Complement C5a receptor 1 antagonist attenuates alveolar hypoplasia induced by pulmonary hypoperfusion and its underlying mechanisms.

BACKGROUND

To elucidate the role of complement component C5a in pulmonary hypoperfusion (PHypo)-induced alveolar hypoplasia, given its centrality in sterile inflammation and the recent implication of immune activation in a neonatal rat PHypo model.

METHODS

PHypo was induced in postnatal day 1 (P1) rats via pulmonary artery banding (PAB). Bulk RNA sequencing of lung tissues was performed at P7 and P14, and Single-cell RNA sequencing was conducted at P7. Alveolar development was assessed histologically (H&E) at P14. PHypo rats were treated with a C5a receptor 1(C5aR1) antagonist (C5aR1 ant) at P1. Key molecular changes (IL-1β, NF-κB, SEMA3a) and alveolar cell number were evaluated. Serum C5a levels were measured in children with PHypo versus controls.

RESULTS

Bulk RNA-sequencing of P7 lungs identified the complement cascade in the top 20 pathway enrichment, with C5aR1 as the most significantly upregulated gene. Single-cell RNA sequencing revealed that C5aR1 and IL-11β are predominantly expressed in monocytes/macrophages, and immunofluorescence further demonstrated cytoplasmic localization of C5aR1. PHypo induced notable alveolar hypoplasia at P14. RNA-sequencing of P14 lungs showed downregulation of genes associated with alveolar formation and upregulation of those related to immune responses in PHypo lungs. Treatment with C5aR1 ant rescued PHypo-induced alveolar hypoplasia. Mechanistically, C5a-induced IL-1β activated NF-κB, inhibiting SEMA3a, crucial for alveolar budding. C5aR1 ant downregulated IL-1β/NF-κB axis and upregulated SEMA3a; direct inhibition of IL-1β replicated these effects and improved alveologenesis.

CONCLUSIONS

This study defines a C5a-IL-1β-NF-κB-SEMA3a axis driving PHypo-induced alveolar hypoplasia. C5aR1 antagonist and IL-1β inhibitors demonstrate therapeutic efficacy, may offer novel strategies to improve long-term outcomes in affected children.