Genome-Wide Detection of Key Genes and Epigenetic Markers for Chicken Fatty Liver

Integrating GWAS and transcriptomics to identify candidate genes conferring relative growth rate trait in white-feathered broiler

Broilers are a globally significant resource for food production, and their relative growth rate (RGR) has attracted increasing attention for improving broiler monitoring, feed management and feed conversion. The main objectives of this study were to identify key candidate genes affecting the RGR in white-feathered broiler by integrating genomic and transcriptomic datasets. This study reports a meta-analysis of genome-wide association studies (GWAS) using 3 purebred lines (n = 3,727) and 5,841,467 input SNPs to understand the genetic control of the RGR. A total of 101 associated SNPs located on 6 chromosomes were identified, 16 of which were common in the GWAS and meta cohorts. Fine mapping of a significant peak with 7 linked SNP (r2 > 0.94) located within the coding region of RAP2C revealed that chr4:3474286 (C > G) among these SNPs was a highly putative causal variant (PIP = 19%) and explained 2.26% of the RGR variation. Further analyses indicated that the surface expression level of the RAP2C gene in the blood, macrophage, lung tissue, and cecum tissue of commercial broiler breed (Ross) was higher than in the corresponding tissues of other egg-laying hens and local breeds. In addition, there was a significant difference in the expression of the RAP2C gene between the high (H, n = 5) and low (L, n = 4) RGR groups. A total of 301 differentially expressed genes (DEGs) related to the RGR in white-feathered broiler were identified by transcriptome differential analysis between the H and L populations, among which NFKBIA, CSF1R and TLR2A were important hub genes. Furthermore, the candidate genes identified based on GWASs, meta-analysis and DEGs analysis were significantly enriched for gene ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways involved in the growth cone, integrated-mediated signaling pathway, and MAPK signaling pathway. Overall, the RAP2C, NFKBIA, CSF1R and TLR2A genes are considered the most important candidate genes influencing RGR trait in white-feathered broiler. These findings provide valuable insights into the complex system that regulates broiler growth.

Dietary supplement of veratric acid alleviates liver steatosis and reduces abdominal fat deposition in broilers

Nonalcoholic fatty liver disease (NAFLD) and obesity are nutritional metabolic diseases that are prevalent in the poultry industry, and have a negative impact on its functioning. Veratric acid (VA) is a phenolic acid compound extracted from the Chinese herbal medicine Trollius chinensis Bunge, known for its anti-inflammatory and antioxidant properties. In this study, we used chicken hepatocytes (Leghorn male hepatoma cells) and treated with a mixture of oleic acid and palmitic acid as well as Yellow-feathered broilers fed a high-fat diet to examine the impact of VA on liver-lipid metabolism and deposition of abdominal fat. The results showed that VA (1μM) reduced the triglyceride and total cholesterol levels in the chicken hepatocytes (p < 0.05). In the broiler NAFLD model, VA significantly reduced liver TG levels (p < 0.05) without affecting growth performance. Dietary supplementation with 0.05% or 0.1% VA supplementation also significantly reduced the mRNA expression levels of key genes involved in the synthesis of fatty acids such as sterol regulatory element-binding protein 1c, fatty acid synthase, and acetyl-CoA carboxylase in broiler livers. In addition, 0.1% VA reduced abdominal fat accumulation and improved blood biochemical indexes in broilers. Network pharmacology analysis suggested that VA may participate in regulating fat metabolism in broilers via the proliferator-activated receptor signaling pathway. Taken together, the study results support VA as a candidate feed additive to provide a novel strategy for preventing NAFLD and excessive fat deposition in chickens.

Epigallocatechin gallate improves oleic acid-induced hepatic steatosis in laying hen hepatocytes via the MAPK pathway

Fatty liver disease in laying hens, characterized by excessive lipid accumulation in hepatocytes, poses significant challenges to poultry health and production efficiency. In this study, we investigated the therapeutic potential of epigallocatechin gallate (EGCG), a bioactive compound found in green tea, in mitigating oleic acid (OA)-induced hepatic steatosis in primary chicken hepatocytes. Treatment with EGCG effectively attenuated lipid deposition by downregulating lipid synthesis-related genes. Moreover, EGCG mitigated oxidative stress, inflammation, DNA damage, and apoptosis induced by OA, thereby preserving hepatocyte viability. Mechanistically, EGCG exerted its protective effects by modulating the p38 MAPK signaling pathway. Our findings suggest that EGCG holds promise as a therapeutic agent for managing fatty liver disease in poultry, offering insights into novel strategies for improving poultry health and production outcomes.

Core competing endogenous RNA network based on mRNA and non-coding RNA expression profiles in chicken fatty liver

Fatty liver disease is a common metabolic disease in chickens. This disease can lead to a decrease in egg production and increase the risk of death in chickens. Long non-coding RNAs (lncRNAs) are involved in fatty liver formation by directly targeting genes or regulating gene expression by competitively binding microRNAs. However, a large proportion of competing endogenous RNA (ceRNA) networks in fatty liver diseases are still unclear. The total of 300 Jingxing-Huang chickens were used for fatty liver model construction. Then, differentially expressed (DE) genes (DEGs) identified through whole-transcriptome sequencing from four chickens with fatty liver and four chickens without fatty liver were chosen from the F1 generation. A total of 953 DEGs were identified between the fatty liver group and the control group, including 26 DE micro (mi)RNAs and 56 DE lncRNAs. Differential expression heatmaps and volcano plots were obtained after clustering expression analysis. Gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses revealed that these DEGs were involved in many biological processes and signaling pathways related to fatty acid metabolism and lipid synthesis. Furthermore, cytoscape was used to construct a ceRNA network of the DE miRNAs, DE mRNAs, and DE lncRNAs. Eleven DE lncRNAs, seven DE miRNAs, and 13 DE mRNAs were found to be associated with the pathogenesis of fatty liver disease. An lncRNA-miRNA-mRNA ceRNA network was constructed to elucidate the mechanisms of fatty liver diseases, and the ENSGALT00000079786-miR-140/miR-143/miR-1a/miR-22/miR-375 network was identified. These results provide a valuable resource for further elucidating the posttranscriptional regulatory mechanisms of chicken liver and adipose fat development or deposition.

Epigenetic regulation of H3K27me3 in laying hens with fatty liver hemorrhagic syndrome induced by high-energy and low-protein diets

BACKGROUND

Fatty liver hemorrhagic syndrome (FLHS) in the modern poultry industry is primarily caused by nutrition. Despite encouraging progress on FLHS, the mechanism through which nutrition influences susceptibility to FLHS is still lacking in terms of epigenetics.

RESULTS

In this study, we analyzed the genome-wide patterns of trimethylated lysine residue 27 of histone H3 (H3K27me3) enrichment by chromatin immunoprecipitation-sequencing (ChIP-seq), and examined its association with transcriptomes in healthy and FLHS hens. The study results indicated that H3K27me3 levels were increased in the FLHS hens on a genome-wide scale. Additionally, H3K27me3 was found to occupy the entire gene and the distant intergenic region, which may function as silencer-like regulatory elements. The analysis of transcription factor (TF) motifs in hypermethylated peaks has demonstrated that 23 TFs are involved in the regulation of liver metabolism and development. Transcriptomic analysis indicated that differentially expressed genes (DEGs) were enriched in fatty acid metabolism, amino acid, and carbohydrate metabolism. The hub gene identified from PPI network is fatty acid synthase (FASN). Combined ChIP-seq and transcriptome analysis revealed that the increased H3K27me3 and down-regulated genes have significant enrichment in the ECM-receptor interaction, tight junction, cell adhesion molecules, adherens junction, and TGF-beta signaling pathways.

CONCLUSIONS

Overall, the trimethylation modification of H3K27 has been shown to have significant regulatory function in FLHS, mediating the expression of crucial genes associated with the ECM-receptor interaction pathway. This highlights the epigenetic mechanisms of H3K27me3 and provides insights into exploring core regulatory targets and nutritional regulation strategies in FLHS.

Comprehensive Atlas of Alternative Splicing Reveals NSRP1 Promoting Adipogenesis through CCDC18

Alternative splicing (AS) plays a crucial role in regulating gene expression, function, and diversity. However, limited reports exist on the identification and comparison of AS in Eastern and Western pigs. Here, we analyzed 243 transcriptome data from eight tissues, integrating information on transcription factors (TFs), selection signals, splicing factors (SFs), and quantitative trait loci (QTL) to comprehensively study alternative splicing events (ASEs) in pigs. Five ASE types were identified, with Mutually Exclusive Exon (MXE) and Skipped Exon (SE) ASEs being the most prevalent. A significant portion of genes with ASEs (ASGs) showed conservation across all eight tissues (63.21-76.13% per tissue). Differentially alternative splicing genes (DASGs) and differentially expressed genes (DEGs) exhibited tissue specificity, with blood and adipose tissues having more DASGs. Functional enrichment analysis revealed coDASG_DEGs in adipose were enriched in pathways associated with adipose deposition and immune inflammation, while coDASG_DEGs in blood were enriched in pathways related to immune inflammation and metabolism. Adipose deposition in Eastern pigs might be linked to the down-regulation of immune-inflammation-related pathways and reduced insulin resistance. The TFs, selection signals, and SFs appeared to regulate ASEs. Notably, ARID4A (TF), NSRP1 (SF), ANKRD12, IFT74, KIAA2026, CCDC18, NEXN, PPIG, and ROCK1 genes in adipose tissue showed potential regulatory effects on adipose-deposition traits. NSRP1 could promote adipogenesis by regulating alternative splicing and expression of CCDC18. Conducting an in-depth investigation into AS, this study has successfully identified key marker genes essential for pig genetic breeding and the enhancement of meat quality, which will play important roles in promoting the diversity of pork quality and meeting market demand.

Mechanisms of hepatic steatosis in chickens: integrated analysis of the host genome, molecular phenomics and gut microbiome

Hepatic steatosis is the initial manifestation of abnormal liver functions and often leads to liver diseases such as nonalcoholic fatty liver disease in humans and fatty liver syndrome in animals. In this study, we conducted a comprehensive analysis of a large chicken population consisting of 705 adult hens by combining host genome resequencing; liver transcriptome, proteome, and metabolome analysis; and microbial 16S ribosomal RNA gene sequencing of each gut segment. The results showed the heritability (h2 = 0.25) and duodenal microbiability (m2 = 0.26) of hepatic steatosis were relatively high, indicating a large effect of host genetics and duodenal microbiota on chicken hepatic steatosis. Individuals with hepatic steatosis had low microbiota diversity and a decreased genetic potential to process triglyceride output from hepatocytes, fatty acid β-oxidation activity, and resistance to fatty acid peroxidation. Furthermore, we revealed a molecular network linking host genomic variants (GGA6: 5.59-5.69 Mb), hepatic gene/protein expression (PEMT, phosphatidyl-ethanolamine N-methyltransferase), metabolite abundances (folate, S-adenosylmethionine, homocysteine, phosphatidyl-ethanolamine, and phosphatidylcholine), and duodenal microbes (genus Lactobacillus) to hepatic steatosis, which could provide new insights into the regulatory mechanism of fatty liver development.

Cross-species analysis of differential transcript usage in humans and chickens with fatty liver disease

Background and Aim

Fatty liver disease is a common condition, characterized by excess fat accumulation in the liver. It can contribute to more severe liver-related health issues, making it a critical concern in avian and human medicine. Apart from modifying the gene expression of liver cells, the disease also alters the expression of specific transcript isoforms, which might serve as new biological markers for both species. This study aimed to identify cross-species genes displaying differential expressions in their transcript isoforms in humans and chickens with fatty liver disease.

Materials and Methods

We performed differential gene expression and differential transcript usage (DTU) analyses on messenger RNA datasets from the livers of both chickens and humans with fatty liver disease. Using appropriate cross-species gene identification methods, we reviewed the acquired candidate genes and their transcript isoforms to determine their potential role in fatty liver disease's pathogenesis.

Results

We identified seven genes - ALG5, BRD7, DIABLO, RSU1, SFXN5, STIMATE, TJP3, and VDAC2 - and their corresponding transcript isoforms as potential candidates (false discovery rate ≤0.05). Our findings showed that these genes most likely contribute to fatty disease development and progression.

Conclusion

This study successfully identified novel human-chicken DTU genes in fatty liver disease. Further research is encouraged to verify the functions and regulations of these transcript isoforms as potential diagnostic markers for fatty liver disease in humans and chickens.

Hepatic steatosis is associated with dysregulated cholesterol metabolism and altered protein acetylation dynamics in chickens

BACKGROUND

Hepatic steatosis is a prevalent manifestation of fatty liver, that has detrimental effect on the health and productivity of laying hens, resulting in economic losses to the poultry industry. Here, we aimed to systematically investigate the genetic regulatory mechanisms of hepatic steatosis in laying hens.

METHODS

Ninety individuals with the most prominent characteristics were selected from 686 laying hens according to the accumulation of lipid droplets in the liver, and were graded into three groups, including the control, mild hepatic steatosis and severe hepatic steatosis groups. A combination of transcriptome, proteome, acetylome and lipidome analyses, along with bioinformatics analysis were used to screen the key biological processes, modifications and lipids associated with hepatic steatosis.

RESULTS

The rationality of the hepatic steatosis grouping was verified through liver biochemical assays and RNA-seq. Hepatic steatosis was characterized by increased lipid deposition and multiple metabolic abnormalities. Integration of proteome and acetylome revealed that differentially expressed proteins (DEPs) interacted with differentially acetylated proteins (DAPs) and were involved in maintaining the metabolic balance in the liver. Acetylation alterations mainly occurred in the progression from mild to severe hepatic steatosis, i.e., the enzymes in the fatty acid oxidation and bile acid synthesis pathways were significantly less acetylated in severe hepatic steatosis group than that in mild group (P < 0.05). Lipidomics detected a variety of sphingolipids (SPs) and glycerophospholipids (GPs) were negatively correlated with hepatic steatosis (r ≤ -0.5, P < 0.05). Furthermore, the severity of hepatic steatosis was associated with a decrease in cholesterol and bile acid synthesis and an increase in exogenous cholesterol transport.

CONCLUSIONS

In addition to acquiring a global and thorough picture of hepatic steatosis in laying hens, we were able to reveal the role of acetylation in hepatic steatosis and depict the changes in hepatic cholesterol metabolism. The findings provides a wealth of information to facilitate a deeper understanding of the pathophysiology of fatty liver and contributes to the development of therapeutic strategies.

DNA methylome and transcriptome identified Key genes and pathways involved in Speckled Eggshell formation in aged laying hens

BACKGROUND

The quality of poultry eggshells is closely related to the profitability of egg production. Eggshell speckles reflect an important quality trait that influences egg appearance and customer preference. However, the mechanism of speckle formation remains poorly understood. In this study, we systematically compared serum immune and antioxidant indices of hens laying speckled and normal eggs. Transcriptome and methylome analyses were used to elucidate the mechanism of eggshell speckle formation.

RESULTS

The results showed that seven differentially expressed genes (DEGs) were identified between the normal and speckle groups. Gene set enrichment analysis (GSEA) revealed that the expressed genes were mainly enriched in the calcium signaling pathway, focal adhesion, and MAPK signaling pathway. Additionally, 282 differentially methylated genes (DMGs) were detected, of which 15 genes were associated with aging, including ARNTL, CAV1, and GCLC. Pathway analysis showed that the DMGs were associated with T cell-mediated immunity, response to oxidative stress, and cellular response to DNA damage stimulus. Integrative analysis of transcriptome and DNA methylation data identified BFSP2 as the only overlapping gene, which was expressed at low levels and hypomethylated in the speckle group.

CONCLUSIONS

Overall, these results indicate that aging- and immune-related genes and pathways play a crucial role in the formation of speckled eggshells, providing useful information for improving eggshell quality.

Oleic acid-induced steatosis model establishment in LMH cells and its effect on lipid metabolism

Hepatic steatosis is a highly prevalent liver disease, yet research on it is hampered by the lack of tractable cellular models in poultry. To examine the possibility of using organoids to model steatosis and detect it efficiently in leghorn male hepatocellular (LMH) cells, we first established steatosis using different concentrations of oleic acid (OA) (0.05-0.75 mmol/L) for 12 or 24 h. The subsequent detections found that the treatment of LMH cells with OA resulted in a dramatic increase in intracellular triglyceride (TG) concentrations, which was positively associated with the concentration of the inducing OA (R2 > 0.9). Then, the modeled steatosis was detected by flow cytometry after NileRed staining and it was found that the intensity of NileRed-A was positively correlated with the TG concentration (R2 > 0.93), which demonstrates that the flow cytometry is suitable for the detection of steatosis in LMH cells. According to the detection results of the different steatosis models, we confirmed that the optimal induction condition for the establishment of the steatosis model in LMH cells is OA (0.375 mmol/L) incubation for 12 h. Finally, the transcription and protein content of fat metabolism-related genes in steatosis model cells were detected. It was found that OA-induced steatosis could significantly decrease the expression of nuclear receptor PPAR-γ and the synthesis of fatty acids (SREBP-1C, ACC1, FASN), increasing the oxidative decomposition of triglycerides (CPT1A) and the assembly of low-density lipoproteins (MTTP, ApoB). Sterol metabolism in model cells was also significantly enhanced (HMGR, ABCA1, L-BABP). This study established, detected, and analyzed an OA-induced steatosis model in LMH cells, which provides a stable model and detection method for the study of poultry steatosis-related diseases.

Whole transcriptome RNA Sequencing Reveals the Global Molecular Responses and circRNA/lncRNA-miRNA-mRNA ceRNA Regulatory Network in Chicken Fat Deposition

Fat deposition is a vital factor affecting the economics of poultry production. Numerous studies on fat deposition have been done. However, the molecular regulatory mechanism is still unclear. In the present study, the whole-transcriptome RNA sequencing in abdominal fat, back skin, and liver both high- and low-abdominal fat groups was used to uncover the competitive endogenous RNA (ceRNA) regulation network related to chicken fat deposition. The results showed that differentially expressed (DE) genes in abdominal fat, back skin, liver were 1207(784 mRNAs, 330 lncRNAs, 41 circRNAs, 52 miRNAs), 860 (607 mRNAs, 166 lncRNAs, 26 circRNAs, 61 miRNAs), and 923 (501 mRNAs, 262 lncRNAs, 15 circRNAs, 145 miRNAs), respectively. The ceRNA regulatory network analysis indicated that the fatty acid metabolic process, monocarboxylic acid metabolic process, carboxylic acid metabolic process, glycerolipid metabolism, fatty acid metabolism, and peroxisome proliferator-activated receptor (PPAR) signaling pathway took part in chicken fat deposition. Meanwhile, we scan the important genes, FADS2, HSD17B12, ELOVL5, AKR1E2, DGKQ, GPAM, PLIN2, which were regulated by gga-miR-460b-5p, gga-miR-199-5p, gga-miR-7470-3p, gga-miR-6595-5p, gga-miR-101-2-5p. While these miRNAs were competitive combined by lncRNAs including MSTRG.18043, MSTRG.7738, MSTRG.21310, MSTRG.19577, and circRNAs including novel_circ_PTPN2, novel_circ_CTNNA1, novel_circ_PTPRD. This finding provides new insights into the regulatory mechanism of mRNA, miRNA, lncRNA, and circRNA in chicken fat deposition.

Analysis of DNA Methylation Profiles in Mandibular Condyle of Chicks With Crossed Beaks Using Whole-Genome Bisulfite Sequencing

Crossed beaks have been observed in at least 12 chicken strains around the world, which severely impairs their growth and welfare. To explore the intrinsic factor causing crossed beaks, this study measured the length of bilateral mandibular ramus of affected birds, and investigated the genome-wide DNA methylation profiles of normal and affected sides of mandibular condyle. Results showed that the trait was caused by impaired development of unilateral mandibular ramus, which is extended through calcification of mandibular condyle. The methylation levels in the CG contexts were higher than that of CHG and CHH, with the highest methylation level of gene body region, followed by transcription termination sites and downstream. Subsequently, we identified 1,568 differentially methylated regions and 1,317 differentially methylated genes in CG contexts. Functional annotation analysis of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes showed that these genes were involved in bone mineralization and bone morphogenesis. Furthermore, by combining the WGBS and previous RNA-Seq data, 11 overlapped genes were regulated by both long non-coding RNA and DNA methylation. Among them, FIGNL1 is an important gene in calcification of mandibular condyle. Generally, because the affected genes play key roles in maintaining mandibular calcification, these changes may be pivotal factors of crossed beaks.

Integrated analysis of the methylome and transcriptome of chickens with fatty liver hemorrhagic syndrome

Background

DNA methylation, a biochemical modification of cytosine, has an important role in lipid metabolism. Fatty liver hemorrhagic syndrome (FLHS) is a serious disease and is tightly linked to lipid homeostasis. Herein, we compared the methylome and transcriptome of chickens with and without FLHS.

Results

We found genome-wide dysregulated DNA methylation pattern in which regions up- and down-stream of gene body were hypo-methylated in chickens with FLHS. A total of 4155 differentially methylated genes and 1389 differentially expressed genes were identified. Genes were focused when a negative relationship between mRNA expression and DNA methylation in promoter and gene body were detected. Based on pathway enrichment analysis, we found expression of genes related to lipogenesis and oxygenolysis (e.g., PPAR signaling pathway, fatty acid biosynthesis, and fatty acid elongation) to be up-regulated with associated down-regulated DNA methylation. In contrast, genes related to cellular junction and communication pathways (e.g., vascular smooth muscle contraction, phosphatidylinositol signaling system, and gap junction) were inhibited and with associated up-regulation of DNA methylation.

Conclusions

In the current study, we provide a genome-wide scale landscape of DNA methylation and gene expression. The hepatic hypo-methylation feature has been identified with FLHS chickens. By integrated analysis, the results strongly suggest that increased lipid accumulation and hepatocyte rupture are central pathways that are regulated by DNA methylation in chickens with FLHS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07305-3.

A comprehensive comparison of residue-level methylation levels with the regression-based gene-level methylation estimations by ReGear

MOTIVATION

DNA methylation is a biological process impacting the gene functions without changing the underlying DNA sequence. The DNA methylation machinery usually attaches methyl groups to some specific cytosine residues, which modify the chromatin architectures. Such modifications in the promoter regions will inactivate some tumor-suppressor genes. DNA methylation within the coding region may significantly reduce the transcription elongation efficiency. The gene function may be tuned through some cytosines are methylated.

METHODS

This study hypothesizes that the overall methylation level across a gene may have a better association with the sample labels like diseases than the methylations of individual cytosines. The gene methylation level is formulated as a regression model using the methylation levels of all the cytosines within this gene. A comprehensive evaluation of various feature selection algorithms and classification algorithms is carried out between the gene-level and residue-level methylation levels.

RESULTS

A comprehensive evaluation was conducted to compare the gene and cytosine methylation levels for their associations with the sample labels and classification performances. The unsupervised clustering was also improved using the gene methylation levels. Some genes demonstrated statistically significant associations with the class label, even when no residue-level methylation features have statistically significant associations with the class label. So in summary, the trained gene methylation levels improved various methylome-based machine learning models. Both methodology development of regression algorithms and experimental validation of the gene-level methylation biomarkers are worth of further investigations in the future studies. The source code, example data files and manual are available at http://www.healthinformaticslab.org/supp/.