CXCL11 Expression by Keratinocytes Occurs Transiently Between Reaching Confluence and Cellular Compaction

Objective: To investigate whether differentiation or cellular confluence is responsible for CXCL11 expression patterns in re-epithelialization. Approach:In vitro model systems of re-epithelialization using the HaCaT keratinocyte cell line were utilized in monitoring expression of differentiation markers, including desmoplakin and various cytokeratins while evaluating for an association with chemokine CXCL11 expression. Results: CXCL11 expression was elevated in sparse culture with peak expression near the time of confluence. This somewhat followed the accumulation of desmoplakin in detergent-insoluble pool of proteins. However, in postconfluent, despite continued accumulation of desmoplakin within cells, CXCL11 expression decreased to baseline levels. This biphasic pattern was also seen in low calcium culture, an environment that inhibits keratinocyte differentiation and accumulation of desmosomal proteins. Highest CXCL11-expressing areas best correlated with newly confluent areas within culture expressing basal keratin 14, but also activated keratin 6. Innovation: Achievement of a threshold cellular density induces cell signaling cascade through CXCR3 that, in addition to other undiscovered pathways, can progress cutaneous wounds from the proliferative into the remodeling phases of cutaneous wound healing. Conclusion: These results suggest that the achievement of confluence with increased cellular density by migrating keratinocytes at the wound edge triggers expression of CXCL11. Since CXCR3 stimulation in endothelial cells results in apoptosis and causes neovascular pruning, whereas stimulation of CXCR3 in fibroblasts results decreased motility and cellular contraction, we speculate that CXCL11 expression by epidermal cells upon achieving cellular confluence could be the source of CXCR3 stimulation in the dermis ushering a transition from proliferative to remodeling phases of wound healing.