Pyruvate kinase M2 is elevated in systemic sclerosis and plays a role in its pathogenesis

Systemic sclerosis is an autoimmune fibrotic skin disease characterised by immune activation and fibrosis. Fibroblasts are at the core of this fibrotic process, differentiating into effector myofibroblasts; however, the drivers of this process remain obscure. Recently, metabolic changes in cells in fibrotic diseases have been uncovered, with changes in the TCA cycle and glycolysis being observed.

The objective of this work was to elucidate the role of the glycolytic enzyme pyruvate kinase M2 (PKM2) in systemic sclerosis.

Serum from early diffuse systemic sclerosis (SSc) patients and healthy controls (HC) was collected for PKM2 analysis by ELISA. Fibroblasts were isolated from HC and SSc biopsies and treated with transforming growth factor-beta 1 (TGF-β1) to assess PKM2 expression. PKM2 was pharmacologically modulated, and collagen and Extracellular Matrix (ECM) regulators were evaluated. Metabolic activity was assessed using Seahorse assays, and lactate transport was chemically inhibited. Chromatin immunoprecipitation was performed using a histone lactylation-specific or isotype antibody, and lactate or acetate supplementation experiments were conducted.

We found significantly elevated circulating and fibroblast PKM2 in SSc patients. Fibroblast PKM2 could be induced in healthy fibroblasts by TGF-β1 exposure. Furthermore, PKM2 drives a metabolic shift to glycolysis that can be blocked by forced tetramerisation of PKM2 from its dimeric form; this resulted in reduced ECM and matrix regulators. Mechanistically, PKM2-mediated glycolysis results in elevated lactate, which drives collagen via epigenetic regulation by histone H3K18 lactylation. Blockade of PKM2 dimerisation reduced Histone H3 at Lysine 18 (H3K18) lactylation at the collagen promoter, which could be restored with lactate but not acetate. We further demonstrated that lactate-induced collagen is partially mediated by HIF-1α.

PKM2 drives activation of fibroblasts in SSc via metabolic changes such as glycolysis. Taking advantage of PKM2 tetramerisation or blockade of lactate generation could be a possible therapeutic option in a disease with few treatment options.