Cellularity of developing subcutaneous adipose tissue in Landrace and Meishan pigs: adipocyte size differences between two breeds

Growth Performance, Carcass Quality, and Lipid Metabolism in Krškopolje Pigs and Modern Hybrid Pigs: Comparison of Genotypes and Evaluation of Dietary Protein Reduction

This study compared the performance, meat quality and adipose tissue characteristics of Krškopolje pigs and modern hybrid pigs under identical rearing conditions, besides examining the effects of dietary protein reduction in both genotypes. A total of 29 pigs (14 Krškopolje and 15 hybrids) were assigned to litter into two dietary groups (high and low protein). The low-protein diet for hybrid pigs corresponded to the high-protein diet for Krškopolje pigs. All diets were iso-energetic. Dietary protein reduction decreased growth rate and muscle development in modern hybrids but had no significant impact on performance, quality or metabolic traits in Krškopolje pigs. Genotype differences revealed that Krškopolje pigs had lower growth rates, less lean and more fat deposition, as reflected in thicker subcutaneous and higher intramuscular fat compared to modern hybrids. Krškopolje pigs also exhibited higher myoglobin concentration and fatty acid saturation. Lipogenic enzyme activity and histo-morphological traits behaved in a tissue-specific manner but still indicated a greater lipogenic potential in Krškopolje pigs. This study provides valuable insights into breed-specific responses to dietary changes and highlights the unique characteristics of Krškopolje pigs.

Omentin expression in the ovarian follicles of Large White and Meishan sows during the oestrous cycle and in vitro effect of gonadotropins and steroids on its level: Role of ERK1/2 and PI3K signaling pathways

Omentin (ITLN1) is a novel adipokine mainly expressed in the white adipose tissue. It plays a crucial role in the metabolic homeostasis and insulin sensitivity. Our last study documented that ITLN1 levels in the adipose tissue and plasma are lower in fat Meishan (MS) compared to normal weight Large White (LW) pigs. The aim of this study was to investigate transcript and protein concentrations of ITLN1 as well as its immunolocalisation in the ovarian follicles and examine the molecular mechanism involved in the regulation of its expression in response to gonadotropins (FSH, LH) and steroids (P4, T, E2). Ovarian follicles were collected from LW and MS sows on days 2-3, 10-12, and 14-16 of the oestrous. We found the elevated ITLN1 expression in the ovarian follicles and the increase of concentrations in follicular fluid (FF) of LW pigs vs MS pigs; in both breeds of pigs, the levels of ITLN1 increased with the oestrous progression. We noted ITLN1 signals in oocyte, granulosa and theca cells. Gonadotropins and steroids increased ITLN1 levels in the ovarian follicle cells of LW pigs, while in MS pigs, we observed only the stimulatory effect of LH and T. Both extracellular signal-regulated kinase (ERK1/2) and phosphatidylinositol 3'-kinase (PI3K) were involved in the regulation of ITLN1. Our study demonstrated the levels and regulation of ITLN1 in the porcine ovarian follicles through ERK1/2 and PI3K signaling pathways.

Tissue properties and respiratory kinematics of the tongue base and soft palate in the obese OSA minipig

Obesity is a common finding and a major pathogenetic factor in obstructive sleep apnea (OSA) in adults. To understand the mechanisms behind this, the present study investigated the tissue properties and respiratory kinematics of the tongue base and soft palate in the obese OSA minipig model. In 4 verified obese/OSA and 3 non-obese/non-OSA control minipigs, MRI fat-weighted images, ultrasound elastography (USE), and sleep video-fluoroscopy (SVF) were performed to quantify the fat composition, tissue stiffness, and respiratory kinematics of the tongue base and soft palate during sedated sleep. The results indicated that the fat composition gradually increased from the rostral to caudal tongue base, particularly in the posterior 1/3 of the tongue base, regardless of the presence of obesity and OSA. However, this trend was not seen in the soft palate and pharyngeal wall. The pharyngeal wall presented the highest fat composition as compared with the tongue base and soft palate. Overall, obese OSA minipigs showed stiffer tongue tissue than the controls, particularly in the rostral region of the tongue in obese Yucatan minipigs. The respiratory moving ranges of the soft palate were greater in both dorsal-ventral and rostral-caudal directions and during both respiratory and expiratory phases in OSA obese than control minipigs, and the largest moving ranges were seen in OSA obese Panepinto minipigs. The moving range of the tongue base was significantly smaller. These results suggest more fat infiltration in the caudal region of the tongue base regardless of the presence of obesity and/or OSA. The greater tissue stiffness of the tongue in obese OSA minipigs may result from altered neuromuscular drive.

Pork Fat and Meat: A Balance between Consumer Expectations and Nutrient Composition of Four Pig Breeds

Food fat content is one of the most controversial factors from a consumer's point of view. Aim: (1) The trends in consumer attitudes towards pork and the fat and meat compositions in Duroc and Altai meat breeds and Livny and Mangalitsa meat and fat breeds were studied. (2) Methods: Netnographic studies were used to assess Russian consumer purchasing behavior. Protein, moisture, fat, backfat fatty acid content from pigs, longissimus muscles, and backfat from (A) Altai, (L) Livny, and (M) Russian Mangalitsa breeds were compared with those from (D) Russian Duroc. Raman spectroscopy and histology were applied to the backfat analysis. (3) Results: The attitude of Russian consumers to fatty pork is contradictory: consumers note its high fat content as a negative factor, but the presence of fat and intramuscular fat is welcomed because consumers positively associate them with better taste, tenderness, flavor, and juiciness. The fat of the 'lean' D pigs did not show a "healthy" fatty acid ratio, while the n-3 PUFA/n-6 PUFA ratio in the fat of the M pigs was the best, with significant amounts of short-chain fatty acids. The highest UFA content, particularly omega 3 and omega 6 PUFA, was found in the backfat of A pigs with a minimum SFA content. The backfat of L pigs was characterized by a larger size of the adipocytes; the highest monounsaturated and medium chain fatty acid contents and the lowest short-chain fatty acid content; the ratio of omega 3 to omega 6 was 0.07, and the atherogenicity index in L backfat was close to that of D, despite the fact that D pigs are a meat type, while L pigs are a meat and fat type. On the contrary, the thrombogenicity index in L backfat was even lower than the D one. (4) Conclusions: Pork from local breeds can be recommended for functional food production. The requirement to change the promotion strategy for local pork consumption from the position of dietary diversity and health is stated.

Differences in histomorphology and expression of key lipid regulated genes of four adipose tissues from Tibetan pigs

Tibetan pigs, an indigenous pig breed in China, have high overall fat deposition and flavorful and tasty meat. They are thus good models for studying adipogenesis. Few studies have been conducted focusing on expression of lipid regulated genes in different adipose tissues of Tibetan pigs. Therefore, we compared the difference of histomorphology and expression level of lipid regulated genes through qPCR and western blot in subcutaneous fat, perirenal fat, omental adipose tissue, and inguinal fat of Tibetan pigs. Our results showed that the area of subcutaneous adipocytes in Tibetan pigs was smaller, while the other three adipose tissues (perirenal fat, greater omentum fat, inguinal fat) had cell areas of similar size. The gene expression of FABP4, FASN, FABP3, and ME1 in subcutaneous fat was significantly higher than that in perirenal fat. Furthermore, the protein expression of FABP4 was significantly lower in subcutaneous fat than in perirenal fat (p < 0.05), and the expression of FASN was higher in greater omentum fat than in subcutaneous fat (p = 0.084). The difference in adipocyte cell size and expression of lipid-regulated genes in adipose tissues from the various parts of the pig body is likely due to the different cellular lipid metabolic processes. Specially, FABP4 and FASN may be involved in the regulation of fat deposition in different adipose tissues of Tibetan pigs.

Pig adipose tissue of two different breeds and locations: morphology and Raman studies

According to the recent data, there are 4–5-local pig breeds left in Russia by now. Livni is among them. This breed is characterized by high fat content. Back fat has been analyzed earlier. We aimed to assess fat morphometrics from other localizations in pigs. Sacral, axillary, and perirenal fat samples from 6-month-old Duroc and Livni pig breeds were analyzed using morphological and Raman-based techniques. Livni adipocytes were characterized by dense packing with a polyhedron-like structure. In Duroc fat, they were more rounded (spherical). A “two-phase” cell disperse was identified in all samples. Fat cells in Livni pigs were bigger than those in the Duroc breed: 70–102%; 15–18 and 26% for sacral, axillary, and perirenal locations. Differences in the intensity of the Raman signal between the samples were found: in the samples of subcutaneous adipose tissue, more intense peaks were observed, which are responsible for unsaturation; the samples of Livni axillary fat were characterized by greater unsaturation than sacral fat. Livni and Duroc adipocytes differ from each other in form and size and the difference depends on location. Pork fat from local breeds is expected to have potentially more health protecting (for animals) and health promoting (for consumers) properties.

Difference in developmental dynamics between subcutaneous and abdominal adipose tissues in goose (Anser Cygnoides)

Goose (Anas cygnoides), as a typical species domesticated from a migratory bird, has maintained the capability of depositing excess lipid and preferentially accumulating fat within the abdomen and subcutaneous, which not only leads to decrease in yield of meat product, but also affects the feed conversion rate. Here, an experiment was conducted to examine the difference in developmental dynamics between subcutaneous (SAT) and abdominal adipose tissues (AAT) in goose. The results showed that SAT could be clearly observed at embryonic days (E) 15, whereas AAT were clearer until E20. Although the weights of SAT and AAT showed a significant rising with advancing age (P < 0.05), their gains were not completely uniform, and more adipose deposited preferentially toward AAT after birth (P < 0.05). Additionally, a clear expansion in adipocyte size was observed in AAT and SAT during embryonic stages (P < 0.05). The average adipocyte area in AAT continued to increase after birth (P < 0.05), while the cell areas in SAT were relatively invariable (P > 0.05). Furthermore, the expression levels of FABP4/aP2, ACSL1 and PPARγ were much higher in SAT than in AAT, whereas relative higher expression level of IL-6 was observed in the AAT during embryonic stages. After birth, the more expression of LPL and PPARα were detected in AAT than did in SAT (P < 0.05), whereas greater ATGL expression was in SAT (P < 0.05). Taken together, these findings suggest that AAT may display greater fat storage capacity than SAT accompanied by changes in cell area and lipogenic capacity. Considering that there is disparity in the individual adipose tissues, we suggested that careful consideration for the precise interventions used to control SAT or AAT deposition in meat-producing animals to improve feed efficiency.

Adipokines expression profiles in both plasma and peri renal adipose tissue in Large White and Meishan sows: A possible involvement in the fattening and the onset of puberty

In pig, backfat deposition is strongly related to the growth and reproductive performance. However, the molecular regulatory mechanisms of adipose tissue are not clearly understood. Adipose tissue is now recognized as an important endocrine organ that secretes a variety of factors including adipokines. However, the regulation of expression pattern of these adipokines in both plasma and visceral white adipose tissue (WAT) in lean and fat pig is unclear. In the present study, we used two representative porcine breeds (Large White, LW; Meishan, MS) with contrasting backfat thickness and sexual maturity age. Using specific ELISA assays, we determined the plasma profile of eight adipokines, leptin, adiponectin, visfatin, apelin, chemerin, resistin, omentin and vaspin in LW and MS sows. By RT-qPCR and western-blot we also investigated the mRNA and protein levels of these adipokines and their cognate receptors (LEPR, ADIPOR1, ADIPOR2, CMKLR1, CCRL2, GPR1, APLNR, TLR4, ROR1, CAP1 and HSPA5) in the peri renal WAT, respectively. At both plasma and peri renal WAT level, we found that the amounts of leptin, chemerin, resistin and vaspin were higher whereas those of adiponectin and omentin were lower in MS than LW sows. Plasma and adipose tissue visfatin and apelin levels were not different between the two breeds. Moreover, we noted that the variations of peri renal WAT adipokines observed between MS and LW were similar at the protein and mRNA level except for chemerin and apelin suggesting post-transcriptional modifications for these two adipokines. Finally, among the eight adipokines studied, we showed that only the plasma concentrations of leptin and chemerin were positively and those of adiponectin, negatively associated with the thickness of fat and opposite correlation was found for the onset of puberty in both LW and MS animals. Taken together, these results support a potential involvement of adipokines in WAT regulation and its link with the onset of the puberty in sows.

Lipid Deposition and Metabolism in Local and Modern Pig Breeds: A Review

Modern pig breeds, which have been genetically improved to achieve fast growth and a lean meat deposition, differ from local pig breeds with respect to fat deposition, fat specific metabolic characteristics and various other properties. The present review aimed to elucidate the mechanisms underlying the differences between fatty local and modern lean pig breeds in adipose tissue deposition and lipid metabolism, taking into consideration morphological, cellular, biochemical, transcriptomic and proteomic perspectives. Compared to modern breeds, local pig breeds accumulate larger amounts of fat, which generally contains more monounsaturated and saturated fatty acids; they exhibit a higher adipocyte size and higher activity of lipogenic enzymes. Studies using transcriptomic and proteomic approaches highlighted several processes like immune response, fatty-acid turn-over, oxidoreductase activity, mitochondrial function, etc. which differ between local and modern pig breeds.

Comparing pig breeds with genetically low and high backfat thickness: differences in expression of adiponectin, its receptor, and blood metabolites

Here we characterized gene expressions in subcutaneous adipose tissue and blood metabolites of pigs with genetically low backfat (Landrace) and high backfat (Meishan). As pigs aged from 1 wk-to 3-mo old, mRNA levels of adipose-specific genes increased, although their gene expressions coding for major enzymes involved in lipid metabolism (lipoprotein lipase, fatty acid synthase, and hormone-sensitive lipase) did not differ between lean and fat pigs. Instead, there were significant effects for adiponectin and its receptor AdipoR1 mRNA levels between the two breeds of which respective expressions were lower and higher in Meishan by 3 mo of age. Contrary to changes in gene expressions, the concentrations of blood glucose, triglyceride (TG), and NEFA in both breeds decreased during growth, and 3-mo-old Meishan evidenced lower glucose with higher TG than the Landrace. The homeostasis model assessment insulin resistance (HOMA-IR) index was also calculated from the measurements of fasting glucose and insulin concentration, and Meishan showed a higher value than the Landrace. We next examined these differences in Landrace and Meishan crossbreds, which were phenotypically distinguishable by the backfat thickness as the former lean type and the latter fat type. As with the purebreds, high backfat Meishan crosses showed the characteristics of lower glucose and higher TG in circulating levels and also lower adiponectin transcripts in subcutaneous adipose tissue. Collectively, our results demonstrate that levels of adiponectin and its receptor gene expressions, blood glucose, blood lipids, and HOMA-IR in pigs vary between lean and fat. These observations strongly suggest the possibility that overall metabolic differences rather than adipocyte ability itself contribute to the fatness of genetically high backfat pigs.

Differences in gene expression profiles for subcutaneous adipose, liver, and skeletal muscle tissues between Meishan and Landrace pigs with different backfat thicknesses

Backfat thickness is one of the most important traits of commercially raised pigs. Meishan pigs are renowned for having thicker backfat than Landrace pigs. To examine the genetic factors responsible for the differences, we first produced female crossbred pig lines by mating Landrace (L) × Large White (W) × Duroc (D) females (LWD) with Landrace (L) or Meishan (M) boars (i.e., LWD × L = LWDL for Landrace offspring and LWD × M = LWDM for the Meishan offspring). We confirmed that LWDM pigs indeed had a thicker backfat than LWDL pigs. Next, we performed gene expression microarray analysis in both genetic lines to examine differentially expressed genes (DEGs) in energy metabolism-related tissues, subcutaneous adipose (fat), liver, and longissimus dorsi muscle tissues. We analyzed the annotation of DEGs (2-fold cutoff) to functionally categorize them by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathways. The number of DEGs in muscle tissues of both lines was much less than that in fat and liver tissues, indicating that DEGs in muscle tissues may not contribute much to differences in backfat thickness. In contrast, several genes related to muscle (in fat tissue) and lipid metabolism (in liver tissue) were more upregulated in LWDM pigs than LWDL pigs, indicating that those DEGs might be responsible for differences in backfat thickness. The different genome-wide gene expression profiles in the fat, liver, and muscle tissues between genetic lines can provide useful information for pig breeders.

Changes in adipose cells of Longissimus dorsi muscle in Iberian pigs raised under extensive conditions

Twenty-four Iberian castrated male pigs were used to characterize and evaluate the effect of the duration of "Montanera" in the adipocytes size and its relation with the backfat thickness and intramuscular fat. The animals were fed under extensive conditions during 30, 60 and 90 days in the "Dehesa" before slaughtered. Carcass weight, percentage of intramuscular fat, thickness of backfat and its three layers and adipocytes size of the intramuscular fat were obtained. The group which expended 90 days on fattening obtained the highest adipocytes, with an area higher by a 50% than those that only expended 30 days. The differences in diameter and perimeter adipocyte were not as marked as area. A significant positive correlation between the diameter, area and perimeter of adipocyte with the backfat thickness were found. The fat cells in Iberian pig hypertrophy during the "montanera stage", being this increase significant from month to month in this period of fattening. Also, this adipocyte increase is correlated with the animal weight. The correlation between adipocyte size and inner layer of backfat shows that the inner layer obtained in live pig by ultrasound techniques could be a good marker of fat infiltration in pigs fattening in "montanera" system.

Genomic signatures reveal selection of characteristics within and between Meishan pig populations

The Chinese Meishan pig breed is well known for its high prolificacy. Moreover, this breed can be divided into three types based on their body size: big Meishan, middle Meishan (MMS) and small Meishan (SMS) pigs. Few studies have reported on the genetic signatures of Meishan pigs, particularly on a genome-wide scale. Exploring for genetic signatures could be quite valuable for revealing the genetic architecture of phenotypic variation. Thus, we performed research in two parts based on the genome reducing and sequencing data of 143 Meishan pigs (74 MMS pigs, 69 SMS pigs). First, we detected the selection signatures among all Meishan pigs studied using the relative extended haplotype homozygosity test. Second, we detected the selection signatures between MMS and SMS pigs using the cross-population extended haplotype homozygosity and F_ST methods. A total of 111 398 SNPs were identified from the sequenced genomes. In the population analysis, the most significant genes were associated with the mental development (RGMA), reproduction (HDAC4, FOXL2) and lipid metabolism (ACACB). From the cross-population analysis, we detected genes related to body weight (SPDEF, PACSIN1) in both methods. We suggest that rs341373351, located within the PACSIN1 gene, might be the causal variant. This study may have achieved consistency between selection signatures and characteristics within and between Meishan pig populations. These findings can provide insight into investigating the molecular background of high prolificacy and body size in pig.

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.

A novel and robust method for testing bimodality and characterizing porcine adipocytes of adipose tissue of 5 purebred lines of pig

Adipocyte sizes from adipose tissue of mature animals form a bimodal distribution, thus reporting mean cell size is misleading. The objectives of this study were to develop a robust method for testing bimodality of porcine adipocytes, describe the size distribution with an informative metric, and statistically test hypertrophy and appearance of new small adipocytes, possibly resulting from hyperplasia or lipid filling of previously divided fibroblastic cells. Ninety-three percent of adipose samples measured were bimodal (P < 0.0001); therefore, we describe and propose a method of testing hyperplasia or lipid filling of previously divided fibroblastic cells based upon the probability of an adipocyte falling into 2 chosen competing “bins” as adiposity increases. We also conclude that increased adiposity is correlated positively with an adipocyte being found in the minor mode (r = 0.46) and correlated negatively with an adipocyte being found in the major mode (r = −0.22), providing evidence of either hyperplasia or lipid filling of previously divided fibroblastic cells. We additionally conclude that as adiposity increases, the mode of the major distribution of cells occurs at a larger diameter of adipocyte, indicating hypertrophy.

The relationship between adipocyte size and the transcript levels of SNAP23, BSCL2 and COPA genes in pigs

Breed-specific differences in fat tissue accumulation in the pig provide an opportunity to study the genetic background of this process. In the present study three pig breeds, differing in fatness, were analyzed in terms of the size of adipocytes derived from three tissues (subcutaneous, visceral and longissimus dorsi muscle) in relation to transcript levels of genes (SNAP23, BSCL2 and COPA), which encode proteins involved in lipid droplet formation. The analysis of adipocyte size revealed significant effects of breed and tissue and confirmed earlier reports that an elevated backfat thickness in some pig breeds is correlated with a larger adipocyte size. Variability in the transcript abundance of the studied genes among breeds and tissues was observed. We found a positive correlation between the abundance of the SNAP23 transcript and adipocyte diameter. The obtained results indicate that SNAP23 may be considered as an interesting candidate gene involved in adipose tissue growth in the pig.

Genetics of Adiposity in Large Animal Models for Human Obesity-Studies on Pigs and Dogs

The role of domestic mammals in the development of human biomedical sciences has been widely documented. Among these model species the pig and dog are of special importance. Both are useful for studies on the etiology of human obesity. Genome sequences of both species are known and advanced genetic tools [eg, microarray SNP for genome wide association studies (GWAS), next generation sequencing (NGS), etc.] are commonly used in such studies. In the domestic pig the accumulation of adipose tissue is an important trait, which influences meat quality and fattening efficiency. Numerous quantitative trait loci (QTLs) for pig fatness traits were identified, while gene polymorphisms associated with these traits were also described. The situation is different in dog population. Generally, excessive accumulation of adipose tissue is considered, similar to humans, as a complex disease. However, research on the genetic background of canine obesity is still in its infancy. Between-breed differences in terms of adipose tissue accumulation are well known in both animal species. In this review we show recent advances of studies on adipose tissue accumulation in pigs and dogs, and their potential importance for studies on human obesity.

Breed-specific lipid-related gene expression in the subcutaneous fat of Large White and Erhualian pigs at weaning

Abstract. The Erhualian (EHL) pig possesses significantly lower growth rates and higher adipose deposition compared with the Large White (LW) pig. To further understand the mechanism of breed lipid deposition difference at the early postnatal age, we employed an animal model of EHL and LW pigs at weaning age to compare the lipid metabolism differences in subcutaneous fat. The result showed that serum triglyceride in EHL was significantly higher (P < 0.05) than that of LW. Peroxisome proliferator-activated receptor-γ protein level in EHL was significantly higher (P < 0.01) though CCTTA enhancer-binding protein level demonstrated no change compared with LW pigs. Hormone sensitive lipase, adipose tissue triglyceride lipase mRNA expression and the lipase activity were significantly lower (P < 0.05) in EHL. Uncoupling protein-2 protein content was significantly lower (P < 0.01) in EHL than that in LW pigs. We first cloned the nucleotide sequence of Zinc-α2-glycoprotein (ZAG) with 1090 bp and found that both ZAG mRNA expression and protein level in EHL pigs was significantly lower (P < 0.01) than that of LW pigs. β3 adrenergic receptor mRNA expression in EHL pigs was significantly higher (P < 0.01) than that of LW pigs, though tumour necrosis factor α gene expression demonstrated no significant difference. Therefore, the significant breed lipid metabolism difference in subcutaneous fat exists at an early postnatal age between EHL and LW pigs, and this difference may originate from two causes including the increased lipid synthesis and reduced lipid mobilization in EHL pigs compared with LW pigs.

MicroRNA-33b downregulates the differentiation and development of porcine preadipocytes

Sterol regulatory element binding transcription factor (SREBF) is a key transcription regulator for lipid homeostasis. MicroRNA-33b (miR-33b) is embedded in intron 16 of porcine SREBF1 and is conserved among most mammals. Here, we investigated the effect of miR-33b on adipocyte differentiation and development in porcine subcutaneous pre-adipocytes (PSPA). PSPA were transiently transfected with miR-33b, and adipose differentiation was then induced. Delayed adipose differentiation and decreased lipid accumulation were observed in miR-33b-transfected PSPA. Computational predictions suggested that miR-33b may target early B cell factor 1 (EBF1), an adipocyte activator of lipogenesis regulators such as CCAAT-enhancer binding protein alpha (C/EBPα) and peroxisome proliferator-activated receptor gamma (PPARγ). Both gene and protein expression of EBF1 were downregulated in miR-33b-transfected PSPA, followed by considerable decreases in the expression of C/EBPα and PPARγ and their downstream lipogenic genes. However, miR-33b transfection did not markedly affect mRNA and protein expression of SREBF1. We also investigated differences in the expression of miR-33b and lipogenic genes in subcutaneous fat tissues between 5-month-old crossbred gilts derived from Landrace (lean-type) and Meishan (fatty-type) boars. Landrace-derived crossbred gilts expressed more miR-33b and less lipogenic genes than did gilts derived from Meishan. Our results suggest that miR-33b affected the differentiation and development of PSPA by attenuating the lipogenic gene expression cascade through EBF1 to C/EBPα and PPARγ. The differential expression of miR-33b observed in crossbred gilts may in part account for differences in lipogenic gene expression and the fat:lean ratio between pig breeds.