Human Mesenchymal Stromal Cell-Derived Extracellular Vesicles Modify Microglial Response and Improve Clinical Outcomes in Experimental Spinal Cord Injury

Abstract

No current clinical intervention can alter the course of acute spinal cord injury (SCI), or appreciably improve neurological outcome. Mesenchymal stromal cells (MSCs) have been shown to modulate the injury sequelae of SCI largely via paracrine effects, although the mechanisms remain incompletely understood. One potential modality is through secretion of extracellular vesicles (EVs). In this study, we investigate whether systemic administration of EVs isolated from human MSCs (MSCEv) has the potential to be efficacious as an alternative to cell-based therapy for SCI. Additionally, we investigate whether EVs isolated from human MSCs stimulated with pro-inflammatory cytokines have enhanced anti-inflammatory effects when administered after SCI. Immunohistochemistry supported the quantitative analysis, demonstrating a diminished inflammatory response with apparent astrocyte and microglia disorganization in cord tissue up to 10 mm caudal to the injury site. Locomotor recovery scores showed significant improvement among animals treated with MSCEv. Significant increases in mechanical sensitivity threshold were observed in animals treated with EVs from either naïve MSC (MSCEvwt) or stimulated MSC (MSCEv+), with a statistically significant increase in threshold for MSCEv+-treated animals when compared to those that received MSCEvwt. In conclusion, these data show that treatment of acute SCI with extracellular vesicles derived from human MSCs attenuates neuroinflammation and improves functional recovery.

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

“…Additionally, MSC transplantation can reduce the levels of proinflammatory cytokines, such as TNF-α and IL-1 [11,47], and inhibit NFκB signaling [12,48,49]. Moreover, MSCs are capable of switching microglia from a proinflammatory M1 phenotype towards an anti-inflammatory M2 phenotype in vitro [13] and in SCI models [50]. Furthermore, MSCs inhibit reactive astrogliosis in inflammationinduced preterm brain injury [51], attenuate GFAP overexpression in astrocytes in stroke [52], and modulate astrocytic end-feet in lipopolysaccharide-treated rats [53].…”

“…Activated microglia/macrophages and immune cells at the lesion site after SCI can produce a series of proinflammatory cytokines, including TNF-α, IL-1 and IL-6 [88,89] that may lead to the activation of astroglial NFκB. Given that both MSCs and MSC-exo have been confirmed to inhibit proinflammatory microglia in SCI [50], it is possible that MSCs and MSC-exo exert effects on A1 astrocytes not only in a direct way but also mediated by a variety of inflammatory cells.…”

How to reprogram microglia toward beneficial functions

“…MSCs, indirectly co‐cultured with microglia in vitro , directly counteract the pro‐inflammatory response of cells activated with inflammatory cytokines and induce persistent pro‐regenerative traits (Giunti et al, ; Zanier et al, ). More recent studies demonstrated that MSCs‐derived EVs may be sufficient to significantly dampen microglia response and improve functional recovery upon intravenous administration in traumatic brain or spinal cord injuries (L. X. Zhang, Yin, Zhang, & Deng, ; J. W. Kim, Ha, Molon, & Kim, ; Ruppert et al, ) as well as in a mouse model of AD. Despite these findings offer a hopeful opportunity to advance novel cell‐free therapeutic strategies that might prevail over the risks associated with the use of cells, a still unresolved issue is the molecular mechanism whereby the infused EVs reduce inflammation and rescue cognitive impairments in rodent models of neuroinflammatory diseases.…”

“…Zhang, Yin, Zhang, & Deng, 2015;J. W. Kim, Ha, Molon, & Kim, 2013;Ruppert et al, 2018) as well as in a mouse model of AD. Despite these findings offer a hopeful opportunity to advance novel cell-free therapeutic strategies that might prevail over the risks associated with the use of cells, a still unresolved issue is the molecular mechanism whereby the infused EVs reduce inflammation and rescue cognitive impairments in rodent models of neuroinflammatory diseases.…”

BRD4 inhibition attenuates inflammatory response in microglia and facilitates recovery after spinal cord injury in rats

“…To the best of our knowledge, this is the first study exploring the role of BRD4 in inflammatory response regulation after SCI and describing a BRD4 inhibitor capable of suppressing inflammatory response via negatively modulating NF-κB and MAPK signalling pathways (Figure 8).BET family such as BRD4 are reported to activate many inflammation-related genes,26 and inflammation blocks functional recovery and aggravates neuropathic paresthesia in damaged spinal cord 27,28. To the best of our knowledge, this is the first study exploring the role of BRD4 in inflammatory response regulation after SCI and describing a BRD4 inhibitor capable of suppressing inflammatory response via negatively modulating NF-κB and MAPK signalling pathways (Figure 8).BET family such as BRD4 are reported to activate many inflammation-related genes,26 and inflammation blocks functional recovery and aggravates neuropathic paresthesia in damaged spinal cord 27,28.…”