Isolation and Characterization of Exosomes from Skeletal Muscle Fibroblasts

Continuous nutrient supply culture strategy controls multivesicular endosomes pathway and anti-photo-aging miRNA cargo loading of extracellular vesicles

Extracellular vesicle (EV) therapy recently had shown significant efficacy in various diseases. Serum starvation culture (SC) is one of the most widely used methods for collecting EVs. However, SC may cause inadvertent effects and eventually dampen the therapeutic potential of EVs. Therefore, we developed a novel method for EV collection, continuous nutrient supply culture (CC), which can provide an optimal condition for mesenchymal stem cells (MSCs) by continuously supplying essential nutrients to MSCs. By comparing with SC strategy, we revealed that CC could maintain CC-MSCs in a normal autophagy and apoptotic state, which reduced the shunting of EV precursors in cells and useless information material carried by EVs. In CC-MSCs, the expression levels of endosomal sorting complexes required for transport (ESCRT) and targeting GTPase27 (Rab27) were upregulated compared to those in SC-MSCs. Besides, we analyzed the membrane transport efficiency of EV formation, which demonstrated the CC strategy could promote the formation of EV precursors and the release of EVs. In addition, miRNA analysis revealed that CC-EVs were enriched with anti-chronic inflammatory factors, which could inhibit the nuclear factor kappa-B (NF-κB) pathway, mitigate chronic inflammation, and effectively repair skin photo-aging damage.

Distinct functions of dimeric and monomeric scaffold protein Alix in regulating F-actin assembly and loading of exosomal cargo

Alix is a ubiquitously expressed scaffold protein that participates in numerous cellular processes related to the remodeling/repair of membranes and the actin cytoskeleton. Alix exists in monomeric and dimeric/multimeric configurations, but how dimer formation occurs and what role the dimer has in Alix-mediated processes are still largely elusive. Here, we reveal a mechanism for Alix homodimerization mediated by disulfide bonds under physiological conditions and demonstrate that the Alix dimer is enriched in exosomes and F-actin cytoskeleton subcellular fractions. Proteomic analysis of exosomes derived from Alix-/- primary cells underlined the indispensable role of Alix in loading syntenin into exosomes, thereby regulating the cellular levels of this protein. Using a set of deletion mutants, we define the function of Alix Bro1 domain, which is solely required for its exosomal localization, and that of the V domain, which is needed for recruiting syntenin into exosomes. We reveal an essential role for Cys814 within the disordered proline-rich domain for Alix dimerization. By mutating this residue, we show that Alix remains exclusively monomeric and, in this configuration, is effective in loading syntenin into exosomes. In contrast, loss of dimerization affects the ability of Alix to associate with F-actin, thereby compromising Alix-mediated cytoskeleton remodeling. We propose that dimeric and monomeric forms of Alix selectively execute two of the protein's main functions: exosomal cargo loading and cytoskeleton remodeling.

Single-Particle Interferometric Reflectance Imaging Characterization of Individual Extracellular Vesicles and Population Dynamics

Extracellular vesicles (EVs) are nanometer-sized vesicles with a lipid bilayer that are secreted by most cells. EVs carry a multitude of different biological molecules, including protein, lipid, DNA, and RNA, and are postulated to facilitate cell-to-cell communication in diverse tissues and organs. Recently, EVs have attracted significant attention as biomarkers for diagnostics and therapeutic agents for various diseases. Many methods have been developed for EV characterization. However, current methods for EV analysis all have different limitations. Thus, developing efficient and effective methods for EV isolation and characterization remains one of the crucial steps for this cutting-edge research field as it matures. Here, we provide a detailed protocol outlining a single-particle interferometric reflectance imaging sensor (SP-IRIS), as a method that is capable of detecting and characterizing EVs from unpurified biological sources and purified EVs by other methodologies. This advanced technique can be used for multi-level and comprehensive measurements for the analysis of EV size, EV count, EV phenotype, and biomarker colocalization.