Upregulated Glomerular Rubicon is Associated with Decreased Glomerular Filtration Rate in Males and Immune Infiltration in Chronic Kidney Disease

Abstract

Background: Rubicon is highly expressed in aging kidneys, but its role in chronic kidney disease (CKD) has not been investigated. This study aimed to explore the altered expression of Rubicon in the kidneys, tubulointerstitia, and glomeruli of CKD patients. Additionally, this study analyzed glomerular Rubicon expression based on different disease types and patient sex and investigated potential mechanisms of glomerular Rubicon through bioinformatic methods. Methods: This study analyzed sequencing and clinical data of 61 kidney samples, 199 glomerulus samples, and 201 tubulointerstitium samples from the Nephroseq database. The aim was to investigate the correlation between Rubicon and the sex-based estimated glomerular filtration rate (eGFR) and the predictive value of Rubicon for CKD. Glomerular Rubicon alternation was validated through immunohistochemical analysis of 56 kidney samples collected from CKD patients, as well as the correlation between Rubicon expression and eGFR. Furthermore, correlation analysis and weighted gene co-expression network analysis were performed to identify genes associated with Rubicon, followed by pathway enrichment analysis. Immune cell types associated with Rubicon were identified via correlation analysis between glomerular Rubicon and immune cell proportion counted through the microenvironment cell populations counter (MCP-counter) algorithm. Results: Rubicon expression was found to be upregulated in the kidneys of CKD patients, particularly in the glomeruli. Moreover, baseline Rubicon expression in glomeruli was higher in females than in males. In males, glomerular Rubicon expression was affected by and inversely correlated with the eGFR. A receiver operating characteristic curve analysis revealed that glomerular Rubicon expression might have predictive value for male patients with CKD. Results of immunohistochemistry (IHC) analysis and correlation analysis validated glomerular Rubicon upregulation in kidneys of CKD patients and a negative correlation between glomerular Rubicon and eGFR in males. Further bioinformatic analysis showed that Rubicon expression was associated with immune and inflammatory pathways, particularly those involved in immune cell activation and migration. Rubicon expression was closely correlated with monocyte/macrophage and dendritic cell infiltration scores. Conclusions: Rubicon is a protein that is upregulated in the glomeruli of patients with CKD. In males, its expression is negatively correlated with eGFR. Rubicon is closely related to immune and inflammatory pathways, especially those involving monocyte/macrophage and dendritic cell infiltration.