MiR-31 Mediates Inflammatory Signaling To Promote Re-epithelialization During Skin Wound Healing

Wound healing is the physiological response to injury in skin,restoring its integrity and functions.It consists of hemostasis,inflammation,re-epithelialization and remodeling phases.Acute wounds can be healed rapidly by properly executing all of the phases.However,the repair process becomes defective in chronic wounds,and the healing failure poses an increasingly urgent clinical challenge worldwide.Elucidating the molecular mechanism underlying normal wound healing can help to understand the principle of skin repair and provide new insights into the pathogenesis of chronic wounds.Successful re-epithelialization,which relies on proliferation and migration of epidermal keratinocytes,requires reduction in tissue inflammation.Therefore,understanding the molecular mechanism underlying the transition from inflammation to re-epithelialization will help to better understand the principles of wound healing.Recently,microRNA have been shown to modulate wound re-epithelialization by regulating different pathways involved in keratinocyte proliferation and migration.Currently,the in vivo functions of specific microRNA in wound healing are not fully understood.Many microRNA dynamically change during the wound healing process.Among them,miR-31 is of great interest,because it has been implicated in promoting epidermal hyperplasia in psoriasis,enhancing stem cell self-renewal in the mammary gland and intestine,and functioning as an oncogene in lung and colorectal cancers.Firstly,utilizing qRT-PCR analysis and In situ hybridization,we observed that miR-31 expression is strongly induced in wound edge keratinocytes,and its expression is much higher than the level in the normal keratinocytes,suggesting the importance of miR-31 in wound healing.When the skin is wounded,the inflammatory NF-?B ? STAT3 signaling pathways are activated.We found that miR-31 promoter contains p65 and Stat3 binding sites.The luciferase reporter assay revealed that miR-31 expression is induced in keratinocytes after wounding by NF-?B and STAT3 signaling pathways.To determine the function of miR-31 in the mouse skin,this study takes advantage of K14Cre;miR-31(?)/(?)(cKO)and miR-31-/-mouse models.We found that miR-31 is expressed in the skin at a moderate level under normal condition,compared to other tissues.Loss of miR-31 does not result in any apparent phenotype under physiological conditions.However,we found that loss of miR-31 lead to delayed wound healing in the skin,due to the impairment of keratinocyte proliferation and migration.,Mechanistically,we found that miR-31 activates the RAS/MAPK signaling and upregulates its downstream target genes such as CyclinDl,c-Myc and Slug,by directly targeting Rasal,Spredl,Spred2 and Spry4,which are negative regulators of the RAS/MAPK pathway.As such,miR-31 promotes keratinocyte proliferation and migration to accelerate wound healing by activating the RAS/MAPK signaling pathway.More importantly,knockdown of these miR-31 targets at least partially rescues the delayed wound healing phenotype observed in vitro in miR-31 knockdown keratinocytes.Taken together,here we found that miR-31 can be up-regulated by NF-?B and STAT3,which are two inflammatory signalling pathways and promotes wound healing by directly regulating the RAS/MAPK signaling pathway.These findings identify miR-31 as an important cell-autonomous mediator during the transition from inflammation to re-epithelialization phases of wound healingin vivo?It provideds evidence for the potential of miR-31 as a therapeutic target for wound healing.