Dysregulated Expression of microRNA-21 and Disease-Related Genes in Human Patients and in a Mouse Model of Alport Syndrome.

Alport syndrome is a genetic disease caused by mutations in type IV collagen and is characterized by progressive kidney disease. The Col4α3-/- mouse model recapitulates the main features of human Alport syndrome. Previously, it was reported that kidney microRNA-21 (miR-21) expression is significantly increased in Col4α3-/- mice, and administration of anti-miR-21 oligonucleotides (anti-miR-21) attenuates kidney disease progression in Col4α3-/- mice, indicating that miR-21 is a viable therapeutic target for Alport syndrome. However, the expression pattern of miR-21 in the kidneys of patients with human Alport syndrome has not been evaluated. Paraffin-embedded kidney specimens were obtained from 27 patients with Alport syndrome and from 10 normal controls. They were evaluated for miR-21 expression and for in situ hybridization and mRNA expression by quantitative polymerase chain reaction. In addition, anti-miR-21 was administrated to Col4α3-/- mice at different stages of disease, and changes in proteinuria, kidney function, and survival were monitored. Transcriptomic analysis of mouse kidney was conducted using RNA sequencing. miR-21 expression was significantly elevated in kidney specimens from patients with Alport syndrome compared to normal controls. Elevated renal miR-21 expression positively correlated with 24 h urine protein, serum blood urea nitrogen, serum creatinine, and severity of kidney pathology. On histological evaluation, high levels of miR-21 were localized to damaged tubular epithelial cells and glomeruli. Kidney specimens from both humans and mice with Alport syndrome exhibited abnormal expression of genes involved in kidney injury, fibrosis, inflammation, mitochondrial function, and lipid metabolism. Administration of anti-miR-21 to Alport mice resulted in slowing of kidney function decline, partial reversal of abnormal gene expression associated with disease pathology, and improved survival. Increased levels of miR-21 in human Alport kidney samples showed a correlation with kidney disease severity measured by proteinuria, biomarkers of kidney function, and kidney histopathology scores. These human data, combined with the finding that a reduction of miR-21 in Col4α3-/- mice improves kidney phenotype and survival, support miR-21 as a viable therapeutic target for the treatment of Alport syndrome.