Renal Tubular Calcium Oxalate Crystals Induce Mitochondrial Damage and cGAS-STING Activation

Background: The kidney is subject to the formation of microscopic calcium oxalate (CaOx) crystals which can cause damage. Previous in vitro studies indicate that CaOx-induced damage involves mitochondrial dysfunction, but the specific pathways have yet to be elucidated. The cGAS-STING pathway is a key regulator of the inflammatory response and fibrosis in acute kidney injury (AKI), and activation by cytosolic dsDNA leads to the production of pro-inflammatory cytokines. Activated STING recruits kinases TBK1 and IKK, resulting in activation of transcription factors IRF3 and NF-κB. Activation is triggered by both foreign and self-DNA, including mitochondrial DNA released after mitochondrial damage. Here, we found that mitochondrial damage and activation of the cGAS-STING pathways occurs following acute CaOx crystal deposition in wild type (WT) rats. Methods: WT S.D. rats received 1 mg/kg sodium oxalate (NaOx) by intraperitoneal injection to induce acute CaOx crystal formation. Immunohistochemical and immunofluorescence staining was used to visualize protein localization in kidney sections at various time points post-injection. Results: NaOx administration led to decreased mitochondrial HSP60 in renal epithelial cells (Figure 1A), indicative of mitochondrial damage. NaOx also promoted activation of downstream STING targets, including an increase in p-TBK1 and p-IRF3 (Figure 1B), as well as nuclear translocation of NF-κB (Figure 1C). Conclusion: CaOx crystals promote mitochondrial damage and subsequent activation of the cGAS-STING pathway. Persistent CaOx crystal deposition as a form of subclinical AKI throughout life may drive renal functional decline.Staining of kidneys from WT S.D. rats at indicated timepoints post-injection with NaOx or saline control (A) IF staining of HSP60 (B) IHC staining of p-IRF3, IRF3, and p-TBK1 (C) IF staining of of NF-κB