NAD+-dependent Sirt6 is a key regulator involved in telomere shortening of in vitro-cultured preimplantation embryos

Telomere length is important for the maintaining the individual health of a species. However, recent studies have indicated that the telomere length of somatic cells can be drastically decreased in the offspring receiving in vitro fertilization (IVF) therapy, however, the underlying molecular mechanism remains unknown. Sirt6 is a NAD+-dependent epigenetic regulator that has recently been found to play an important role in maintaining telomere stability. Here, we report for the first time that NAD+ levels are significantly lower in blastocysts cultured in vitro than that in blastocysts developed in vivo, leading to impaired Sirt6 function, further triggering telomere shortening of the inner cell mass and possibly affecting newborn offspring. This phenotype could be effectively mitigated by supplementation with NMN, a precursor of NAD+, during in vitro culture.While it could not be achieved in Sirt6 conditional knockout embryos. Our results reveal the mechanism by which in vitro culture induces telomere shortening in preimplantation embryos, providing a potential target for improving in vitro culture conditions.