USP7 Controls Macrophage Function via PKM2-Mediated Metabolic Reprogramming in Severe Acute Pancreatitis

Study Background and Research Question

Severe acute pancreatitis (SAP) is a rapidly progressing inflammatory disease marked by high morbidity and mortality, largely due to excessive inflammatory responses and organ failure. Macrophages—innate immune cells with the capacity to polarize into pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes—play a key role in orchestrating tissue inflammation and repair. In SAP, the early influx of M1 macrophages amplifies inflammation, while a subsequent shift to M2 macrophages helps resolve tissue damage. Understanding the molecular mechanisms governing this polarization is critical for developing new interventions for SAP, a condition for which effective targeted therapies remain lacking. The recent reference study focused on the role of ubiquitin-specific protease 7 (USP7) in regulating macrophage polarization through pyruvate kinase M2 (PKM2)-mediated metabolic pathways, aiming to clarify its function in SAP pathogenesis and therapeutic potential.

Key Innovation from the Reference Study

The central innovation of this work lies in elucidating a previously uncharacterized molecular axis: USP7 directly modulates PKM2 activity by influencing its ubiquitination status, thereby affecting the metabolic profile and inflammatory phenotype of macrophages during SAP. This study is the first to show that USP7 is upregulated in pancreatic macrophages during SAP and that its inhibition not only suppresses pro-inflammatory cytokine production but also shifts macrophage polarization from the inflammatory M1 state to the anti-inflammatory M2 phenotype. Importantly, the research demonstrates that the beneficial effects of USP7 knockdown are dependent on PKM2 activity, as pharmacological inhibition of PKM2 partially abrogates these effects. This positions the USP7–PKM2 axis as a novel target for modulating macrophage-driven inflammation in SAP.

Methods and Experimental Design Insights

The study combined in vivo and in vitro approaches to dissect the interplay between USP7, PKM2, and macrophage polarization in SAP. Key methodological highlights include:

• Induction of SAP in murine models followed by assessment of pancreatic injury and systemic inflammation.
• Measurement of USP7 expression in pancreatic macrophages via immunofluorescence and Western blotting.
• Flow cytometry and histological analyses to distinguish M1 versus M2 macrophage populations in situ and in cultured cells.
• Seahorse extracellular flux assays to quantify glycolytic (ECAR) and oxidative (OCR) metabolic profiles of macrophages.
• Co-immunoprecipitation and ubiquitination assays to explore the physical and regulatory interaction between USP7 and PKM2.
• Pharmacological and genetic manipulation: siRNA knockdown of USP7 and administration of a PKM2 inhibitor (compound 3k) to interrogate the functional dependency of USP7's effects on PKM2 activity.

This integrated approach enabled a mechanistic dissection of how metabolic reprogramming underlies immune cell function in the context of sterile inflammation.

Core Findings and Why They Matter

Several key findings emerged from the study:

• USP7 is upregulated in SAP and promotes inflammation: Elevated USP7 expression was observed in the pancreas of SAP mice, correlating with increased pro-inflammatory cytokine production and disease severity.
• USP7 knockdown reduces SAP severity: Genetic silencing of USP7 led to lower serum amylase and lipase (biomarkers of pancreatic injury), reduced inflammatory cytokines, and histologically milder pancreatic damage.
• Macrophage polarization is metabolically regulated via PKM2: USP7 knockdown promoted a shift from M1 to M2 macrophage phenotypes, both in vivo and in vitro, with associated changes in cellular metabolism (reduced glycolysis, increased OXPHOS).
• USP7 directly regulates PKM2 function: Co-IP and ubiquitination assays confirmed that USP7 modulates PKM2 by controlling its ubiquitination status, which in turn affects PKM2 phosphorylation and subcellular localization.
• PKM2 inhibition reverses USP7 knockdown benefits: Administration of a pyruvate kinase M2 inhibitor partially negated the anti-inflammatory and tissue-protective effects of USP7 knockdown, demonstrating that PKM2 activity is indispensable for the observed phenotype shifts.

These findings underscore the importance of metabolic programming in immune responses and suggest that targeting the USP7–PKM2 axis could be a promising strategy to modulate macrophage-driven inflammation in SAP and potentially other inflammatory disorders.

Comparison with Existing Internal Articles

Previous internal reviews and technical guides, such as the "PKM2 Inhibitor (Compound 3k): Protocols and Precision in Cancer Metabolism" and "Advancing Targeted Cancer Metabolism with PKM2 Inhibitor (Compound 3k)", have focused primarily on the role of PKM2 inhibition in cancer cell metabolism, where disruption of glycolysis drives antiproliferative effects and modulates immune cell phenotypes. These resources position PKM2 inhibitor (compound 3k) as a benchmark tool for targeting aerobic glycolysis in tumor models and for studying immune cell metabolism in the tumor microenvironment.

The current reference study extends this knowledge base by directly implicating PKM2's metabolic role in sterile inflammatory diseases beyond cancer—specifically, in the context of SAP and macrophage polarization. While the mechanism of aerobic glycolysis disruption and its impact on immune cell function are consistent with prior cancer-focused research, the application to acute inflammatory tissue injury highlights broader implications for PKM2-targeting strategies. Thus, this work bridges immunometabolism findings from oncology to inflammatory disease models, with strong mechanistic support.

Limitations and Transferability

Despite robust mechanistic insights, several limitations warrant consideration:

• Species specificity: The findings rely largely on murine SAP models. Although mechanistic conservation is likely, confirmation in human macrophages and clinical SAP samples remains necessary.
• Complexity of in vivo inflammatory environments: The interplay of metabolic enzymes, immune regulation, and tissue context is intricate. While PKM2 inhibition clearly impacted macrophage polarization, off-target effects and compensatory pathways could modulate outcomes in more complex or chronic disease scenarios.
• Therapeutic applicability: While the data suggest that targeting USP7 or PKM2 could be beneficial in SAP, translation to clinical practice will require careful pharmacokinetic, safety, and efficacy evaluation, especially given the pleiotropic roles of these proteins in other cell types.

Nevertheless, the demonstration that pharmacological PKM2 inhibition recapitulates the metabolic and immunological effects of USP7 modulation suggests strong potential for cross-model transferability, particularly in studies of macrophage-driven inflammation and metabolic reprogramming.

Protocol Parameters

• SAP model induction: Use established murine protocols for pancreatitis induction; assess pancreatic injury and systemic inflammation markers (serum amylase, lipase).
• Macrophage isolation and polarization: Employ flow cytometry and immunofluorescence for M1/M2 phenotyping; consider in vitro LPS/IFN-γ (M1) or IL-4/IL-13 (M2) stimulation as per standard protocols.
• Metabolic assays: Apply Seahorse extracellular flux analysis for ECAR and OCR measurements to distinguish glycolytic versus oxidative metabolism in macrophages.
• PKM2 inhibition: In preclinical workflows, administer a selective pyruvate kinase M2 inhibitor at doses validated in the literature (e.g., 5 mg/kg for in vivo studies) to assess impact on macrophage polarization and tissue injury.
• USP7 manipulation: Utilize genetic knockdown or specific inhibitors to probe the effect on PKM2 ubiquitination and function.

Research Support Resources

Researchers investigating macrophage polarization, metabolic reprogramming, or inflammation in SAP and related models can leverage small molecule tools to probe PKM2-dependent pathways. PKM2 inhibitor (compound 3k) (SKU B8217) from APExBIO is a selective and potent pyruvate kinase M2 inhibitor, validated in both in vitro and in vivo systems for disrupting aerobic glycolysis and modulating immune cell phenotypes. For workflow optimization, protocol troubleshooting, and advanced use-cases, several internal guides provide technical context and application strategies for metabolic and immunological research using PKM2-targeting compounds.