Krüppel-like factor 15 in liver diseases: Insights into metabolic reprogramming

Mitochondrial Calcium Signaling Regulates Branched-Chain Amino Acid Catabolism in Fibrolamellar Carcinoma

Metabolic adaptations in response to changes in energy supply and demand are essential for survival. The mitochondrial calcium uniporter coordinates metabolic homeostasis by regulating TCA cycle activation, mitochondrial fatty acid oxidation and cellular calcium signaling. However, a comprehensive analysis of uniporter-regulated mitochondrial metabolic pathways has remained unexplored. Here, we investigate the metabolic consequences of uniporter loss- and gain-of-function, and identify a key transcriptional regulator that mediates these effects. Using gene expression profiling and proteomic, we find that loss of uniporter function increases the expression of proteins in the branched-chain amino acid (BCAA) catabolism pathway. Activity is further augmented through phosphorylation of the enzyme that catalyzes this pathway's committed step. Conversely, in the liver cancer fibrolamellar carcinoma (FLC)-which we demonstrate to have high mitochondrial calcium levels- expression of BCAA catabolism enzymes is suppressed. We also observe uniporter-dependent suppression of the transcription factor KLF15, a master regulator of liver metabolic gene expression, including those involved in BCAA catabolism. Notably, loss of uniporter activity upregulates KLF15, along with its transcriptional target ornithine transcarbamylase (OTC), a component of the urea cycle, suggesting that uniporter hyperactivation may contribute to the hyperammonemia observed in FLC patients. Collectively, we establish that FLC has increased mitochondrial calcium levels, and identify an important role for mitochondrial calcium signaling in metabolic adaptation through the transcriptional regulation of metabolism.

Establishment and Validation of Novel Prognostic Subtypes in Hepatocellular Carcinoma Based on Bile Acid Metabolism Gene Signatures Using Bulk and Single-Cell RNA-Seq Data

Hepatocellular carcinoma (HCC) is a highly detrimental cancer type and has limited therapeutic options, posing significant threats to human health. The development of HCC has been associated with a disorder in bile acid (BA) metabolism. In this study, we employed an integrative approach, combining various datasets and omics analyses, to comprehensively characterize the tumor microenvironment in HCC based on genes related to BA metabolism. Our analysis resulted in the classification of HCC samples into four subtypes (C1, C2a, C2b, and C3). Notably, subtype C2a, characterized by the highest bile acid metabolism score (BAMS), exhibited the highest survival probability. This subtype also demonstrated increased immune cell infiltration, lower cell cycle scores, reduced AFP levels, and a lower risk of metastasis compared to subtypes C1 and C3. Subtype C1 displayed poorer survival probability and elevated cell cycle scores. Importantly, the identified subtypes based on BAMS showed potential relevance to the gene expression of drug targets in currently approved drugs and those under clinical research. Genes encoding VEGFR (FLT4 and KDR) and MET were elevated in C2, while genes such as TGFBR1, TGFB1, ADORA3, SRC, BRAF, RET, FLT3, KIT, PDGFRA, and PDGFRB were elevated in C1. Additionally, FGFR2 and FGFR3, along with immune target genes including PDCD1 and CTLA4, were higher in C3. This suggests that subtypes C1, C2, and C3 might represent distinct potential candidates for TGFB1 inhibitors, VEGFR inhibitors, and immune checkpoint blockade treatments, respectively. Significantly, both bulk and single-cell transcriptome analyses unveiled a negative correlation between BA metabolism and cell cycle-related pathways. In vitro experiments further confirmed that the treatment of HCC cell lines with BA receptor agonist ursodeoxycholic acid led to the downregulation of the expression of cell cycle-related genes. Our findings suggest a plausible involvement of BA metabolism in liver carcinogenesis, potentially mediated through the regulation of tumor cell cycles and the immune microenvironment. This preliminary understanding lays the groundwork for future investigations to validate and elucidate the specific mechanisms underlying this potential association. Furthermore, this study provides a novel foundation for future precise molecular typing and the design of systemic clinical trials for HCC therapy.

The GR-KLF15 axis promotes suppression of hepatic lipogenesis during fasting

Fasting leads to many physiological changes in peripheral tissues, including the liver, where suppression of de novo lipogenesis through inhibition of sterol regulatory element-binding protein 1 (SREBP-1) expression and/or activity is a key adaptation to preserve glucose for maintenance of blood glucose levels. Yoshinori Takeuchi and colleagues provide novel mechanistic insights into the regulation of SREBP-1 expression during fasting and highlight the importance of the hypothalamic-pituitary-adrenal axis and, particularly, glucocorticoid-induced binding of the glucocorticoid receptor to enhancer regions of the KLF15 (Kruppel-like factor 15) gene as a novel mechanism underlying the suppression of SREBP-1 during fasting.