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: Purified pDCs from Healthy donors were cultured at different stiffness (low stiffness: 0.2kPa and high stiffness: 50kPa) in the absence or presence of a TLR9 agonist (C274 at 0.075uM)) for 5h. Or  Purified pDCs from HDs (n=3) were cultured in media alone or with the NRF2 activator (KI696) for 1h, followed by the TLR9 agonist (C274 at 0.075uM) for 5h.  RNA was extreacted and preformed RNA-sequencing