Mesenchymal stromal cell secretome reduces lung injury and thrombo-inflammation induced by SARS-CoV-2 spike protein

Abstract

Severe COVID-19 is characterized by thrombo-inflammatory processes within the lung microvasculature. In pursuit of effective treatments, clinical studies explored mesenchymal stromal cells (MSCs) as a promising approach due to their anti-inflammatory, immunomodulatory, and regenerative properties, through their paracrine action. Here, we tested the conditioned medium (CM) derived from human umbilical cord (UC)-MSCs in acute lung injury induced by the spike protein subunit 1 (S1) in ACE2-humanized male mice. Injection of CM significantly limited S1-induced lung injury, edema, and fibrosis. This was associated with reduced vascular dysfunction, in terms of restored thrombomodulin levels and decreased von Willebrand (vWF) expression. By preserving endothelial glycocalyx, CM reduced complement C3 accumulation, favoring factor H binding on the lung microvasculature. Reduced oxidative stress, nuclear NF-κB p65 accumulation, and inflammatory cell infiltration were also observed in response to CM in S1-injected mice. In vitro, CM counteracted thrombo-inflammation by preserving thrombomodulin, as well as limiting vWF expression, due to endothelial glycocalyx recovery. CM reduced nuclear translocation of NF-κB p65 and its downstream targets, ICAM-1 and P-selectin, translating in decreased C3 deposits, platelet aggregation, and leukocyte adhesion on S1-challenged endothelial cells. Collectively, these data indicate that UC-MSC-derived secretome represents a promising therapy in COVID-19 due to its potent anti-thrombotic and anti-inflammatory effects on lung microcirculation.

1. Introduction

COVID-19 is a respiratory illness caused by the novel β-coronavirus SARS-CoV-2. Since the initial outbreak in 2019, almost 800 million infections have been diagnosed globally, with more than 7 million deaths [1]. As of November 2024, 260,000 infections and 5,000 deaths are still reported every month worldwide [1].

COVID-19 is a self-limiting illness in approximately 90% of infected subjects, who develop a mild flu-like syndrome [2]. In the remaining cases, uncontrolled viral shedding causes pneumonia, acute respiratory distress syndrome (ARDS), and death [3, 4]. In this subset of critically-ill patients, immune system overactivation and inflammatory hyper-response contribute to diffuse pulmonary damage and multiorgan failure [5–7]. During these excessive inflammatory processes, endothelial cell activation and injury play a pivotal role in the microthrombotic complications, which are strongly associated with mortality in severe COVID-19 patients [8–12].

Even though endothelial cells are not permissive for SARS-CoV-2 replication [13, 14], emerging evidence indicates that these cells are considerably damaged by direct interaction with the virus. Specifically, viral components, such as the spike protein, induce marked alterations in endothelial cell phenotype, including heightened cytokine expression, upregulated adhesion molecules, and oxidative stress, as well as compromised permeability and metabolic function [13, 14]. Of clinical relevance, SARS-CoV-2 antigens, particularly the subunit 1 of the spike protein (S1), can be detected in the blood of a substantial proportion of individuals after infection, correlating with cardiopulmonary symptoms [15, 16].