The Skin-to-Mucosa Ratio Defines the Osteogenic Potential of Lip Fibroblasts

Fibroblasts isolated from discarded lip tissue obtained during cheiloplasty in patients with cleft lip/palate (CLP) show promising osteogenic potential and may be an appealing cell source for autologous bone regeneration. As the lip is a mucocutaneous junction, explant cultures from unseparated lip biopsies produce mesenchymal outgrowths composed of skin- and mucosa-derived fibroblasts. The proportions of the 2 fibroblast populations, however, differ among CLP patients and depend on the morphology of the excised sample, which is unique for each donor. Understanding the osteogenic activities of CLP fibroblast populations with varying skin-to-mucosa ratios is critical for their therapeutic application. We isolated CLP fibroblasts from 10 unseparated lip biopsies and comprehensively evaluated them for their bone differentiation capacities in vitro, demonstrating heterogeneous osteogenic potentials. Because there are no markers that can distinguish skin from mucosa fibroblasts, we used the respective and matching CLP keratinocytes to ascertain the skin-to-mucosa ratio of the 10 specimens. Thus, we found that CLP fibroblasts isolated from biopsies with high skin-to-mucosa ratios had a much higher osteogenic capacity than those derived from biopsies with low skin-to-mucosa ratios. To validate and solidify these findings, we carefully separated skin and mucosa tissues during corrective lip surgery to isolate pure skin and mucosa CLP lip fibroblasts. Indeed, skin had a higher osteogenic potential than their mucosal counterparts did. Furthermore, we discovered that the high osteogenic activity in skin was limited to specific subpopulations of yet unknown identities. Our findings indicate that skin fibroblasts perform better than their mucosal counterparts do, even though both types of fibroblasts can differentiate into bone-forming cells.