Cell-Cell communication between skin keratinocytes and fibroblasts is non-redundantly coded through inflammatory cytokines

Cell-cell communication between keratinocytes and fibroblasts is essential for skin homeostasis, regulation and regeneration. How extracellular cytokine signaling, intra-cellular protein signaling and transcriptional regulation initiate and maintain this communication is still largely unknown. Here, we study in vitro the secretome and transcriptome dynamics that establish double paracrine cell-cell communication between primary human keratinocytes and fibroblasts. We find that keratinocyte-derived interleukin 1α initiates the cell communication, eliciting a constitutive NF-κB-mediated inflammation response in the fibroblasts. Their resulting transcriptome response over at least 12 hours induces a fibroblast secretome capable of enhancing keratinocyte migration. Applying partial least square regression to secretome perturbation experiments using recombinant proteins or antibodies demonstrates the synergistic interaction of early and late secreted inflammatory CC and CXC chemokines as well as IL6, whose relative composition directly controls keratinocyte migration. Conversely, inhibiting individual cytokines during cell-communication abrogates the keratinocyte phenotype. Hence, only the simultaneous activity of multiple inflammatory cytokines together with prolonged inflammatory response in the fibroblasts lead to increased keratinocyte migration after double paracrine cell communication, putatively serving as safeguard mechanisms for proper skin regeneration. The isolation time points for keratinocyte conditioned medium-treated human dermal fibroblasts were recorded at t=[1,2,3,4,6,8,10,12,24] hours after stimulation. Unstimulated control time points were taken at t=[0,2,4,8,12,24] hours.