Epi-nutrients in the oviductal environment: Folate levels and differential gene expression of its receptors and transporters in the bovine oviduct

Effects of short-term rumen-protected folic acid supplementation on pregnancy rate, one-carbon metabolism, and steroid hormone in Holstein dairy cows

This study investigated the effects of rumen-protected folic acid (RPFA) supplementation on pregnancy rate at first artificial insemination (AI) and metabolic parameters in dairy cows. A total of 256 multiparous Holstein dairy cows were blocked by parity, average daily milk yield, days in milk, and body condition scores, and then randomly assigned to 1 of 4 treatments: cows were orally given 0, 3, 6, or 9 g RPFA per day. RPFA feeding was started from 50 ± 3 days in milk through 36 days post-timed AI. Pregnancy rate at first-AI was not significantly affected by RPFA supplementation. Comparisons of folic acid metabolism, one-carbon metabolism, and steroid hormone concentration in both blood plasma and follicular fluids were carried out between 3 g RPFA group and control. Cows supplemented with 3 g RPFA had greater plasma concentrations of folic acid, 5-methyltetrahydrofolate (5-MTHF), S-adenosylmethionine, and leucovorin, while reduced homocysteine and p-aminobenzoylglutamate. One-carbon metabolic analysis showed 3 g RPFA supply increased folinic acid and 5-MTHF concentrations in follicular fluids. Meanwhile, cows in 3 g RPFA group had elevated plasma estradiol concentration, while decreased androstenedione in both plasma and follicular fluids. Enhanced CYP19A1 gene expression in granulosa cells was examined when supplied with 50 μM folic acid in vitro. These findings indicated that the pregnancy rate at first-AI were not affected by short-term RPFA supplementation during the estrus synchronization period, it reduced plasma homocysteine levels without altering follicular fluid homocysteine concentrations. Additionally, RPFA supplementation was associated with changes in steroid hormone regulation, although further studies are needed to investigate the underlying mechanisms.

Expression patterns of folate metabolism-related enzymes in the bovine oviduct: estrous cycle-dependent modulation and responsiveness to folic acid

Folate metabolism is required for important biochemical processes that regulate cell functioning, but its role in female reproductive physiology in cattle during peri- and post-conceptional periods has not been thoroughly explored. Previous studies have shown the presence of folate in bovine oviductal fluid, as well as finely regulated gene expression of folate receptors and transporters in bovine oviduct epithelial cells (BOECs). Additionally, extracellular folic acid (FA) affects the transcriptional levels of genes important for the functioning of BOECs. However, it remains unknown whether the anatomical and cyclic features inherent to the oviduct affect regulation of folate metabolism. The present study aimed to characterize the gene expression pattern of folate cycle enzymes in BOECs from different anatomical regions during the estrous cycle and to determine the transcriptional response of these genes to increasing concentrations of exogenous FA. A first PCR screening showed the presence of transcripts encoding dihydrofolate reductase (DHFR), methylenetetrahydrofolate reductase (MTHFR), and methionine synthase (MTR) in bovine reproductive tissues (ovary, oviduct and uterus), with expression levels in oviductal tissues comparable to, or even higher than, those detected in ovarian and uterine tissues. Moreover, expression analysis through RT-qPCR in BOECs from the ampulla and isthmus during different stages of the estrous cycle demonstrated that folate metabolism-related enzymes exhibited cycle-dependent variations. In both anatomical regions, DHFR was upregulated during the preovulatory stage, while MTHFR and MTR exhibited increased expression levels during the postovulatory stage. Under in vitro culture conditions, ampullary and isthmic cells were cultured in the presence of 10, 50, and 100 μM FA for 24 h. Under these conditions, isthmus epithelial cells exhibited a unique transcriptional response to exogenous FA, showing a pronounced increase in MTR expression levels. Our results suggest that the expression of folate metabolism-related genes in BOECs is differentially regulated during the estrous cycle and may respond to exogenous levels of folate. This offers a new perspective on the transcriptional regulation of genes associated with the folate cycle in oviductal cells and provides groundwork for future studies on their functional and epigenetic implications within the oviductal microenvironment.

Impact of extracellular folic acid levels on oviductal gene expression

Folate plays a specific role as methyl donor for nucleotide synthesis and genomic methylation patterns, which in turn are important epigenetic determinants in gene expression. Previous studies have revealed the presence of folate in bovine oviductal fluid as well as the existence of a fine-tuned regulation of the gene expression of folate receptors and transporters in bovine oviduct epithelial cells (BOECs). However, the functional implications of folate in the oviduct remain unknown. The present study aimed to assess the effect of folic acid (FA) on expression levels of selected genes that potentially respond to the folate status in in vitro BOECs. To obtain an insight into the optimization of a culture system for assays, gene expression of folate receptors and transporters was compared between BOECs grown in monolayers and in suspension. The results showed that BOECs from isthmus and ampulla in suspension culture better preserved the region-dependent gene expression profile than in monolayers. Subsequently, BOECs from both anatomical regions were separately cultured in suspension for 24 h assaying different FA concentrations: I) TCM-199 (control); II) TCM-199 + 1 μM FA (similar to the oviduct concentration); III) TCM-199 + 10 μM FA and IV) TCM-199 + 100 μM FA. Expression analysis of genes related to important cellular processes including folate transport, DNA methylation, cell-cell interaction, antioxidant activity and signaling pathways was performed in BOECs using RT-qPCR. Our data demonstrated that addition of 1 μM FA did not affect mRNA levels of most genes analyzed. In contrast, BOECs cultured with 10 μM FA exhibited increased mRNA expression levels of genes involved in folate intake, DNA methylation and antioxidant protection. It is worth noting that at 100 μM FA, transcriptional response in BOECs mainly resulted in decreased mRNA levels of the majority of the genes assayed. Interestingly, cytotoxicity analysis showed a similar LDH activity in the culture media of the experimental groups, indicating that cell integrity was not affected by the FA concentrations assayed. In conclusion, our findings suggest that folate can affect BOECs, promoting changes in gene activity in a framework of functional readjustments in response to environmental conditions.