Hypertrophy and Fibrosis of the Ligamentum Flavum in Lumbar Spinal Stenosis is Associated With Increased Expression of LPA and LPAR1.

STUDY DESIGN: Histologic, immunohistochemical (IHC), and enzyme-linked immunosorbent assay analysis of the human ligamentum flavum (LF). OBJECTIVE: The purpose of this study was to determine the level of expression of lysophosphatidic acid (LPA) in the LF from lumbar spinal stenosis (LSS) patients and to analyze the relationship among LPA, LPA receptors (LPARs), and LF hypertrophy. SUMMARY OF BACKGROUND DATA: LF hypertrophy and fibrosis are important causes of LSS. LPA is involved in the fibrotic process in multiple organ systems. Therefore, we hypothesized that LPA and its receptors might also play a role in degeneration of the LF in LSS patients. METHODS: Forty-one LF samples were enrolled in this study. The thickness of the LF was measured by magnetic resonance imaging. Histologic analysis using hematoxylin and eosin and Masson trichrome stain was performed for each LF to evaluate the architecture of the extracellular matrix. The content of LPA and connective tissue growth factor (CTGF) in LF samples was analyzed using enzyme-linked immunosorbent assay. The expression of LPAR1 was determined by IHC. RESULTS: Degeneration of the LF was characterized by an increase in disorganized elastic fibers and fibrotic transformation by extracellular collagen deposition. The thickness of the LF and the concentration of LPA and CTGF in the hypertrophic LF group were significantly higher than the control group. Furthermore, the LPA and CTGF concentrations had a positive correlation with the LF thickness (r=0.91, P<0.001 and r=0.943, P<0.001, respectively). On the basis of IHC analysis, the expression of LPAR1 was increased in the hypertrophy group. CONCLUSIONS: The increased expression of LPA and LPAR1 is associated with the fibrosis and hypertrophy of the LF in patients with LSS. Further study on the mechanism underlying LF fibrosis may lead to new therapies for LF hypertrophy and fibrosis.

Effect of perfusion flow rate on proliferation and osteoblastic differentiation of human mesenchymal stem cells / 医用生物力学

Objective To investigate the effect of different perfusion flow rates on proliferation and osteoblastic differentiation of human mesenchymal stem cells (hMSCs) in large scale β-TCP (tricalcium phosphate) scaffold at perfusion bioreactor. Methods hMSCs isolated from iliac bone marrow aspiration were loaded into large scale β-TCP scaffold and cultured in perfusion bioreactor at the perfusion flow rate of 3, 6 or 9 mL/min for 15 days. The culture media were collected for D-glucose consumption assay every 3 days. After perfusion culture for 15 days, the cell-scaffold composites were harvested for assessment of cell viability by MTT colorimetric method, SEM observation and osteogenic gene expression by real-time PCR. Results The proliferation of hMSCs assayed by daily glucose consumption showed that at early stage of culture, cells proliferated faster at flow rate of 9 mL/min than at 3 or 6 mL/min (P<0.001); while at late stage of culture, cells proliferated faster at flow rate of 6 mL/min (P<0.05). The cell viability indicated that the cell-scaffold composites at flow rate of 6 mL/min exhibited the most viable cells (P<0.001). SEM indicated that all the macropores of the scaffold at different flow rates were filled with cellular layers. All cellular layers at flow rate of 3 mL/min were incompact, but that at 9 mL/min were compact; at flow rate of 6 mL/min, the cellular layers were either compact or incompact. Real-time PCR revealed that after perfusion culture for 15 days, the mRNA expression of osteobalstic genes including ALP and OP, were enhanced significantly at flow rate of 6 and 9 mL/min as compared to that at 3 mL/min (P<0.01); however, the 9 mL/min group presented the higher OC expression than 3 and 6 mL/min group (P<0.001). Conclusions At early stage of perfusion culture, the proliferation of hMSCs was promoted at flow rate of 9 mL/min, while at late stage, there was more viable cells in scaffolds at flow rate of 6 mL/min. The osteoblastic differentiation of hMSCs was facilitated with the increase of perfusion flow rate, which was attributed to the increased flow shear stress.