Cyclic Stretching Triggers Cell Orientation and Extracellular Matrix Remodeling in a Periodontal Ligament 3D In Vitro Model.

During orthodontic tooth movement (OTM), the periodontal ligament (PDL) plays a crucial role in regulating the tissue remodeling process. To decipher the cellular and molecular mechanisms underlying this process in vitro, suitable 3D models are needed that more closely approximate the situation in vivo. Here, a customized bioreactor is developed that allows dynamic loading of PDL-derived fibroblasts (PDLF). A collagen-based hydrogel mixture is optimized to maintain structural integrity and constant cell growth during stretching. Numerical simulations show a uniform stress distribution in the hydrogel construct under stretching. Compared to static conditions, controlled cyclic stretching results in directional alignment of collagen fibers and enhances proliferation and spreading ability of the embedded PDLF cells. Effective force transmission to the embedded cells is demonstrated by a more than threefold increase in Periostin protein expression. The cyclic stretch conditions also promote extensive remodeling of the extracellular matrix, as confirmed by increased glycosaminoglycan production. These results highlight the importance of dynamic loading over an extended period of time to determine the behavior of PDLF and to identify in vitro mechanobiological cues triggered during OTM-like stimulus. The introduced dynamic bioreactor is therefore a useful in vitro tool to study these mechanisms.

Genome-Wide Analysis of Gene Regulatory Networks of the FVE-HDA6-FLD Complex in Arabidopsis.

FVE/MSI4 is a homolog of the mammalian RbAp48 protein. We found that FVE regulates flowering time by repressing FLC through decreasing histone H3K4 trimethylation and H3 acetylation. Furthermore, FVE interacts with the histone deacetylase HDA6 and the histone demethylase FLD, suggesting that these proteins may form a protein complex to regulate flowering time. To further investigate the function of the FVE-FLD-HDA6 complex, we compared the gene expression profiles of fve, fld, and hda6 mutant plants by using RNA-seq analysis. Among the mis-regulated genes found in fve plants, 51.8 and 36.5% of them were also mis-regulated in fld and hda6 plants, respectively, suggesting that FVE, HDA6, and FLD may regulate the gene expression in the same developmental processes in Arabidopsis. Gene ontology analysis revealed that among 383 genes co-regulated by FVE, HDA6, and FLD, 15.6% of them are involved in transcription, 8.2% in RNA metabolic process, 7.7% in response to abiotic stress, and 6.3% in hormone stimulus. Taken together, these results indicate that HDA6, FVE, and FLD co-regulate the gene expression in multiple development processes and pathways.