Intravenously delivered mesenchymal stem cell-derived exosomes target M2-type macrophages in the injured spinal cord

Abstract

In a previous report we showed that intravenous infusion of bone marrow-derived mesenchymal stem cells (MSCs) improved functional recovery after contusive spinal cord injury (SCI) in the non-immunosuppressed rat, although the MSCs themselves were not detected at the spinal cord injury (SCI) site [1]. Rather, the MSCs lodged transiently in the lungs for about two days post-infusion. Preliminary studies and a recent report [2] suggest that the effects of intravenous (IV) infusion of MSCs could be mimicked by IV infusion of exosomes isolated from conditioned media of MSC cultures (MSC exos ). In this study, we assessed the possible mechanism of MSC exos action on SCI by investigating the tissue distribution and cellular targeting of DiR fluorescent labeled MSC exos at 3 hours and 24 hours after IV infusion in rats with SCI. The IV delivered MSC exos were detected in contused regions of the spinal cord, but not in the noninjured region of the spinal cord, and were also detected in the spleen, which was notably reduced in weight in the SCI rat, compared to control animals. DiR "hotspots" were specifically associated with CD206-expressing M2 macrophages in the spinal cord and this was confirmed by co-localization with anti-CD63 antibodies labeling a tetraspanin characteristically expressed on exosomes. Our findings that MSC exos specifically target M2-type macrophages at the site of SCI, support the idea that extracellular vesicles, released by MSCs, may mediate at least some of the therapeutic effects of IV MSC administration.

Exosome-shuttled miR-216a-5p from hypoxic preconditioned mesenchymal stem cells repair traumatic spinal cord injury by shifting microglial M1/M2 polarization

“…Xiao et al reported that chitinase1 might exert protective effects against Alzheimer's disease by polarizing microglia towards the M2 phenotype [81]. Taking the role of the M2 phenotype with characteristics of anti-inflammation and neuroprotection into consideration, therapeutic treatments that can shift differentiated microglia from the M1 towards the M2 phenotype are encouraged in traumatic neuro-diseases [11,[48][49][50]. In this study, administration of HExos was shown to promote microglial M2 polarization and produce anti-inflammatory cytokines in vivo and in vitro.…”

“…Indeed, hypoxic preconditioning of MSCs can significantly enhance their biological function and activity, thereby improving the transplantation efficacy of MSCs in the treatment of various disease models [46,47]. Although some studies have reported that MSC exosomes could suppress the development of inflammation by shifting the microglia/macrophage phenotype in traumatic CNS diseases [48][49][50], it is still unclear whether MSCs under hypoxic conditions can exert better therapeutic effects to promote SCI functional recovery and whether such enhancement is mediated by exosomal signaling.…”

Mesenchymal Stem Cell-Derived Exosomes Reduce A1 Astrocytes via Downregulation of Phosphorylated NFκB P65 Subunit in Spinal Cord Injury

“…Likewise, in a paper by Xiong et al, intravenously injected CD63 GFP-tagged MSC-exo were found taken up by neurons and astrocytes in traumatic brain injury rat brains [86]. However, a recent study reported that intravenously delivered DiR-labeled MSC-exo were detected predominantly within M2 macrophages, but only a small amount of them localized within astrocytic process endings in contused spinal cord [87]. It shall be noted that in this study, DiR-labeled MSC-exo were infused at one week post-contusion, whereas in our study, PKH26-labeled MSC-exo were infused at 30-min and 1-day post-injury.…”

Ultrafiltration Segregates Tissue Regenerative Stimuli Harboured Within and Independent of Extracellular Vesicles

“…Losordo and colleagues demonstrated human CD34+ hematopoietic progenitors generated exosomes in vitro that transferred miR-126-3p to reduce SPRED1 mRNA in murine endothelial cells in vivo, in return enhancing hindlimb revascularization and recovery from ischemia 80 . The secretome of MSC is also known to influence the infiltration hematopoietic cells following tissue injury, including the promotion of a pro-regenerative M2 macrophage differentiation via the transfer of nucleic acid cargo [81][82][83] . Thus, future studies will need to determine whether cargo enriched in EV+ CM can influence the phenotypic and tissue regenerative properties of infiltrating hematopoietic, stromal, or progenitor cells.…”