Insights into novel cellular injury mechanisms by gene expression profiling in nephropathic cystinosis

Abstract

Nephropathic cystinosis is a rare, inherited metabolic disease caused by functional defects of cystinosin associated with mutations in the CTNS gene. The mechanisms underlying the phenotypic alterations associated with this disease are not well known. In this study, gene expression profiles in peripheral blood of nephropathic cystinosis patients (N = 7) were compared with controls (N = 7) using microarray technology. In unsupervised hierarchical clustering analysis, cystinosis samples co-clustered, and 1,604 genes were significantly differentially expressed between both groups. Gene ontology analysis revealed that differentially expressed genes in cystinosis were enriched in cell organelles such as mitochondria, lysosomes, and endoplasmic reticulum (p ≤ 0.030). The majority of the differentially regulated genes were involved in oxidative phosphorylation, apoptosis, mitochondrial dysfunction, endoplasmic reticulum stress, antigen processing and presentation, B-cell-receptor signaling, and oxidative stress (p ≤ 0.003). Validation of selected genes involved in apoptosis and oxidative phosphorylation was performed by quantitative real-time polymerase chain reaction (PCR). Electron microscopy and confocal imaging of cystinotic renal proximal tubular epithelial cells further confirmed anomalies in the cellular organelles and pathways identified by microarray analysis. Further analysis of these genes and pathways may offer critical insights into the clinical spectrum of cystinosis patients and ultimately lead to novel links for targeted therapy.

Inhibition of Intracellular Clusterin Attenuates Cell Death in Nephropathic Cystinosis

“…Recent advances in the field of cystinosis and other lysosomal storage diseases have provided insights into novel mechanisms of pathogenesis in cystinosis. 7,[10][11][12] Autophagy and mitochondrial pathways have been implicated in the disease pathogenesis. [29][30][31] In this study, we investigate the role of CLU, an enigmatic molecule, in renal injury in patients with nephropathic cystinosis.…”

“…4 Various reports have indicated the association of processes, such as ATP depletion, mitochondrial dysfunction, autophagy, apoptosis, and cellular stress, with proximal tubule damage in the cystinotic kidney. [5][6][7][8][9][10][11][12] Although cystine accumulation is regarded as the primary defect in cystinosis, increasing evidence indicates that cystine accumulation alone may not be responsible (or may be insufficient) for metabolic alterations in cystinosis. The idea is supported by the findings that renal Fanconi syndrome is not cured after cystine depletion in patients with cystinosis and that, despite high levels of renal cystine accumulation in ctns 2/2 mice, renal Fanconi syndrome is absent in these mice.…”

“…Our previously published study using high-throughput cDNA microarrays to assay human blood samples from patients with and without nephropathic cystinosis identified various cell death molecules. 11 Analyzing the gene expression pattern suggested clusterin (CLU) as a potential target for additional investigation for the pathophysiology of renal injury in nephropathic cystinosis.…”

A Mouse Model Suggests Two Mechanisms for Thyroid Alterations in Infantile Cystinosis: Decreased Thyroglobulin Synthesis Due to Endoplasmic Reticulum Stress/Unfolded Protein Response and Impaired Lysosomal Processing

“…Formation of mixed-disulfide folding intermediates between Tg and the ER oxidoreductase, PDI, is crucial for Tg maturation and export (63). These chaperones functionally depend on ER redox homeostasis and high ATP levels, both of which are impaired in cystinosis (51,64,65). Combined with general concepts from literature, our data on Ctns Ϫ/Ϫ thyrocytes are thus consistent with the following hypotheses: 1) correct Tg disulfide bonding is slower due to impaired luminal redox, which results in misfolded/unfolded Tg accumulation in ER, triggering the UPR response; 2) consequently, slower ER exit/impaired secretion leads to ER dilatation and contributes to colloid exhaustion.…”

“…Ctns Ϫ/Ϫ thyrocytes develop the unfolded protein response to ER stress Secretory cells are particularly prone to ER stress, previously documented in activated thyrocytes (38,50). Moreover, cystinosis has been associated with ER stress (51). We thus evaluated whether the UPR was activated in response to ER stress in Ctns Ϫ/Ϫ thyroid by looking at UPR-target genes and products (52,53).…”