Inhibition of lysyl oxidase accelerates intervertebral disc degeneration induced by apoptosis of nucleus pulposus cells

To explore the role and possible mechanism of lysyl oxidase（LOX）in age-related degeneration of intervertebral disc.

Six SD rats, aged of 2, 8 and 20 months respectively, were subjected, and then underwent intervertebral disc MRI and X-ray to evaluate the effect of age on intervertebral disc degeneration. Then, the total proteins of intervertebral disc from different age groups were isolated and detected for the expression of LOX protein by Western blotting. The hypoxia apoptosis model of nucleus pulposus cells was established by CoCl₂ treatment. Through LOX protein inhibitor BAPN and plasmid pcDNA3.1（+）-LOX, the effect of LOX protein on apoptosis of nucleus pulposus cells under different hypoxia conditions was studied. Fifteen 6-week-old SD rats were randomly divided into blank control group, vehicle group and BAPN group, with 5 animals in each group. PBS buffer of 20 μL or BAPN of 100 μg/mL was injected into the rats from the vehicle or BAPN group via caudal vertebrae. X-ray film examination was taken at 2 and 4 weeks after operation to evaluate intervertebral disc degeneration.

With the increase of age, X-ray films showed that the intervertebral disc height of 20-month-old rats was decreased significantly compared with 2-month-old rats（P<0.01）, and MRI displayed reduced T2 signals, indicating appearance of intervertebral disc degeneration. The protein level of LOX was decreased significantly in intervertebral disc of 20-month-old rats（P<0.01）. Treatment of 300 mmol/L CoCl₂ induced obvious apoptosis of nucleus pulposus cells as severe hypoxic condition（P<0.05）and subsequently down-regulated the expression of LOX protein（P<0.05）. In vivo experiment showed that after LOX inhibitor BAPN treatment for 4 weeks, the height of intervertebral disc was significantly declined in the BAPN group when compared with the PBS group（P<0.01）, suggesting more serious degeneration of intervertebral disc.

LOX protein can regulate the apoptosis of nucleus pulposus cells induced by hypoxia and thus affect intervertebral disc degeneration.