Reaching a Better Fibroblast Differentiation

The fibroblast is the most common cell type of the body’s connective tissues and a key player in their repair. These cells are so ubiquitous, so biologically diverse, and yet lacking in unique surface markers to easily confirm their identity, that scientists sometimes assume that any uncharacterized cell that looks and acts like a fibroblast must be a fibroblast. In the September 1, 2010 issue of the Journal of Clinical Investigation, National Institute of Dental and Craniofacial Research (NIDCR) grantees and colleagues show laboratory studies indicating that fibroblasts originate from mesenchyme stem cells (MSCs), also known as marrow stromal cells, the source of the body’s connective tissue. Importantly, the researchers showed that MSCs stimulated in culture with a protein called connective tissue growth factor (CTGF) tend to favor the production of stable fibroblastic lineages. The fibroblast cell lines were stable for further replication and study; moreover, within 4 weeks of treatment with CTGF, the MSCs largely lost their ability to reprogram themselves to form bone- and cartilage-producing cells. The researchers then determined that fibroblasts differentiate in a gradual, step-wise fashion that is observable in the patterns of protein markers displayed on their cell surface. That is, their initial cell lines arose lacking the alphasmooth muscle actin (aSMA) protein marker, the hallmark of a myofibroblast. (While fibroblasts play an important role in normal wound healing, myofibroblasts are associated with excessive scarring.) When they stimulated the fibroblasts with transforming growth factor beta, or TGF-ß, a growth factor that affects cellular proliferation, differentiation, and other basic functions, the cells then transitioned into myofibroblasts that displayed the hallmark aSMA protein. These data suggest that fibroblastic differentiation, connective tissue repair, and fibrosis (the formation of excessive tissue) must be 3 distinct processes, and suggest that targeting fibroblasts with CTGF during the repair process could push them toward a desired outcome that could make wound healing more predictable. To put this idea to a first test, the scientists turned to an established rodent model for craniosynostosis. This common human cranial condition is characterized by the premature fusion, or mineralization, of the fibrous sutures that naturally stitch the large, plate-like calvarial bones into place to form a normally shaped skull. Children born with this condition may develop a malformed face, and the premature fusion produces an irregularly shaped skull that typically requires surgery to remove the sutures and reshape the calvarial bones. The scientists used a tissue engineering approach to microencapsulate stores of CTGF for timerelease in the skulls of the rodents during development. They found that the slow release of CTFG alone induced connective tissue repair, or fibrogenesis, and restored the normal shape and anatomic structure of the calvarial sutures. Later, under the microscope, the sutures appeared to consist of fibroblast-like cells where sutures interact with bone. In the rodents that were not treated with CTGF, the sutures prematurely mineralized as expected. The findings suggest the possibility of a minimally invasive, localized surgery to correct craniosynostosis that perhaps one day could provide an alternative to highly invasive surgeries to reshape multiple skull bones. (Source: NIDCR, Science News in Brief, October 26, 2010)