MicroRNA-2400 promotes bovine preadipocyte proliferation

SGK1 promotes the lipid accumulation via regulating the transcriptional activity of FOXO1 in bovine

OBJECTIVES

Serum/glucocorticoid-inducible kinase 1 (SGK1) gene encodes a serine/threonine protein kinase that plays an essential role in cellular stress response and regulation of multiple metabolic processes. However, its role in bovine adipogenesis remains unknown. In this study, we aimed to clarify the role of SGK1 in bovine lipid accumulation and improvement of meat quality.

METHODS

Preadipocytes were induced to differentiation to detect the temporal expression pattern of SGK1. Heart, liver, lung, spleen, kidney, muscle and fat tissues were collected to detect its tissue expression profile. Recombinant adenovirus and the lentivirus were packaged for overexpression and knockdown. Oil Red O staining, quantitative real-time PCR, Western blot analysis, Yeast two-hybrid assay, luciferase assay and RNA-seq were performed to study the regulatory mechanism of SGK1.

RESULTS

SGK1 showed significantly higher expression in adipose and significantly induced expression in differentiated adipocytes. Furthermore, overexpression of SGK1 greatly promoted adipogenesis and inhibited proliferation, which could be shown by the remarkable increasement of lipid droplet, and the expression levels of adipogenic marker genes and cell cycle-related genes. Inversely, its knockdown inhibited adipogenesis and facilitated proliferation. Mechanistically, SGK1 regulates the phosphorylation and expression of two critical proteins of FoxO family, FOXO1/FOXO3. Importantly, SGK1 attenuates the transcriptional repression role of FOXO1 for PPARγ via phosphorylating the site S256, then promoting the bovine fat deposition.

CONCLUSIONS

SGK1 is a required epigenetic regulatory factor for bovine preadipocyte proliferation and differentiation, which contributes to a better understanding of fat deposition and meat quality improvement in cattle.

IFRD2, a target of miR-2400, regulates myogenic differentiation of bovine skeletal muscle satellite cells via decreased phosphorylation of ERK1/2 proteins

The proliferation and differentiation of skeletal muscle satellite cells is a complex physiological process involving various transcription factors and small RNA molecules. This study aimed to understand the regulatory mechanisms underlying these processes, focusing on interferon-related development factor 2 (IFRD2) as a target gene of miRNA-2400 in bovine skeletal MuSCs (MuSCs). IFRD2 was identified as a target gene of miRNA-2400 involved in regulating the proliferation and differentiation of bovine skeletal MuSCs. Our results indicate that miR-2400 can target binding the 3'UTR of IFRD2 and inhibit its translation. mRNA and protein expression levels of IFRD2 increased significantly with increasing days of differentiation. Moreover, overexpression of the IFRD2 gene inhibited proliferation and promoted differentiation of bovine MuSCs. Conversely, the knockdown of the gene had the opposite effect. Overexpression of IFRD2 resulted in the inhibition of ERK1/2 phosphorylation levels in bovine MuSCs, which in turn promoted differentiation. In summary, IFRD2, as a target gene of miR-2400, crucially affects bovine skeletal muscle proliferation and differentiation by precisely regulating ERK1/2 phosphorylation.

SNPs in microRNA seed region and impact of miR-375 in concurrent regulation of multiple lipid accumulation-related genes

Bovine intramuscular fat (IMF), commonly referred to as marbling, is regulated by lipid metabolism, which includes adipogenesis, lipogenesis, glycerolipid synthesis, and lipolysis. In recent years, breeding researchers have identified single nucleotide polymorphisms (SNPs) as useful marker-assisted selection tools for improving marbling scores in national breeding programs. These included causal SNPs that induce phenotypic variation. MicroRNAs (miRNAs) are small highly conserved non-coding RNA molecules that bind to multiple non-coding regions. They are involved in post-transcriptional regulation. Multiple miRNAs may regulate a given target. Previously, three SNPs in the GPAM 3' UTR and four miRNAs were identified through in silico assays. The aim of this study is to verify the binding ability of the four miRNAs to the SNPs within the 3'UTR of GPAM, and to identify the regulatory function of miR-375 in the expression of genes related to lipid metabolism in mammalian adipocytes. It was verified that the four miRNAs bind to the GPAM 3'UTR, and identified that the miR-375 sequence is highly conserved. Furthermore, it was founded that miR-375 upregulated the GPAM gene, C/EBPα, PPARγ and lipid metabolism-related genes and promoted lipid droplet accumulation in 3T3-L1 cells. In conclusion, these results suggest that miR-375 is a multifunctional regulator of multiple lipid metabolism-related genes and may aid in obesity research as a biomarker.

CircSSBP2 acts as a MiR-2400 sponge to promote intramuscular preadipocyte proliferation by regulating NDRG1

Intramuscular fat (IMF) is a critical factor in beef quality. IMF is mainly distributed between muscle fibres and its accumulation can affect the marbling and meat quality of beef. IMF formation and deposition is a complex process and in recent years a group of non-coding RNAs (ncRNAs), known as circRNAs, have been discovered to play an important role in regulating intramuscular fat deposition. CircRNAs form a covalent loop structure after reverse splicing of precursor mRNAs. They can act by adsorbing miRNAs, thereby reducing their repressive effects on downstream target genes. Based on high-throughput sequencing of circRNAs in intramuscular fat of Qinchuan and Japanese black cattle, we identified a novel circSSBP2 that is differentially expressed between the two species and associated with adipogenesis. We show that circSSBP2 knockdown promotes bovine intramuscular preadipocyte proliferation, whereas overexpression inhibits bovine intramuscular preadipocyte proliferation. We also show that circSSBP2 can act as a molecular sponge for miR-2400 and that miR-2400 overexpression promotes bovine intramuscular preadipocyte proliferation. Furthermore, N-myc downstream-regulated gene 1 (NDRG1) was identified as a direct target gene of miR-2400, and NDRG1 interference promoted the proliferation of bovine intramuscular preadipocytes. In conclusion, our results suggest that circSSBP2 inhibits the proliferation of bovine intramuscular preadipocytes by regulating the miR-2400/NDRG1 axis.

MicroRNA-378 regulates adipogenic differentiation in bovine intramuscular preadipocytes by targeting CaMKK2

Intramuscular fat, as one of the most important palatability attribute of beef carcase, is the primary determinant of beef quality. The research of adipogenesis mechanism would provide new insight into intramuscular fatty deposition. Here, the role of microRNA-378 was investigated during bovine adipogenic differentiation. It was revealed that miR-378 expression exists variably in bovine major tissue and organs by RT-qPCR. It was predicted that miR-378 targets CaMKK2, as an AMPKα kinase, by DIANA Tools. For better research, primary preadipocytes with stable transfection for up-/down-regulated expression of miR-378 were constructed by lentiviral vectors with GFP gene. The analyses of qPCR showed that PPARγ and adiponectin mRNA levels increased, but C/EBPβ, pref-1 and CaMKK2 mRNA levels decreased during adipogenic differentiation. When miR-378 was overexpressed, preadipocytes proliferation became slower, there are more cellular lipid droplets, and PPARγ and C/EBPβ mRNA levels were higher, but pref-1, adiponectin and CaMKK2 were lower than control groups. Luciferase assay and western blot analysis validated that miR-378 binds the nucleotide sites of the 3′- untranslated region of CaMKK2, which inhibits the mRNA and protein expression of CaMKK2. These findings suggest that miR-378 promotes adipogenic differentiation in bovine intramuscular preadipocytes by targeting CaMKK2 via AMPK signalling pathway.

MiR-33a plays an crucial role in the proliferation of bovine preadipocytes

Preadipocyte proliferation is a critical and precisely orchestrated procedure in adipogenesis, which is highly regulated by microRNAs (miRNAs). A previous study identified that the expression of miR-33a is different in intramuscular fat (IMF) tissues from steers and bulls. In the present study, miR-33a was overexpressed in bovine preadipocytes, and a total of 781 differentialy expressed genes were found, including 348 upregulated and 433 downregulated genes. Gene Ontology and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway analyses of the differentially expressed genes enriched cell division and cell cycle respectively. MiR-33a overexpression decreased the rate of preadipocyte proliferation. Synchronously, the mRNA and protein expression levels of proliferation-related marker genes, including cyclin B1 (CCNB1) and proliferating cell nuclear antigen (PCNA), were decreased. In contrast, inhibiting miR-33a increased the rate of preadipocyte proliferation, and expression levels of CCNB1 and PCNA. Furthermore, based on luciferase reporter assays, miR-33a targeted directly cyclin-dependent kinase 6 (CDK6)-3'UTR and inhibited CDK6 protein expression. Interestingly, the silencing of CDK6 inhibited bovine preadipocyte proliferation and proliferation-related genes. Therefore, miR-33a inhibits the proliferation of bovine preadipocytes. CDK6 is the target gene of miR-33a and may be involved in the effects of miR-33a on bovine preadipocyte proliferation.

RNA-Seq Reveals Function of Bta-miR-149-5p in the Regulation of Bovine Adipocyte Differentiation

Intramuscular fat is a real challenge for the experts of animal science to improve meat quality traits. Research on the mechanism of adipogenesis provides invaluable information for the improvement of meat quality traits. This study investigated the effect of bta-miR-149-5p and its underlying mechanism on lipid metabolism in bovine adipocytes. Bovine adipocytes were differentiated and transfected with bta-miR-149-5p mimics or its negative control (NC). A total of 115 DEGs including 72 upregulated and 43 downregulated genes were identified in bovine adipocytes. The unigenes and GO term biological processes were the most annotated unigene contributor parts at 80.08%, followed by cellular component at 13.4% and molecular function at 6.7%. The KEGG pathways regulated by the DEGs were PI3K-Akt signaling pathway, calcium signaling pathway, pathways in cancer, MAPK signaling pathway, lipid metabolism/metabolic pathway, PPAR signaling pathway, AMPK signaling pathway, TGF-beta signaling pathway, cAMP signaling pathway, cholesterol metabolism, Wnt signaling pathway, and FoxO signaling pathway. In addition to this, the most important reactome enrichment pathways were R-BTA-373813 receptor CXCR2 binding ligands CXCL1 to 7, R-BTA-373791 receptor CXCR1 binding CXCL6 and CXCL8 ligands, R-BTA-210991 basigin interactions, R-BTA-380108 chemokine receptors binding chemokines, R-BTA-445704 calcium binding caldesmon, and R-BTA-5669034 TNFs binding their physiological receptors. Furthermore, the expression trend of the DEGs in these pathways were also exploited. Moreover, the bta-miR-149-5p significantly (p < 0.01) downregulated the mRNA levels of adipogenic marker genes such as CCND2, KLF6, ACSL1, Cdk2, SCD, SIK2, and ZEB1 in bovine adipocytes. In conclusion, our results suggest that bta-miR-149-5p regulates lipid metabolism in bovine adipocytes. The results of this study provide a basis for studying the function and molecular mechanism of the bta-miR-149-5p in regulating bovine adipogenesis.

Genome-wide analysis of circular RNAs in bovine cumulus cells treated with BMP15 and GDF9

Circular RNAs (circRNAs) are important members of the non-coding RNA family, and those relating to animal physiologies have been widely studied in recent years. This study aimed to explore the roles of circRNAs in the regulation of follicular development. We constructed four bovine cumulus cell cDNA libraries, including a negative control group (NC) and groups treated with BMP15, GDF9 and BMP15 + GDF9, and we sequenced the libraries on the Illumina HiSeq Xten platform. We identified 1706 circRNAs and screened for differential circRNA expression. We conducted a bioinformatics analysis of these circRNAs and screened for differential circRNAs. Functional annotation and enrichment analysis of the host genes showed that the differential circRNAs were related to locomotion, reproduction, biological adhesion, growth, rhythmic processes, biological phases and hormone secretion. According to the differential expression of circRNA between groups, there were 3 up-regulated and 6 down-regulated circRNAs in the BMP15 group as well as 12 up-regulated and 24 down-regulated circRNAs in the GDF9 group. Co-addition of both BMP15 and GDF9 resulted in 15 up-regulated and 13 down-regulated circRNAs. circ_n/a_75,circ_12691_1 and circ_n/a_303 were altered in both the BMP15 and GDF9 groups as well as in the BMP15 + GDF9 combination group. We focused on these three circRNAs because they were potentially associated with the additive effect of BMP15 and GDF9. Quantitative PCR analysis showed that the expression levels of these three circRNAs were consistent with the sequencing results. In addition, the target miRNAs of circ_n/a_75 and circ_n/a_303, miR-339a, miR-2400 and miR-30c, were down-regulated in the experimental group, which was in contrast to the circRNAs trend. These findings demonstrated that BMP15 and GDF9 may regulate the target gene through circRNA, as a miRNA sponge, in order to regulate the status of bovine cumulus cells and affect follicular development.