Impact of autophagy inhibition on intervertebral disc cells and extracellular matrix.

Background: Intervertebral disc degeneration (IDD) is a leading contributor to low back pain (LBP). Autophagy, strongly activated by hypoxia and nutrient starvation, is a vital intracellular quality control process that removes damaged proteins and organelles to recycle them for cellular biosynthesis and energy production. While well-established as a major driver of many age-related diseases, autophagy dysregulation or deficiency has yet been confirmed to cause IDD.

Methods: In vitro, rat nucleus pulposus (NP) cells treated with bafilomycin A1 to inhibit autophagy were assessed for glycosaminoglycan (GAG) content, proteoglycan synthesis, and cell viability. In vivo, a transgenic strain (; ) mice were successfully generated to inhibit autophagy primarily in NP tissues. ; mouse intervertebral discs (IVDs) were evaluated for biomarkers for apoptosis and cellular senescence, aggrecan content, and histological changes up to 12 months of age.

Results: Here, we demonstrated inhibition of autophagy by bafilomycin produced IDD features in the rat NP cells, including increased apoptosis and cellular senescence ( ) and decreased expression of disc matrix genes and . H&E histologic staining showed significant but modest degenerative changes in NP tissue of mice compared to controls at 6 and 12 months of age. Intriguingly, 12-month-old mice did not display increased loss of NP proteoglycan. Moreover, markers of apoptosis (cleaved caspase-3, TUNEL), and cellular senescence (p53, IL-1β, TNF-α) were not affected in 12-month-old mice compared to controls. However, and gene expression were upregulated in NP tissue of 12-month-old mice compared to controls, suggesting -mediated cellular senescence resulted from NP-targeted knockout might contribute to the observed histological changes.

Conclusion: The absence of overt IDD features from disrupting -mediated macroautophagy in NP tissue implicates other compensatory mechanisms, highlighting additional research needed to elucidate the complex biology of autophagy in regulating age-dependent IDD.