Co‐treatment with erythropoietin derived <scp>HBSP</scp> and caspase‐3 <scp>siRNA</scp>: A promising approach to prevent fibrosis after acute kidney injury

Acute kidney injury (AKI) is a risk factor of chronic kidney disease, without specific treatment. This study investigated the effect of co-treatment using erythropoietin-derived helix B surface peptide (HBSP) and caspase-3 small interfering RNA (CASP3siRNA) on preventing fibrosis post AKI in order to achieve better efficacy by different action mechanisms. Ischemia-reperfusion (IR) in mice was induced by clamping bilateral renal pedicles for 30 min followed by 2-week reperfusion, with HBSP and/or CASP3siRNA administered at the onset of IR. Serum creatinine, apoptosis, active caspase-3 and high mobility group protein B1 (HMGB1) in kidneys were decreased by HBSP, CASP3siRNA or both, with increased PCNA. α-SMA expression and collagen I deposition were also reduced by CASP3siRNA and both. Most interestingly, the co-treatment further reduced tubulointerstitial damage and fibrosis, but raised PCNA compared to CASP3siRNA. EPOR/βcR was reduced by HBSP, and positively correlated with Sirius red staining, whereas EPOR was unchanged. In TCMK-1 cells, H₂O₂ raised apoptosis and α-SMA were reduced by HBSP, while the same was occurred to HMGB1. However, HMGB1 was further increased by EPOR siRNA under H₂O₂ stimulation with/without HBSP treatment. In conclusion, this study demonstrated synergistic long-term renoprotection post IR-AKI by HBSP and CASP3siRNA, which may be due to co-inhibiting inflammation and stimulating repair at early stage, and subsequently preventing fibrosis.