Minimal active domain of human salivary histatin 1 is efficacious in promoting acute skin wound healing

Dear Editor,The skin barrier can be impaired by acute skin wounds,which may lead to a series of complications.It is essential to accelerate wound healing and rapidly restore the structural integrity and functionality of skin.One of the promising bioactive agents is human salivary histatin 1(Hst1),a 38-amino acid histidine-rich peptide that functions to maintain the homeostasis of oral mucosa with a cellular mechanism of promoting the adhesion,spreading,migration of epithelial cells and thus re-epithelialization[1].In recent years,Hst1 has been shown to be effective against various skin-related cell types,such as fibroblasts,myo-fibroblasts,keratinocytes and endothelial cells.In our latest in-vivo study,Hst1 not only promotes angiogenesis,re-epithelialization and collagen production,but also suppresses inflammation,thereby significantly accelerating acute skin wound healing in mice[2].All these studies show that Hst1 is a potent bioactive agent for accelerating acute skin wound healing.

GPCR/endocytosis/ERK signaling/S2R is involved in the regulation of the internalization,mitochondria-targeting and-activating properties of human salivary histatin 1

Human salivary histatin 1(Hst1)exhibits a series of cell-activating properties,such as promoting cell spreading,migration,and metabolic activity.We recently have shown that fluorescently labeled Hst1(F-Hst1)targets and activates mitochondria,presenting an important molecular mechanism.However,its regulating signaling pathways remain to be elucidated.We investigated the influence of specific inhibitors of G protein-coupled receptors(GPCR),endocytosis pathways,extracellular signal-regulated kinases1/2(ERK1/2)signaling,p38 signaling,mitochondrial respiration and Na+/K+-ATPase activity on the uptake,mitochondria-targeting and-activating properties of F-Hst1.We performed a si RNA knockdown(KD)to assess the effect of Sigma-2 receptor(S2R)/Transmembrane Protein 97(TMEM97)—a recently identified target protein of Hst1.We also adopted live cell imaging to monitor the whole intracellular trafficking process of F-Hst1.Our results showed that the inhibition of cellular respiration hindered the internalization of F-Hst1.The inhibitors of GPCR,ERK1/2,phagocytosis,and clathrin-mediated endocytosis(CME)as well as siRNA KD of S2R/TMEM97 significantly reduced the uptake,which was accompanied by the nullification of the promoting effect of F-Hst1 on cell metabolic activity.Only the inhibitor of CME and KD of S2R/TMEM97 significantly compromised the mitochondria-targeting of Hst1.We further showed the intracellular trafficking and targeting process of F-Hst1,in which early endosome plays an important role.Overall,phagocytosis,CME,GPCR,ERK signaling,and S2R/TMEM97 are involved in the internalization of Hst1,while only CME and S2R/TMEM97 are critical for its subcellular targeting.The inhibition of either internalization or mitochondria-targeting of Hst1 could significantly compromise its mitochondria-activating property.