USP7–PKM2 Axis Regulates Macrophage Polarization and Metabolic Reprogramming in Severe Acute Pancreatitis

Study Background and Research Question

Severe acute pancreatitis (SAP) is a critical inflammatory disorder characterized by rapid progression, high morbidity, and the risk of multi-organ failure. Despite intensive research, no disease-modifying therapies currently exist to interrupt or reverse SAP’s underlying pathogenic processes. Macrophages are central to SAP pathogenesis, with the pro-inflammatory M1 and anti-inflammatory M2 phenotypes orchestrating the course of tissue injury and resolution. The transition from M1 to M2 polarization is essential to curbing inflammatory damage, but the molecular switches driving this process remain incompletely understood. Recent evidence implicates metabolic reprogramming—especially shifts in glycolysis and oxidative phosphorylation—as an important determinant of macrophage function in inflammatory contexts.

This reference study (Wu et al., 2025) investigates how ubiquitin-specific protease 7 (USP7) regulates macrophage polarization in SAP through modulation of pyruvate kinase M2 (PKM2), a key glycolytic enzyme with established roles in cancer and immune cell metabolism.

Key Innovation from the Reference Study

The central innovation lies in uncovering a mechanistic link between USP7 and PKM2 in the control of macrophage phenotype and metabolic profile during SAP. The authors demonstrate that USP7, which is upregulated in pancreatic macrophages during SAP, promotes the pro-inflammatory M1 state by modulating PKM2 deubiquitination and function. Notably, they show that genetic knockdown of USP7 not only alleviates SAP severity but also shifts macrophage polarization toward the anti-inflammatory M2 phenotype. Crucially, these effects are dependent on PKM2 activity, as pharmacological PKM2 inhibition partially abrogates the protective effects of USP7 knockdown. This establishes the USP7–PKM2 axis as a key immunometabolic node in SAP pathogenesis and suggests new therapeutic avenues for intervention.

Methods and Experimental Design Insights

The study utilizes a robust combination of in vivo and in vitro approaches to dissect the USP7–PKM2 relationship:

• Animal Model: SAP was induced in mice, and pancreatic tissue was analyzed for USP7 and PKM2 expression, along with markers of inflammation and macrophage phenotype.
• Genetic Manipulation: USP7 knockdown was achieved via targeted siRNA in both murine models and cultured macrophages.
• Pharmacological Intervention: A selective PKM2 inhibitor was administered to assess the dependency of observed effects on PKM2 activity.
• Phenotypic Assessment: Histology, immunofluorescence, flow cytometry, and Western blotting characterized macrophage subsets and inflammatory markers.
• Metabolic Profiling: Seahorse assays measured extracellular acidification rate (ECAR) and oxygen consumption rate (OCR), providing functional readouts of glycolytic and oxidative metabolism.
• Protein Interaction Studies: Co-immunoprecipitation and ubiquitination assays elucidated direct interactions between USP7 and PKM2.

Protocol Parameters

• SAP induction: Standardized protocol in mice with endpoint analysis at 24–48 hours post-induction, enabling robust inflammatory readouts.
• USP7 knockdown: siRNA transfection in vitro or in vivo, with controls for off-target effects.
• PKM2 inhibitor administration: Dosage and timing aligned with peak SAP inflammatory response to specifically assess dependence on PKM2 activity.
• Macrophage polarization analysis: Phenotyping conducted using CD86 (M1) and CD206 (M2) markers by flow cytometry and immunofluorescence.
• Metabolic assays: ECAR and OCR measurements performed on sorted macrophage populations to directly link metabolic state to phenotypic outcome.

Core Findings and Why They Matter

Key findings from the reference study include:

• USP7 upregulation in SAP: SAP mice exhibited increased USP7 expression in pancreatic macrophages, correlating with heightened inflammation and disease severity.
• USP7 knockdown alleviates SAP: Reduced serum amylase/lipase, lower pro-inflammatory cytokines, and diminished histological injury following USP7 silencing.
• Shift in macrophage polarization: USP7 knockdown promoted a transition from M1 (pro-inflammatory) to M2 (anti-inflammatory) macrophages, both in vivo and in vitro.
• Metabolic reprogramming via PKM2: USP7 modulated PKM2 deubiquitination, influencing its phosphorylation and nuclear translocation. This, in turn, drove metabolic reprogramming in macrophages—favoring glycolysis in M1 and oxidative metabolism in M2 states.
• PKM2 inhibition partially reverses USP7 effects: Application of a PKM2 inhibitor blunted the protective and polarization-shifting benefits of USP7 knockdown, confirming that USP7’s functions are contingent on PKM2 activity.

These results provide the first direct evidence that immune cell phenotype and inflammatory outcomes in SAP are governed by a USP7–PKM2 metabolic axis. Targeting this pathway may offer a rational strategy for modulating inflammation and improving outcomes in SAP and related diseases where macrophage polarization is dysregulated.

Comparison with Existing Internal Articles

Several recent articles have explored the role of PKM2 inhibition in cancer and inflammatory models, highlighting the translational potential of targeting PKM2:

• "PKM2 Inhibition: Transforming Cancer and Inflammation Research" contextualizes PKM2 inhibitor (compound 3k) as a precision tool for disrupting both tumor glycolysis and immune cell metabolic reprogramming. It aligns with the present reference study by emphasizing the relevance of PKM2 modulation in both oncology and immunology.
• "USP7–PKM2 Axis Controls Macrophage Polarization in Pancreatitis" provides a focused summary of the mechanistic findings from the same reference study, positioning the USP7–PKM2 relationship as a new target for immunometabolic intervention in SAP.
• "PKM2 Inhibitor (Compound 3k): Selective Disruption of Cancer Cell Metabolism" details the use of PKM2 inhibitor (compound 3k) in oncology models, but its mechanistic rationale—disrupting aerobic glycolysis—parallels the metabolic reprogramming described in macrophages within the pancreatitis model.

Collectively, these resources frame PKM2 as a convergent target in both cancer and inflammation, and reinforce the translational bridge between immunometabolism and disease intervention.

Limitations and Transferability

The study’s strengths lie in its multi-modal approach and clear demonstration of the USP7–PKM2 axis in SAP. However, several limitations should be noted:

• Model specificity: While the murine SAP model recapitulates key features of human disease, species differences and the acute nature of experimental induction may limit direct clinical translation.
• Pharmacological inhibitor selectivity: The PKM2 inhibitor used in the study is selective, but potential off-target effects and pharmacokinetic properties in humans require further validation.
• Broader applicability: The findings are robust for SAP, but whether the USP7–PKM2 axis similarly governs macrophage polarization in other inflammatory or fibrotic diseases remains to be established.

Why this cross-domain matters, maturity, and limitations

The intersection of cancer metabolism and immune cell reprogramming is a rapidly evolving field. The USP7–PKM2 axis, long studied in cancer, now emerges as a regulator of inflammation, providing a conceptual framework for cross-domain therapeutic strategies. However, the maturity of this approach for clinical translation in either domain is still nascent; further preclinical and translational research is warranted.

Research Support Resources

Researchers aiming to interrogate the USP7–PKM2 axis in immunometabolic models can leverage validated reagents such as PKM2 inhibitor (compound 3k) (SKU B8217) from APExBIO. This selective small molecule enables targeted modulation of PKM2 activity in both cancer and non-cancer models, supporting workflows that require precise disruption of glycolytic and inflammatory pathways. For protocol guidance, refer to literature-backed dosing and timing parameters as outlined above.