Murine TMJ loading causes increased proliferation and chondrocyte maturation

Regulation of PTHrP expression by cyclic mechanical strain in postnatal growth plate chondrocytes

Mechanical loading has been widely considered to be a crucial regulatory factor for growth plate development, but the exact mechanisms of this regulation are still not completely understood. In the growth plate, parathyroid hormone-related protein (PTHrP) regulates chondrocyte differentiation and longitudinal growth. Cyclic mechanical strain has been demonstrated to influence growth plate chondrocyte differentiation and metabolism, whereas the relationship between cyclic mechanical strain and PTHrP expression is not clear. The objective of this study was to investigate whether short-term cyclic tensile strain regulates PTHrP expression in postnatal growth plate chondrocytes in vitro and to explore whether the organization of cytoskeletal F-actin microfilaments is involved in this process. To this end, we obtained growth plate chondrocytes from 2-week-old Sprague-Dawley rats and sorted prehypertrophic and hypertrophic chondrocytes using immunomagnetic beads coated with anti-CD200 antibody. The sorted chondrocytes were subjected to cyclic tensile strain of varying magnitude and duration at a frequency of 0.5 Hz. We found that cyclic strain regulates PTHrP expression in a magnitude- and time-dependent manner. Incubation of chondrocytes with cytochalasin D, an actin microfilament-disrupting reagent, blocked the induction of PTHrP expression in response to strain. The results suggest that short-term cyclic tensile strain induces PTHrP expression in postnatal growth plate prehypertrophic and hypertrophic chondrocytes and that PTHrP expression by these chondrocytes may subsequently affect growth plate development. The results also support the idea that the organization of cytoskeletal F-actin microfilaments plays an important role in mechanotransduction.

New therapeutics in promoting and modulating mandibular growth in cases with mandibular hypoplasia

Children with mandibular growth deficiency may develop airway obstruction. The standard treatment of severe airway obstruction involves invasive procedures such as tracheostomy. Mandibular distraction osteogenesis has been proposed in neonates with mandibular deficiency as a treatment option to avoid tracheostomy procedure later in life. Both tracheostomy and distraction osteogenesis procedures suffer from substantial shortcomings including scarring, unpredictability, and surgical complications. Forward jaw positioning appliances have been also used to enhance mandible growth. However, the effectiveness of these appliances is limited and lacks predictability. Current and future approaches to enhance mandibular growth, both experimental and clinical trials, and their effectiveness are presented and discussed.

Increased mandibular condylar growth in mice with estrogen receptor beta deficiency

Temporomandibular joint (TMJ) disorders predominantly afflict women of childbearing age, suggesting a role for female hormones in the disease process. In long bones, estrogen acting via estrogen receptor beta (ERβ) inhibits axial skeletal growth in female mice. However, the role of ERβ in the mandibular condyle is largely unknown. We hypothesize that female ERβ-deficient mice will have increased mandibular condylar growth compared to wild-type (WT) female mice. This study examined female 7-day-old, 49-day-old, and 120-day-old WT and ERβ knockout (KO) mice. There was a significant increase in mandibular condylar cartilage thickness as a result of an increased number of cells, in the 49-day-old and 120-day-old female ERβ KO compared with WT controls. Analysis in 49-day-old female ERβ KO mice revealed a significant increase in collagen type X, parathyroid hormone-related protein (Pthrp), and osteoprotegerin gene expression and a significant decrease in receptor activator for nuclear factor κ B ligand (Rankl) and Indian hedgehog (Ihh) gene expression, compared with WT controls. Subchondral bone analysis revealed a significant increase in total condylar volume and a decrease in the number of osteoclasts in the 49-day-old ERβ KO compared with WT female mice. There was no difference in cell proliferation in condylar cartilage between the genotypes. However, there were differences in the expression of proteins that regulate the cell cycle; we found a decrease in the expression of Tieg1 and p57 in the mandibular condylar cartilage from ERβ KO mice compared with WT mice. Taken together, our results suggest that ERβ deficiency increases condylar growth in female mice by inhibiting the turnover of fibrocartilage.