The mechanisms underlying COVID-19–associated acute kidney injury (AKI) are incompletely understood. This study aimed to determine whether activation of the complement-derived C5a-C5aR1 axis regulates formation of neutrophil extracellular traps (NETs) in AKI driven by the SARS-CoV-2 nucleocapsid (N protein). The authors sought to connect N protein expression in kidney tissue with complement activation, neutrophil recruitment, NET deposition, and downstream measures of renal dysfunction.
A murine AKI model with kidney-specific expression of the SARS-CoV-2 N protein was established using ultrasound-microbubble-mediated delivery technology. The abstract reports that this targeted expression produced renal pathology characterized by neutrophil infiltration and NET formation. The abstract does not provide additional methodological details such as vector design, timing of expression, or sample sizes.
To interrogate the role of the complement receptor axis and NETs, the investigators used two interventions: a C5aR1 inhibitor (DF2593A) to block receptor-mediated C5a signaling, and DNase I (Pulmozyme) to enzymatically degrade extracellular DNA structures comprising NETs. The abstract states these agents were administered in the AKI model to assess effects on inflammatory and functional renal endpoints. Specific dosing regimens, routes of administration, and timing relative to N protein expression were not reported in the abstract.
Outcome measures described in the abstract included histologic and immunologic measures of renal inflammation (neutrophil infiltration and NET deposition), indices of complement activation (serum C5a level and renal C5aR1 expression), and standard renal function biomarkers: serum creatinine, blood urea nitrogen (BUN), and kidney injury molecule-1 (KIM-1). The abstract indicates these variables were used to evaluate disease severity and response to interventions.
The authors report that kidney-targeted expression of SARS-CoV-2 N protein significantly induced neutrophil infiltration and NET formation in the kidney. Accompanying these changes, serum C5a was elevated and renal C5aR1 expression was upregulated, indicating complement activation involving the C5a–C5aR1 axis.
Intervention with the C5aR1 inhibitor DF2593A or degradation of NETs with DNase I effectively attenuated histologic renal tubular injury. These treatments were also associated with reductions in functional biomarkers of renal injury: decreased serum creatinine, decreased BUN, and lower levels of KIM-1. The abstract presents these findings in qualitative terms; numerical values, effect sizes, and statistical analyses are not provided in the abstract.
Based on the reported findings, the authors interpret that activation of the C5a-C5aR1 axis contributes to N protein–mediated AKI by promoting NET formation, and that NETs are mechanistic effectors of tubular injury in this model. Blocking C5aR1 signaling or removing NETs mitigated tissue damage and improved biochemical markers of kidney injury, supporting a causal role for complement-driven NETosis in this context.
The abstract does not present detailed methodological parameters (for example, sample sizes, controls, timing, or statistical significance measures), nor does it provide safety or off-target data for the interventions used. The model is an animal disease model with kidney-specific expression of viral protein; translational relevance to human COVID-19-associated AKI requires further study and validation beyond the scope of the abstract.
In this experimental AKI model, SARS-CoV-2 N protein expression was associated with complement activation, neutrophil recruitment, and NET deposition; blockade of C5aR1 or enzymatic NET degradation reduced renal tubular injury and lowered serum creatinine, BUN, and KIM-1. The authors conclude that the C5a-C5aR1 axis drives NET formation and contributes to N protein–mediated AKI, and they suggest that targeting this axis or NETs may represent a potential therapeutic strategy for COVID-19–associated renal injury. Specific translational recommendations, clinical trial data, and safety considerations were not included in the abstract.
Conflict of interest statement: The authors declared no conflicts of interest in the publication abstract.
Keywords: Acute kidney injury; C5a-C5aR1 axis; Complement activation; Neutrophil extracellular traps; SARS-CoV-2 N protein.