Dietary alpha-lipoic acid alleviates heat stress by modulating insulin-like signaling to maintain homeostasis in C. elegans

Prolonged exposure to high temperatures can cause oxidative stress in the body, negatively impacting human health. Alpha-lipoic acid (ALA) is a naturally occurring antioxidant prevalent in both plant and animal foods, exhibiting bioactivity comparable to that of vitamins. Although its roles in antioxidant defense and metabolic regulation have been extensively studied, its potential to mitigate heat stress in organisms is less explored and deserves further study. Our research demonstrates that ALA significantly improves the survival rates of Caenorhabditis elegans under heat stress. ALA achieves this by activating heat shock factor 1 (HSF-1) and promoting mitochondrial fission and mitophagy through the transcription factor HLH-30. These processes help alleviate oxidative damage from heat stress, maintain mitochondrial function, and stabilize cellular energy metabolism. Furthermore, the activation of HSF-1 and enhanced mitophagy by dietary ALA depend on the insulin-like signaling peptide 19 (INS-19), suggesting that ALA may target the insulin-like signaling pathway to combat heat stress and maintain homeostasis. These findings indicate that ALA could serve as a valuable dietary supplement for enhancing heat stress resistance in organisms and may inspire the development of novel food ingredients with protective properties against thermal challenges.

Impact of Heat Stress on Oocyte Developmental Competence and Pre-Implantation Embryo Viability in Cattle

Rectal and vaginal temperatures are utilised in both in vivo and in vitro models to study the effects of heat stress on oocyte competence and embryo viability in cattle. However, uterine temperature increases by only 0.5 °C in heat-stressed cows, significantly lower than simulated increases in in vitro models. Temperature variations within oviducts and ovarian follicles during heat stress are poorly understood or unavailable, and evidence is lacking that oocytes and pre-implantation embryos experience mild (40 °C) or severe (41 °C) heat stress inside the ovarian follicle and the oviduct and uterus, respectively. Gathering detailed temperature data from the reproductive tract and follicles is crucial to accurately assess oocyte competence and embryo viability under realistic heat stress conditions. Potential harm from heat stress on oocytes and embryos may result from reduced nutrient availability (e.g., diminished blood flow to the reproductive tract) or other unidentified mechanisms affecting tissue function rather than direct thermal effects. Refining in vivo stress models in cattle is essential to accurately identify animals truly experiencing heat stress, rather than assuming heat stress exposure as done in most studies. This will improve model reliability and aid in the selection of heat-tolerant animals.

The Anti-Müllerian Hormone as Endocrine and Molecular Marker Associated with Reproductive Performance in Holstein Dairy Cows Exposed to Heat Stress

Anti-Müllerian hormone (AMH) is proposed as a biomarker for fertility in cattle, yet this associative relationship appears to be influenced by heat stress (HS). The objective was to test serum AMH and AMH-related single nucleotide polymorphisms (SNPs) as markers potentially predictive of reproductive traits in dairy cows experiencing HS. The study included 300 Holstein cows that were genotyped using BovineSNP50 (54,000 SNP). A genome-wide association study was then executed. Nine intragenic SNPs within the pathways that influence the AMH gene were found important with multiple comparisons adjustment tests (p < 1.09 × 10-6). A further validation study was performed in an independent Holstein cattle population, which was divided into moderate (MH; n = 152) and severe heat-stressed (SH; n = 128) groups and then subjected to a summer reproductive management program. Serum AMH was confirmed as a predictor of fertility measures (p < 0.05) in MH but not in the SH group. Cows were genotyped, which revealed four SNPs as predictive markers for serum AMH (p < 0.01), reproductive traits (p < 0.01), and additional physiological variables (p < 0.05). These SNPs were in the genes AMH, IGFBP1, LGR5, and TLR4. In conclusion, serum AMH concentrations and AMH polymorphisms are proposed as predictive markers that can be used in conjunction with genomic breeding value approaches to improve reproductive performance in Holstein cows exposed to summer HS conditions.

Insulin-like growth factor 1 in heat stress-induced neuroinflammation: novel perspective about the neuroprotective role of chromium

Heat stress (HS) can cause a series of stress responses, resulting in numerous negative effects on the body, such as the diminished food intake, carcass quality and reproductive capacity. In addition to the negative effects on the peripheral system, HS leads to central nervous system (CNS) disorders given its toll on neuroinflammation. This neuroinflammatory process is mainly mediated by microglia and astrocytes, which are involved in the activation of glial cells and the secretion of cytokines. While the regulation of inflammatory signaling has a close relationship with the expression of heat shock protein 70 (Hsp70), HS-induced neuroinflammation is closely related to the activation of the TLR4/NF-κB pathway. Moreover, oxidative stress and endoplasmic reticulum (ER) stress are key players in the development of neuroinflammation. Chromium (Cr) has been widely shown to have neuroprotective effects in both humans and animals, despite the lack of mechanistic evidence. Evidence has shown that Cr supplementation can increase the levels of insulin-like growth factor 1 (IGF-1), a major neurotrophic factor with anti-inflammatory and antioxidant effects. This review highlights recent advances in the attenuating effects and potential mechanisms of Cr-mediated IGF-1 actions on HS-induced neuroinflammation, providing presently existing evidence supporting the neuroprotective role of Cr.

Thermoprotective molecules: Effect of insulin-like growth factor type I (IGF-1) in cattle oocytes exposed to high temperatures

The adverse effects of heat stress (HS) on the welfare and productivity of cattle are the result of the associated hyperthermia and the physiological and behavioral mechanisms performed by the animal to regulate body temperature. The negative effects of HS on in vitro oocyte maturation and in vitro bovine embryo production have been reported; being one of the major concerns due to economic and productive losses, and several mechanisms have been implemented to reduce its impact. These mechanisms include supplementation of the medium with hormones, adjuvants, identification of protective genes, among others. This review aims to explore the cellular and molecular mechanisms of insulin-like growth factor-1 (IGF-1) during in vitro and in vivo maturation of bovine oocytes and its thermoprotective effect under HS. Although the supplementation of the culture medium during oocyte maturation with IGF-1 has been implemented during the last years, there are still controversial results, however, supplementation with low concentration showed a positive effect on maturation and thermoprotection of oocytes exposed to higher temperatures. Additionally, IGF-1 is involved in multiple cellular pathways, and it may regulate cell apoptosis in cases of HS and protect oocyte competence under in vitro conditions.

Colony stimulating factor 2 protects the preimplantation bovine embryo from heat shock

Heat stress can have severe deleterious effects on embryo development and survival. The present study evaluated whether CSF2 can protect the developmental competence of the bovine embryo following exposure to a heat shock of 41°C at the zygote and morula stages. In the first experiment, putative zygotes and 2-cell embryos were assigned to receive either 10 ng/ml CSF2 or vehicle, and then cultured for 15 h at either 38.5°C or 41°C and then at 38.5°C until day 7.5. Heat shock reduced blastocyst development for embryos treated with vehicle but not for embryos cultured with CSF2. In the second experiment, day 5 embryos (morula) were treated with CSF2 or vehicle and then cultured for 15 h at either 38.5°C or 41°C and then at 38.5°C until day 7.5. Temperature treatment did not affect development to the blastocyst stage and there was no effect of CSF2 treatment or the interaction. Results indicate that CSF2 can reduce the deleterious effects of heat shock at the zygote or two-cell stage when the embryo is transcriptionally inactive.

Cellular responses and microRNA profiling in bovine spermatozoa under heat shock

Sperm function is susceptible to adverse environmental conditions. It has been demonstrated that in vivo and in vitro exposure of bovine sperm to elevated temperature reduces sperm motility and fertilizing potential. However, the cascade of functional, cellular and molecular events triggered by elevated temperature in the mature sperm cell remains not fully understood. Therefore, the aim of this study was to determine the effect of heat shock on mature sperm cells. Frozen-thawed Holstein sperm were evaluated immediately after Percoll purification (0 h non-incubation control) or after incubation at 35°C, 38.5°C, and 41°C for 4 h. Heat shock reduced sperm motility after 3 - 4 h at 41°C while mitochondrial activity was reduced by 38.5 and 41°C when compared to the control. Heat shock also increased sperm reactive oxygen species production and caspase activity. Heat-shocked sperm had lower fertilizing ability, which led to diminished cleaved and blastocyst rates. Preimplantation embryo developmental kinetics was also slowed and reduced by sperm heat shock. The microRNA (miR) profiling identified >300 miRs in bovine sperm. Among these, three and seven miRs were exclusively identified in sperm cells exposed to 35 and 41°C, respectively.

Effect of season on germinal vesicle stage, quality, and subsequent in vitro developmental competence in bovine cumulus-oocyte complexes

Although the reproductive performance of grazing cattle is lower in summer compared to winter, the effect of season on oocyte developmental competence has not been thoroughly examined. We measured the effect of season on oocyte chromatin compaction, cumulus cell quality, and embryonic development after in vitro fertilization. Cumulus oocytes-complexes (COCs) were collected from abattoir cows' ovaries during the winter and summer months. First, we evaluated the degree of chromatin compaction in germinal vesicle (GV) oocytes (GV1 through GV3), which is associated with different degrees of developmental competence. Then, we determined the apoptotic index in cumulus cells from immature and in vitro matured COCs. Finally, in vitro matured oocytes were fertilized to determine blastocyst rate and embryo quality. During the summer months, we observed a significantly lower proportion of oocytes reaching the GV3 stage and higher levels of DNA fragmentation in cumulus cell. As a result, blastocyst yield and quality were reduced during the summer months. In conclusion, summer negatively affected oocyte GV stage progression, cumulus cell quality, and embryo development. Increased cumulus cell DNA fragmentation during summer, may partially explain the reduced oocyte maturation capacity, considering the relevance of cumulus-oocyte communication during this stage.

Influence of long-term thermal stress on the in vitro maturation on embryo development and Heat Shock Protein abundance in zebu cattle

The objective of this study was to investigate the influence of long-term temperature stress during the in vitro maturation (IVM) of oocytes on the in vitro embryo production (IVP) and the abundance of HSP70 and HSP90 in zebu cattle. Viable cumulus-oocyte complexes (COCs) were incubated for 24 h at 37 °C, 38.5 °C, or 40 °C for the low-, physiological, and high-temperature stress treatments, respectively. Thereafter, they were subjected to in vitro fertilization and culture. Temperature did not affect the polar body extrusion. However, IVP was adversely affected when IVM took place at 37 °C and 40 °C. The highest abundance of HSP70 was observed in cumulus cells after maturation of COCs at 40 °C. In contrast, HSP70 was more abundant in oocytes at both 37 °C and 40 °C; however, at 40 °C, the difference to the control group (38.5 °C) was not significant. In contrast, the highest abundance of HSP90 was observed in oocytes and cumulus cells at 37 °C. It appears that HSP70 and HSP90 respond to cold and heat stress in different ways. In conclusion, moderately high (40 °C) and low (37 °C) thermal stress for 24 h during IVM is detrimental to the developmental competence of oocyte and is accompanied by changes in the abundances of HSP70 and HSP90, especially in cumulus cells.

Thermoprotective molecules to improve oocyte competence under elevated temperature

Heat stress is an environmental factor that challenges livestock by disturbing animal homeostasis. Despite the broad detrimental effects of heat stress on reproductive function, the germline and the early preimplantation embryo are particularly prone. There is extensive evidence that elevated temperature reduces oocyte developmental competence through a series of cellular and molecular damages. Further research revealed that the oocyte respond to stress by activating cellular mechanisms such as heat shock response, unfolded protein response and autophagy to improve survival under heat shock. Such knowledge paved the way for the identification of thermoprotective molecules that alleviate heat-induced oocyte oxidative stress, organelle damage, and apoptosis. Therefore, this review depicts the deleterious effects of heat shock on oocyte developmental competence, heat-induced cellular and molecular changes, outlines pro-survival cellular mechanisms and explores thermoprotective molecules to improve oocyte competence.

Shading effect on physiological parameters and in vitro embryo production of tropical adapted Nellore heifers in integrated crop-livestock-forest systems

The aim of this study was to evaluate the impact of increased shadow supply in integrated crop-livestock-forest systems on in vitro embryonic development and physiological parameters related to stress response in Nellore heifers (Bos indicus). For the study, animals (n = 16) were randomly divided into two groups and kept in areas with different afforestation systems, the integrated crop-livestock-forest (ICLF) and the integrated crop-livestock (ICL) system. The microclimate of the ICLF system provided better comfort conditions than ICL. No differences of respiratory rate, rectal temperature, cortisol, T3, T4, oocyte quality, and cleavage rate between the systems were verified. A higher blastocyst rate was observed in the ICLF (p < 0.05). The results demonstrate that Nellore heifers managed in ICLF during summer in Midwest of Brazil showed higher production of in vitro embryos, without typical changes in its physiological parameters. The results observed in the present study indicate that zebu females are able to respond satisfactorily to the intense heat conditions; however, we believe that the long period to which these animals are exposed to these conditions interferes in the oocyte competence and embryo development.

Time-dependent effects of heat shock on the zona pellucida ultrastructure and in vitro developmental competence of bovine oocytes

The aim of this study was to determine the effects of different exposure lenght to heat shock (HS) during in vitro maturation (IVM) on zona pellucida (ZP) ultrastructure and developmental competence of bovine oocytes. Cumulus-oocyte complexes (COCs) were matured in vitro (IVM) at 38.5 °C for 24 h (control group, CG), or incubated at 41 °C (HS) for 6 h (HS-6h), 12 h (HS-12h), 18 h (HS-18h), and 22h (HS-22h) followed by incubation at 38.5 °C to complete a full 24-h period of maturation. After IVM, oocytes were subjected to scanning electron microscopy (SEM) or in vitro fertilization and culture until the blastocyst stage. For heat-shocked oocytes, with exception of those in the HS-6h group, SEM examinations revealed that ZP surfaces were rough and characterized by a presence of spongy network. Oocytes from the HS-22h group displayed an increase in the number of pores, as well as a higher proportion of oocytes with amorphous ZPs. The proportion of oocytes that reached metaphase II (MII) stage decreased in all HS groups, regardless of the duration of exposure to 41 °C. These results provide evidence that HS during IVM for 12-22 h reduces the developmental competence of bovine oocytes, increasing the percentage of oocytes with abnormal chromosomal organization, and reducing fertilization and blastocysts formation rate. The effects of HS were more pronounced for the 22-h exposure group. The damage induced by HS on oocyte function clearly increased upon exposure to elevated temperature.

Follicular fluid exosomes act on the bovine oocyte to improve oocyte competence to support development and survival to heat shock

Addition of follicular fluid to oocyte maturation medium can affect cumulus cell function, increase competence of the oocytes to be fertilised and develop to the blastocyst stage and protect the oocyte from heat shock. Here, it was tested whether exosomes in follicular fluid are responsible for the effects of follicular fluid on the function of the cumulus–oocyte complex (COC). This was accomplished by culturing COCs during oocyte maturation at 38.5°C (body temperature of the cow) or 41°C (heat shock) with follicular fluid or exosomes derived from follicular fluid and evaluating various aspects of function of the oocyte and the embryo derived from it. Negative effects of heat shock on cleavage and blastocyst development, but not cumulus expansion, were reduced by follicular fluid and exosomes. The results support the idea that exosomes in follicular fluid play important roles during oocyte maturation to enhance oocyte function and protect it from stress.

Astaxanthin counteracts the effects of heat shock on the maturation of bovine oocytes

The cellular mechanisms induced by elevated temperature on oocytes are not fully understood. However, there is evidence that some of the deleterious effects of heat shock are mediated by a heat-induced increase in reactive oxygen species (ROS). In this context, carotenoid antioxidants might have a thermoprotective effect. Therefore, the objective of this study was to determine the role of astaxanthin (AST) on oocyte ROS production and on the redox profile and developmental competency of cumulus-oocyte complexes (COCs) after 14 h heat shock (41°C) during in vitro maturation (IVM). Exposure of oocytes to heat shock during IVM increased ROS and reduced the ability of the oocyte to cleave and develop to the blastocyst stage. However, 12.5 and 25 nM astaxanthin rescued these negative effects of heat shock; astaxanthin counteracted the heat shock-induced increase in ROS and restored oocyte developmental competency. There was no effect of astaxanthin on maturation medium lipid peroxidation or on glutathione peroxidase and catalase activity in oocytes and cumulus cells. However, astaxanthin stimulated superoxide dismutase (SOD) activity in heat-shocked cumulus cells. In conclusion, direct heat shock reduced oocyte competence, which was restored by astaxanthin, possibly through regulation of ROS and SOD activity in oocytes and COCs.