Effect of Flightless I Expression on Epidermal Stem Cell Niche During Wound Repair

Abstract

Objective:

Activation of epidermal stem cells (EpSCs) from their quiescent niche is an integral component of wound reepithelialization and involves Wnt/β-catenin (β-Cat) signaling and remodeling of the actin cytoskeleton. The aim of this study was to investigate the effect of Flightless I (Flii), a cytoskeletal protein and inhibitor of wound healing, on EpSC activation during wound repair.

Approach:

Genetically modified Flii mice (Flii knockdown: Flii^+/− , wild type: WT, Flii overexpressing: Flii^Tg/Tg ) received two incisional wounds along the lateral axis of the dorsal skin. Indicators of EpSC activation (epidermal growth factor receptor 1 [EGFR1], leucine-rich repeats and immunoglobulin-like domains-1 [Lrig1], K14), Wnt/β-Cat signaling (Lgr6, Flap2, β-Cat, and axis inhibition protein 2 [Axin2]), and cell proliferation (proliferating cell nuclear antigen [PCNA]) were assessed using immunohistochemistry. β-Cat stabilization was examined using western blotting with cell cycling and differentiation of isolated CD34⁺ITGA6^high EpSCs examined using real time-quantitative polymerase chain reaction after treatment with wound-conditioned media.

Results:

Flii^+/− led to increased numbers of activated EpSCs expressing PCNA, elevated EGFR1, and decreased Lrig1. EpSCs in Flii^+/− hair follicle niches adjacent to the wounds also showed expression of Wnt-activation markers including increased β-Cat and Lgr6, and decreased Axin2. EpSCs (CD34⁺ITGA6^high) isolated from Flii^+/− unwounded skin showed elevated expression of cell-cycling genes including ΔNp63, filaggrin (Fila), involucrin (Invo), cyclin D1 (Ccnd1), and cell-division cycle protein-20 (Cdc20); and elevated ΔNp63 and Invo after treatment with wound-conditioned media compared with WT and Flii^Tg/Tg counterparts.

Innovation:

Flii was identified as an inhibitor of EpSC activation that may explain its negative effects on wound reepithelialization.

Conclusion:

Flii may inhibit EpSC activation by interrupting Wnt/β-Cat signaling. Strategies that reduce Flii may increase activation of EpSCs and promote reepithelialization of wounds.