Exosomes are nano-sized cargos with a lipid bilayer structure carrying diverse biomolecules including lipids, proteins, and nucleic acids. These small vesicles are secreted by most types of cells to communicate with each other. Since exosomes circulate through bodily fluids, they can transfer information not only to local cells but also to remote cells. Therefore, exosomes are considered potential biomarkers for various treatments. Recently, studies have shown the efficacy of exosomes in skin defects such as aging, atopic dermatitis, and wounds. Also, exosomes are being studied to be used as ingredients in commercialized skin treatment products. In this review, we discussed the need for exosomes in skin therapy together with the current challenges. Moreover, the functional roles of exosomes in terms of skin treatment and regeneration are overviewed. Finally, we highlighted the major limitations and the future perspective in exosome engineering.
Background
In the early 2000s, mesenchymal stem cell therapy had risen as an alternative for the treatment of various defects and diseases [1]. Mesenchymal stem cells (MSCs) are widely used in clinical trials not only due to their multipotency but also the ease of accessibility, expansion, and isolation from various adult tissues such as skin, placenta, cord blood, cord tissue, adipose tissue, dental pulp, testicles, and brain [2,3,4,5,6,7,8,9]. However, the safety and efficacy of stem cell therapy have been controversial [10]. Furthermore, several studies have shown that MSCs themselves were not engaged in the therapeutic process [11]. The stem cells injected in the defected site showed low cell viability and low numbers of cells tend to fuse with the recipient cells in the host tissue [12,13,14]. Instead, recent studies have revealed that the therapeutic efficacy of MSCs was beneficial through the release of biological molecules. These biologically active factors are secreted in the form of micro to nanosized particles called extracellular vesicles (EVs) by cells [15]. EVs contain signals in the form of lipids, proteins, and nucleic acids which can be exchanged between cells engaged in the regulation of physiological and pathological activities. Depending on the size of the particle, EVs can be divided into exosomes (40 to 100 nm), microvesicles (150 to 1000 nm), and apoptotic bodies (> 1000 nm) (Table 1) [16,17,18]. Moreover, the release mechanisms are different in which microvesicles are released directly from the cell membrane, while exosomes are released via the fusion of the multivesicular bodies (MVBs) and the plasma membrane. In this review, we will focus on the smaller particles in the EVs, the exosomes.
