Effects of Metabolic Syndrome and Its Components on Chronic Kidney Disease and Renal Function: A Two-Sample Mendelian Randomization Study

Objective: The association of metabolic syndrome (MetS) and its components with chronic kidney disease (CKD) and renal function remains controversial in observational studies. To comprehensively investigate the association between MetS and its components with CKD and renal function, a Mendelian randomization (MR) study was performed. Methods: The inverse variance weighting (IVW) of random effects was used as the main estimation method, while MR-Egger and weighted median analysis results were used for auxiliary judgments. Cochran's Q test, MR-Egger intercept test, leave-one-out analysis, and funnel plots were used to assess heterogeneity and pleiotropy. Results: The MR analyses of genetically predicted MetS and its components' association with CKD risk and renal function showed the following causal associations: hypertension with CKD risk; MetS and obesity with increased blood urea nitrogen and decreased estimated glomerular filtration rate based on cystatin C; hypertension and diabetes with increased urine albumin-creatinine ratio and increased risk of microalbuminuria; and CKD with increased triglyceride. Conclusion: Based on genetic data, this study demonstrated an association between hypertension and CKD risk and a causal association between other MetS components and renal function. The early diagnosis and prevention of MetS and its components might be essential for CKD management.

Effects of NRF2 polymorphisms on safety and efficacy of bardoxolone methyl: subanalysis of TSUBAKI study

BACKGROUND

In the TSUBAKI study, bardoxolone methyl significantly increased measured and estimated glomerular filtration rates (GFR) in patients with multiple forms of chronic kidney disease (CKD), including Japanese patients with type 2 diabetes and stage 3-4 CKD. Since bardoxolone methyl targets the nuclear factor erythroid 2-related factor 2 pathway, this exploratory analysis of the TSUBAKI study investigated the impact of the regulatory single nucleotide polymorphism, rs6721961, on the effects of bardoxolone methyl.

METHODS

Japanese patients aged 20-79 years with type 2 diabetes and stage 3-4 CKD were randomized to bardoxolone methyl 5-15 mg/day (titrated as tolerated) or placebo for 16 weeks. Genotype frequency, clinical characteristics, renal function, and adverse events were primarily assessed.

RESULTS

Of 104 patients (bardoxolone methyl n = 55, placebo n = 49); 57% were genotype C/C, 32% C/A and 12% A/A. The frequency of the A/A genotype was higher among patients with diabetic kidney disease than in the general Japanese population (~ 5%). Measured and estimated GFRs increased from baseline in all genotypes receiving bardoxolone methyl. There were no significant differences between genotypes for safety parameters, including blood pressure, bodyweight, and levels of B-type natriuretic peptide, or in the type and frequency of adverse events, suggesting that the efficacy and safety of bardoxolone methyl are unaffected by the rs6721961 polymorphism-617 (C→A) genotype.

CONCLUSIONS

Our approach of combining genome analysis with clinical trials for an investigational drug provides important and useful clues for exploring the efficacy and safety of the drug.

TRIAL REGISTRATION

ClinicalTrials.gov; NCT02316821.

Prophylactic bilateral nephrectomy and preemptive kidney transplantation for Denys-Drash syndrome prior to development of kidney failure

BACKGROUND  : Nephropathy in Denys-Drash syndrome (DDS) develops within a few months of birth, often progressing to kidney failure. Wilms tumors also develop at an early age with a high rate of incidence. When a patient does not have Wilms tumor but develops kidney failure, prophylactic bilateral nephrectomy, and kidney transplantation (KTX) is an optimal approach owing to the high risk of Wilms tumor development. In the case presented here, prophylactic bilateral nephrectomy and KTX were performed in a patient who had not developed Wilms tumor or kidney failure. However, the treatment option is controversial as it involves the removal of a tumor-free kidney and performing KTX in the absence of kidney failure. CASE DIAGNOSIS/TREATMENT: We present the case of a 7-year-old boy, born at 38 weeks gestation. Examinations at the age of 1 year revealed severe proteinuria and abnormal internal and external genitalia. Genetic testing identified a missense mutation in exon 9 of the WT1 gene, leading to the diagnosis of DDS. At the age of 6 years, he had not yet developed Wilms tumor and had grown to a size that allowed him to safely undergo a KTX. His kidney function was slowly deteriorating (chronic kidney disease (CKD) stage 3), but he had not yet developed kidney failure. Two treatment options were considered for this patient: observation until the development of kidney failure or prophylactic bilateral nephrectomy with KTX to avoid Wilms tumor development. After a detailed explanation of options to the patient and family, they decided to proceed with prophylactic bilateral nephrectomy and KTX. At the latest follow-up 4 months after KTX, the patient's kidney functioned well without proteinuria. CONCLUSION: We performed prophylactic bilateral nephrectomy with KTX on a DDS patient who had not developed kidney failure or Wilms tumor by the age of 7 years. Although the risk of development of Wilms tumor in such a patient is unclear, this treatment may be an optimal approach for patients who are physically able to undergo KTX, considering the potentially lethal nature of Wilms tumor in CKD patients.

Phenome-wide analysis reveals epistatic associations between APOL1 variants and chronic kidney disease and multiple other disorders

BACKGROUND

APOL1 variants G1 and G2 are common in populations with recent African ancestry. They are associated with protection from African sleeping sickness, however homozygosity or compound heterozygosity for these variants is associated with chronic kidney disease (CKD) and related conditions. What is not clear is the extent of associations with non-kidney-related disorders, and whether there are clusters of diseases associated with individual APOL1 genotypes.

METHODS

Using a cohort of 7462 UK Biobank participants with recent African ancestry, we conducted a phenome-wide association study investigating associations between individual APOL1 genotypes and conditions identified by the International Classification of Disease phenotypes.

FINDINGS

We identified 27 potential associations between individual APOL1 genotypes and a diverse range of conditions. G1/G2 compound heterozygotes were specifically associated with 26 of these conditions (all deleteriously), with an over-representation of infectious diseases (including hospitalisation and death resulting from COVID-19). The analysis also exposed complexities in the relationship between APOL1 and CKD that are not evident when risk variants are grouped together: G1 homozygosity, G2 homozygosity, and G1/G2 compound heterozygosity were each shown to be associated with distinct CKD phenotypes. The multi-locus nature of the G1/G2 genotype means that its associations would go undetected in a standard genome-wide association study.

INTERPRETATION

Our findings have implications for understanding health risks and better-targeted detection, intervention, and therapeutic strategies, particularly in populations where APOL1 G1 and G2 are common such as in sub-Saharan Africa and its diaspora.

FUNDING

This study was funded by the Wellcome Trust (209511/Z/17/Z) and H3Africa (H3A/18/004).

Idiopathic collapsing glomerulopathy is associated with APOL1 high-risk genotypes or Mendelian variants in most affected individuals in a highly admixed population

Collapsing glomerulopathy (CG) is most often associated with fast progression to kidney failure with an incidence apparently higher in Brazil than in other countries. However, the reason for this occurrence is unknown. To better understand this, we performed an integrated analysis of clinical, histological, therapeutic, causative genetic and genetic ancestry data in a highly genetically admixed cohort of 70 children and adult patients with idiopathic CG (ICG). The disease onset occurred at 23 (interquartile range: 17-31) years and approximately half of patients progressed to chronic kidney disease requiring kidney replacement therapy (CKD-KRT) 36 months after diagnosis. Causative genetic bases, assessed by targeted-gene panel or whole-exome sequencing, were identified in 58.6% of patients. Among these cases, 80.5% harbored APOL1 high-risk genotypes (HRG) and 19.5% causative Mendelian variants (MV). Self-reported non-White patients more frequently had HRG. MV was an independent risk factor for progression to CKD-KRT by 36 months and the end of follow-up, while remission was an independent protective factor. All patients with HRG manifested CG at 9-44 years of age, whereas in those with APOL1 low-risk genotype, the disease arose throughout life. HRGs were associated with higher proportion of African genetic ancestry. Novel causative MVs were identified in COL4A5, COQ2 and PLCE1 and previously described causative MVs were identified in MYH9, TRPC6, COQ2, COL4A3 and TTC21B. Three patients displayed HRG combined with a variant of uncertain significance (ITGB4, LAMA5 or PTPRO). MVs were associated with worse kidney prognosis. Thus, our data reveal that the genetic status plays a major role in ICG pathogenesis, accounting for more than half of cases in a highly admixed Brazilian population.

Role of CD44 expressed in renal tubules during maladaptive repair in renal fibrogenesis in an allopurinol-induced rat model of chronic kidney disease

The kidney is a major target organ for the adverse effects of pharmaceuticals; renal tubular epithelial cells (TECs) are particularly vulnerable to drug-induced toxicity. TECs have regenerative capacity; however, maladaptive repair of TECs after injury leads to renal fibrosis, resulting in chronic kidney disease (CKD). We previously reported the specific expression of CD44 in failed-repair TECs of rat CKD model induced by ischemia reperfusion injury. Here, we investigated the pathophysiological role of CD44 in renal fibrogenesis in allopurinol-treated rat CKD model. Dilated or atrophic TECs expressing CD44 in fibrotic areas were collected by laser microdissection and subjected to microarray analysis. Gene ontology showed that extracellular matrix (ECM)-related genes were upregulated and differentiation-related genes were downregulated in dilated/atrophic TECs. Ingenuity Pathway Analysis identified CD44 as an upstream regulator of fibrosis-related genes, including Fn1, which encodes fibronectin. Immunohistochemistry demonstrated that dilated/atrophic TECs expressing CD44 showed decreases in differentiation markers of TECs and clear expression of mesenchymal markers during basement membrane attachment. In situ hybridization revealed an increase in Fn1 mRNA in the cytoplasm of dilated/atrophic TECs, whereas fibronectin was localized in the stroma around these TECs, supporting the production/secretion of ECM by dilated/atrophic TECs. Overall, these data indicated that dilated/atrophic TECs underwent a partial epithelial-mesenchymal transition (pEMT) and that CD44 promoted renal fibrogenesis via induction of ECM production in failed-repair TECs exhibiting pEMT. CD44 was detected in the urine and serum of APL-treated rats, which may reflect the expression of CD44 in the kidney.

New insights into the role of immunity and inflammation in diabetic kidney disease in the omics era

Diabetic kidney disease (DKD) is becoming the leading cause of chronic kidney disease, especially in the industrialized world. Despite mounting evidence has demonstrated that immunity and inflammation are highly involved in the pathogenesis and progression of DKD, the underlying mechanisms remain incompletely understood. Substantial molecules, signaling pathways, and cell types participate in DKD inflammation, by integrating into a complex regulatory network. Most of the studies have focused on individual components, without presenting their importance in the global or system-based processes, which largely hinders clinical translation. Besides, conventional technologies failed to monitor the different behaviors of resident renal cells and immune cells, making it difficult to understand their contributions to inflammation in DKD. Recently, the advancement of omics technologies including genomics, epigenomics, transcriptomics, proteomics, and metabolomics has revolutionized biomedical research, which allows an unbiased global analysis of changes in DNA, RNA, proteins, and metabolites in disease settings, even at single-cell and spatial resolutions. They help us to identify critical regulators of inflammation processes and provide an overview of cell heterogeneity in DKD. This review aims to summarize the application of multiple omics in the field of DKD and emphasize the latest evidence on the interplay of inflammation and DKD revealed by these technologies, which will provide new insights into the role of inflammation in the pathogenesis of DKD and lead to the development of novel therapeutic approaches and diagnostic biomarkers.

Genome-wide association studies reconstructing chronic kidney disease

Chronic kidney disease (CKD) is a major health problem with an increasing epidemiological burden, and is the 16th leading cause of years of life lost worldwide. It is estimated that more than 10% of the population have a variable stage of CKD, while about 850 million people worldwide are affected. Nevertheless, public awareness remains low, clinical access is inappropriate in many circumstances and medication is still ineffective due to the lack of clear therapeutic targets. One of the main issues that drives these problems is the fact that CKD remains a clinical entity with significant causal ambiguity. Beyond diabetes mellitus and hypertension, which are the two major causes of kidney disease, there are still many gray areas in the diagnostic context of CKD. Genetics nowadays emerges as a promising field in nephrology. The role of genetic factors in CKD's causes and predisposition is well documented and thousands of genetic variants are well established to contribute to the high burden of disease. Next-generation sequencing is increasingly revealing old and new rare variants that cause Mendelian forms of chronic nephropathy while genome-wide association studies (GWAS) uncover common variants associated with CKD-defining traits in the general population. In this article we review how GWAS has revolutionized-and continues to revolutionize-the old concept of CKD. Furthermore, we present how the investigation of common genetic variants with previously unknown kidney significance has begun to expand our knowledge on disease understanding, providing valuable insights into disease mechanisms and perhaps paving the way for novel therapeutic targets.

Genetic and environmental factors driving congenital solitary functioning kidney

BACKGROUND

Congenital solitary functioning kidney (CSFK) is an anomaly predisposing to hypertension, albuminuria and chronic kidney disease. Its aetiology is complex and includes genetic and environmental factors. The role of gene-environment interactions (G×E), although relevant for other congenital anomalies, has not yet been investigated. Therefore, we performed a genome-wide G×E analysis with six preselected environmental factors to explore the role of these interactions in the aetiology of CSFK.

METHODS

In the AGORA (Aetiologic research into Genetic and Occupational/environmental Risk factors for Anomalies in children) data- and biobank, genome-wide single-nucleotide variant (SNV) data and questionnaire data on prenatal exposure to environmental risk factors were available for 381 CSFK patients and 598 healthy controls. Using a two-step strategy, we first selected independent significant SNVs associated with one of the six environmental risk factors. These SNVs were subsequently tested in G×E analyses using logistic regression models, with Bonferroni-corrected P-value thresholds based on the number of SNVs selected in step one.

RESULTS

In step one, 7-40 SNVs were selected per environmental factor, of which only rs3098698 reached statistical significance (P = .0016, Bonferroni-corrected threshold 0.0045) for interaction in step two. The interaction between maternal overweight and this SNV, which results in lower expression of the Arylsulfatase B (ARSB) gene, could be explained by lower insulin receptor activity in children heterozygous for rs3098698. Eight other G×E interactions had a P-value <.05, of which two were biologically plausible and warrant further study.

CONCLUSIONS

Interactions between genetic and environmental factors may contribute to the aetiology of CSFK. To better determine their role, large studies combining data on genetic and environmental risk factors are warranted.

The characterization and comorbidities of heterozygous Bardet-Biedl syndrome carriers

Introduction: Bardet-Biedl syndrome (BBS) is a rare autosomal recessive disorder with clinical features of retinal dystrophy, obesity, postaxial polydactyly, renal anomalies, learning disabilities, hypogonadism, and genitourinary abnormalities. Nevertheless, previous studies on the phenotypic traits of BBS heterozygous carriers have generated inconclusive results. The aim of our study was to investigate the impact of BBS heterozygosity on carriers when compared to non-carriers within the Taiwanese population. Materials and Methods: This study follows a hospital-based case-control design. We employed the Taiwan Biobank version 2 (TWBv2) array to identify three specific loci associated with BBS (rs773862084, rs567573386, and rs199910690). In total, 716 patients were included in the case group, and they were compared to a control group of 2,864 patients who lacked BBS alleles. The control group was selected through gender and age matching at a ratio of 1:4. The association between BBS-related loci and comorbidity was assessed using logistic regression models. Results: We found that BBS heterozygous carriers exhibited a significant association with elevated BMI levels, especially the variant rs199910690 in MKS1 (p=0.0037). The prevalence of comorbidities in the carriers' group was not higher than that in the non-carriers' group. Besides, the average values of the biochemistry data showed no significant differences, except for creatinine level. Furthermore, we conducted a BMI-based analysis to identify specific risk factors for chronic kidney disease (CKD). Our findings revealed that individuals carrying the CA/AA genotype of the BBS2 rs773862084 variant or the CT/TT genotype of the MKS1 rs199910690 variant showed a reduced risk of developing CKD, irrespective of their BMI levels. When stratified by BMI level, obese males with the MKS1 rs199910690 variant and obese females with the BBS2 rs773862084 variant exhibited a negative association with CKD development. Conclusion: We found that aside from the association with overweight and obesity, heterozygous BBS mutations did not appear to increase the predisposition of individuals to comorbidities and metabolic diseases. To gain a more comprehensive understanding of the genetic susceptibility associated with Bardet-Biedl Syndrome (BBS), further research is warranted.

SOX9 switch links regeneration to fibrosis at the single-cell level in mammalian kidneys

The steps governing healing with or without fibrosis within the same microenvironment are unclear. After acute kidney injury (AKI), injured proximal tubular epithelial cells activate SOX9 for self-restoration. Using a multimodal approach for a head-to-head comparison of injury-induced SOX9 lineages, we identified a dynamic SOX9 switch in repairing epithelia. Lineages that regenerated epithelia silenced SOX9 and healed without fibrosis (SOX9on-off). By contrast, lineages with unrestored apicobasal polarity maintained SOX9 activity in sustained efforts to regenerate, which were identified as a SOX9on-on Cadherin6pos cell state. These reprogrammed cells generated substantial single-cell WNT activity to provoke a fibroproliferative response in adjacent fibroblasts, driving AKI to chronic kidney disease. Transplanted human kidneys displayed similar SOX9/CDH6/WNT2B responses. Thus, we have uncovered a sensor of epithelial repair status, the activity of which determines regeneration with or without fibrosis.

lncRNA FAS-AS1 served as a diagnostic biomarker of end-stage renal disease and mediated vascular calcification via regulating oxidative stress and inflammation

PURPOSE

Vascular calcification is a frequently occurring complication of end-stage renal disease (ESRD). This study focused on the significance of long non-coding RNA Fas cell surface death receptor-antisense 1(lncRNA FAS-AS1) in ESRD-related vascular calcification aiming to explore a potential biomarker for the detection.

METHODS

The study enrolled 65 healthy individuals, 79 ESRD patients (48 patients with vascular calcification), and 93 early-stage (I-IV) chronic kidney disease (CKD) patients. The expression of FAS-AS1 in serum was evaluated by real-time quantitative polymerase chain reaction (PCR). The diagnostic potential of FAS-AS1 was assessed in discriminating ESRD patients, vascular calcification, and the severity of vascular calcification. In vitro, the vascular smooth muscle cells (VSMCs) were treated with a hyperphosphatemia medium to evaluate the effect of FAS-AS1 on VSMCs calcification.

RESULTS

Elevated serum FAS-AS1 was observed in ESRD patients, which could discriminate from healthy individuals and early-stage CKD patients. FAS-AS1 was associated with the development of ESRD and the occurrence of vascular calcification. FAS-AS1 was also upregulated in vascular calcification patients, especially the patients with severe calcification, which showed diagnostic significance in evaluating vascular calcification degrees. Calcified VSMCs showed significantly increased levels of Ca2+, reactive oxygen species (ROS), tumor necrosis factor-α (TNF-α), and interleukin 6 (IL-6), which was attenuated by silencing FAS-AS1.

CONCLUSIONS

FAS-AS1 discriminated ERSD patients and was associated with the occurrence of vascular calcification. The knockdown of FAS-AS1 suppressed hyperphosphatemia-induced vascular calcification via alleviating oxidative stress and inflammation.

Mannose and glycine: Metabolites with potentially causal implications in chronic kidney disease pathogenesis

BACKGROUND

Chronic Kidney Disease (CKD) represents a global health challenge, with its etiology and underlying mechanisms yet to be fully elucidated. Integrating genomics with metabolomics can offer insights into the putatively causal relationships between serum metabolites and CKD.

METHODS

Utilizing bidirectional Mendelian Randomization (MR), we assessed the putatively causal associations between 486 serum metabolites and CKD. Genetic data for these metabolites were sourced from comprehensive genome-wide association studies, and CKD data were obtained from the CKDGen Consortium.

RESULTS

Our analysis identified four metabolites with a robust association with CKD risk, of which mannose and glycine showed the most reliable causal relationships. Pathway analysis spotlighted five significant metabolic pathways, notably including "Methionine Metabolism" and "Arginine and Proline Metabolism", as key contributors to CKD pathogenesis.

CONCLUSION

This study underscores the potential of certain serum metabolites as biomarkers for CKD and illuminates pivotal metabolic pathways in CKD's pathogenesis. Our findings lay the groundwork for potential therapeutic interventions and warrant further research for validation.

Retinoic acid receptor α activity in proximal tubules prevents kidney injury and fibrosis

Chronic kidney disease (CKD) is characterized by a gradual loss of kidney function and affects ~13.4% of the global population. Progressive tubulointerstitial fibrosis, driven in part by proximal tubule (PT) damage, is a hallmark of late stages of CKD and contributes to the development of kidney failure, for which there are limited treatment options. Normal kidney development requires signaling by vitamin A (retinol), which is metabolized to retinoic acid (RA), an endogenous agonist for the RA receptors (RARα, β, γ). RARα levels are decreased in a mouse model of diabetic nephropathy and restored with RA administration; additionally, RA treatment reduced fibrosis. We developed a mouse model in which a spatiotemporal (tamoxifen-inducible) deletion of RARα in kidney PT cells of adult mice causes mitochondrial dysfunction, massive PT injury, and apoptosis without the use of additional nephrotoxic substances. Long-term effects (3 to 4.5 mo) of RARα deletion include increased PT secretion of transforming growth factor β1, inflammation, interstitial fibrosis, and decreased kidney function, all of which are major features of human CKD. Therefore, RARα's actions in PTs are crucial for PT homeostasis, and loss of RARα causes injury and a key CKD phenotype.

Kidney-specific methylation patterns correlate with kidney function and are lost upon kidney disease progression

BACKGROUND

Chronological and biological age correlate with DNA methylation levels at specific sites in the genome. Linear combinations of multiple methylation sites, termed epigenetic clocks, can inform us the chronological age and predict multiple health-related outcomes. However, why some sites correlating with lifespan, healthspan, or specific medical conditions remain poorly understood. Kidney fibrosis is the common pathway for chronic kidney disease, which affects 10% of European and US populations.

RESULTS

Here we identify epigenetic clocks and methylation sites that correlate with kidney function. Moreover, we identify methylation sites that have a unique methylation signature in the kidney. Methylation levels in majority of these sites correlate with kidney state and function. When kidney function deteriorates, all of these sites regress toward the common methylation pattern observed in other tissues. Interestingly, while the majority of sites are less methylated in the kidney and become more methylated with loss of function, a fraction of the sites are highly methylated in the kidney and become less methylated when kidney function declines. These methylation sites are enriched for specific transcription-factor binding sites. In a large subset of sites, changes in methylation patterns are accompanied by changes in gene expression in kidneys of chronic kidney disease patients.

CONCLUSIONS

These results support the information theory of aging, and the hypothesis that the unique tissue identity, as captured by methylation patterns, is lost as tissue function declines. However, this information loss is not random, but guided toward a baseline that is dependent on the genomic loci.

SIGNIFICANCE STATEMENT

DNA methylation at specific sites accurately reflects chronological and biological age. We identify sites that have a unique methylation pattern in the kidney. Methylation levels in the majority of these sites correlate with kidney state and function. Moreover, when kidney function deteriorates, all of these sites regress toward the common methylation pattern observed in other tissues. Thus, the unique methylation signature of the kidney is degraded, and epigenetic information is lost, when kidney disease progresses. These methylation sites are enriched for specific and methylation-sensitive transcription-factor binding sites, and associated genes show disease-dependent changes in expression. These results support the information theory of aging, and the hypothesis that the unique tissue identity, as captured by methylation patterns, is lost as tissue function declines.

Novel genetic markers for chronic kidney disease in a geographically isolated population of Indigenous Australians: Individual and multiple phenotype genome-wide association study

BACKGROUND

Chronic kidney disease (CKD) is highly prevalent among Indigenous Australians, especially those in remote regions. The Tiwi population has been isolated from mainland Australia for millennia and exhibits unique genetic characteristics that distinguish them from other Indigenous and non-Indigenous populations. Notably, the rate of end-stage renal disease is up to 20 times greater in this population compared to non-Indigenous populations. Despite the identification of numerous genetic loci associated with kidney disease through GWAS, the Indigenous population such as Tiwi remains severely underrepresented and the increased prevalence of CKD in this population may be due to unique disease-causing alleles/genes.

METHODS

We used albumin-to-creatinine ratio (ACR) and estimated glomerular filtration rate (eGFR) to estimate the prevalence of kidney disease in the Tiwi population (N = 492) in comparison to the UK Biobank (UKBB) (N = 134,724) database. We then performed an exploratory factor analysis to identify correlations among 10 CKD-related phenotypes and identify new multi-phenotype factors. We subsequently conducted a genome-wide association study (GWAS) on all single and multiple phenotype factors using mixed linear regression models, adjusted for age, sex, population stratification, and genetic relatedness between individuals.

RESULTS

Based on ACR, 20.3% of the population was at severely increased risk of CKD progression and showed elevated levels of ACR compared to the UKBB population independent of HbA1c. A GWAS of ACR revealed novel association loci in the genes MEG3 (chr14:100812018:T:A), RAB36 (rs11704318), and TIAM2 (rs9689640). Additionally, multiple phenotypes GWAS of ACR, eGFR, urine albumin, and serum creatinine identified a novel variant that mapped to the gene MEIS2 (chr15:37218869:A:G). Most of the identified variants were found to be either absent or rare in the UKBB population.

CONCLUSIONS

Our study highlights the Tiwi population's predisposition towards elevated ACR, and the collection of novel genetic variants associated with kidney function. These associations may prove valuable in the early diagnosis and treatment of renal disease in this underrepresented population. Additionally, further research is needed to comprehensively validate the functions of the identified variants/genes.

Therapeutic potential for renal fibrosis by targeting Smad3-dependent noncoding RNAs

Renal fibrosis is a characteristic hallmark of chronic kidney disease (CKD) that ultimately results in renal failure, leaving patients with few therapeutic options. TGF-β is a master regulator of renal fibrosis and mediates progressive renal fibrosis via both canonical and noncanonical signaling pathways. In the canonical Smad signaling, Smad3 is a key mediator in tissue fibrosis and mediates renal fibrosis via a number of noncoding RNAs (ncRNAs). In this regard, targeting Smad3-dependent ncRNAs may offer a specific therapy for renal fibrosis. This review highlights the significance and innovation of TGF-β/Smad3-associated ncRNAs as biomarkers and therapeutic targets in renal fibrogenesis. In addition, the underlying mechanisms of these ncRNAs and their future perspectives in the treatment of renal fibrosis are discussed.

Role of protease-activated receptor 4 in mouse models of acute and chronic kidney injury

Protease-activated receptor 4 (PAR4) is a G protein-coupled receptor activated by thrombin. In the platelet, response to thrombin PAR4 contributes to the predominant procoagulant microparticle formation, increased fibrin deposition, and initiation of platelet-stimulated inflammation. In addition, PAR4 is expressed in other cell types, including endothelial cells. Under inflammatory conditions, PAR4 is overexpressed via epigenetic demethylation of the PAR4 gene, F2RL3. PAR4 knockout (KO) studies have determined a role for PAR4 in ischemia-reperfusion injury in the brain, and PAR4 KO mice display normal cardiac function but present less myocyte death and cardiac dysfunction in response to acute myocardial infarction. Although PAR4 has been reported to be expressed within the kidney, the contribution of PAR4 to acute kidney injury (AKI) and chronic kidney disease (CKD) is not well understood. Here we report that PAR4 KO mice are protected against kidney injury in two mouse models. First, PAR4 KO mice are protected against induction of markers of both fibrosis and inflammation in two different models of kidney injury: 1) 7 days following unilateral ureter obstruction (UUO) and 2) an AKI-CKD model of ischemia-reperfusion followed by 8 days of contralateral nephrectomy. We further show that PAR4 expression in the kidney is low in the control mouse kidney but induced over time following UUO. PAR4 KO mice are protected against blood urea nitrogen (BUN) and glomerular filtration rate (GFR) kidney function pathologies in the AKI-CKD model. Following the AKI-CKD model, PAR4 is expressed in the collecting duct colocalizing with Dolichos biflorus agglutinin (DBA), but not in the proximal tubule with Lotus tetragonolobus lectin (LTL). Collectively, the results reported in this study implicate PAR4 as contributing to the pathology in mouse models of acute and chronic kidney injury.NEW & NOTEWORTHY The contribution of the thrombin receptor protease-activated receptor 4 (PAR4) to acute kidney injury (AKI) and chronic kidney disease (CKD) is not well understood. Here we report that PAR4 expression is upregulated after kidney injury and PAR4 knockout (KO) mice are protected against fibrosis following kidney injury in two mouse models. First, PAR4 KO mice are protected against unilateral ureter obstruction. Second, PAR4 KO mice are protected against an AKI-CKD model of ischemia-reperfusion followed by contralateral nephrectomy.

Downregulation of PDZK1 by TGF-β1 promotes renal fibrosis via inducing epithelial-mesenchymal transition of renal tubular cells

Transforming growth factor-beta 1 (TGF-β1)-induced epithelial-mesenchymal transition (EMT) of renal tubular cells promotes renal fibrosis and the progression of chronic kidney disease (CKD). PDZ domain-containing 1 (PDZK1) is highly expressed in renal tubular epithelial cells; however, its role in TGF-β1-induced EMT remains poorly understood. The present study showed that PDZK1 expression was extremely downregulated in fibrotic mouse kidneys and its negative correlation with TGF-β1 expression and the degree of renal fibrosis. In addition, TGF-β1 downregulated the mRNA expression of PDZK1 in a time- and concentration-dependent manner in vitro. The downregulation of PDZK1 exacerbated TGF-β1-induced EMT upon oxidative stress, while the overexpression of PDZK1 had the converse effect. Subsequent investigations demonstrated that TGF-β1 downregulated PDZK1 expression via p38 MAPK or PI3K/AKT signaling in vitro, but independently of ERK/JNK MAPK signaling. Meanwhile, inhibition of the p38/JNK MAPK or PI3K/AKT signaling using chemical inhibitors restored the PDZK1 expression, mitigated renal fibrosis, and elevated renal levels of endogenous antioxidants carnitine and ergothioneine in adenine-induced CKD mice. These findings provide the first evidence suggesting a negative correlation between PDZK1 and renal fibrosis, and identifying PDZK1 as a novel suppressor of renal fibrosis in CKD through ameliorating oxidant stress.

Mitochondrial genetic variation and risk of chronic kidney disease and acute kidney injury in UK Biobank participants

Experimental models suggest an important role for mitochondrial dysfunction in the pathogenesis of chronic kidney disease (CKD) and acute kidney injury (AKI), but little is known regarding the impact of common mitochondrial genetic variation on kidney health. We sought to evaluate associations of inherited mitochondrial DNA (mtDNA) variation with risk of CKD and AKI in a large population-based cohort. We categorized UK Biobank participants who self-identified as white into eight distinct mtDNA haplotypes, which were previously identified based on their associations with phenotypes associated with mitochondrial DNA copy number, a measure of mitochondrial function. We used linear and logistic regression models to evaluate associations of these mtDNA haplotypes with estimated glomerular filtration rate by serum creatinine and cystatin C (eGFRCr-CysC, N = 362,802), prevalent (N = 416 cases) and incident (N = 405 cases) end-stage kidney disease (ESKD), AKI defined by diagnostic codes (N = 14,170 cases), and urine albumin/creatinine ratio (ACR, N = 114,662). The mean age was 57 ± 8 years and the mean eGFR was 90 ± 14 ml/min/1.73 m2. MtDNA haplotype was significantly associated with eGFR (p = 2.8E-12), but not with prevalent ESKD (p = 5.9E-2), incident ESKD (p = 0.93), AKI (p = 0.26), or urine ACR (p = 0.54). The association of mtDNA haplotype with eGFR remained significant after adjustment for diabetes mellitus and hypertension (p = 1.2E-10). When compared to the reference haplotype, mtDNA haplotypes I (β = 0.402, standard error (SE) = 0.111; p = 2.7E-4), IV (β = 0.430, SE = 0.073; p = 4.2E-9), and V (β = 0.233, SE = 0.050; p = 2.7E-6) were each associated with higher eGFR. Among self-identified white UK Biobank participants, mtDNA haplotype was associated with eGFR, but not with ESKD, AKI or albuminuria.

Targeting the m6A RNA methyltransferase METTL3 attenuates the development of kidney fibrosis

Kidney fibrosis is a major mechanism underlying chronic kidney disease (CKD). N6-methyladenosine (m6A) RNA methylation is associated with organ fibrosis. We investigated m6A profile alterations and the inhibitory effect of RNA methylation in kidney fibrosis in vitro (TGF-β-treated HK-2 cells) and in vivo (unilateral ureteral obstruction [UUO] mouse model). METTL3-mediated signaling was inhibited using siRNA in vitro or the METTL3-specific inhibitor STM2457 in vivo and in vitro. In HK-2 cells, METTL3 protein levels increased in a dose- and time-dependent manner along with an increase in the cellular m6A levels. In the UUO model, METTL3 expression and m6A levels were significantly increased. Transcriptomic and m6A profiling demonstrated that epithelial-to-mesenchymal transition- and inflammation-related pathways were significantly associated with RNA m6A methylation. Genetic and pharmacologic inhibition of METTL3 in HK-2 cells decreased TGF-β-induced fibrotic marker expression. STM2457-induced inhibition of METTL3 attenuated the degree of kidney fibrosis in vivo. Furthermore, METTL3 protein expression was significantly increased in the tissues of CKD patients with diabetic or IgA nephropathy. Therefore, targeting alterations in RNA methylation could be a potential therapeutic strategy for treating kidney fibrosis.

Zic family member 3 attenuates oxidative stress-induced vascular smooth muscle cell apoptosis in patients with chronic kidney disease

Neointimal hyperplasia is reportedly essential for arteriovenous fistulas (AVF) in patients undergoing hemodialysis. Oxidative stress is vital in the progression of uremic venous intimal hyperplasia. Studies have suggested that zinc ions obstruct vascular calcification in patients with chronic kidney disease (CKD). Recent studies have shown that the zinc finger protein, Zic family member 3 (ZIC3), is crucial for the earliest cardiovascular progenitors. ZIC3 mutations are associated with congenital heart disease. However, the mechanism of action of ZIC3 in vascular intimal hyperplasia in CKD remains unelucidated. Venous specimens were collected during primary AVF surgery and traumatic amputation, and serum samples were collected from patients with CKD and healthy controls. Mouse vascular smooth muscle cells (VSMCs) were treated with hydrogen peroxide (H2O2) to clarify the role of ZIC3 in CKD. ZIC3 expression was reduced in the veins of patients with uremia and the serum of those with CKD. Zic3 and Bcl2 levels were significantly decreased in mouse VSMCs treated with H2O2·H2O2 inhibited mouse VSMC activity, upregulated Bax, and cleaved caspase 3 expression. Following Zic3 overexpression, Bcl2 expression level and cell viability were elevated, whereas Bax and cleaved caspase 3 expression levels were downregulated. In contrast, Zic3 knockdown yielded the opposite results. Therefore, ZIC3 could be a new therapeutic target in venous neointimal hyperplasia of CKD.

Coffee consumption affects kidney function based on GCKR polymorphism in a Korean population

Kidney function can be preserved through pharmacological interventions and nonpharmacological strategies, such as lifestyle and dietary adjustments. Among these, coffee has been linked to protective effects on kidney function. However, few studies have investigated the effect of coffee consumption on kidney function according to specific genes. We hypothesized that the impact of coffee consumption on kidney function might vary depending on GCKR polymorphism. GCKR rs1260326 polymorphism was examined using the Korean genome and epidemiology data from 656 chronic kidney disease (CKD) cases and 38,540 individuals without CKD (non-CKD). GCKR polymorphism has been previously associated with both coffee consumption and kidney function in Europeans. We replicated the associations between GCKR rs1260326 and coffee consumption and kidney function in Korean individuals. We also explored the effect of coffee consumption on kidney function by multivariate logistic regression analysis. Individuals with the rs1260326 (TC/CC) genotype did not experience significant changes in CKD risk based on their coffee consumption habits. In contrast, individuals with the TT genotype exhibited a significantly lower risk of CKD based on coffee consumption. Interestingly, in the non-CKD group, a beneficial effect on estimated glomerular filtration rate was observed in individuals with the T allele as coffee consumption increased. Our findings supported the hypothesis and revealed that the impact of coffee consumption habits on kidney function may vary based on the GCKR rs1260326 genotype of Korean individuals.

Interaction of Sp1 and Setd8 promotes vascular smooth muscle cells apoptosis by activating Mark4 in vascular calcification

Vascular calcification (VC) is directly related to high mortality in chronic kidney disease (CKD), and cellular apoptosis of vascular smooth muscle cells (VSMCs) is a crucial process in the initiation of VC. Microtubule affinity-regulating kinase 4 (Mark4), known as a serine/threonine protein kinase, can induce cell apoptosis and autophagy by modulating Akt phosphorylation. However, the potential functions and molecular mechanisms of Mark4 in VSMCs apoptosis and calcification need to be further explored. Initially, our data indicated that the mRNA expression of Mark4 was prominently elevated in high phosphorus-stimulated human VSMCs compared with the other members in Marks. Consistently, Mark4 expression was found to be significantly increased in the calcified arteries of both CKD patients and rats. In vitro, silencing Mark4 suppressed apoptosis-specific marker expression by promoting Akt phosphorylation, finally attenuating VSMCs calcification induced by high phosphate. Mechanically, the transcription factor Sp1 was enriched in the Mark4 promoter region and modulated Mark4 transcription. Moreover, SET domain-containing protein 8 (Setd8) was proved to interact with Sp1 and jointly participated in the transcriptional regulation of Mark4. Finally, rescue experiments revealed that Setd8 contributed to VSMCs apoptosis and calcification by modulating Mark4 expression. In conclusion, these findings reveal that Mark4 is transcriptionally activated by Sp1, which is interacted with Setd8, to promote VSMCs calcification through Akt-mediated antiapoptotic effects, suggesting that Mark4 represents a potent and promising therapeutic target for VC in CKD.