Mesenchymal stem cell derived secretome and extracellular vesicles for acute lung injury and other inflammatory lung diseases

Abstract

Introduction: Acute respiratory distress syndrome is a major cause of respiratory failure in critically ill patients. Despite extensive research into its pathophysiology, mortality remains high. No effective pharmacotherapy exists. Based largely on numerous preclinical studies, administration of mesenchymal stem or stromal cell (MSC) as a therapeutic for acute lung injury holds great promise, and clinical trials are currently underway. However, concern for the use of stem cells, specifically the risk of iatrogenic tumor formation, remains unresolved. Accumulating evidence now suggest that novel cell-free therapies including MSC-derived conditioned medium and extracellular vesicles released from MSCs might constitute compelling alternatives.

Areas covered: The current review summarizes the preclinical studies testing MSC conditioned medium and/or MSC extracellular vesicles as treatment for acute lung injury and other inflammatory lung diseases.

Expert opinion: While certain logistical obstacles limit the clinical applications of MSC conditioned medium such as the volume required for treatment, the therapeutic application of MSC extracellular vesicles remains promising, primarily due to ability of extracellular vesicles to maintain the functional phenotype of the parent cell. However, utilization of MSC extracellular vesicles will require large-scale production and standardization concerning identification, characterization and quantification.

Keywords: Acute lung injury; acute respiratory distress syndrome; exosomes; extracellular vesicles; mesenchymal stem cells; microvesicles.

Conflict of interest statement

Declaration of interest This paper was funded by National Institutes of Health grant HL-113022. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Figures

Figure 1. Components of Mesenchymal Stem Cell Derived Conditioned Medium with Reparative Properties

A) A wide array of immunomodulatory soluble factors with reparative properties is secreted by human MSCs, such as keratinocyte growth factor, angiopoietin-1, interleukin-10, prostaglandin-E2 and transforming growth factor-β; B) No longer considered cellular debris, extracellular vesicles released by MSCs, which contain proteins, peptides, lipids, mRNAs, microRNAs and DNA, are biologically active and may participate in the therapeutic effect. Largely classified based on size, source and content, extracellular vesicles are comprised of exosomes, microvesicles and apoptotic bodies; C) MSCs are now recognized to be capable of transporting cellular organelles (e.g., mitochondria) to recipient cells through microtubules.

Figure 2. Extracellular Vesicles Biogenesis and Interactions with Recipient Cells

Biogenesis Extracellular vesicles originate from distinct intracellular compartments: 1) Microvesicles which contain cytoplasmic molecules, are formed by direct budding off the plasma membrane into the extracellular space; 2) Invagination of late endosomes, which is loaded with Golgi or cell surface-related molecules, forms multivesicular bodies that fuse with plasma membrane giving rise to exosomes; 3) Apoptotic bodies are released from cells undergoing programmed cell death. They contain potentially toxic or immunogenic cellular components, such as DNA fragments, non-coding RNAs, and cellular organelles, which are destined to be cleared through phagocytosis. Interaction Between Extracellular Vesicles and Recipient Cells. Internalization of extracellular vesicles leading to the release of their content within recipient cells can be mediated through (a) phagocytosis, (b) endocytosis, or (c) direct membrane fusion.

Figure 3. Therapeutic Properties of Extracellular Vesicles Derived From Mesenchymal Stem Cells in Various Organ Injuries

A) Acute Kidney Injury: MSC EV provided reno-protection by horizontal transfer of IGF-1R mRNA to renal tubular cells and by activating ERK½ MAPK; B) Myocardial Infarction: MSC EV contained: 1) Integrins that could home exosomes to cardiomyocytes that expressed ICAM-1, a ligand for integrins, or to VCAM-1 on endothelial cells; 2) CD73, present on the surface of exosomes, activated reperfusion injury salvage kinases by increased expression of pro-survival protein kinases such as Akt and ERK½; 3) CD59 (protectin), a widely expressed glycosylphosphatidylinositol-anchored membrane protein, prevented the formation of membrane attack complexes and inhibited complement-mediated lysis; 4) Glycolytic enzymes that could ameliorate energy deficit and potentially increase glycolytic flux and ATP production in the reperfused myocardium; 5) Active 20S proteasomes, which is responsible for the degradation of approximately 90% of all intracellular protein damaged by oxidation; 6) And microRNAs, such as the anti-apoptotic effect of miR-22, which directly targeted Mecp2 and reduced the expression of p53 upregulated modulator of apoptosis via miR-221; C) Liver Injury: MSC EV inhibited epithelial to mesenchymal transition and collagen production by suppressing the activation of TGF-β1/Smad signaling pathway. MSC EV administration was also associated with higher expression of proliferation proteins (PCNA and cyclin D1), the anti-apoptotic gene, Bcl-xL, and STAT3; D) Brain Injury: MSCs transferred to injured neural cells EV microRNAs, such as miR-133b, which were involved in regeneration of motor neuron axons.

Figure 4. Therapeutic Properties of Extracellular Vesicles Derived from Mesenchymal Stem Cells in Lung Injury

1) In a mouse model of hypoxia-induced pulmonary artery hypertension, MSC EVs suppressed the hypoxic induction of STAT3 and up-regulated miR-204 levels, interfering with the STAT3-miR-204-STAT3 feed-forward loop and shifting the balance to an anti-proliferative state; 2) In a mouse model of aspergillus hyphal extract-induced asthma, MSC EVs mitigated Th2/Th17-mediated airway hyper-responsiveness by shifting the Th2/Th17 inflammatory response towards a counter-regulatory Th1 response; 3) In a mouse model of endotoxin-induced ALI, MSC EVs suppressed inflammation and restored lung protein permeability by transferring KGF mRNA to the injured alveolus, which restored both vectorial ion and fluid transport; 4) In a mouse model of Escherichia coli pneumonia, MSC EVs reduced inflammation, lung protein permeability and pulmonary edema by decreased bacterial counts in the injured alveolus, leading to improved survival. MSC EVs were also found to enhance monocyte phagocytosis of bacteria, restore intracellular ATP levels in injured human alveolar epithelial type 2 cells, and repolarized monocytes/macrophages from a M1 to a M2 phenotype by possible transfer COX2 mRNA with subsequent secretion of PGE2; 5) In silica-induced ALI in mice, MSC-derived exosomes modulated toll-like receptor (TLR) signaling and cytokine secretion in macrophages, in part, by transfer of regulatory microRNAs such as mir-451 and prevented the recruitment of Ly6Chi monocytes and reduced secretion of pro-fibrotic IL-10 and TGFβ by these cells in the lung. In addition, MSCs managed intracellular oxidative stress by the extracellular transfer of depolarized mitochondria in vesicles to macrophages, improving bioenergetics; 6) And in an ex vivo lung perfusion model of ischemia/reperfusion injury, restoration of alveolar fluid clearance by MSC EV was dependent on the internalization of EV into the injured host cells via CD44.