Macrophage is vital for C5b-9-induced cyst formation and enlargement in Pkd1 -/- mice

C5b-9 complex, the final product of complement, is overproduced during cystogenesis in the kidneys of rapid-onset mice with Pkd 1 gene deficiency at postnatal day (PD)10. Compared with rapid-onset polycystic kidney disease (PKD) model, cyst enlargement is much less progressive in mice when Pkd 1 gene inactivation at PD30 (chronic-onset model); however, C5b-9 infusion significantly accelerated ADPKD progression in this model. These histological data provide evidence that C5b-9 triggers renal cell apoptosis in the middle stage (PD180) and promotes cell proliferation in the late stage (PD240) in PKD mice. However, in vitro C5b-9 neither stimulated renal tubular epithelial cell (RTEC) apoptosis nor promoted RTEC proliferation, indicating that the C5b-9 indirectly affects RTECs. Furthermore, our results demonstrate that the impact of C5b-9 on cyst enlargement is significantly weakened when macrophages are depleted with liposomal clodronate (LC), suggesting that macrophages play a key role in the development of ADPKD. Moreover, C5b-9 drives bone-marrow-derived macrophages (BMDMs) to highly express TNF-α in vitro , resulting in increased cell apoptosis and contributing to cystogenesis. Additionally, the macrophages underwent M1-to-M2 transition and secreted high levels of IL-10, when cocultured with RTECs. IL-10, an M2-specific cytokine marker, remarkably stimulated RTEC proliferation. After LC-induced macrophage depletion, infusion of C5b-9-activated BMDMs significantly increased cystic phenotype in mice, proving that macrophages are vital for C5b-9-induced ADPKD.