Keratinocyte-Macrophage Crosstalk by the Nrf2/Ccl2/EGF Signaling Axis Orchestrates Tissue Regeneration

Unveiling the molecular mechanisms underlying tissue regeneration provides new opportunities to develop treatments for diabetic ulcers and other chronic skin lesions. Here, to gain insight into critical wound response mechanisms regulated by epidermal Nrf2, we micro dissected a ~2.5mm concentric ring around the 10mm wound at 5 days-post-wounding (DPW) and used flow cytometry to isolate wound-associated keratinocytes from Nrf2 +/+ Ker and Nrf2 ∆/∆ Ker mice for bulk RNA-seq. Combining in vivo and ex vivo data with next generation sequencing, we show that Ccl2 secretion by epidermal keratinocytes is directly orchestrated by Nrf2, a prominent transcriptional regulator of tissue regeneration that is activated early after cutaneous injury. Through a unique feedback mechanism, we find that Ccl2 from epidermal keratinocytes not only drives chemotaxis of macrophages into the wound, but also triggers macrophage expression of EGF, which in turn activates basal epidermal keratinocyte proliferation. Notably, we find dysfunctional activation of Nrf2 in epidermal keratinocytes of diabetic mice after wounding, which in part, explains regenerative impairments associated with diabetes. These findings provide mechanistic insight into the critical relationship between keratinocyte-macrophage signaling during tissue regeneration, providing the basis for continued investigation of the therapeutic value of Nrf2.