Alport syndrome: Proteomic analysis identifies early molecular pathway alterations in Col4a3 knock out mice

Abstract

Aim: Alport syndrome (AS) is the second most common hereditary kidney disease caused by mutations in collagen IV genes. Patients present with microhaematuria that progressively leads to proteinuria and end stage renal disease. Currently, no specific treatment exists for AS. Using mass spectrometry based proteomics, we aimed to detect early alterations in molecular pathways implicated in AS before the stage of overt proteinuria, which could be amenable to therapeutic intervention. Methods: Kidneys were harvested from male Col4a3 −/− knock out and sex and agematched Col4a3 +/+ wild-type mice at 4 weeks of age. Purified peptides were separated by liquid chromatography and analysed by high resolution mass spectrometry. The Cytoscape bioinformatics tool was used for function enrichment and pathway analysis. PPARα expression levels were evaluated by immunofluorescence and immunoblotting. Results: Proteomic analysis identified 415 significantly differentially expressed proteins, which were mainly involved in metabolic and cellular processes, the extracellular matrix, binding and catalytic activity. Pathway enrichment analysis revealed among others, downregulation of the proteasome and PPAR pathways. PPARα protein expression levels were observed to be downregulated in Alport mice, supporting further the results of the discovery proteomics. Conclusion: This study provides additional evidence that alterations in proteins which participate in cellular metabolism and mitochondrial homeostasis in kidney cells are early events in the development of chronic kidney disease in AS. Of note is the dysregulation of the PPAR pathway, which is amenable to therapeutic intervention and provides a new potential target for therapy in AS.

The Effect of Fibrates on Kidney Function and Chronic Kidney Disease Progression: A Systematic Review and Meta-Analysis of Randomised Studies

“…In part, it can be explained by the involvement of the peroxisome proliferator receptors, that generate vasodilatory prostaglandins resulting in an increase in kidney blood filtration which increases serum creatinine and decreases GFR [44]. Moreover, emerging evidence, suggest that alterations in the PPAR pathway at the molecular level are both early and late events in CKD and CKD progression mouse models [45,46] and fenofibrate treatment exerts nephroprotective effects thought the attenuation of inflammatory and fibrotic pathways [41,47,48]. Enhancing binding at the PPARa receptor is a promising development, influencing downstream gene and physiological effects of PPRAa activation.…”

Patient-derived podocyte spheroids reveal new insights into the etiopathogenesis of Alport syndrome

“…Mouse and immortalized cell line models of AS have shown that ER stress (measured as activation of unfolded protein response pathway), as well as metabolic alterations, occur in AS (Pieri et al, 2014;Jao et al, 2019). Other studies in AS mice reported defective mitochondrial respiration and disrupted mitochondrial morphology in isolated tubular cells as well as alterations in mitochondrial homeostasis very early in the disease development (Ding et al, 2018;Nicolaou et al, 2020). In this study, we found several pieces of evidence that highlight metabolic disturbances in mitochondrial proteins, possibly due to excessive ROS production and delayed maturation in AS patient-derived podocytes.…”

Urinary Protein-Biomarkers Reliably Indicate Very Early Kidney Damage in Children With Alport Syndrome Independently of Albuminuria and Inflammation

“…Therefore, there is no practicable BM yet in use for the preclinical detection of AS despite several early cellular alterations recently being claimed as potential “early” BMs. 2 , 3 , 4 , 5 , 6 , 7 Histopathological changes occur only late in disease progression. Genetic testing is recommended in symptomatic children.…”