Abstract
By forming a protective barrier, epidermal keratinocytes represent the first line of defense against environmental insults. UVB radiation of the sun is a major challenge for the skin and can induce inflammation, aging and eventually skin cancer. UVB induces an immune response in human keratinocytes resulting in activation and secretion of the pro-inflammatory cytokines proIL-1β and -18. This is mediated by assembly of protein complexes, termed inflammasomes. However, the mechanisms underlying sensing of UVB by keratinocytes, and particularly the types of inflammasomes required for cytokine secretion, are a matter of debate. To address these questions, we established a protocol that allows the generation of CRISPR/Cas9-targeted human primary keratinocytes. Our experiments revealed an essential role of the NLRP1 rather than the NLRP3 inflammasome in UVB sensing and subsequent IL-1β and -18 secretion by keratinocytes. Moreover, NLRP1 but not NLRP3 was required for inflammasome activation in response to nigericin, a potassium ionophore and well-established NLRP3 activator in immune cells. Since the CRISPR/Cas9-targeted cells retained their full differentiation capacity, genome editing of human primary keratinocytes might be useful for numerous research and medical applications.