BackgroundBased on evidence from several other tissues, cartilage stem/progenitor cells in the auricular cartilage presumably contribute to tissue development or homeostasis of the auricle. However, no definitive studies have identified or characterized a stem/progenitor population in mice auricle.Methodology/Principal FindingsThe 5-bromo-2′-deoxyuridine (BrdU) label-retaining technique was used to label dividing cells in fetal mice. Observations one year following the labeling revealed that label-retaining cells (LRCs) were present specifically in auricular perichondrium at a rate of 0.08±0.06%, but LRCs were not present in chondrium. Furthermore, LRCs were successfully isolated and cultivated from auricular cartilage. Immunocytochemical analyses showed that LRCs express CD44 and integrin-α5. These LRCs, putative stem/progenitor cells, possess clonogenicity and chondrogenic capability in vitro.Conclusions/SignificanceWe have identified a population of putative cartilage stem/progenitor cells in the auricular perichondrium of mice. Further characterization and utilization of the cell population should improve our understanding of basic cartilage biology and lead to advances in cartilage tissue engineering and novel therapeutic strategies for patients with craniofacial defects, including long-term tissue restoration.

Although further study is required to determine factors leading to anastomotic obstruction and to optimize the results of microlymphatic surgery, the present LVSEA technique appears promising.

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We recently developed a promising regenerative method based on the xenotransplantation of human cartilage progenitor cells, demonstrating self-renewing elastic cartilage reconstruction with expected long-term tissue restoration. However, it remains unclear whether autotransplantation of cartilage progenitors may work by a similar principle in immunocompetent individuals. We used a nonhuman primate (monkey) model to assess the safety and efficacy of our regenerative approach because the model shares characteristics with humans in terms of biological functions, including anatomical features. First, we identified the expandable and multipotent progenitor population from monkey ear perichondrium and succeeded in inducing chondrocyte differentiation in vitro. Second, in vivo transplanted progenitor cells were capable of reconstructing elastic cartilage by xenotransplantation into an immunodeficient mouse. Finally, the autologous monkey progenitor cells were transplanted into the subcutaneous region of a craniofacial section and developed mature elastic cartilage of their own 3 months after transplantation. Furthermore, we attempted to develop a clinically relevant, noninvasive monitoring method using magnetic resonance imaging (MRI). Collectively, this report shows that the autologous transplantation of cartilage progenitors is potentially effective for reconstructing elastic cartilage. This principle will be invaluable for repairing craniofacial injuries and abnormalities in the context of plastic and reconstructive surgery.

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