Dietary vitamin A restriction affects adipocyte differentiation and fatty acid composition of intramuscular fat in Iberian pigs

Fat infiltration in skeletal muscle: Influential triggers and regulatory mechanism

Fat infiltration in skeletal muscle (also known as myosteatosis) is now recognized as a distinct disease from sarcopenia and is directly related to declining muscle capacity. Hence, understanding the origins and regulatory mechanisms of fat infiltration is vital for maintaining skeletal muscle development and improving human health. In this article, we summarized the triggering factors such as aging, metabolic diseases and metabolic syndromes, nonmetabolic diseases, and muscle injury that all induce fat infiltration in skeletal muscle. We discussed recent advances on the cellular origins of fat infiltration and found several cell types including myogenic cells and non-myogenic cells that contribute to myosteatosis. Furthermore, we reviewed the molecular regulatory mechanism, detection methods, and intervention strategies of fat infiltration in skeletal muscle. Based on the current findings, our review will provide new insight into regulating function and lipid metabolism of skeletal muscle and treating muscle-related diseases.

Selection signature analysis reveals RDH5 performed key function in vision during sheep domestication process

Abstract. As one of the most successful domesticated animals in the Neolithic age, sheep gradually migrated all over the world with human activities. During the domestication process, remarkable changes have taken place in morphology, physiology, and behavior, resulting in different breeds with different characters via artificial and natural selection. However, the genetic background responsible for these phenotypic variations remains largely unclear. Here, we used whole genome resequencing technology to compare and analyze the genome differences between Asiatic mouflon wild sheep (Ovis orientalis) and Hu sheep (Ovis aries). A total of 755 genes were positively selected in the process of domestication and selection, and the genes related to sensory perception had directional evolution in the autosomal region, such as OPRL1, LEF1, TAS1R3, ATF6, VSX2, MYO1A, RDH5, and some novel genes. A missense mutation of c.T722C/p.M241T in exon 4 of RDH5 existing in sheep were found, and the T allele was completely fixed in Hu sheep. In addition, the mutation with the C allele reduced the retinol dehydrogenase activity encoding by RDH5, which can impair retinoic acid metabolism and further influenced the visual cycle. Overall, our results showed significant enrichment for positively selected genes involved in sensory perception development during sheep domestication; RDH5 and its variants may be related to the retinal degeneration in sheep. We infer that the wild sheep ancestors with weaker visual sensitivity were weeded out by humans, and the mutation was selective, swept by the dual pressures of natural and artificial selection.

Transcriptome shifts triggered by vitamin A and SCD genotype interaction in Duroc pigs

BACKGROUND

The composition of intramuscular fat depends on genetic and environmental factors, including the diet. In pigs, we identified a haplotype of three SNP mutations in the stearoyl-coA desaturase (SCD) gene promoter associated with higher content of monounsaturated fatty acids in intramuscular fat. The second of these three SNPs (rs80912566, C > T) affected a putative retinol response element in the SCD promoter. The effect of dietary vitamin A restriction over intramuscular fat content is controversial as it depends on the pig genetic line and the duration of the restriction. This study aims to investigate changes in the muscle transcriptome in SCD rs80912566 TT and CC pigs fed with and without a vitamin A supplement during the fattening period.

RESULTS

Vitamin A did not affect carcass traits or intramuscular fat content and fatty acid composition, but we observed an interaction between vitamin A and SCD genotype on the desaturation of fatty acids in muscle. As reported before, the SCD-TT pigs had more monounsaturated fat than the SCD-CC animals. The diet lacking the vitamin A supplement enlarged fatty acid compositional differences between SCD genotypes, partly because vitamin A had a bigger effect on fatty acid desaturation in SCD-CC pigs (positive) than in SCD-TT and SCD-TC animals (negative). The interaction between diet and genotype was also evident at the transcriptome level; the highest number of differentially expressed genes were detected between SCD-TT pigs fed with the two diets. The genes modulated by the diet with the vitamin A supplement belonged to metabolic and signalling pathways related to immunity and inflammation, transport through membrane-bounded vesicles, fat metabolism and transport, reflecting the impact of retinol on a wide range of metabolic processes.

CONCLUSIONS

Restricting dietary vitamin A during the fattening period did not improve intramuscular fat content despite relevant changes in muscle gene expression, both in coding and non-coding genes. Vitamin A activated general pathways of retinol response in a SCD genotype-dependant manner, which affected the monounsaturated fatty acid content, particularly in SCD-CC pigs.

Whole-Genome Selective Scans Detect Genes Associated With Important Phenotypic Traits in Sheep (Ovis aries)

Sheep (Ovis aries) is one of the important livestock with diverse phenotypic traits. However, little is known about the molecular mechanism of diverse phenotypic traits in domestic sheep. Using the genome-wide high-density SNP data (600K) in 253 samples from 13 populations, we conducted the tests of selective sweeps (i.e., pairwise F_ST and XP-CLR) associated with several important phenotypic traits (e.g., tail types, horn morphology, prolificacy, coat pigmentation, ear size, milk production, meat production, body size and wool fineness). We identified strong selective signatures in previously reported (e.g., T, RXFP2, BMPR1B, TYRP1, MSRB3, TF, CEBPA, GPR21 and HOXC8) and novel genes associated with the traits, such as CERS6, BTG1, RYR3, SLC6A4, NNAT and OGT for fat deposition in the tails, FOXO4 for fertility, PTCH1 and EMX2 for ear size, and RMI1 and SCD5 for body size. Further gene annotation analysis showed that these genes were identified to be the most probable genes accounting for the diverse phenotypic traits. Our results provide novel insights into the genetic mechanisms underlying the traits and also new genetic markers for genetic improvement in sheep and other livestock.

Piglet birthweight and sex affect growth performance and fatty acid composition in fatty pigs

This study aimed to determine the effects of piglet birthweight (BIW) and sex, and within-litter BIW variation, on postnatal growth traits and meat quality in fatty breeds of pig. In total, 406 crossbred piglets (half male, half female) born to Iberian sows were studied during their postnatal development until slaughter. After birth, piglets were classified into four BIW categories: very low, low, medium and high. There was a negative effect of low BIW on growth patterns and fatty acid (FA) composition, but effects of litter size and within-litter BIW variation were not found. The very low BIW piglets underwent a period of significant catch-up growth (P < 0.005) relative to high BIW piglets during the early postnatal phase, but also showed a higher feed conversion rate and lower average daily weight gain (P < 0.05 for both measures) throughout the study period. BIW affected development during the entire productive life, and the sex effect increased with age. As a result, the period to reach market weight was longer in very low BIW piglets, by 43 days for females and 15 days for males, compared with their high BIW counterparts. BIW and sex also influenced amount of intramuscular fat, n-3 FA content and monounsaturated FA composition. The study indicates that BIW, modulated by sex, is a critical point for productive traits in fatty pigs. These results provide a basis for future strategies to enhance productive efficiency and meat quality of traditional swine breeds.

Polyphenols and IUGR Pregnancies: Effects of Maternal Hydroxytyrosol Supplementation on Postnatal Growth, Metabolism and Body Composition of the Offspring

Maternal supplementation with the polyphenol hydroxytyrosol in a swine model of intrauterine growth restriction (IUGR) improves the fetal oxidative status, decreases the appearance of low birth-weight neonates and favors growth during early postnatal stages (lactation). The current study aimed to determine whether hydroxytyrosol supplementation can also improve developmental patterns, metabolic traits, and body composition of the offspring during later postnatal stages (from weaning to adulthood). A total of 21 piglets born from control untreated sows and 20 piglets born from sows treated with hydroxytyrosol during the last two-thirds of pregnancy were selected on the basis of similar body weights at weaning, for avoiding any interfering effects occurred during lactation. The pigs in the treated group had higher average daily weight gain (ADWG) and, therefore, reached higher body weight and corpulence, greater muscle development and higher adiposity than their control counterparts. The following were not found: significant effects on metabolism and body composition except changes in the muscular fatty acid composition of the treated pigs coming from the largest litters; those more affected by IUGR processes. These findings suggest that maternal supplementation with hydroxytyrosol may improve juvenile development of offspring in at-risk pregnancies and pave the way for more specific studies aiming to elucidate effects on adiposity, metabolism, and meat organoleptic characteristics.

Supplementation of All-Trans-Retinoic Acid Below Cytotoxic Levels Promotes Adipogenesis in 3T3-L1 Cells

Vitamin A, referred to as retinol, is an essential nutrient that affects the cell growth and differentiation including adipogenesis. Although previous studies using supraphysiological doses (over 1 μM) of all-trans-retinoic acid (atRA) demonstrated antiadipogenic activity, effects of atRA at various levels on differentiation of 3T3-L1 preadipocytes have not been extensively investigated. Our study showed that the amount of cellular triacylglycerol (TAG) and intensities of Oil-Red-O staining were decreased by supplementing atRA (1 and 10 μM) but increased by low concentrations of atRA (0.01 to 100 nM) compared with the control. Also PPARγ and FABP4 were gradually overexpressed by atRA up to 1 nM but decreased at over 1 nM concentrations. Moreover, mitotic clonal expansion (MCE) and consequential growth-arrest were analyzed as important steps in adipogenesis of 3T3-L1 cells. The 1 nM group showed more cell proliferation and thereafter a higher ratio of the G0/G1 phase on Day 2. Protein levels of S/G2-phase factors were dose dependently increased by atRA up to 1 nM on Day 1, but the factors were highly expressed in higher doses on Day 2. G0/G1 markers were higher at the higher doses of atRA on Day 1; whereas, they were highly expressed in mild or medium doses on Day 2. These data indicate that atRA controls adipogenesis with accompanied changes in cell proliferation and follow-up growth-arrest. These results indicate that atRA can function both as a negative and positive regulator of adipogenesis depending on dosages, providing a strategy for achieving proper nutritional balance for treatment of obesity.

Differential expression of mRNA isoforms in the skeletal muscle of pigs with distinct growth and fatness profiles

Background

The identification of genes differentially expressed in the skeletal muscle of pigs displaying distinct growth and fatness profiles might contribute to identify the genetic factors that influence the phenotypic variation of such traits. So far, the majority of porcine transcriptomic studies have investigated differences in gene expression at a global scale rather than at the mRNA isoform level. In the current work, we have investigated the differential expression of mRNA isoforms in the gluteus medius (GM) muscle of 52 Duroc HIGH (increased backfat thickness, intramuscular fat and saturated and monounsaturated fatty acids contents) and LOW pigs (opposite phenotype, with an increased polyunsaturated fatty acids content).

Results

Our analysis revealed that 10.9% of genes expressed in the GM muscle generate alternative mRNA isoforms, with an average of 2.9 transcripts per gene. By using two different pipelines, one based on the CLC Genomics Workbench and another one on the STAR, RSEM and DESeq2 softwares, we have identified 10 mRNA isoforms that both pipelines categorize as differentially expressed in HIGH vs LOW pigs (P-value < 0.01 and ±0.6 log₂fold-change). Only five mRNA isoforms, produced by the ITGA5, SEMA4D, LITAF, TIMP1 and ANXA2 genes, remain significant after correction for multiple testing (q-value < 0.05 and ±0.6 log₂fold-change), being upregulated in HIGH pigs.

Conclusions

The increased levels of specific ITGA5, LITAF, TIMP1 and ANXA2 mRNA isoforms in HIGH pigs is consistent with reports indicating that the overexpression of these four genes is associated with obesity and metabolic disorders in humans. A broader knowledge about the functional attributes of these mRNA variants would be fundamental to elucidate the consequences of transcript diversity on the determinism of porcine phenotypes of economic interest.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4515-2) contains supplementary material, which is available to authorized users.

TRIENNIAL GROWTH AND DEVELOPMENT SYMPOSIUM: Genetics and breeding for intramuscular fat and oleic acid content in pigs

The intramuscular fat (IMF) and oleic acid (OL) content have been favorably related to pork quality and human health. This influences the purchasing behavior of consumers and, therefore, also shifts the attention of breeding companies toward whether these traits are included into the breeding goal of the lines producing for high-valued markets. Because IMF and OL are unfavorably associated with lean content, a key economic trait, the real challenge for the industry is not simply to increase IMF and OL, but rather to come up with the right trade-off between them and lean content. In this paper we review the efforts performed to genetically improve IMF and OL, with particular reference to the research we conducted in a Duroc line aimed at producing high quality fresh and dry-cured pork products. Based on this research, we conclude that there are selection strategies that lead to response scenarios where IMF, OL, and lean content can be simultaneously improved. Such scenarios involve regular recording of IMF and OL, so that developing a cost-efficient phenotyping system for these traits is paramount. With the economic benefits of genomic selection needing further assessment in pigs, selection on a combination of pedigree-connected phenotypes and genotypes from a panel of selected genetic markers is presented as a suitable alternative. Evidence is provided supporting that at least a polymorphism in the leptin receptor and another in the stearoyl-CoA desaturase genes should be in that panel. Selection for IMF and OL results in an opportunity cost on lean growth. The extent to which it is affordable relies on the consumers' willingness to pay for premium products and on the cost to benefit ratio of alternative management strategies, such as specific dietary manipulations. How the genotype can influence the effect of the diet on IMF and OL remains a topic for further research.

Carotenoid intake and SCD genotype exert complementary effects over fat content and fatty acid composition in Duroc pigs

Nutritional and genetic strategies are needed to enhance intramuscular fat (IMF) and MUFA content without altering carcass leanness. Dietary vitamin A restriction has been suggested to specifically promote IMF, whereas a polymorphism of the () gene has shown to specifically increase MUFA. The purpose of this study was to investigate the combined effects of provitamin A (PVA) carotenoid intake and genotype (>) on hepatic retinoid content and on the liver, muscle (LM and gluteus medius [GM]), and subcutaneous fat (SF) content and fatty acid composition. Following a split-plot design, 32 castrated Duroc pigs, half of each of the 2 homozygous genotypes (CC and TT), were subjected from 165 to 195 d of age to 2 finishing diets differing in the PVA carotenoid content (an enriched-carotene diet [C+] and a control diet [C-]). Both diets were identical except for the corn line used in the feed. The C+ was formulated with 20% of a carotenoid-fortified corn (M37W-Ph3) whereas the C- instead used 20% of its near isogenic M37W line, which did not contain PVA carotenoids. No vitamin A was added to the diets. The C- was estimated to provide, at most, 1,300 IU of vitamin A/kg and the C+ to supply an extra amount of at least 800 IU vitamin A/kg. Compared with the pigs fed the C-, pigs fed with C+ had 3-fold more retinoic acid ( < 0.01) and 4-fold more gene expression in the liver ( = 0.06). The diet did not affect performance traits and backfat thickness, but pigs fed the C+ had less fat (4.0 vs. 5.0%; = 0.07) and MUFA (18.3 vs. 22.5%; = 0.01) in the liver, less IMF (5.4 vs. 8.3%; = 0.04) in the GM, and more fat content (90.4 vs. 87.9%; = 0.09) and MUFA (48.0 vs. 46.6%; = 0.04) in SF. The TT genotype at the gene increased MUFA ( < 0.05) in all tissues (21.4 vs. 19.5% in the liver, 55.0 vs. 53.1% in the LM, 53.9 vs. 51.7% in the GM, and 48.0 vs. 46.7% in SF for TT and CC genotypes, respectively). Liver fat and MUFA content nonlinearly declined with liver all- retinoic acid, indicating a saturation point at relatively low all- retinoic acid content. The results obtained provide evidence for a complementary role between dietary PVA and genotype, in the sense that the TT pigs fed with a low-PVA diet are expected to show higher and more monounsaturated IMF without increasing total fat content.

Transcriptomic Analysis Identifies Candidate Genes Related to Intramuscular Fat Deposition and Fatty Acid Composition in the Breast Muscle of Squabs (Columba)

Despite the fact that squab is consumed throughout the world because of its high nutritional value and appreciated sensory attributes, aspects related to its characterization, and in particular genetic issues, have rarely been studied. In this study, meat traits in terms of pH, water-holding capacity, intramuscular fat content, and fatty acid profile of the breast muscle of squabs from two meat pigeon breeds were determined. Breed-specific differences were detected in fat-related traits of intramuscular fat content and fatty acid composition. RNA-Sequencing was applied to compare the transcriptomes of muscle and liver tissues between squabs of two breeds to identify candidate genes associated with the differences in the capacity of fat deposition. A total of 27 differentially expressed genes assigned to pathways of lipid metabolism were identified, of which, six genes belonged to the peroxisome proliferator-activated receptor signaling pathway along with four other genes. Our results confirmed in part previous reports in livestock and provided also a number of genes which had not been related to fat deposition so far. These genes can serve as a basis for further investigations to screen markers closely associated with intramuscular fat content and fatty acid composition in squabs. The data from this study were deposited in the National Center for Biotechnology Information (NCBI)’s Sequence Read Archive under the accession numbers SRX1680021 and SRX1680022. This is the first transcriptome analysis of the muscle and liver tissue in Columba using next generation sequencing technology. Data provided here are of potential value to dissect functional genes influencing fat deposition in squabs.

Verification of suitable and reliable reference genes for quantitative real-time PCR during adipogenic differentiation in porcine intramuscular stromal-vascular cells

Intramuscular fat (IMF) is an important trait influencing meat quality, and intramuscular stromal-vascular cell (MSVC) differentiation is a key factor affecting IMF deposition. Quantitative real-time PCR (qPCR) is often used to screen the differentially expressed genes during differentiation of MSVCs, where proper reference genes are essential. In this study, we assessed 31 of previously reported reference genes for their expression suitability in porcine MSVCs derived form longissimus dorsi with qPCR. The expression stability of these genes was evaluated using NormFinder, geNorm and BestKeeper algorithms. NormFinder and geNorm uncovered ACTB, ALDOA and RPS18 as the most three stable genes. BestKeeper identified RPL13A, SSU72 and DAK as the most three stable genes. GAPDH was found to be the least stable gene by all of the three software packages, indicating it is not an appropriate reference gene in qPCR assay. These results might be helpful for further studies in pigs that explore the molecular mechanism underlying IMF deposition.