Nonesterified Fatty Acid-Induced Endoplasmic Reticulum Stress in Cattle Cumulus Oocyte Complexes Alters Cell Metabolism and Developmental Competence1

Abstract

Reduced oocyte quality has been associated with poor fertility of high-performance dairy cows during peak lactation, due to negative energy balance. We examined the role of nonesterified fatty acids (NEFAs), known to accumulate within follicular fluid during under- and overnutrition scenarios, in causing endoplasmic reticulum (ER) stress of in vitro maturated cattle cumulus-oocyte complexes (COCs). NEFA concentrations were: palmitic acid (150 μM), oleic acid (200 μM), and steric acid (75 μM). Abattoir-derived COCs were randomly matured for 24 h in the presence of NEFAs and/or an ER stress inhibitor, salubrinal. Total and hatched blastocyst yields were negatively impacted by NEFA treatment compared with controls, but this was reversed by salubrinal. ER stress markers, activating transcription factor 4 (Atf4) and heat shock protein 5 (Hspa5), but not Atf6, were significantly up-regulated by NEFA treatment within whole COCs but reversed by coincubation with salubrinal. Likewise, glucose uptake and lactate production, measured in spent medium samples, showed a similar pattern, suggesting that cumulus cell metabolism is sensitive to NEFAs via an ER stress-mediated process. In contrast, while mitochondrial DNA copy number was recovered in NEFA-treated oocytes, oocyte autofluorescence of the respiratory chain cofactor, FAD, was lower following NEFA treatment of COCs, and this was not reversed by salubrinal, suggesting the negative impact was via reduced mitochondrial function. These results reveal the significance of NEFA-induced ER stress on bovine COC developmental competence, revealing a potential therapeutic target for improving oocyte quality during peak lactation.

Fibroblast growth factor 2 induces proliferation and distribution of G2/M phase of bovine endometrial cells involving activation of PI3K/AKT and MAPK cell signaling and prevention of effects of ER stress

“…In reproduction, ER stress influences gametogenesis, implantation, embryogenesis, and uterine functions (Guzel et al, ; Michalak & Gye, ; Sutton‐McDowall et al, ). The ER is an organelle in eukaryotic cells involved with protein folding and synthesis, biosynthesis of lipids, and maintenance of calcium levels for cellular homeostasis and development (Bravo et al, ).…”

Energy metabolism of follicular environment during oocyte growth and maturation

“…In cattle, when NEFA was added to IVM medium, cleavage rate was not affected, however the blastocyst rate was decreased [50]. This result was not confirmed by the studies of De Bie et al [51], who has not observed any changes in both cleavage and blastocyst rate.…”

“…This result was not confirmed by the studies of De Bie et al [51], who has not observed any changes in both cleavage and blastocyst rate. However both manuscripts describe no impact of NEFA supplementation during IVM on blastocyst quality, revealed by total cell number [50,51], ICM and TE cell number [50,51] or apoptotic index [50]. Therefore detrimental lipid conditions of oocyte maturation reduce the chance to develop to the blastocyst stage, but the embryos that do develop, are of good quality.…”

Non‐esterified fatty acid‐associated ability of follicular fluid to support porcine oocyte maturation and development

“…Non‐esterified fatty acids (NEFAs) are a major component of FF and the composition and concentration of NEFAs depend on the maternal physiological conditions . High NEFA levels in FF are believed to be toxic for oocytes, as a high NEFA concentration (150 μ mol L −1 palmitic acid + 200 μ mol L −1 oleic acid + 75 μ mol L −1 stearic acid) adversely affects bovine oocyte developmental ability through endoplasmic reticulum (ER) stress . In addition, one study showed that high NEFA levels in the maturation medium reduced bovine oocyte development, whereas inhibiting beta oxidation restored oocyte maturation .…”

“…1,2 High NEFA levels in FF are believed to be toxic for oocytes, as a high NEFA concentration (150 μ mol L −1 palmitic acid + 200 μ mol L −1 oleic acid + 75 μ mol L −1 stearic acid) adversely affects bovine oocyte developmental ability through endoplasmic reticulum (ER) stress. 3 In addition, one study showed that high NEFA levels in the maturation medium reduced bovine oocyte development, whereas inhibiting beta oxidation restored oocyte maturation. 4 Most of these findings were obtained from studies in which a single, or a combination of major fatty acids, was added to oocyte culture media 5−7 and the significance of either intrinsic NEFA in the FF or properties of the FF that are associated with the NEFA content has not yet been clarified.…”