To determine the relevance of DNA-PKcs activity and renal fibrosis in vivo, expression of fibronectin (FN), a crucial gene related to kidney fibrosis, was analyzed by immunohistochemical staining, and Sirius red staining was also performed to analyze the degree of interstitial fibrosis in CKD patients (Fig. 1a). The gene discussed is FN1; the disease is chronic kidney disease.