Focal segmental glomerulosclerosis and proteinuria associated with Myo1E mutations: novel variants and histological phenotype analysis

A nonsense mutation in the Tripartite motif containing 8 (TRIM8) gene, mimicking collagenopathy

Tripartite motif-containing 8 (TRIM8) gene mutations are associated with autosomal dominantly inherited neurorenal syndrome. The kidney manifestations range from nephrotic range proteinuria to nephrotic syndrome and kidney failure. The histopathology has been focal segmental glomerulosclerosis (FSGS) in all reported cases. We now report a nonsense mutation in TRIM8 in a 1-year-old boy, mimicking collagenopathy in kidney biopsy.

Advances in focal segmental glomerulosclerosis research: genetic causes to non-coding RNAs

Focal Segmental Glomerulosclerosis (FSGS) is a clinicopathological illness characterized by podocyte damage, impairing glomerular filtration, and substantial proteinuria, which often results in end-stage renal disease (ESRD). Divided into primary, secondary, genetic, and idiopathic categories, its diverse origin highlights the intricacy of its diagnosis and treatment. The existing dependence on immunosuppressive medicines highlights their side effects and inconsistent efficacy, underscoring the pressing necessity for innovative, focused treatments. Recent advancements in genomics and molecular biology have shown the significant involvement of genetic alterations, especially in podocyte-associated proteins, in the pathogenesis of FSGS. Identifying possible novel biomarkers for diagnosing FSGS and monitoring disease activity has revitalized interest in this condition. Recent data underscores the significance of non-coding RNAs, including microRNAs (miRNAs), circular RNAs (circRNAs), and long non-coding RNAs (lncRNAs), in the modulation of gene expression and podocyte functionality. Please check and confirm that the authors and their respective affiliations have been correctly identified and amend if necessary. Particular dysregulated miRNAs and circRNAs have demonstrated potential as biomarkers for early diagnosis and disease monitoring. Furthermore, understanding lncRNA-mediated pathways provides novel therapeutic targets. This review consolidates current progress in elucidating the genetic and molecular processes of FSGS, emphasizing biomarker identification and treatment innovation.

When should the nephrologist think about genetics in patients with glomerular diseases?

This review discusses the significance of genetics in diagnosing glomerular diseases. Advances in genetic testing, particularly next-generation sequencing, have improved the accessibility and accuracy of diagnosing monogenic diseases, allowing for targeted gene panels and whole-exome/genome sequencing to identify genetic variants associated with glomerular diseases. Key indicators for considering a genetic cause include the age of onset, extrarenal features, family history, and inconclusive kidney biopsy results. Early-onset diseases, for instance, have a higher likelihood of being genetically caused, while extrarenal manifestations can also suggest an underlying genetic condition. A thorough family history can reveal patterns of inheritance that point to monogenic causes, although complexities like incomplete penetrance, skewed X inactivation and mosaicism can complicate the assessment. Also, autosomal recessive conditions imply asymptomatic parents, making genetic suspicion less likely, while de novo mutations can occur without any family history, further obscuring genetic assessment. Focal segmental glomerulosclerosis (FSGS) is characterized by podocyte injury and depletion, presenting in various forms, including primary, genetic, and secondary FSGS. Accurate classification of FSGS patients based on clinical and histological features is essential for guiding treatment decisions, optimizing therapeutic plans, avoiding unnecessary immunosuppression, and predicting relapse risk after kidney transplantation. Overall, a clinicopathological approach, enriched by genetic testing, offers a precise framework for diagnosis and management in glomerular diseases. Future directions for research and clinical practice include potential advancements in genetic testing and personalized medicine, which could further improve diagnostic precision and individualized treatment strategies.

Indications for genetic testing in adults with focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a histological pattern of injury that derives from various pathological processes that affect podocytes, resulting in loss of selectivity of the glomerular filtration membrane, proteinuria and the development of renal failure that progresses to end-stage kidney disease in a significant number of patients. The classification proposed by the 2021 KDIGO guidelines divides FSGS into four categories: primary, secondary, genetic, and FSGS of undetermined cause, thus facilitating its diagnosis and management. Genetic causes of FSGS present significant clinical variability, complicating their identification. Genetic testing is crucial to identify FSGS of genetic cause. The prevalence of genetic FSGS is significant in children and considerable in adults, highlighting the importance of early diagnosis to avoid unnecessary treatments and facilitate genetic counselling. Massive sequencing techniques have revolutionized genetic diagnosis, allowing the identification of more than 60 genes responsible for podocyte damage. This document proposes clinical recommendations for carrying out genetic studies in adults with FSGS, highlighting the need for a correct classification for adequate therapeutic planning and improvement of results in clinical trials.

The Ca2+-actin-cytoskeleton axis in podocytes is an important, non-immunologic target of immunosuppressive therapy in proteinuric kidney diseases

The integrity of the filtration barrier of the kidney relies on the proper composition of podocyte interdigitating foot processes. Their architecture is supported by a complex actin-cytoskeleton. Following podocyte stress or injury, podocytes encounter structural changes, including rearrangement of the actin network and subsequent effacement of the foot processes. Immunosuppressive drugs, which are currently used as treatment in proteinuric kidney diseases, have been shown to exert not only immune-mediated effects. This review will focus on the direct effects of glucocorticoids, cyclosporine A, tacrolimus, mycophenolate mofetil, and rituximab on podocytes by regulation of Ca2+ ion channels and consecutive downstream signaling which prevent cytoskeletal rearrangements and ultimately proteinuria. In addition, the efficacy of these drugs in genetic nephrotic syndrome will be discussed.

Roles of myosin 1e and the actin cytoskeleton in kidney functions and familial kidney disease

Mammalian kidneys are responsible for removing metabolic waste and maintaining fluid and electrolyte homeostasis via selective filtration. One of the proteins closely linked to selective renal filtration is myosin 1e (Myo1e), an actin-dependent molecular motor found in the specialized kidney epithelial cells involved in the assembly and maintenance of the renal filter. Point mutations in the gene encoding Myo1e, MYO1E, have been linked to familial kidney disease, and Myo1e knockout in mice leads to the disruption of selective filtration. In this review, we discuss the role of the actin cytoskeleton in renal filtration, the known and hypothesized functions of Myo1e, and the possible explanations for the impact of MYO1E mutations on renal function.

Cuproptosis associated cytoskeletal destruction contributes to podocyte injury in chronic kidney disease

The podocyte cytoskeleton determines the stability of podocyte structure and function, and their imbalance plays a pathogenic role in podocyte diseases. However, the underlying mechanism of podocyte cytoskeleton damage is not fully understood. Here, we investigate the specific role of cuproptosis in inducing podocyte cytoskeleton injury. In in vitro and in vivo studies, exposure to high levels of copper and adriamycin (ADR) caused significant increases in copper concentration in intracellular and renal tissue. Moreover, excessive accumulation of copper induced cuproptosis, resulting in the destruction of the podocyte cytoskeleton. However, inhibition of copper accumulation to reduce cuproptosis also significantly alleviated the damage of podocyte cytoskeleton. In addition, inhibition of cuproptosis mitigated ADR-induced mitochondrial damage as well as the production of reactive oxygen species and depolarization of mitochondrial membrane potential, and restored adenosine triphosphate (ATP) synthesis. Among the transcriptome sequencing data, the difference of CXCL5 (C-X-C motif chemokine ligand 5) was the most significant. Both high copper and ADR exposure can cause upregulation of CXCL5, and CXCL5 deletion inhibits the occurrence of cuproptosis, thereby alleviating the podocyte cytoskeleton damage. This suggests that CXCL5 may act upstream of cuproptosis that mediates podocyte cytoskeleton damage. In conclusion, cuproptosis induced by excessive copper accumulation may induce podocyte cytoskeleton damage by promoting mitochondrial dysfunction, thereby causing podocyte injury. This indicates that cuproptosis plays an important role in the pathogenesis of podocyte injury and provides a basis for seeking potential targets for the treatment of chronic kidney disease.NEW & NOTEWORTHY Cuproptosis induced by excessive copper accumulation leads to podocyte cytoskeleton damage by promoting mitochondrial dysfunction, and CXCL5 acts as an upstream signal mediating the occurrence of cuproptosis.

The clinical relevance of native vitamin D in pediatric kidney disease

Hypovitaminosis D has been reported to be common in chronic kidney disease (CKD) as well as in proteinuric disorders. We reviewed available evidence to assess clinically relevant effects of low vitamin D status and native vitamin D (NVD) therapy, in pediatric renal diseases. Online medical databases were searched for articles related to vitamin D status, associations of hypovitaminosis D and effects of NVD therapy in kidney disease. Hypovitaminosis D was associated with worse skeletal, cardiovascular, inflammatory, and renal survival outcomes in CKD. Low serum 25 hydroxy-vitamin D (25[OH]D) levels correlated positively with glomerular filtration rate and negatively with serum parathyroid (PTH) levels. However, to date, evidence of benefit of NVD supplementation is restricted mainly to improvements in serum PTH, and biochemical 25[OH]D targets form the basis of clinical practice recommendations for NVD therapy. In nephrotic syndrome (NS) relapse, studies indicate loss of 25[OH]D along with vitamin D binding protein in urine, and serum total 25[OH]D levels are low. Preliminary evidence indicates that free 25[OH]D may be a better guide to the biologically active fraction. NVD therapy in NS does not show consistent results in improving skeletal outcomes and hypercalciuria has been reported when total 25[OH]D levels were considered as indication for therapy. NVD formulations should be regularised, and therapy monitored adequately to avoid adverse effects.