GLI1 activation induced by intermittent hypoxia drives cardiac fibroblast activation via enhanced PKM2-mediated glycolysis

BACKGROUND AND AIMS: Cardiac fibroblast (CF) activation in response to injury or inflammation is a central driver of pathological cardiac fibrosis, contributing to arrhythmias and heart failure. As previously demonstrated, intermittent hypoxia (IH), the hallmark pathophysiological feature of obstructive sleep apnoea (OSA), induces cardiac fibrosis. However, the mechanisms by which IH promotes CF activation and the key molecular mediators involved remain unclear. METHODS: Single-cell RNA sequencing (scRNA-seq) was performed on heart tissue from IH-exposed mice to characterize CF populations. Mice with myofibroblast-specific GLI1 overexpression or knockout were generated to evaluate the role of GLI1 in cardiac fibrosis under normoxic and IH conditions. Integrated RNA sequencing and ChIP sequencing were used to identify potential GLI1 target genes. The therapeutic effects of pharmacological GLI1 inhibition on CF activation and cardiac fibrosis were assessed. RESULTS: scRNA-seq revealed that Hedgehog signalling is activated in CFs during IH-induced cardiac fibrosis. IH promoted GLI1 nuclear translocation and increased its expression in CFs. GLI1 overexpression recapitulated the effects of IH, inducing CF activation and spontaneous cardiac fibrosis. Conversely, both genetic deletion and pharmacological inhibition of GLI1 attenuated IH-induced CF activation and cardiac dysfunction. Mechanistically, enhanced glycolysis was identified as a downstream effector of GLI1- and IH-induced fibrosis, with PKM2 identified as a direct transcriptional target of GLI1. Finally, a positive association of elevated plasma lactate concentration with a higher cumulative incidence of heart failure events was observed in 1509 patients with OSA. CONCLUSIONS: GLI1 is a critical pro-fibrotic transcription factor mediating IH-induced CF activation and cardiac fibrosis. Targeting GLI1 may offer a promising therapeutic strategy for the treatment of cardiac fibrosis, particularly in patients with OSA.