Metabolic Rewiring Controlled by HIF-1α Tunes IgA-Producing B-Cell Differentiation and Intestinal Inflammation

Background Introduction

Germinal centers (GC) are critical sites for the clonal expansion of immune B cells and the affinity maturation of antibodies, as well as the occurrence of antibody class switching. Within the GC, B cells undergo somatic hypermutation (SHM) and class-switch recombination (CSR) to generate antibodies such as IgG and IgA. During these processes, epigenetic histone modifications play pivotal roles in transcriptional accessibility and DNA double-strand break repair. However, the precise mechanisms by which the hypoxic microenvironment of GCs influences immune cell metabolism and function are not yet fully understood.

Previous studies have shown that hypoxia-inducible factor-1α (HIF-1α) is a central regulator of cellular metabolism and activity. However, the specific effects of HIF-1α on IgA class switching and its role in maintaining intestinal immune homeostasis remain poorly studied. As the most abundant mucosal antibody, IgA is crucial for maintaining gut microbial balance and regulating intestinal inflammation. Understanding the role of HIF-1α in the metabolic regulation of IgA B-cell differentiation is therefore essential for uncovering mechanisms underlying inflammatory bowel disease (IBD) and developing potential therapeutic strategies.

Paper Source and Author Information

The paper was led by Xianyi Meng, with Aline Bozec as the corresponding author. The research team mainly stems from various departments of Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) and its affiliated hospital in Germany. This study was published online in Cellular & Molecular Immunology on November 14, 2024, with the DOI: https://doi.org/10.1038/s41423-024-01233-y.

Detailed Research Process

1. Research Design and Objectives

The study investigated the role of HIF-1α in IgA-producing B-cell differentiation and its effects on intestinal inflammation through the following steps: 1. Examining HIF-1α expression in GC B cells and the impact of its deletion on IgA differentiation. 2. Exploring the relationship between HIF-1α-dependent glycolysis and IgA production. 3. Evaluating the protective role of HIF-1α in dextran sulfate sodium (DSS)-induced colitis. 4. Testing pharmacological interventions (roxadustat stabilization) and metabolic supplementation (enhancement of acetyl-CoA) for their effects on IgA production and colitis mitigation.

2. Methods and Specific Experiments

Expression Analysis

Using immunofluorescence and flow cytometry, the study revealed that HIF-1α is highly expressed in GC B cells of mice, significantly more so than in other immune cells. Conditional knockout (cKO) to remove HIF-1α in B cells resulted in a notable reduction of IgA levels, while IgG1 and IgM levels remained unaffected.

Glycolytic Metabolism Studies

Single-cell RNA sequencing (scRNA-seq) and metabolic-marker experiments showed that IgA+ B cells exhibited significant glycolytic activity. The loss of HIF-1α weakened glucose-dependent metabolic activity, reducing IgA class-switch efficiency. RNA-seq further demonstrated downregulated glycolysis-related genes in HIF-1α-deficient B cells.

Epigenetic and Metabolic Regulation

Chromatin immunoprecipitation sequencing (ChIP-seq) analysis demonstrated that the absence of HIF-1α disrupted histone H3K27 acetylation modification in the IgA class-switching region (Sα). This affected RNA polymerase II and AID (activation-induced deaminase) recruitment.

Inflammatory Model and Drug Intervention

In a DSS-induced colitis mouse model, HIF-1α-deficient mice showed more severe weight loss, shorter colons, and worsened tissue damage. Stabilizing HIF-1α with roxadustat notably restored IgA levels, reduced inflammatory cytokines, and alleviated DSS-induced intestinal inflammation.

Metabolic Supplementation

The study examined the reversal of IgA production impairment caused by HIF-1α deficiency using acetyl-CoA supplementation. Oral supplementation of glyceryl triacetate (GTA) restored IgA levels, alleviated colitis symptoms, and highlighted its potential therapeutic application.

Research Results

Key Findings

1. HIF-1α is selectively expressed in GC B cells and initiates IgA class switching via glycolytic regulation.
2. The loss of HIF-1α impaired IgA+ B cells’ glycolysis, acetyl-CoA levels, and histone acetylation at Sα regions, disrupting IgA class switching.
3. In DSS colitis models, HIF-1α deficiency aggravated intestinal inflammation, whereas the stabilization of HIF-1α increased IgA secretion and alleviated inflammation.
4. Acetyl-CoA supplementation using GTA improved IgA differentiation defects caused by HIF-1α deficiency and reduced colitis severity.

Significance and Highlights

Scientific Importance

This study provides the first comprehensive insight into the involvement of HIF-1α in the metabolic-epigenetic pathway regulating IgA class switching. The findings enhance our understanding of immune metabolic regulation mechanisms and shed light on potential therapeutic strategies for inflammatory diseases like IBD.

Clinical Relevance

Stabilizing HIF-1α with roxadustat, in addition to its established use in treating renal anemia, shows promise for mitigating gut inflammation. Furthermore, metabolic supplementation (e.g., GTA) demonstrates synergistic potential, providing a new combination therapy approach for IBD treatment.

Conclusion

Through extensive experimental analyses, this paper unveils the critical role of HIF-1α in regulating glycolysis and IgA production in GC B cells, offering new avenues for IBD treatment. Moving forward, targeted interventions involving HIF-1α warrant further clinical validation to establish their effectiveness in managing human inflammatory diseases.