About 10% of the world’s population is affected by chronic kidney disease (CKD). The risk of CKD progressing to end-stage kidney disease (ESRD) is exceptionally high, requiring dialysis or a kidney transplant. At present, there is no effective treatment for chronic kidney disease. Thus, there is an urgent need to uncover the pathophysiological mechanisms underlying CKD to help formulate effective treatment strategies to prevent and treat the disease. newly Nature Communications The study suggested that DNA-PKcs could be a potential target for the treatment of CKD.
Stady: The catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) drives the development of chronic kidney disease in male mice.. Image credit: Crystal light/Shutterstock
An important pathological feature of chronic kidney disease is renal interstitial fibrosis, associated with atypical expression of protrophotrophic factors, such as transforming growth factor beta 1 (TGF-β1), myofibroblast activation, and epithelial dedifferentiation. TGF-β1 plays an important role in interstitial fibrosis involving the activation of fibrogenic genes, such as fibronectin (FN), α-smooth muscle actin (α-SMA), and collagen. In addition, it is also associated with the metabolic reprogramming of kidney cells.
While analyzing the relationship between metabolic dysregulation and interstitial fibrosis, the researchers observed the metabolic reprogramming of kidney cells, namely myofibroblasts and renal tubular epithelial cells, during kidney injury. This occurrence affects the progression of chronic kidney disease.
During the metabolic reprogramming of kidney cells, a significant decrease in fatty acid oxidation (FAO) occurs along with a metabolic switch to glycolysis. These manifestations lead to immune cell infiltration and interstitial fibrosis. Several animal models of renal fibrosis have shown that attenuation of fibrosis is possible through inhibition of glycolysis and restoration of FAO using genetic or pharmacological approaches.
DNA-dependent protein kinase (DNA-PK), a ternary complex consisting of a catalytic subunit (DNA-PKcs) and a Ku70/80 heterodimer, is activated by reactive oxygen species (ROS) or DNA double-strand breaks (DSBs). DNA-PK facilitates non-homologous end joining (NHEJ) by connecting reprogrammed DSBs, which is critical for lymphocyte recombination. Therefore, DNA-PKcs mutations inhibit the development of T and B lymphocytes.
DNA-PKcs plays an essential role in various metabolic functions, such as phosphorylation of the transcription factor USF-1 that promotes insulin-induced fatty acid synthesis and metabolic degradation during aging. In addition, a previous study revealed that DNA-PKcs regulates the activation target of rapamycin (mTOR). Although the DNA damage response (DDR) has been associated with renal epithelial injury, little evidence has been documented about its role in epithelial dedifferentiation and myofibroblast activation in progressive CKD.
About the study
Increased expression of DNA-PKcs has been found in fibrotic kidneys, leading to the development of CKD. The present study also revealed that DNA-PKcs expression was induced by TGFβ1-SMAD signaling, and knockdown of DNA-PKcs blocked SMAD2/SMAD3. These results indicate a new pathway associated with the activation of TGFβ1-SMAD signaling in fibrosis.
worldwide prkdc A gene knockout mouse model was developed and used in this study. in vivo Experiments using this rat model suggested that elimination of DNA-PKcs resulted in a debilitating renal tubular injury along with a reduction in the progression of renal interstitial fibrosis in unilateral ureteral obstruction (UUO) and ischemic ischemia (UIR) rat models.
The current study failed to confirm whether DNA-PK promotes renal fibrosis independently of lymphocytes because lymphocyte deficiency is the most prominent phenotype of DNA-PKcs.– / – mice. Therefore, to remove the effect of lymphocyte deficiency, the authors generated proximal renal tubular epithelial cells that possess specific knockdown of DNA-PKcs. in vivousing CRISPR/cas9-compatible mice.
a Metabolic analysis of kidney tissue from each group as indicated. The heatmap image shows the relative levels of metabolites in the glycolysis pathway, fatty acid metabolism and the Krebs cycle in kidneys from each group (n = 4). Bars represent statistical analysis of representative metabolites in the kidneys of each group (mean ± SD, n = 4 mice per group). One-way ANOVA followed by Tukey’s multiple comparisons test was used to determine p-values. B A working model (template generated with BioRender.com) demonstrates that DNA-PKcs mediates activation of Raptor/mTORC1 signaling through TAF7 phosphorylation and promotes metabolic reprogramming in injured epithelial cells and myofibroblasts.
Remarkably, a renal tubular deletion of DNA-PKcs was also found to impede the progression of renal interstitial fibrosis in UUO. in the laboratory Experiments revealed that DNA-PKcs deficiency was able to maintain the phenotype of tubular epithelial cells and regulate interstitial fibroblast activation in vitro. These results indicate that DNA-PKcs facilitate myofibroblast activation and epithelial dissociation without any direct association with lymphocyte deficiency.
The antifibrotic effects of NU7441, a highly specific DNA-PKcs inhibitor, were studied. In both UUO and UIR mouse models, NU7441 treatment was able to significantly attenuate the progression of renal interstitial cells. At physiological doses, NU7441 can partially inhibit DNA-PK.
both of them in vivo And in the laboratory Studies have shown that DNA-PKcs deficiency does not exacerbate DSBs, indicating that DNA-PKcs mediates renal injury and renal interstitial fibrosis. Furthermore, analysis of phosphoproteomics revealed reduced TAF7 phosphorylation in DNA-PKcs kidney tissues.– / – mice. Interestingly, TAF7 deficiency prevented the proteolytic phenotype of TGFβ1-induced renal fibroblasts and epithelial cells.
The occupational effects of TAF7 were almost completely blocked by the lack of DNA-PKcs in renal epithelial cells. Our results indicate that TAF7 is a substrate for DNA-PKcs kinase activity and that DNA-PKcs-mediated phosphorylation of TAF7 exacerbates renal fibrosis. ChIP screening showed that TAF7 could bind to Raptor promoter directly, however, the underlying mechanism must be elucidated in future research. The authors indicated that DNA-PKcs mediates activation of RAPTOR/mTORC1 signaling through TAF7 phosphorylation.
DNA-PKcs activity was found to be undetectable in normal kidneys, in contrast to a significant increase during CKD. DNA-PKcs facilitate activation of RAPTOR/mTORC1 signaling via phosphorylation of TATA box-binding protein-binding factor 7 (TAF7) in CKD. DNA-PKcs inhibition restores metabolic reprogramming in affected kidney cells, such as epithelial cells and myofibroblasts, in chronic kidney disease. Thus, DNA-PKcs could be an important target for the treatment of CKD.