Objective  To investigate the role and mechanism of circular RNA SNRK (circSNRK) in ischemia-reperfusion injury (IRI).

  Methods  A hypoxia-reoxygenation (IRI) cell model was established. The expression level of circSNRK after IRI treatment and the effect of overexpression of circSNRK on cell proliferation and apoptosis were detected. The targets of circSNRK were identified. HK2 cells were divided into the blank group (Mock group), IRI group, control plasmid+IRI group (IRI+NC group), human circSNRK overexpression+IRI group (IRI+circSNRK group), human circSNRK overexpression+IRI+protein kinase B (Akt) inhibitor group (IRI+circSNRK+MK2206 group) and control plasmid group (NC group). Cell proliferation and apoptosis were detected in the Mock, IRI, IRI+NC and IRI+circSNRK groups. The gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses of the target of circSNRK were carried out. The expression levels of CDKN1A, Akt, B-cell lymphoma (Bcl)-2, cysteinyl aspartate specific proteinase (Caspase)-9 messenger RNA (mRNA), and those of p21, Bcl-2, Caspase-9, Akt and p-Akt proteins were detected in the Mock, IRI, IRI+NC and IRI+circSNRK groups, respectively. Cell proliferation and apoptosis were determined in the NC, IRI+NC, IRI+circSNRK and IRI+circSNRK+MK2206 groups.

  Results  Compared with the Mock group, the expression level of circSNRK was lower, and cell proliferation capability of HK2 cells was decreased and cell apoptosis was increased in the IRI group. In the IRI+circSNRK group, cell proliferation capability was higher, whereas cell apoptosis was lower than those in the IRI+NC group. circSNRK could act on 648 targets through 51 microRNAs (miRNAs). GO enrichment analysis revealed that the targets of circSNRK were mainly enriched in biological processes (such as cell process and biological regulation), cell components (such as cell parts, cells and extracellular parts), and molecular functions (such as binding, binding proteins and enzymes). KEGG enrichment analysis showed that the targets of circSNRK were mainly enriched in cancer signaling pathway, phosphatidylinositol 3-kinase (PI3K)-Akt signaling pathway, miRNA in cancer and other related signaling pathways. Compared with the Mock group, the relative expression levels of CDKN1A and Caspase-9 mRNA were higher, the expression level of miR-99a-5p RNA was higher and the relative expression levels of Akt and Bcl-2 mRNA were lower in the IRI group. Compared with the IRI+NC group, the relative expression levels of CDKN1A and Caspase-9 mRNA were lower, those of Akt and Bcl-2 mRNA were higher, and the expression level of miR-99a-5p RNA was lower in the IRI+circSNRK group, and the differences were statistically significant (all P < 0.05). Compared with the Mock group, the expression levels of p21 and Caspase-9 proteins were higher, while those of p-Akt, Akt and Bcl-2 proteins were lower in the IRI group. Compared with the IRI+NC group, the expression levels of p21 and Caspase-9 proteins were lower, whereas those of p-Akt, Akt and Bcl-2 proteins were higher in the IRI+circSNRK group. The miR-99a-5p binding sites were observed in circSNRK and Akt. Compared with the NC group, cell proliferation capability was declined in the IRI+NC group. Compared with the IRI+NC group, cell proliferation capability was elevated in the IRI+circSNRK group. Compared with the IRI+circSNRK group, cell proliferation capability was declined in the IRI+circSNRK+MK2206 group (all P < 0.05). The cell apoptosis level in the IRI+NC group was higher than that in the NC group. The cell apoptosis level in the IRI+circSNRK group was lower compared with that in the IRI+NC group. The cell apoptosis level in the IRI+circSNRK+MK2206 group was higher than that in the IRI+circSNRK group.

  Conclusions  Under IRI conditions, circSNRK may affect the proliferation and apoptosis of HK2 cells probably via the Akt signaling pathway.