Fatty Acid Supplementation During in vitro Embryo Production Determines Cryosurvival Characteristics of Bovine Blastocysts

In vitro production (IVP) embryos have a reduced quality and poor cryotolerance in comparison to in vivo embryos. This study investigated whether free fatty acid (FFA) conditions, fatty acid free (FAF)- synthetic oviduct fluid (SOF) without or with 25 μM of saturated stearic (C_18:0) or unsaturated oleic (C_18:1) acid during the first 5 IVP days, relate to quality and cryosurvival of day 8 blastocysts. Apart from the blastocyst scores, both 1) number and size of lipid droplets of fresh blastocysts and 2) total number and apoptotic and necrotic cells, before and after freezing-thawing, were scored by confocal microscopy. Blastocyst rates were significantly lower in the FAF SOF condition in comparison to other groups. Interestingly, blastocysts originating from the C_18:1 group, with a significantly higher lipid content, and blastocysts from the FAF SOF group demonstrated a high cryosurvival rate (70.1 and 67.4%, respectively) comparable with in vivo blastocysts (68%), in contrast to the poor cryosurvival of C_18:0 exposed embryos (17.6%). In all freeze-thawed embryos the average amount of apoptotic and necrotic cells increased albeit that the C_18:0 condition rates were higher (43.2%) when compared to C_18:1 (26.0%) and FAF SOF conditions (26.5%). The current data show that FFA administered during early embryonic development significantly affect the cryotolerance of blastocysts.

149 Uptake of C18:0 from culture media during invitro culture decreases cryosurvival rates of bovine embryos

Cryosurvival of invitro-produced bovine embryos is lower than that of invivo-produced embryos, limiting their usability in the field. Previous work showed that the embryo’s lipid composition relates to its quality and cryosurvival. The present study aimed to investigate the effects of free fatty acid (FA) additions to embryo culture media during the oviduct phase of embryonic development on the improvement of cryosurvival of invitro-produced blastocysts. Bovine cumulus–oocyte complexes (n=1675, 3 replicates) were harvested from slaughterhouse ovaries, invitro matured (23h), and subsequently fertilized (18–20h). Embryos were cultured until Day 5 post-fertilization in synthetic oviductal fluid (SOF) with (1) bovine serum albumin (BSA; control, n=253); (2) delipidified BSA (>96% FA free, n=460); (3), delipidified BSA complexed with 25µM unsaturated oleic acid (C18:1, n=455); or (4) with saturated stearic acid (C18:0, n=507) with a stoichiometry of 5:1. At Day 5, SOF was refreshed and embryos were cultured without supplementation. At Days 7 and 8, blastocyst rates were determined. Blastocysts were LD540 stained for lipid droplets (LD), and the LD number and size were analysed by ANOVA. Cryosurvival%, defined by re-expansion of the blastocoel, was analysed by logistic regression. Additionally, fresh and frozen–thawed blastocysts were stained for apoptosis (terminal deoxynucleotidyl transferase dUTP nick-end labelling, TUNEL), necrosis (EthD-1), and DNA (Hoechst 33342) and analysed using negative binomial regression. Group differences were tested using a post hoc Tukey test. Statistical analysis was performed in R Studio (version 3.4.2), and P-values <0.05 were considered significant. FA-free culture delayed and decreased blastocyst rates to 19% compared with any FA supplementation: 35%, 27%, and 29% for control, C18:1, and C18:0, respectively (P<0.04). Cryosurvival doubled with culture in FA-free SOF (58%) and C18:1 (63%) compared with C18:0 (23% P=0.01 and P<0.01, respectively) and control (29%; P=0.15 and P<0.02, respectively), approaching cryosurvival rates of donated multiple ovulation embryo transfer (MOET) embryos (CRV Company; 67%). C18:0 exposure also resulted in elevated necrosis levels after cryopreservation (5–8% of cells), compared with all groups (2–4%; P<0.016). The LD size increased in blastocysts cultured with C18:1 compared with all groups (3.1µm2 vs. 2.4–2.7µm2; P<0.016). C18:0 addition to SOF during embryo culture invitro, as well as a mixture of FA in control SOF (including C18:0), caused a reduction of ∼50% in blastocyst cryosurvival compared with MOET blastocysts. Interestingly, either C18:1 addition or the complete omission of FA in SOF during embryo culture invitro restored the cryosurvival of blastocysts to the level of MOET blastocysts. Currently, we are investigating whether the free FA conditions in the oviduct endorse the distinct quality between invivo- and invitro-produced embryos.

Mice without phosphatidylcholine transfer protein have no defects in the secretion of phosphatidylcholine into bile or into lung airspaces

Phosphatidylcholine transfer protein (Pc-tp) is a highly specific carrier of phosphatidylcholine (PC) without known function. Proposed functions include the supply of PC required for secretion into bile or lung air space (surfactant) and the facilitation of enzymatic reactions involving PC synthesis or breakdown. To test these functions, we generated knock-out mice unable to make Pc-tp. Remarkably, these mice are normal and have no defect in any of the postulated Pc-tp functions analyzed. The lipid content and composition of the bile, as well as lung surfactant secretion and composition, of Pc-tp (-/-) mice, is normal. The lack of a Pc-tp contribution to biliary lipid secretion is in agreement with our finding that Pc-tp is down-regulated in adult mouse liver: whereas Pc-tp is abundant in the liver of mouse pups, Pc-tp levels decrease > 10-fold around 2 wk after birth, when bile formation starts. In adult mice, Pc-tp levels are high only in epididymis, testis, kidney, and bone marrow-derived mast cells. Absence of Pc-tp in bone marrow-derived mast cells does not affect their lipid composition or PC synthesis and degradation. We discuss how PC might reach the canalicular membrane of the hepatocyte for secretion into the bile, if not by Pc-tp.