Mechanistic insights into the kidney injury in chickens induced by hypervirulent fowl adenovirus serotype 4.

Hypervirulent fowl adenovirus serotype 4 (FAdV-4) has emerged as a significant poultry pathogen since 2015, exhibiting clinical multi-organ and multi-tissue tropism post-infection, resulting in substantial economic losses in the poultry industry. However, the molecular mechanism underlying kidney injury caused by FAdV-4 infection remains unclear. Our results indicated that FAdV-4 infection in chickens induces damage to kidney tissues, characterized by the degeneration and necrosis of kidney epithelial cells, glomerular injury, endoplasmic reticulum stress, and the activation of a robust inflammatory response in the kidney cells. Notably, autophagosome-like vesicles enclosed clusters of viral particles that were transmitted between kidney cells post-infection. There might be a novel mechanism of vesicle-mediated cell-to-cell transmission of hypervirulent FAdV-4 that hijacks autophagosome-like vesicles. We also investigated cellular autophagy in kidney cells in vivo and in vitro during early FAdV-4 infection. The autophagy-related marker proteins LC3B, ATG5, and BECN1 were upregulated post-infection, whereas SQSTM1 was downregulated, indicating that FAdV-4 infection enhances autophagic flux and induces complete autophagy. The viral structural protein Fiber 2 was also observed to colocalize with the autophagy-related marker protein LC3B and the exosome-specific marker protein CD63 in the kidney cells at 24 hpi, suggesting that FAdV-4-induced cellular autophagy promotes viral replication in kidney cells and that autophagosome-like vesicles are involved in early FAdV-4 replication in vivo in chickens. Our results offer novel insights into the pathogenesis of hypervirulent FAdV-4 from the perspective of kidney injury post-infection. IMPORTANCE: Hypervirulent fowl adenovirus serotype 4 (FAdV-4) has become globally prevalent since 2015 as a predominant pathogen on poultry farms, leading to substantial economic losses for the poultry industry. However, the molecular mechanisms underlying kidney injury induced by FAdV-4 infection remain unclear. In this study, we primarily elucidated the mechanisms of kidney injury induced by FAdV-4 infection in chickens, utilizing both in vitro and in vivo models. Our results demonstrate that FAdV-4 infection in chickens causes degeneration and necrosis of kidney epithelial cells, glomerular injury, and expansion of the endoplasmic reticulum, while also triggering a robust inflammatory response in kidney cells. Notably, we observed the cell-to-cell transmission of virus particles delivered by autophagosome-like vesicles, and the viral infection-induced cellular autophagy facilitated viral replication in the kidney cells. These findings offer a novel perspective to understand the molecular mechanisms of FAdV-4-induced kidney injury and establish a basis for further investigation into the molecular pathogenesis of hypervirulent FAdV-4.