To explore the early differential expression of microRNA (miRNA) of rat's injured kidney induced by cadmium exposure, and to predict the target genes which mainly participate in the Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Gene and Genomes (KEGG) pathway.

Twenty-four SPF-grade SD male rats were randomly divided into four groups and given subcutaneous injection of 0, 0.5, 1.0, and 2.0 mg/kg CdCl₂, respectively, 5 days per week for 2 weeks. Gene chip technology and real time polymerase chain reaction were employed to explore and verify the differential expression of miRNA. The miR-21 with differential expression was subjected to bioinformatics analysis. Enzyme-linked immunosorbent assay was used to detect the indices of renal function.

Compared with the control group, renal damage were found in the 2.0 mg/kg Cd-exposed group (P < 0.05) and the expression of miR-21 was enhanced (P < 0.05). miR-21 target genes were mainly enriched in biological processes (DNA regulated transcription, amino acid phosphorylation, and oxidative stress), molecular factions (protein binding and transcription factors binding), and cell components such as cell nucleus, membrane, cytoplasm, mitochondria, and endoplasmic reticulum. They also involved in MAPK and transforming growth factor-β signaling pathways.

miR-21 is up-regulated in the injured rat renal tissues induced by cadmium exposure and may play an important role through multiple signal transduction pathways.