Mesenchymal stem cells (MSCs) have been used in clinical studies to treat neurological diseases and damage. However, implanted MSCs do not achieve their regenerative effects by differentiating into and replacing neural cells. Instead, MSC secretome components mediate the regenerative effects of MSCs. MSC‐derived extracellular vesicles (EVs)/exosomes carry cargo responsible for rescuing brain damage. We previously showed that EP4 antagonist‐induced MSC EVs/exosomes have enhanced regenerative potential to rescue hippocampal damage, compared with EVs/exosomes from untreated MSCs. Here we show that EP4 antagonist‐induced MSC EVs/exosomes promote neurosphere formation in vitro and increase neurogenesis and neuritogenesis in damaged hippocampi; basal MSC EVs/exosomes do not contribute to these regenerative effects. 2′,3′‐Cyclic nucleotide 3′‐phosphodiesterase (CNP) levels in EP4 antagonist‐induced MSC EVs/exosomes are 20‐fold higher than CNP levels in basal MSC EVs/exosomes. Decreasing elevated exosomal CNP levels in EP4 antagonist‐induced MSC EVs/exosomes reduced the efficacy of these EVs/exosomes in promoting β3‐tubulin polymerization and in converting toxic 2′,3′‐cAMP into neuroprotective adenosine. CNP‐depleted EP4 antagonist‐induced MSC EVs/exosomes lost the ability to promote neurogenesis and neuritogenesis in damaged hippocampi. Systemic administration of EV/exosomes from EP4‐antagonist derived MSC EVs/exosomes repaired cognition, learning, and memory deficiencies in mice caused by hippocampal damage. In contrast, CNP‐depleted EP4 antagonist‐induced MSC EVs/exosomes failed to repair this damage. Exosomal CNP contributes to the ability of EP4 antagonist‐elicited MSC EVs/exosomes to promote neurogenesis and neuritogenesis in damaged hippocampi and recovery of cognition, memory, and learning. This experimental approach should be generally applicable to identifying the role of EV/exosomal components in eliciting a variety of biological responses.

Cells can communicate via exosomes, ~100-nm extracellular vesicles (EVs) that contain proteins, lipids, and nucleic acids. Non-adherent/mesenchymal mammary epithelial cell (NAMEC)-derived extracellular vesicles can be isolated from NAMEC medium via differential ultracentrifugation. Based on their density, EVs can be purified via ultracentrifugation at 110,000 x g. The EV preparation from ultracentrifugation can be further separated using a continuous density gradient to prevent contamination with soluble proteins. The purified EVs can then be further evaluated using nanoparticle-tracking analysis, which measures the size and number of vesicles in the preparation. The extracellular vesicles with a size ranging from 50 to 150 nm are exosomes. The NAMEC-derived EVs/exosomes can be ingested by mammary epithelial cells, which can be measured by flow cytometry and confocal microscopy. Some mammary stem cell properties (e.g., mammary gland-forming ability) can be transferred from the stem-like NAMECs to mammary epithelial cells via the NAMEC-derived EVs/exosomes. Isolated primary EpCAM/CD49f luminal mammary epithelial cells cannot form mammary glands after being transplanted into mouse fat pads, while EpCAM/CD49f basal mammary epithelial cells form mammary glands after transplantation. Uptake of NAMEC-derived EVs/exosomes by EpCAM/CD49f luminal mammary epithelial cells allows them to generate mammary glands after being transplanted into fat pads. The EVs/exosomes derived from stem-like mammary epithelial cells transfer mammary gland-forming ability to EpCAM/CD49f luminal mammary epithelial cells.

Synovial sarcoma is a rare but aggressive soft-tissue sarcoma associated with translocation t(X;18). Metastasis occurs in approximately 50% of all patients, and curative outcomes are difficult to achieve in this group. Since the efficacies of current therapeutic approaches for metastatic synovial sarcoma remain limited, new therapeutic agents are urgently needed. Tilapia piscidin 4 (TP4), a marine antimicrobial peptide, is known to exhibit multiple biological functions, including anti-bacterial, wound-healing, immunomodulatory, and anticancer activities. In the present study, we assessed the anticancer activity of TP4 in human synovial sarcoma cells and determined the underlying mechanisms. We first demonstrated that TP4 can induce necrotic cell death in human synovial sarcoma AsKa-SS and SW982 cells lines. In addition, we saw that TP4 initiates reactive oxygen species (ROS) production and downregulates antioxidant proteins, such as uncoupling protein-2, superoxide dismutase (SOD)-1, and SOD-2. Moreover, TP4-induced mitochondrial hyperpolarization is followed by elevation of mitochondrial ROS. Calcium overload is also triggered by TP4, and cell death can be attenuated by a necrosis inhibitor, ROS scavenger or calcium chelator. In our experiments, TP4 displayed strong anticancer activity in human synovial sarcoma cells by disrupting oxidative status, promoting mitochondrial hyperpolarization and causing calcium overload.

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