<p>Exosomes Derived From Bone Marrow Mesenchymal Stem Cells Inhibit Complement Activation In Rats With Spinal Cord Injury</p>

Abstract

PurposeSpinal cord injury (SCI) is a relatively common, devastating traumatic condition resulting in permanent disability. In this study, the use of exosomes derived from bone mesenchymal stem cells (BMSCs-Exo) as a cell-free therapy for the treatment of SCI in rats was investigated to gain insights into their mechanisms of action.MethodsRats were randomly divided into three groups, Sham (treated with PBS), SCI (SCI injury + PBS) and SCI + Exo (SCI injury + BMSCs-Exo). Changes in the complement system between the three groups were assessed with the use of proteomics. The proteomic data were verified using reverse transcription-polymerase chain reaction (RT-PCR). In addition, the distributions of BMSCs-Exo in rats with SCI were detected by immunofluorescence. Moreover, SCI-activated NF-κB levels were determined using Western blot.ResultsSCI insult increased complement levels, including C4, C5, C6, C4 binding protein alpha and complement factor H. In contrast, the SCI + BMSCs-Exo group exhibited attenuated SCI-induced complement levels. Immunofluorescence assay results revealed that BMSCs-Exo mainly accumulated at the spinal cord injury site and were bound to microglia cells. Western blot analysis of tissue lysates showed that BMSCs-Exo treatment also inhibited SCI-activated nuclear factor kappa-B (NF-κB).ConclusionBMSCs-Exo play a protective role in spinal cord injury by inhibiting complement mRNA synthesis and release and by inhibiting SCI-activated NF-κB by binding to microglia.

Treatment of rats with spinal cord injury using human bone marrow-derived stromal cells prepared by negative selection

“…To date, more than 25 studies have been published using bone marrow-derived stem cells to treat SCI in rats [8,15,25,26]. In the past, the cells were usually expanded before use and their phenotype was not characterized.…”

“…This raises the question regarding the mechanisms by which the injected bmSC were effective in our experiments. Increasing evidence suggests that extracellular vehicles (EVs) are important players in mediating the therapeutic effects of therapeutically applied stem cells [15,26,46,47]. Exosomes from mesenchymal stem cells exert immune-suppressive effects by enforcing M2 macrophage polarization, inhibiting complement activation [26] and indirectly driving regulatory T cell induction [14].…”

“…Increasing evidence suggests that extracellular vehicles (EVs) are important players in mediating the therapeutic effects of therapeutically applied stem cells [15,26,46,47]. Exosomes from mesenchymal stem cells exert immune-suppressive effects by enforcing M2 macrophage polarization, inhibiting complement activation [26] and indirectly driving regulatory T cell induction [14]. In addition, classical mechanisms of paracrine release of cytokines and growth factors are likely to be involved [48,49], although attempts at isolating these factors so far have failed to replace stem cells with a pure pharmacological intervention.…”

Immunoregulatory Effects of Stem Cell-Derived Extracellular Vesicles on Immune Cells

“…SC-EVs have been observed to regulate the activation of microglia in a variety of NS disease models (46,57,58,85,86,105). For example, MSC-EVs suppressed the activated microglia by inhibiting the phosphorylation of mitogen-activated protein kinase (MAPK) family members extracellular signal kinase 1/2 (ERK1/2), c-Jun N-terminal kinases (JNKs), and the p38 molecules in microglia (46,57,85) (Table 1).…”

“…For example, MSC-EVs suppressed the activated microglia by inhibiting the phosphorylation of mitogen-activated protein kinase (MAPK) family members extracellular signal kinase 1/2 (ERK1/2), c-Jun N-terminal kinases (JNKs), and the p38 molecules in microglia (46,57,85) (Table 1). Notable studies have reported that BM-MSC exosomes could repair spinal cord injury by suppressing the activation of A1 neurotoxic reactive astrocytes induced by activated microglia (86) or by inhibiting the complement system (105) and the NF-κB signaling pathway (46,57,105). Meanwhile, SC-EVs have been observed to polarize microglia from classic M1 to antiinflammatory M2 phenotypes (59,85,106,107), which might be attributed to the targeted suppression of the 3 ′ -UTR mRNA expression in Beclin-1 and Atg5 and inhibition of autophagymediated microglial polarization toward pro-inflammatory state by miR-30d-5p-expressing EVs (59) ( Table 1).…”