Abstract
Nicotinamide (NAM), the amide form of vitamin B3, plays pivotal roles in regulating various cellular processes including energy production and maintenance of genomic stability. The current study aimed at deciphering the effect of NAM, when administered during in vitro maturation (IVM), on the developmental competence of bovine preimplantation embryos. Our results showed that low NAM concentrations reduced the oxidative stress and improved mitochondrial profile, total cleavage and 8–16 cell stage embryo development whereas the opposite profile was observed upon exposure to high NAM concentrations (10 mM onward). Remarkably, the hatching rates of day-7 and day-8 blastocysts were significantly improved under 0.1 mM NAM treatment. Using RT-qPCR and immunofluorescence, the autophagy-related (Beclin-1 (BECN1), LC3B, and ATG5) and the apoptotic (Caspases; CASP3 and 9) markers were upregulated in oocytes exposed to high NAM concentration (40 mM), whereas only CASP3 was affected, downregulated, following 0.1 mM treatment. Additionally, the number of cells per blastocyst and the levels of SIRT1, PI3K, AKT, and mTOR were higher, while the inner cell mass-specific transcription factors GATA6, SOX2, and OCT4 were more abundant, in day-8 embryos of NAM-treated group. Taken together, to our knowledge, this is the first study reporting that administration of low NAM concentrations during IVM can ameliorate the developmental competence of embryos through the potential regulation of oxidative stress, apoptosis, and SIRT1/AKT signaling.
Highlights
Nicotinamide (NAM), known as niacinamide, is engaged in therapeutics of various diseases including diabetes, tumor metastasis, Alzheimer’s, and multiple sclerosis [1]
Microscopic investigation of Cumulus–oocyte complexes (COCs) at the start and end of maturation showed a significant improvement in the expansion pattern of cumulus cells in 0.1 NAM-treated groups (30.20 ± 2.53 vs. 19.43 ± 2.19 for control) (Figure 1A,C)
The effect of low and high NAM concentrations on the in vitro maturation (IVM) was firstly assessed through the direct investigation of polar body extrusion, 18–20 h from the onset of maturation, under microscope
Summary
Nicotinamide (NAM), known as niacinamide, is engaged in therapeutics of various diseases including diabetes, tumor metastasis, Alzheimer’s, and multiple sclerosis [1]. Cells 2020, 9, 1550 assisted reproductive technology (ART), accumulation of reactive oxygen species (ROS) during the in vitro maturation (IVM) and culturing processes represents a significant barrier for efficient embryo development. This is mainly attributed to the major difference in the levels of oxygen and antioxidants between the in vivo environment and in vitro culturing conditions [2]. It was reported that NAM exhibits an antioxidant activity in addition to its role in the improvement of mitochondrial profile in different cells [5,6]; its actual role during the developmental process of preimplantation embryos is not completely clarified
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