Schisandrin B regulates mitochondrial dynamics via AKT1 activation and mitochondrial targeting to ameliorate renal ischemia-reperfusion injury

Abstract

Background

Renal ischemia-reperfusion injury (RIRI) is a significant cause of acute kidney injury(AKI) and delayed graft function(DGF), impacting post-transplant outcomes. Mitochondrial dynamics, in particular fission and fusion, play a pivotal role in the cellular response to RIRI. The modulation of these dynamics represents a potential therapeutic target. Schisandrin B (Sch B), a component derived from traditional Chinese medicine, has shown protective roles in various organ injuries, but its effect on RIRI through mitochondrial dynamics remains unexplored.

Objective

This study explores the previously uninvestigated role of Sch B in modulating mitochondrial dynamics as a potential means of alleviating RIRI. By focusing on mitochondrial fission and fusion, this research provides novel insights into the therapeutic potential of Sch B, distinguishing it from existing approaches.

Methods

HK-2 cells were treated with hypoxia/reoxygenation (HR) in order to simulate renal ischemia-reperfusion injury (RIRI) in vitro. In vivo, mice underwent renal ischemia followed by reperfusion, which allowed for the simulation of the injury. Sch B's impact on mitochondrial dynamics, apoptosis, and oxidative stress was assessed through mitochondrial morphology assays, Western blotting for mitochondrial and apoptotic markers, TUNEL staining, and measurement of reactive oxygen species. Key molecular interactions were explored via Western blotting, molecular docking, SPR, and cellular thermal shift assays. In vivo, renal pathological damage was evaluated using HE, PAS, and TUNEL staining, while immunohistochemistry and immunofluorescence were employed to detect the expression levels of mitochondrial dynamics proteins and p-AKT1.

Results

First, we unveiled that Schisandrin B (Sch B) significantly mitigated oxidative stress and apoptosis in HK-2 cells subjected to hypoxia-reoxygenation conditions. Sch B pretreatment notably enhanced cell viability and mitochondrial function, demonstrating its superior antioxidant capabilities compared to NAC. Second, we discovered that Sch B's protective effects involve regulating mitochondrial dynamics by decreasing fission markers, such as DRP1, while increasing fusion proteins, including OPA1 and MFN2. Furthermore, our studies revealed that Sch B directly binds to AKT1, promoting its phosphorylation and localization to mitochondria, thereby enhancing mitochondrial resilience. Finally, we demonstrated that in vivo administration of Sch B reduced renal damage and apoptosis in mouse models of renal ischemia-reperfusion injury (RIRI), while immunohistochemical analyses unveiled its role in promoting mitochondrial fusion and reducing fission, marking a significant advancement in understanding Sch B's therapeutic potential in RIRI.

Conclusion

Our findings demonstrate for the first time that Sch B directly interacts with AKT1 protein, enhancing its phosphorylation and promoting mitochondrial localization. This innovative mechanism reduces oxidative stress, apoptosis, and mitochondrial fission, highlighting Sch B's unique capability to modulate mitochondrial dynamics in RIRI. These results establish Sch B as a promising therapeutic agent, offering a new dimension in the management of RIRI by targeting mitochondrial health.