mTORC1 links pathology in experimental models of Still's disease and macrophage activation syndrome

Still's disease is a severe inflammatory syndrome characterized by fever, skin rash and arthritis affecting children and adults. Patients with Still's disease may also develop macrophage activation syndrome, a potentially fatal complication of immune dysregulation resulting in cytokine storm. Here we show that mTORC1 (mechanistic target of rapamycin complex 1) underpins the pathology of Still's disease and macrophage activation syndrome. Single-cell RNA sequencing in a murine model of Still's disease shows preferential activation of mTORC1 in monocytes; both mTOR inhibition and monocyte depletion attenuate disease severity. Transcriptomic data from patients with Still's disease suggest decreased expression of the mTORC1 inhibitors TSC1/TSC2 and an mTORC1 gene signature that strongly correlates with disease activity and treatment response. Unrestricted activation of mTORC1 by Tsc2 deletion in mice is sufficient to trigger a Still's disease-like syndrome, including both inflammatory arthritis and macrophage activation syndrome with hemophagocytosis, a cellular manifestation that is reproduced in human monocytes by CRISPR/Cas-mediated deletion of TSC2. Consistent with this observation, hemophagocytic histiocytes from patients with macrophage activation syndrome display prominent mTORC1 activity. Our study suggests a mechanistic link of mTORC1 to inflammation that connects the pathogenesis of Still's disease and macrophage activation syndrome. Still's disease is an inflammatory syndrome linked to the development of further immune dysregulation and hypercytokinaemia termed macrophage activation syndrome. Here the authors implicate the mechanistic target of rapamycin complex 1 in murine models of Still's disease and macrophage activation syndrome, and provide associations with clinical cases in patients

Automated summary

This study reveals the involvement of mTORC1 in the pathogenesis of Still's disease and macrophage activation syndrome. Activation of mTORC1 was found to be preferential in monocytes, and inhibiting mTORC1 or depleting monocytes attenuated disease severity. Additionally, decreased expression of mTORC1 inhibitors TSC1/TSC2 was observed in patients with Still's disease and correlated with disease activity and treatment response.