Novel Mechanisms of Exosome-Mediated Phagocytosis of Dead Cells in Injured Heart

Abstract

Rationale: After myocardial ischemic injury, improper phagocytic clearance of dying cardiac cells and the ensuing lack of inflammation resolution results in adverse cardiac remodeling and dysfunction that might lead to heart failure. Therefore, therapeutic strategies to ameliorate immune cell phagocytic function is critical for augmenting cardiac repair after injury. Objective: To determine if mesenchymal stem cell-derived exosomes (MSC-Exo) act as opsonin for apoptotic cells and/or trigger "eat me" phagocytic signaling in resident/recruited phagocytes after myocardial ischemic injury. Methods and Results: We evaluated MSC-Exo-mediated opsonization of apoptotic cardiomyocytes; and invitro and invivo effects of milk fat globule- epidermal growth factor-factor VIII (MFGE8)-deficient mouse MSC-Exo on macrophage engulfment of apoptotic cardiomyocytes and its implications on cardiac remodeling, repair and function. Microscopy and FACS analyses show that opsonization of apoptotic cardiomyocytes with MSC-Exo enhances their engulfment by macrophages. Furthermore, pre-incubation of macrophages with MSC-Exo reprogrammed the signaling pathways involved in phagocytosis and expression of pro-reparative cytokines. Protein analysis of MSC-Exo reveals expression of MFGE8, a glycoprotein which bridges externalized phosphatidylserine (PS) on the apoptotic cell surface to alphaVbeta3 or alphaVbeta5 integrins on the phagocyte. Most intriguingly, siRNA inhibition of MFGE8 significantly reduced the MSC-Exo-mediated augmentation of dead cell engulfment, associated signaling and pro-reparative phenotype. After myocardial ischemic injury, intramyocardial administration of MSC-Exo increases macrophage uptake of apoptotic bodies in the border zone of infarct and is associated with reduced proinflammatory response, increase in neovascularization, lower infarct size and an improvement in cardiac function and MFGE8-deficient MSC-Exo administration failed to protect mice against MI. Conclusions: Our data demonstrates that exosome-associated MFGE8 on one hand enhances opsonization of dead cells and on the other activates phagocytic signaling thus augmenting removal of apoptotic cells, resolution of inflammation and therefore efficient cardiac recovery after injury.

Bone marrow-derived mesenchymal stem cells ameliorate severe acute pancreatitis by inhibiting oxidative stress in rats

“…BMSCs have the functions of self-renewal, multidirectional differentiation, immune regulation and paracrine [ 29 ]. Patil et al found that MSC-derived exosomes could reduce inflammation, promote angiogenesis, and decrease infarct volume in myocardial ischemic injury, which confirmed the anti-inflammatory and reparative action of MSCs [ 30 ]. In addition, our previous studies have also shown that BMSCs reduce both local pancreatic injury and systemic inflammation by repairing vascular injury and inhibiting cell necroptosis [ 31 , 32 ].…”

Extracellular vesicles, the emerging mirrors of brain physiopathology

“…EVs could enhance antibacterial immune responses by promoting bacterial antigen presentation from macrophage-derived EVs, which subsequently influences the adaptive immune response (45). Likewise, Patil et al also demonstrated the opsonization role of EVs in mediated phagocytosis of dead cells in the injured heart (46). The nucleic acids' EV cargo, mainly DNA and miRNAs, has also been identified to regulate innate and adaptive immune responses.…”

Inflammation and resolution signaling in cardiac repair and heart failure

“…Particularly, MFGE8 enhances opsonization of myocardial debris and also activates phagocytic signaling that facilitate removal of apoptotic cells after ischemic injury. 46 Apoptotic neutrophils express different receptors (GPCR or G-protein-coupled ALX/FPR2), which are required for the functionality of pro-resolving mediators during the resolution process, such as lipoxins, resolvins, protectins. 18 SPM entities, such as resolvin D1, and aspirin-triggered lipoxins, promote clearance of leukocytes from the infarcted site, thus promote the resolution of inflammation and cardiac repair this in turn changes the phenotype of macrophages from pro-inflammatory to anti-inflammatory and initiates the pathway of resolution.…”