Role of Phosphotyrosine Interaction Domain Containing 1 in Porcine Intramuscular Preadipocyte Proliferation and Differentiation

Smartphone-based digital phenotyping for genome-wide association study of intramuscular fat traits in longissimus dorsi muscle of pigs

Intramuscular fat (IMF) content and distribution significantly contribute to the eating quality of pork. However, the current methods used for measuring these traits are complex, time-consuming and costly. To simplify the measurement process, this study developed a smartphone application (App) called Pork IMF. This App serves as a rapid and portable phenotyping tool for acquiring pork images and extracting the image-based IMF traits through embedded deep-learning algorithms. Utilizing this App, we collected the IMF traits of the longissimus dorsi muscle in a crossbred population of Large White × Tongcheng pigs. Genome-wide association studies detected 13 and 16 SNPs that were significantly associated with IMF content and distribution, respectively, highlighting NR2F2, MCTP2, MTLN, ST3GAL5, NDUFAB1 and PID1 as candidate genes. Our research introduces a user-friendly digital phenotyping technology for quantifying IMF traits and suggests candidate genes and SNPs for genetic improvement of IMF traits in pigs.

Overexpression of cholinergic receptor nicotinic gamma subunit inhibits proliferation and differentiation of bovine preadipocytes

OBJECTIVE

Muscle acetylcholine receptors have five alpha subunits (α, β, δ, ε, or γ), and cholinergic receptor nicotinic gamma subunit (CHRNG) is the γ subunit. It may also play an essential role in biological processes, including cell differentiation, growth, and survival, while the role of CHRNG has not been studied in the literature. Therefore, the purpose of this study is to clarify the effect of CHRNG on the proliferation and differentiation of bovine preadipocytes.

METHODS

We constructed a CHRNG overexpression adenovirus vector and successfully overexpressed it on bovine preadipocytes. The effects of CHRNG on bovine preadipocyte proliferation were detected by Edu assay, cell counting Kit-8 (CCK-8), real-time fluorescence quantitative polymerase chain reaction (RT-qPCR), Western blot and other techniques. We also performed oil red O, RT-qPCR, Western blot to explore its effect on the differentiation of preadipocytes.

RESULTS

The results of Edu proliferation experiments showed that the number of EDU-positive cells in the overexpression group was significantly less. CCK-8 experiments found that the optical density values of the cells in the overexpression group were lower than those of the control group, the mRNA levels of proliferating cell nuclear antigen (PCNA), cyclin A2 (CCNA2), cyclin B1 (CCNB1), cyclin D2 (CCND2) decreased significantly after CHRNG gene overexpression, the mRNA levels of cyclin dependent kinase inhibitor 1A (CDKN1A) increased significantly, and the protein levels of PCNA, CCNB1, CCND2 decreased significantly. Overexpression of CHRNG inhibited the differentiation of bovine preadipocytes. The results of oil red O and triglyceride determination showed that the size and speed of lipid droplets accumulation in the overexpression group were significantly lower. The mRNA and protein levels of peroxisome proliferator activated receptor gamma (PPARγ), CCAAT enhancer binding protein alpha (CEBPα), fatty acid binding protein 4 (FABP4), fatty acid synthase (FASN) decreased significantly.

CONCLUSION

Overexpression of CHRNG in bovine preadipocytes inhibits the proliferation and differentiation of bovine preadipocytes.

ACADL Promotes the Differentiation of Goat Intramuscular Adipocytes

Intramuscular fat (IMF) deposits help improve meat quality such as marbling, juicy, flavor and tenderness. Long-chain acyl-CoA dehydrogenase (ACADL) is a key enzyme for catalyzing fatty acid oxidation, and studies have shown ACADL is involved in the deposition and differentiation of intramuscular adipocytes. However, the effect of ACADL on intramuscular adipocytes differentiation in goats needs further study. In this study, to explore the mechanism of ACADL on the development of goat intramuscular adipocytes, we constructed an over-expression plasmids and a SI-RNA of ACADL to explore the function of ACADL on the development of goat IMF. It was found that overexpression of ACADL promoted the differentiation of goat intramuscular adipocytes, and promoted the expression of fat cell differentiation marker genes lipoprotein lipase (LPL), peroxisome proliferator activated receptor gamma (PPARγ), APETALA-2-like transcription factor gene (AP2), CCAT enhancer binding protein (CEBPα), preadipocyte Factor 1 (Pref-1) and CCAT enhancer binding protein (CEBPβ), and the opposite trend occurred after interference. In addition, we screened of this related tumor necrosis factor (TNF) signaling pathway by RNA-Seq. So, we validate the signaling pathway with inhibitor of TNF signaling pathway. In summary, these results indicate that ACADL promotes intramuscular adipocytes differentiation through activation TNF signaling pathway. This study provides an important basis for the mechanism of IMF development.

Overexpression of Krueppel like factor 3 promotes subcutaneous adipocytes differentiation in goat Capra hircus

Previous research reported that KLF3 plays different roles in the regulation of adipose deposition across species. However, the exact function of KLF3 in goat subcutaneous adipocyte remains unknown. Here, the goat KLF3 gene was firstly cloned and showed that the mRNA sequence of the goat KLF3 gene was 1,264 bp (GenBank accession number: KU041753.1) and its coding sequence was 1,037 bp, encoding 345 amino acids with three classic zinc finger domains of KLFs family at its C-terminus. The alignment of the amino acid sequence of KLF3 among various species demonstrated that goat had the highest homology to that of sheep, presenting 99.4% similarity, while the homology similarity to that of mice presented only 93.62% in contrast. Furthermore, KLF3 had highest mRNA level in fat tissue and lowest level in the heart in comparison. Additionally, the mRNA level of KLF3 gradually tended to increase during adipogenesis. Interestingly, overexpression of KLF3 increased lipid accumulation. In line with this, the gain-of-function of KLF3 dramatically elevated the mRNA levels of TG synthetic genes and adipogenic maker genes (p < .01) . Moreover, overexpression of KLF3 upregulated all the potential target genes, except for C/EBPα. These results suggested that KLF3 is a positive regulator for subcutaneous adipocyte differentiation in goats.

PPAR γ/Nnat/NF-κB Axis Involved in Promoting Effects of Adiponectin on Preadipocyte Differentiation

A previous study has demonstrated that adiponectin (APN) could promote preadipocyte differentiation, and the present study further explored its mechanism. 3T3-L1 cells were infected with adenovirus holding human adiponectin gene apM1 and mouse neuronatin (Nnat) shRNA and initiated differentiation while coculturing with mature adipocytes stimulated with LPS. After 8 days, preadipocyte differentiation was observed by Oil Red O staining. Real-time quantitative PCR was used to evaluate mRNA expression levels of monocyte chemoattractant protein-1 (MCP-1), interleukin- (IL-) 6, IL-8, and tumor necrosis factor α (TNF-α). The levels of reactive oxygen species (ROS), total antioxidant capacity (T-AOC), malondialdehyde (MDA), and superoxide dismutase (SOD) in 3T3-L1 cells were detected. Western blotting was done to quantify the protein expression levels of Nnat, peroxisome proliferator-activated receptor (PPAR) γ, p65, and inhibitor of nuclear factor κB (IκB) α. Results demonstrated that APN overexpression markedly increased preadipocyte differentiation; inhibited gene expression of MCP-1, IL-6, IL-8, and TNF-α; reduced ROS and MDA release; increased T-AOC and SOD levels; upregulated Nnat, PPAR γ, and IκB α protein expressions; and downregulated p65 protein expression under LPS stimulation. However, the effects of APN were markedly attenuated when Nnat expression was knocked down. Taken together, the present study provided evidences that the effects of APN on promoting preadipocyte differentiation under inflammatory conditions via anti-inflammation and antioxidative stress may be regulated by the PPAR γ/Nnat/NF-κB signaling pathway.

MAT2A/2B promote porcine intramuscular preadipocyte proliferation through ERK signaling pathway

Intramuscular fat (IMF) content has been identified as a crucial factor of porcine meat quality. MAT2A and MAT2B coordinately catalyzes the synthesis of the major biological methyl donor S-adenosylmethionine (SAMe). However, the regulatory effect of MAT2A and MAT2B on porcine intramuscular preadipocyte proliferation has not been clarified. In this study, we investigated the effect of MAT2A and MAT2B and its potential mechanism during porcine intramuscular proliferation. We demonstrated that overexpression of MAT2A and MAT2B promoted the cell cycle progression of porcine preadipocyte by flow cytometry and EdU-labeling assay, as well as promoted the expression of cell cycle marker genes including Cyclin B, Cyclin D, and Cyclin-dependent kinase 4, but reduced the expression of cell cycle inhibitor P27. Consistently, knockdown of MAT2A and MAT2B inhibited cell cycle progression and downregulated the mRNA and protein levels of the above genes. Furthermore, overexpression of MAT2A and MAT2B activated the phosphorylation of ERK1/2. Moreover, the inhibitory effect of U0126 (a specific ERK1/2 inhibitor) on the ERK1/2 activities was partially recovered by overexpression of MAT2A and MAT2B in porcine intramuscular preadipocytes. Taken together, our findings suggested that MAT2A and MAT2B promote porcine preadipocyte proliferation by ERK1/2 signaling pathway.

Adiponectin promotes preadipocyte differentiation via the PPARγ pathway

According to the results of a preliminary study, it was hypothesized that the effects of adiponectin (APN) on the improvement of atherosclerosis may be associated with adipocyte differentiation and peroxisome proliferator‑activated receptor γ (PPARγ). The present study simulated the inflammatory environment of epicardial adipose tissue by stimulating mature adipocytes with lipopolysaccharide (LPS); subsequently, the differentiation of 3T3‑L1 preadipocytes was observed. 3T3‑L1 preadipocytes were infected with an adenovirus containing the human adiponectin gene apM1 (Ad‑apM1) and were co‑cultured with mature adipocytes stimulated with LPS. Differentiation into mature adipocytes was initiated using differentiation medium. After 8 days, an MTT assay was used to examine cell viability and oil red O staining was used to observe preadipocyte differentiation. In addition, the mRNA expression levels of monocyte chemoattractant protein‑1 (MCP‑1), interleukin (IL)‑6, IL‑8 and tumor necrosis factor α (TNF‑α) were examined by quantitative polymerase chain reaction, and the protein expression levels of PPARγ, CCAAT/enhancer binding protein α (C/EBPα) and preadipocyte factor‑1 (Pref‑1) were measured by western blotting. The results indicated that APN overexpression significantly increased preadipocyte differentiation and cell viability, inhibited MCP‑1, IL‑6, IL‑8 and TNF‑α expression, upregulated PPARγ and C/EBPα expression, and downregulated Pref‑1 under LPS stimulation. In addition, inhibition of PPARγ activity by T0070907 markedly attenuated the effects of APN overexpression. Taken together, the present study demonstrated that the effects of APN on the promotion of preadipocyte differentiation under inflammatory conditions may involve the PPARγ signaling pathway, and at least partly depends on upregulation of PPARγ expression.

miR-425-5p Inhibits Differentiation and Proliferation in Porcine Intramuscular Preadipocytes

Intramuscular fat (IMF) content affects the tenderness, juiciness, and flavor of pork. An increasing number of studies are focusing on the functions of microRNAs (miRs) during porcine intramuscular preadipocyte development. Previous studies have proved that miR-425-5p was enriched in porcine skeletal muscles and played important roles in multiple physiological processes; however, its functions during intramuscular adipogenesis remain unclear. To explore the role of miR-425-5p in porcine intramuscular adipogenesis, miR-425-5p agomir and inhibitor were used to perform miR-425-5p overexpression and knockdown in intramuscular preadipocytes, respectively. Our results showed that the agomir of miR-425-5p dramatically inhibited intramuscular adipogenic differentiation and downregulated the expression levels of adipogenic marker genes PPARγ, FABP4, and FASN, whereas its inhibitor promoted adipogenesis. Interestingly, the agomir repressed proliferation of porcine intramuscular preadipocytes by downregulation of cyclin B and cyclin E. Furthermore, we demonstrated that miR-425-5p inhibited adipogenesis via targeting and repressing the translation of KLF13. Taken together, our findings identified that miR-425-5p is a novel inhibitor of porcine intramuscular adipogenesis possibly through targeting KLF13 and subsequently downregulating PPARγ.