Bone Marrow-Derived Mesenchymal Stem Cells Promoted Cutaneous Wound Healing by Regulating Keratinocyte Migration via β2-Adrenergic Receptor Signaling

Mesenchymal stem cells (MSCs) play an important role in cutaneous wound healing; however, the functional mechanisms involved in the healing process are poorly understood. A series of studies indicate that keratinocytes that migrate into the wound bed rely on an epithelial-mesenchymal transition (EMT)-like process to initiate re-epithelialization. We therefore examined whether bone marrow-derived MSCs (BMSCs) could affect biological behavior and induce EMT-like characteristics in the human epidermal keratinocytes (HEKs) and in the immortalized human keratinocyte cell line HaCaT cells, and we investigated the signaling pathways of BMSC-mediated phenotypic changes. By assessing the expression of EMT-related markers including E-cadherin, α-SMA, and Snail family transcription factors by β2-adrenergic receptor (β2-AR) blockage using ICI-118,551, a β2-AR selective antagonist, or β2-AR small interfering RNA (siRNA), we showed an involvement of β2-AR signaling in the induction of EMT-like alterations in human keratinocytes in vitro. β2-AR signaling also affected collective and individual cell migration in human keratinocyte cell lines, which was attenuated by administration of ICI-118,551. Treating the cells with BMSC-conditioned media (BMSC-CM) not only recapitulated the effect of isoproterenol (ISO) on cell migration but also induced the expression of β2-AR and a panel of proteins associated with mesenchymal phenotype in HEKs and HaCaT cells. Similarly, a blockade of the β2-AR by either ICI-118,551 or β2-AR siRNAs reversed both responses of the epidermal keratinocyte cell lines relative to BMSC-CM exposure. These results were further verified in our vivo findings and indicated that the exogenous application of MSCs promoted cutaneous wound healing and endowed the keratinocytes surrounding the wound area with an increased migratory phenotype through activation of β2-AR signaling. Our findings suggest a biochemical mechanism underlying the function of MSCs in wound re-epithelization, which provides a reliable theoretical basis for the wide application of MSCs in the treatment of chronic wounds.