The onset of DN is instigated by a confluence of various factors, nevertheless, the specific mechanisms of this phenomenon are yet to be elucidated19, 20. Currently, the early diagnosis and treatment of DN present challenges, necessitating the exploration of novel molecular pathways to solving this problem. Based on prior studies and experiments, the onset of DN, to some extent, is associated with immune infiltration, immune mediators, and oxidative stress21–23. The NEBL gene, located on chromosome 10q22.2, codes for a protein called Nebulette, which has traditionally been linked to heart function. However, recent studies have revealed its relationship with nephropathy, arousing curiosity about its potential significance in DN24. This study involved the retrieval of transcriptomic datasets from the GEO database, employing bioinformatics methodologies to pinpoint differentially expressed genes pivotal in DN. Through ML-based screening, four NEBL-related genes, MPP5, TGFBR3, PCMTD2, and C1orf21, were identified. ROC analysis showed that the NEBL gene and four NEBL-related genes possessed the btility of distinguishing DN samples and controls, suggesting that they might be developed as diagnostic biomarkers. In addition, the functions of NEBL genes and biomarkers were investigated with the aim of understanding their potential molecular mechanisms of them on occurrence and development of DN.
Membrane Protein Palmitoylated 5 (MPP5), also recognized as Protein Associated with Lin7 (PALS1), functions as a fundamental constituent of the apical membrane determining CRB complex within the nephron, and the absence of Pals1 leads to tubular dilation and cyst formation25. However, there are a scarcity of studies investigating the role of MPP5 in the development of DN. In our study, we observed that down-regulated MPP5 also had better diagnostic efficacy as a result of its AUC value of 1.
TGFBR3, a membrane proteoglycan, serves as a co-receptor with other transforming growth factor receptors and is expressed in glomerular podocytes, mesangial cells, and endothelial cells26, 27. With a high specificity for the glomerulus, TGFBR3 exhibits a particular affinity for two subtypes of TGF-β, forming specific binding interactions A decrease in TGF-β secretion triggers cytokines to stimulate T helper1 (Th1) cells, leading to the production of macrophage M1 and fostering the inflammatory response of Th1 cells, which is an essential factor in the progression of DN. The study suggested that a potential therapeutic target for DN involving intervention with TGF-β could be TGFBR328. Additionally, we observed elevated levels of TGFBR3 in DN patients, demonstrating diagnostic accuracy values with AUC exceeding 0.70. The outcomes from GeneMANIA indicated that TGFBR3, TGF-β1, TGF-β2, and TGF-β3 might collaboratively influence the progression of DN through physical interactions. This reinforces the credibility of the findings in this study.
Protein-L-Isoaspartate O-Methyltransferase Domain Containing 2 (PCMTD2) is anticipated to possess protein-L-isoaspartate (D-aspartate) O-methyltransferase activity and play a role in protein methylation, and its predicted activity is situated in the cytoplasm. Chromosome 1 Open Reading Frame 21 (C1orf21) is classified as a protein-coding gene. Diseases linked to C1orf21 encompass thymoma type B2 and renal artery atheroma. PCMTD2 and C1orf21, particularly in the context of kidney disease, have limited existing knowledge. However, our study heightened the enhanced expression levels of PCMTD2 and C1orf21 in DN patients compared to controls. Considering the limited available literature regarding the influence of PCMTD2 and C1orf21 on the progression of DN, it is prudent to make inference based on the results of this study, generally, increased gene expression levels is believed to be linked with an elevated disease risk. The study's findings revealed increased expression of PCMTD2 and C1orf21 in DN patients, suggesting that these genes might serve as potential risk factors for DN. However, further analysis and experimental validation are requisite to substantiate this hypothesis.
GO and KEGG enrichment analysis found that DEGs mainly enriched in BPs related to kidney development, indicating that these DEGs might be related to the development of DN, and this result further verified the reliability of DEGs. In our analysis, we found that the AGE-RAGE signaling pathway played an important role in DN. Previous studies have demonstrated that the presence and expression of AGE and RAGE have increased in human diabetic kidneys, especially in the glomerulus, glomerular epithelial cells (podocytes) and endothelial cells29. The absence of RAGE has been found to effectively mitigate glomerular sclerosis, glomerular basement membrane thickening, podocyte loss, as well as decline in glomerular filtration rate (GFR). In addition, RAGE is also present in the angiotensin II (angII) axis, which is also associated with the expression of RAGE and the occurrence of ND30.
GSEA revealed that the NEBL gene demonstrated enrichment in immune-related pathways. Additionally, GSEA demonstrated significant enrichment of the NEBL gene and four biomarkers in pathways associated with ribosomes, the IgA-produced intestinal immune network, systemic lupus erythematosus, primary immunodeficiency, leishmania infection, cell adhesion molecules (CAM), glutathione metabolism, and others. Besides, a significant enrichment of biomarkers, such as the NEBL and TGFBR3, in pathways associated with immunity. In conclusion, we infered that NEBL and TGFBR3 might play similar immune functions in the development of DN.
The findings of immune infiltration analysis elucidated a close association between the development of DN and CD56 NK cells, mast cells, and regulatory T cells. According to previous studies, Natural Killer T (NKT) cells can be found to be associated with kidney damage as well as vascular damage in type 2 diabetes, but few studies have focused on NKT cells and DN, especially CD56 NK cells, which would be a new focus on DN31–33.
Drug prediction revealed two compounds that were most closely targeted towards NEBL gene and biomarkers, bisphenol A (BPA) and Valproic Acid. BPA demonstrates an association with low-grade albuminuria, a manifestation characteristic of the initial phases of DN34. Moreover, findings certified that valproic acid mitigated the diabetes-induced upregulation of complement C5a receptors, concurrently diminishing indicators of cellular senescence and the senescence-associated secretory phenotype. The attenuation of cellular senescence in the diabetic context assumes significance, given its implication in the pathogenesis of diabetic kidney disease35. Consequently, therapeutic interventions targeting cellular senescence, such as complement inhibitors, emerge as a novel and promising avenue for the treatment of diabetic kidney disease. Based on current research, the reduction of NEBL in DN may exacerbate the condition. We hypothesize that BPA may reverse the expression of NEBL in DN, thereby potentially alleviating the progression of DN.
Nevertheless, it is crucial to acknowledge the limitations of this study. The evidence relies on publicly available data, and while we validated the expression using another dataset, additional experiments are imperative to substantiate NEBL and the four associated genes as diagnostic markers before their clinical applicability can be established. At the same time, the clinical application research of drugs also needs experimental proof, and we will continue to pay attention to the relevant research progress of DN.