[Comparative study on biological characteristics between different generations of rabbit nucleus pulposus cells]

To research the biological characteristics of different generations of rabbit nucleus pulposus cells (NPCs) that were cultured with natural culture and subculture method.

The thoracolumbar segments of New Zealand white rabbits (6-8 weeks old and weighing 1.5-2.5 kg) were obtained and nucleus pulposus were isolated from disc regions. And NPCs were harvested by enzymatic digestion from nucleus pulposus. Primary NPCs were counted as P0 generation. Then, NPCs were passaged by trypsin and counted as P1, P2, P3 with a totle of 4 generations. P0 to P3 generations NPCs were separately examined by observation of cell morphology and proliferation time, detection of apoptosis rates of cells by flow cytometry, and detection of hypoxia-inducible factor 1α (HIF-1α), matrix metalloproteinases 2 (MMP-2), Aggrecan, and collagen type Ⅱ proteins by immunofluorescence and Western blot.

The morphology of NPCs transformed from triangular or polygonal in P0 generation to spindle in P3 generation; the characteristic vacuolated cells gradually disappeared; and the cell volume and cell proliferation time increased. The cell apoptosis rates were 5.47%±0.91%, 13.77%±2.42%, 33.46%±1.82%, and 38.76%±1.50% from P0 to P3 generations, with the increase of culture time, and there were significant differences between 4 generations ( P<0.05). Immunofluorescence staining showed that with the increase of cells generation, the fluorescence intensity of HIF-1α, collagen type Ⅱ, and Aggrecan decreased, and the fluorescence intensity of MMP-2 increased. Western blot results showed that the relative expression of HIF-1α protein was high in P0 generation, the P1 generation has a rising trend, and then gradually decreased; the differences between generations were significant ( P<0.05). The relative expression of collagen type Ⅱ protein decreased from P0 to P3 generations and there were significant differences between generations ( P<0.05). The relative expression of Aggrecan protein decreased from P0 to P2 generations and there were significant differences between generations ( P<0.05); but no significant difference was found between P2 and P3 generations ( P>0.05). The relative expression of MMP-2 protein increased significantly in P3 generation; except that the difference between P0 and P2 generations was not significant ( P>0.05), the significant differences were found between the other generations ( P<0.05).

Rabbit NPCs degeneration model was successfully established by the natural culture and subculture method. Transforming of NPCs morphology, increasing of cell apoptosis rates, decreasing of anabolism, and increasing of catabolism were presented in NPCs degeneration model.