Carbon dioxide regulates cholesterol levels through SREBP2

Gene Expression Profiling of Pancreatic Ductal Adenocarcinoma Cells in Hypercapnia Identifies SIAH3 as a Novel Prognostic Biomarker

Hypercapnia is a key feature of the respiratory microenvironment in many pathologic conditions. It occurs both as a regional and as a systemic process, and it is associated with multiple metabolic changes such as mitochondrial dysfunction, decreased ATP production, and metabolic shift from glycolytic energy production to fatty acid metabolism. In the cancer tumor microenvironment, hypercapnia has been linked at times to enhanced cell migration, invasion, and chemoresistance. Our previous work has shown that hypercapnia-associated gene signatures can be used as prognostic biomarkers. However, unlike the hypoxia-inducible factor pathway, there are no validated targets to quantify hypercapnia. In this study, we investigated the phenotypic and transcriptomic changes occurring in pancreatic ductal adenocarcinoma (PDAC) due to chronic exposure to hypercapnic atmospheres. We then identified and validated SIAH3 as a hypercapnia-affected target and explored its clinical relevance as a prognostic factor in PDAC.

The regulation of cell metabolism by hypoxia and hypercapnia

Every cell in the body is exposed to a certain level of CO2 and O2. Hypercapnia and hypoxia elicit stress signals to influence cellular metabolism and function. Both conditions exert profound yet distinct effects on metabolic pathways and mitochondrial dynamics, highlighting the need for cells to adapt to changes in the gaseous microenvironment. The interplay between hypercapnia and hypoxia signaling is the key for dictating cellular homeostasis as microenvironmental CO2 and O2 levels are inextricably linked. Hypercapnia, characterized by elevated pCO2, introduces metabolic adaptations within the aerobic metabolism pathways, affecting tricarboxylic acid cycle flux, lipid, and amino acid metabolism, oxidative phosphorylation and the electron transport chain. Hypoxia, defined by reduced oxygen availability, necessitates a shift from oxidative phosphorylation to anaerobic glycolysis to sustain ATP production, a process orchestrated by the stabilization of hypoxia-inducible factor-1α. Given that hypoxia and hypercapnia are present in both physiological and cancerous microenvironments, how might the coexistence of hypercapnia and hypoxia influence metabolic pathways and cellular function in physiological niches and the tumor microenvironment?

miR-18a-5p/PXR/SREBP2 Was Involved in MAFLD Associated With Methyl Tert-Butyl Ether Among Petrol Station Workers

BACKGROUND

Metabolic associated fatty liver disease (MAFLD), previously defined as non-alcoholic fatty liver disease (NAFLD), has been shown to be closely related to many environmental pollutants. Lately, we found methyl tert-butyl ether (MTBE), a new environmental pollutant, could increase NAFLD risk in American adults, which still needs more population epidemiological studies to verify, and its pathogenic mechanism is not yet clear.

METHODS

We conducted a cross-sectional study among petrol station workers, diagnosed their MAFLD according to internationally recognised diagnostic criteria, assessed the potential association of MTBE exposure with MAFLD risk, and explored the miR-18a-5p/PXR/SREBP2 pathway as possible pathogenic mechanisms in male Wistar rats and HepaRG cells treated with MTBE.

RESULTS

Blood MTBE levels were found to be significantly correlated with an increased risk of MAFLD, and MAFLD risk increased by 24.3% for every 0.1 μg/L increase in blood MTBE. Consistently, we found that MTBE exposure could induce MAFLD in rats and HepaRG cells, and activate pregnane X receptor (PXR) by inhibiting miR-18a-5p to upregulate the expression of sterol regulatory element-binding protein 2 (SREBP2) and its nuclear translocation, thereby upregulating the expression of its downstream target genes.

CONCLUSIONS

Our study demonstrated that MTBE exposure might be a significant risk factor for MAFLD, and MTBE could promote liver cholesterol synthesis and lipid deposition by activating the miRNA-18a-5p/PXR/SREBP2 pathway.

Ubiquitination and De-Ubiquitination in the Synthesis of Cow Milk Fat: Reality and Prospects

Ubiquitination modifications permit the degradation of labelled target proteins with the assistance of proteasomes and lysosomes, which is the main protein degradation pathway in eukaryotic cells. Polyubiquitination modifications of proteins can also affect their functions. De-ubiquitinating enzymes reverse the process of ubiquitination via cleavage of the ubiquitin molecule, which is known as a de-ubiquitination. It was demonstrated that ubiquitination and de-ubiquitination play key regulatory roles in fatty acid transport, de novo synthesis, and desaturation in dairy mammary epithelial cells. In addition, natural plant extracts, such as stigmasterol, promote milk fat synthesis in epithelial cells via the ubiquitination pathway. This paper reviews the current research on ubiquitination and de-ubiquitination in dairy milk fat production, with a view to providing a reference for subsequent research on milk fat and exploring new directions for the improvement of milk quality.

A novel insight into cancer therapy: Lipid metabolism in tumor-associated macrophages

The tumor immune microenvironment (TIME) can limit the effectiveness and often leads to significant side effects of conventional cancer therapies. Consequently, there is a growing interest in identifying novel targets to enhance the efficacy of targeted cancer therapy. More research indicates that tumor-associated macrophages (TAMs), originating from peripheral blood monocytes generated from bone marrow myeloid progenitor cells, play a crucial role in the tumor microenvironment (TME) and are closely associated with resistance to traditional cancer therapies. Lipid metabolism alterations have been widely recognized as having a significant impact on tumors and their immune microenvironment. Lipids, lipid derivatives, and key substances in their metabolic pathways can influence the carcinogenesis and progression of cancer cells by modulating the phenotype, function, and activity of TAMs. Therefore, this review focuses on the reprogramming of lipid metabolism in cancer cells and their immune microenvironment, in which the TAMs are especially concentrated. Such changes impact TAMs activation and polarization, thereby affecting the tumor cell response to treatment. Furthermore, the article explores the potential of targeting the lipid metabolism of TAMs as a supplementary approach to conventional cancer therapies. It reviews and evaluates current strategies for enhancing efficacy through TAMs' lipid metabolism and proposes new lipid metabolism targets as potential synergistic options for chemo-radiotherapy and immunotherapy. These efforts aim to stimulate further research in this area.

Orphan Nuclear Receptor Family 4A (NR4A) Members NR4A2 and NR4A3 Selectively Modulate Elements of the Monocyte Response to Buffered Hypercapnia

Hypercapnia occurs when the partial pressure of carbon dioxide (CO2) in the blood exceeds 45 mmHg. Hypercapnia is associated with several lung pathologies and is transcriptionally linked to suppression of immune and inflammatory signalling through poorly understood mechanisms. Here we propose Orphan Nuclear Receptor Family 4A (NR4A) family members NR4A2 and NR4A3 as potential transcriptional regulators of the cellular response to hypercapnia in monocytes. Using a THP-1 monocyte model, we investigated the sensitivity of NR4A family members to CO2 and the impact of depleting NR4A2 and NR4A3 on the monocyte response to buffered hypercapnia (10% CO2) using RNA-sequencing. We observed that NR4A2 and NR4A3 are CO2-sensitive transcription factors and that depletion of NR4A2 and NR4A3 led to reduced CO2-sensitivity of mitochondrial and heat shock protein (Hsp)-related genes, respectively. Several CO2-sensitive genes were, however, refractory to depletion of NR4A2 and NR4A3, indicating that NR4As regulate certain elements of the cellular response to buffered hypercapnia but that other transcription factors also contribute. Bioinformatic analysis of conserved CO2-sensitive genes implicated several novel putative CO2-sensitive transcription factors, of which the ETS Proto-Oncogene 1 Transcription Factor (ETS-1) was validated to show increased nuclear expression in buffered hypercapnia. These data give significant insights into the understanding of immune responses in patients experiencing hypercapnia.

A tale of 2 gasses, 1 regulator, and cholesterol homeostasis

There is a burgeoning appreciation for the wide-ranging effects of carbon dioxide on transcriptional regulation and metabolism. Here, Bolshette and colleagues provide the first link between carbon dioxide and the master transcriptional regulator of cholesterol homeostasis.