Angiopoietin 2 Is Associated with Vascular Necroptosis Induction in Coronavirus Disease 2019 Acute Respiratory Distress Syndrome

Vascular injury is a well-established, disease-modifying factor in acute respiratory distress syndrome (ARDS) pathogenesis. Recently, coronavirus disease 2019 (COVID-19)–induced injury to the vascular compartment has been linked to complement activation, microvascular thrombosis, and dysregulated immune responses. This study sought to assess whether aberrant vascular activation in this prothrombotic context was associated with the induction of necroptotic vascular cell death. To achieve this, proteomic analysis was performed on blood samples from COVID-19 subjects at distinct time points during ARDS pathogenesis (hospitalized at risk, N = 59; ARDS, N = 31; and recovery, N = 12). Assessment of circulating vascular markers in the at-risk cohort revealed a signature of low vascular protein abundance that tracked with low platelet levels and increased mortality. This signature was replicated in the ARDS cohort and correlated with increased plasma angiopoietin 2 levels. COVID-19 ARDS lung autopsy immunostaining confirmed a link between vascular injury (angiopoietin 2) and platelet-rich microthrombi (CD61) and induction of necrotic cell death [phosphorylated mixed lineage kinase domain-like (pMLKL)]. Among recovery subjects, the vascular signature identified patients with poor functional outcomes. Taken together, this vascular injury signature was associated with low platelet levels and increased mortality and can be used to identify ARDS patients most likely to benefit from vascular targeted therapies.

For decades, vascular injury has been recognized as a key element in the pathogenesis of acute respiratory distress syndrome (ARDS).¹ However, this has not translated into vascular targeted therapies for ARDS. This may, in part, be related to heterogeneity in the vascular response to injury among ARDS subjects, as well as to difficulty in selecting patients most at risk for ARDS vascular injury. Blood proteomics has been proposed as a novel translational approach to better match patients to precision therapies for ARDS.² A better understanding of the blood proteomic changes associated with ARDS vascular injury could therefore help identify patients likely to benefit from vascular therapies.Previous targeted studies of circulating vascular proteins have greatly enhanced the understanding of ARDS vascular injury. For example, measurement of the plasma angiocrine factor angiopoietin 2 (ANGPT2) in patients at the early stages of ARDS demonstrates that vascular injury likely precedes mechanical ventilation³ and is associated with ARDS disease mortality.⁴ However, these ANGPT2-mediated vascular disruptions can be countered. In mice, systemic administration of platelet-derived pericyte chemokines, such as angiopoietin 1 (ANGPT1) and platelet-derived growth factor B (PDGFB), counter ANGPT2-mediated vascular disruption, demonstrating the homeostatic potential of the blood vascular proteome.⁵ Improved understanding of the blood proteomic changes in subjects with ARDS with high or low vascular injury can build on these prior observations, shed further light onto disease pathogenesis, and identify protein targets for further investigation.More recently, vascular injury has been associated with coronavirus disease 2019 (COVID-19) ARDS,^6,7 including the vascular complications of inflammation and thrombosis. In this context, COVID-19–induced injury to the vascular compartment has been associated with complement activation and microvascular thrombosis,8, 9, 10 systemic thrombosis,^9,11 and dysregulated immune responses.^12,13 However, this focus on inflammation and thrombosis limits our insights into other disruptions associated with aberrant vascular activation, including angiogenesis, junctional barrier integrity, the role of activated platelets in vascular injury, and induction of vascular cell death, including specialized receptor-interacting protein kinase 3 (RIPK3)–mediated necrotic cell death. Specifically, although ANGPT2-mediated vascular disruption has been documented in COVID-19,¹⁴ the association between ANGPT2 and induction of vascular cell death remains largely unexplored in ARDS investigations.The purpose of this study was to assess whether aberrant vascular activation in COVID-19 was associated with the induction of necroptotic vascular cell death. To this aim, blood proteomics was performed in three independent COVID-19 cohorts, which enrolled patients at distinct time points in disease pathogenesis and included non–COVID-19 ARDS samples as control. Protein expression was linked to relevant clinical outcomes, vascular injury, and cell death markers in COVID-19 autopsy lung tissue.