| Summary: | 博士 === 國立成功大學 === 臨床醫學研究所 === 105 === Keloids are pathologic scars and the exact pathogenesis remains unclear. Keloids are more likely to form in areas of the body subjected to increased skin tension or stiffness. We hypothesize that keloid results from the hyper-responsiveness of keloid fibroblasts (KF) to mechanical stimulation. The overall goal of this thesis is to understand the clinical manifestation of keloid and its relationship with mechanical effects, the biomechanical properties of keloid, and elucidate the molecular mechanism(s) regulating the hyper-responsiveness of KF to mechanical stimulation. The four specific aims are: (I) to confirm the preferred site of keloid formation is associated with mechanical tension(II) to investigate the mechanical properties of KF and its response to mechanical stimulation, (III) to identify the molecular mechanisms involved in the hyper-responsiveness of KF, and (IV) to elucidate the possible mechanisms contributing to the mechanical properties of KF.Clinically, we analyzed 3978 keloid lesionsof 664 Taiwanese keloid patients (258 males, 406 females, average age 33.7 years). The largest number of cases was in the age period 20 to 29 years (278 patients; 41.9%), and there were only 55 (8.3%) patients who were more than 60 years old. There were 1809 (45.5%) located on chest region and 864 (21.7%) on shoulder and back. The age and site distributions indicated that keloid tends to occur in the skin area with high skin tension of the young people.In our experimental design, we applied atomic force microscopy to detect the stiffness of KF and keloid tissue, and cultured fibroblasts on collagen-coated polyacrylamide gels with different stiffness to understand the effects of mechanical stimulation on KF. We found that KF were softer and produced more extracellular matrix (fibronectin) than NF under the mechanical stimulation (substratum stiffness). Using Ingenuity Pathway Analysis on microarray data, we identified RUNX2 as a potential key regulator in the pathogenesis of keloid. RUNX2 is ectopically expressed in keloid tissue. In addition, under mechanical stimulation, the upregulation of mRNA level and the nuclear translocation of RUNX2 were noted. Caveolin-1 (CAV1), the principal coat protein of caveolae, has been associated with the regulation of cell mechanics. We found that CAV1 was downregulated in keloid, and responsible for cell softening, the activation of RUNX2 and increased migratory ability in KFs. Furthermore, we found that histone deacetylase (HDAC) inhibitor, trichostatin A (TSA)increased CAV1 and decreased RUNX2 and fibronectin. TSA treatment also resulted in cell stiffening and decreased migratory ability in KFs.Collectively,these results suggest mechanical stimulation plays an important role in the pathogenesis of keloid formation. We found the novel role for CAV1 downregulation in linking the aberrant responsiveness to mechanical stimulation and extracellular matrix accumulation with the progression of keloids, findings that may lead to new developments in the prevention and treatment of keloid scar.
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