USP7–PKM2 Axis Drives Macrophage Polarization in Acute Pancreatitis

Study Background and Research Question

Severe acute pancreatitis (SAP) is a critical inflammatory disorder characterized by high morbidity and mortality, frequently complicated by multiple organ failure and systemic inflammatory response syndrome. The cellular immune landscape, particularly the polarization state of macrophages, plays a pivotal role in SAP pathogenesis. Macrophages can be broadly classified into two phenotypes: pro-inflammatory (M1) and anti-inflammatory (M2). Early SAP is marked by M1 macrophage infiltration, which amplifies tissue injury, while a subsequent shift to M2 macrophages helps resolve inflammation. Despite advances in understanding the inflammatory mediators involved, there are currently no approved therapies that directly modulate these immune mechanisms in SAP.

Recent immunometabolic research has highlighted the significance of cellular metabolism in macrophage phenotype determination. Specifically, M1 macrophages rely on increased glycolytic flux, whereas M2 polarization is associated with enhanced oxidative phosphorylation (OXPHOS). The glycolytic enzyme pyruvate kinase M2 (PKM2) is a key regulator of this metabolic reprogramming. However, the upstream mechanisms controlling PKM2 activity and their relevance in SAP have remained largely unexplored. The reference study (Wu et al., 2025) addresses this knowledge gap by investigating the role of ubiquitin-specific protease 7 (USP7) in macrophage polarization through PKM2 modulation during SAP.

Key Innovation from the Reference Study

The core innovation of the reference paper is the identification of USP7 as a critical regulator of macrophage polarization in SAP via post-translational control of PKM2. The study demonstrates that USP7, a deubiquitinating enzyme, is upregulated in pancreatic macrophages during SAP and modulates PKM2's stability and function through deubiquitination. By influencing PKM2's phosphorylation state, USP7 alters its metabolic activity and subcellular localization, ultimately driving the pro-inflammatory M1 phenotype. This mechanistic insight establishes a direct connection between ubiquitin signaling and immune metabolic reprogramming in the context of acute inflammation.

Methods and Experimental Design Insights

The research team utilized a multifaceted approach combining in vivo and in vitro experiments to dissect the USP7–PKM2 axis. Major methodological highlights include:

• Use of murine models of SAP to evaluate pancreatic tissue inflammation and macrophage infiltration.
• Histological analysis, immunofluorescence, and flow cytometry to phenotype macrophage populations and measure inflammatory markers.
• Western blotting to quantify protein expression and modification states.
• Seahorse extracellular flux assays to assess changes in glycolytic metabolism (ECAR) and mitochondrial respiration (OCR).
• Co-immunoprecipitation (Co-IP) and ubiquitinated immunoprecipitation (IP) to probe USP7–PKM2 interactions and PKM2 ubiquitination status.
• Genetic knockdown of USP7 to evaluate its functional impact in both cell culture and animal models.
• Pharmacological intervention with a PKM2 inhibitor to clarify pathway dependence.

Core Findings and Why They Matter

The study's findings provide several key advances in the understanding of SAP pathogenesis and immunometabolic regulation:

• USP7 upregulation in SAP: Pancreatic macrophages from SAP mice exhibit significantly increased USP7 expression, correlating with heightened inflammation (Wu et al., 2025).
• Inflammation alleviation via USP7 knockdown: Targeted USP7 suppression leads to lower serum amylase and lipase levels and reduced pro-inflammatory cytokine expression, indicating disease amelioration.
• Macrophage polarization shift: USP7 knockdown promotes a transition from the pro-inflammatory M1 phenotype to the anti-inflammatory M2 phenotype, both in vivo and in vitro.
• Metabolic reprogramming through PKM2: Mechanistically, USP7 deubiquitinates PKM2, stabilizing it in forms that favor glycolysis and M1 polarization. Reduced USP7 activity leads to PKM2 degradation, diminished glycolysis, and supports M2 polarization, aligning with prior work on macrophage immunometabolism.
• Pathway validation with PKM2 inhibition: Administration of a PKM2 inhibitor partially reverses the protective effects of USP7 knockdown, confirming that the observed immune modulation is PKM2-dependent.

Collectively, these results reveal a novel regulatory axis at the intersection of ubiquitin signaling and metabolic control, with broad implications for the management of inflammatory diseases beyond SAP.

Comparison with Existing Internal Articles

Several internal resources provide complementary perspectives on PKM2 inhibition and immunometabolic control:

• The article "USP7–PKM2 Axis Modulates Macrophage Polarization in Pancreatitis" concisely summarizes the mechanistic findings of the reference study, underscoring the role of ubiquitin signaling in glycolytic regulation and immune phenotype determination.
• "PKM2 Inhibitor (Compound 3k): Redefining Tumor Glycolysis..." and "PKM2 Inhibitor (Compound 3k): Precision Disruption of Cancer Glycolysis" discuss PKM2 inhibitor (compound 3k) as a potent and selective agent for disrupting tumor cell glycolysis. While primarily focused on oncology, these articles note the relevance of PKM2 inhibition in modulating immune cell metabolism and macrophage polarization, reflecting the cross-domain significance highlighted by the reference study.
• The article "USP7 Controls Macrophage Polarization via PKM2 in Pancreatitis" further elaborates on the intersection of USP7 activity, PKM2 function, and inflammatory control in SAP, reinforcing the translational potential of targeting this regulatory axis.

Unlike the oncology-focused articles, the reference study directly demonstrates the immunomodulatory consequences of PKM2 regulation in acute inflammation, adding a new dimension to the therapeutic rationale for PKM2-targeted interventions.

Limitations and Transferability

While the study robustly demonstrates the USP7–PKM2 axis in murine SAP models and cultured macrophages, several limitations should be considered:

• Species and model specificity: Findings are based on mouse models, and the degree to which these mechanisms are conserved in human SAP remains to be established.
• Cellular heterogeneity: The focus on macrophages does not address potential contributions from other immune or stromal cell populations in the pancreas.
• Pharmacological targeting: The PKM2 inhibitor was used to validate pathway dependence, but detailed pharmacokinetic and safety assessments in SAP settings are needed for clinical translation.
• Temporal dynamics: The progression from M1 to M2 macrophages is complex, and intervention timing may critically influence therapeutic efficacy.

Nonetheless, the study offers a valuable paradigm for linking metabolic enzymes to immune regulation, with possible relevance to diverse contexts such as sepsis or chronic inflammatory diseases where macrophage polarization is pivotal.

Protocol Parameters

• SAP induction in mice: Typically carried out using caerulein or sodium taurocholate injection; refer to detailed protocols for dosage and timing.
• USP7 knockdown: Achieved via siRNA or shRNA transfection; verify gene silencing by Western blot and qPCR prior to functional assays.
• PKM2 inhibition: PKM2 inhibitor (compound 3k) was administered to SAP mice to dissect pathway dependence; dose and frequency should be optimized based on pilot tolerability studies and published IC₅₀ data.
• Metabolic flux assays: Seahorse assays for ECAR and OCR provide quantitative readouts of glycolytic and mitochondrial activity post-treatment.
• Macrophage phenotyping: Flow cytometry with markers such as CD86 (M1) and CD206 (M2) is recommended for robust polarization analysis.

Research Support Resources

Researchers interested in probing PKM2-dependent immunometabolic pathways can leverage selective inhibitors such as PKM2 inhibitor (compound 3k) (SKU B8217), which offers high selectivity and demonstrated efficacy in both cancer cell and macrophage polarization models according to the product information. This small molecule can be integrated into in vitro and in vivo workflows to validate PKM2’s role in immune cell metabolism and support the design of targeted intervention studies. For best results, consult detailed compound handling instructions and consider pilot experiments to optimize dosing and compatibility with your experimental models.