohydrates, is deregulated in several pathologies, including obesity, non-alcoholic fatty liver disease, metabolic syndrome, and cancer. However, its direct impact on infertility remains unknown, particularly on preimplantation embryonic development. In this work, we start to investigate DNL in preimplantation sheep embryos as a human model. The main carbon source for DNL is the cytoplasmic acetyl coenzyme A (Acetyl-CoA), which is derived from citrate through the activities of ATP Citrate Lyase (ACLY). In our experiments, immunofluorescence staining on 2-4 cells of IVF sheep embryos showed an intense protein signal of ACLY, compared with sheep embryonic fibroblasts, in the cytoplasm and nuclear compartment. In order to understand ACLY’s role in embryonic development, we downregulated its expression by microinjection of a siRNA targeting mouse ACLY gene (siACLY) and a non-targeting siRNA (siCTR). Following siRNA injection into fertilized zygotes, we report that Acly knockdown results in obvious morphologically abnormal blastocysts, with a lower rate development rate than control (siCTR 20/62, 32% versus siAcly 15/67, 22%, blastocysts/zygotes). These results highlight the DNL, particularly its starting point directed by ACLY, is essential for physiological preimplantation embryo development. Based on the known competition between DNL and histone acetylation for the Acetyl-CoA ACLY-produced, we will focus our future investigations on histone acetylation induced by ACLY-depleted zygotes. Our research aims to raise innovative strategies to rescue human preimplantation embryo arrests induced by metabolic diseases where the DNL is deregulated.