Associations of Genetic Variants Contributing to Gut Microbiota Composition in Immunoglobin A Nephropathy

Association between the gut microbiota and diabetic nephropathy: a two-sample Mendelian randomization study

Numerous studies have revealed a correlation between the risk of developing diabetic nephropathy (DN) and the gut microbiota (GM) composition. However, it remains uncertain whether the GM composition causes DN. We aimed to explore any potential causal links between the GM composition and the risk of developing DN. A meta-analysis conducted by the MiBioGen consortium of the largest genome-wide association study (GWAS) provided aggregated data on the GM. DN data were obtained from the IEU database. The inverse-variance weighting (IVW) method was employed as the primary analytical approach. The IVW analysis indicated that genus Dialister (OR = 0.51, 95% CI: 0.34-0.77, p = 0.00118) was protective against DN. In addition, class Gammaproteobacteria (OR = 0.47, 95% CI: 0.27-0.83, p = 0.0096), class Lentisphaeria (OR =0.76, 95% CI: 0.68-0.99, p = 0.04), order Victivallales (OR = 0.76, 95% CI: 0.58-0.99, p = 0.04), and phylum Proteobacteria (OR = 0.53, 95% CI: 0.33-0.85, p = 0.00872) were negatively associated with the risk of developing DN. Genus LachnospiraceaeUCG008 (OR =1.45, 95% CI: 1.08-1.95, p = 0.01), order Bacteroidales (OR = 1.59, 95% CI: 1.02-2.49, p = 0.04), and genus Terrisporobacter (OR = 1.98, 95% CI: 1.14-3.45, p = 0.015) were positively associated with the risk of developing DN. In this study, we established a causal relationship between the genus Dialister and the risk of developing DN. Further trials are required to confirm the protective effects of probiotics on DN and to elucidate the precise protective mechanisms involving genus Dialister and DN.

Importance of good hosting: reviewing the bi-directionality of the microbiome-gut-brain-axis

Gut microorganisms have been shown to significantly impact on central function and studies that have associated brain disorders with specific bacterial genera have advocated an anomalous gut microbiome as the pathophysiological basis of several psychiatric and neurological conditions. Thus, our knowledge of brain-to-gut-to microbiome communication in this bidirectional axis seems to have been overlooked. This review examines the known mechanisms of the microbiome-to-gut-to-brain axis, highlighting how brain-to-gut-to-microbiome signaling may be key to understanding the cause of disrupted gut microbial communities. We show that brain disorders can alter the function of the brain-to-gut-to-microbiome axis, which will in turn contribute to disease progression, while the microbiome-to gut-to brain direction presents as a more versatile therapeutic axis, since current psychotropic/neurosurgical interventions may have unwanted side effects that further cause disruption to the gut microbiome. A consideration of the brain-to-gut-to-microbiome axis is imperative to better understand how the microbiome-gut-brain axis overall is involved in brain illnesses, and how it may be utilized as a preventive and therapeutic tool.

Causal relationship between gut microbiota and kidney diseases: a two-sample Mendelian randomization study

Background

The interplay between gut microbiome genera and inflammatory kidney-related diseases, such as nephrotic syndrome, glomerulonephritis, tubulo-interstitial nephritis, and chronic kidney disease, has been observed. However, the causal relationships between specific bacterial genera and these renal diseases have not been fully elucidated.

Objective

To investigate the potential causal links between different genera of the gut microbiome and the susceptibility to various renal conditions utilizing two-sample Mendelian randomization (MR) analyses.

Materials and methods

Genome-wide association study (GWAS) summary statistics of gut microbiota and inflammatory kidney-related diseases were obtained from published GWASs. Two-sample MR analyses were conducted using methods including inverse-variance weighted (IVW), MR Egger, and others to identify potential causal links between gut microbial genera and renal conditions. Sensitivity analyses, including Cochran's Q test and the MR-PRESSO global test, were performed to validate the robustness of the results and detect horizontal pleiotropy. In addition, a reverse MR analysis was conducted to assess reverse causation possibilities.

Results

By synthesizing insights from both primary and sensitivity analyses, this study unveiled critical associations of 12 bacterial genera with nephrotic syndrome, 7 bacterial genera with membranous nephropathy, 3 bacterial genera with glomerulonephritis, 4 bacterial genera with acute tubulo-interstitial nephritis, 6 bacterial genera with chronic tubulo-interstitial nephritis, and 7 bacterial genera with chronic kidney disease. Various genera were pinpointed as having either positive or negative causal relationships with these renal conditions, as evidenced by specific ranges of IVW-OR values (all P< 0.05). The congruence of the sensitivity analyses bolstered the primary findings, displaying no marked heterogeneity or horizontal pleiotropy. Notably, the reverse MR analysis with nephritis as the exposure did not reveal any causal relationships, thereby strengthening the resilience and validity of the primary associations.

Conclusion

This study explored the causal associations between several gut microbial genera and the risk of several inflammatory kidney-related diseases, uncovering several associations between specific gut microbial genera and nephrotic syndrome, membranous nephropathy, glomerulonephritis, tubulo-interstitial nephritis, and chronic kidney disease. These findings enhance our understanding of the complex interplay between the gut microbiome and kidney diseases, and they will be beneficial for early diagnosis and subsequent treatment.

Associations of genetic variants contributing to gut microbiota composition in diabetic nephropathy

Introduction

The gut microbiota is strongly associated with multiple kidney diseases, and since microbial composition is heritable, we hypothesized that genetic variations controlling gut microbiota composition were associated with diabetic nephropathy susceptibility or clinical subphenotypes.

Methods

The genetic variations associated with gut microbiota were retrieved from the genome-wide association study database and analysed in our diabetic nephropathy susceptibility gene screening cohort. Candidate microorganisms with possible genetic associations were identified using the annotation of microbial quantitative trait loci. Finally, the candidate microorganisms were verified by 16S rDNA gene sequencing.

Results

There were 13 genetic variation loci associated with susceptibility to diabetic nephropathy. The TCF7L2 risk genotype was associated with a long duration of diabetes and high diastolic blood pressure, the ZCWPW2 risk genotype was associated with increased glycosylated hemoglobin, and the ZNRF3 risk genotype was associated with an increased urinary microalbumin-to-creatinine ratio. Both the ZNRF3 and SPECC1L risk genotypes were associated with the abundance of Lactococcus. 16S rDNA sequencing confirmed that there was indeed a significant difference in the Lactococcus genus between DN and DM patients.

Conclusions

In this study, we preliminarily confirmed that the gut microbiota of diabetic nephropathy patients is influenced by host genetics and provide a new basis for future accurate diagnosis and treatment.

Leveraging molecular quantitative trait loci to comprehend complex diseases/traits from the omics perspective

Comprehending the molecular basis of quantitative genetic variation is a principal goal for complex diseases or traits. Molecular quantitative trait loci (molQTLs) have made it possible to investigate the effects of genetic variants hiding behind large-scale omics data. A deeper understanding of molQTL is urgently required in light of the multi-dimensionalization of omics data to more fully elucidate the pertinent biological mechanisms. Herein, we reviewed molQTLs with the corresponding resource from the omics perspective and further discussed the integrative strategy of GWAS-molQTL to infer their causal effects. Subsequently, we described the opportunities and challenges encountered by molQTL. The case studies showed that molQTL is essential for complex diseases and traits, whether single- or multi-omics QTLs. Overall, we highlighted the functional significance of genetic variants to employ the discovery of molQTL in complex diseases and traits.

Does inflammatory bowel disease promote kidney diseases: a mendelian randomization study with populations of European ancestry

BACKGROUND

This study aimed to investigate a causal relationship between IBD and multiple kidney diseases using two-sample Mendelian randomization (MR) analyses.

METHODS

We selected a group of single nucleotide polymorphisms (SNPs) specific to IBD as instrumental variables from a published genome-wide association study (GWAS) with 86,640 individuals of European ancestry. Summary statistics for multiple kidney diseases were obtained from the publicly available GWAS. Genetic data from one GWAS involving 210 extensive T-cell traits was used to estimate the mediating effect on specific kidney disease. Inverse-variance weighted method were used to evaluate the MR estimates for primary analysis.

RESULTS

Genetic predisposition to IBD was associated with higher risk of IgA nephropathy (IgAN) (OR, 1.78; 95% CI, 1.45-2.19), but not membranous nephropathy, diabetic nephropathy, glomerulonephritis, nephrotic syndrome, chronic kidney disease, and urolithiasis. CD4 expression on CD4 + T cell had a significant genetic association with the risk of IgAN (OR, 2.72; 95% CI, 1.10-6.72). Additionally, consistent results were also observed when IBD was subclassified as ulcerative colitis (OR, 1.38; 95% CI, 1.10-1.71) and Crohn's disease (OR, 1.37; 95% CI, 1.12-1.68). MR-PRESSO and the MR-Egger intercept did not identify pleiotropic SNPs.

CONCLUSIONS

This study provides genetic evidence supporting a positive casual association between IBD, including its subclassification as ulcerative colitis and Crohn's disease, and the risk of IgAN. However, no casual association was found between IBD and other types of kidney diseases. Further exploration of IBD interventions as potential preventive measures for IgAN is warranted.

The Effects of Specific Gut Microbiota and Metabolites on IgA Nephropathy-Based on Mendelian Randomization and Clinical Validation

BACKGROUND

Although recent research suggests that alterations in gut microbiota and metabolites play a critical role in the pathophysiology of immunoglobulin A nephropathy (IgAN), the causal relationship between specific intestinal flora and metabolites and the risk of IgAN remains unclear.

METHOD

This study employed Mendelian randomization (MR) to investigate the causal association between gut microbiota and IgAN. To explore potential associations between gut microbiota and various outcomes, four MR methods were applied: inverse variance weighted (IVW), MR-Egger, weighted median, and weighted mode. If the results of the four methods are inconclusive, we prefer the IVW as the primary outcome. Additionally, MR-Egger, MR-PRESSO-Global, and Cochrane's Q tests were used to detect heterogeneity and pleiotropy. The stability of MR findings was assessed using the leave-one-out approach, and the strength of the causal relationship between exposure and outcome was tested using Bonferroni correction. Additional clinical samples were utilized to validate the results of Mendelian randomization, and the outcomes were visualized through an ROC curve, confusion matrix, and correlation analysis.

RESULT

This study examined a total of 15 metabolites and 211 microorganisms. Among them, eight bacteria and one metabolite were found to be associated with the risk of IgAN (p < 0.05). The Bonferroni-corrected test reveals that only Class. Actinobacteria (OR: 1.20, 95% CI: 1.07-1.36, p = 0.0029) have a significant causal relationship with IgAN. According to Cochrane's Q test, there is no substantial heterogeneity across different single-nucleotide polymorphisms (p > 0.05). Furthermore, MR-Egger and MR-PRESSO-Global tests (p > 0.05) showed no evidence of pleiotropy. No reverse causal association was found between the risk of IgAN and microbiota or metabolites (p > 0.05). Clinical specimens demonstrated the effectiveness and accuracy of Actinobacteria in distinguishing IgAN patients from those with other glomerular diseases (AUC = 0.9, 95% CI: 0.78-1.00). Additionally, our correlation analysis revealed a potential association between Actinobacteria abundance and increased albuminuria (r = 0.85) and poorer prognosis in IgAN patients (p = 0.01).

CONCLUSION

Through MR analysis, we established a causal link between Actinobacteria and the incidence of IgAN. Moreover, clinical validation using fecal samples indicated that Actinobacteria might be associated with the onset and poorer prognosis of IgAN. This finding could provide valuable biomarkers for early, noninvasive detection of the disease and potential therapeutic targets in IgAN.

IgA Nephropathy: Current Understanding and Perspectives on Pathogenesis and Targeted Treatment

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis worldwide, with varied clinical and histopathological features between individuals, particularly across races. As an autoimmune disease, IgAN arises from consequences of increased circulating levels of galactose-deficient IgA1 and mesangial deposition of IgA-containing immune complexes, which are recognized as key events in the widely accepted "multi-hit" pathogenesis of IgAN. The emerging evidence further provides insights into the role of genes, environment, mucosal immunity and complement system. These developments are paralleled by the increasing availability of diagnostic tools, potential biomarkers and therapeutic agents. In this review, we summarize current evidence and outline novel findings in the prognosis, clinical trials and translational research from the updated perspectives of IgAN pathogenesis.

Time-restricted feeding's effect on overweight and obese patients with chronic kidney disease stages 3-4: A prospective non-randomized control pilot study

Background

Time-restricted feeding (TRF) has become a popular weight loss method in recent years. It is widely used in the nutritional treatment of normal obese people and obese people with chronic diseases such as diabetes mellitus and hypertension, and has shown many benefits. However, most TRF studies have excluded chronic kidney disease (CKD) patients, resulting in a lack of sufficient evidence-based practice for the efficacy and safety of TRF therapy for CKD. Therefore, we explore the efficacy and safety of TRF in overweight and obese patients with moderate-to-severe stage CKD through this pilot study, and observe patient compliance to assess the feasibility of the therapy.

Methods

This is a prospective, non-randomized controlled short-term clinical trial. We recruited overweight and obese patients with CKD stages 3-4 from an outpatient clinic and assigned them to either a TRF group or a control diet (CD) group according to their preferences. Changes in renal function, other biochemical data, anthropometric parameters, gut microbiota, and adverse events were measured before the intervention and after 12 weeks.

Results

The change in estimated glomerular filtration rate (eGFR) before and after intervention in the TRF group (Δ = 3.1 ± 5.3 ml/min/1.73m²) showed significant improvement compared with the CD group (Δ = -0.8 ± 4.4 ml/min/1.73m²). Furthermore, the TRF group had a significant decrease in uric acid (Δ = -70.8 ± 124.2 μmol/L), but an increase in total protein (Δ = 1.7 ± 2.5 g/L), while the changes were inconsistent for inflammatory factors. In addition, the TRF group showed a significant decrease in body weight (Δ = -2.8 ± 2.9 kg) compared to the CD group, and body composition indicated the same decrease in body fat mass, fat free mass and body water. Additionally, TRF shifted the gut microbiota in a positive direction.

Conclusion

Preliminary studies suggest that overweight and obese patients with moderate-to-severe CKD with weight loss needs, and who were under strict medical supervision by healthcare professionals, performed TRF with good compliance. They did so without apparent adverse events, and showed efficacy in protecting renal function. These results may be due to changes in body composition and alterations in gut microbiota.

Microbiota and glomerulonephritis: An immunological point of view

Glomerular injury is the major cause of chronic kidney diseases (CKD) worldwide and is characterized by proteinuria. Glomerulonephritis (GN) has a wide spectrum of etiologies, the intensity of glomerular damage, histopathology, and clinical outcomes that can be associated with the landscape of the nephritogenic immune response. Beyond impaired immune responses and genetic factors, recent evidence indicates that microbiota can be contributed to the pathogenesis of GN and patients' outcomes by impacting many aspects of the innate and adaptive immune systems. It is still unknown whether dysbiosis induces GN or it is a secondary effect of the disease. Several factors such as drugs and nutritional problems can lead to dysbiosis in GN patients. It has been postulated that gut dysbiosis activates immune responses, promotes a state of systemic inflammation, and produces uremic toxins contributing to kidney tissue inflammation, apoptosis, and subsequent proteinuric nephropathy. In this review, the impact of gastrointestinal tract (GI) microbiota on the pathogenesis of the primary GN will be highlighted. The application of therapeutic interventions based on the manipulation of gut microbiota with special diets and probiotic supplementation can be effective in GN.

Expansion of Escherichia-Shigella in Gut Is Associated with the Onset and Response to Immunosuppressive Therapy of IgA Nephropathy

BACKGROUND

Gut dysbiosis is postulated to participate in the pathogenesis of IgA nephropathy (IgAN). However, the key bacterial taxa closely associated with IgAN onset and treatment response have not been identified.

METHODS

We recruited 127 patients with IgAN who were treatment naive and 127 matched healthy controls (HCs) who were randomly divided into discovery and validation cohorts to investigate the characteristics of their gut microbiota and establish a bacterial diagnosis model for IgAN. A separate cohort of 56 patients and HCs was investigated to assess crossregional validation. A further 40 patients with primary membranous nephropathy (MN) were enrolled to probe disease-specific validation. A subgroup of 77 patients was prospectively followed to further dissect the association between alterations in gut microbiota and treatment response after 6 months of immunosuppressive therapy. Fecal microbiota samples were collected from all participants and analyzed using 16S ribosomal RNA sequencing.

RESULTS

Decreased α-diversity (Shannon, P=0.03), altered microbial composition (Adonis, P=0.0001), and a striking expansion of the taxonomic chain Proteobacteria-Gammaproteobacteria-Enterobacteriales-Enterobacteriaceae-Escherichia-Shigella (all P<0.001) were observed in patients with IgAN who were treatment naive, which reversed only in patients who achieved clinical remission after 6 months of immunosuppressive therapy. Importantly, seven operational taxa units, of which Escherichia-Shigella contributed the most, were determined to be the optimal bacterial classifier of IgAN (AUC=0.8635, 0.8551, 0.8026 in discovery, validation, and cross-regional validation sets, respectively), but did not effectively distinguish patients with IgAN versus those with MN (AUC=0.6183). Bacterial function prediction further verified enrichment of the shigellosis infection pathway in IgAN.

CONCLUSION

Gut dysbiosis, characterized by a striking expansion of genus Escherichia-Shigella, is a hallmark of patients with IgAN and may serve as a promising diagnostic biomarker and therapeutic target for IgAN. Further studies are warranted to investigate the potential contribution of Escherichia-Shigella in IgAN pathogenesis.

Findings on the Relationship Between Intestinal Microbiome and Vasculitis

The microbiome has been implicated in small-, medium-, large-, and variable-vessel vasculitis. Dysbiosis can frequently be found in vasculitis patients with altered microbial diversity and abundance, compared with those with other diseases and healthy controls. Dominant bacteria discovered in different studies vary greatly, but in general, the intestinal microbiome in vasculitis patients tends to contain more pathogenic and less beneficial bacteria. Improvement or resolution of dysbiosis has been observed after treatment in a few longitudinal studies. In addition, some molecular changes in intestinal permeability and immune response have been found in animal models of vasculitis diseases.

Gut Microbes in Immunoglobulin A Nephropathy and Their Potential Therapeutic Applications

Microbial ecosystem consists of a complex community of bacterial interactions and its host microenvironment (tissue, cell, metabolite). Because the interaction between gut microbiota and host involves many diseases and seriously affects human health, the study of the interaction mechanism between gut microbiota and host has attracted great attention. The gut microbiome is made up of 100 trillion bacteria that have both beneficial and adverse effects on human health. The development of IgA Nephropathy results in changes in the intestinal microbial ecosystem that affect host physiology and health. Similarly, changes in intestinal microbiota also affect the development of IgA Nephropathy. Thus, the gut microbiome represents a novel therapeutic target for improving the outcome of IgA Nephropathy, including hematuria symptoms and disease progression. In this review, we summarize the effect of intestinal microbiota on IgA Nephropathy in recent years and it has been clarified that the intestinal microbiota has a great influence on the pathogenesis and treatment of IgA Nephropathy.

Gut Microbiome Characteristics in IgA Nephropathy: Qualitative and Quantitative Analysis from Observational Studies

Background

Recent data indicate the importance of gut-kidney axis in the pathogenesis of Immunoglobulin A nephropathy (IgAN). Growing evidence suggests the alterations of diversity and composition of gut microbiome among patients with IgAN, however, the details are not yet fully understood.

Methods

Eligible studies comparing the gut microbiome between patients with IgAN and non-IgAN individuals were systematically searched from PubMed, Embase, Web of Science, Cochrane Library, China National Knowledge Infrastructure, and ClinicalTrials.gov. The primary outcomes were alpha- and beta-diversity, and the differences in gut microbiota composition between patients with IgAN and non-IgAN persons. Qualitative analysis and meta-analysis were performed according to available data.

Results

Eleven cross-sectional studies, including 409 patients with IgAN and 243 healthy controls, were enrolled. No significant differences in the diversity and enrichment of gut bacteria were found between IgAN and healthy individuals, whereas the beta-diversity consistently showed significant microbial dissimilarities among the two groups. Firmicutes, Bacteroidetes, Actinobacteria, Proteobacteria, Fusobacteria, and Verrucomicrobia were the dominant phyla, however, no significant differences were found between IgAN patients and healthy controls at the phylum level. The genera, Streptococcus and Paraprevotella showed a higher proportion in patients with IgAN compared to healthy individuals, whereas Fusicatenibacter showed a lower abundance according to meta-analysis. Qualitative analyses suggested that Escherichia-Shigella might be increased in IgAN patients; the genera, Clostridium, Prevotella 9,and Roseburia, members of Ruminococcaceae and Lachnospiraceae families, were likely to have decreased abundances in patients with IgAN compared to healthy individuals.

Conclusion

Gut microbiota dysbiosis was demonstrated in IgAN, which might be involved in the pathogenesis of IgAN. Further studies are needed to confirm the findings of this study, due to the substantial heterogeneity.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/, identifier PROSPERO (CRD42022304034).

Fecal Capsule as a Therapeutic Strategy in IgA Nephropathy: A Brief Report

In this brief report, we reported an IgA nephropathy (IgAN) patient who presented in November 2020 with an acute exacerbation with massive proteinuria and diarrhea. He had the earliest onset in 2018 when his IgAN was diagnosed by renal biopsy. He has been treated with active ACEI/ARB drugs for more than 90 days, intermittent steroid therapy, combined with anti-infective therapy. Although his acute symptoms resolved with each episode, he became increasingly severe as the interval between episodes shortened. Accordingly, the immunosuppressive drugs were administered under the KDIGO guidelines and related guidelines. However, the patient and his family refused this treatment. We pondered over the possible pathogenesis of IgAN, and after a full discussion with the patient and his family, FMT was administered to him after obtaining his informed consent. During the FMT procedure, one healthy volunteer (the doctor himself) also took the FMT capsules. In the end, the patient’s urine protein dropped significantly and even turned negative after treatment. Neither the patient nor the healthy volunteer experienced any serious adverse effects during the use of the capsules and the subsequent 6-month follow-up period. We also used metagenomic sequencing to analyze the intestinal flora of patients before and after treatment, and a gradual increase stood out in the abundance of the patient’s intestinal flora after drug administration.

Role of gut-kidney axis in renal diseases and IgA nephropathy

PURPOSE OF REVIEW

Growing evidence show the importance of gut/kidney axis in renal diseases. Advances in gut microbiome sequencing, associated metabolites, detection of gut permeability and inflammation provide new therapeutic strategies targeting gut for kidney diseases and particularly for Immunoglobulin A (IgA) nephropathy (IgAN).

RECENT FINDINGS

The diversity and composition of gut flora have been recently deeply explored in kidney diseases. Modulation and depletion of microbiota in animal models allowed the understanding of molecular mechanisms involved in the crosstalk between gut, immune system and kidney. New clinical trials in order to positively modulate microbiota result in improvement of gastrointestinal disorders and inflammation in patients suffering with kidney diseases.

SUMMARY

The investigation of gut alterations in kidney diseases open new therapeutic strategies. In IgAN, targeted treatments for intestinal inflammation and modifications of gut microbiota seem promising.

Immunoglobulin A, an Active Liaison for Host-Microbiota Homeostasis

Mucosal surfaces in the gastrointestinal tract are continually exposed to native, commensal antigens and susceptible to foreign, infectious antigens. Immunoglobulin A (IgA) provides dual humoral responses that create a symbiotic environment for the resident gut microbiota and prevent the invasion of enteric pathogens. This review features recent immunological and microbial studies that elucidate the underlying IgA and microbiota-dependent mechanisms for mutualism at physiological conditions. IgA derailment and concurrent microbiota instability in pathological diseases are also discussed in detail. Highlights of this review underscore that the source of IgA and its structural form can dictate microbiota reactivity to sustain a diverse niche where both host and bacteria benefit. Other important studies emphasize IgA insufficiency can result in the bloom of opportunistic pathogens that encroach the intestinal epithelia and disseminate into circulation. The continual growth of knowledge in these subjects can lead to the development of therapeutics targeting IgA and/or the microbiota to treat life threatening diseases.

An Update on Targeted Treatment of IgA Nephropathy: An Autoimmune Perspective

Immunoglobulin (Ig) A nephropathy (IgAN) is the commonest form of primary glomerulonephritis worldwide and is, considered a significant cause of end-stage renal disease in young adults. The precise pathogenesis of IgAN is unclear. The clinical and pathological features vary significantly between individuals and races, which makes treating IgAN difficult. Currently, the therapeutic strategies in IgAN are still optimal blood pressure control and proteinuria remission to improve the renal function in most cases. Immunosuppressive drugs such as corticosteroids can be considered in patients with persistent proteinuria and a high risk of renal function decline; however, they include a high toxicity profile. Therefore, the safety and selectivity of medications are critical concerns in the treatment of IgAN. Various pharmacological therapeutic targets have emerged based on the evolving understanding of the autoimmune pathogenesis of IgAN, which involves the immune response, mucosal immunity, renal inflammation, complement activation, and autophagy; treatments based on these mechanisms have been explored in preclinical and clinical studies. This review summarizes the progress concerning targeted therapeutic strategies and the relevant autoimmune pathogenesis in IgAN.

The Gut and Blood Microbiome in IgA Nephropathy and Healthy Controls

Background

IgA nephropathy (IgAN) has been associated with gut dysbiosis, intestinal membrane disruption, and translocation of bacteria into blood. Our study aimed to understand the association of gut and blood microbiomes in patients with IgAN in relation to healthy controls.

Methods

We conducted a case-control study with 20 patients with progressive IgAN, matched with 20 healthy controls, and analyzed bacterial DNA quantitatively in blood using 16S PCR and qualitatively in blood and stool using 16S metagenomic sequencing. We conducted between-group comparisons as well as comparisons between the blood and gut microbiomes.

Results

Higher median 16S bacterial DNA in blood was found in the IgAN group compared with the healthy controls group (7410 versus 6030 16S rDNA copies/μl blood, P=0.04). α- and β-Diversity in both blood and stool was largely similar between the IgAN and healthy groups. In patients with IgAN, in comparison with healthy controls, we observed higher proportions of the class Coriobacteriia and species of the genera Legionella, Enhydrobacter, and Parabacteroides in blood, and species of the genera Bacteroides, Escherichia-Shigella, and some Ruminococcus in stool. Taxa distribution were markedly different between the blood and stool samples of each subject in both IgAN and healthy groups, without any significant correlation between corresponding gut and blood phyla.

Conclusions

Important bacterial taxonomic differences, quantitatively in blood and qualitatively in both blood and stool samples, that were detected between IgAN and healthy groups warrant further investigation into their roles in the pathogenesis of IgAN. Although gut bacterial translocation into blood may be one of the potential sources of the blood microbiome, marked taxonomic differences between gut and blood samples in each subject in both groups confirms that the blood microbiome does not directly reflect the gut microbiome. Further research is needed into other possible sites of origin and internal regulation of the blood microbiome.