Hfq mediates transcriptome-wide RNA structurome reprogramming under virulence-inducing conditions in a phytopathogen.

Although RNA structures play important roles in regulating gene expression, the mechanism and function of mRNA folding in plant bacterial pathogens remain elusive. Therefore, we perform dimethyl sulfate sequencing (DMS-seq) on the Pseudomonas syringae under nutrition-rich and -deficient conditions, revealing that the mRNA structure changes substantially in the minimal medium (MM) that tunes global translation efficiency (TE), thereby inducing virulence. This process is led by the increased expression of hfq, which is directly activated by transcription regulators RpoS and CysB. The co-occurrence of Hfq and RpoS in diverse bacteria and the deep conservation of Hfq Y25 is critical for RNA-mediated regulation and implicates the wider biological importance of mRNA structure and feedback loops in the control of global gene expression.

c-di-GMP signaling in Pseudomonas syringae complex.

The Pseudomonas syringae Complex is one of the model phytopathogenic bacteria for exploring plant-microbe interactions, causing devastating plant diseases and economic losses worldwide. The ubiquitous second messenger bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) plays an important role in the 'lifestyle switch' from single motile cells to biofilm formation and modulates bacterial behavior, thus influencing virulence in Pseudomonas and other bacterial species. However, less is known about the role of c-di-GMP in the P. syringae complex, in which c-di-GMP levels are controlled by diguanylate cyclases (DGCs) and phosphodiesterases (PDEs), such as Chp8, BifA and WspR. Deletion the chemotaxis receptor PscA also influences c-di-GMP levels, suggesting a cross-talk between chemotaxis and c-di-GMP pathways. Another transcription factor, FleQ, plays a dual role (positive or negative) in regulating cellulose synthesis as a c-di-GMP effector, whereas the transcription factor AmrZ regulates local c-di-GMP levels by inhibiting the DGC enzyme AdcA and the PDE enzyme MorA. Our recent research demonstrated that an increase in the c-di-GMP concentration increased biofilm development, siderophore biosynthesis and oxidative stress tolerance, while it decreased the siderophore content, bacterial motility and type III secretion system activity in P. syringae complex. These findings show that c-di-GMP intricately controls virulence in P. syringae complex, indicating that adjusting c-di-GMP levels may be a valuable tactic for defending plants against pathogens. This review highlights recent research on metabolic enzymes, regulatory mechanisms and the phenotypic consequences of c-di-GMP signaling in the P. syringae.

Bacterial Transcription Factors Bind to Coding Regions and Regulate Internal Cryptic Promoters.

Transcription factors (TFs) regulate transcription by binding to the specific sequences at the promoter region. However, the mechanisms and functions of TFs binding within the coding sequences (CDS) remain largely elusive in prokaryotes. To this end, we collected 409 data sets for bacterial TFs, including 104 chromatin immunoprecipitation sequencing (ChIP-seq) assays and 305 data sets from the systematic evolution of ligands by exponential enrichment (SELEX) in seven model bacteria. Interestingly, these TFs displayed the same binding capabilities for both coding and intergenic regions. Subsequent biochemical and genetic experiments demonstrated that several TFs bound to the coding regions and regulated the transcription of the binding or adjacent genes. Strand-specific RNA sequencing revealed that these CDS-binding TFs regulated the activity of the cryptic promoters, resulting in the altered transcription of the corresponding antisense RNA. TF RhpR hindered the transcriptional elongation of a subgenic transcript within a CDS. A ChIP-seq and Ribo-seq coanalysis revealed that RhpR influenced the translational efficiency of binding genes. Taken together, the present study reveals three regulatory mechanisms of CDS-bound TFs within individual genes, operons, and antisense RNAs, which demonstrate the variability of the regulatory mechanisms of TFs and expand upon the complexity of bacterial transcriptomes. IMPORTANCE Although bacterial TFs regulate transcription by binding to specific sequences at the promoter region, little is known about the mechanisms and functions of TFs binding within the CDS. In this study, we show that bacterial TFs have same binding pattern in both CDS and promoter regions, and we reveal three regulatory mechanisms of CDS-bound TF that together demonstrate the complexity of the regulatory mechanisms of bacterial TFs and the wide spread of internal cryptic promoters in CDS.

Integrated regulatory network in Pseudomonas syringae reveals dynamics of virulence.

Pseudomonas syringae, a Gram-negative plant pathogen, expresses multitudinous transcriptional regulators to control the type III secretion system (T3SS) and response to diverse environmental challenges. Although the mechanisms of virulence-associated regulators of P. syringae have been studied for decades, the overall crosstalk underlying these regulators is still elusive. Here, we identify five T3SS regulators (EnvZ-OmpR, CbrAB2, PhoPQ, PilRS, and MgrA), and find that the two-component systems EnvZ-OmpR and CbrAB2 negatively regulate the T3SS. To elucidate crosstalk between 16 virulence-associated regulators in P. syringae, we map an online intricate network called "PSRnet" (Pseudomonas syringae regulatory network) by combining the differentially expressed genes (DEGs) of these 16 regulators by RNA sequencing (RNA-seq) and their binding loci by chromatin immunoprecipitation sequencing (ChIP-seq). Consequently, we identify 238 and 153 functional genes involved in the T3SS and other virulence-related pathways in KB and MM media, respectively. Our results provide insights into the mechanism of plant infections caused by P. syringae.

An atlas of the binding specificities of transcription factors in Pseudomonas aeruginosa directs prediction of novel regulators in virulence.

A high-throughput systematic evolution of ligands by exponential enrichment assay was applied to 371 putative TFs in Pseudomonas aeruginosa, which resulted in the robust enrichment of 199 unique sequence motifs describing the binding specificities of 182 TFs. By scanning the genome, we predicted in total 33,709 significant interactions between TFs and their target loci, which were more than 11-fold enriched in the intergenic regions but depleted in the gene body regions. To further explore and delineate the physiological and pathogenic roles of TFs in P. aeruginosa, we constructed regulatory networks for nine major virulence-associated pathways and found that 51 TFs were potentially significantly associated with these virulence pathways, 32 of which had not been characterized before, and some were even involved in multiple pathways. These results will significantly facilitate future studies on transcriptional regulation in P. aeruginosa and other relevant pathogens, and accelerate to discover effective treatment and prevention strategies for the associated infectious diseases.

A compendium of DNA-binding specificities of transcription factors in Pseudomonas syringae.

Pseudomonas syringae is a Gram-negative and model pathogenic bacterium that causes plant diseases worldwide. Here, we set out to identify binding motifs for all 301 annotated transcription factors (TFs) of P. syringae using HT-SELEX. We successfully identify binding motifs for 100 TFs. We map functional interactions between the TFs and their targets in virulence-associated pathways, and validate many of these interactions and functions using additional methods such as ChIP-seq, electrophoretic mobility shift assay (EMSA), RT-qPCR, and reporter assays. Our work identifies 25 virulence-associated master regulators, 14 of which had not been characterized as TFs before.

Pseudomonas syringae dual-function protein Lon switches between virulence and metabolism by acting as both DNA-binding transcriptional regulator and protease in different environments.

Lon, a member of the AAA+ protease family, plays vital roles in Type III secretion systems (T3SS), agglutination and colony shape in the model plant pathogen Pseudomonas syringae. Lon also functions as a transcriptional regulator in other bacterial species such as Escherichia coli and Brevibacillus thermoruber. To reveal the molecular mechanisms of Lon as a dual-function protein in P. syringae, we studied Lon-regulated genes by using RNA sequencing (RNA-seq), chromatin immunoprecipitation sequencing (ChIP-seq) and liquid chromatography-tandem mass spectrometry. As a transcriptional regulator, Lon directly regulated a group of genes (PSPPH_4788, gacA, fur, gntR, clpS, lon and glyA) and consequently regulated their functions, such as 1-dodecanol oxidation activity, motility, pyoverdine production, glucokinase activity, N-end rule pathway, lon expression and serine hydroxymethyltransferase activity. Mass spectrometry results revealed that the expression levels of five T3SS proteins (such as HrcV, HrpW1) were higher in the ∆lon strain than the wild-type (WT) strain in KB. In MM, 12 metabolic proteins (such as AcdS and NuoI) showed lower levels in the ∆lon strain than the WT strain. Taken together, these data demonstrate that the dual-function protein Lon sophisticatedly regulates virulence and metabolism in P. syringae.

Chronic Dexamethasone exposure activates the TLR4-Mediated inflammation pathway and induces epithelial apoptosis in the goat colon.

Chronic stress has a profound effect on health in both animals and humans. Dexamethasone (Dex), a synthetic glucocorticoid, is used to induce chronic stress in many studies. The impact of chronic stress on epithelial cells of hindgut of ruminants is still unknown. In this study, we investigated the effect of chronic stress induced by long term injection of low dosage of Dex on the colonic epithelium of goats. The results showed that Dex exposure increased the number of TUNEL-positive cells, upregulated caspase-3 and caspase-8 enzyme activity, but decreased protein expression of cell proliferation markers proliferating cell nuclear antigen (PCNA) and Cyclin D2(CCND2). It also activated TLR-4 and NF-κB pathway and increased the transcription levels of vital inflammatory cytokines such as interleukin-10 (IL-10), interleukin-1ß (IL-1ß), and inducible nitric oxide synthase 2 (iNOS2). Chronic stress down-regulated the methylation level of total DNA, suggesting a mechanism for the transcriptional activation of genes, such as claudin-1, claudin-4, ZO-1, and cell cycle-related genes. Taken together, long-term injection of a low dosage of Dex caused damage to the colon epithelium accompanied with the inhibition of cell proliferation and the activation of cell apoptosis and inflammation. However, a general up-regulation of genes expression induced by Dex is due to a lower level of genomic DNA methylation.

Pseudomonas savastanoi Two-Component System RhpRS Switches between Virulence and Metabolism by Tuning Phosphorylation State and Sensing Nutritional Conditions.

Pseudomonas savastanoi uses a type III secretion system (T3SS) to invade host plants. Our previous studies have demonstrated that a two-component system (TCS), RhpRS, enables P. savastanoi to coordinate the T3SS gene expression, which depends on the phosphorylation state of RhpR under different environmental conditions. Orthologues of RhpRS are distributed in a wide range of bacterial species, indicating a general regulatory mechanism. How RhpRS uses external signals and the phosphorylation state to exercise its regulatory functions remains unknown. We performed chromatin immunoprecipitation sequencing (ChIP-seq) assays to identify the specific binding sites of RhpR and RhpRD70A in either King's B medium (KB [a T3SS-inhibiting medium]) or minimal medium (MM [a T3SS-inducing medium]). We identified 125 KB-dependent binding sites and 188 phosphorylation-dependent binding sites of RhpR. In KB, RhpR directly and positively regulated cytochrome c550 production (via ccmA) and alcohol dehydrogenase activity (via adhB) but negatively regulated anthranilate synthase activity (via trpG) and protease activity (via hemB). In addition, phosphorylated RhpR (RhpR-P) directly and negatively regulated the T3SS (via hrpR and hopR1), swimming motility (via flhA), c-di-GMP levels (via PSPPH_2590), and biofilm formation (via algD). It positively regulated twitching motility (via fimA) and lipopolysaccharide production (via PSPPH_2653). Our transcriptome sequencing (RNA-seq) analyses identified 474 and 840 new genes that were regulated by RhpR in KB and MM, respectively. We showed nutrient-rich conditions allowed RhpR to directly regulate multiple metabolic pathways of P. savastanoi and phosphorylation enabled RhpR to specifically control virulence and the cell envelope. The action of RhpRS switched between virulence and regulation of multiple metabolic pathways by tuning its phosphorylation and sensing environmental signals in KB, respectively.IMPORTANCE The plant pathogen Pseudomonas savastanoi invades host plants through a type III secretion system, which is strictly regulated by a two-component system called RhpRS. The orthologues of RhpRS are widely distributed in the bacterial kingdom. The master regulator RhpR specifically depends on the phosphorylation state to regulate the majority of the virulence-related genes. Under nutrient-rich conditions, it modulates many important metabolic pathways, which consist of one-fifth of the genome. We propose that RhpRS uses phosphorylation- and nutrition-dependent mechanisms to switch between regulating virulence and metabolism, and this functionality is widely conserved among bacterial species.

Pleiotropic Effects of c-di-GMP Content in Pseudomonas syringae.

Although the ubiquitous bacterial secondary messenger cyclic diguanylate (c-di-GMP) has important cellular functions in a wide range of bacteria, its function in the model plant pathogen Pseudomonas syringae remains largely elusive. To this end, we overexpressed Escherichia coli diguanylate cyclase (YedQ) and phosphodiesterase (YhjH) in P. syringae, resulting in high and low in vivo levels of c-di-GMP, respectively. Via genome-wide RNA sequencing of these two strains, we found that c-di-GMP regulates (i) fliN, fliE, and flhA, which are associated with flagellar assembly; (ii) alg8 and alg44, which are related to the exopolysaccharide biosynthesis pathway; (iii) pvdE, pvdP, and pvsA, which are associated with the siderophore biosynthesis pathway; and (iv) sodA, which encodes a superoxide dismutase. In particular, we identified three promoters that are sensitive to elevated levels of c-di-GMP and inserted them into luciferase-based reporters that respond effectively to the c-di-GMP levels in P. syringae; these promoters could be useful in the measurement of in vivo levels of c-di-GMP in real time. Further phenotypic assays validated the RNA sequencing (RNA-seq) results and confirmed the effect on c-di-GMP-associated pathways, such as repressing the type III secretion system (T3SS) and motility while inducing biofilm production, siderophore production, and oxidative stress resistance. Taken together, these results demonstrate that c-di-GMP regulates the virulence and stress response in P. syringae, which suggests that tuning its level could be a new strategy to protect plants from attacks by this pathogen.IMPORTANCE The present work comprehensively analyzed the transcriptome and phenotypes that were regulated by c-di-GMP in P. syringae Given that the majority of diguanylate cyclases and phosphodiesterases have not been characterized in P. syringae, this work provided a very useful database for the future study on regulatory mechanism (especially its relationship with T3SS) of c-di-GMP in P. syringae In particular, we identified three promoters that were sensitive to elevated c-di-GMP levels and inserted them into luciferase-based reporters that effectively respond to intracellular levels of c-di-GMP in P. syringae, which could be used as an economic and efficient way to measure relative c-di-GMP levels in vivo in the future.

Caspase-1-dependent mechanism mediating the harmful impacts of the quorum-sensing molecule N-(3-oxo-dodecanoyl)-l-homoserine lactone on the intestinal cells.

N-(3-oxododecanoyl)-l-homoserine lactone (3-oxo-C12-HSL), a quorum-sensing (QS) molecule produced by Gram-negative bacteria in the gastrointestinal tract, adversly impacts host cells. Our previous study demonstrated that 3-oxo-C12-HSL induced a decrease in cell viability via cell apoptosis and eventually disrupted mucin synthesis from LS174T goblet cells. However, the molecular mechanism underlying cell apoptosis and whether pyroptosis was involved in this process are still unknown. In this study, we emphasized on the caspases signal pathway and sterile inflammation to reveal the harmful effects of 3-oxo-C12-HSL on LS174T goblet cells. Our data showed that 3-oxo-C12-HSL is a major inducer of oxidative stress indicated by a high level of intracellular reactive oxygen species (ROS). However, TQ416, an inhibitor of paraoxonase 2, can effectively block oxidative stress. A higher ROS level is the trigger for activating the caspase-1 and 3 cascade signal pathways. Blockade of ROS synthesis and caspase-1 and 3 cascades can obviously rescue the viability of LS174T cells after 3-oxo-C12-HSL treatment. We also found that paralleled with a higher level of ROS and caspases activation, an abnormal expression of proinflammatory cytokines was induced by 3-oxo-C12-HSL treatment; however, the blockage of TLRs-NF-κB pathway cannot restore cell viability and secretary function. These data collectively indicate that 3-oxo-C12-HSL exposure induces damages to cell viability and secretary function of LS174T goblet cells, which is mediated by oxidative stress, cell apoptosis, and sterile inflammation. Overall, the data in this study will provide a better understanding of the harmful impacts of some QS molecules on host cells and their underlying mechanism.

Chronic dexamethasone exposure retards growth without altering the digestive tract microbiota composition in goats.

BACKGROUND: Dexamethasone (Dex), an artificially synthetic cortisol substitute, is commonly used as an anti-inflammatory drug, and is also employed to mimic the stress state experimentally. It is well known that chronic stress disturbs the gut microbiota community and digestive functions. However, no relevant studies have been conducted in ruminants. RESULTS: In this study, a low dosage of Dex (0.2 mg/kg body weight, Dex group, n = 5) was consecutively injected intramuscularly for 21 days to simulate chronic stress in growing goats. Goats were injected with saline (0.2 mg/kg body weight) as the control group (Con, n = 5). Dex-treated goats showed a higher number of white blood cells and blood glucose levels (p < 0.01), but lower dry matter intake (DMI) and body weight (p < 0.01) than those of saline-injected goats. Plasma cortisol concentration decreased significantly in response to the Dex injection compared to the control (p < 0.05). The Dex treatment did not change most ruminal volatile fatty acid (VFAs) concentrations before the morning feeding after 1-21 days of treatment (p > 0.05); however, ruminal VFA concentrations decreased dramatically 2, 4, 6, and 8 h after the morning feeding on day 21 of the Dex injections. In this study, chronic Dex exposure did not alter the community structure of microbes or methanogenes in the rumen, caecum, or colonic digesta. Only Prevotella increased on days 7 and 14 of Dex treatment, but decreased on day 21, and Methanosphaera was the only genus of methanogene that decreased. CONCLUSIONS: Our results suggest that chronic Dex exposure retards growth by decreasing DMI, which may be mediated by higher levels of blood glucose and lower ruminal VFA production. Microbiota in the digestive tract was highly resistant to chronic Dex exposure.

Dexamethasone impacts zinc levels in goats by regulating zinc transportation in the colon and the metabolism in the liver.

The aim of this study was to investigate the effects of dexamethasone (DEX) on zinc metabolism in goats. In this study, 10 goats were randomly divided into two groups. One group was injected with dexamethasone (Dex group) and the other group was injected with saline (Con group). Dex treatment significantly decreased hepatic zinc levels (p < .01) and increased Zn transporters 1 (ZNT-1) expression (p < .05). The concentration of zinc in the cecal and colonic contents was significantly increased (p < .05). However, zinc levels were increased only in the colon tissues (p < .05) but not in the cecal tissues (p > .05). A dramatic increase in Zrt-, Irt-related proteins 14 (ZIP-14) expression (p < .05) following Dex treatment was also observed and likely induced the elevated zinc levels in the colon, and a significant reduction in Zip-14 methylation (p < .05) may be responsible for the observed increase in Zip-14 expression. Together, these results indicate that Dex influences zinc homeostasis by increasing hepatic ZNT-1 and colonic ZIP-14 expression. Additionally, these results provide valuable information for the clinical application of Dex.

N-(3-oxododecanoyl)-l-homoserine lactone modulates mitochondrial function and suppresses proliferation in intestinal goblet cells.

AIMS: The quorum-sensing molecule N­(3­oxododecanoyl)­l­homoserine lactone (C12-HSL), produced by the Gram negative human pathogenic bacterium Pseudomonas aeruginosa, modulates mammalian cell behavior. Our previous findings suggested that C12-HSL rapidly decreases viability and induces apoptosis in LS174T goblet cells. MAIN METHODS: In this study, the effects of 100 µM C12-HSL on mitochondrial function and cell proliferation in LS174T cells treated for 4 h were evaluated by real-time PCR, enzyme-linked immunosorbent assay (ELISA) and flow cytometry. KEY FINDINGS: The results showed that the activities of mitochondrial respiratory chain complexes IV and V were significantly increased (P < 0.05) in LS174T cells after C12-HSL treatment, with elevated intracellular ATP generation (P < 0.05). Flow cytometry analysis revealed significantly increased intracellular Ca2+ levels (P < 0.05), as well as disrupted mitochondrial activity and cell cycle arrest upon C12-HSL treatment. Apoptosis and cell proliferation related genes showed markedly altered expression levels (P < 0.05) in LS174T cells after C12-HSL treatment. Moreover, the paraoxonase 2 (PON2) inhibitor TQ416 (1 µM) remarkably reversed the above C12-HSL associated effects in LS174T cells. SIGNIFICANCE: These findings indicated that C12-HSL alters mitochondrial energy production and function, and inhibits cell proliferation in LS174T cells, with PON2 involvement.

Exploring differentially expressed genes related to metabolism by RNA-Seq in goat liver after dexamethasone treatment.

Chronic stress severely threatens the welfare and health of animals and humans. In order to study the effects of chronic stress on metabolism, de novo transcriptome sequencing was used to generate the expressed sequence tag dataset for the goat, using nextgeneration sequencing technology. For this study, consecutive dexamethasone (Dex) injection was used in 10 healthy male goats (body weight 25 ±â€¯1.0 kg) to mimic chronic stress. Ten male goats were randomly assigned into two groups, one group was injected intramuscularly with the same volume of saline as control (Con) group, and another (Dex) group was injected intramuscularly with 0.2 mg/kg Dex for 21 days. To elucidate the resulting changes in genes, transcriptome profiling of liver was conducted by analysing samples from three goats of each group using RNA-Seq. A total of 137 differentially expressed genes (DEGs) were identified between Con group and Dex group. GO classification showed rhythmic process and hormone secretion in term cellular, and chemoattractant activity in term molecular function had noticeable differences in the proportion between DEGs and all genes. By mapping the DEGs to the COG database, we found that general function prediction only, energy production and conversion, and amino acid transport and metabolism were the most frequently represented functional clusters. We mapped the unigenes to the KEGG pathway database and found most annotated genes were involved in the AMPK signalling pathway as well as pathways in cancer and insulin signalling pathway. Via KEGG enrichment analysis, we found the DEGs were significantly enriched in insulin signalling pathway, AMPK signalling pathway and adipocytokine signalling pathway. In addition, these pathways have close relationship with metabolism, which resulted in metabolic changes in which the identified DEGs may play important roles. These results provide valuable information for further research on the complex molecular mechanisms of dexamethasone in goats and will provide a foundation for future studies.

Effects of chronic dexamethasone administration on hyperglycemia and insulin release in goats.

BACKGROUND: Dexamethasone (Dex), a synthetic glucocorticoid, is among the most commonly used drugs worldwide in animals and humans as an anti-inflammatory and immunosuppressive agent. GC has profound effects on plasma glucose level and other metabolic conditions. However, the effect of prolonged use of Dex on glucose metabolism in ruminants is still unclear. RESULTS: Ten goats were randomly assigned to two groups: the control goats were injected with saline, and the Dex-treated goats were intramuscularly injected daily for 21 d with 0.2 mg/kg Dex. The results showed that plasma glucose and insulin concentrations were significantly increased after Dex administration (P < 0.05). Additionally, the content of hepatic glycogen was also markedly increased in Dex-treated goats (P < 0.01), while the content of glycogen in dorsal longissimus was unchanged by Dex (P > 0.05). The expression of several key genes, involved in blood glucose regulation, was detected by real-time PCR in the small intestine, skeletal muscle and liver. The expression of glucose transporter type 2 (GLUT2), sodium-glucose transporter 1 (SGLT1) and sodium-potassium ATPase (Na-K/ATPase) in the small intestine were generally increased by Dex, and GLUT2 mRNA expression was significantly up-regulated (P < 0.05). In liver, the expression of genes involved in gluconeogenesis including glucose-6-phosphatase catalytic subunit (G6PC), cytosolic form of phosphoenolpyruvate carboxykinase (PCK1) and pyruvate carboxylase (PC), were significantly down-regulated by Dex. However, the protein expression levels of PCK1 & PCK2 were significantly increased by Dex, suggesting a post-transcriptional regulation. In dorsal longissimus, the mRNA expression of genes associated with gluconeogenesis and the insulin signaling pathway were generally up-regulated by Dex, but the mRNA expression of two markers of muscle atrophy, namely F-box protein 32 (FBXO32/Atrogin1) and muscle RING-finger protein 1 (MuRF1), was not altered by Dex. CONCLUSIONS: Taken together, these results indicate that chronic administration of a low dosage of Dex induces hyperglycemia mainly through gluconeogenesis activation in the goat liver.

Chronic dexamethasone exposure markedly decreased the hepatic triglyceride accumulation in growing goats.

Chronic stress seriously threatens welfare and health in animals and humans. Consecutive dexamethasone (Dex) injection was used to mimic chronic stress previously. In order to investigate the effect of chronic stress on hepatic lipids metabolism, in this study, 10 healthy male goats were randomly allocated into two groups, one received a consecutive injection of Dex via intramuscularly for 3 weeks (Dex group), the other received the same volume of saline as the control group (Con group). Hepatic health and triglyceride (TG) metabolism were analyzed and compared between two groups. The data showed that a significant decrease of TG in plasma and the liver was significantly decreased by Dex (P < .05), while the hepatic nonesterified fatty acid (NEFA) concentration was increased compared to the Con group (P < .05). Consistent with the decrease of TG level, the activity of hepatic lipoprotein lipase (LPL) and hepatic lipase (HL) enzymes activities were significantly enhanced by Dex. Real-time PCR results showed that the mRNA expression of sterol regulatory element binding transcription factor 1 (SREBP-1), acyl-CoA dehydrogenase long chain (ACADL) and acyl-CoA synthetase bubblegum family member 1 (ACSBG1) genes in liver was significantly up-regulated by chronic Dex injection (P < .05), whereas perilipin 2 (PLIN2) and adipose triglyceride lipase (ATGL) mRNA expression was significantly decreased by Dex (P < .05). In addition, no obvious damages were observed in the liver in both Con and Dex groups demonstrating by the sirius red staining, HE staining as well as several biochemical parameters related to the functional status of hepatocytes. Our data indicate that chronic Dex exposure decreases TG levels in the circulation and the liver through activating lipolysis and inhibiting lipogenesis without causing hepatic damages in the growing goats.

Negative effects of long-term feeding of high-grain diets to lactating goats on milk fat production and composition by regulating gene expression and DNA methylation in the mammary gland.

BACKGROUND: It is well known that feeding a high concentrate (HC) diet to lactating ruminants likely induces subacute ruminal acidosis (SARA) and leads to a decrease in milk fat production. However, the effects of feeding a HC diet for long periods on milk fatty acids composition and the mechanism behind the decline of milk fat still remains poorly understood. The aim of this study was to investigate the impact of feeding a HC diet to lactating dairy goats on milk fat yield and fatty acids composition with an emphasis on the mechanisms underlying the milk fat depression. Seventeen mid-lactating dairy goats were randomly allocated to three groups. The control treatment was fed a low-concentrate diet (35% concentrate, n = 5, LC) and there were two high-concentrate treatments (65% concentrate, HC), one fed a high concentrate diet for a long period (19 wks, n = 7, HL); one fed a high concentrate diet for a short period of time (4 wk, n = 5, HS). Milk fat production and fatty acids profiles were measured. In order to investigate the mechanisms underlying the changes in milk fat production and composition, the gene expression involved in lipid metabolism and DNA methylation in the mammary gland were also analyzed. RESULTS: Milk production was increased by feeding the HC diet in the HS and HL groups compared with the LC diet (P < 0.01), while the percentage of milk fat was lower in the HL (P < 0.05) but not in the HS group. The total amount of saturated fatty acids (SFA) in the milk was not changed by feeding the HC diet, whereas the levels of unsaturated fatty acids (UFA) and monounsaturated fatty acids (MUFA) were markedly decreased in the HL group compared with the LC group (P < 0.05). Among these fatty acids, the concentrations of C15:0 (P < 0.01), C17:0 (P < 0.01), C17:1 (P < 0.01), C18:1n-9c (P < 0.05), C18:3n-3r (P < 0.01) and C20:0 (P < 0.01) were markedly lower in the HL group, and the concentrations of C20:0 (P < 0.05) and C18:3n-3r (P < 0.01) were lower in the HS group compared with the LC group. However, the concentrations of C18:2n-6c (P < 0.05) and C20:4n-6 (P < 0.05) in the milk fat were higher in the HS group. Real-time PCR results showed that the mRNA expression of the genes involved in milk fat production in the mammary gland was generally decreased in the HL and HS groups compared with the LC group. Among these genes, ACSL1, ACSS1 & 2, ACACA, FAS, SCD, FADS2, and SREBP1 were down-regulated in the mammary gland of the HL group (P < 0.05), and the expressions of ACSS2, ACACA, and FADS2 mRNA were markedly decreased in the HS goats compared with the LC group (P < 0.05). In contrast to the gene expression, the level of DNA methylation in the promoter regions of the ACACA and SCD genes was increased in the HL group compared with the LC group (P < 0.05). The levels of ACSL1 protein expression and FAS enzyme activity were also decreased in the mammary gland of the HL compared with the LC group (P < 0.05). CONCLUSIONS: Long-term feeding of a HC diet to lactating goats induced milk fat depression and FAs profile shift with lower MUFAs but higher SFAs. A general down-regulation of the gene expression involved in the milk fat production and a higher DNA methylation in the mammary gland may contribute to the decrease in milk fat production in goats fed a HC diet for long time periods.

Microbiome-Metabolome Responses to a High-Grain Diet Associated with the Hind-Gut Health of Goats.

Studies on the effect of a high-concentrate (HC) diet on the hindgut microbiota and metabolome of ruminants are rarely reported. We used 454 pyrosequencing of 16S rDNA genes and gas chromatography-mass spectrometry to evaluate the effects of long-term feeding (HL) or short-term (HS) feeding of an HC diet on changes in bacterial microbiota and their metabolites in the hindgut, with Guanzhong goat as a ruminant model. Results indicated that an HC diet decreased bacterial diversity and induced metabolic disorder in the hindgut. The levels of lactate, endotoxin (lipopolysaccharide, LPS), and volatile fatty acid concentrations were higher in the intestinal digesta of the HC goats than in those of the LC goats (P < 0.05). The level of beta-alanine decreased, whereas the levels of stigmasterol and quinic acid decreased in the cecal and colonic digesta of the HC goats. At the genus level, the abundance of Clostridium and Turicibacter was significantly increased in both the colonic and cecal digesta of the HC goats. Several potential relationships between metabolites and several microbial species were revealed in this study. The mRNA expression of the genes functionally associated with nutrients transport, including NHE2, NHE3, MCT1, and MCT4 were significantly downregulated in the colonic mucosa by the HC diet (P < 0.05). The expression levels of the genes related to the inflammatory response, including TLR4, MYD88, TNF-α, and IL-1ß were markedly upregulated in the cecal mucosa by the HC diet (P < 0.05). Our results indicate that an HC diet induces microbiota dysbiosis, metabolic disorders, and mucosal damage in the hindgut of goats.

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.