Preferential recruitment of bone marrow-derived cells to rat palatal wounds but not to skin wounds.

OBJECTIVE: To investigate the contribution of bone marrow-derived cells to oral mucosa wounds and skin wounds. BACKGROUND: Bone marrow-derived cells are known to contribute to wound healing, and are able to differentiate in many different tissue-specific cell types. As wound healing in oral mucosa generally proceeds faster and with less scarring than in skin, we compared the bone marrow contribution in these two tissues. DESIGN: Bone marrow cells from GFP-transgenic rats were transplanted to irradiated wild-type rats. After recovery, 4-mm wounds were made in the mucoperiosteum or the skin. Two weeks later, wound tissue with adjacent normal tissue was stained for GFP-positive cells, myofibroblasts (a-smooth muscle actin), activated fibroblasts (HSP47), and myeloid cells (CD68). RESULTS: The fraction of GFP-positive cells in unwounded skin (19%) was larger than in unwounded mucoperiosteum (0.7%). Upon wounding, the fraction of GFP-positive cells in mucoperiosteum increased (8.1%), whilst it was unchanged in skin. About 7% of the myofibroblasts in both wounds were GFP-positive, 10% of the activated fibroblasts, and 25% of the myeloid cells. CONCLUSIONS: The results indicate that bone marrow-derived cells are preferentially recruited to wounded oral mucosa but not to wounded skin. This might be related to the larger healing potential of oral mucosa.

Orthodontic force stimulates eNOS and iNOS in rat osteocytes.

Mechanosensitive osteocytes are essential for bone remodeling. Nitric oxide, an important regulator of bone remodeling, is produced by osteocytes through the activity of constitutive endothelial nitric oxide synthase (eNOS) or inducible nitric oxide synthase (iNOS). We hypothesized that these enzymes regulate the tissue response to orthodontic force, and therefore we investigated eNOS and iNOS expression in osteocytes during orthodontic force application. The upper rat molars were moved mesially by NiTi coil springs (10 cN, 120 hrs) in a split-mouth design. Immunohistochemical staining revealed that, in the tension area, eNOS-positive osteocytes increased from 24 hrs on, while iNOS-positive osteocytes remained largely constant. In the compression area, iNOS-positive osteocytes increased after 6 hrs, while eNOS- positive osteocytes increased after 24 hrs. This suggests that eNOS mediates bone formation in the tension area, while iNOS mediates inflammation-induced bone resorption in the compression area. Both eNOS and iNOS seem to be important regulators of bone remodeling during orthodontic force application.

Oral keratinocytes cultured on dermal matrices form a mucosa-like tissue.

Oral reconstructions for cleft palate repair are often complicated by a shortage of mucosal tissue. This shortage causes scar tissue formation leading to impaired growth of the dento-maxillary complex. The overall aim of our research is to develop a substitute. which limits the iatrogenic effects of cleft palate surgery. This study describes the culture and characterization of mucosal substitutes containing keratinocytes. Epidermal and oral keratinocytes from a beagle dog were cultured on several skin-derived and collagen-based substrates. Oral keratinocytes cultured on the skin-derived substrates closely resembled normal oral epithelium of the dog. A multi-layered epithelium was formed showing parakeratosis, expression of cytokeratin 16 and the formation of a basement membrane. Epidermal keratinocytes cultured on the skin-derived substrates formed an epithelium which was similar to dog epidermis. In contrast, keratinocytes cultured on the collagen-based substrates invaded the substrate without the formation of a multi-layered epithelium. In conclusion, this study shows that oral canine keratinocytes cultured on skin-derived substrates exhibit a tissue organization that resembles normal oral mucosa. This type of mucosal substitute will therefore be used in further studies for implantation on the palate of beagle dogs. These studies might eventually lead to an improvement of cleft palate surgery in humans.