Monocarboxylate transporter 1 (MCT1) plays a direct role in short-chain fatty acids absorption in caprine rumen

Enhanced propionate and butyrate metabolism in cecal microbiota contributes to cold-stress adaptation in sheep

BACKGROUND

During cold stress, gut microbes play crucial roles in orchestrating energy metabolism to enhance environmental adaptation. In sheep, hindgut microbes ferment carbohydrates to generate short-chain fatty acids (SCFAs) as an energy source. However, the mechanisms by which hindgut microbes and their metabolites interact with the host to facilitate adaptation to cold environments remain ambiguous. Herein, we simulated a winter environment (- 20 °C) and provided a rationed diet to compare the cold adaptation mechanisms between Hulunbuir and Hu sheep.

RESULTS

Our findings show that cold exposure enhances SCFA metabolism in the sheep cecum. In Hu sheep, acetate, butyrate, and total SCFA concentrations increased, whereas in Hulunbuir sheep, propionate and butyrate concentrations increased, with a notable increase in total SCFAs. Notably, butyrate concentration was higher in Hulunbuir sheep than in Hu sheep under cold stress. Following cold exposure, the proinflammatory cytokine IL-1β levels increased in both breeds. In addition, Hu sheep showed increased IL-10, whereas Hulunbuir sheep exhibited elevated secretory IgA levels. The cecal microbiota responded differently, Hu sheep showed no notable changes in alpha and beta diversity, whereas Hulunbuir sheep exhibited considerable alterations. In Hu sheep, the abundance of fungi, specifically Blastocystis sp. subtype 4, decreased, and that of several Lachnospiraceae species (Roseburia hominis, Faecalicatena contorta, and Ruminococcus gnavus) involved in SCFA metabolism increased. Pathways related to carbohydrate metabolism, such as starch and sucrose metabolism, galactose metabolism, and pentose and glucuronate interconversions, were upregulated. In Hulunbuir sheep, the abundance of Treponema bryantii, Roseburia sp. 499, and Prevotella copri increased, with upregulation in pathways related to amino acid metabolism and energy metabolism. Cold exposure increased node connectivity within the symbiotic networks of both breeds, with increased network vulnerability in Hu sheep. Following cold exposure, the microbial community of Hulunbuir sheep showed a decrease in the influence of stochastic processes on community assembly, with a corresponding increase in the role of environmental selection. Conversely, no such shift was evident in Hu sheep. Further transcriptomic analysis revealed distinct regulatory mechanisms between breeds. In Hu sheep, protein synthesis, energy metabolism, and thermogenesis pathways were substantially upregulated. By contrast, Hulunbuir sheep showed considerable upregulation of immune pathways and energy conservation through reduced ribosome synthesis. Correlation analysis indicated that butyrate holds a central position in both networks, with Hulunbuir sheep exhibiting a more complex and tightly regulated network involving SCFAs, microbiota, microbial functions, and transcriptomes. Partial least squares path modeling revealed that cold exposure substantially altered the cecal microbiota and transcriptomes of Hulunbuir sheep, affecting SCFAs and cytokines.

CONCLUSIONS

The findings of this study suggest that under cold exposure, Hu sheep enhance acetate fermentation and rely on tissue thermogenesis for adaptation. By contrast, Hulunbuir sheep exhibit changes in microbial diversity and function, leading to increased propionate and butyrate metabolism. This may promote physiological energy conservation and innate immune defense, balancing heat loss and enhancing cold adaptation.

Effects of dietary energy levels on production and absorption of hindgut short-chain fatty acids in two sheep breeds

Hindgut fermentation is a crucial process in the production of short-chain fatty acids (SCFAs) and the provision of energy for ruminants. However, hindgut fermentation is not well-researched and has only recently received more attention. Tibetan sheep (T-sheep), an indigenous sheep breed raised on the Qinghai-Tibetan Plateau (QTP), play a vital role in the livelihood of the residents and in ecosystem services in the region. They have adapted well to the fluctuating supply of energy and nutrition under the harsh environment of the QTP. As part of the same study as the present study, T-sheep produced more ruminal SCFAs and had a greater capacity to absorb SCFAs than Small-tailed Han sheep (H-sheep), a breed introduced to the QTP due to their high reproductive rate. These findings raised intriguing questions about whether T-sheep also produce and absorb a greater amount of hindgut SCFAs to adapt to the harsh QTP environment, and whether there is a link between rumen and hindgut dietary digestion. Twenty-four T-sheep and 24 H-sheep, all 1.5-year-old wethers, were divided randomly into four groups of six sheep in each breed, and each group received a diet of different energy yield, namely, 8.21, 9.33, 10.45 or 11.57 MJ digestible energy (DE)/kg DM. After 49 days of treatment, all sheep were slaughtered, and tissues and digesta from the cecum, colon, and rectum were collected. The morphology of tissues was examined, and the concentrations of SCFAs in digesta and the expressions of related genes involved in the absorption and metabolism of SCFAs were determined. The concentration of total SCFAs and the molar proportion of butyrate increased in each site as the dietary energy level increased, and the H-sheep produced greater yields of total SCFAs in both the colon and rectum than T-sheep. This indicated a greater production of SCFAs in the hindgut of H-sheep than T-sheep, compensating for their lesser production in the rumen. T-sheep had a greater absorption surface area of the hindgut and greater mRNA expressions of SCFA transporters, indicating a greater capacity to absorb SCFAs than H-sheep. However, T-sheep had lesser mRNA expressions of the rate-limiting enzymes and regulators in SCFAs metabolism, indicating a lesser capacity for metabolism of SCFAs in the hindgut than H-sheep. These characteristics confer T-sheep with an advantage in the absorption and metabolism of SCFAs in the hindgut, enabling them to adapt rapidly to the highly fluctuating energy intake on the harsh QTP.

Circadian Rhythm Enhances mTORC1/AMPK Pathway-Mediated Milk Fat Synthesis in Dairy Cows via the Microbial Metabolite Acetic Acid

Livestock may respond differently to circadian rhythms, leading to differences in the composition of the animal products. Nevertheless, the circadian effects on rumen microorganisms and animal products are poorly understood. In the study, it was found that dairy cows exhibited increased milk fat levels, decreased acetic acid concentrations in the rumen fluid, and elevated acetic acid levels in the blood during the night compared to those of the day. Correlational analyses suggested a high association between Succiniclasticum, Lactobacillus, Prevotellacene NK3B31_group, Muribaculaceae_unclassified, etc., which were significantly enriched in rumen fluid at night, and milk fat levels. The differential metabolite Vitamin B6, significantly elevated at night, promoted the translocation of acetic acid into the circulation by increasing the level of rumen epithelial MCT1 protein expression. In addition, we found that both acetic acid treatment time and dose modulated the expression of lipid metabolism transcription factors (PPARγ, PPARα, and SREBP1c) and downstream genes (FASN, SCD1, ACCα, and CPT1A). Additionally, the mTORC1 and AMPK pathways were responsible for the effects of acetic acid on transcription factors and genes involved in lipid metabolism. Differences in rumen microbial taxa were observed between the day and night. Microbial metabolite (acetic acid) was found to be absorbed into the bloodstream and entered the mammary gland at night at a significantly elevated level. This regulation impacted the expression of lipid metabolism-related transcription factors (PPARγ, PPARα, and SREBP1c), as well as downstream genes through the mTORC1 and AMPK signaling pathways, ultimately affecting milk fat synthesis. These findings provide a new perspective for the microbial regulation of milk synthesis.

The Role of Short-Chain Fatty Acids in Myocardial Ischemia-Reperfusion Injury

PURPOSE OF REVIEW

This study aims to review the effects of short-chain fatty acids (SCFAs) in regulating the myocardial ischemia-reperfusion injury (MIRI).

RECENT FINDINGS

Coronary heart disease (CHD) is a well-known leading cause of death and disability worldwide. Cardiac substrate metabolism plays the determinant role in assessing the severity of heart injury due to the abruptly shifted energy production during the MIRI. Fatty acids are the main energy fuels for the heart, which are classified into long-, medium- and short chain fatty acids by the length of carbon chain. SCFAs are the main metabolites derived from the anaerobic bacterial fermentation of fiber-rich diets, which are shown to play a protective role in cerebrovascular disease previously. Meanwhile, accumulating evidences suggest that SCFAs can also play a crucial role in cardiac energy metabolism. Results of various studies revealed the cardioprotective effects of SCFAs by displaying anti-inflammatory and anti-ferroptotic function, connecting gut-brain neural circuit and regulating the intestinal flora.

2-[18F]Fluoropropionic Acid PET Imaging of Doxorubicin-induced Cardiotoxicity

Purpose

Treatment of pediatric cancers with doxorubicin is a common and predictable cause of cardiomyopathy. Early diagnosis of treatment-induced cardiotoxicity and intervention are major determinants for the prevention of advanced disease. The onset of cardiomyopathies is often accompanied by profound changes in lipid metabolism, including an enhanced uptake of short-chain fatty acids (SCFA). Therefore, we explored the utility of 2-[18F]fluoropropionic acid ([18F]FPA), an SCFA analog, as an imaging biomarker of cardiac injury in mice exposed to doxorubicin. Procedures: Cardiotoxicity and cardiac dysfunction were induced in mice by an 8-dose regimen of doxorubicin (cumulative dose 24 mg/kg) administered over 14 days. The effects of doxorubicin exposure were assessed by measurement of heart weights, left ventricular ejection fractions, and blood cardiac troponin levels. Whole body and cardiac [18F]FPA uptakes were determined by PET and tissue gamma counting in the presence or absence of AZD3965, a pharmacological inhibitor of monocarboxylate transporter 1 (MCT1). Radiation absorbed doses were estimated using tissue time-activity concentrations.

Results

Significantly higher cardiac [18F]FPA uptake was observed in doxorubicin-treated animals. This uptake remained constant from 30 min to 120 min post-injection. Pharmacological inhibition of MCT1-mediated transport by AZD3965 selectively decreased the uptake of [18F]FPA in tissues other than the heart. Co-administration of [18F]FPA and AZD3965 enhanced the imaging contrast of the diseased heart while reducing overall exposure to radioactivity.

Conclusions

[18F]FPA, especially when co-administered with AZD3965, is a new tool for imaging changes in fatty acid metabolism occurring in response to doxorubicin-induced cardiomyopathy by PET.

Unique rumen micromorphology and microbiota-metabolite interactions: features and strategies for Tibetan sheep adaptation to the plateau

The rumen microbiota-a symbiont to its host and consists of critical functional substances-plays a vital role in the animal body and represents a new perspective in the study of adaptive evolution in animals. This study used Slide Viewer slicing analysis system, gas chromatography, RT-qPCR and other technologies, as well as 16S and metabolomics determination methods, to measure and analyze the microstructure of rumen epithelium, rumen fermentation parameters, rumen transport genes, rumen microbiota and metabolites in Tibetan sheep and Hu sheep. The results indicate that the rumen nipple height and cuticle thickness of Tibetan sheep are significantly greater than those of Hu sheep (p < 0.01) and that the digestion and absorption of forage are greater. The levels of carbohydrate metabolism, lipid metabolism, and protein turnover were increased in Tibetan sheep, which enabled them to ferment efficiently, utilize forage, and absorb metabolic volatile fatty acids (VFAs). Tibetan sheep rumen metabolites are related to immune function and energy metabolism, which regulate rumen growth and development and gastrointestinal homeostasis. Thus, compared with Hu sheep, Tibetan sheep have more rumen papilla and cuticle corneum, and the synergistic effect of the microbiota and its metabolites is a characteristic and strategy for adapting to high-altitude environments.

Integrated multi-omics reveals the relationship between growth performance, rumen microbes and metabolic status of Hu sheep with different residual feed intakes

Residual feed intake (RFI) is a metric that provides a more accurate measure of feed efficiency. The lower the RFI, the higher the feed efficiency. The changes in the host microbiome and metabolome contribute to the greater feed efficiency of low RFI (LRFI) animals. The aim of this study was to explore the differences in rumen microorganisms, rumen metabolites and plasma metabolites of Hu sheep with differing RFI through the microbiome and metabolome. A total of 80 Hu sheep were used. The experiment consisted of a 15-d pretrial period and a 128-d experimental period. The RFI in the experimental period was calculated for all sheep, and the sheep were screened into high RFI (HRFI, n = 8) and LRFI (n = 8) groups. The HRFI and LRFI sheep did not differ in their initial and final body weights, average daily gain and body measurements, but the dry matter intake of LRFI sheep was significantly decreased (28.4%, P < 0.001). The sheep with LRFI had higher digestibility of crude protein (P = 0.010) and ether extract (P = 0.010) compared to HRFI group. The concentrations of acetate (P = 0.036), propionate (P = 0.010), valerate (P = 0.027) and total volatile fatty acids (P = 0.048) in rumen of LRFI group were higher compared to HRFI group. The results of 16S rDNA sequencing indicated that the sheep with LRFI had higher proportions of Prevotella genus in rumen liquid (P = 0.031). The rumen metabolome and plasma metabolome results showed that the citrate cycle, pyruvate metabolism and alanine, aspartate and glutamate metabolism processes were more active for sheep in LRFI group, which provided more energy substrate such as malic acid, oxoglutaric acid and citric acid. In conclusion, sheep with LRFI can utilize feed more efficiently, and the more active energy metabolism pathway and the production of energy substances may account for the higher feed efficiency.

Benefits of barley straw as a forage for dairy calves before and after weaning

The aim of this study was to assess the potential consequences on calf intake, performance, behavior, ruminal microbiome, and ruminal epithelium development of combining the inclusion of chopped barley straw and alfalfa hay during the pre- and postweaning periods keeping concentrate to forage ratio constant among dietary treatments. Forty-five Holstein calves (44 ± 5.7 kg of body weight [BW] and 3 ± 1.5 d of age) individually penned were blocked by BW and randomly assigned to a common pellet concentrate fed ad libitum along with one of following forage feeding strategies: barley straw before and after weaning (S-S), barley straw before and alfalfa hay after weaning (S-A), or alfalfa hay before and after weaning (A-A). All calves received the same milk replacer regimen. Forage was supplied in a separated bucket at the rate of 7.5% (preweaning) and 15% (postweaning) of total solid feed intake of the previous day. Feed intake and BW were recorded daily and weekly, respectively. Rumen samples were obtained via a stomach tube at 53, 66, and 87 d and were composite in 3 samples of 5 animals each for subsequent rumen microbiome analysis. A rumen epithelium sample was taken by endoscopy at 90 d to assess gene expression of OCLN, CLDN4, SLC9A1, SLC9A3, SLC16A1, SLC16A4, IL6, and TGFB1. Data were analyzed with a mixed-effects model accounting for the fixed effects of block, forage, week of study, and their interaction, and calf as a random effect. The type of forage fed did not affect concentrate feed, forage, or total DM intake before weaning. However, S-A and A-A calves consumed less concentrate feed and S-A calves grew at a lower rate after weaning than S-S calves. Expression of the gene coding for SLC16A1 in the rumen epithelium was greatest in S-S among treatments. Rumen microbiome did not differ among treatments, while the relative abundance of Acidaminococcus and Selenomas genera increased, while Alloprevotella, Bifidobaterium, Olsenella, and Succiclasticum genera decreased with age. In conclusion, feeding barley straw before and after weaning was more effective than feeding alfalfa hay in promoting concentrate feed intake after weaning and fostering an increase in the expression of SLC16A1 in the rumen epithelium.

Transcriptome profiling revealed that key rumen epithelium functions change in relation to short-chain fatty acids and rumen epithelium-attached microbiota during the weaning transition

This study aims to characterize the functional changes of the rumen epithelium associated with ruminal short-chain fatty acid (SCFA) concentration and epithelium-attached microbes during the weaning transition in dairy calves. Ruminal SCFA concentrations were determined, and transcriptome and microbiota profiling in biopsied rumen papillae were obtained from Holstein calves before and after weaning using RNA- and amplicon sequencing. Metabolic pathway analysis showed that pathways related to SCFA metabolism and cell apoptosis were up- and down-regulated postweaning, respectively. Functional analysis showed that genes related to SCFA absorption, metabolism, and protective roles against oxidative stress were positively correlated with ruminal SCFA concentrations. The relative abundance of epithelium-attached Rikenellaceae RC9 gut group and Campylobacter was positively correlated with genes involved in SCFA absorption and metabolism, suggesting that these microbes can cooperatively affect host functions. Future research should examine the contribution of attenuated apoptosis on rumen epithelial functional shifts during the weaning transition.

Revitalizing myocarditis treatment through gut microbiota modulation: unveiling a promising therapeutic avenue

Numerous studies have demonstrated that gut microbiota plays an important role in the development and treatment of different cardiovascular diseases, including hypertension, heart failure, myocardial infarction, arrhythmia, and atherosclerosis. Furthermore, evidence from recent studies has shown that gut microbiota contributes to the development of myocarditis. Myocarditis is an inflammatory disease that often results in myocardial damage. Myocarditis is a common cause of sudden cardiac death in young adults. The incidence of myocarditis and its associated dilated cardiomyopathy has been increasing yearly. Myocarditis has gained significant attention on social media due to its association with both COVID-19 and COVID-19 vaccinations. However, the current therapeutic options for myocarditis are limited. In addition, little is known about the potential therapeutic targets of myocarditis. In this study, we review (1) the evidence on the gut-heart axis, (2) the crosslink between gut microbiota and the immune system, (3) the association between myocarditis and the immune system, (4) the impact of gut microbiota and its metabolites on myocarditis, (5) current strategies for modulating gut microbiota, (6) challenges and future directions for targeted gut microbiota in the treatment of myocarditis. The approach of targeting the gut microbiota in myocarditis is still in its infancy, and this is the study to explore the gut microbiota-immune system-myocarditis axis. Our findings are expected to pave the way for the use of gut microbiota as a potential therapeutic target in the treatment of myocarditis.

Fatty Acid Sensing in the Gastrointestinal Tract of Rainbow Trout: Different to Mammalian Model?

It is well established in mammals that the gastrointestinal tract (GIT) senses the luminal presence of nutrients and responds to such information by releasing signaling molecules that ultimately regulate feeding. However, gut nutrient sensing mechanisms are poorly known in fish. This research characterized fatty acid (FA) sensing mechanisms in the GIT of a fish species with great interest in aquaculture: the rainbow trout (Oncorhynchus mykiss). Main results showed that: (i) the trout GIT has mRNAs encoding numerous key FA transporters characterized in mammals (FA transporter CD36 -FAT/CD36-, FA transport protein 4 -FATP4-, and monocarboxylate transporter isoform-1 -MCT-1-) and receptors (several free FA receptor -Ffar- isoforms, and G protein-coupled receptors 84 and 119 -Gpr84 and Gpr119-), and (ii) intragastrically-administered FAs differing in their length and degree of unsaturation (i.e., medium-chain (octanoate), long-chain (oleate), long-chain polyunsaturated (α-linolenate), and short-chain (butyrate) FAs) exert a differential modulation of the gastrointestinal abundance of mRNAs encoding the identified transporters and receptors and intracellular signaling elements, as well as gastrointestinal appetite-regulatory hormone mRNAs and proteins. Together, results from this study offer the first set of evidence supporting the existence of FA sensing mechanisms n the fish GIT. Additionally, we detected several differences in FA sensing mechanisms of rainbow trout vs. mammals, which may suggest evolutionary divergence between fish and mammals.

The interaction among gut microbes, the intestinal barrier and short chain fatty acids

The mammalian gut is inhabited by a massive and complicated microbial community, in which the host achieves a stable symbiotic environment through the interdependence, coordination, reciprocal constraints and participation in an immune response. The interaction between the host gut and the microbiota is essential for maintaining and achieving the homeostasis of the organism. Consequently, gut homeostasis is pivotal in safeguarding the growth and development and potential productive performance of the host. As metabolites of microorganisms, short chain fatty acids are not only the preferred energy metabolic feedstock for host intestinal epithelial cells, but also exert vital effects on antioxidants and the regulation of intestinal community homeostasis. Herein, we summarize the effects of intestinal microorganisms on the host gut and the mechanisms of action of short chain fatty acids on the four intestinal barriers of the organism, which will shed light on the manipulation of the intestinal community to achieve precise nutrition for specific individuals and provide a novel perspective for the prevention and treatment of diseases.

Normal Light-Dark and Short-Light Cycles Regulate Intestinal Inflammation, Circulating Short-chain Fatty Acids and Gut Microbiota in Period2 Gene Knockout Mice

Regular environmental light–dark (LD) cycle-regulated period circadian clock 2 (Per2) gene expression is essential for circadian oscillation, nutrient metabolism, and intestinal microbiota balance. Herein, we combined environmental LD cycles with Per2 gene knockout to investigate how LD cycles mediate Per2 expression to regulate colonic and cecal inflammatory and barrier functions, microbiome, and short-chain fatty acids (SCFAs) in the circulation. Mice were divided into knockout (KO) and wild type (CON) under normal light–dark cycle (NLD) and short-light (SL) cycle for 2 weeks after 4 weeks of adaptation. The concentrations of SCFAs in the serum and large intestine, the colonic and cecal epithelial circadian rhythm, SCFAs transporter, inflammatory and barrier-related genes, and Illumina 16S rRNA sequencing were measured after euthanasia during 10:00–12:00. KO decreased the feeding frequency at 0:00–2:00 but increased at 12:00–14:00 both under NLD and SL. KO upregulated the expression of Per1 and Rev-erbα in the colon and cecum, while it downregulated Clock and Bmal1. In terms of inflammatory and barrier functions, KO increased the expression of Tnf-α, Tlr2, and Nf-κb p65 in the colon and cecum, while it decreased Claudin and Occludin-1. KO decreased the concentrations of total SCFAs and acetate in the colon and cecum, but it increased butyrate, while it had no impact on SCFAs in the serum. KO increased the SCFAs transporter because of the upregulation of Nhe1, Nhe3, and Mct4. Sequencing data revealed that KO improved bacteria α-diversity and increased Lachnospiraceae and Ruminococcaceae abundance, while it downregulated Erysipelatoclostridium, Prevotellaceae UCG_001, Olsenella, and Christensenellaceae R-7 under NLD in KO mice. Most of the differential bacterial genus were enriched in amino acid and carbohydrate metabolism pathways. Overall, Per2 knockout altered circadian oscillation in the large intestine, KO improved intestinal microbiota diversity, the increase in Clostridiales abundance led to the reduction in SCFAs in the circulation, concentrations of total SCFAs and acetate decreased, while butyrate increased and SCFAs transport was enhanced. These alterations may potentially lead to inflammation of the large intestine. Short-light treatment had minor impact on intestinal microbiome and metabolism.

Lactate-related metabolic reprogramming and immune regulation in colorectal cancer

Changes in cellular metabolism involving fuel sources are well-known mechanisms of cancer cell differentiation in the context of carcinogenesis. Metabolic reprogramming is regulated by oncogenic signaling and transcriptional networks and has been identified as an essential component of malignant transformation. Hypoxic and acidified tumor microenvironment contributes mainly to the production of glycolytic products known as lactate. Mounting evidence suggests that lactate in the tumor microenvironment of colorectal cancer(CRC) contributes to cancer therapeutic resistance and metastasis. The contents related to the regulatory effects of lactate on metabolism, immune response, and intercellular communication in the tumor microenvironment of CRC are also constantly updated. Here we summarize the latest studies about the pleiotropic effects of lactate in CRC and the clinical value of targeting lactate metabolism as treatment. Different effects of lactate on various immune cell types, microenvironment characteristics, and pathophysiological processes have also emerged. Potential specific therapeutic targeting of CRC lactate metabolism is also discussed. With increased knowledge, effective druggable targets might be identified, with the aim of improving treatment outcomes by reducing chemoresistance.

Effects of body condition at far-off dry period on blood biochemistry, liver triacylglycerol and muscular monocarboxylate transporter-1 mRNA expression in tropical Holstein dairy cows during peripartum period

Effects of body condition score (BCS) at far-off dry period on blood biochemistry, liver triacylglycerol, and muscular monocarboxylate transporter-1 mRNA expression in tropical Holstein dairy cows during peripartum period were studied. Eight dry cows were divided into two groups of four cows based on their BCS at 8 weeks prepartum: high BCS (HBS) and low BCS (LBS). Blood samples were collected weekly from 8 weeks before expected calving date until 8 weeks postpartum for determination of serum glucose, non-esterified fatty acid (NEFA), and β-hydroxybutyrate (BHBA). Muscle and liver samples were biopsied at 2 weeks before expected calving date and at 2 weeks postpartum for determination of muscular monocarboxylate transporter-1 (MCT-1) mRNA expression and liver triacylglycerol concentrations. Decreased BCS and elevated serum NEFA and BHBA indicated that LBS cows entered to the NEB period earlier than did HBS cows. LBS cows showed lower liver TAG and higher muscular MCT-1 mRNA expression than did HBS cows. The MCT-1 mRNA expression at 2 weeks prepartum was negatively correlated with BCSs at 2-3 weeks prepartum and at 1-2 weeks postpartum. In conclusion, LBS cows most likely adapted to NEB by upregulation of muscular MCT-1 expression and had lower NEB consequences during postpartum period.

Effects of weaning on regulators of volatile fatty acid absorption and intracellular pH in Holstein calves

This study examined the effects of changes in rumen fermentation during the weaning transition on abundance of transporters involved in volatile fatty acid (VFA) absorption or intracellular pH homeostasis. Holstein bull calves (n = 27) were assigned to 1 of 3 treatment groups in a randomized, complete block design: 2 preweaning groups [animals fed milk only (PRE-M) or milk, calf starter, and hay (PRE-S)] and 1 postweaning group (animals fed milk, starter, and hay with a 2-wk weaning transition; POST-S). Calves were euthanized at 42 d of age (PRE-M and PRE-S) or at 63 d of age (POST-S), and rumen epithelium and rumen fluid samples were collected. Rumen fluid was analyzed for VFA concentration, and rumen epithelium was analyzed for the abundance of VFA transporter monocarboxylate transporter isoform 1 (MCT1) and the intracellular pH regulators sodium bicarbonate co-transporter 1 (NBC1) and sodium-proton exchanger 3 (NHE3) protein. Preweaning, total VFA concentrations tended to increase and NBC1 abundance increased with starter intake. Between pre- and postweaning, total VFA concentrations increased but NHE3 protein abundance decreased. In calves, rumen epithelial development during the weaning transition appears to show more pronounced changes in intracellular pH homeostasis than in VFA transport capacity.

Relative bioavailability of 3 rumen-undegradable methionine sources in dairy cows using the area under the curve technique

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Plasma kinetics of 3 sources of metabolizable Met were tested.

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The two 2-hydroxy-4-(methylthio)butanoic isopropyl ester products (Kessent, Kemin Animal Nutrition and Health, KES; Metasmart, Adisseo SAS, MtS) had a similar pattern.

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Smartamine (Adisseo SAS, SmT) peaked later and had a greater area under the curve.

The objective of this study was to evaluate the relative bioavailability of two 2-hydroxy-4-(methylthio)butanoic isopropyl esters (HMBi) obtained through different production processes and an encapsulated rumen-protected Met using the area under the curve (AUC) method. The new HMBi product (Kessent MF Liquid, Kemin Animal Nutrition and Health) was compared with an existing HMBi product (Metasmart, Adisseo SAS) and a pH-sensitive coated Met (Smartamine, Adisseo SAS). Nine multiparous lactating cows (30 kg of milk/d and 227 d in milk) fed a 45:55 forage:concentrate diet were randomly assigned within square to a triplicate 3 × 3 Latin square design. Each period consisted of a 3-d sampling period and a 3-d washout period. Treatments were dosed on d 1 of each period, and blood samples were collected from the coccygeal vein at 0, 1, 2, 3, 4, 6, 9, 12, 24, 30, and 48 h thereafter. The daily dose was 50 g of Met equivalent of each treatment. The HMBi treatments were administered directly into the cow's mouth, whereas Smartamine was fed mixed with 0.5 kg of concentrate and fully consumed within 15 min. Nonlinear models were fitted to raw data, and the basal concentration at time 0 h, time at peak (Tmax), concentration at peak, and AUC of plasma Met were determined. The Met basal concentration at t = 0 h (26.7 ± 7.67 µM) and concentration at peak (210 ± 22.2 µM) were similar among treatments, but the Tmax (11.3 vs. 1.4 h) was delayed and the AUC was 1.8-fold larger (3,457 vs. 1,868 arbitrary units) in Smartamine compared with HMBi. Results of this study indicate that the 2 HMBi products have similar plasma kinetics and bioavailability. Smartamine had different kinetics compared with HMBi products, with delayed Tmax and larger AUC and relative bioavailability.

Diet Transition from High-Forage to High-Concentrate Alters Rumen Bacterial Community Composition, Epithelial Transcriptomes and Ruminal Fermentation Parameters in Dairy Cows

Effects of changing diet on rumen fermentation parameters, bacterial community composition, and transcriptome profiles were determined in three rumen-cannulated Holstein Friesian cows using a 3 × 4 cross-over design. Treatments include HF-1 (first high-forage diet), HC-1 (first high-concentrate diet), HC-2 (succeeding high-concentrate diet), and HF-2 (second high-forage diet as a recovery period). Animal diets contained Klein grass and concentrate at ratios of 8:2, 2:8, 2:8, and 8:2 (two weeks each), respectively. Ammonia-nitrogen and individual and total volatile fatty acid concentrations were increased significantly during HC-1 and HC-2. Rumen species richness significantly increased for HF-1 and HF-2. Bacteroidetes were dominant for all treatments, while phylum Firmicutes significantly increased during the HC period. Prevotella, Erysipelothrix, and Galbibacter significantly differed between HF and HC diet periods. Ruminococcus abundance was lower during HF feeding and tended to increase during successive HC feeding periods. Prevotellaruminicola was the predominant species for all diets. The RNA sequence analysis revealed the keratin gene as differentially expressed during the HF diet, while carbonic-anhydrase I and S100 calcium-binding protein were expressed in the HC diet. Most of these genes were highly expressed for HC-1 and HC-2. These results suggested that ruminal bacterial community composition, transcriptome profile, and rumen fermentation characteristics were altered by the diet transitions in dairy cows.

Forestomach developmental failure in an 11-month-old Japanese Black steer with severely retarded growth and chronic ruminal tympany

This study reports findings from the pathological examination of the forestomach of an 11-month-old Japanese Black steer with severely retarded growth (41% of expected weight) and chronic ruminal tympany. The ruminal papillae were weakly formed (0.3–0.5 cm long) and unevenly distributed. The cellulae and cristae reticuli were underdeveloped; the cristae were 0.4–0.7 cm in height and milky white. The keratinized layer in the stratified squamous epithelium was thickened. Ruminal pH was 5.25, and ruminal volatile fatty acid concentration was 11.7 mM. The steer’s severely retarded growth was considered to be caused by malnutrition due to developmental and functional failure of the forestomach.

The effects of tributyrin supplementation on weight gain and intestinal gene expression in broiler chickens during Eimeria maxima-induced coccidiosis

Butyrate is a feed additive that has been shown to have antibacterial properties and improve gut health in broilers. Here, we examined the performance and gene expression changes in the ileum of tributyrin–supplemented broilers infected with coccidia. Ninety-six, Ross 708 broilers were fed either a control corn–soybean–based diet (−BE) or a diet supplemented with 0.25% (w/w) tributyrin (+BE). Birds were further divided into groups that were inoculated with Eimeria maxima oocysts (EM) or sham-inoculated (C) on day 21 posthatch. At 7 d postinfection (7 d PI), the peak of pathology in E. maxima infection, tributyrin-supplemented birds had significantly improved feed conversion ratios (FCR, P < 0.05) and body weight gain (BWG, P < 0.05) compared with -BE-infected birds, despite both groups having similar feed intake (FI, P > 0.05). However, at 10 d post-infection (10 d PI) no significant effects of feed type or infection were observed. Gene expression in the ileum was examined for insights into possible effects of infection and tributyrin supplementation on genes encoding proteins related to immunity, digestion, and gut barrier integrity. Among immune-related genes examined, IL-1B and LEAP2 were only significantly affected at 7 d PI. Transcription of genes related to digestion (APN, MCT1, FABP2, and MUC2) were primarily influenced by infection at 7 d PI and tributyrin supplementation (FABP2 and MUC2) at 10 d PI. With exception of ZO1, tight junction genes were affected by either infection or feed type at 7 d PI. At 10 d PI, only CLDN1 was not affected by either infection or feed type. Overall tributyrin shows promise as a supplement to improve performance during coccidiosis in broiler chickens; however, its effect on gene expression and mode of action requires further research.

The role of short-chain fatty acids in immunity, inflammation and metabolism

Short-chain fatty acids (SCFAs) are carboxylic acids with carbon atom numbers less than 6, which are important metabolites of gut microbiome. Existing research shows that SCFAs play a vital role in the health and disease of the host. First, SCFAs are the key energy source for colon and ileum cells, and affect the intestinal epithelial barrier and defense functions by regulating related gene expression. Second, SCFAs regulate the function of innate immune cells to participate in the immune system, such as macrophages, neutrophils and dendritic cells. Third, SCFAs can also regulate the differentiation of T cells and B cells and the antigen-specific adaptive immunity mediated by them. Besides, SCFAs are raw materials for sugar and lipid synthesis, which provides a theoretical basis for studying the potential role of SCFAs in regulating energy homeostasis and metabolism. There are also studies showing that SCFAs inhibit tumor cell proliferation and promote apoptosis. In this article, we summarized in detail the role of SCFAs in immunity, inflammation and metabolism, and briefly introduced the role of SCFAs in tumor cell survival. It provides a systematic theoretical basis for the study of SCFAs as potential drugs to promote human health.

Butyrate Permeation across the Isolated Ovine Reticulum Epithelium

Simple Summary

Short-chain fatty acids are the main source of energy for ruminants. The effective uptake of these substrates from the forestomach is a prerequisite for the health and performance of these animals. Thus far, the mechanisms of uptake have been investigated almost exclusively in the epithelium of the largest forestomach section, the rumen. Previous research suggests that the reticulum is also involved in the uptake of short-chain fatty acids, but the mechanisms involved have not been studied and may differ from those known from the rumen epithelium due to the different milieu in this compartment. To investigate this, ovine reticulum epithelium was mounted in Ussing chambers, and the transport of radiolabeled butyrate (as a representative of short-chain fatty acids) across the tissue was measured with and without the addition of inhibitors of particular transport proteins. Our results show that butyrate can be taken up effectively across the reticulum epithelium via pathways that are energized by the Na⁺/K⁺-ATPase and may involve monocarboxylate transporters, sodium-proton exchangers, and anion channels. However, our results are not completely congruent to those obtained in the rumen epithelium. These modifications could assure the effective uptake of short-chain fatty acids from the reticulum lumen under the particular conditions (p. e. high pH) of this forestomach compartment.

Abstract

We hypothesized that, due to the high pH of this compartment, the reticulum epithelium displays particular features in the transport of short-chain fatty acids (SCFA). Ovine reticulum epithelium was incubated in Ussing chambers using a bicarbonate-free buffer solution containing butyrate (20 mmol L⁻¹). p-hydroxymercuribenzoic acid (pHMB), 5-(N-Ethyl-N-isopropyl)amiloride (EIPA), or ouabain were added to the buffer solution as inhibitors of monocarboxylate transporters, sodium-proton-exchangers, or the Na⁺/K⁺-ATPase, respectively. The short-circuit current (I_sc) and transepithelial conductance (G_t) were monitored continuously while the flux rates of ¹⁴C-labelled butyrate were measured in the mucosal-to-serosal (J_ms^but) or serosal-to-mucosal direction (J_sm^but). Under control conditions, the mean values of I_sc and G_t amounted to 2.54 ± 0.46 µEq cm⁻² h⁻¹ and 6.02 ± 3.3 mS cm⁻², respectively. J_ms^but was 2.1 ± 1.01 µmol cm⁻² h⁻¹ on average and about twice as high as J_sm^but. Incubation with ouabain reduced J_ms^but, while J_sm^but was not affected. The serosal addition of EIPA did not affect J_ms^but but reduced J_sm^but by about 10%. The addition of pHMB to the mucosal or serosal solution reduced J_ms^but but had no effect on J_sm^but. Mucosally applied pHMB provoked a transient increase in the I_sc. The serosal pHMB sharply reduced I_sc. Our results demonstrate that butyrate can be effectively transported across the reticulum epithelium. The mechanisms involved in this absorption differ from those known from the rumen epithelium.

Ruminal epithelial cell proliferation and short-chain fatty acid transporters in vitro are associated with abundance of period circadian regulator 2 (PER2)

The major circadian clock gene PER2 is closely related to cell proliferation and lipid metabolism in various nonruminant cell types. Objectives of the study were to evaluate circadian clock-related mRNA abundance in cultured goat ruminal epithelial cells (REC), and to determine effects of PER2 on cell proliferation and mRNA abundance of short-chain fatty acid (SCFA) transporters, genes associated with lipid metabolism, cell proliferation, and apoptosis. Ruminal epithelial cells were isolated from weaned Boer goats (n = 3; 2 mo old; ∼10 kg of body weight) by serial trypsin digestion and cultured at 37°C for 24 h. Abundance of CLOCK and PER2 proteins in cells was determined by immunofluorescence. The role of PER2 was assessed through the use of a knockout model with short interfering RNA, and sodium butyrate (15 mM) was used to assess the effect of upregulating PER2. Both CLOCK and PER2 were expressed in REC in vitro. Sodium butyrate stimulation increased mRNA and protein abundance of PER2 and PER3. Furthermore, PER2 gene silencing enhanced cell proliferation and reduced cellular apoptosis in isolated REC. In contrast, PER2 overexpression in response to sodium butyrate led to lower cellular proliferation and ratio of cells in the S phase along with greater ratio of cells in the G₂/M phase. Those responses were accompanied by downregulated mRNA abundance of CCND1, CCNB1, CDK1, and CDK2. Among the SCFA transporters, PER2 silencing upregulated mRNA abundance of MCT1 and MCT4. However, it downregulated mRNA abundance of PPARA and PPARG. Overexpression of PER2 resulted in lower mRNA abundance of MCT1 and MCT4, and greater PPARA abundance. Overall, data suggest that CLOCK and PER2 might play a role in the control of cell proliferation, SCFA, and lipid metabolism. Further studies should be conducted to evaluate potential mechanistic relationships between circadian clock and SCFA absorption in vivo.

The Role of Diet Related Short-Chain Fatty Acids in Colorectal Cancer Metabolism and Survival: Prevention and Therapeutic Implications

Colorectal Cancer (CRC) is a major cause of cancer-related death worldwide. CRC increased risk has been associated with alterations in the intestinal microbiota, with decreased production of Short Chain Fatty Acids (SCFAs). SCFAs produced in the human colon are the major products of bacterial fermentation of undigested dietary fiber and starch. While colonocytes use the three major SCFAs, namely acetate, propionate and butyrate, as energy sources, transformed CRC cells primarily undergo aerobic glycolysis. Compared to normal colonocytes, CRC cells exhibit increased sensitivity to SCFAs, thus indicating they play an important role in cell homeostasis. Manipulation of SCFA levels in the intestine, through changes in microbiota, has therefore emerged as a potential preventive/therapeutic strategy for CRC. Interest in understanding SCFAs mechanism of action in CRC cells has increased in the last years. Several SCFA transporters like SMCT-1, MCT-1 and aquaporins have been identified as the main transmembrane transporters in intestinal cells. Recently, it was shown that acetate promotes plasma membrane re-localization of MCT-1 and triggers changes in the glucose metabolism. SCFAs induce apoptotic cell death in CRC cells, and further mechanisms have been discovered, including the involvement of lysosomal membrane permeabilization, associated with mitochondria dysfunction and degradation. In this review, we will discuss the current knowledge on the transport of SCFAs by CRC cells and their effects on CRC metabolism and survival. The impact of increasing SCFA production by manipulation of colon microbiota on the prevention/therapy of CRC will also be addressed.

Establishment and identification of primary bovine omasal epithelial cells

The establishment and culture of bovine omasal epithelial cells (BOECs) in vitro is a valuable tool for the study of the physiological function, nutrient absorption, and transport mechanisms of the omasum in dairy cows. This paper proposes a method for the culture of primary BOECs. Trypsin digestion was used to subculture the BOECs, which were passaged for 20 generations in vitro, and showed typical epithelial-like characteristics and a cobblestone morphology. The primary BOECs had a fast growth phase (between days 4 and 5) and were validated by their slight β-galactosidase and visible cytokerat in 18 expression. In addition, RT-PCR results demonstrated that the monocarboxylate transporter 1 (MCT1), Na+/H+exchanger 1 (NHE1), and Na+/H+ exchanger 3 (NHE3) were expressed in the isolated primary BOECs. In conclusion, this primary BOEC isolation and culture model is a promising method for the study of nutrient absorption and regulation, as well as the immune regulation of epithelial cell transport in vitro.

Acetate Promotes T Cell Effector Function during Glucose Restriction

Competition for nutrients like glucose can metabolically restrict T cells and contribute to their hyporesponsiveness during cancer. Metabolic adaptation to the surrounding microenvironment is therefore key for maintaining appropriate cell function. For instance, cancer cells use acetate as a substrate alternative to glucose to fuel metabolism and growth. Here, we show that acetate rescues effector function in glucose-restricted CD8⁺ T cells. Mechanistically, acetate promotes histone acetylation and chromatin accessibility and enhances IFN-γ gene transcription and cytokine production in an acetyl-CoA synthetase (ACSS)-dependent manner. Ex vivo acetate treatment increases IFN-γ production by exhausted T cells, whereas reducing ACSS expression in T cells impairs IFN-γ production by tumor-infiltrating lymphocytes and tumor clearance. Thus, hyporesponsive T cells can be epigenetically remodeled and reactivated by acetate, suggesting that pathways regulating the use of substrates alternative to glucose could be therapeutically targeted to promote T cell function during cancer.

Ruminal epithelium: a checkpoint for cattle health

The reticulorumen, as the main fermentation site of ruminants, delivers energy in the form of short-chain fatty acids (SCFA) for both the animal as well as the ruminal wall. By absorbing these SCFA, the ruminal epithelium plays a major role in the maintenance of intraruminal and intraepithelial acid-base homoeostasis as well as the balance of osmolarity. It takes up SCFA via several pathways which additionally lead to either a reduction of protons in the ruminal lumen or the secretion of bicarbonate, ultimately buffering the ruminal content effectively. Nutrition of the epithelium itself is achieved by catabolism of the SCFA, especially butyrate. Catabolism of SCFA also helps to maintain a concentration gradient across the epithelium to ensure efficient SCFA uptake and stability of the epithelial osmolarity. Furthermore, the ruminal epithelium forms a tight barrier against pathogens, endotoxins or biogenic amines, which may emerge from ruminal microorganisms and feed. Under physiological conditions, it reduces toxin uptake to a minimum. Moreover, the epithelium seems to have the ability to degrade biogenic amines like histamine. Nonetheless, in high performance production animals like dairy cattle, the reticulorumen is confronted with large amounts of rapidly fermentable carbohydrates. This may push the epithelium to its limits, even though it possesses a great capacity to adapt to varying feeding conditions. If the epithelial limit is exceeded, increasing amounts of SCFA lead to an acidotic imbalance that provokes epithelial damage and thereby elevates the entrance of pathogens and other potentially harmful substances into the animal's body. Hence, the ruminal epithelium lays the foundation for the animal's health, and in order to ensure longevity and high performance of ruminant farm animals, it should never be overburdened.

Possible influence of free fatty acid receptors on pH regulation in the ruminal epithelium of sheep

High amounts of short-chain fatty acids (SCFAs) occur in the ovine rumen and constitute the animal's main energy source. However, they lead to an acidification of the ruminal epithelium. Therefore, effective intracellular pH (pH_i ) regulation by transport proteins like monocarboxylate transporter 1 (MCT1) and Na⁺ /H⁺ exchangers (NHEs) is pivotal to ruminants to avoid epithelial damage. SCFAs might function not only as nutrients but also as signalling molecules by activating free fatty acid receptors (FFARs) in the ruminal epithelium and thus influence pH_i regulation. FFARs work as nutrient sensors, transducing their information by modulating cyclic adenosine monophosphate (cAMP) levels. We hypothesized that (FFAR-modulated) decreases in cAMP levels stimulate the activity of MCT1 and NHEs in the ruminal epithelium of sheep. We detected two FFARs (GPR109A and FFAR2) immunohistochemically in the ovine ruminal epithelium. Administration of 10 mM butyrate to Ussing chamber-mounted epithelia provoked a significant reduction in intraepithelial cAMP levels. However, application of the GPR109A agonist niacin did not affect cAMP levels. MCT1 activity was analysed by measuring transepithelial ¹⁴ C-acetate fluxes, which were not inhibited by forskolin-induced increased cAMP levels. The recovery of pH_i after acidification was assessed as an indicator of NHE activity in primary cultured ruminal epithelial cells. Recovery was significantly reduced when cells with increased cAMP levels were subjected to the NHE inhibitor 5-(N-ethyl-N-isopropyl)-amiloride (10 µM). Nonetheless, with augmented cAMP levels alone, NHE activity tended to decline. We hypothesize that modulation of cAMP levels by butyrate is accomplished by FFAR2 activation, regulating NHE activity for pH_i homoeostasis at least in part.

Review: How Forage Feeding Early in Life Influences the Growth Rate, Ruminal Environment, and the Establishment of Feeding Behavior in Pre-Weaned Calves

Simple Summary

Under natural grazing systems, calves are likely to consume forage in early life. However, forage inclusion in the diet of pre-weaned calves has long been a controversial issue due to it possibly being associated with negative calf performance. Recent published literature seems to confound previous research. This review aims to understand the factors that may influence forage inclusion in the ration of pre-weaned calves. We have explored research related to the effect of feeding forage on rumen and behavioral development to better understand whether forage should be fed to the young calf. Based on the findings, it is concluded that a small amount of good quality forage is recommended for calves to improve their behavioral expression and rumen environment, which may further improve calf performance.

Abstract

The provision of forage to pre-weaned calves has been continuously researched and discussed by scientists, though results associated with calf growth and performance have remained inconsistent. Multiple factors, including forage type, intake level, physical form, and feeding method of both solid and liquid feed, can influence the outcomes of forage inclusion on calf performance. In the current review, we summarized published literature in order to get a comprehensive understanding of how early forage inclusion in diets affects calf growth performance, rumen fermentation, microbiota composition, and the development of feeding behavior. A small amount of good quality forage, such as alfalfa hay, supplemented in the diet, is likely to improve calf feed intake and growth rate. Provision of forage early in life may result in greater chewing (eating and ruminating) activity. Moreover, forage supplementation decreases non-nutritive oral and feed sorting behaviors, which can help to maintain rumen fluid pH and increase the number of cellulolytic bacteria in the rumen. This review argues that forage provision early in life has the potential to affect the rumen environment and the development of feeding behavior in dairy calves. Continued research is required to further understand the long-term effects of forage supplementation in pre-weaned calves, because animal-related factors, such as feed selection and sorting, early in life may persist until later in adult life.

Tibetan sheep have a high capacity to absorb and to regulate metabolism of SCFA in the rumen epithelium to adapt to low energy intake

The nutritional intake of Tibetan sheep on the harsh Qinghai-Tibetan Plateau is often under maintenance requirements, especially during the long, cold winter. However, they have adapted well and even thrive under these conditions. The aim of the present study was to gain insight into how the rumen epithelium of Tibetan sheep has adapted to the consumption of low-energy-level diets. For this purpose, we compared Tibetan and small-tailed Han sheep (n 24 of each breed, all wethers and 1·5 years of age), which were divided randomly into one of four groups and offered ad libitum diets of different digestible energy (DE) densities: 8·21, 9·33, 10·45 and 11·57 MJ DE/kg DM. The Tibetan sheep had higher rumen concentrations of total SCFA, acetate, butyrate and iso-acids but lower concentrations of propionate than small-tailed Han sheep. The Tibetan sheep had higher absorption capability of SCFA due to the greater absorption surface area and higher mRNA expression of the SCFA absorption relative genes than small-tailed Han sheep. For the metabolism of SCFA in the rumen epithelium, the small-tailed Han sheep showed higher utilisation of the ketogenesis pathway than Tibetan sheep; however, Tibetan sheep had greater regulation capacity in SCFA metabolism pathways. These differences between breeds allowed the Tibetan sheep to have greater capability of absorbing SCFA and better capacity to regulate the metabolism of SCFA, which would allow them to cope with low energy intake better than small-tailed Han sheep.

Characterization and Proteomic-Transcriptomic Investigation of Monocarboxylate Transporter 6 Knockout Mice: Evidence of a Potential Role in Glucose and Lipid Metabolism

Monocarboxylate transporter 6 [(MCT6), SLC16A5] is an orphan transporter with no known endogenous substrates or physiological role. Previous in vitro and in vivo experiments investigated MCT6 substrate/inhibitor specificity in Xenopus laevis oocytes; however, these data remain limited. Transcriptomic changes in the livers of mice undergoing different dieting schemes have suggested that Mct6 plays a role in glucose and lipid metabolism. The objectives of this study were 1) to develop a novel knockout (KO) mouse model (Mct6-/-) using CRISPR/Cas9 technology, 2) to characterize the KO animal model by examining physiological and biochemical parameters, and 3) to understand the physiological role of MCT6 in vivo through global proteomic and liver transcriptomic profiling. mRNA tissue analysis demonstrated knockout of Mct6, which showed greater than 90% knockdown of Mct6 (Slc16a5) gene expression in all major tissues analyzed when normalized to Mct6+/+ mice. Proteomic analyses identified greater than 4000 unique proteins in kidney, liver, and colon tissues, among which 51, 38, and 241 proteins were significantly altered, respectively (for each tissue), between Mct6+/+ and Mct6-/- mice. Additionally, Mct6-/- mice demonstrated significant changes in 199 genes in the liver compared with Mct6+/+ mice. In silico biological pathway analyses revealed significant changes in proteins and genes involved in glucose and lipid metabolism-associated pathways. This study is the first to provide evidence for an association of Mct6 in the regulation of glucose and lipid metabolism. SIGNIFICANCE STATEMENT: This paper focuses on elucidating the innate biological role of an orphan transporter in vivo, which has not been investigated thus far. Using efficient and high-throughput technologies, such as CRISPR/Cas9 gene editing, liquid chromatography-tandem mass spectrometry-based proteomic and RNA-sequencing transcriptomic analyses, our laboratory provides the first existence and characterization of a Mct6 knockout mouse model. The evidence gathered in this paper, as well as other laboratories, support the importance of MCT6 in regulating a variety of glucose and lipid metabolic pathways, which may indicate its significance in metabolic diseases.

Short-Chain Fatty Acids Regulate the Immune Responses via G Protein-Coupled Receptor 41 in Bovine Rumen Epithelial Cells

The rumen immune system often suffers when challenging antigens from lysis of dead microbiota cells in the rumen. However, the rumen epithelium innate immune system can actively respond to the infection. Previous studies have demonstrated G protein-coupled receptors 41 (GPR41) as receptors for short chain fatty acids (SCFAs) in human. We hypothesized that SCFAs, the most abundant microbial metabolites in rumen, may regulate the immune responses by GPR41 in bovine rumen epithelial cells (BRECs). Therefore, the objective of study was to firstly establish an immortal BRECs line and investigate the regulatory effects of SCFAs and GPR41 on innate immunity responses in BRECs. These results showed that long-term BRECs cultures were established by SV40T-induced immortalization. The concentrations of 20 mM SCFAs significantly enhanced the levels of GPR41, IL1β, TNFα, chemokines, and immune barrier genes by transcriptome analysis. Consistent with transcriptome results, the expression of GPR41, IL1β, TNFα, and chemokines were markedly upregulated in BRECs treated with 20 mM SCFAs by qRT-PCR compared with control BRECs. Remarkably, the GPR41 knockdown (GPR41KD) BRECs treated with 20 mM SCFAs significantly enhanced the proinflammatory cytokines IL1β and TNFα expression compared with wild type BRECs treated with 20 mM SCFAs, but reduced the expression of CCL20, CXCL2, CXCL3, CXCL5, CXCL8, CXCL14, Occludin, and ZO-1. Moreover, GPR41 mRNA expression is positively correlated with CCL20, CXCL2, CXCL3, CXCL8, CXCL14, and ZO-1. These findings revealed that SCFAs regulate GPR41-mediated levels of genes involved in immune cell recruitment and epithelial immune barrier and thereby mediate protective innate immunity in BRECs.

MicroRNA Sequencing Reveals the Effect of Different Levels of Non-Fibrous Carbohydrate/Neutral Detergent Fiber on Rumen Development in Calves

Rumen development in calves is affected by many factors, including dietary composition. MicroRNAs (miRNAs) are known to function in the development of the rumen in cattle, what is not known is how these miRNAs function in rumen development of calves fed with high and low ratios of non-fibrous carbohydrate (NFC)/neutral detergent fiber (NDF). A total of six healthy Charolais hybrids bull calves of similar weight were divided into two groups; three calves were fed a mixed diet with NFC/NDF = 1.35 (H group), and three were fed a mixed diet with NFC/NDF = 0.80 (L group). After 105 days on the diet, calves were sacrificed and rumen tissues were collected. Tissues were subjected to histological observation and miRNA expression analysis. Functional enrichment analysis was conducted on the target genes of the miRNAs. Targeting and regulatory relationships were verified by luciferase reporter assay and quantitative PCR (qPCR). We found that the length of rumen papilla in the L group was significantly greater than that in the H group, while the width of rumen papilla in H group was significantly greater than that that in L group. We identified 896 miRNAs; 540 known miRNAs, and 356 novel predicted miRNAs. After statistical testing, we identified 24 differentially expressed miRNAs (DEmiRNAs). miRNA-mRNA-cluster network analysis and literature reviews revealed that cell proliferation, differentiation, physical and nutrient stimuli processes participate in rumen development under different NFC/NDF levels. The regulatory relationships between three DEmiRNAs and five target genes were verified by examining the levels of expression. The binding sites on bta-miR-128 for the peroxisome proliferator activated receptor gamma (PPARG) and solute carrier family 16 member 1 (SLC16A1) genes were investigated using a dual luciferase assay. The results of this study provide insight into the role of miRNAs in rumen development in calves under different NFC/NDF levels.

Effect of exogenous butyrate on the gastrointestinal tract of sheep. I. Structure and function of the rumen, omasum, and abomasum

The aim of this study was to determine the effect of exogenous butyrate on the structure and selected functions of the stomach in sheep. Eighteen rams (30.8 ± 2.1 kg; 12 to 15 mo of age) were allocated to the study and fed a diet for 14 d without (CTRL) or with sodium butyrate (BUT; 36 g/kg of offered DM). Neither DMI nor initial BW differed between treatments (P ≥ 0.61), but final BW was greater for BUT compared with CTRL (P = 0.03). Butyrate concentration in the reticuloruminal fluid and abomasal digesta was greater for BUT compared with CTRL (P ≤ 0.01), but total short-chain fatty acids (SCFA) concentration, as well as concentration of other SCFA, did not differ between treatments (P ≥ 0.07). Relative to BW, reticuloruminal tissue mass tended (P = 0.09) to be greater and omasal digesta was less (P = 0.02) for BUT compared with CTRL. Dietary butyrate did not affect ruminal papillae length, width, and density nor did it affect ruminal epithelium thickness (P ≥ 0.12) in the ventral sac of the rumen. However, the DM of ruminal epithelium (mg/cm2) tended (P = 0.06) to be greater for BUT compared with CTRL. Omasal and abomasal epithelium thicknesses were greater (P ≤ 0.05) for BUT compared with CTRL. Mitosis-to-apoptosis ratio in the abomasal epithelium was less for BUT compared with CTRL (P = 0.04). Finally, the mRNA expression of peptide transporter 1 in the omasal epithelium was less (P = 0.02) and mRNA expression of monocarboxylate transporter 1 in the abomasal epithelium tended (P = 0.07) to be greater for BUT compared with CTRL. It can be concluded that exogenous butyrate supplementation affected not only the rumen but also omasum and abomasum in sheep.

Propionate and butyrate induce gene expression of monocarboxylate transporter 4 and cluster of differentiation 147 in cultured rumen epithelial cells derived from preweaning dairy calves

Short-chain fatty acids (SCFAs) are the main source of energy for postweaning ruminants. The monocarboxylic acid transporters, MCT1 and MCT4, are thought to contribute to the absorption of SCFAs from the surface of the rumen following weaning. The present study measured changes in MCT1 and MCT4 expression in ruminal epithelial cells isolated from male preweaning (22 to 34 d old, n = 6) and postweaning (55 to 58 d old, n = 8) calves after euthanasia and sought to examine whether SCFAs stimulate the expression of these transporters. In the current study, cluster of differentiation 147 (CD147) gene expression in the rumen was also investigated since CD147 has been considered to act as ancillary protein for MCT1 and MCT4 to express their correct function. The gene expression levels of MCT1, MCT4, and CD147 in the rumen were found to be significantly higher in postweaning calves than in preweaning calves. Strong MCT1 immunoreactivity was detected in both the stratum basale (SB) and the stratum spinosum (SS) in postweaning ruminal epithelium. Expression of MCT1 in preweaning calves was localized to a specific region of the SB and of the SS. MCT4-immunopositive cells were detected in the stratum corneum (SC) of the ruminal epithelium in postweaning calves. However, only a low level of signal was detected in the SC of preweaning animals. Furthermore, in vitro experiments, ruminal epithelial cells were incubated for 24 h with acetate (0.04, 0.4, and 4 mM), propionate (0.2, 2, and 20 mM), butyrate (0.1, 1, and 10 mM), or β-hydroxybutyrate (BHBA; 0.1, 1, and 10 mM), respectively. Both propionate and butyrate induced an increase in the gene expression levels of MCT4 and CD147, but did not affect MCT1 gene expression. There are no significant effects of acetate and BHBA treatment on these gene expressions. Taken together, these results suggest that an increase in MCT4 and CD147 gene expression in the ruminal epithelium of postweaning calves is likely to be due to the effects of propionate and butyrate derived from a solid-based diet, which may contribute to ruminal development following weaning.

Dietary supplements during the cold season increase rumen microbial abundance and improve rumen epithelium development in Tibetan sheep

Livestock on the Qinghai-Tibetan Plateau are faced with extreme harsh winters and are often in negative energy balance during this period. Dietary supplementation can improve growth performance of Tibetan sheep and, consequently, we hypothesized that it would also increase microbial abundance and rumen epithelium development. To test this hypothesis, we examined the effect of feed supplementation during the cold season on rumen microbes, fermentation, epithelium development, and absorptive capability in Tibetan sheep. Eighteen 1-yr-old ewes (BW = 29.4 ± 1.79, kg) were offered oat hay ad libitum for 60 d and divided randomly into three groups: 1) no supplement; control group (CON); 2) urea-molasses lick block supplement (BS); and 3) concentrate feed supplement (CS). The ADG of CS ewes (143.3, g/d) was greater (P < 0.05) than BS ewes (87.9, g/d), which was greater (P < 0.05) than CON ewes (44.5, g/d). Serum concentrations of GH, IGF-1, and IGF-2 in the CS and BS groups were greater than in the CON group (P < 0.05). Greater relative abundance of protozoa, Ruminococcus albus, Fibrobacter succinogenes, Streptococcus bovis, and Ruminobacter amylophilus was observed in the CS and BS groups than in the CON group (P < 0.05), and relative abundances of rumen fungi, Butyrivibrio fibrisolvens, and Prevotella ruminicola in the CS group were greater than in the BS and CON groups (P < 0.05). Ruminal total VFA, ammonia, and microbial protein concentrations in the CS and BS groups were greater than in the CON group (P < 0.05), and in the CS group were greater than in the BS group (P < 0.05). Ruminal papillae width and surface area in the CS and BS groups were greater than in the CON group (P < 0.05), while in the CS group were greater than in the BS group (P < 0.05). The mRNA expressions of IGFBP5, NHE1 (sodium/hydrogen antiporter, isoform 1), DRA (downregulated in adenoma), and Na+/K+-ATPase (sodium/potassium ATPase pump) in ruminal epithelium were greater in the CS and BS groups than in the CON group (P < 0.05), and in the CS group was greater than in the BS group (P < 0.05), while NHE3 (sodium/hydrogen antiporter, isoform 3), MCT1 (monocarboxylate transporter 1), and MCT4 (monocarboxylate transporter 4) mRNA expressions in the CS group were greater than in the BS and CON groups (P < 0.05). It was concluded that supplementing Tibetan sheep during the cold season increases rumen microbial abundance and improves fermentation parameters, rumen epithelium development, and absorptive capability.

A look at the smelly side of physiology: transport of short chain fatty acids

Fermentative organs such as the caecum, the colon, and the rumen have evolved to produce and absorb energy rich short chain fatty acids (SCFA) from otherwise indigestible substrates. Classical models postulate diffusional uptake of the undissociated acid (HSCFA). However, in net terms, a major part of SCFA absorption occurs with uptake of Na⁺ and resembles classical, coupled electroneutral NaCl transport. Considerable evidence suggests that the anion transporting proteins expressed by epithelia of fermentative organs are poorly selective and that their main function may be to transport acetate^-, propionate^-, butyrate^- and HCO₃^- as the physiologically relevant anions. Apical uptake of SCFA thus involves non-saturable diffusion of the undissociated acid (HSCFA), SCFA^-/HCO₃^- exchange via DRA (SLC26A3) and/or SCFA^--H⁺ symport (MCT1, SLC16A1). All mechanisms lead to cytosolic acidification with stimulation of Na⁺/H⁺ exchange via NHE (SLC9A2/3). Basolaterally, Na⁺ leaves via the Na⁺/K⁺-ATPase with recirculation of K⁺. Na⁺ efflux drives the transport of SCFA^- anions through volume-regulated anion channels, such as maxi-anion channels (possibly SLCO2A1), LRRC8, anoctamins, or uncoupled exchangers. When luminal buffering is inadequate, basolateral efflux will increasingly involve SCFA^-/ HCO₃^- exchange (AE1/2, SCL4A1/2), or efflux of SCFA^- with H⁺ (MCT1/4, SLC16A1/3). Furthermore, protons can be basolaterally removed by NHE1 (SCL9A1) or NBCe1 (SLC4A4). The purpose of these transport proteins is to maximize the amount of SCFA transported from the tightly buffered ingesta while minimizing acid transport through the epithelium. As known from the rumen for many decades, a disturbance of these processes is likely to cause severe colonic disease.

Changes in gene expression in the rumen and colon epithelia during the dry period through lactation of dairy cows and effects of live yeast supplementation

The objectives of this study were (1) to use endoscopy to collect biopsies from the rumen and colon epithelia to describe changes in gene expression in these 2 tissues as cows move from a dry to a lactation ration and (2) to evaluate the potential influence that supplementation of live yeast could exert on these 2 epithelia. Twenty-one Holstein cows were split into 2 treatments and received either 300 g/d of corn containing 1 × 10¹⁰ cfu/d of live yeast (LY; n = 10) or 300 g/d of corn with no supplementation (control; n = 11) starting 21 ± 2.6 d (average ± SD) before until 21 d after calving. At 14 ± 2.6 d before the expected calving date, and exactly at 7 and 21 d after calving, rumen and colon biopsies were obtained from each cow using an endoscope. Total RNA was extracted from rumen and colon tissues, and the expression of IL10, TNFA, TLR4, IL1B, PCNA, MKI67, SGLT1, BAX, CASP3, OCLN, CLDN4, HSPA1A, HSPB1, DEFB1, and MCT1 (the latter only in rumen samples) was quantified by quantitative PCR. Overall, fluctuations in expression of the selected genes in the colon between the 2 stages of production and the 2 treatments were smaller than those found in the rumen. In the rumen epithelium, expression of TLR4 and DEFB1 was greatest before calving, with LY cows having a greater expression of TLR4 than control cows. Similarly, expression of IL10 was greatest in LY cows before calving. Expression of TNFA in the rumen epithelium of control cows was lowest at 21 DIM but in LY cows was kept steady among production stages. The expression of PCNA and MKI67 in the rumen epithelium was greatest at 7 DIM, indicating a high proliferation rate of this epithelium after calving. In the colon mucosa, expression of TLR4 and DEFB1 was greater than in the rumen, and DEFB1 expression was greater in LY cows than in control cows. The use of an endoscope allowed us to study the dynamics of rumen epithelium adaptation to increased supply of concentrate after calving, consisting of increased epithelia remodeling, reduction of the TLR4, and increased IL10 expression. Furthermore, the rumen epithelium of dry cows responded rapidly to live yeast, with changes in the expression of genes involved in the immune response becoming evident after 7 d of exposure to yeast. The expression of genes related to the immune response (mainly TLR4 and DEFB1) in the colon mucosa was greater than in the rumen, and the expression of DEFB1 was further stimulated by live yeast. It is concluded that the use of an endoscope allows the study of gene expression patterns in the rumen and hindgut epithelia. We report marked changes in the rumen wall and more modest changes in the colon when transitioning from a dry to a lactation ration. Furthermore, supplementation of live yeast fostered and increased expression of genes regulating inflammation and epithelial barrier in the rumen, and in the colon it increased the expression of DFEB1 coding for an antimicrobial peptide.

Short-Chain Fatty Acid Transporters: Role in Colonic Homeostasis

Short-chain fatty acids (SCFA; acetate, propionate, and butyrate) are generated in colon by bacterial fermentation of dietary fiber. Though diffusion in protonated form is a significant route, carrier-mediated mechanisms constitute the major route for the entry of SCFA in their anionic form into colonic epithelium. Several transport systems operate in cellular uptake of SCFA. MCT1 (SLC16A1) and MCT4 (SLC16A3) are H+-coupled and mediate electroneutral transport of SCFA (H+: SCFA stoichiometry; 1:1). MCT1 is expressed both in the apical membrane and basolateral membrane of colonic epithelium whereas MCT4 specifically in the basolateral membrane. SMCT1 (SLC5A8) and SMCT2 (SLC5A12) are Na+-coupled; SMCT1-mediated transport is electrogenic (Na+: SCFA stoichiometry; 2:1) whereas SMCT2-mediated transport is electroneutral (Na+: SCFA stoichiometry; 1:1). SMCT1 and SMCT2 are expressed exclusively in the apical membrane. An anion-exchange mechanism also operates in the apical membrane in which SCFA entry in anionic form is coupled to bicarbonate efflux; the molecular identity of this exchanger however remains unknown. All these transporters are subject to regulation, notably by their substrates themselves; this process involves cell-surface receptors with SCFA as signaling molecules. There are significant alterations in the expression of these transporters in ulcerative colitis and colon cancer. The tumor-associated changes occur via transcriptional regulation by p53 and HIF1α and by promoter methylation. As SCFA are obligatory for optimal colonic health, the transporters responsible for the entry and transcellular transfer of these bacterial products in colonic epithelium are critical determinants of colonic function under physiological conditions and in disease states. © 2018 American Physiological Society. Compr Physiol 8:299-314, 2018.

Feeding a High Concentration Diet Induces Unhealthy Alterations in the Composition and Metabolism of Ruminal Microbiota and Host Response in a Goat Model

There is limited knowledge about the impact of long-term feeding a high-concentrate (HC) diet on rumen microbiota, metabolome, and host cell functions. In this study, a combination of mass spectrometry-based metabolomics techniques, 454 pyrosequencing of 16S rDNA genes, and RT-PCR was applied to evaluate the changes of ruminal microbiota composition, ruminal metabolites, and related genes expression in rumen epithelial cells of lactating goats received either a 35% concentrate diet or a 65% concentrate diet for 4 or 19 weeks, respectively. Results show that feeding a HC diet reduced the microbiota diversity and led to the disorders of metabolism in the rumen. The concentrations of lactate, phosphorus, NH3-N and endotoxin Lipopolysaccharide in ruminal fluids, and plasma histamine, lactate and urine N (UN) were increased significantly in goats fed with a HC diet. A significant increase of genes expression related to volatile fatty acids transport, cell apoptosis, and inflammatory responses were also observed in goats fed with a HC diet. Correlation analysis revealed some potential relationships between bacteria abundance and metabolites concentrations. Our findings indicate that a HC diet can induce ruminal microbiota dysbiosis and metabolic disorders, thus increasing risks to host health and potential harm to the environment.

Effects of dietary forage and calf starter on ruminal pH and transcriptomic adaptation of the rumen epithelium in Holstein calves during the weaning transition

We investigated the relationship between ruminal pH and transcriptomic adaptation of the rumen epithelium (RE) of calves fed calf starter with and without forage during the weaning transition. Holstein calves were assigned to groups fed calf starter either with forage (HAY group, n = 3) or without forage (CON group, n = 4). Ruminal pH was measured continuously, and rumen fluid and epithelium were collected 3 wk after weaning. mRNA expression profiles of the RE were examined by one-color microarray. Differentially expressed genes (DEGs) were investigated using the Ingenuity Pathway Analysis (IPA). Mean and maximum ruminal pH were significantly ( P < 0.05) higher, and the duration of pH < 5.8 during 1 day was significantly ( P < 0.05) shorter, in the HAY group. The proportion of ruminal acetate and the acetate-to-propionate ratio were significantly ( P < 0.05) lower in the CON group. DEGs encoding transcription regulators (SREBP1), insulin-like growth factor binding proteins (IGFBP7 and CTGF), ketogenic enzymes (HMGCL, BDH1, and BDH2), and a transporter (SLC16A3) were identified ( P < 0.05) between the two groups. A growth factor (TGFB1) and signaling pathway (EGF and EGFR) were activated as upstream regulators. These results suggest that dietary forage alleviates ruminal acidosis, and the decrease in ruminal pH may damage the RE, leading to changes in gene expression to repair the damage. Furthermore, rumen development may be regulated by growth factor (TGFB1) and signaling pathways (EGF and IGFBP) for adaptation to feeding on calf starter with and without forage during the weaning transition.

Differential protein abundance of a basolateral MCT1 transporter in the human gastrointestinal tract

Bacterially derived short chain fatty acids (SCFAs), such as butyrate, are vital in maintaining the symbiotic relationship that exists between humans and their gastrointestinal microbial populations. A key step in this process is the transport of SCFAs across colonic epithelial cells via MCT1 transporters. This study investigated MCT1 protein abundance in various human intestinal tissues. Initial RT-PCR analysis confirmed the expected MCT1 RNA expression pattern of colon > small intestine > stomach. Using surgical resection samples, immunoblot analysis detected higher abundance of a 45 kDa MCT1 protein in colonic tissue compared to ileum tissue (P < 0.001, N = 4, unpaired t-test). Importantly, MCT1 abundance was found to be significantly lower in sigmoid colon compared to ascending colon (P < 0.01, N = 8-11, ANOVA). Finally, immunolocalization studies confirmed MCT1 to be abundant in the basolateral membranes of surface epithelial cells of the ascending, transverse, and descending colon, but significantly less prevalent in the sigmoid colon (P < 0.05, N = 5-21, ANOVA). In conclusion, these data confirm that basolateral MCT1 protein abundance is correlated to levels of bacterially derived SCFAs along the human gastrointestinal tract. These findings highlight the importance of precise tissue location in studies comparing colonic MCT1 abundance between normal and diseased states.

Inhibition of monocarboxylate transporter 1 suppresses the proliferation of glioblastoma stem cells

Recent evidence suggests that a minor subset of cancer cells, termed cancer stem cells (CSCs), have self-renewal and tumorigenic potential. Therefore, the characterization of CSCs is important for developing therapeutic strategies against cancer. Cancer cells rely on anaerobic glycolysis to produce ATP even under normoxic conditions, resulting in the generation of excess acidic substances. Cancer cells maintain a weakly alkaline intracellular pH to support functions. Glioblastoma is an aggressive malignancy with a poor 5-year survival rate. Based on the hypothesis that ion transport-related molecules regulate the viability and function of CSCs, we investigated the expression of ion transport-related molecules in glioblastoma CSCs (GSCs). Quantitative RT-PCR analysis showed that monocarboxylate transporter1 (MCT1) were upregulated in GSCs, and inhibition of MCT1 decreased the viability of GSCs compared with that of non-GSCs. Our findings indicate that MCT1 is involved in the maintenance of GSCs and is a promising therapeutic target for glioblastoma.