Two enzyme families with opposite actions regulate the differentiation of stem cells, and could be exploited to enhance bone repair. The enzymes catalyse modifications of proteins called histones, around which DNA molecules are wrapped; one enzyme family adds methyl groups, the other removes them. These modifications affect gene expression and regulate the development of mesenchymal stem cells (MSCs). Christine Hong and Cun-Yu Wang from the University of California, USA, and colleagues have reviewed the roles of these enzymes. Both enzyme families are essential in determining whether MSCs develop into bone or fat cells, so manipulating them could enable directed differentiation to aid bone repair. The authors conclude that in order to realize the full clinical potential, future work must determine exactly how the opposing functions of the enzymes are balanced during differentiation.

Adult stem cells in dental pulp can be isolated via a single surface protein and efficiently grow into various cell types. It has been a matter of debate how best to isolate these cells so that they retain the ability to develop into various specialized tissues. Cun-Yu Wang and Christine Hong from the UCLA School of Dentistry in Los Angeles used various combinations of antibodies against surface proteins to purify the stem cells but none led to a uniform stem cell population that efficiently grew into different cell types. However, the researchers found that a single surface protein was sufficient to isolate the stem cells, which could then be successfully grown into mature cells forming teeth or cartilage. This isolation protocol will be of interest for future application in dentistry.

Dental stem cells with the greatest potential for regenerating bone and cartilage can be identified by three proteins on the cell surface. Christine Hong and co-workers at the University of California Los Angeles investigated stem cells purified from the ligaments that attach teeth to the jaw bone. This tissue can be readily obtained from extracted teeth. It offers a convenient source of stem cells that have previously been shown to regenerate bone, the surface layer of tooth root, and the ligament itself. Hong’s team found that human stem cells obtained in this way vary significantly in their regenerative capacity and therefore therapeutic potential. They identified the combination of surface proteins that marks out the best cells for repairing bone and cartilage. This will assist the isolation of uniform preparations of these cells for regenerative therapy.

Signaling molecules released by bone-resorbing cells (osteoclasts) can regulate the activity of the gelatinase enzyme in cartilage. Xiao-Xiao Cai and co-workers at Sichuan University in China explored the hypothesis that cartilage metabolism might be controlled by signals from bone cells. They found that the protein interleukin-1β (IL-1β) in the fluid around osteoclasts increased the activity of gelatinase in mouse cartilage cells in tissue culture. Changes in gelatinase activity have previously been implicated in diseases that involve disruption of cartilage metabolism, including osteoarthritis. The researchers also found that IL-1βs effect on gelatinase activity was mediated through pathways involving regulatory proteins known as mitogen-activated protein kinases. These insights will help in understanding the role of gelatinase in the maintenance of cartilage in both health and disease.

Although orthodontic braces apply constant force to teeth, researchers have found thatthe strain on gum tissue varies with time. To move teeth, orthodontists must apply justenough force to trigger remodelling of bone and gum tissues around tooth roots.However, these forces cannot be directly measured in living tissue. An internationalteam at Texas A&M University in Dallas, US, and Sichuan University, China, led by Xiang-Long Han used molecular markers to reveal stress in the periodontal ligament,which attaches tooth roots to gum tissue. Using cultured cells and cells from ratsundergoing orthodontic treatment, the researchers measured expression of the proteinsalpha-smooth muscle actin, which enhances tissue contraction, and tenascin-C, whichloosens tissue to prevent overstretching. Levels of both markers varied over time,corresponding to patterns of tooth movement.

Fluoride should be evaluated as a potential treatment for severe gum disease Japanese and Korean researchers say. Sodium fluoride has been shown to increase bone mass and has been investigated as a treatment for postmenopausal osteoporosis in adults. In the current study a team led by Ujjal Bahwal from the Nihon University School of Dentistry, Matsudo, Japan, used bone marrow cells from rats to assess the effects of sodium fluoride on bone loss induced by Porphyromonas.gingivalis, a bacterial species associated with gum disease. They discovered that sodium fluoride suppressed the growth of the bacteria. It also prevented bone loss by inhibiting bacterial effects on bone resorption. Fluoride application may help maintain a healthy oral microbial balance and is a promising approach to peridontitis management the researchers concluded.

The risk of infection may be reduced by constructing dental implants from combinations of materials that resist bacterial growth. Microbes can potentially form antibiotic-resistant biofilms on the surface of implants, particularly if the surrounding tissue does not form a tight seal. Researchers led by Yijin Ren at the University of Groningen in The Netherlands devised a ‘coculture’ model to study how oral bacteria interfere with bone cell growth on different implant materials. Although smooth titanium surfaces work well in gum tissue, the researchers found that oral bacteria readily displaced bone cells from this material. Materials based on zirconium or titanium-zirconium alloys provided a far more hospitable environment for bone cell growth, even amid biofilm-forming pathogens. These results suggest that implants composed of two different materials may facilitate better integration of implants.