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LKB1 Regulates Goat Intramuscular Adipogenesis Through Focal Adhesion Pathway

ABSTRACT: Intramuscular fat (IMF) deposition is one of the most important factors to affect meat quality in livestock and induce insulin resistance and adverse metabolic phenotypes for humans. However, the key regulators involved in this process remain largely unknown. Although liver kinase B1 (LKB1) was reported to participate in the development of skeletal muscles and classical adipose tissues. Due to the specific autonomic location of intramuscular adipocytes, deposited between or within muscle bundles, the exact roles of LKB1 in IMF deposition need further verified. Here, we cloned the goat LKB1 coding sequence with 1,317 bp, encoding a 438 amino acid peptide. LKB1 was extensively expressed in detected tissues and displayed a trend from decline to rise during intramuscular adipogenesis. Functionally, knockdown of LKB1 by two individual siRNAs enhanced the intramuscular preadipocytes differentiation, accompanied by promoting lipid accumulation and inducing adipogenic transcriptional factors and triglyceride synthesis-related genes expression. Conversely, overexpression of LKB1 restrained these biological signatures. To further explore the mechanisms, the RNA-seq technique was performed to compare the difference between siLKB1 and the control group. There were 1,043 differential expression genes (DEGs) were screened, i.e., 425 upregulated genes and 618 downregulated genes in the siLKB1 group. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis predicted that the DEGs were mainly enriched in the focal adhesion pathway and its classical downstream signal, the PI3K-Akt signaling pathway. Specifically, knockdown of LKB1 increased the mRNA level of focal adhesion kinase (FAK) and vice versa in LKB1-overexpressed cells, a key component of the activated focal adhesion pathway. Convincingly, blocking this pathway by a specific FAK inhibitor (PF573228) rescued the observed phenotypes in LKB1 knockdown adipocytes. In conclusion, LKB1 inhibited goat intramuscular adipogenesis through the focal adhesion pathway. This work expanded the genetic regulator networks of IMF deposition and provided theoretical support for improving human health and meat quality from the aspect of IMF deposition.

SUBMITTER: Xiong Y

PROVIDER: S-EPMC8548615 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:CPT1B, as the major rate-limiting enzyme for fatty acid β-oxidation, involved in the regulation of adipose tissue lipid deposition, but its role in the regulation of goat intramuscular fat (IMF) remains unclear. Here, we conducted knockdown experiments targeting the CPT1B gene in goat intramuscular preadipocytes, resulting in a significant increase in intracellular triglyceride (TAG) content and lipid droplet accumulation. Conversely, the overexpression of CPT1B led to a significant decrease in intracellular TAG content and lipid droplet accumulation. Mechanistically, through RNA-seq analysis of CPT1B knockdown samples, we identified 285 differentially expressed genes (DEGs), including 71 up-regulated and 214 down-regulated genes. Notably, these DEGs were significantly enriched in various KEGG signaling pathways, such as fatty acid metabolism, focal adhesion, FoxO signaling, PI3K-Akt signaling, and MAPK signaling pathways. Gene Set Enrichment Analysis (GSEA) further confirmed the upregulation of the MAPK signaling pathway upon CPT1B knockdown in adipocytes. In rescue experiments, we demonstrated that the addition of a p38MAPK inhibitor (PD169316) to CPT1B-knockdown adipocytes counteracted the increase in lipid deposition caused by the loss of CPT1B function. These findings suggest that CPT1B inhibits lipid deposition in goat intramuscular preadipocytes via the p38MAPK signaling pathway. In addition, we observed a potential interaction between CPT1B and CPT1A through Protein-Protein Interaction Networks (PPIs). Interestingly, CPT1A exhibited a similar regulatory function to CPT1B, and they both were able to partially restore the changes in lipid deposition induced by each other. This observation supports the hypothesis of synergistic effects between CPT1B and CPT1A. Collectively, our results elucidate the role of CPT1B in the regulation of lipid deposition in goat intramuscular adipocytes through the p38MAPK signaling pathway, providing valuable insights for enhancing the quality of goat intramuscular fat.

Project description:BackgroundUrsolic acid (UA) is a triterpenoid compound with multiple biological functions. This compound has recently been reported to possess an anti-obesity effect; however, the mechanisms are less understood.ObjectiveAs adipogenesis plays a critical role in obesity, the present study was conducted to investigate the effect of UA on adipogenesis and mechanisms of action in 3T3-L1 preadipocytes.Methods and resultsThe 3T3-L1 preadipocytes were induced to differentiate in the presence or absence of UA for 6 days. The cells were determined for proliferation, differentiation, fat accumulation as well as the protein expressions of molecular targets that regulate or are involved in fatty acid synthesis and oxidation. The results demonstrated that ursolic acid at concentrations ranging from 2.5 µM to 10 µM dose-dependently attenuated adipogenesis, accompanied by reduced protein expression of CCAAT element binding protein ? (C/EBP?), peroxisome proliferator-activated receptor ? (PPAR?), CCAAT element binding protein ? (C/EBP?) and sterol regulatory element binding protein 1c (SREBP-1c), respectively. Ursolic acid increased the phosphorylation of acetyl-CoA carboxylase (ACC) and protein expression of carnitine palmitoyltransferase 1 (CPT1), but decreased protein expression of fatty acid synthase (FAS) and fatty acid-binding protein 4 (FABP4). Ursolic acid increased the phosphorylation of AMP-activated protein kinase (AMPK) and protein expression of (silent mating type information regulation 2, homolog) 1 (Sirt1). Further studies demonstrated that the anti-adipogenic effect of UA was reversed by the AMPK siRNA, but not by the Sirt1 inhibitor nicotinamide. Liver kinase B1 (LKB1), the upstream kinase of AMPK, was upregulated by UA. When LKB1 was silenced with siRNA or the inhibitor radicicol, the effect of UA on AMPK activation was diminished.ConclusionsUrsolic acid inhibited 3T3-L1 preadipocyte differentiation and adipogenesis through the LKB1/AMPK pathway. There is potential to develop UA into a therapeutic agent for the prevention or treatment of obesity.

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LKB1 Regulates Goat Intramuscular Adipogenesis Through Focal Adhesion Pathway

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