Differential regulation of IL-17A and IL-17F via STAT5 contributes to psoriatic disease

Abstract

IL-17A has a pivotal pathogenic role in several immune-mediated inflammatory diseases. Despite sharing 50% sequence homology with IL-17A, the role of IL-17F remains less clear. Recent clinical findings suggest that dual inhibition of IL-17A and IL-17F in psoriatic disease is more efficacious than IL-17A inhibition alone, positing a pathogenic role for IL-17F. To characterize the regulation of IL-17A and IL-17F in psoriatic disease. Using both in vitro systems and lesional skin tissue from patients, we interrogated the chromosomal, transcriptional and protein expression landscape of IL-17A+ and IL-17F+ Th17 cells. Alongside established assays such as single-cell RNA sequencing, we developed a novel cytokine-capture technique that was combined with ChIP-seq and RNA-seq. We confirm a preferential elevation of IL-17F over IL-17A in psoriatic disease, and show that expression of each isoform predominantly occurs in distinct cell populations. The expression of both IL-17A and IL-17F exhibited a high degree of plasticity, with the balance between the two isoforms influenced by pro-inflammatory signaling and by anti-inflammatory drugs such as methylprednisolone. This plasticity was reflected in a broad H3K4me3 region at the IL17A-F locus, while opposing effects of STAT5/IL-2 signaling were observed for each of the two genes. Functionally, higher IL17F expression was linked to greater cell proliferation. Our data suggest there are key differences in the regulation of IL-17A and IL-17F in psoriatic disease, leading to distinct inflammatory cell populations. As such, we propose that both IL-17A and IL-17F neutralization may be required to maximally inhibit IL-17-driven pathology.