Introduction
Intramuscular adipocytes were mainly generated at the foetal and neonatal stages (Tong et al., Reference Tong, Zhu, Underwood, Hess, Ford and Du2008), they would provide the sites for intramuscular fat (IMF) accumulation that generate marbling at the fattening stage in offspring (Du et al., Reference Du, Tong, Zhao, Underwood, Zhu, Ford and Nathanielsz2010). Zhu et al. (Reference Zhu, Ford, Means, Hess, Nathanielsz and Du2006) reported that adipose tissue occurred before mid-gestation in many mammals, and maternal malnutrition or over-nutrition affected the overall fat accumulation of offspring. These results suggested that lipid synthesis and degradation in offspring were impacted by maternal nutrition. Previous reports demonstrated that adipose tissue deposition depends on the balance between lipid synthesis and degradation (Qiao et al., Reference Qiao, Huang, Li, Liu, Hao, Shi, Dai and Xie2007; Miao et al., Reference Miao, Zhu, Zhang, Chang, Xie, Zhang and Xu2010). This process is mainly regulated by fatty acids synthase (FASN) and hormone-sensitive lipase (LIPE). The FASN exerts a vital role in de novo lipogenesis of mammals (Smith et al., Reference Smith, Witkowski and Joshi2003). Whereas, the LIPE plays an important role in hydrolysing triglycerol (TG) to free fatty acids (FFA) in adipose tissue, and regulates the lipolysis of animals (Haemmerle et al., Reference Haemmerle, Zimmermann and Zechner2003). The ratio of FASN/LIPE mRNA expression and FASN mRNA expression was positively related to carcass fat content in pigs (Miao et al., Reference Miao, Zhu, Zhang, Chang, Xie, Zhang and Xu2010). Growing evidence showed that vitamin D3, the active metabolite of vitamin D, is recognized as a potential regulator of adipogenesis (Wang et al., Reference Wang, Yang, Harris, Nelson, Busboom, Zhu and Du2016). There is a negative relationship between obesity (excessive fat accumulation) and vitamin D deficiency (Caron-Jobin et al., Reference Caron-Jobin, Morisset, Tremblay, Huot, Légaré and Tchernof2011; Marcotorchino et al., Reference Marcotorchino, Tournaiaire and Landrier2013). In addition, serum vitamin D levels are negatively correlated with body fat content (Boon et al., Reference Boon, Hul, Sicard, Kole, Van Den Berg, Viguerie, Langin and Saris2006; Fish et al., Reference Fish, Beverstein, Olson, Reinhardt, Garren and Gould2010), and obese individual had lower serum vitamin D levels (Beckman et al., Reference Beckman, Earthman, Thomas, Compher, Muniz, Horst, Ikramuddin, Kellogg and Sibley2013; Carrelli et al., Reference Carrelli, Bucovsky, Horst, Cremers, Zhang, Bessler, Schrope, Evanko, Blanco, Silverberg and Stein2017). These results indicated that adipogenesis was affected by vitamin D status. Previous studies observed that vitamin D3 inhibited differentiation and adipogenesis of 3T3-L1 preadipocytes by inhibiting peroxisome proliferator-activated receptor-γ (PPARγ), CCAAT/enhancer binding protein alpha, fatty acid binding protein 4 and stearoyl-CoA desaturase-1 expression (Ishida et al., Reference Ishida, Taniguchi and Baba1988; Ji et al., Reference Ji, Doumit and Hill2015). Dix et al. (Reference Dix, Barcley and Wright2018) found that TG accumulation in 3T3-L1 preadipocytes was increased by lower vitamin D3 dosage. Zhuang et al. (Reference Zhuang, Lin and Yang2007) also reported that vitamin D3 inhibited porcine preadipocyte differentiation via reducing the expression of PPARγ and retinoid X receptor alpha mRNA. Whereas, vitamin D3 inhibited proliferation in bone marrow stromal cells from pigs and increased lipid accumulation (Zhuang et al., Reference Zhuang, Lin and Yang2007). Mahajan and Stahl, (Reference Mahajan and Stahl2009) also observed that vitamin D3 enhanced PPARγ, lipoprotein lipase and adipocyte fatty acid binding protein 2 expression in mature adipocytes from porcine subcutaneous adipose tissue. These results suggested that vitamin D had a stimulatory effect on adipogenesis in mature adipocytes. Although, it is clear that vitamin D3 is involved in the regulation of fat accumulation and lipid metabolism by regulating adipogenic gene expression, reports about the role of maternal vitamin D3 during pregnancy in adipogenic genes expression of muscle and adipose tissue from offspring pigs are missing. Because maternal nutrition could affect foetal epigenome by improving the intrauterine environment (Sinclair et al., Reference Sinclair, Allegrucci, Singh, Gardner, Sebastian, Bispham, Thurston, Huntley, Rees, Maloney, Lea, Craigon, McEvoy and Young2007; Chango and Pogribny, Reference Chango and Pogribny2015). Therefore, the aim of this present study was to explore the effects of maternal vitamin D3 during pregnancy on FASN and LIPE mRNA expression in longissimus dorsal muscle and subcutaneous adipose tissue from offspring pigs, and relation with carcass fat, IMF content and average backfat thickness (ABFT).
Material and methods
Experimental design and diets
All animals handing protocols in this study were approved by the Animal Care and Use Committee of Henan Institute of Science and Technology (Xinxiang, P.R. China). A total of nine pregnant sows (41 days of gestation) with the same parities and similar body weights (143.47 ± 2.1 kg) were randomly divided into low vitamin D3 (LD), normal vitamin D3 (ND) and high vitamin D3 (HD) groups, which were fed 200, 800 and 3200 IU of vitamin D3/kg basal diet, respectively. Each group includes three replicates with 1 sow per replicate. The feeding trials were separated into two stages, including pregnant sows and their offspring pigs in this present study. All diets for pregnant sows and their offspring pigs were formulated to meet or exceed the national research council (NRC 2012) recommendations, and shown in Tables 1–3, respectively. The feeding trial of pregnant sows from 41 days of gestation until birth. From birth, A total of 72 piglets (sex balance) from all their 119 offspring were allotted into three groups again according to their mother fed different vitamin D3 concentrations. Each group has three replicates with eight offspring piglets (sex balance) per replicate, and all groups fed the same vitamin D3 replete diet. The feeding trial of their offspring pigs from birth to 150 days of age. A total of 18 offspring pigs (six offspring pigs per maternal diet group, sex balance) were weighed and slaughtered for tissue collection at 150 days of age. During this period all piglets were reared in the same condition, and had ad libitum access to an experimental diet and water via nipple drinkers.
Table 1. Gestation diet composition of sowa
DE, digestible energy; CP, crude protein; Lys, lysine; Met, methionine; Cys, cystine.
a Gestation diet for low vitamin D3 (LD), normal vitamin D3 (ND) and high vitamin D3 (HD) groups from 41 days of age until birth. Their compositions were similar except vitamin D3 levels.
b All data were analysed values except digestible energy, which was calculated using swine National Research Council (NRC) (2012) values.
c Provided the following (unit/kg): 10 mg of Cu, 80 mg of Fe, 25 mg of Mn, 100 mg of Zn, 0.2 mg of I and 0.2 mg of Se. A total of 4000 IU of vitamin A, 200 IU of vitamin D3 (LD group), 800 IU of vitamin D3 (ND group), 3200 IU of vitamin D3 (HD group), 44 IU of vitamin E, 1.0 mg of vitamin K3, 1 mg of vitamin B1, 3.75 mg of riboflavin, 1 mg of vitamin B6, 15 mg of vitamin B12, 12 mg of pantothenic acid, 10 mg of niacin and 1.25 mg of choline.
Table 2. Lactation diet composition of sowa
DE, digestible energy; CP, crude protein; Lys, lysine; Met, methionine; Cys, cystine.
a Lactation diets with the same vitamin D3 levels were fed lactating sows in low vitamin D3 (LD), normal vitamin D3 (ND) and high vitamin D3 (HD) groups, and their offspring piglets were weaned 28 days of age.
b All data were analysed values except digestible energy, which was calculated using swine National Research Council (NRC) (2012) values.
c Provided the following (unit/kg): 20 mg of Cu, 80 mg of Fe, 25 mg of Mn, 100 mg of Zn, 0.2 mg of I and 0.2 mg of Se. A total of 2000 IU of vitamin A, 800 IU of vitamin D3, 44 IU of vitamin E, 1.0 mg of vitamin K3, 1 mg of vitamin B1, 3.75 mg of riboflavin, 1 mg of vitamin B6, 15 mg of vitamin B12, 12 mg of pantothenic acid, 10 mg of niacin and 1 mg of choline.
Table 3. Ingredients and nutrients of basal experiment diets of offspring pigs
DE, digestible energy; CP, crude protein; Lys, lysine; Met, methionine; Cys, cystine.
a Provided the following (unit/kg): 10 mg of Cu, 80 mg of Fe, 30 mg of Mn, 80 mg of Zn, 0.5 mg of I and 0.3 mg of Se. A total of 5850 IU of vitamin A, 1251 IU of vitamin D3, 20 IU of vitamin E, 1.86 mg of vitamin K3, 3 mg of vitamin B1, 3.6 mg of riboflavin, 1.5 mg of vitamin B6, 20 mg of vitamin B12, 18 mg of pantothenic acid, 26 mg of niacin and 56 mg of choline.
b All data were analysed values except digestible energy, which was calculated using swine National Research Council (NRC) (2012) values.
Slaughter and samples collection
At 150 days of age, 18 offspring pigs (six pigs per group) were selected to weight and slaughter according to the method described by Miao et al. (Reference Miao, Wang, Xu, Huang and Wang2009). Briefly, the pigs were electrically stunned, exsanguinated, dehaired and eviscerated after fasting 12 h. The head was removed and the carcass was split longitudinally, the subcutaneous adipose tissue and longissimus dorsal muscle were quickly dissected and frozen in liquid nitrogen, and then stored at −80°C until extraction for total RNA. Samples of blood were collected from 18 offspring pigs (six pigs each group), and allowed to clot overnight at 4°C. Serum was harvested following centrifugation (3000 g for 10 min, at 4°C) and stored at −80°C until analysis (Miao et al., Reference Miao, Wang, Xu, Huang and Wang2008). Left half-carcasses without head, legs and guts (except kidney) were weighed. Adipose and muscle tissue in the left half-carcass was dissected and weighed, the carcass fat content and carcass dressing percentage was calculated. The ABFT was taken in the midline with a sliding caliper, and the average of three backfat thickness, measured on the first rib, last rib and last lumbar vertebrae. The analysis of IMF in the longissimus dorsal muscle was measured according to the AOAC (1990) procedures.
Real-time PCR
Total RNA of subcutaneous adipose tissue and longissimus dorsal muscle was extracted using TRIzol reagent (Invitrogen, Carlsbad, CA, USA), and then removed DNA via DNase treatment (NEB, Ipswich, MA, USA). Approximately 1 μg of the total RNA in each sample was used to synthesize cDNA by the PrimeScript™ RT Reagent Kit (Takara Bio Inc., Tokyo, Japan). The reverse transcription polymerase chain reaction (RT-PCR) was performed with the ViiA™ 7 real-time PCR System (Applied BioSystems, Foster City, CA, USA) using a SYBR green RT-PCR kit from Bio-Rad (Hercules, CA, USA). Primer sequences were designed according to the basis of known sequences deposited in GenBank (Table 4). Relative expression of mRNA was determined after normalization to β-actin reference using the 2−△△Ct method.
Table 4. Primer sequences used for quantitative RT-PCR analyses
FASN, fatty acid synthase; LIPE, hormone-sensitive lipase.
Serum biochemistry analysis
Serum 25OHD concentration was determined using an EIA kit (IDS Immunodiagnostic Systems Ltd., Tyne and Wear, UK) according to the previous method described by Wallace et al. (Reference Wallace, Gibson, De La Hunty, Lamberg-Allardt and Ashwell2010). Insulin concentrations were measured with the RIA kits (Beijing North Institute of Biotechnology, Beijing, China) in a Gamma-counter (Packard 8500, Packard Instrument Co., Downers Grove, Illinois, USA). Leptin levels were measured with a commercially available kit (Multispecies Radioimmunoassay Kit; Linco Research, St. Charles, MO). Serum FFA and TG concentrations were determined with an enzymatic colorimetric procedure (Nanjing Jiancheng Bioengineering Institute, China) in a UV-visible spectrophotometer (Ultrospec 2000, Sweeden).
Statistical analysis
Statistical analysis of variance (Uhlirova et al.) was performed using the one-way ANOVA procedure of SPSS 17.0 for Windows (SPSS Inc., Chicago, IL, USA). The post-hoc analysis for comparing group means (offspring pigs) was measured by Duncan's multiple range tests, and significance was declared at P < 0.05. Adipogenic genes expression analysis (FASN and LIPE) was performed using REST 2009 software (https://www.gene-quantification.de/rest-2009.html). Linear and quadratic polynomials were performed to study the effect of vitamin D3 levels. Replicate was used as experimental materials unit for the study of carcass traits, meat quality, serum biochemical indicators and gene expression. Bivariate correlations were used to evaluate the correlation between meat quality (carcass fat, IMF content and ABFT) and adipogenic gene (FASN and LIPE) expression.
Results
Carcass characteristics and meat quality
The effects of maternal vitamin D3 during pregnancy on carcass characteristics and meat quality in offspring pigs are shown in Table 5. There were no significant differences in carcass weight (P = 0.440) and dressing percentage (P = 0.910) among all groups. The offspring pigs born to the LD group had higher carcass fat content ((P = 0.001) and ABFT (P = 0.001)) compared with the ND and HD groups, respectively. Whereas, IMF content of longissimus dorsal muscle in offspring pigs born to the LD group was lower than those born to the ND and HD groups, respectively (P = 0.001). In addition, no significant differences in carcass fat, ABFT and IMF content were measured between the ND and HD groups.
Table 5. Carcass characteristics and meat quality in offspring pigs
LD, low vitamin D3 group; ND, normal vitamin D3 group; HD, high vitamin D3 group; ABFT, average backfat thickness; IMF, intramuscular fat; SEM, standard error of the mean.
Serum biochemical index
As shown in Table 6, no significant differences in serum 25OHD concentration were observed among all groups (P = 0.376). The offspring pigs born to the LD group had higher concentrations of serum insulin (P = 0.001) and leptin (P = 0.010) compared with the ND and HD groups, respectively. Whereas, serum FFA (P = 0.020) and TG (P = 0.026) concentrations of offspring pigs born to the LD group were lower than those born to the ND and HD groups, respectively. Meanwhile, the offspring pigs born to the HD group had lower serum insulin, leptin and higher FFA, TG levels compared with the ND group, respectively.
Table 6. Serum biochemical index in offspring pigs
LD, low vitamin D3 group; ND, normal vitamin D3 group; HD, high vitamin D3 group; FFA, free fatty acids; TG, triacylglycerol; SEM, standard error of the mean.
FASN and LIPE gene expression
As shown in Table 7, FASN mRNA expression (P = 0.009) and the ratio of FASN/LIPE mRNA expression (P = 0.002) in subcutaneous adipose tissue of offspring pigs born to the LD group was higher than those born to the ND and HD groups, respectively. Meanwhile, offspring pigs born to the HD group had lower expression of FASN and the ratio of FASN/LIPE mRNA expression compared with the ND group. Whereas, no differences in LIPE expression were observed among all groups (P = 0.268).
Table 7. FASN, LEPE and the ratio of FASN/LIPE mRNA expression in subcutaneous adipose tissue of offspring pigs at 150 days of age
LD, low vitamin D3 group; ND, normal vitamin D3 group; HD, high vitamin D3 group; SEM, Standard error of the mean.
As shown in Table 8, offspring pigs born to the LD group had lower the ratio of FASN/LIPE mRNA expression in longissimus dorsal muscle compared with those born to the ND and HD groups, respectively (P = 0.011), and the ratio of FASN/LIPE mRNA expression in offspring pigs born to the ND group was lower than that born to the HD group (P = 0.011). Compared with the LD group, the ND and HD groups had lower expression of LIPE mRNA in longissimus dorsal muscle (P = 0.001). The FASN mRNA expression in the ND group was lower than that in the LD and HD groups, respectively (P = 0.006). Whereas, no differences in FASN mRNA expression between the LD and HD groups, as well as LIPE expression between the ND and HD groups, respectively.
Table 8. FASN, LEPE and the ratio of FASN/LIPE mRNA expression in longissimus dorsal muscle tissue of offspring pigs at 150 days of age
LD, low vitamin D3 group; ND, normal vitamin D3 group; HD, high vitamin D3 group; SEM, standard error of the mean.
Correlation between genes expression and meat quality parameters
As shown in Table 9, the ratio of FASN/LIPE mRNA expression in longissimus dorsal muscle was negatively correlated with IMF content of offspring pigs (r = −0.868, P = 0.002). Whereas, there is no relationship between FASN, LIPE mRNA expression and IMF content. In addition, the FASN mRNA expression (r = 0.843, P = 0.021) and the ratio of FASN/LIPE mRNA expression (r = 0.890, P = 0.001) in subcutaneous adipose tissue were both positively correlated with carcass fat content. Meanwhile, the FASN mRNA expression was negatively correlated with the ABFT (r = −0.746, P = 0.021). Whereas, the ratio of FASN/LIPE mRNA expression was positively correlated with ABFT in offspring pigs (r = 0.795, P = 0.010).
Table 9. Correlations between FASN and LIPE mRNA expression levels and carcass fat content, ABFT and IMF in offspring pigs
ABFT, average backfat thickness; IMF = intramuscular fat tissue.
Discussion
Carcass characteristics and meat quality
Previous research showed that production efficiency and meat quality in mammals (including cattle, sheep and pigs) were affected by nutrient fluctuations during the foetal stage (Du et al., Reference Du, Wang, Fu, Yang and Zhu2015). Yang et al. (Reference Yang, Liang, Rogers, Zhao, Zhu and Du2013) also found that offspring growth performance was impacted by nutrition concentrations during gestation. Our research observed that there were differences in carcass fat content, ABFT and IMF content in offspring pigs born to the LD group compared with the ND group. These results suggested that maternal vitamin D3 status could improve growth performance, carcass characteristics and meat quality of offspring pigs. These results are in accordance with previous research studies. Belenchia et al. (Reference Belenchia, Jones, Will, Beversdorf, Vieira-Potter, Rosenfeld and Peterson2018) observed that maternal vitamin D concentrations during pregnancy have lasting effects on adipose tissue development in offspring mice. Zhou et al. (Reference Zhou, Chen, Lv, Zhuo, Lin, Feng, Fang, Che, Li, Xu and Wu2016) also found that improving maternal vitamin D status promoted postnatal skeletal muscle development of pig offspring. Flohr et al. (Reference Flohr, Woodworth, Bergstrom, Tokach, Dritz, Goodband and DeRouchey2016) observed that pigs from sows fed 25(OH)D3 had higher ADG compared with pigs from sows fed 800 of vitamin D3, and higher final body weight and hot carcass weight compared with pigs from sows fed 9600 IU of vitamin D3. These data indicated that maternal vitamin D supplementation affected subsequent growth performance and carcass characteristics in offspring pigs. In addition, offspring pigs born to the LD group had higher carcass fat and ABFT compared with the ND and HD groups, which suggested that maternal vitamin D3 deficiency could increase adipogenesis in adipose tissue of offspring pigs. The season may be supported that maternal vitamin D3 inhibited the differentiation of preadipocyte, decreased the number of preadipocytes in foetal, which reduced the fat deposition in offspring pigs. Similar results are reported by Kong and Li (Reference Kong and Li2006), who demonstrated that vitamin D3 decreased 3T3-L1 preadipocyte differentiation by inhibiting adipogenic genes expression. Wang et al. (Reference Wang, Fu, Liang, Wang, Yang, Zou, Nie, Zhao, Gao, Zhu, De Avila, Maricelli, Rodgers and Du2017) observed that maternal vitamin A administration expanded PDGFRa+ adipose progenitor population in offspring mice. PDGFRa+ adipose progenitor is differentiated into both beige and white adipocytes (Lee et al., Reference Lee, Petkova, Mottillo and Granneman2012). In this study, we observed that maternal vitamin D3 increased IMF content in offspring pigs. The reason may be that maternal vitamin D3 increased PDGFRa+ adipose progenitor population which differentiated into white adipocytes in longissimus dorsal muscle, thereby enhanced IMF content in offspring pigs. Certainly, the mechanism underlying still needs to be proved by further investigation.
Serum biochemical index
Serum 25OHD is the liver metabolite and primary circulating form of vitamin D, and used to determine the vitamin D status of pigs (Jakobsen et al., Reference Jakobsen, Maribo, Bysted, Sommer and Hels2007). In this study, no differences in serum vitamin D status were observed among all groups, which indicated that maternal vitamin D3 didn't change the serum vitamin D concentration in later offspring pigs (at 150 days of age). A similar result was reported by Flohr et al. (Reference Flohr, Woodworth, Bergstrom, Tokach, Dritz, Goodband and DeRouchey2016), who observed that maternal vitamin D influenced serum concentration in growing offspring pigs until 35 days post weaning. Flohr et al. (Reference Flohr, Tokach, Dritz, DeRouchey, Goodband, Nelssen and Bergstrom2014) demonstrated that serum vitamin D3 of weaned pigs (21 days of age) was not affected by maternal vitamin D status. These results suggested that maternal vitamin D3 during pregnancy mainly affected the serum vitamin D levels in early offspring pigs, but had no significant effect on the later offspring pigs. The previous study has shown that insulin suppressed lipolysis of rats by increasing FASN and acetyl-COA carboxylase (ACC) expression, which indicated that lipogenesis is regulated by insulin (Scherer et al., Reference Scherer, O'Hare, Diggs-Andrews, Schweiger, Cheng, Lindtner, Zielinski, Vempati, Su, Dighe, Milsom, Puchowicz, Scheja, Zechner, Fisher, Previs and Buettner2011). Whereas, leptin could induce lipolysis and inhibit lipogenesis (Buettner and Camacho, Reference Buettner and Camacho2008). Serum 25OHD decreased leptin concentrations, which was negatively associated with leptin levels (Gangloff et al., Reference Gangloff, Bergeron, Lemieux, Tremblay, Poirier, Alméras and Després2020). Meanwhile, vitamin D deficiency is correlated with elevated insulin resistance, which regulated lipid metabolism process (Leung, Reference Leung2016). In addition, offspring pigs born to the LD group had higher serum insulin, leptin levels and lower FFA and TG concentrations compared with the ND and HD groups, which indicated that maternal vitamin D3 status affected adipogenesis in offspring pigs by regulating the levels of serum biochemical parameters related to lipid metabolism. A similar result was reported by Wen et al. (Reference Wen, Hong, Wang, Zhu, Wu, Xu, Fu, You, Wang, Ji and Guo2018), who found that maternal vitamin D deficiency increased the adiposity in offspring mice through regulating serum biochemical index concentrations. However, no significant differences in serum insulin and leptin levels in offspring mice were observed between maternal vitamin D deficiency and the control groups (Belenchia et al., Reference Belenchia, Jones, Will, Beversdorf, Vieira-Potter, Rosenfeld and Peterson2018). Inconsistent research results in serum biochemical parameters might be due to differential species of animals, dosage of vitamin D, duration of feeding, and feeding methods, but the reasons and its mechanism have not been unclear.
FASN and LIPE gene expression
The FASN promotes the conversion of acetyl-CoA and malonyl-CoA to TG, which controlling de novo lipogenesis of mammals (Semenkovich, Reference Semenkovich1997). Whereas, LIPE mainly catalyses hydrolysis of stored TG in adipose tissue into FFA and glycerol to regulate lipolysis in animals (Haemmerle et al., Reference Haemmerle, Zimmermann and Zechner2003). Fat accumulation is determined by the balance between FASN and LIPE (the ratio of FASN/LIPE) expression, FASN mRNA expression and the ratio of FASN/LIPE mRNA expression is positively correlated with carcass fat content in pigs (Miao et al., Reference Miao, Zhu, Zhang, Chang, Xie, Zhang and Xu2010). In this study, we observed that maternal vitamin D3 deficiency increased carcass fat content and ABFT by increasing FASN mRNA expression and the ratio of FASN/LIPE mRNA expression. These results are in accordance with previous reports, Yao et al. (Reference Yao, Zhu, He, Duan, Liang, Nie, Jin, Wu and Fang2015) demonstrated that obesity is associated with vitamin D deficiency, and vitamin D suppresses adipogenesis. Whereas, Bhat et al. (Reference Bhat, Noolu, Qadri and Ismail2014) observed that vitamin D-deficient rats decreased visceral fat content and FASN and PPARγ expression. Inconsistent research results may be due to differential adipose tissue and species of animals. Meanwhile, our research also found that maternal vitamin D3 deficiency had lower the ratio of FASN/LIPE expression in longissimus dorsal muscle, and these results are in accordance with lower IMF content. The reason may be that maternal vitamin D3 deficiency suppressed PDGFRa+ adipose progenitor population which differentiation into white adipocyte in longissimus dorsal muscle, further decreased IMF of offspring pigs by decreasing the ratio of FASN/LIPE mRNA expression. So, the ratio of FASN/LIPE mRNA expression was opposite between the longissimus dorsal muscle tissue and subcutaneous adipose tissue with the same VD3 diet in this study. Certainly, the mechanism underlying still needs to be proved by further investigation.
Taken together, these results indicated that maternal vitamin D3 status could change adipose tissue metabolism, carcass characteristics and meat quality in offspring pigs by regulating gene expression involved in lipid accumulation. Whereas, the mechanism and signal pathway underlying still needs to be proved by further investigation.
Correlation between genes expression and meat quality parameters
Fat accumulation in adipose tissue is associated with FASN mRNA expression (Huang et al., Reference Huang, Xu, Han and Li2008). Backfat thickness, a good indicator of fat deposition, is closely correlated with carcass fat and IMF of pigs (Suzuki et al., Reference Suzuki, Inomata, Katoh, Kadowaki and Shibata2009). In this present experiment, we found that the ratio of FASN/LIPE mRNA expression in adipose tissue was positively correlated with carcass fat content and ABFT, which suggested that carcass content and ABFT in pigs were affected by the ratio of FASN/LIPE mRNA expression. Similar results were reported by Miao et al. (Reference Miao, Zhu, Zhang, Chang, Xie, Zhang and Xu2010), who demonstrated that there was a positive relationship between the ratio of FASN/LIPE mRNA expression and carcass fat in pigs. Meanwhile, FASN mRNA expression was negatively correlated with AFBT, whereas, there was a positive correlation between the ratio of FASN/LIPE mRNA expression and AFBT. These results confirmed that fat accumulation in subcutaneous adipose tissue of pigs was a balance between FASN and LIPE expression levels, and fat deposition was increased when FASN expression was higher than LIPE expression. In addition, our study also observed that the ratio of FASN/LIPE mRNA expression in longissimus dorsal muscle was negatively correlated with IMF content in offspring pigs. Similar results were reported by Qiao et al. (Reference Qiao, Huang, Li, Liu, Hao, Shi, Dai and Xie2007), who found that there was a negative relationship between the ratio of FASN/LIPE expression and IMF content in Kazak sheep. However, other study reported that the ratio of FASN/LIPE expression was positively correlated with IMF content in Sutai pigs (Chen et al., Reference Chen, Yang, Tong, Chen and Zhao2004). Inconsistent research results may be due to the different patterns of IMF storage or breeds (Barber et al., Reference Barber, Ward, Richards, Salter, Buttery, Vernon and Travers2000). Taken together, our results in the present study indicated that maternal vitamin D3 status regulated adipogenic genes expression in IMF, whereas, didn't alter the relationship between the ratio of FASN/LIPE expression and carcass content, ABFT, as well as IMF content in offspring pigs.
Conclusion
LD offspring pigs had higher carcass fat and ABFT, serum levels of insulin and leptin, FASN and FASN/LIPE mRNA expression in subcutaneous adipose tissue, LIPE mRNA expression of longissimus dorsal muscle, whereas, had lower IMF, serum FFA and TG levels, FASN/LIPE mRNA expression in longissimus dorsal muscle compared with ND and HD offspring pigs. Meanwhile, the ratio of FASN/LIPE mRNA expression was negatively correlated with IMF content, and positively correlated with carcass fat content, as well as ABFT in offspring pigs. In addition, FASN mRNA expression was positively correlated with carcass fat content, and negatively correlated with ABFT in offspring pigs. These results suggested that maternal vitamin D3 status during pregnancy has a long-lasting impact on lipid accumulation in offspring pigs.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S0021859620000210.
Financial support
This study was supported by grants from the Henan joint funds of the National Natural Science Foundation of China (U1604102 and 31572417) and the Provincial key Technology Research and development program of Henan (192102110069).
Conflict of interest
None.
Ethical standards
All experimental animal procedures were approved by the Animal Care and Use Committee of Henan Institute of Science and Technology.
