Abstract:

Objective To evaluate the expression characteristics of the FBJ murine osteosarcoma viral oncogene homolog B（FOSB） gene in immunoglobulin A nephropathy （IgAN） and common chronic kidney diseases （CKDs）， and to determine its value as a potential key candidate gene or biomarker. Methods The RNA sequencing datasets for IgAN，diabetic kidney disease （DKD）， membranous nephropathy（MN）， and minimal change disease（MCD） glomerular samples were downloaded from the Gene Expression Omnibus（GEO） database. The feature genes for CKD were identified using machine learning methods including least absolute shrinkage and selection operator（LASSO） regression， random forest（RF）， and support vector machine（SVM）. Gene Ontology（GO） functional enrichment and Kyoto Encyclopedia of Genes and Genomes（KEGG） signaling pathway enrichment analyses were performed on the identified IgAN feature genes. The “pROC” package was used to plot the receiver operating characteristic（ROC） curves to evaluate the diagnostic efficacy of IgAN feature genes.The gene with the highest diagnostic value was selected for Gene Set Enrichment Analysis（GSEA） and correlation analysis with core immune cells in IgAN. Clinical correlation analysis between the FOSB expression level in kidney tissue and renal function was performed using the Nephroseq v5 platform. Kidney tissue samples were collected from 5 cases of IgAN patients，DKD patients， MCD patients， and MN patients，respectively，along with 5 samples of adjacent normal kidney tissues （control group）. Immunohistochemistry staining method was used to detect the expression levels of FOSB protein in tissue samples in various groups. Results A total of 110 differentially expressed genes（DEGs） were identified in IgAN glomeruli， among which FOSB， NR4A2， and DUSP1 were identified as the feature genes. Compared with control group， the expression level of FOSB mRNA in IgAN group was significantly decreased（P<0.05）. The GO fuctional enrichment analysis results revealed that these IgAN feature genes were primarily enriched in biological processes related to dopamine biosynthesis，midbrain dopaminergic neuron differentiation， peptidyl-serine/threonine dephosphorylation， and response to corticosterone. The KEGG signaling pathway enrichment analysis results showed that the DEGs were significantly enriched in cocaine addiction，amphetamine addiction， interleukin 17 （IL-17） signaling pathway，aldosterone synthesis and secretion， and serotonergic synapse. The ROC curve analysis results demonstrated that FOSB showed high diagnostic accuracy for IgAN. GSEA analysis revealed that arginine and proline metabolism，butyrate metabolism， erythroblastic leukemia viral oncogene homolog（ERBB） signaling pathway，mitogen-activated protein kinase （MAPK） signaling pathway， and fructose and mannose metabolism pathways were enriched in FOSB high-expression group， while allograft rejection， extracellular matrix receptor interaction，and type 1 diabetes pathways were significantly enriched in FOSB low-expression group. The immune cell infiltration analysis results identified natural killer cells， neutrophils，and M1 macrophages as core immune cells in IgAN， and the expression of FOSB gene was positively correlated with neutrophil infiltration （r=0.42， P<0.05）. The immunohistochemistry analysis results demonstrated that compared with control group，the expression level of FOSB protein in glomeruli of the patients in IgAN， DKD， MN， and MCD groups were significantly decreased（P<0.05）. Conclusion The expressions of FOSB gene in the glomeruli tissue of IgAN，DKD，MN，and MCD patients ware decreased， suggesting FOSB may represent a potential biomarker for IgAN.

Key words: FBJ murine osteosarcoma viral oncogene homolog B, Immunoglobulin A nephropathy, Bioinformatics analysis, Immunohistochemistry, Chronic kidney disease, Candidate gene