Glomerular Basement Membrane Research Articles

Glomerular basement membrane thickness estimation and stratification via active semi-supervised learning model.

The measure of Glomerular Basement Membrane (GBM) thickness is used as diagnostic criteria for kidney glomerular diseases. The GBM thickness measurement, a time-consuming task, is performed by expert pathologists on transmission electron microscopy (TEM) images, therefore, it is affected by subjectivity and reproducibility issues. Here we introduce a fully automated pipeline for the GBM segmentation and successive thickness estimation, starting from TEM images. This method is based on an active semi-supervised learning training procedure of a convolutional neural network model. Starting from the areas automatically identified by the model, we provide a robust measurement of membrane thickness using pixels distance matrix and computer vision techniques. Using these values, we trained a machine learning model to automatically determine the GBM thickness. To verify the accuracy of the method, we compared the predicted results with the full iconographic materials and diagnostic record reports from 42 renal biopsies having normal-thick (n. 21), thin- (n. 10), thick-GBM (n. 11). The obtained segmentations were used for the automated estimation of GBM thickness via computer vision algorithms and compared with manual measurements, obtaining a correlation of Pearson's R2 of 0.85. The GBM thickness was stratified into 3 classes, namely normal, thin, thick with a 0.63 Matthews correlation coefficient and a 0.76 accuracy. The proposed pipeline obtained state-of-the-art performance in GBM segmentation, proving its robustness under image variations, such as magnification, contrast, and complex geometrical shapes. Automated measures could assist clinicians in standard clinical practice speeding up routine procedures with high diagnostic accuracy.

Collagen IV of basement membranes: I. Origin and diversification of COL4 genes enabling metazoan multicellularity, evolution and adaptation.

Collagen IV is a major component of basement membranes, a specialized form of extracellular matrix that enabled the assembly of multicellular epithelial tissues. In mammals, collagen IV assembles from a family of six α-chains (α1 to α6), forming three supramolecular scaffolds: Col-IVα121, Col-IVα345 and Col-IVα121-α556. The α-chains are encoded by six genes (COL4A1-6) that occur in pairs in a head-to-head arrangement. In Alport syndrome, variants in COL4A3, 4 or 5 genes, encoding Col-IVα345 scaffold in glomerular basement membrane (GBM), the kidney ultrafilter, cause progressive renal failure in millions of people worldwide. The molecular mechanisms of how variants cause dysfunction remain obscure. Here, we gained insights into Col-IVα345 function by determining its evolutionary lineage, as revealed from phylogenetic analyses and tissue expression of COL4 gene-pairs. We found that the COL4A⟨1|2⟩ gene-pair emerged in basal Ctenophores and Cnidaria phyla and is highly conserved across metazoans. The COL4A⟨1|2⟩ duplicated and arose as the progenitor to the COL4A⟨3|4⟩ gene-pair in cyclostomes, coinciding with emergence of kidney GBM, and expressed and conserved in jawed-vertebrates, except for amphibians, and a second duplication as the progenitor to the COL4A⟨5|6⟩ gene-pair and conserved in jawed-vertebrates. These findings revealed that Col-IVα121 is the progenitor scaffold, expressed ubiquitously in metazoan basement membranes, and which evolved into vertebrate Col-IVα345 and expressed in GBM. The Col-IVα345 scaffold, in comparison, has an increased number of cysteine residues, varying in number with osmolarity of the environment. Cysteines mediate disulfide crosslinks between protomers, an adaptation enabling a compact GBM that withstands the high hydrostatic pressure associated with glomerular ultrafiltration.

Revisiting Alport syndrome: Genetic background, phenotypic variability, and therapeutic approaches

Nearly a century has passed since Cecil A. Alport first described the triad of nephritis, hearing loss, and ocular abnormalities that would later be recognized as the second most common inherited nephropathy and a significant cause of end-stage kidney disease. Pathogenic variants in COL4A3, COL4A4, and COL4A5 genes lead to compromised synthesis, assembly, and/or function of α3, α4, and α5 chains of type IV collagen (COL4). This disruption leads to an abnormal trimerization of COL4 into a stable network, impairing the integrity and function of glomerular, cochlear, and ocular basement membranes. The gold standard for Alport syndrome diagnosis is molecular genetic testing, which provides a non-invasive and highly specific approach. In settings with limited access to genetic testing, kidney biopsy with electron microscopy remains essential, revealing characteristic glomerular basement membrane abnormalities. Despite significant advancements in understanding its genetic and molecular basis, Alport syndrome remains a relentlessly progressive disorder, often culminating in end-stage kidney disease during early adulthood. While no disease-specific therapy exists, early initiation of renin-angiotensin-aldosterone system blockade is the cornerstone of AS management, delaying disease progression. Emerging therapies, including sodium-glucose cotransporter-2 inhibitors and mineralocorticoid receptor antagonists, are being investigated for their nephroprotective potential. In addition, recent breakthroughs in therapeutic research – including gene- and cell-based treatments – hold the potential to transform disease management. Genetic factors influence treatment response, reinforcing the need for personalized therapeutic approaches. In this review, we discuss the genetic background and phenotypic correlations of Alport syndrome, the pathophysiological mechanisms driving both renal and extrarenal manifestations, and explore diagnostic approaches and emerging strategies aimed at modifying the natural course of this disease.

<i>LMX1B</i>-associated steroid-resistant nephrotic syndrome with focal segmental glomerulosclerosis (case report)

Pathogenic variants in the LMX1B gene cause nail-patella syndrome, characterized by dysplasia of the patella, nails and elbows, and renal damage with focal segmental glomerulosclerosis (FSGS) with specific ultrastructural lesions of the glomerular basal membrane (GBM). We present a clinical observation of a girl with LMX1B-associated steroid-resistant nephrotic syndrome without the extrarenal characteristic of nail-patella syndrome with specific ultrastructural changes of the GBM. The presented clinical observation emphasizes the necessity to exclude proteinuria in family members with a child with FSGS and to perform molecular genetic study in all children with FSGS before prescribing immunosuppressive therapy with inclusion of LMX1B gene even in case of isolated kidney pathology.

Comprehending the Role of Metabolic and Hemodynamic Factors Alongside Different Signaling Pathways in the Pathogenesis of Diabetic Nephropathy.

Diabetic nephropathy (DN) is a progressive microvascular disorder of diabetes that contributes as a primary reason for end-stage renal disease worldwide. The pathological hallmarks of DN include diffuse mesangial expansion, thicker basement membrane of glomeruli, and arteriole hyalinosis. Hypertension and chronic hyperglycemia are the primary risk factors contributing to the occurrence of DN. The complex pathophysiology of DN involves the interplay amongst metabolic and hemodynamic pathways, growth factors and cytokines production, oxidative stress, and ultimately impaired kidney function. Hyperglycemia-induced vascular dysfunction is the main pathological mechanism that initiates DN. However, several other pathogenic mechanisms, such as oxidative stress, inflammatory cell infiltration, and fibrosis, contribute to disease progression. Different vasoactive hormone processes, including endothelin and renin-angiotensin, are activated as a part of the pathophysiology of DN, which also involves increased intraglomerular and systemic pressure. The pathophysiology of DN will continue to be better understood because of recent developments in genomics and molecular biology, but attempts to develop a comprehensive theory that explains all existing cellular and biochemical pathways have been thwarted by the disease's multifactorial nature. This review extensively discusses the current understanding regarding the metabolic and hemodynamic pathological mechanisms, along with other signaling pathways and molecules responsible for the pathogenesis of DN. This work will encourage a greater in-depth understanding and investigation of the present status of the biochemical mechanistic processes underlying the pathogenesis of DN, which may assist in the determination of different biomarkers and help in the design and development of novel drug candidates in the near future.

Association of Urinary Podocalyxin with Albumin Creatinine Ratio in T2DM Patients

Podocalyxin is a negatively charged protein located in the kidney podocyte membrane, which is a glycosylated cell surface sialomucin of the CD34 family. It is the main component of the glomerular basement membrane charge barrier and has an important role in the regulation of glomerular filtration barrier permeability. There is an argument on the association of PCX with diabetic renal complications and its probability to be a new marker for early diagnosis of diabetic renal complications. The aim of the study was determination of urinary podocalyxin levels in T2DM patients and to analyze its correlation with albumin to creatinine ratio and glycemic control. By consecutive sampling, 82 samples were selected and divided into two groups. The control group consisted of 20 healthy subjects, and the case group was 62 subjects with T2DM. Albumin creatinine ratio, serum creatinine, glycemic control, body mass index and urinary podocalyxin were measured for both groups. Significant higher levels of urinary podocalyxin were found in the case group compared to the control group (p =0.005). There was a significant difference in urinary podocalyxin levels between case groups (normoalbuminuria, microalbuminuria, and macroalbuminuria) (p<0.001). Urinary podocalyxin levels had a significant strong positive correlation with albumin creatinine ratio (p<0.001), and weak positive correlation with serum creatinine and HbA1c. Due to significant differences in urinary podocalyxin levels between the case and control group and within case groups, as well as its positive correlation with albumin creatinine ratio, it might be a good marker for the diagnosis of diabetic kidney disease.

Adenovirus infection and anti-GBM disease (Goodpasture syndrome): a clinical case

Goodpasture’s syndrome, an autoimmune disease resulting from the appearance of antibodies to the glomerular basement membrane, is a rare and potentially dangerous complication of infectious diseases such as influenza, new coronavirus infection, adenovirus infection. The course may be atypical and manifest as a severe form of viral disease complicated by acute respiratory distress syndrome and sepsis against the background of an accompanying bacterial infection. The necessary diagnostic methods may be unavailable or performed with a significant delay if biological material is sent to third-party organizations. Timely diagnosis and initiation of specific treatment can reduce mortality by almost half. The article presents a clinical case of a patient with Goodpasture syndrome who was at the clinic of infectious diseases S.M. Kirov Military Medical Academy with acute respiratory viral infection complicated by polysegmental pneumonia.

A Self-Adaptive Strip Pooling Network for Segmenting the Kidney Glomerular Basement Membrane

Accurate semantic segmentation and automatic thickness measurement of the glomerular basement membrane (GBM) can aid pathologists in carrying out subsequent pathological diagnoses. The GBM has a complex ultrastructure and irregular shape, which makes it difficult to segment accurately. We found that the shape of the GBM is striped, so we proposed an RSP model to extract both the strip and square features of the GBM. Additionally, grayscale images of the GBM are similar to those of surrounding tissues, and the contrast is low. We added an edge attention mechanism to further improve the quality of segmentation. Moreover, we revised the pixel-level loss function to consider the tissues around the GBM and locate the GBM as a doctor would, i.e., by using the tissues as the reference object. Ablation experiments with each module showed that SSPNet can better segment the GBM. The proposed method was also compared with the existing medical semantic segmentation model. The experimental results showed that the proposed method can obtain high-precision segmentation results for the GBM and completely segment the target. Finally, the thickness of the GBM was calculated using a skeleton extraction method to provide quantitative data for expert diagnosis.

The secreted protease ADAMTS18 links early isoform transformation and maturation of glomerular basement membrane macromolecules to the integrity of the glomerular filtration barrier.

The secreted protease ADAMTS18 links early isoform transformation and maturation of glomerular basement membrane macromolecules to the integrity of the glomerular filtration barrier.

A novel variation in the LMX1B gene with nail-patella syndrome.

A novel variation in the LMX1B gene with nail-patella syndrome.

Podocyte infolding glomerulopathy in a school-aged child.

Podocyte infolding glomerulopathy (PIG) is a rare kidney disorder characterized by the infolding of podocyte processes into the glomerular basement membrane. The condition presents with nephrotic syndrome, yet its pathogenesis and clinical implications remain poorly understood due to limited case reports. Most documented cases have originated from Japan, highlighting a significant gap in the literature regarding its prevalence and characteristics in other regions, including the Indian subcontinent. A 5-year-old boy presented with hypertension, edema, nephrotic range proteinuria, and 3 weeks later developed macroscopic hematuria. Kidney biopsy revealed characteristic microtubule formation within the glomerular basement membrane, confirming the diagnosis of PIG. Initial treatment with prednisolone was unsuccessful, leading to the addition of tacrolimus which resulted in significant improvements in the child's proteinuria and hematuria. This case contributes to the limited literature on PIG and highlights the need for more research to establish standardized treatment protocols.

Obinutuzumab in membranous nephropathy: a potential game-changer in treatment.

Membranous nephropathy (MN) is a kidney disease characterized by thickening of the glomerular basement membrane due to immune complex deposition, often leading to nephrotic syndrome and potentially progressing to end-stage renal disease. Traditional treatments, including corticosteroids and immunosuppressive agents, have significant side-effects and variable efficacy. Recently, obinutuzumab, a fully humanized monoclonal antibody targeting CD20, has emerged as a promising therapeutic option for MN. Herein, we review the pathophysiology of MN, the mechanism of action of obinutuzumab, clinical data supporting its use and highlight its potential as a game changer in MN treatment.

Advances in understanding and managing diabetic kidney disease: An updated review

Chronic kidney disease (CKD) and end-stage kidney disease (ESKD) are common complications of diabetes. Proteinuria is an early indicator of glomerular basement membrane damage caused by diabetes, leading to diabetic kidney disease (DKD). Edema, hypoproteinemia, and proteinuria are common characteristics of DKD. Blood sugar and blood pressure control, along with early detection, are the primary strategies for preventing DKD and slowing its progression. This review examines and updates the epidemiology, pathogenesis, and prevention of DKD. Various keywords and phrases are used to search Google, EMBASE, PubMed, Scopus, and Google Scholar for the most recent articles published from January 2023 to December 2024. Despite advancements in understanding DKD pathogenesis and the development of novel therapies, the disease remains highly prevalent with poor outcomes. The pathophysiology is still not fully understood, leading to gaps in prevention and treatment strategies. Therefore, this review aims to explore these gaps and propose potential new therapies and future research directions.

G protein-coupled receptor 107 deficiency promotes development of diabetic nephropathy

Diabetic nephropathy (DN) is characterized by glomerular basement membrane (GBM) thickening, primarily due to the abnormal accumulation of collagen type IV (COL4) in the extracellular matrix (ECM) of podocytes. Podocytes endocytosis is crucial for maintaining COL4 balance and GBM integrity. Previous studies have shown that G protein-coupled receptor 107 (GPR107) facilitates clathrin-dependent transferrin internalization and recycling in murine embryonic fibroblast cells. Therefore, the aim of the study is to investigate the role of GPR107 in regulating COL4 balance within the podocytes ECM and its potential as a therapeutic target for DN. Here, we found a significant decrease in GPR107 expression in renal tissues from DN patients and streptozocin (STZ)-induced DN mice. Furthermore, GPR107-deficient mice with STZ-induced DN exhibited more severe kidney damage, marked by increased GBM thickening and COL4 accumulation. In vitro, GPR107 deficiency under high-glucose conditions promoted COL4 accumulation in the ECM of podocytes due to increased COL4 production and decreased COL4 degradation. Mechanistically, we demonstrated that GPR107 contributes to angiotensin II receptor type 1 (AT1R) internalization through clathrin-mediated endocytosis (CME) in podocytes. Therefore, GPR107 deficiency impairs AT1R internalization, leading to increased membrane-bound AT1R. This, in turn, activates the AT1R/Ca2+ signaling pathway to promote phosphorylation of cAMP-response element-binding protein (CREB), ultimately enhancing COL4 synthesis and inhibiting the expression of matrix metalloproteinase 2 (MMP-2). These findings shed light on new functions of GPR107 in DN and offer new insights into a therapeutic target for DN.

Case of maternal uniparental isodisomy with autosomal recessive Alport syndrome combined with congenital myasthenia and Oguchi disease.

Uniparental isodisomy (UPiD) is a genetic condition in which an individual inherits two identical copies of a chromosome, or part of a chromosome, from one parent. UPiD can result in the development of autosomal recessive disorders if the chromosome inherited from one parent has a pathogenic variant. Herein, we present a 20year-old female patient who had no significant family history including kidney, muscular, or ocular diseases. She had muscle weakness since infancy and was suspected with congenital myasthenia. She was diagnosed with Oguchi disease, a congenital condition characterized by night blindness, by an ophthalmologist. At 3years of age, hematuria was noted, and gross hematuria was occasionally observed thereafter. Exome analysis revealed homozygous variants in the COL4A4, CHRND, and SAG genes on chromosome 2, which are the causative genes of Alport syndrome, congenital myasthenic syndrome, and Oguchi disease, respectively. Array comparative genomic hybridization analysis and microsatellite analysis revealed maternal UPiD. At approximately 18years of age, she presented with proteinuria withmild kidney impairment, and kidney biopsy was performed at 20years of age. Type IV collagen α5 chain staining showed a weak but positive image in the glomerular basement membrane. However, thinning and irregular thickening of the glomerular basement membrane and reticular changes in the dense layer were observed, which were consistent with Alport syndrome. Angiotensin II receptor blocker (candesartan) was administered, and her urinary protein levels decreased. She had a homozygous missense variant, positive α5 chain staining, and a mild phenotype.

Berberine Inhibits Migration and Apoptosis of Rat Podocytes in Diabetic Nephropathy via the Novel lncRNA LOC102549726 Related Pathway.

Diabetic nephropathy (DN) stands as one of the most severe complications of diabetes. Podocytes injury, particularly its attachment to the lateral glomerular basement membrane, serves as a crucial indicator of DN. Growing evidence suggests that berberine (BBR) can mitigate the onset and progression of DN. However, the molecular mechanisms through which BBR exerts its beneficial effects in the treatment of DN remain incompletely elucidated. To explore the underlying mechanisms by which BBR exerts its therapeutic effects in DN. High-throughput lncRNA sequencing on the renal cortex of both the DN model group and the normal SD group was performed to dig for differentially expressed lncRNAs. The expression of LOC102549726 was evaluated using qPCR. The biological functions of LOC102549726 were analyzed in podocyets and DN rats. The bioinformatics techniques, qPCR and WB were used to explore the potential molecular mechanisms. We found that lncRNA LOC102549726 was highly expressed in renal cortex of DN rats and podocytes subjected to high glucose conditions. Silencing LOC102549726 inhibited migration and apoptosis of podocytes. Mechanistically, LOC102549726 was identified as a facilitator of the expression of EGF and forkhead box O1 (FOXO1). BBR, a known therapeutic agent for DN, exhibited the ability to diminish the level of LOC102549726, EGF and FOXO1 in both DN rats and podocytes. Our findings suggested that BBR suppresses migration and apoptosis of podocytes in DN through targeting the LOC102549726/EGF/FOXO1 axis. This sheds light on a potential therapeutic avenue for mitigating the impact of DN on podocyte function.

Genotype-Based Molecular Mechanisms in Alport Syndrome.

Alport syndrome is an inherited disorder characterized by kidney disease, sensorineural hearing loss, and ocular abnormalities. Alport syndrome is caused by pathogenic variants in COL4A3 , COL4A4 , or COL4A5 , which encode the α 3, α 4, and α 5 chains of type 4 collagen that forms a heterotrimer expressed in the glomerular basement membrane. Knowledge of its genetic basis has informed the development of different models in dogs, mice, and rats that reflect its autosomal and X-linked inheritance patterns as well as different mutation types, including protein-truncating and missense variants. A key difference between these two types is the synthesis of α 3 α 4 α 5(IV), which is not made in autosomal Alport syndrome (two pathogenic variants in trans or biallelic) or male patients with X-linked Alport syndrome due to protein-truncating variants. By contrast, α 3 α 4 α 5(IV) is synthesized in Alport syndrome because of missense variants. For missense variants, in vitro studies suggest that these cause impaired type 4 collagen trafficking and endoplasmic reticulum stress. For protein-truncating variants, knockout models suggest that persistence of an immature α 1 α 1 α 2(IV) network is associated with biomechanical strain, which activates endothelin-A receptors leading to mesangial filopodia formation. Moreover, studies suggest that activation of collagen receptors, integrins and discoidin domain receptor 1, play a role in disease propagation. In this review, we provide an overview of how these genotype-phenotype mechanisms are key for a precision medicine-based approach in the future.

Collagen IV of basement membranes: I. Origin and diversification of COL4 genes enabling animal evolution and adaptation.

Collagen IV is a major component of basement membranes, a specialized form of extracellular matrix that enabled the assembly of multicellular epithelial tissues. In mammals, collagen IV assembles from a family of six α-chains (α1 to α6), forming three supramolecular scaffolds: Col-IVα121, Col-IVα345 and Col-IVα121-α556. The α-chains are encoded by six genes (COL4A1-6) that occur in pairs in a head-to-head arrangement. In Alport syndrome, variants in COL4A3, 4 or 5 genes, encoding Col-IVα345 scaffold in glomerular basement membrane (GBM), the kidney ultrafilter, cause progressive renal failure in millions of people worldwide. How variants cause dysfunction remains obscure. Here, we gained insights into Col-IVα345 function by determining its evolutionary lineage, as revealed from phylogenetic analyses and tissue expression of COL4 gene-pairs. We found that the COL4A⟨1|2⟩ gene-pair emerged in basal Ctenophores and Cnidaria phyla and is highly conserved across metazoans. The COL4A⟨1|2⟩ duplicated and arose as the progenitor to the COL4A⟨3|4⟩ gene-pair in cyclostomes, coinciding with emergence of kidney GBM, and expressed and conserved in jawed-vertebrates, except for amphibians, and a second duplication as the progenitor to the COL4A⟨5|6⟩ gene-pair and conserved in jawed-vertebrates. These findings revealed that Col-IVα121 is the progenitor scaffold, expressed ubiquitously in metazoan basement membranes, and which evolved into vertebrate Col-IVα345 and expressed in GBM. The Col-IVα345 scaffold, in comparison, has an increased number of cysteine residues, varying in number with osmolarity of the environment. Cysteines mediate disulfide crosslinks between protomers, an adaptation enabling a compact GBM that withstands the high hydrostatic pressure associated with glomerular ultrafiltration.

Effects of a Novel COL4A3 Homozygous/Heterozygous Splicing Mutation on the Mild Phenotype in a Family With Autosomal Recessive Alport Syndrome and a Literature Review.

Alport syndrome involves chronic progressive kidney failure and extrarenal organ damage caused by COL4A3, COL4A4, and COL4A5 mutations. We initially discerned a COL4A3 splicing mutation via next-generation sequencing. Next, we used bioinformatics, renal biopsy pathology, and an invitro minigene experiment. Complementary analysis of clinical data was carried out, and we explored the expression and function of the variants to verify their pathogenicity. A splicing mutation (c.687 + 1G > T) in COL4A3 was found in a Chinese family. Bioinformatics analysis revealed its impact on splicing, causing a translational frameshift, which was confirmed by an invitro minigene assay. The proband's glomerular basement membrane displayed reduced type IV collagen α3, α4, and α5 chains, with some absent, suggesting disruption of collagen IV trimers in the glomerular basement membrane, potentially damaging the glomerular filtration barrier. We present a novel finding of a previously unreported c.687 + 1G > T mutation in COL4A3 that disrupts transcription and translation, impairing α3α4α5 (IV) chain formation, altering the integrity of the glomerular basement membrane, causing hereditary Alport syndrome. This discovery enriches the genetic map of Alport syndrome, aiding in clinical genetic guidance, and enhancing the efficacy of prenatal testing.

Clinicopathological analysis of anti-VEGF drug-associated renal thrombotic microangiopathy: A case series and review of the literature.

Clinicopathological analysis of anti-VEGF drug-associated renal thrombotic microangiopathy: A case series and review of the literature.