Abstract
Degenerative disk disease (DDD) that aggravates structural deterioration of intervertebral disks (IVDs) can be accompanied by painful inflammation and immunopathological progressions. Current surgical or pharmacological therapies cannot repair the structure and function of IVDs. Nucleus pulposus (NP) cells are crucial for the preservation or restoration of IVDs by balancing the anabolic and catabolic factors affecting the extracellular matrix. Imbalanced anabolic and catabolic factors cause increased degradation of aggrecan. Aggrecanases A Disintegrin And Metalloproteinase with ThromboSpondin motifs (ADAMTS)4 and ADAMTS5 are the main degrading enzymes of aggrecan. Previously, we characterized adeno-associated virus (AAV6) as the most suitable serotype with marked NP cellular tropism and demonstrated that ADAMTS4 could be silenced by self-complementary adeno-associated virus grade 6 small helix ribonucleic acid (scAAV6-shRNA) in NP cells of degeneration grade III, which resulted in enrichment of aggrecan. Nonetheless, neither scAAV6-shRNA-mediated inhibition of ADAMTS5 nor joint inhibitions of ADAMTS4 and ADAMTS5 have been investigated, although both enzymes are regulated by analogous proinflammatory cytokines and have the same cleavage sites in aggrecan. Therefore, we attempted scAAV6-shRNA-mediated inhibitions of both enzymes in NP cells of degeneration grade IV to increase efficacies in treatments of DDD. The degeneration grade of IVDs in patients was determined by magnetic resonance imaging (MRI) before surgical operations. After isolation and culturing of NP cells, cells were transduced with scAAV6-shRNAs targeting ADAMTS4 or ADAMTS5. Transduced cells were analyzed by reverse transcription quantitative polymerase chain reaction (RT-qPCR), fluorescence microscopy, flow cytometry-assisted cell sorting (FACS), MTT assay (3-(4, 5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide assay), immunoblotting, and enzyme-linked immunosorbent assay (ELISA). Joint transduction of NP cells exhibited high transduction efficacies (98.1%), high transduction units (TU) (1381 TU/Cell), and no effect on cell viability or proliferation. Above all joint treatments resulted in effective knockdown of ADAMTS4 (92.8%) and ADAMTS5 (93.4%) along with additive enrichment of aggrecan (113.9%). Treatment effects were significant for more than 56 days after transduction (P < 0.001). In conclusion, scAAV6-shRNA-mediated combined molecular therapy could be very valuable for more effective, durable, and less immunogenic treatment approaches in DDD.