USP7 Modulates Macrophage Polarization via PKM2-Mediated Metabolic Reprogramming in Severe Acute Pancreatitis

Study Background and Research Question

Severe acute pancreatitis (SAP) is a life-threatening inflammatory condition characterized by rapid progression, multi-organ involvement, and high mortality rates. Despite advances in supportive care, there are currently no targeted therapies that can halt or reverse the inflammatory cascade characteristic of SAP. Macrophages, which can adopt either pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes, are central to the immune response in SAP. The balance between these two states shapes disease progression: M1 macrophages amplify inflammation, while M2 macrophages promote resolution and tissue repair. Recent research has established that macrophage polarization is tightly linked to their metabolic status, with glycolytic reprogramming favoring the M1 phenotype.

However, the upstream regulators orchestrating this metabolic-immune axis in SAP remained unclear. The reference study (Wu et al., 2025) aimed to dissect the role of ubiquitin-specific protease 7 (USP7) in macrophage polarization and its mechanistic interplay with pyruvate kinase M2 (PKM2), a key enzyme in glycolysis, during SAP.

Key Innovation from the Reference Study

The pivotal innovation of the study lies in identifying USP7 as a central regulator of macrophage polarization through its control of PKM2-dependent metabolic reprogramming. By demonstrating that USP7 modulates PKM2 deubiquitination and thereby influences PKM2's phosphorylation state and subcellular localization, the authors provide a direct mechanistic link between ubiquitin signaling, metabolic flux, and immune phenotype in SAP. Crucially, the work also shows that pharmacological inhibition of PKM2 can modify the protective effects of USP7 knockdown, cementing PKM2 as an essential effector downstream of USP7 in this context. This USP7–PKM2 axis represents a novel targetable pathway for controlling inflammation in SAP and potentially other inflammatory disorders.

Methods and Experimental Design Insights

The authors employed a multifaceted approach in both in vivo and in vitro settings. SAP was induced in mice, and pancreatic tissue was analyzed to evaluate USP7 expression, macrophage infiltration, and phenotype by histology, immunofluorescence, flow cytometry, and Western blotting. In parallel, cultured macrophages were subjected to USP7 knockdown to assess changes in polarization markers and metabolic activity. Key metabolic parameters—including extracellular acidification rate (ECAR) and oxygen consumption rate (OCR)—were measured using Seahorse assays to profile glycolytic and oxidative phosphorylation activity.

To probe the mechanistic relationship between USP7 and PKM2, the study utilized co-immunoprecipitation and ubiquitinated immunoprecipitation assays to assess protein-protein interactions and post-translational modifications. Importantly, a selective PKM2 inhibitor was administered to SAP mice to test whether PKM2 activity was necessary for the immunomodulatory effects of USP7 knockdown. This pharmacological approach provided functional evidence supporting the genetic and biochemical findings.

Core Findings and Why They Matter

The study reports several interlinked findings of high significance:

• USP7 Is Upregulated in SAP: Pancreatic macrophages from SAP mice exhibited increased USP7 expression, correlating with disease severity.
• USP7 Knockdown Reduces Inflammation: Silencing USP7 in vivo led to reduced serum amylase and lipase levels, lower expression of pro-inflammatory cytokines, and attenuation of histological pancreatic damage.
• Metabolic Reprogramming via PKM2: USP7 knockdown shifted macrophage metabolism away from glycolysis, as evidenced by decreased ECAR and increased OCR, and promoted M2 (anti-inflammatory) polarization.
• USP7 Modulates PKM2 Stability and Activity: Mechanistic experiments demonstrated that USP7 stabilizes PKM2 by deubiquitination, facilitating its phosphorylation and nuclear translocation—events known to support the M1 phenotype and inflammatory gene expression.
• PKM2 Inhibition Attenuates USP7 Effects: Administration of a PKM2 inhibitor partially reversed the anti-inflammatory benefits of USP7 knockdown, establishing PKM2 as a necessary mediator of USP7-driven macrophage polarization.

Together, these results clarify the molecular basis by which metabolic reprogramming governs immune cell fate in SAP and highlight the USP7–PKM2 axis as a lever to modulate inflammation.

Comparison with Existing Internal Articles

Several recent internal resources echo and extend these findings. For example, "USP7 Controls Macrophage Polarization via PKM2 in Severe Pancreatitis" and "USP7 Modulates Macrophage Polarization via PKM2 in Pancreatitis" both underscore the importance of the USP7–PKM2 axis in immune regulation during SAP, emphasizing the metabolic underpinnings of macrophage function and the therapeutic promise of targeting this pathway. In addition, "Applied Workflows with PKM2 Inhibitor (compound 3k): Protocols & Pitfalls" provides workflow-driven guidance for deploying PKM2 inhibitors in translational models, reinforcing the practical relevance of selective pyruvate kinase M2 inhibitors for both oncology and immunometabolic research. These internal articles collectively support the external study's mechanistic insights and suggest robust consensus within the field regarding the centrality of PKM2 in immune-metabolic reprogramming.

Limitations and Transferability

While the reference study establishes a strong mechanistic framework, several limitations warrant consideration. The work is primarily based on murine SAP models and in vitro macrophage cultures, which may not fully recapitulate the complexity of human disease. The long-term effects and safety of targeting USP7 or PKM2 in clinical settings remain undetermined. Furthermore, while PKM2 inhibition partially reversed the benefits of USP7 knockdown, it did not abrogate them entirely—indicating the existence of additional USP7-regulated pathways. Future studies in human tissues or clinical cohorts, as well as broader profiling of immune and metabolic networks, will be essential to validate and expand these findings.

Protocol Parameters

• SAP induction in mice: Typically performed via intraperitoneal injection of caerulein or other established methods; timing and dosing must be tailored to experimental goals.
• USP7 knockdown: Achieved via siRNA or lentiviral transduction in primary macrophages or in vivo models; efficacy confirmed by Western blot and qPCR.
• PKM2 inhibitor administration: In the reference study, dosing regimens aligned with published protocols for PKM2 inhibition and rescue experiments; consult product guidelines for compound stability and formulation.
• Metabolic assays: ECAR and OCR measurements using Seahorse XF analyzers require precise cell seeding densities and substrate supplementation.
• Macrophage polarization assessment: Flow cytometry and immunofluorescence using established M1/M2 surface markers (e.g., CD86, CD206).

Research Support Resources

For researchers aiming to investigate PKM2-dependent metabolic reprogramming in immune or cancer models, PKM2 inhibitor (compound 3k) (SKU B8217) from APExBIO offers a selective and potent tool, with demonstrated efficacy in both cellular and in vivo contexts. This compound enables targeted disruption of glycolytic flux and can be integrated into workflows exploring immunometabolic regulation, as discussed in both the reference study and internal workflow articles. Careful attention to compound solubility, storage, and dosing is recommended for optimal experimental reliability.