The organelle-tethering protein PDZD8 regulates endolysosomal maturation and TLR9-NF-κB signaling in cisplatin-induced acute kidney injury.

Acute kidney injury (AKI) is a life-threatening condition with high morbidity and mortality, characterized by inflammation linked to organelle stress. Despite its clinical significance, effective therapies remain limited. Although organelle dysfunction is recognized as a driver of inflammation in AKI, the role of interorganelle communication in this process remains poorly understood. PDZ domain-containing 8 (PDZD8), a tethering protein on the endoplasmic reticulum (ER), facilitates ER-endolysosome contact that is essential for endolysosomal maturation. The mature endolysosome is a prerequisite for activating the DNA-sensing innate immune receptor, Toll-like receptor 9 (TLR9). Here, we investigated the role of PDZD8 in the TLR9-NF-κB pathway during AKI using knockout (KO) mice and in vitro knockdown in human proximal tubular cells (PTCs). KO mice showed reduced severity of cisplatin-induced AKI and reduced activation of the NF-κB pathway. Mechanistically, PDZD8 knockdown in PTCs impaired endolysosomal maturation and acidification. This functional disruption impeded the proper translocation of TLR9 to endolysosomes, thereby inhibiting the signaling cascade leading to NF-κB activation. Notably, PDZD8 knockdown did not alter mitochondrial morphology or the cytosolic leakage of mitochondrial DNA, an endogenous ligand for TLR9. These findings indicate that PDZD8 is crucial for maintaining endolysosomal homeostasis and regulating the TLR9-NF-κB pathway in cisplatin-induced tubular injury. This study reveals the critical role of PDZD8 in maintaining endolysosomal homeostasis and regulating the TLR9-NF-κB inflammatory pathway in cisplatin-induced acute kidney injury (AKI). Loss of PDZD8 impaired endolysosomal function, suppressing TLR9 activation and downstream inflammation, leading to reduced tubular damage.