Unveiling the Function of the Mitochondrial Filament-Forming Protein LACTB in Lipid Metabolism and Cancer

Epigenetic silencing of KCTD8 promotes hepatocellular carcinoma growth by activating PI3K/AKT signaling

Aim: The aim of current study is to explore the epigenetic changes and function of KCTD8 in human hepatocellular carcinoma (HCC). Materials & methods: HCC cell lines and tissue samples were employed. Methylation specific PCR, flow cytometry, immunoprecipitation and xenograft mouse models were used.Results: KCTD8 was methylated in 44.83% (104/232) of HCC and its methylation may act as an independent poor prognostic marker. KCTD8 expression was regulated by DNA methylation. KCTD8 suppressed HCC cell growth both in vitro and in vivo via inhibiting PI3K/AKT pathway.Conclusion: Methylation of KCTD8 is an independent poor prognostic marker, and epigenetic silencing of KCTD8 increases the malignant tendency in HCC.

Mitochondrial proteases modulate mitochondrial stress signalling and cellular homeostasis in health and disease

Maintenance of mitochondrial homeostasis requires a plethora of coordinated quality control and adaptations' mechanisms in which mitochondrial proteases play a key role. Their activation or loss of function reverberate beyond local mitochondrial biochemical and metabolic remodelling into coordinated cellular pathways and stress responses that feedback onto the mitochondrial functionality and adaptability. Mitochondrial proteolysis modulates molecular and organellar quality control, metabolic adaptations, lipid homeostasis and regulates transcriptional stress responses. Defective mitochondrial proteolysis results in disease conditions most notably, mitochondrial diseases, neurodegeneration and cancer. Here, it will be discussed how mitochondrial proteases and mitochondria stress signalling impact cellular homeostasis and determine the cellular decision to survive or die, how these processes may impact disease etiopathology, and how modulation of proteolysis may offer novel therapeutic strategies.

Identification and analysis of mitochondria-related central genes in steroid-induced osteonecrosis of the femoral head, along with drug prediction

Purpose

Steroid-induced osteonecrosis of the femoral head (SONFH) is a refractory orthopedic hip joint disease that primarily affects middle-aged and young individuals. SONFH may be caused by ischemia and hypoxia of the femoral head, where mitochondria play a crucial role in oxidative reactions. Currently, there is limited literature on whether mitochondria are involved in the progression of SONFH. Here, we aim to identify and validate key potential mitochondrial-related genes in SONFH through bioinformatics analysis. This study aims to provide initial evidence that mitochondria play a role in the progression of SONFH and further elucidate the mechanisms of mitochondria in SONFH.

Methods

The GSE123568 mRNA expression profile dataset includes 10 non-SONFH (non-steroid-induced osteonecrosis of the femoral head) samples and 30 SONFH samples. The GSE74089 mRNA expression profile dataset includes 4 healthy samples and 4 samples with ischemic necrosis of the femoral head. Both datasets were downloaded from the Gene Expression Omnibus (GEO) database. The mitochondrial-related genes are derived from MitoCarta3.0, which includes data for all 1136 human genes with high confidence in mitochondrial localization based on integrated proteomics, computational, and microscopy approaches. By intersecting the GSE123568 and GSE74089 datasets with a set of mitochondrial-related genes, we screened for mitochondrial-related genes involved in SONFH. Subsequently, we used the good Samples Genes method in R language to remove outlier genes and samples in the GSE123568 dataset. We further used WGCNA to construct a scale-free co-expression network and selected the hub gene set with the highest connectivity. We then intersected this gene set with the previously identified mitochondrial-related genes to select the genes with the highest correlation. A total of 7 mitochondrial-related genes were selected. Next, we performed Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis on the selected mitochondrial-related genes using R software. Furthermore, we performed protein network analysis on the differentially expressed proteins encoded by the mitochondrial genes using STRING. We used the GSEA software to group the genes within the gene set in the GSE123568 dataset based on their coordinated changes and evaluate their impact on phenotype changes. Subsequently, we grouped the samples based on the 7 selected mitochondrial-related genes using R software and observed the differences in immune cell infiltration between the groups. Finally, we evaluated the prognostic significance of these features in the two datasets, consisting of a total of 48 samples, by integrating disease status and the 7 gene features using the cox method in the survival R package. We performed ROC analysis using the roc function in the pROC package and evaluated the AUC and confidence intervals using the ci function to obtain the final AUC results.

Results

Identification and analysis of 7 intersecting DEGs (differentially expressed genes) were obtained among peripheral blood, cartilage samples, hub genes, and mitochondrial-related genes. These 7 DEGs include FTH1, LACTB, PDK3, RAB5IF, SOD2, and SQOR, all of which are upregulated genes with no intersection in the downregulated gene set. Subsequently, GO and KEGG pathway enrichment analysis revealed that the upregulated DEGs are primarily involved in processes such as oxidative stress, release of cytochrome C from mitochondria, negative regulation of intrinsic apoptotic signaling pathway, cell apoptosis, mitochondrial metabolism, p53 signaling pathway, and NK cell-mediated cytotoxicity. GSEA also revealed enriched pathways associated with hub genes. Finally, the diagnostic value of these key genes for hormone-related ischemic necrosis of the femoral head (SONFH) was confirmed using ROC curves.

Conclusion

BID, FTH1, LACTB, PDK3, RAB5IF, SOD2, and SQOR may serve as potential diagnostic mitochondrial-related biomarkers for SONFH. Additionally, they hold research value in investigating the involvement of mitochondria in the pathogenesis of ischemic necrosis of the femoral head.

Metabolic enzyme Suclg2 maintains tolerogenicity of regulatory dendritic cells diffDCs by suppressing Lactb succinylation

Metabolic reprogramming plays a pivotal role in the differentiation and function of immune cells including dendritic cells (DCs). Regulatory DCs can be generated in regional tissue niches like splenic stroma and act as an important part of stromal control of immune response for the maintenance of immune tolerance. However, the metabolic alterations during splenic stroma-driven regulatory DCs differentiation and the metabolic enzyme involved in regulatory DCs function remain poorly understood. By combining metabolomic, transcriptomic, and functional investigations of mature DCs (maDCs) and diffDCs (regulatory DCs differentiated from activated mature DCs through coculturing with splenic stroma), here we identified succinate-CoA ligase subunit beta Suclg2 as a key metabolic enzyme that reprograms the proinflammatory status of mature DCs into a tolerogenic phenotype via preventing NF-κB signaling activation. diffDCs downregulate succinic acid levels and increase the Suclg2 expression along with their differentiation from mature DCs. Suclg2-interference impaired the tolerogenic function of diffDCs in inducing T cell apoptosis and enhanced activation of NF-κB signaling and expression of inflammatory genes CD40, Ccl5, and Il12b in diffDCs. Furthermore, we identified Lactb as a new positive regulator of NF-κB signaling in diffDCs whose succinylation at the lysine 288 residue was inhibited by Suclg2. Our study reveals that the metabolic enzyme Suclg2 is required to maintain the immunoregulatory function of diffDCs, adding mechanistic insights into the metabolic regulation of DC-based immunity and tolerance.

LACTB exerts tumor suppressor properties in epithelial ovarian cancer through regulation of Slug

Epithelial-mesenchymal transition (EMT) is a cellular mechanism used by cancer cells to acquire migratory and stemness properties. In this study, we show, through in vitro, in vivo, and 3D culture experiments, that the mitochondrial protein LACTB manifests tumor suppressor properties in ovarian cancer. We show that LACTB is significantly down-regulated in epithelial ovarian cancer cells and clinical tissues. Re-expression of LACTB negatively effects the growth of cancer cells but not of non-tumorigenic cells. Mechanistically, we show that LACTB leads to differentiation of ovarian cancer cells and loss of their stemness properties, which is achieved through the inhibition of the EMT program and the LACTB-dependent down-regulation of Snail2/Slug transcription factor. This study uncovers a novel role of LACTB in ovarian cancer and proposes new ways of counteracting the oncogenic EMT program in this model system.

LACTB, a Metabolic Therapeutic Target in Clinical Cancer Application

Serine beta-lactamase-like protein (LACTB) is the only mammalian mitochondrial homolog evolved from penicillin-binding proteins and β-lactamases (PBP-βLs) in bacteria. LACTB, an active-site serine protease, polymerizes into stable filaments, which are localized to the intermembrane space (IMS) of mitochondrion and involved in the submitochondrial organization, modulating mitochondrial lipid metabolism. Cancer pathogenesis and progression are relevant to the alterations in mitochondrial metabolism. Metabolic reprogramming contributes to cancer cell behavior. This article (1) evidences the clinical implications of LACTB on neoplastic cell proliferation and migration and tumor growth and metastasis as well as LACTB’s involvement in chemotherapeutic and immunotherapeutic responses; (2) sketches the structural basis for LACTB activity and function; and (3) highlights the relevant regulatory mechanisms to LACTB. The abnormal expression of LACTB has been associated with clinicopathological features of cancer tissues and outcomes of anticancer therapies. With the current pioneer researches on the tumor-suppressed function, structural basis, and regulatory mechanism of LACTB, the perspective hints at a great appeal of enzymic property, polymerization, mutation, and epigenetic and post-translational modifications in investigating LACTB’s role in cancer pathogenesis. This perspective provides novel insights for LACTB as a metabolic regulator with potential to develop targeted cancer therapies or neoadjuvant therapeutic interventions.