Mechanosensing regulates plasmacytoid DCs activation in the skin through NRF2 activation
Plasmacytoid dendritic cells (pDCs) infiltrate the skin, chronically produce type I interferon (IFN-I) and promote skin lesions and fibrosis in autoimmune patients. However, what controls their activation in the skin is unknown. Here, we report that increased stiffness, characteristic of the skin microenvironment, inhibits the production of IFN-I by TLR-activated pDCs. Mechanistically, mechanosensing activates stress pathways including the transcription factor NRF2, which, by triggering the pentose phosphate pathway, rewires glycolysis and reduces pyruvate levels, a product necessary for pDC responses. Modulating NRF2 expression in skin-infiltrating pDCs controlled the IFN-I response, leading to either resolution or the sustained activation of pathologic IFN-I pathway in the skin. Moreover, we observed that CXCL4, a pro-fibrotic chemokine that is elevated in fibrotic skin, was able to overcome stiffness-mediated IFN-I inhibition, allowing chronic IFN-I responses by pDCs in the skin. Furthermore, in the skin of patients with systemic sclerosis (SSc), although NRF2 was induced in skin-infiltrating pDCs as compared to blood pDCs, the IFN-response was maintained. Hence, these data identify a novel regulatory mechanism exerted by the skin microenvironment and identify points of dysregulation of this mechanism in patients with skin inflammation and fibrosis. Overall design: We purified pDC from human buffy coats. pDCs were cultured overnight at 37°C, 5% CO2 in RPMI-1640 medium supplemented with 10% heat-inactivated defined FBS, penicillin-streptomycin, L-glutamine and treated with indicated stimulation.