Developmental and Molecular Effects of CNP Supplementation in In Vitro Culture of Bovine Embryos

The use of C-type natriuretic peptide (CNP) in the interaction with the oocyte and in the temporary postponement of spontaneous meiosis resumption has already been well described. However, its action in pre-implantation developmental stage embryos remains to be understood. Thus, our study aimed to detect the presence of the canonical CNP receptor (natriuretic peptide receptor, NPR2) in germinal vesicle (GV), metaphase II (MII), presumptive zygotes (PZ), morula (MO), and blastocyst (BL) stage embryos and, later, to observe possible modulations on the embryos when co-cultured with CNP. In the Experiment I, we detected and quantified the NPR2 on the above-mentioned embryo stages. Following, Experiment II, intended to test different concentrations (100, 200, or 400 nM of CNP) at different times of inclusion in the in vitro culture (IVC; inclusion from the beginning, i.e. day 1, or from day 5). In Experiment III, it was used 400 nM of CNP on day 1 (D1) in the IVC, which did no demonstrate to be embryotoxic, and it showed potentially promising results in blastocyst production rate, when compared to the control. Thus, we analyzed the embryonic development rates of bovine embryos (D7) and hatching kinetics (D7, D8, and D9). Subsequently, morula and blastocyst were collected and evaluated for transcript abundance to competence and quality (apoptosis, oxidative stress, proliferation and differentiation) and lipid metabolism. Differences with probabilities less than P < 0.05, and/or Foldchange (FC) ˃1.5 were considered significant. We demonstrate the presence of NPR2 until the blastocyst development stage when there was a significant decrease in membrane receptors. There was no statistical difference in production rate after co-culture with 400 nM CNP. However, when we evaluated the abundance of morula transcripts, there was an upregulated transcription in ADCY6 (P=0.057), and downregulated transcripts, in BMP15 (P= 0.013), ACAT1 (P= 0.040), CASP3 (P=0.082). In addition, a total of 12 transcriptions in morula presented variation FC ˃1.5. In blastocysts, the treatment with CNP induced upregulation in BID, CASP3, SOX2, HSPA5 transcripts, and downregulation in BDNF, NLRP5, ELOVL1, ELOVL4, IGFBP4, and FDX1 transcripts (FC >1.5). Thus, our study identified and quantified the presence of NPR2 in bovine pre-implantation embryos. Furthermore, 400 nM of CNP in IVC, a concentration not previously described in the literature, modulated some transcripts related to embryonic metabolism and it was not embryotoxic morphologically.