The Clinical Impact of Glomerular Immunoglobulin M Deposition in Patients with Type 2 Diabetic Nephropathy

Pathological mechanism of immune disorders in diabetic kidney disease and intervention strategies

Diabetic kidney disease is one of the most severe chronic microvascular complications of diabetes and a primary cause of end-stage renal disease. Clinical studies have shown that renal inflammation is a key factor determining kidney damage during diabetes. With the development of immunological technology, many studies have shown that diabetic nephropathy is an immune complex disease, and that most patients have immune dysfunction. However, the immune response associated with diabetic nephropathy and autoimmune kidney disease, or caused by ischemia or infection with acute renal injury, is different, and has a com-plicated pathological mechanism. In this review, we discuss the pathogenesis of diabetic nephropathy in immune disorders and the intervention mechanism, to provide guidance and advice for early intervention and treatment of diabetic nephropathy.

Complement Cascade Proteins Correlate with Fibrosis and Inflammation in Early-Stage Type 1 Diabetic Kidney Disease in the Ins2Akita Mouse Model

Diabetic kidney disease (DKD) is characterized by histological changes including fibrosis and inflammation. Evidence supports that DKD is mediated by the innate immune system and more specifically by the complement system. Using Ins2Akita T1D diabetic mice, we studied the connection between the complement cascade, inflammation, and fibrosis in early DKD. Data were extracted from a previously published quantitative-mass-spectrometry-based proteomics analysis of kidney glomeruli of 2 (early DKD) and 4 months (moderately advanced DKD)-old Ins2Akita mice and their controls A Spearman rho correlation analysis of complement- versus inflammation- and fibrosis-related protein expression was performed. A cross-omics validation of the correlation analyses' results was performed using public-domain transcriptomics datasets (Nephroseq). Tissue sections from 43 patients with DKD were analyzed using immunofluorescence. Among the differentially expressed proteins, the complement cascade proteins C3, C4B, and IGHM were significantly increased in both early and later stages of DKD. Inflammation-related proteins were mainly upregulated in early DKD, and fibrotic proteins were induced in moderately advanced stages of DKD. The abundance of complement proteins with fibrosis- and inflammation-related proteins was mostly positively correlated in early stages of DKD. This was confirmed in seven additional human and mouse transcriptomics DKD datasets. Moreover, C3 and IGHM mRNA levels were found to be negatively correlated with the estimated glomerular filtration rate (range for C3 rs = -0.58 to -0.842 and range for IGHM rs = -0.6 to -0.74) in these datasets. Immunohistology of human kidney biopsies revealed that C3, C1q, and IGM proteins were induced in patients with DKD and were correlated with fibrosis and inflammation. Our study shows for the first time the potential activation of the complement cascade associated with inflammation-mediated kidney fibrosis in the Ins2Akita T1D mouse model. Our findings could provide new perspectives for the treatment of early DKD as well as support the use of Ins2Akita T1D in pre-clinical studies.

The Complement Pathway: New Insights into Immunometabolic Signaling in Diabetic Kidney Disease

Significance: The metabolic disorder, diabetes mellitus, results in microvascular complications, including diabetic kidney disease (DKD), which is partly believe to involve disrupted energy generation in the kidney, leading to injury that is characterized by inflammation and fibrosis. An increasing body of evidence indicates that the innate immune complement system is involved in the pathogenesis of DKD; however, the precise mechanisms remain unclear. Recent Advances: Complement, traditionally thought of as the prime line of defense against microbial intrusion, has recently been recognized to regulate immunometabolism. Studies have shown that the complement activation products, Complement C5a and C3a, which are potent pro-inflammatory mediators, can mediate an array of metabolic responses in the kidney in the diabetic setting, including altered fuel utilization, disrupted mitochondrial respiratory function, and reactive oxygen species generation. In diabetes, the lectin pathway is activated via autoreactivity toward altered self-surfaces known as danger-associated molecular patterns, or via sensing altered carbohydrate and acetylation signatures. In addition, endogenous complement inhibitors can be glycated, whereas diet-derived glycated proteins can themselves promote complement activation, worsening DKD, and lending support for environmental influences as an additional avenue for propagating complement-induced inflammation and kidney injury. Critical Issues: Recent evidence indicates that conventional renoprotective agents used in DKD do not target the complement, leaving this web of inflammatory stimuli intact. Future Directions: Future studies should focus on the development of novel pharmacological agents that target the complement pathway to alleviate inflammation, oxidative stress, and kidney fibrosis, thereby reducing the burden of microvascular diseases in diabetes. Antioxid. Redox Signal. 37, 781-801.

Immune repertoire and evolutionary trajectory analysis in the development of diabetic nephropathy

Diabetic nephropathy (DN) is the leading cause of death and the greatest risk to the lives of people with advanced diabetes. Yet, the molecular mechanisms underlying its development and progression remain unknown. In this research, we studied the primary pathways driving DN using transcriptome sequencing and immune repertoire analysis. Firstly, we found that the diversity and abundance of the immune repertoire in late DN were significantly increased, while there was no significant change in early DN. Furthermore, B cell-mediated antibody responses may be the leading cause of DN progression. By analyzing master regulators, we found the key DN-driving transcription factors. In the late stage of DN, immune cells, fibroblasts, and epithelial cells were abundant, but other stromal cells were few. Early DN kidneys had a higher tissue stemness score than normal and advanced DN kidneys. We showed that DN progression involves proximal tubular metabolic reprogramming and stemness restoration using Monocle3. Through WGCNA, we found that co-expression modules that regulate DN progression and immune repertoire diversity mainly regulate immune-related signaling pathways. In addition, we also found that early DN had apparent activation of immune-related signaling pathways mainly enriched in immune cells. Finally, we found that activation of fibroblasts is typical of early DN. These results provide a research basis for further exploring the molecular biology and cellular mechanisms of the occurrence and development of DN and provide a theoretical basis for the prevention and treatment of DN.

Meta-Analysis and Bioinformatics Detection of Susceptibility Genes in Diabetic Nephropathy

The latest meta-analysis of genome-wide linkage studies (GWLS) identified nine cytogenetic locations suggestive of a linkage with diabetic nephropathy (DN) due to type 1 diabetes mellitus (T1DM) and seven locations due to type 2 diabetes mellitus (T2DM). In order to gain biological insight about the functional role of the genes located in these regions and to prioritize the most significant genetic loci for further research, we conducted a gene ontology analysis with an over representation test for the functional annotation of the protein coding genes. Protein analysis through evolutionary relationships (PANTHER) version 16.0 software and Cytoscape with the relevant plugins were used for the gene ontology analysis, and the overrepresentation test and STRING database were used for the construction of the protein network. The findings of the over-representation test highlight the contribution of immune related molecules like immunoglobulins, cytokines, and chemokines with regard to the most overrepresented protein classes, whereas the most enriched signaling pathways include the VEGF signaling pathway, the Cadherin pathway, the Wnt pathway, the angiogenesis pathway, the p38 MAPK pathway, and the EGF receptor signaling pathway. The common section of T1DM and T2DM results include the significant over representation of immune related molecules, and the Cadherin and Wnt signaling pathways that could constitute potential therapeutic targets for the treatment of DN, irrespective of the type of diabetes.

Clinical relevance of glomerular IgM deposition in patients with lupus nephritis

BACKGROUND

The aim of the study was to investigate the clinical relevance of IgM deposition in patients with lupus nephritis (LN) in a large cohort.

RESULTS

217 patients with renal biopsy-proven active LN were enrolled. The associations between glomerular IgM deposition and clinicopathological parameters were further analyzed. IgM deposition was positively correlated with glomerular C1q and C3 deposition moderately (r = 0.436, P < 0.001; r = 0.408, P < 0.001, respectively), and inversely correlated with plasma levels of C3 and CFH mildly (r =  - 0.138, P = 0.043; r =  - 0.147, P = 0.037, respectively). By multivariate analysis, we found that glomerular IgM deposition independently contributed to glomerular C3 deposition in patients with LN (OR = 2.002, 95% CI 1.295-3.094, P = 0.002). In addition, we also found that patients with IgM 0-2+ had similar plasma CFH levels, but in patients with IgM3+-4+, plasma CFH levels were significantly lower (300.4 ± 155.8 μg/mL vs. 429.9 ± 187.5 μg/mL, P < 0.001). Furthermore, patients with high density of glomerular IgM and low levels of CFH had heavier proteinuria, higher serum creatinine and lower plasma C3 levels (5.7 ± 3.1 g/d vs. 4.7 ± 3.5 g/d, P = 0.037; 150.1 ± 121.0 μmol/L vs. 105.6 ± 97.1 μmol/L, P = 0.005; 0.3 ± 0.2 μg/L vs. 0.4 ± 0.2 μg/L, P = 0.04, respectively), comparing with those with low density of glomerular IgM and low levels of CFH.

CONCLUSIONS

Our results suggested the involvement of glomerular deposited IgM in complement activation and renal injury in LN.

Identification of fibronectin 1 (FN1) and complement component 3 (C3) as immune infiltration-related biomarkers for diabetic nephropathy using integrated bioinformatic analysis

Immune cell infiltration (ICI) plays a pivotal role in the development of diabetic nephropathy (DN). Evidence suggests that immune-related genes play an important role in the initiation of inflammation and the recruitment of immune cells. However, the underlying mechanisms and immune-related biomarkers in DN have not been elucidated. Therefore, this study aimed to explore immune-related biomarkers in DN and the underlying mechanisms using bioinformatic approaches. In this study, four DN glomerular datasets were downloaded, merged, and divided into training and test cohorts. First, we identified 55 differentially expressed immune-related genes; their biological functions were mainly enriched in leukocyte chemotaxis and neutrophil migration. The CIBERSORT algorithm was then used to evaluate the infiltrated immune cells; macrophages M1/M2, T cells CD8, and resting mast cells were strongly associated with DN. The ICI-related gene modules as well as 25 candidate hub genes were identified to construct a protein-protein interactive network and conduct molecular complex detection using the GOSemSim algorithm. Consequently, FN1, C3, and VEGFC were identified as immune-related biomarkers in DN, and a related transcription factor-miRNA-target network was constructed. Receiver operating characteristic curve analysis was estimated in the test cohort; FN1 and C3 had large area under the curve values (0.837 and 0.824, respectively). Clinical validation showed that FN1 and C3 were negatively related to the glomerular filtration rate in patients with DN. Six potential therapeutic small molecule compounds, such as calyculin, phenamil, and clofazimine, were discovered in the connectivity map. In conclusion, FN1 and C3 are immune-related biomarkers of DN.

Solidified glomerulosclerosis, identified using single glomerular proteomics, predicts end-stage renal disease in Chinese patients with type 2 diabetes

Few histological prognostic indicators for end-stage renal disease (ESRD) have been validated in diabetic patients. This biopsy-based study aimed to identify nephropathological risk factors for ESRD in Chinese patients with type 2 diabetes. Histological features of 322 Chinese type 2 diabetic patients with biopsy-confirmed diabetic nephropathy (DN) were retrospectively analysed. Cox proportional hazards analysis was used to estimate the hazard ratio (HR) for ESRD. Single glomerular proteomics and immunohistochemistry were used to identify differentially expressed proteins and enriched pathways in glomeruli. During the median follow-up period of 24 months, 144 (45%) patients progressed to ESRD. In multivariable models, the Renal Pathology Society classification failed to predict ESRD, although the solidified glomerulosclerosis (score 1: HR 1.65, 95% confidence interval [CI] 1.04-2.60; score 2: HR 2.48, 95% CI 1.40-4.37) and extracapillary hypercellularity (HR 2.68, 95% CI 1.55-4.62) were identified as independent risk factors. Additionally, single glomerular proteomics, combined with immunohistochemistry, revealed that complement C9 and apolipoprotein E were highly expressed in solidified glomerulosclerosis. Therefore, solidified glomerulosclerosis and extracapillary hypercellularity predict diabetic ESRD in Chinese patients. Single glomerular proteomics identified solidified glomerulosclerosis as a unique pathological change that may be associated with complement overactivation and abnormal lipid metabolism.

Clinical and Pathological Characteristics of Patients With Nonproteinuric Diabetic Nephropathy

INTRODUCTION

As the most common complication of diabetes mellitus (DM), diabetic nephropathy (DN) was initially considered to begin with proteinuria preceding the progression of renal insufficiency. This clinical paradigm has been questioned in the late decades, as many DM patients without proteinuria have progressive renal insufficiency. However, the characteristics of nonproteinuric DN were not fully clear yet.

PATIENTS AND METHODS

A total of 390 patients with renal biopsy-proven DN in our center were retrospectively recruited in the current study. Clinical and histopathological data of the patients were analyzed. We used propensity score-matching methods to address the imbalance of age, sex, and diabetes duration for comparative analyses.

RESULTS

Among all the renal biopsy-proven DN patients with renal biopsy proven DN, 18 patients were classified as nonproteinuric DN. Compared with 36 propensity score-matched proteinuric DN patients, diabetic retinopathy (DR) was less frequent in nonproteinuric DN patients (38.9% vs. 66.4%, p<0.05). During the follow-up of 24.0 (12.0-42.0) months, the probability of developing the end-stage renal disease (ESRD) was significantly lower in nonproteinuric DN patients than in proteinuric ones in both the propensity score-matched cohort and overall cohort (log-rank test, p<0.001 and p<0.001, respectively).

CONCLUSIONS

Compared with proteinuric DN patients, DR was less frequent in nonproteinuric DN patients. Nonproteinuric DN patients had better renal outcomes than proteinuric DN patients.

Implications of immunoglobulin G deposit in glomeruli in Chinese patients with diabetic nephropathy

BACKGROUND

In the current study, we explored the associations of glomerular immunoglobulin G (IgG) deposit and further investigated the pattern of IgG subclass deposition in the renal biopsy specimens from patients with diabetic nephropathy (DN).

METHODS

A total of 170 inpatients with type 2 diabetes mellitus and biopsy-proven DN who were followed up for at least 1 year were retrospectively recruited. Renal outcomes were defined by DN progression (end-stage renal disease [ESRD] or ≥ 50% reduction in estimated glomerular filtration rate [eGFR] from baseline). Additionally, 38 renal biopsy specimens of patients with renal IgG deposit underwent the immunofluorescence IgG1-4 staining.

RESULTS

The median follow-up period was 22 months. During follow-up, 38.23% (65) of patients progressed to ESRD, and 6.47% (11) of patients had an eGFR decline ≥50%. The multivariate Cox analysis demonstrated that the glomerular IgG deposit (hazard ratio, 1.835; 95% CI, 1.013-3.324, P = .045) was still significantly associated with DN progression when adjusted for the important clinical variables and pathological findings. In addition, a logistic regression showed that the glomerular IgG deposit was independently associated with glomerular basement membrane (GBM) thickness (odds ratio [OR], 1.276; 95% CI, 1.046-1.558; P = .016), Kimmelstiel-Wilson nodules formation (OR, 3.822; 95% CI, 1.052-13.881; P = .042), and C3 deposit in the glomeruli (OR, 124.883; 95% CI, 20.754-751.472; P < .001). The IgG subclass staining showed that IgG1 deposit along the GBM tended to be dominant (28/38) in IgG (+) patients with DN.

CONCLUSIONS

The glomerular IgG deposit affected glomerular structure and emerged as an independent risk factor for the renal clinical outcomes. In addition, IgG1 predominantly deposited along the GBM among the DN patients with IgG (+), which might be involved in the renal injury and progression of DN.