1156 Single-cell RNA sequencing of photoaged skin reveals SLC46A2 as potential cGAMP transporter in keratinocytes

The cGAS-STING pathway is an important driver of UVB-induced skin inflammation. In addition to genomic instability activating DNA sensor cGAS, cells with activated cGAS can deposit secondary messenger cGAMP into nearby cells, directly activating STING and type I interferon (IFN) production. The solute carrier (SLC) family of transporters has recently been shown to transport extracellular cGAMP, but it is not yet known which transporter is most relevant for keratinocytes (KCs), particularly with UV irradiation. To identify potential candidates, we analyzed KCs in a single-cell RNA seq dataset of sun-exposed (SE) and sun-protected (SP) skin samples from donors in their 20s and 80s (n=8). Differential expression analysis was first performed to find core genes upregulated in older SE skin relative to both older SP and younger SE skin. Among the 5 genes identified, only IFI27 is classically induced by type I IFN, so we identified genes correlating with IFI27. We then performed transcriptional factor enrichment analysis and confirmed that STAT1 and STAT2 were the only statistically significant hits (p<0.0001), consistent with type I IFN activity. Among the top genes correlating with IFI27 was SLC46A2 (r=0.35, p=0.002), recently identified as the major cGAMP transporter in myeloid cells. Strikingly, most SLC46A2-expressing cells were KCs (86.4% of SLC46A2+ cells), and virtually all of the SLC46A2+ IFI27+ cells (98.7%) were KCs as well. In contrast, SLC19A1, the other major cGAMP carrier identified recently, was neither correlated with IFI27 (p=0.34) nor specifically expressed in KCs, comprising only 4.7% of SLC19A1+ IFI27+ cells. Thus, our studies suggest that SLC46A2 could be the primary epidermal cGAMP transporter. These findings reveal potential mechanisms relevant to not only photoaging but also inflammatory diseases associated with the cGAS-STING axis like lupus erythematosus.