β-Catenin Elicits Drp1-Mediated Mitochondrial Fission Activating the Pro-Apoptotic Caspase-1/IL-1β Signalosome in Aeromonas hydrophila-Infected Zebrafish Macrophages

Canonical Wnt signaling plays a major role in regulating microbial pathogenesis. However, to date, its involvement in A. hydrophila infection is not well known. Using zebrafish (Danio rerio) kidney macrophages (ZKM), we report that A. hydrophila infection upregulates wnt2, wnt3a, fzd5, lrp6, and beta-catenin (ctnnb1) expression, coinciding with the decreased expression of gsk3b and axin. Additionally, increased nuclear beta-catenin protein accumulation was observed in infected ZKM, thereby suggesting the activation of canonical Wnt signaling in A. hydrophila infection. Our studies with the beta-catenin specific inhibitor JW67 demonstrated beta-catenin to be pro-apoptotic, which initiates the apoptosis of A. hydrophila-infected ZKM. beta-catenin induces NADPH oxidase (NOX)-mediated ROS production, which orchestrates sustained mitochondrial ROS (mtROS) generation in the infected ZKM. Elevated mtROS favors the dissipation of the mitochondrial membrane potential (Delta psi(m)) and downstream Drp1-mediated mitochondrial fission, leading to cytochrome c release. We also report that beta-catenin-induced mitochondrial fission is an upstream regulator of the caspase-1/IL-1 beta signalosome, which triggers the caspase-3 mediated apoptosis of the ZKM as well as A. hydrophila clearance. This is the first study suggesting a host-centric role of canonical Wnt signaling pathway in A. hydrophila pathogenesis wherein beta-catenin plays a primal role in activating the mitochondrial fission machinery, which actively promotes ZKM apoptosis and helps in containing the bacteria.

Automated summary

By studying zebrafish kidney macrophages during A. hydrophila infection, we found that the canonical Wnt signaling pathway is activated, leading to mitochondrial fission, cell apoptosis, and bacterial clearance. This study reveals the host-centric role of the canonical Wnt signaling pathway in A. hydrophila pathogenesis.