Enhanced osteogenesis of human mesenchymal stem cells by periodic heat shock in self-assembling peptide hydrogel

Influence of substrate curvature on osteoblast orientation and extracellular matrix deposition

Background

The effects of microchannel diameter in hydroxyapatite (HAp) substrates on osteoblast behavior were investigated in this study. Microchannels of 100, 250 and 500 μm diameter were created on hydroxyapatite disks. The changes in osteoblast precursor growth, differentiation, extra cellular matrix (ECM) secretion and cell attachment/orientation were investigated as a function of microchannel diameter.

Results

Curvature did not impact cellular differentiation, however organized cellular orientation was achieved within the 100 and 250 μm microchannels (mc) after 6 days compared to the 12 days it took for the 500mc group, while the flat substrate remained disorganized. Moreover, the 100, 250 and 500mc groups expressed a specific shift in orientation of 17.45°, 9.05°, and 22.86° respectively in 24 days. The secreted/mineralized ECM showed the 100 and 250mc groups to have higher modulus (E) and hardness (h) (E = 42.6GPa; h = 1.6GPa) than human bone (E = 13.4-25.7GPa; h = 0.47-0.74GPa), which was significantly greater than the 500mc and control groups (p < 0.05). It was determined that substrate curvature affects the cell orientation, the time required for initial response, and the shift in orientation with time.

Conclusions

These findings demonstrate the ability of osteoblasts to organize and mineralize differentially in microchannels similar to those found in the osteons of compact bone. These investigations could lead to the development of osteon-like scaffolds to support the regeneration of organized bone.

Aberrant CpG islands' hypermethylation of ABCB1 in mesenchymal stem cells of patients with steroid-associated osteonecrosis

OBJECTIVE

Patients carrying an ABCB1 polymorphism have a higher risk of developing osteonecrosis of the femoral head (ONFH). We investigated whether aberrant dinucleotide CpG islands' hypermethylation of ABCB1 gene existed in mesenchymal stem cells (MSC) of patients with ONFH, which results in cell dysfunction.

METHODS

Bone marrow was collected from the proximal femur of patients with glucocorticoid (GC)-associated ONFH (n = 22) and patients with new femoral neck fractures (n = 25). MSC were isolated by density gradient centrifugation. We investigated cell viability, intracellular reactive oxygen species (ROS) level, mitochondrial membrane potential (MMP), the amount of P-glycoprotein (P-gp) and ABCB1 transcripts, and methylation at CpG islands of ABCB1 promoter from both the femoral neck fractures group and the GC-associated ONFH group treated with or without the DNA methyltransferase inhibitor, 5'-Aza-2-deoxycytidine (5'-Aza-dC).

RESULTS

We observed that MSC from GC-associated ONFH groups showed reduced proliferation ability, elevated ROS levels, and depressed MMP when compared with the other 2 groups. Low levels of P-gp and ABCB1 transcript, as well as ABCB1 gene hypermethylation, in patients with GC-associated ONFH were also noted. Treatment with 5'-Aza-dC rapidly restored ABCB1 expression. Analysis of general expression revealed that aberrant CpG islands' hypermethylation of ABCB1 caused sensitivity to GC and induced changes in the proliferation and oxidative stress of MSC under GC administration.

CONCLUSION

These data suggest that aberrant CpG islands' hypermethylation of ABCB1 gene may be responsible for individual differences in the development of GC-associated ONFH.