Urinary exosomal transcription factors, a new class of biomarkers for renal disease

Abstract

Urinary exosomes are excreted from all nephron segments and constitute a rich source of intracellular kidney injury biomarkers. To study whether they contain transcription factors, we collected urine from two acute kidney injury models (cisplatin or ischemia-reperfusion), two podocyte injury models (puromycin-treated rats or podocin-Vpr transgenic mice) and from patients with focal segmental glomerulosclerosis, acute kidney injury and matched controls. Exosomes were isolated by differential centrifugation and found to contain activating transcription factor 3 (ATF3) and Wilms Tumor 1 (WT-1) proteins detected by Western blot. These factors were found in the concentrated exosomal fraction, but not in whole urine. ATF3 was continuously present in urine exosomes of the rat models following acute injury at times earlier than the increase in serum creatinine. ATF3 was found in exosomes isolated from patients with acute kidney injury but not from patients with chronic kidney disease or controls. Urinary WT-1 was present in animal models before significant glomerular sclerosis and in 9/10 patients with focal segmental glomerulosclerosis but not in 8 controls. Our findings suggest that transcription factor ATF3 may provide a novel renal tubular cell biomarker for acute kidney injury while WT-1 may detect early podocyte injury. Measurement of urinary exosomal transcription factors may offer insight into cellular regulatory pathways.

Extracellular Vesicles in Renal Diseases

“…10 Exosomes can, therefore, incorporate cargo, such as soluble proteins, mRNAs, microRNAs (miRNAs), noncoding RNA, mitochondrial DNA, transcription factors, and other cytosolic components and molecules. 10,22,23 After these vesicles fuse with the plasma membranes of the parent cell, they are released as exosomes into the extracellular environment ( Figure 1). Interestingly, the lipid-bilayered exosomes seem to be protected from RNAses, 24,25 sheltering the genetic cargo in exosomes.…”

Metabolomics Reveals Signature of Mitochondrial Dysfunction in Diabetic Kidney Disease

“…There was a reduction of mitochondrial cytochrome C oxidase in the diabetic kidneys compared with control kidneys (Figure 4, A and B). Second, mitochondrial DNA in urine exosomes was measured because urine exosomes are largely derived from renal epithelial cells 17 Figure 4C). The reduction in mitochondrial protein and mtDNA indicate an overall reduction in mitochondrial biogenesis.…”

MicroRNA-494 Reduces ATF3 Expression and Promotes AKI

“…18 Therefore, we explored the possibility of miR-494, an ATF3-related miRNA, becoming an alternative indicator for AKI. We found that, in mice, urinary miR-494 levels were increased 1 hour after reperfusion, but the elevated levels were reduced dramatically 12 hours later ( Figure 7A).…”