Recombinant Treponema pallidum Protein Tp47 Promoted the Phagocytosis of Macrophages by Activating NLRP3 Inflammasome Induced by PKM2-Dependent Glycolysis

Background: Glycolysis is a critical pathway in cellular glucose metabolism that provides energy and participates in immune responses. However, whether glycolysis is involved in NOD-like receptor family protein 3 (NLRP3) inflammasome activation and phagocytosis of macrophages in response to Treponema pallidum infection remains unclear.

Objectives: To investigate the role of glycolysis in activating the NLRP3 inflammasome for regulating phagocytosis in macrophages in response to Treponema pallidum protein Tp47 and its associated mechanisms.

Methods: Interactions between activation of the NLRP3 inflammasome and phagocytosis and the role of glycolysis in Tp47-treated macrophages were investigated through experiments on peritoneal macrophages and human monocytic cell line-derived macrophages.

Results: Activation of phagocytosis and NLRP3 inflammasome were observed in Tp47-treated macrophages. Treatment with NLRP3 inhibitor MCC950 or si-NLRP3 attenuated Tp47-induced phagocytosis. Glycolysis and glycolytic capacity were enhanced by Tp47 stimulation in macrophages, and a change in the levels of glycolytic metabolites (phosphoenolpyruvate, citrate, and lactate) was induced by Tp47 in macrophages. Inhibition of glycolysis with 2-deoxy-D-glucose, a glycolysis inhibitor, decreased the activation of NLRP3. Expression of M2 isoform of pyruvate kinase (PKM2), an enzyme catalyzing a rate-limiting reaction in the glycolytic pathway, was upregulated in Tp47-stimulated macrophages. Inhibition of PKM2 with shikonin or si-PKM2 decreased glycolysis and NLRP3 activation.

Conclusion: Tp47 promotes phagocytosis in macrophages by activating the NLRP3 inflammasome, which is induced by the enhancement of PKM2-dependent glycolysis.

 

Comments:

The study aimed to investigate the role of glycolysis in the activation of the NLRP3 inflammasome and phagocytosis in macrophages in response to Treponema pallidum infection. The researchers conducted experiments using peritoneal macrophages and human monocytic cell line-derived macrophages to examine the interactions between NLRP3 inflammasome activation, phagocytosis, and glycolysis in Tp47-treated macrophages.

The results showed that Tp47 treatment led to the activation of phagocytosis and the NLRP3 inflammasome in macrophages. Inhibition of NLRP3 using MCC950 or si-NLRP3 attenuated Tp47-induced phagocytosis, suggesting the involvement of NLRP3 in this process.

Furthermore, Tp47 stimulation enhanced glycolysis and glycolytic capacity in macrophages. Tp47 treatment also induced changes in the levels of glycolytic metabolites such as phosphoenolpyruvate, citrate, and lactate in macrophages. To investigate the role of glycolysis in NLRP3 activation, the researchers inhibited glycolysis using 2-deoxy-D-glucose, a glycolysis inhibitor. They found that inhibiting glycolysis decreased the activation of NLRP3, indicating that glycolysis is involved in the activation of the NLRP3 inflammasome.

The study also examined the expression of the M2 isoform of pyruvate kinase (PKM2), an enzyme that catalyzes a rate-limiting step in the glycolytic pathway. The researchers observed an upregulation of PKM2 expression in Tp47-stimulated macrophages. To further investigate the role of PKM2 in glycolysis and NLRP3 activation, they inhibited PKM2 using shikonin or si-PKM2. Inhibition of PKM2 resulted in decreased glycolysis and NLRP3 activation, suggesting that PKM2-dependent glycolysis is involved in the activation of the NLRP3 inflammasome.

In conclusion, the findings of this study demonstrate that Tp47 promotes phagocytosis in macrophages by activating the NLRP3 inflammasome, and this activation is mediated by the enhancement of PKM2-dependent glycolysis. These results provide insights into the mechanisms underlying the immune response to Treponema pallidum infection and the role of glycolysis in regulating macrophage function.

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