Glomerular cell cross talk in diabetic kidney diseases

Diabetic kidney disease (DKD) is a severe microvascular complication of diabetes mellitus. It is the leading inducement of end-stage renal disease (ESRD), and its global incidence has been increasing at an alarming rate. The strict control of blood pressure and blood glucose can delay the progression of DKD, but intensive treatment is challenging to maintain. Studies to date have failed to find a complete cure. The glomerulus's alterations and injuries play a pivotal role in the initiation and development of DKD. A wealth of data indicates that the interdependent relationship between resident cells in the glomerulus will provide clues to the mechanism of DKD and new ways for therapeutic intervention. This review summarizes the significant findings of glomerular cell cross talk in DKD, focusing on cellular signaling pathways, regulators, and potential novel avenues for treating progressive DKD.

A glomerular transcriptomic landscape of apolipoprotein L1 in Black patients with focal segmental glomerulosclerosis

Apolipoprotein L1 (APOL1)-associated focal segmental glomerulosclerosis (FSGS) is the dominant form of FSGS in Black individuals. There are no targeted therapies for this condition, in part because the molecular mechanisms underlying APOL1's pathogenic contribution to FSGS are incompletely understood. Studying the transcriptomic landscape of APOL1 FSGS in patient kidneys is an important way to discover genes and molecular behaviors that are unique or most relevant to the human disease. With the hypothesis that the pathology driven by the high-risk APOL1 genotype is reflected in alteration of gene expression across the glomerular transcriptome, we compared expression and co-expression profiles of 15,703 genes in 16 Black patients with FSGS at high-risk vs 14 Black patients with a low-risk APOL1 genotype. Expression data from APOL1-inducible HEK293 cells and normal human glomeruli were used to pursue genes and molecular pathways uncovered in these studies. We discovered increased expression of APOL1 and nine other significant differentially expressed genes in high-risk patients. This included stanniocalcin, which has a role in mitochondrial and calcium-related processes along with differential correlations between high- and low-risk APOL1 and metabolism pathway genes. There were similar correlations with extracellular matrix- and immune-related genes, but significant loss of co-expression of mitochondrial genes in high-risk FSGS, and an NF-κB-down regulating gene, NKIRAS1, as the most significant hub gene with strong differential correlations with NDUF family (mitochondrial respiratory genes) and immune-related (JAK-STAT) genes. Thus, differences in mitochondrial gene regulation appear to underlie many differences observed between high- and low-risk Black patients with FSGS.

Identification of Genes Reveals the Mechanism of Cell Ferroptosis in Diabetic Nephropathy

Aims/Introduction: Diabetic nephropathy (DN) is one of the main complications of diabetes. Genomics may reveal the essential pathogenesis of DN. We analyzed datasets to search for key genes to explore pathological mechanisms of DN.

Materials and Methods: In this study, weighted gene co-expression network analysis (WGCNA) was used to divide the differential expression genes (DEGs) from GSE142025 into different modules, and enrichment pathway analysis was conducted for each module to find key genes related to cell death pathway. Then, verification was carried out through network and histopathology. Finally, the regulatory mechanisms of key gene expression, including transcription factors (TFs), miRNA and E3 ligases related to ubiquitination, were predicted through website prediction and then miRNA results were validated using GSE51674 dataset.

Results: The results of WGCNA and enrichment pathway analysis indicated that ferroptosis had significantly occurred in advanced DN (AND) group. Analysis of DEGs indicated that the occurrence and development of ferroptosis are mainly through ALOX15-mediated lipid metabolism pathway, which was found in all intrinsic cells of the glomerulus detected by IHC and IF staining. Moreover, network predictions were used for searching ALOX15-related TFs and ubiquitination. Meanwhile, the network predictions combining with other dataset furtherly discovered miRNAs which regulated ALOX15 expression. This study showed that the levels of mmu-miR-142-3p increased in DN mice kidney tissues, compared with the NC group.

Conclusion: Ferroptosis existed in glomerular intrinsic cells of ADN group and its potential key candidate gene was ALOX15 which may be regulated by miR-142 and miRNA-650, TFs (CREBBP, EP300, HDAC1, MTA1, SPI1, STAT6) and E3 ligases related to ubiquitination (PML, ZMIZ1, MARCHF1, MARCHF3, MARCHF8, MARCHF11).

Suppressing the activity of CXCR4 down-regulates the expression of renal fibrosis related genes in primary glomerular cells

BACKGROUND

C-X-C chemokine receptor type 4 (CXCR4) has a certain effect on renal fibrosis, and there are few specific studies in cells. We want to investigate the impact of suppressing CXCR4 activity on the expression of renal fibrosis-related genes in primary glomerular endothelial cells, mesangial cells, and podocytes.

METHODS

Immunofluorescence assays were used to determine the purity of isolated glomerular endothelial cells, mesangial cells, and podocytes. CXCR4 knockdown cell lines were established by transfecting the short hairpin (sh)RNA against CXCR4. T140 and AMD3100 were used to inhibit the activity of CXCR4. LY294002 was used to inhibit the activity of phosphoinositide 3-kinase (PI3K). The mRNA expression of CXCR4 was determined by real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). The protein expression of CXCR4, collagen IV, matrix metallopeptidase (MMP)-9, PI3K, Rac1, and vascular cell adhesion protein 1 (VCAM-1) was evaluated by Western blot analysis.

RESULTS

High purity was observed on isolated primary glomerular endothelial cells and podocytes. However, the purity of isolated mesangial cells was relatively low. The mRNA expression of CXCR4 was significantly suppressed by the transfection of shRNA. Compared to control cells, the expression of CXCR4, collagen IV, MMP-9, PI3K, Rac1, and VCAM-1 were dramatically downregulated in cell lines transfected with shRNA against CXCR4. Furthermore, cell lines treated with T140, AMD3100, or LY294002 also showed downregulated expression of these proteins compared to untreated cells. No significant differences were observed in the protein expression of these proteins between control cells and cells transfected with the shRNA negative control (NC).

CONCLUSIONS

Suppressing the activity of CXCR4 downregulated the expression of renal fibrosis-related genes in primary glomerular cells, even under a non-inflammatory state.

Low-Flow Acute Kidney Injury: The Pathophysiology of Prerenal Azotemia, Abdominal Compartment Syndrome, and Obstructive Uropathy

AKI is a syndrome, not a disease. It results from many different primary and/or secondary etiologies and is often multifactorial, especially in the hospitalized patient. This review discusses the pathophysiology of three etiologies that cause AKI, those being kidney hypoperfusion, abdominal compartment syndrome, and urinary tract obstruction. The pathophysiology of these three causes of AKI differs but is overlapping. They all lead to a low urine flow rate and low urine sodium initially. In all three cases, with early recognition and correction of the underlying process, the resulting functional AKI can be rapidly reversed. However, with continued duration and/or increased severity, cell injury occurs within the kidney, resulting in structural AKI and a longer and more severe disease state with increased morbidity and mortality. This is why early recognition and reversal are critical.

The ShGlomAssay Combines High-Throughput Drug Screening With Downstream Analyses and Reveals the Protective Role of Vitamin D3 and Calcipotriol on Podocytes

Chronic kidney disease (CKD) is a major public health burden affecting more than 500 million people worldwide. Podocytopathies are the main cause for the majority of CKD cases due to pathogenic morphological as well as molecular biological alterations of postmitotic podocytes. Podocyte de-differentiation is associated with foot process effacement subsequently leading to proteinuria. Since currently no curative drugs are available, high throughput screening methods using a small number of animals are a promising and essential tool to identify potential drugs against CKD in the near future. Our study presents the implementation of the already established mouse GlomAssay as a semi-automated high-throughput screening method-shGlomAssay-allowing the analysis of several hundreds of FDA-verified compounds in combination with downstream pathway analysis like transcriptomic and proteomic analyses from the same samples, using a small number of animals. In an initial prescreening we have identified vitamin D3 and its analog calcipotriol to be protective on podocytes. Furthermore, by using RT-qPCR, Western blot, and RNA sequencing, we found that mRNA and protein expression of nephrin, the vitamin D receptor and specific podocyte markers were significantly up-regulated due to vitamin D3- and calcipotriol-treatment. In contrast, kidney injury markers were significantly down-regulated. Additionally, we found that vitamin D3 and calcipotriol have had neither influence on the expression of the miR-21 and miR-30a nor on miR-125a/b, a miRNA described to regulate the vitamin D receptor. In summary, we advanced the established mouse GlomAssay to a semi-automated high-throughput assay and combined it with downstream analysis techniques by using only a minimum number of animals. Hereby, we identified the vitamin D signaling pathway as podocyte protective and to be counteracting their de-differentiation.

Kidney repair and regeneration: perspectives of the NIDDK (Re)Building a Kidney consortium

Acute kidney injury impacts ∼13.3 million individuals and causes ∼1.7 million deaths per year globally. Numerous injury pathways contribute to acute kidney injury, including cell cycle arrest, senescence, inflammation, mitochondrial dysfunction, and endothelial injury and dysfunction, and can lead to chronic inflammation and fibrosis. However, factors enabling productive repair versus nonproductive, persistent injury states remain less understood. The (Re)Building a Kidney (RBK) consortium is a National Institute of Diabetes and Digestive and Kidney Diseases consortium focused on both endogenous kidney repair mechanisms and the generation of new kidney tissue. This short review provides an update on RBK studies of endogenous nephron repair, addressing the following questions: (i) What is productive nephron repair? (ii) What are the cellular sources and drivers of repair? and (iii) How do RBK studies promote development of therapeutics? Also, we provide a guide to RBK's open access data hub for accessing, downloading, and further analyzing data sets.

Blood Flow Regulates Glomerular Capillary Formation in Zebrafish Pronephros

BACKGROUND

The renal glomerulus is a tuft of capillaries in Bowman's capsule and functions as a blood-filtration unit in the kidney. The unique glomerular capillary tuft structure is relatively conserved through vertebrate species. However, the morphogenetic mechanism governing glomerular capillary tuft formation remains elusive.

METHODS

To clarify how glomerular capillaries develop, we analyzed glomerular capillary formation in the zebrafish pronephros by exploiting fluorescence-based bio-imaging technology.

RESULTS

During glomerular capillary formation in the zebrafish pronephros, endothelial cells initially sprouted from the dorsal aorta and formed the capillaries surrounding the bilateral glomerular primordia in response to podocyte progenitor-derived vascular endothelial growth factor-A. After formation, blood flow immediately occurred in the glomerular primordia-associated capillaries, while in the absence of blood flow, they were transformed into sheet-like structures enveloping the glomerular primordia. Subsequently, blood flow induced formation of Bowman's space at the lateral sides of the bilateral glomerular primordia. Concomitantly, podocyte progenitors enveloped their surrounding capillaries while moving toward and coalescing at the midline. These capillaries then underwent extensive expansion and remodeling to establish a functional glomerular capillary tuft. However, stopping blood flow inhibited the remodeling of bilateral glomerular primordia, which therefore remained unvascularized but covered by the vascular sheets.

CONCLUSIONS

We delineated the morphogenetic processes governing glomerular capillary tuft formation in the zebrafish pronephros and demonstrated crucial roles of blood flow in its formation. Blood flow maintains tubular structures of the capillaries surrounding the glomerular primordia and promotes glomerular incorporation of these vessels by inducing the remodeling of glomerular primordia.

Expression Profile of Human Renal Mesangial Cells Is Altered by Infection with Pathogenic Puumala Orthohantavirus

Acute kidney injury (AKI) with proteinuria is a hallmark of infections with Eurasian orthohantaviruses. Different kidney cells are identified as target cells of hantaviruses. Mesangial cells may play a central role in the pathogenesis of AKI by regulation of inflammatory mediators and signaling cascades. Therefore, we examined the characteristics of hantavirus infection on human renal mesangial cells (HRMCs). Receptor expression and infection with pathogenic Puumala virus (PUUV) and low-pathogenic Tula virus (TULV) were explored. To analyze changes in protein expression in infected mesangial cells, we performed a proteome profiler assay analyzing 38 markers of kidney damage. We compared the proteome profile of in vitro-infected HRMCs with the profile detected in urine samples of 11 patients with acute hantavirus infection. We observed effective productive infection of HRMCs with pathogenic PUUV, but only poor abortive infection for low-pathogenic TULV. PUUV infection resulted in the deregulation of proteases, adhesion proteins, and cytokines associated with renal damage. The urinary proteome profile of hantavirus patients demonstrated also massive changes, which in part correspond to the alterations observed in the in vitro infection of HRMCs. The direct infection of mesangial cells may induce a local environment of signal mediators that contributes to AKI in hantavirus infection.

A novel model of nephrotic syndrome results from a point mutation in Lama5 and is modified by genetic background

Nephrotic syndrome is characterized by severe proteinuria, hypoalbuminaemia, edema and hyperlipidaemia. Genetic studies of nephrotic syndrome have led to the identification of proteins playing a crucial role in slit diaphragm signaling, regulation of actin cytoskeleton dynamics and cell-matrix interactions. The laminin α5 chain is essential for embryonic development and, in association with laminin β2 and laminin γ1, is a major component of the glomerular basement membrane, a critical component of the glomerular filtration barrier. Mutations in LAMA5 were recently identified in children with nephrotic syndrome. Here, we have identified a novel missense mutation (E884G) in the uncharacterized L4a domain of LAMA5 where homozygous mice develop nephrotic syndrome with severe proteinuria with histological and ultrastructural changes in the glomerulus mimicking the progression seen in most patients. The levels of LAMA5 are reduced in vivo and the assembly of the laminin 521 heterotrimer significantly reduced in vitro. Proteomic analysis of the glomerular extracellular fraction revealed changes in the matrix composition. Importantly, the genetic background of the mice had a significant effect on aspects of disease progression from proteinuria to changes in podocyte morphology. Thus, our novel model will provide insights into pathologic mechanisms of nephrotic syndrome and pathways that influence the response to a dysfunctional glomerular basement membrane that may be important in a range of kidney diseases.

Molecular and Cellular Mechanisms Underlying the Initiation and Progression of Alport Glomerular Pathology

Alport syndrome results from a myriad of variants in the COL4A3, COL4A4, or COL4A5 genes that encode type IV (basement membrane) collagens. Unlike type IV collagen α1(IV)₂α2(IV)₁ heterotrimers, which are ubiquitous in basement membranes, α3/α4/α5 have a limited tissue distribution. The absence of these basement membrane networks causes pathologies in some, but not all these tissues. Primarily the kidney glomerulus, the stria vascularis of the inner ear, the lens, and the retina as well as a rare link with aortic aneurisms. Defects in the glomerular basement membranes results in delayed onset and progressive focal segmental glomerulosclerosis ultimately requiring the patient to undergo dialysis and if accessible, kidney transplant. The lifespan of patients with Alport syndrome is ultimately significantly shortened. This review addresses the consequences of the altered glomerular basement membrane composition in Alport syndrome with specific emphasis on the mechanisms underlying initiation and progression of glomerular pathology.

The Glomerulus According to the Mesangium

The glomerulus is the functional unit for filtration of blood and formation of primary urine. This intricate structure is composed of the endothelium with its glycocalyx facing the blood, the glomerular basement membrane and the podocytes facing the urinary space of Bowman's capsule. The mesangial cells are the central hub connecting and supporting all these structures. The components as a unit ensure a high permselectivity hindering large plasma proteins from passing into the urine while readily filtering water and small solutes. There has been a long-standing interest and discussion regarding the functional contribution of the different cellular components but the mesangial cells have been somewhat overlooked in this context. The mesangium is situated in close proximity to all other cellular components of the glomerulus and should be considered important in pathophysiological events leading to glomerular disease. This review will highlight the role of the mesangium in both glomerular function and intra-glomerular crosstalk. It also aims to explain the role of the mesangium as a central component involved in disease onset and progression as well as signaling to maintain the functions of other glomerular cells to uphold permselectivity and glomerular health.

Impact of Consensus Definitions on Identification of Glomerular Lesions by Light and Electron Microscopy

Introduction

In 2020, a working group of 13 renal pathologists published consensus definitions for 47 individual glomerular lesions found on light microscopy (LM) and 47 glomerular lesions and 9 normal structures found on electron microscopy (EM).

Methods

To test the impact of these definitions on identification of these lesions and structures, 2 surveys were circulated to all members of the Renal Pathology Society (RPS), each having 32 images (19 LM, 13 EM) and accompanying questions with 5 multiple-choice answers, one being the consensus choice of the working group. The first survey (survey 1 [S1]), answered by 297 RPS members, was sent in September 2020, before publication of the consensus definitions. The second (survey 2 [S2]), with images of the same lesions and structures (but not the same images) and the same questions and multiple choices in different order, was sent in April 2020, 5 months after the publication of the definitions.

Results

S2 was taken by 181 RPS members; 64% also took S1 and 61% reported having read the definitions paper (def. paper). Mean agreement with the consensus answers increased modestly between the 2 surveys (65.2% vs. 72.0%, P = 0.097); the increase was greater and significant when only respondents to S2 who read the def. paper were considered (65.2% vs. 74.8%, P = 0.026). Furthermore, in S2 agreement with consensus answers was greater among respondents who read this paper versus those who did not (66.9% vs. 74.8%, P < 0.0001).

Conclusions

Publication of the consensus definitions modestly improved interobserver agreement in identification of glomerular lesions.

Clinical Significance of Glomerular Autophagy in Evaluation of Diabetic Kidney Disease Progression

BACKGROUND

Diabetic kidney disease (DKD) is closely associated with the death or survival of resident kidney cells.

AIM

The purpose of this study was to determine the changes in renal cell survival and death in DKD and their diagnostic values in DKD progression.

MATERIALS AND METHODS

This study analyzed a dataset of renal tissues from DKD patients to identify changes in genes associated with renal cell death and survival. Our findings were subsequently validated in human kidney tissues. Differential indicators of DKD patients' clinicopathological data screened by stepwise regression and glomerular P62 protein expression were included in binary logistic regression analysis to assess the impact of these parameters on DKD progression. A receiver operating characteristic (ROC) curve analysis was employed to evaluate the diagnostic value of P62 protein in DKD progression.

RESULTS

Bioinformatics analysis results revealed that glomerular autophagy in DKD was more significantly altered, which was consistent with the semi-quantitative results of P62 in glomeruli. Further studies established that P62 expression was mainly increased in podocytes. Stepwise regression analysis indicated that changes in the expressions of glomerular P62 and apolipoprotein A1 (ApoA1) might be involved in the progression of DKD. However, binary logistic regression analysis results suggested that only P62 was significantly associated with DKD development. ROC curve analysis showed that the area under the curve (AUC) of P62 for the detection of DKD was 0.905.

CONCLUSION

Autophagy inhibition occurred in both glomeruli and tubules, and was most pronounced in glomerular podocytes. The levels of P62 protein in glomeruli, as an autophagy activity indicator, was one of the predictors of entering the stage of macroalbuminuria in DKD.

Targeted delivery of celastrol to glomerular endothelium and podocytes for chronic kidney disease treatment

The etiology of chronic kidney disease (CKD) is complex and diverse, which could be briefly categorized to glomerular- or tubular-originated. However, the final outcomes of CKD are mainly glomerular sclerosis, endothelial dysfunction and injury, and chronic inflammation. Thus, targeted delivery of drugs to the glomeruli in order to ameliorate glomerular endothelial damage may help alleviate CKD and help enrich our knowledge. The herb tripterygium wilfordii shows therapeutic effect on kidney disease, and celastrol (CLT) is one of its active ingredients but with strong toxicity. Therefore, based on the unique structure and pathological characteristics of the glomerulus, we designed a targeted delivery system named peptides coupled CLT-phospholipid lipid nanoparticles (PC-PLNs) to efficiently deliver CLT to damaged endothelial cells and podocytes in the glomerulus for CKD treatment and research. PC-PLNs could effectively inhibit inflammation, reduce endothelial damage, alleviate CKD severity, and reduce the toxicity of CLT. We also studied the mechanism of CLT in the treatment of nephropathy and found that CLT can increase the level of NO by increasing eNOS while inhibiting the expression of VCAM-1, thus provides an anti-inflammatory effect. Therefore, our study not only offered an efficient CKD drug formulation for further development, but also provided new medical knowledge about CKD.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material (attached with all the supporting tables and figures mentioned in this work) is available in the online version of this article at 10.1007/s12274-021-3894-x.

Dysregulation of Lysyl Oxidases Expression in Diabetic Nephropathy and Renal Cell Carcinoma

Lysyl oxidases (LOXs) are amino oxidase enzymes that catalyze the oxidative deamination of lysine and hydroxylysine residues to form allysine, the first step towards the development of the final cross-linking reaction in collagens, a crucial macromolecule that reinforces extracellular matrices. Basement membranes are specialized extracellular matrices that are essential components of the glomerular filtration barrier, which also support tubular epithelial cells. Lysyl oxidases are post-translational enzymes indispensable for tissue architecture, participating actively in the development and function of kidneys. The differential expression and dysregulation of these enzymes promote diabetic nephropathy, one of the major complications observed in end-stage renal diseases. In addition, these enzymes act as transcription factors that trigger the epithelial-mesenchymal transition responsible for the generation of different cancers. In the kidney, the expression studies in physiological conditions identified LOXL1 and LOXL2 as constituent proteins of glomerular basement membranes. Besides, LOX and LOXL2 are upregulated in fibrosis and renal cell carcinoma. The current review summarizes the physiological expression of LOXs enzymes in the nephrons, including glomerulus and tubules. Their roles in renal diseases are particularly highlighted in diabetic nephropathy and renal cell carcinoma, two pathophysiological conditions where these enzymes have been demonstrated to participate. The focus of the present study is to describe and discuss the current understanding in this field. The current potential of LOXs enzymes as a biomarker and pharmacological target to kidney diseases that involves extracellular matrix cross-linking enzymes is also discussed. LOXs isoforms and their capacity as therapeutic targets could be used for diagnostic and prognostic purposes and in treating these renal complications.

The therapeutic potential of apelin in kidney disease

Chronic kidney disease (CKD) is a leading cause of global morbidity and mortality and is independently associated with cardiovascular disease. The mainstay of treatment for CKD is blockade of the renin-angiotensin-aldosterone system (RAAS), which reduces blood pressure and proteinuria and slows kidney function decline. Despite this treatment, many patients progress to kidney failure, which requires dialysis or kidney transplantation, and/or die as a result of cardiovascular disease. The apelin system is an endogenous physiological regulator that is emerging as a potential therapeutic target for many diseases. This system comprises the apelin receptor and its two families of endogenous ligands, apelin and elabela/toddler. Preclinical and clinical studies show that apelin receptor ligands are endothelium-dependent vasodilators and potent inotropes, and the apelin system has a reciprocal relationship with the RAAS. In preclinical studies, apelin regulates glomerular haemodynamics and acts on the tubule to promote aquaresis. In addition, apelin is protective in several kidney injury models. Although the apelin system has not yet been studied in patients with CKD, the available data suggest that apelin is a promising potential therapeutic target for kidney disease.

Renal morphology and glomerular capillarisation in young adult sheep born moderately preterm

Preterm birth (delivery <37 weeks of gestation) is associated with impaired glomerular capillary growth in neonates; if this persists, it may be a contributing factor in the increased risk of hypertension and chronic kidney disease in people born preterm. Therefore, in this study, we aimed to determine the long-term impact of preterm birth on renal morphology, in adult sheep. Singleton male sheep were delivered moderately preterm at 132 days (~0.9) of gestation (n = 6) or at term (147 days gestation; n = 6) and euthanised at 14.5 months of age (early adulthood). Stereological methods were used to determine mean renal corpuscle and glomerular volumes, and glomerular capillary length and surface area, in the outer, mid and inner regions of the renal cortex. Glomerulosclerosis and interstitial collagen levels were assessed histologically. By 14.5 months of age, there was no difference between the term and preterm sheep in body or kidney weight. Renal corpuscle volume was significantly larger in the preterm sheep than the term sheep, with the preterm sheep exhibiting enlarged Bowman's spaces; however, there was no difference in glomerular volume between groups, with no impact of preterm birth on capillary length or surface area per glomerulus. There was also no difference in interstitial collagen levels or glomerulosclerosis index between groups. Findings suggest that moderate preterm birth does not adversely affect glomerular structure in early adulthood. The enlarged Bowman's space in the renal corpuscles of the preterm sheep kidneys, however, is of concern and merits further research into its cause and functional consequences.

Renal cell markers: lighthouses for managing renal diseases

Kidneys, one of the vital organs in our body, are responsible for maintaining whole body homeostasis. The complexity of renal function (e.g., filtration, reabsorption, fluid and electrolyte regulation, and urine production) demands diversity not only at the level of cell types but also in their overall distribution and structural framework within the kidney. To gain an in depth molecular-level understanding of the renal system, it is imperative to discern the components of kidney and the types of cells residing in each of the subregions. Recent developments in labeling, tracing, and imaging techniques have enabled us to mark, monitor, and identify these cells in vivo with high efficiency in a minimally invasive manner. In this review, we summarize different cell types, specific markers that are uniquely associated with those cell types, and their distribution in the kidney, which altogether make kidneys so special and different. Cellular sorting based on the presence of certain proteins on the cell surface allowed for the assignment of multiple markers for each cell type. However, different studies using different techniques have found contradictions in cell type-specific markers. Thus, the term "cell marker" might be imprecise and suboptimal, leading to uncertainty when interpreting the data. Therefore, we strongly believe that there is an unmet need to define the best cell markers for a cell type. Although the compendium of renal-selective marker proteins presented in this review is a resource that may be useful to researchers, we acknowledge that the list may not be necessarily exhaustive.

Podocyte Aging: Why and How Getting Old Matters

The effects of healthy aging on the kidney, and how these effects intersect with superimposed diseases, are highly relevant in the context of the population's increasing longevity. Age-associated changes to podocytes, which are terminally differentiated glomerular epithelial cells, adversely affect kidney health. This review discusses the molecular and cellular mechanisms underlying podocyte aging, how these mechanisms might be augmented by disease in the aged kidney, and approaches to mitigate progressive damage to podocytes. Furthermore, we address how biologic pathways such as those associated with cellular growth confound aging in humans and rodents.

Podocytopathy in Obesity: Challenges of Living Large

Renal injury resulting from obesity is a growing concern caused by the global obesity epidemic. We discuss the glomerular structure, obesity-related glomerular changes, and diagnostic pathologic criteria for obesity-related glomerulopathy. The three main hypothesized mechanisms of podocyte injury are mechanical stress on the podocytes, metabolic derangement, and genetic/molecular factors. Weight loss, renin-angiotensin-aldosterone system inhibitors, and improved insulin resistance may slow the progression. A more comprehensive understanding of obesity-related glomerulopathy will help in developing more effective therapies.

Single Cell Transcriptome Helps Better Understanding Crosstalk in Diabetic Kidney Disease

Years of research revealed that crosstalk extensively existed among kidney cells, cell factors and metabolites and played an important role in the development of diabetic kidney disease (DKD). In the last few years, single-cell RNA sequencing (scRNA-seq) technology provided new insight into cellular heterogeneity and genetic susceptibility regarding DKD at cell-specific level. The studies based on scRNA-seq enable a much deeper understanding of cell-specific processes such as interaction between cells. In this paper, we aim to review recent progress in single cell transcriptomic analyses of DKD, particularly highlighting on intra- or extra-glomerular cell crosstalk, cellular targets and potential therapeutic strategies for DKD.

Application of direct stochastic optical reconstruction microscopy (dSTORM) to the histological analysis of human glomerular disease

Electron microscopy (EM) following immunofluorescence (IF) imaging is a vital tool for the diagnosis of human glomerular diseases, but the implementation of EM is limited to specialised institutions and it is not available in many countries. Recent progress in fluorescence microscopy now enables conventional widefield fluorescence microscopes to be adapted at modest cost to provide resolution below 50 nm in biological specimens. We show that stochastically switched single-molecule localisation microscopy can be applied to clinical histological sections stained with standard IF techniques and that such super-resolved IF may provide an alternative means to resolve ultrastructure to aid the diagnosis of kidney disease where EM is not available. We have implemented the direct stochastic optical reconstruction microscopy technique with human kidney biopsy frozen sections stained with clinically approved immunofluorescent probes for the basal laminae and immunoglobulin G deposits. Using cases of membranous glomerulonephritis, thin basement membrane lesion, and lupus nephritis, we compare this approach to clinical EM images and demonstrate enhanced imaging compared to conventional IF microscopy. With minor modifications in established IF protocols of clinical frozen renal biopsies, we believe the cost-effective adaptation of conventional widefield microscopes can be widely implemented to provide super-resolved image information to aid diagnosis of human glomerular disease.

ShcA expression in podocytes is dispensable for glomerular development but its upregulation is associated with kidney disease

BACKGROUND

ShcA (SHC1) is a phosphotyrosine adaptor protein which plays broad signaling roles within the cell. Systemic loss of ShcA during embryogenesis is lethal, while its aberrant expression contributes to disease. We recently demonstrated that ShcA is highly expressed during glomerular development and that it is upregulated within podocytes in experimental kidney injury and chronic kidney disease. The objective of this study was to analyze the in vivo role of ShcA in podocytes.

METHODS

We selectively deleted all three isoforms of ShcA from mouse kidney podocytes using the Cre/lox system driven by the podocyte-specific podocin promoter (Nphs2). Immunostaining of kidney sections was used to confirm ShcA deletion in podocytes. Coomassie blue staining of protein gels was used to detect urinary albumin. Light and electron microscopy were used to assess glomerular morphology. Transcript levels of SHC1 in human renal disease were assessed using the Nephroseq database.

RESULTS

Mice lacking podocyte ShcA were born at the expected Mendelian frequency and did not display overt renal impairment or changes in podocyte architecture beyond one year of age. In parallel, we correlated increased ShcA mRNA expression in the human kidney with proteinuria and reduced glomerular filtration rate.

CONCLUSION

Our studies reveal that ShcA is dispensable for normal kidney function, but its upregulation is associated with disease.