Morroniside promotes skin wound re-epithelialization by facilitating epidermal stem cell proliferation through GLP-1R-mediated upregulation of β-catenin expression

Abstract

Epidermal stem cells (EpSCs) play a vital role in skin wound healing through re-epithelialization. Identifying chemicals that can promote EpSC proliferation is helpful for treating skin wounds. This study investigates the effect of morroniside on cutaneous wound healing in mice and explores the underlying mechanisms. Application of 10‒50 μg/mL of morroniside to the skin wound promotes wound healing in mice. In vitro studies demonstrate that morroniside stimulates the proliferation of mouse and human EpSCs in a time- and dose-dependent manner. Mechanistic studies reveal that morroniside promotes the proliferation of EpSCs by facilitating the cell cycle transition from the G1 to S phase. Morroniside increases the expression of β-catenin via the glucagon-like peptide-1 receptor (GLP-1R)-mediated PKA, PKA/PI3K/AKT and PKA/ERK signaling pathways, resulting in an increase in cyclin D1 and cyclin E1 expression, either directly or by upregulating c-Myc expression. This process ultimately leads to EpSC proliferation. Administration of morroniside to mouse skin wounds increases the phosphorylation of AKT and ERK, the expressions of β-catenin, c-Myc, cyclin D1, and cyclin E1, as well as the proliferation of EpSCs, in periwound skin tissue, and accelerates wound re-epithelialization. These effects of morroniside are mediated by the GLP-1R. Overall, these results indicate that morroniside promotes skin wound healing by stimulating the proliferation of EpSCs via increasing β-catenin expression and subsequently upregulating c-Myc, cyclin D1, and cyclin E1 expressions through GLP-1R signaling pathways. Morroniside has clinical potential for treating skin wounds.

1. Introduction

The skin wound healing process consists of 4 sequential and overlapping phases: homeostasis, inflammation, proliferation, and remodeling. A variety of cells are involved in this process, including neutrophils, macrophages, and lymphocytes in the inflammatory phase and epidermal stem cells/keratinocytes, fibroblasts, and vascular endothelial cells in the proliferative phase [1,2]. After skin injury, epidermal stem cells (EpSCs) situated in the basal layer of the epidermis surrounding the wound edge proliferate, migrate towards the wound area, and differentiate into keratinocytes to repair the epidermis [3]. Stem cells located in the outer root sheath of hair follicles along the wound edge also participate in wound re-epithelialization [4]. To accelerate skin wound healing, research has mainly focused on regulating neutrophils, macrophages, and vascular endothelial cells to modulate inflammation and promote angiogenesis at the wound site [5–8]. However, there are limited reports on regulating the proliferation and differentiation of EpSCs for cutaneous wound re-epithelialization [9].

Morroniside is an iridoid glycoside extracted from the sarcocarp of Cornus officinalis [10]. It has been reported to promote angiogenesis in animal models of ischemic focal cerebral infarction [11,12] and myocardial infarction [13], as well as increase the survival of neurons and oligodendrocytes following spinal cord injury [14]. However, its effect on skin wound healing is currently unknown. Previous studies have shown that morroniside promotes cell proliferation [15–18]. Additionally, morroniside has been reported to alleviate neuropathic pain by activating spinal glucagon-like peptide-1 receptors (GLP-1Rs) [19]. GLP-1R agonists have been reported to stimulate the proliferation of cells, including mesenchymal stem cells and pancreatic β-cells [20,21]. Additionally, they have been found to facilitate skin wound healing [22,23]. GLP-1R is expressed in the epidermal cells of mouse skin and human keratinocytes [23]. Thus, we hypothesized that morroniside may have the potential to improve skin wound healing by promoting wound re-epithelialization through GLP-1R.