USP7–PKM2 Axis Orchestrates Macrophage Polarization in Severe Acute Pancreatitis

Study Background and Research Question

Severe acute pancreatitis (SAP) is a highly inflammatory condition with considerable morbidity and mortality, often progressing to systemic inflammatory response and multi-organ failure. Macrophages—particularly their polarization towards pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes—play a central role in the progression and resolution of SAP. However, the molecular determinants that govern this polarization in the pancreatic microenvironment remain incompletely understood. Emerging evidence implicates metabolic reprogramming, especially the glycolytic switch, as a driver of macrophage phenotype and function. The reference study (Wu et al., 2025) specifically interrogates the role of ubiquitin-specific protease 7 (USP7) in regulating macrophage polarization via the metabolic enzyme pyruvate kinase M2 (PKM2)—a known modulator of glycolysis and cellular energy homeostasis.

Key Innovation from the Reference Study

The principal innovation of Wu et al. lies in elucidating a direct mechanistic pathway whereby USP7 regulates macrophage polarization in SAP through PKM2-dependent metabolic reprogramming. While previous studies have recognized the importance of both USP7 and PKM2 in immune and metabolic contexts, this work is the first to connect USP7-mediated deubiquitination of PKM2 with functional consequences for macrophage phenotype and inflammatory progression in pancreatitis. The study demonstrates that USP7 upregulation in SAP skews macrophages toward the M1 pro-inflammatory state by stabilizing and activating PKM2, thereby shifting cellular metabolism toward aerobic glycolysis (the Warburg effect), a hallmark of inflammatory M1 macrophages. Importantly, pharmacological or genetic inhibition of USP7 not only reverses this polarization but also alleviates pancreatic inflammation and tissue damage.

Methods and Experimental Design Insights

The authors employed a robust combination of in vivo and in vitro approaches. In mouse models of SAP, USP7 expression was manipulated via genetic knockdown. Pancreatic tissues were analyzed histologically and by immunofluorescence to assess inflammatory cell infiltration and phenotype. Flow cytometry and Western blotting profiled macrophage polarization markers and inflammatory cytokines. To dissect metabolic alterations, Seahorse assays quantified extracellular acidification rate (ECAR) and oxygen consumption rate (OCR), directly measuring glycolysis and oxidative phosphorylation. Co-immunoprecipitation and ubiquitination assays established the physical and functional interaction between USP7 and PKM2. Critically, the study incorporated rescue experiments: selective pharmacological inhibition of PKM2 using compound 3k in the context of USP7 knockdown to determine functional dependency.

Protocol Parameters

• SAP induction in mice: Standard caerulein and LPS protocols for robust modeling of acute pancreatic inflammation.
• USP7 knockdown: Lentiviral shRNA delivery, with validation at mRNA and protein levels.
• Macrophage polarization assessment: Flow cytometric analysis of CD86 (M1) and CD206 (M2) markers in pancreatic immune cells.
• Metabolic flux analysis: Seahorse XF Analyzer to assess ECAR (glycolysis) and OCR (mitochondrial respiration) in isolated macrophages.
• PKM2 inhibition (rescue): Administration of a pyruvate kinase M2 inhibitor (compound 3k) at doses paralleling literature-reported efficacious concentrations in vivo (see below for product-specific suggestions).

Core Findings and Why They Matter

Key results from Wu et al. include:

• USP7 is upregulated in SAP and promotes M1 macrophage polarization. Knockdown of USP7 significantly reduced pancreatic inflammation, serum amylase and lipase, and pro-inflammatory cytokine levels.
• USP7 modulates macrophage metabolism via PKM2. Mechanistically, USP7 deubiquitinates PKM2, stabilizing it and promoting its nuclear translocation and phosphorylation—events linked to enhanced glycolysis and the M1 phenotype.
• Pharmacological inhibition of PKM2 reverses the protective effect of USP7 knockdown. Administration of a PKM2 inhibitor partially abrogated the reduction in inflammation and M1/M2 shift seen with USP7 depletion, confirming that PKM2 is a critical effector downstream of USP7.
• Metabolic reprogramming underpins immunological outcomes. Seahorse assays confirmed that USP7 drives a metabolic bias toward aerobic glycolysis in macrophages during SAP, and this effect is PKM2-dependent.

These findings spotlight the USP7–PKM2 axis as a metabolic checkpoint governing the inflammatory landscape in SAP. By targeting this axis, it may be possible to therapeutically reprogram macrophage responses and mitigate tissue damage in pancreatitis and potentially other inflammatory disorders.

Comparison with Existing Internal Articles

The mechanistic bridge between USP7 activity and PKM2-mediated metabolic reprogramming is echoed in several internal reviews. For example, "USP7 Modulates Macrophage Polarization via PKM2 in Pancreatitis" and "USP7 Modulates Macrophage Polarization via PKM2 in Acute Pancreatitis" both highlight the immunometabolic role of the USP7–PKM2 axis in SAP, reinforcing the novelty and translational potential of the reference study. These internal articles contextualize the regulatory axis within broader inflammatory and immunometabolic research, suggesting that targeting PKM2 may have significance beyond oncology, extending to immunological pathologies.

Additionally, the utility of PKM2 inhibitors in experimental workflows—discussed in "PKM2 Inhibitor (Compound 3k): Redefining Tumor Metabolism..."—underscores the methodological bridge between cancer metabolism and immune modulation, as PKM2 is a common node in both domains.

Limitations and Transferability

While Wu et al. provide compelling evidence for the USP7–PKM2 axis in murine SAP models, several limitations warrant consideration. The study relies primarily on animal models and in vitro macrophage cultures; thus, the clinical relevance to human SAP patients remains to be fully established. Furthermore, while PKM2 inhibition reversed the benefits of USP7 knockdown, off-target effects or compensatory metabolic pathways were not exhaustively ruled out. The study also does not address potential adverse effects of long-term metabolic intervention, nor does it explore the axis in other inflammatory or fibrotic diseases. These caveats highlight the need for further validation in human tissues and broader disease models before clinical translation.

Why this cross-domain matters, maturity, and limitations

The cross-domain relevance of the USP7–PKM2 axis extends from oncology to immunometabolism. As both fields recognize aerobic glycolysis disruption as a lever for cellular phenotype control—whether for cancer cell proliferation or inflammatory macrophage activation—tools and insights from one domain can accelerate discoveries in the other. However, maturity for clinical application in inflammatory diseases such as SAP is still in its early stages, with most evidence derived from preclinical models. Researchers should be cautious when extrapolating these findings to distinct tissue contexts or chronic diseases.

Research Support Resources

For researchers aiming to experimentally dissect PKM2’s role in macrophage metabolism or validate the metabolic checkpoint axis described above, a selective pyruvate kinase M2 inhibitor such as PKM2 inhibitor (compound 3k) (SKU B8217) offers a practical tool. According to product information, compound 3k is a potent and selective PKM2 inhibitor with proven efficacy in both in vitro and in vivo models, supporting workflows in cancer and inflammatory disease research. For optimal results, solutions should be freshly prepared and stored at -20°C, with application parameters tailored to specific cell lines or animal protocols. This inhibitor enables the precise dissection of PKM2-dependent metabolic reprogramming in macrophages, as demonstrated in the reference study. Use of such validated chemical probes can enhance reproducibility and translational insight across immunometabolic research paradigms.