Exosomes from Mesenchymal Stromal Cells Reduce Murine Colonic Inflammation via a Macrophage-Dependent Mechanism

Abstract

Background: Conventional treatments for inflammatory bowel disease (IBD) have multiple potential side effects. Therefore, alternative treatments are desperately needed. This work investigated the therapeutic effects of exosomes derived from mesenchymal stromal cells (MSC-Exos) in murine models of IBD and to explored the underlying mechanisms. Methods: MSC-Exos were isolated from human bone marrow-derived mesenchymal stromal cells. Experimental colitis was induced by administration of dextran sulfate sodium (DSS) in C57BL/6 mice (male, 6-8 weeks), or 2, 4, 6-trinitrobenzenesulfonic acid (TNBS) in Balb/c mice (male, 7-9 weeks). Macrophage depletion was performed via intraperitoneal injection of clodronate-liposomes. Colitic mice were treated intravenously with MSC-Exos or saline, and mortality and diverse disease signs were tracked. Findings: Systemic administration of MSC-Exos significantly mitigated colitis in various models of IBD. MSC-Exos treatment downregulated inflammatory responses, maintained intestinal barrier integrity and polarized M2 macrophages, but did not favor intestinal fibrosis. Mechanistically, infused MSC-Exos mainly acted on colonic macrophages and macrophages from colitic colons acquired obvious resistance to inflammatory re-stimulation when prepared from mice treated with MSC-Exos versus untreated mice. The beneficial effect of MSC-Exos was blocked by macrophage depletion. Besides, the induction of IL10 production from macrophages was partially involved in the beneficial effect of MSC-Exos. MSC-Exos were enriched in proteins involved in regulating multiple biological processes associated with the anti-colitic benefit of MSC-Exos. Particularly, metallothionein-2 in MSC-Exos was required for the suppression of inflammatory responses in macrophages. Interpretation: MSC-Exos are critical regulators of inflammatory responses and may be promising candidates for IBD treatment. Funding Statement: National Natural Science Foundation of China (No. 81870383), Science and Technology Planning Project of Guangzhou City (No. 201804010014), Science and Technology Planning Project of Guangdong Province (No. 2015B020229001), Clinical Innovation Research Program of Guangzhou Regenerative Medicine and Health Guangdong Laboratory (No. 2018GZR0201005)，Guangdong Natural Science Foundation (No. 2017A030313785), National Key R&D Program of China (No. 2017YFC1308800) and Science and Technology Planning Project of Guangdong Province (No. 20160916). Declaration of Interests: The authors declare that no conflict of interest exists. Ethics Approval Statement: This study was approved by the Institutional Review Board (IRB) of the Sixth Affiliated Hospital, Sun Yat-sen University. Informed written consent was obtained from all donors. All animal experiments were approved by the Institutional Animal Care and Use Committee of the Sun Yat-sen university and conformed to the “Guide for the Care and Use of Laboratory Animals” of the National Institute of Health in China.