Targeted delivery of Bak BH3 peptide to renal myofibroblast for renal fibrosis treatment by activating the mitochondrial-dependent apoptosis pathway.

Background: Renal fibrosis is positively associated with the increased number of renal myofibroblasts with over-expressed platelet-derived growth factor β receptor (PDGFβR). Reducing the number of renal myofibroblasts by inducing cell apoptosis is a novel strategy for treating renal fibrosis. The functional domain BH3 from protein Bak (BH3 peptide) exerts pro-apoptotic activity and the affibody Z_PDGFβR shows a superior high affinity for PDGFβR. This study aimed to evaluate renal fibrosis treatment by targeting delivery of BH3 to fibrotic kidney using Z_PDGFβR as a carrier.

Methods: The targeting potential of Z-BH3 (BH3 genetically fused to Z_PDGFβR) on the TGF-β1-activated NIH3T3 cell model and UUO mice model of renal fibrosis were evaluated by fluorescence-tracer imaging. Anti-renal fibrosis effect of Z-BH3 on kidney fibrosis in vitro and in vivo was evaluated by TUNEL, ROS, immunofluorescence, immunohistochemical and pathological staining and western blot.

Results: Z-BH3 highly targeted activated NIH3T3 cells and fibrotic kidney from UUO mice. Z-BH3 significantly induced cell apoptosis, reduced the fibrosis-related protein levels in activated NIH3T3 cells. Z-BH3 markedly promoted cell apoptosis, attenuated the pathological changes, and mitigated fibrosis responses in UUO mice. Z-BH3 remarkably reduced the mitochondrial membrane potential (MMP), increased the levels of pro-apoptotic Bax, cleaved caspase-3 and PARP as well as ROS generation, and inhibited anti-apoptotic Bcl-2 expressions in vitro and in vivo.

Conclusion: Z-BH3 attenuated renal fibrosis in vitro and in vivo by targeting induction of cell apoptosis in renal myofibroblasts via the mitochondrial-dependent pathway. This study provides a novel avenue for renal fibrosis therapy.