Background

Glucagon plays a central role in hepatic adaptation during fasting, with the upregulation of hepatic phosphoenolpyruvate carboxykinase 1 (PCK1) traditionally associated with increased gluconeogenesis. However, recent experimental models and clinical studies have challenged this view, suggesting a more complex interplay between PCK1 and glucagon, which extends beyond gluconeogenesis and has broader implications for metabolic regulation in health and disease.

Scope of review

This review provides a comprehensive overview of the current evidence on the multifaceted roles of PCK1 in glucagon-dependent hepatic adaptation during fasting, which is crucial for maintaining systemic homeostasis not only of glucose, but also of lipids and amino acids. We explore the relationship between PCK1 deficiency and glucagon resistance in metabolic disorders, including inherited PCK1 deficiency and metabolic dysfunction-associated steatotic liver disease (MASLD), and compare findings from experimental animal models with whole-body or tissue-specific ablation of PCK1 or the glucagon receptor. We propose new research platforms to advance the therapeutic potential of targeting PCK1 in metabolic diseases.

Major conclusions

We propose that hepatic PCK1 deficiency might be an acquired metabolic disorder linking alterations in lipid metabolism with impaired glucagon signaling. Our findings highlight interesting links between glycerol, PCK1 deficiency, elevated plasma alanine levels and glucagon resistance. We conclude that the roles of PCK1 and glucagon in metabolic regulation are more complex than previously assumed. In this (un)expected scenario, hepatic PCK1 deficiency and glucagon resistance appear to exert limited control over glycemia, but have broader metabolic effects related to lipid and amino acid dysregulation. Given the shift in glucagon research from receptor inhibition to activation, we propose that a similar paradigm shift is needed in the study of hepatic PCK1. Understanding PCK1 expression and activity in the glucagon-dependent hepatic adaptation to fasting might provide new perspectives and therapeutic opportunities for metabolic diseases.

Objective

Regulatory T cells (Tregs) are essential in maintaining immune tolerance and controlling inflammation. Treg stability relies on transcriptional and post-translational mechanisms, including histone acetylation at the Foxp3 locus and FoxP3 protein acetylation. Additionally, Tregs depend on specific metabolic programs for differentiation, yet the underlying molecular mechanisms remain elusive. We aimed to investigate the role of acetyl-CoA carboxylase 1 (ACC1) in the differentiation, stability, and function of regulatory T cells (Tregs).

Methods

We used either T cell-specific ACC1 knockout mice or ACC1 inhibition via a pharmacological agent to examine the effects on Treg differentiation and stability. The impact of ACC1 inhibition on Treg function was assessed in vivo through adoptive transfer models of Th1/Th17-driven inflammatory diseases.

Results

Inhibition or genetic deletion of ACC1 led to an increase in acetyl-CoA availability, promoting enhanced histone and protein acetylation, and sustained FoxP3 transcription even under inflammatory conditions. Mice with T cell-specific ACC1 deletion exhibited an enrichment of double positive RORγt⁺FoxP3⁺ cells. Moreover, Tregs treated with an ACC1 inhibitor demonstrated superior long-term stability and an enhanced capacity to suppress Th1/Th17-driven inflammatory diseases in adoptive transfer models.

Conclusions

We identified ACC1 as a metabolic checkpoint in Treg biology. Our data demonstrate that ACC1 inhibition promotes Treg differentiation and long-term stability in vitro and in vivo. Thus, ACC1 serves as a dual metabolic and epigenetic hub, regulating immune tolerance and inflammation by balancing de novo lipid synthesis and protein acetylation.

Objectives

Increased expression of glutaminase (GLS) has been found to correlate with more aggressive disease and poorer prognosis in patients with several types of cancer, including breast, lung, and pancreatic cancer. G9a histone methyltransferase inhibitors may have anticancer activity. The present study assessed whether BIX01294 (BIX), a G9a histone methyltransferase inhibitor, can inhibit glutaminase (GLS) in pancreatic ductal adenocarcinoma (PDAC) cells.

Methods

The effects of BIX on mitochondrial metabolism in PDAC cells were evaluated by targeted liquid chromatography–tandem mass spectrometry (LC-MS/MS) metabolomic analysis. To assess the impact of BIX on glutathione dynamics, real-time changes in glutathione levels were monitored by FreSHtracer-based GSH assays.

Results

BIX significantly inhibited the growth of PDAC cells, both in vitro and in vivo, and robustly induced apoptotic cell death. BIX significantly increased the cellular NADP⁺/NADPH ratio and decreased the ratio of reduced-to-oxidized glutathione (GSH:GSSG). In addition, BIX decreased GSH levels and increased ROS levels. N-acetyl-l-cysteine (NAC) supplementation dramatically rescued PDAC cells from BIX-induced apoptosis. Furthermore, BIX inhibited the transcription of GLS by inhibiting Jumonji-domain histone demethylases but not G9a histone methyltransferase. One Jumonji-domain histone demethylase, KDM6B, epigenetically regulated GLS expression by binding to the GLS gene promoter.

Conclusions

Collectively, these findings suggest that BIX could be a potent therapeutic agent in patients with PDAC through its inhibition of GLS-mediated cellular redox balance.