Activation of pyruvate kinase M2 protects from Concanavalin A-mediated liver injury

Introduction:

Immune-mediated liver injury is a common complication in autoimmune liver disease. Initiation of inflammation requires a metabolic switch from a resting state that relies on oxidative phosphorylation, to a pro-inflammatory state driven by aerobic glycolysis. Pyruvate kinase M2 (PKM2) is a key regulator of the metabolic switch. Its highly active tetrameric isoform promotes pyruvate formation and oxidative phosphorylation, whereas the PKM2 dimer has poor enzymatic activity. PKM2 dimerization supports formation of lactate and the accumulation of pro-inflammatory citric acid cyle intermediates, such as succinate. Additionally, the PKM2 dimer and HIF-1α act as cofactors in transcription of glycolytic enzymes and pro-inflammatory cytokines, such as IL-1b, that foster M1 macrophage polarization. Contrary, the PKM2 tetramer promotes myeloid M2-type polarization and production of anti-inflammatory cytokines, such as IL-10. The role of PKM2 isoforms in acute immune-mediated liver injury is unknown. Activation of PKM2 by the small molecule activator TEPP-46 could bias myeloid cell polarization towards an anti-inflammatory phenotype and elicit liver protection.

Objectives:

To identify a protective role for PKM2 activation in immune-mediated liver injury.

Methods:

In Concanavalin A (ConA)-induced liver injury in mice with a myeloid-specific knockdown of PKM2 (Pkm2 ^Δmyel), plasma ALT and cytokine levels were measured by enzyme assays/ELISA. Myeloid cells from liver, spleen, bone marrow and peripheral blood were characterized by flow cytometry. Glycolysis enzyme and cytokine profiles in macrophages and liver tissue were analyzed with RT-PCR. Hepatic immune cell influx and necrosis was studied in immune histology. TEPP-46 was applied i.p. prior to i.v. ConA injection.

Results:

ConA-induced liver injury was exacerbated in Pkm2 ^{Δ myel} mice, elevation of plasma ALT, IL-1β, CCL-2, IL-6 and IL-23, and increases in hepatic myeloid cell infiltration and necrosis. Bone marrow-derived macrophages and hepatic tissue exhibited a pro-inflammatory cytokine profile, predominant dimerization of PKM2, and increases of glycolytic regulators. Administration of TEPP-46 attenuated liver injury and M1-type pro-inflammatory cytokine production.

Conclusion:

PKM2-dimerization in myeloid cells exacerbated acute hepatitis in Pkm2 ^{Δ myel}mice. Contrary, activating PKM2 by TEPP-46 prior to ConA challenge conveyed liver protection and impaired M1-type macrophage polarization. PKM2 activation offers a novel strategy to ameliorate immune-mediated liver injury.