Objective  To lay the groundwork for formulating novel immunotherapies through understanding the regulatory role of ferroptosis and its function in immune microenvironment in ANCA-associated vasculitis (AAV) with renal injury.

Methods  Kidney data sets on AAV were downloaded from the database of Gene Expression Omnibus (GEO). Based upon the results of differential expression, consensus clustering algorithm was employed for identifying the subtypes of iron mortality. Single sample gene set enrichment analysis (ssGSEA) and gene set variation analysis (GSVA) were performed for evaluating the immune invasion and signaling pathways of subtypes. Key ferroptosis-related genes (FRGs) were further screened by LASSO and SVM-RFE algorithms and verified by independent data sets. CIBERSORT was utilized for assessing the abundance of infiltrating immune cells for FRGs. Finally a clinical diagnostic model of FRGs was constructed by rsm package. And the correlation between FRGs and renal function was examined by Nephroseq V5 database.

Results  Twenty-four ferroptosis related genes were significantly differentially expressed in AAV with kidney injury. Unsupervised cluster analysis revealed the regulatory patterns of two different ferroptosis subtypes with significant differences in gene expression, immune infiltration and biological functional pathways. A set of FRGs composed of ALOX5, CD44, CRYAB, TP53, and FTH1 was selected by two machine learning algorithms. It could effectively distinguish AAV with kidney injury from normal control group. CCR, macrophage and HLA were correlated positively with FRGs. Area under ROC curve of clinical diagnostic model constructed by FRGs was 0. 961. FRGs were correlated negatively with glomerular filtration rate (GFR). However, except for CRYAB and FTH1, other FRGs were correlated positively with serum creatinine (Scr). It implicated their potential relevance to renal injury in ANCA-associated vasculitis (AAV) and their potential as prognostic biomarkers.

Conclusions  Ferroptosis in AAV with kidney injury is correlated closely with immune microenvironment. It provides rationales for devising new treatments for AAV with kidney injury through a better understanding the pattern of ferroptosis.