Ablation of AMPK-Related Kinase MPK38/MELK Leads to Male-Specific Obesity in Aged Mature Adult Mice

Identification of Key Genes Related to Intramuscular Fat Content of Psoas Major Muscle in Saba Pigs by Integrating Bioinformatics and Machine Learning Based on Transcriptome Data

The psoas major muscle (PMM) is a piece of pork with good tenderness and high value. Intramuscular fat (IMF) content, serving as a pivotal indicator of pork quality, varies greatly among pigs within the same breed. However, there is a paucity of studies focusing on investigating the molecular mechanism of PMM IMF deposition in the same pig breed. The present study aimed to identify the potential genes related to the IMF content of PMM in low- and high-IMF Saba pigs based on transcriptome data analysis. The data used in this study were the RNA sequences of PMM from 12 Saba pigs (PRJNA1223630, from our laboratory) and gene expression profiles (GSE207279) acquired from the NCBI Sequence Read Archive database and the GEO database, respectively, together with data on the fatty acid and amino acid composition of the 12 Saba pigs' PMM. It was found that the high-IMF pigs exhibited significantly elevated levels of saturated fatty acids and (mono)unsaturated fatty acids, especially C14:0, C16:0, C20:0, C16:1, C18:1n9c, and C20:2, compared with those in the low-IMF pigs (p < 0.05 or p < 0.01). A total of 370 differentially expressed genes (DEGs) (221 up- and 149 down-regulated) were identified based on PRJNA1223630. Then, 20 hub genes were identified through protein-protein interaction (PPI) network analysis. Four potential fat-deposition-related genes (DGAT2, PCK1, MELK, and FASN) were further screened via the intersection of the candidate genes identified by the Least Absolute Shrinkage and Selection Operator (LASSO) algorithm and the top five genes ranked by the Random Forest (RF) method based on the 20 hub genes and were validated in the test gene set (GSE207279). The constructed mRNA (gene)-miRNA-lncRNA network, involving miRNAs (miR-103a-3p, miR-107, and miR-485-5p), lncRNAs (XIST, NEAT1, and KCNQ1OT1), and FASN, might be crucial for IMF deposition in pigs. These findings might delineate valuable regulatory molecular mechanisms coordinating IMF deposition and could serve as a beneficial foundation for the genetic improvement of pork quality.

Dysregulation of mitochondrial dynamics and mitophagy are involved in high-fat diet-induced steroidogenesis inhibition

Male obesity is a pandemic health issue and can disrupt testicular steroidogenesis. Here, we explored the mechanism by which a high-fat diet (HFD) induced steroidogenic inhibition. As expected, HFD induced lipid droplet accumulation and reduced the expression of StAR, P450scc, and 3β-HSD, three steroidogenic enzymes, in mouse testes. Palmitic acid (PA), a saturated fatty acid usually used to trigger lipotoxicity in vitro, induced greater accumulation of lipid droplets and the downregulation of steroidogenic enzymes in TM3 cells. Mechanistically, both HFD and PA disturbed mitochondrial fusion/fission dynamics and then induced mitochondrial dysfunction and mitophagy inhibition in mouse Leydig cells. Additionally, mitochondrial fusion promoter M1 attenuated PA-induced imbalance of mitochondrial dynamics, mitophagy inhibition, mitochondrial reactive oxygen species (ROS) production, and mitochondrial dysfunction in TM3 cells. Mitofusin 2 (Mfn2) knock-down further aggravated the PA-induced imbalance of mitochondrial dynamics, mitochondrial ROS production, and mitochondrial dysfunction in TM3 cells. Importantly, M1 rescued PA-induced downregulation of steroidogenic enzymes, whereas Mfn2 knock-down further aggravated PA-induced downregulation of steroidogenic enzymes in TM3 cells. Overall, our results provide laboratory evidence that mitochondrial dysfunction and mitophagy inhibition caused by dysregulation of mitochondrial fusion may be involved in HFD-induced steroidogenesis inhibition in mouse Leydig cells.

DAXX ameliorates metabolic dysfunction in mice with diet-induced obesity by activating the AMP-activated protein kinase-related kinase MPK38/MELK

Death domain-associated protein (DAXX) is involved in the activation of adipocyte apoptosis and is downregulated in response to a high-fat diet (HFD), which implies that the inhibition of adipocyte apoptosis may cause obesity. However, the anti-obesity effects of DAXX in diet-induced obesity (DIO) remain to be characterized. Here, we identified DAXX as an interacting partner of murine protein serine-threonine kinase 38 (MPK38). This interaction was mediated by the C-terminal (amino acids 270-643) domain of MPK38 and the N-terminal (amino acids 1-440) domain of DAXX and was increased by diverse signals that activate ASK1/TGF-β/p53 signaling. MPK38 phosphorylated DAXX at Thr578. Wild-type DAXX, but not a DAXX T578A mutant, stimulated MPK38-dependent ASK1/TGF-β/p53 signaling by increasing the stability of MPK38 and complex formation between MPK38 and its downstream targets, such as ASK1, Smad3, and p53. This mechanism was also shown in MEF cells that were null (-/-) for DAXX. Furthermore, the adenovirally-mediated reinstatement of DAXX expression activated MPK38 and ameliorated diet-induced defects in glucose and lipid metabolism in mice. These results indicate that DAXX limits obesity-induced metabolic abnormalities in DIO mice by activating MPK38.