Chondrocyte-targeted exosome-mediated delivery of Nrf2 alleviates cartilaginous endplate degeneration by modulating mitochondrial fission.

BACKGROUND: Cartilaginous endplate (CEP) degeneration, which is an important contributor to intervertebral disc degeneration (IVDD), is characterized by chondrocyte death. Accumulating evidence has revealed that dynamin-related protein 1 (Drp1)-mediated mitochondrial fission and dysfunction lead to apoptosis during CEP degeneration and IVDD. Exosomes are promising agents for the treatment of many diseases, including osteoporosis, osteosarcoma, osteoarthritis and IVDD. Despite their major success in drug delivery, the full potential of exosomes remains untapped. MATERIALS AND METHODS: In vitro and in vivo models of CEP degeneration were established by using lipopolysaccharide (LPS). We designed genetically engineered exosomes (CAP-Nrf2-Exos) expressing chondrocyte-affinity peptide (CAP) on the surface and carrying the antioxidant transcription factor nuclear factor E2-related factor 2 (Nrf2). The affinity between CAP-Nrf2-Exos and CEP was evaluated by in vitro internalization assays and in vivo imaging assays. qRT‒PCR, Western blotting and immunofluorescence assays were performed to examine the expression level of Nrf2 and the subcellular localization of Nrf2 and Drp1. Mitochondrial function was measured by the JC-1 probe and MitoSOX Red. Mitochondrial morphology was visualized by MitoTracker staining and transmission electron microscopy (TEM). After subendplate injection of the engineered exosomes, the degree of CEP degeneration and IVDD was validated radiologically and histologically. RESULTS: We found that the cargo delivery efficiency of exosomes after cargo packaging was increased by surface modification. CAP-Nrf2-Exos facilitated chondrocyte-targeted delivery of Nrf2 and activated the endogenous antioxidant defence system in CEP cells. The engineered exosomes inhibited Drp1 S616 phosphorylation and mitochondrial translocation, thereby preventing mitochondrial fragmentation and dysfunction. LPS-induced CEP cell apoptosis was alleviated by CAP-Nrf2-Exo treatment. In a rat model of CEP degeneration, the engineered exosomes successfully attenuated CEP degeneration and IVDD and exhibited better repair capacity than natural exosomes. CONCLUSION: Collectively, our findings showed that exosome-mediated chondrocyte-targeted delivery of Nrf2 was an effective strategy for treating CEP degeneration.

Propionibacterium acnes induces cartilaginous endplate degeneration by promoting MIF expression via the NF-κB pathway.

BACKGROUND: Propionibacterium acnes (P. acnes) is a novel pathogenic factor that contributes to cartilaginous endplate (CEP) degeneration. However, the underlying mechanism of P. acnes-induced CEP degeneration remains unclear. The objective of this study is to investigate the underlying mechanism of P. acnes-induced CEP degeneration. METHODS: We first examined MIF expression in degenerated human CEP samples by immunohistochemistry. We developed a P. acnes-induced rat model and detected MIF expression using immunohistochemistry. Additionally, we investigated the mechanism of P. acnes-induced CEP degeneration in CEP cells using western blotting and reverse transcription-quantitative polymerase chain reaction (RT-qPCR). RESULTS: We found that compared with the normal human CEP, the expression of MIF was increased in the degenerated human CEP. In a rat model, P. acnes induced CEP degeneration and upregulated MIF expression significantly. More importantly, we revealed the underlying mechanism of P. acnes-induced CEP degeneration in the rat CEP cells. Firstly, P. acnes induced the expression of MIF in a concentration-dependent manner. Then, MIF upregulated the expression of MMP-13 and promoted the secretion of IL-6 and IL-1ß. Finally, P. acnes may promote MIF expression via NF-κB pathway rather than ERK1/2 pathway. CONCLUSION: P. acnes-induced MIF expression via NF-κB pathway may be the underlying mechanism of CEP degeneration.