Abstract / Summary
Efferocytosis is essential for maintaining epithelial homeostasis, yet whether proximal tubules (PTs) can engulf other PTs and how this process contributes to acute kidney injury (AKI) remain unknown. Ceftazidime–avibactam (CAZ-AVI)-induced AKI and proximal tubule-specific Gusb conditional knockout (CKO) mice both exhibit phagolysosomal dysfunction, suggesting a shared mechanism. We investigated whether (i) CAZ-AVI triggers PT-to-PT efferocytosis, (ii) this leads to polyphagolysosomal failure, and (iii) Gusb overexpression protects against these abnormalities. Wild-type, Gusb-CKO, and Gusb-transgenic mice were treated with CAZ-AVI. Kidney injury was assessed by histology, TUNEL staining, immunostaining for Odc1 and 4-HNE, and transmission electron microscopy. PT-intrinsic transcriptional responses were quantified by real-time PCR for Ccl2, C3, Lcn2, Slc7a13, Acsm3, and Aqp8. Ultrastructural features were evaluated to distinguish efferocytosis from phagolysosomal failure. CAZ-AVI markedly reduced Odc1 in PTs and induced apoptosis localized almost exclusively to PTs, indicating PT-to-PT efferocytosis. CAZ-AVI strongly induced Ccl2, C3, and Lcn2, while suppressing Slc7a13, Acsm3, and Aqp8, reflecting inflammatory recruitment, complement-mediated opsonization, oxidative stress, and metabolic collapse. Electron microscopy revealed numerous polyphagolysosomes containing dense bodies, membrane fragments, small vesicles, and mitochondrial remnants with preserved cristae, without nuclear structures or double-membrane phagosomes, consistent with phagolysosomal failure. Importantly, Gusb-CKO mice phenocopied CAZ-AVI injury, showing Odc1 loss, robust 4-HNE accumulation, PT-restricted apoptosis, and abundant polyphagolysosomes even without drug exposure, demonstrating that Gusb deficiency is sufficient to drive PT-to-PT efferocytosis failure. In contrast, Gusb-overexpressing mice preserved Odc1, prevented apoptosis, normalized all six PT-intrinsic genes, and lacked polyphagolysosomes. CAZ-AVI induces PT-to-PT efferocytosis leading to phagolysosomal overload and oxidative failure. Gusb deficiency reproduces this phenotype, whereas Gusb overexpression preserves PT phagolysosomal homeostasis and prevents AKI progression.