USP7-Driven PKM2 Metabolic Reprogramming in Macrophage Polarization During Severe Acute Pancreatitis

Study Background and Research Question

Severe acute pancreatitis (SAP) is a critical inflammatory disorder with high morbidity and mortality, largely due to systemic inflammatory responses and multiple organ failure. Despite advances in supportive care, effective therapeutic agents that can disrupt the underlying disease mechanisms remain elusive. In SAP, macrophages play a central role: the early infiltration and activation of pro-inflammatory M1 macrophages exacerbate tissue injury, while later anti-inflammatory M2 macrophages limit damage and promote resolution. However, the molecular regulators orchestrating this phenotypic switch, especially those related to metabolic control, are not fully understood. The reference study (Wu et al., 2025) investigates whether ubiquitin-specific protease 7 (USP7) modulates macrophage polarization through PKM2-dependent metabolic reprogramming in SAP.

Key Innovation from the Reference Study

The principal innovation of the study lies in delineating the USP7–PKM2 axis as a core pathway regulating the inflammatory phenotype of macrophages in SAP. Specifically, USP7 was found to promote the pro-inflammatory M1 phenotype by supporting PKM2 activity, thus enhancing glycolytic metabolism. Knockdown of USP7 not only reduced disease severity in mouse models but also shifted macrophage populations toward the anti-inflammatory M2 state. Importantly, the study provides mechanistic evidence that USP7 exerts these effects through post-translational modification of PKM2, influencing its phosphorylation, nuclear localization, and function in metabolic reprogramming.

Methods and Experimental Design Insights

The research team implemented a multi-layered approach to dissect the immunometabolic mechanisms in SAP. Experimental SAP was induced in mice, followed by comprehensive analyses of pancreatic macrophages, including:

• Expression profiling: USP7 and PKM2 levels were quantified in pancreatic tissues from both SAP and control mice using immunohistochemistry and Western blotting.
• Macrophage phenotyping: Immunofluorescence and flow cytometry characterized M1/M2 polarization markers in tissue and isolated cells.
• Metabolic assays: Seahorse extracellular flux analysis measured extracellular acidification rates (ECAR) and oxygen consumption rates (OCR) to assess glycolytic and oxidative phosphorylation (OXPHOS) activities.
• Protein–protein interaction studies: Co-immunoprecipitation (Co-IP) and ubiquitinated immunoprecipitation (IP) assays evaluated USP7's direct interaction with PKM2 and its effect on PKM2 deubiquitination and phosphorylation.
• PKM2 inhibition rescue: To dissect the functional dependency on PKM2, a selective PKM2 inhibitor was administered to SAP mice with USP7 knockdown, assessing the reversal of protective effects.

This multifaceted approach ensured robust mechanistic validation of the USP7–PKM2 pathway in SAP-related inflammation.

Core Findings and Why They Matter

• USP7 upregulation in SAP: Pancreatic tissues from SAP mice displayed significantly increased USP7 expression, particularly in infiltrating macrophages (Wu et al., 2025).
• USP7 knockdown attenuates SAP severity: Genetic silencing of USP7 led to reduced serum amylase and lipase activities, diminished pro-inflammatory cytokine production, and less pancreatic tissue injury, demonstrating a functional role in disease progression.
• Macrophage polarization shift: USP7 knockdown favored M2 (anti-inflammatory) over M1 (pro-inflammatory) macrophage phenotypes, both in vivo and in vitro, supporting the therapeutic relevance of targeting metabolic polarization.
• Metabolic reprogramming via PKM2: USP7 was shown to enhance glycolysis in M1 macrophages by stabilizing PKM2 through deubiquitination and promoting its nuclear translocation. This led to increased glycolytic flux (higher ECAR) and suppressed OXPHOS activity, which are hallmarks of inflammatory macrophages.
• Dependency on PKM2 activity: Administration of a PKM2 inhibitor partially reversed the anti-inflammatory and protective effects of USP7 knockdown, confirming the centrality of PKM2 in mediating USP7’s functions.

These findings underscore a critical immunometabolic feedback loop in SAP, where USP7 amplifies inflammatory responses via PKM2-driven aerobic glycolysis disruption, offering new strategies for therapeutic intervention.

Comparison with Existing Internal Articles

Recent internal articles, such as "PKM2 Inhibitor (Compound 3k): Precision in Cancer and Immunometabolic Research", highlight the translational value of targeting PKM2 for both cancer and inflammation models. While prior literature primarily focuses on the role of PKM2 inhibition in tumor metabolism and antiproliferative effects—such as disruption of glycolytic flux in cancer cell lines—the reference study extends this paradigm to immunometabolic regulation in acute inflammation. The use of PKM2 inhibitors to probe the metabolic underpinnings of macrophage polarization aligns with workflow recommendations in "PKM2 Inhibitor (Compound 3k): Precision Disruption of Cancer Cell Metabolism", which discusses best practices for deploying selective PKM2 inhibitors in immune cell studies. Collectively, these resources support a growing consensus that selective PKM2 inhibition is a versatile approach for dissecting both cancerous and immune cell metabolic dependencies.

Limitations and Transferability

• Translational maturity: The findings are robust in mouse models, but direct translation to human SAP or other inflammatory diseases requires further validation, including studies in primary human macrophages and clinical tissues.
• Specificity of metabolic targeting: Although the study establishes PKM2 as a key mediator, off-target effects of metabolic inhibitors and the redundancy of metabolic pathways in immune cells may complicate therapeutic development.
• Temporal and dosage parameters: The precise timing and dosage of PKM2 inhibition needed to optimize therapeutic benefit without impairing essential immune functions remain to be determined.

Protocol Parameters

• USP7 knockdown: Achieved via genetic silencing in mice prior to SAP induction for mechanistic interrogation of inflammatory pathways.
• PKM2 inhibitor administration: In referenced workflows, selective PKM2 inhibitors such as compound 3k are typically delivered at 5 mg/kg orally every two days in rodent models, with monitoring for toxicity and metabolic endpoints (product information).
• Metabolic assessment: Use of Seahorse XF analysis to measure ECAR and OCR, capturing glycolytic and OXPHOS fluxes during macrophage polarization studies.
• Macrophage phenotyping: Flow cytometry and immunofluorescence for M1/M2 markers (e.g., CD86, CD206) in both tissue and isolated immune cell populations.

Research Support Resources

Researchers aiming to model SAP or explore immunometabolic regulation can leverage selective PKM2 inhibitors to dissect the metabolic controls of macrophage polarization. The PKM2 inhibitor (compound 3k) (SKU B8217) is a potent, selective agent suitable for both in vitro and in vivo studies, as validated in cancer and inflammation contexts. This compound is especially useful for experiments requiring disruption of PKM2-dependent glycolysis, aligning with the approaches described in the reference study and internal workflow articles. Proper storage and handling protocols, along with careful experimental design, are essential to ensure reproducibility and interpretability in immunometabolic research.