Background: Keloids are pathologic fibrotic scars characterized by excessive accumulation of the extracellular matrix (ECM). Genetic predisposition, mechanical tension, and inflammation are suspected to contribute to keloid formation. However, detailed mechanism underlying the pathogenesis of keloid formation is complex and not well known. Keloids not only cause physical discomfort, pain, and pruritus, but also can induce significant psychological stress due to the development of disfiguring scars. Unfortunately, current therapies including surgery, radiation, and intra-lesional corticosteroids have limited efficacy, and the development of more effective treatments is hindered by lack of suitable animal models. Tension-loading device on skin wound induced hypertrophic scar formation in vivo. CAV1 encodes caveolin-1, a scaffolding protein involved with lipid transportation and cellular mechanosensory processes. Reduced expression of caveolin-1 increases ECM production and migration of keloid fibroblasts. We hypothesize that mechanical traction device will induce greater scar formation on Cav1 mutant mice skin.
Aim: Herein, we aim to create the first animal model of keloid-like scar by using a traction device on full-thickness wounds in Cav1 mutant mice.
Material and Methods: Mice with caveolin-1 protein haploinsufficiency secondary to a heterozygous Cav1 mutation were bred. Traction devices were inserted on the dorsal skin of 10 batches of 40 mice to apply traction force upon an incisional wound, thereby enhancing skin tension during the subsequent wound healing process. Due to excessive weight, the original traction device was redesigned with a lighter and shortened material. The traction amount was also decreased to reduce inflammation. The severity of scar formation was assessed using gross photos, high frequency ultrasound, and histological studies including Masson’s trichrome staining. Reverse transcription polymerase chain reaction and immunoblotting were performed to assess RNA and protein expression of fibrosis-related genes such as fibronectin.
Results: The traction device on the wounded mouse skin induced significant inflammation and skin necrosis. High frequency ultrasound did not provide sufficient resolution for accurate visualization and assessment of the scar tissue. After several modifications of the protocol, traction force induced a tendency of greater ECM formation both in wild type and Cav1 mutant mice. The wound growth mimicking tongue-like advancing edge which is one of the characteristics of keloids was found on the side of wound tissue in the mutant traction cohort. However, it was not distinguished from edema and squeezing of the tissue.
Conclusion: The model was not optimal to reflect early keloid-like scar. Designing an alternative device with lighter material and further explorations such as harvesting mice in different time points will improve our understanding of the early keloid-like scarring process.

1. Mari, W., S.G. Alsabri, N. Tabal, S. Younes, A. Sherif, and R. Simman, Novel Insights on Understanding of Keloid Scar: Article Review. J Amer College Clin Wound Specialists, 2015. 7(1-3): p. 1-7.
2. Muir, I.F., On the nature of keloid and hypertrophic scars. Br J Plast Surg, 1990. 43(1): p. 61-9.
3. Ayeni, O.A., O.O. Ayeni, and R. Jackson, Observations on the Procedural Aspects and Health Effects of Scarification in Sub-Saharan Africa. J Cutan Med Surg, 2007. 11(6): p. 217-21.
4. Young, W.G., M.J. Worsham, C.L.M. Joseph, G.W. Divine, and L.R.D. Jones, Incidence of Keloid and Risk Factors Following Head and Neck Surgery. JAMA Facial Plast Surg, 2014. 16(5): p. 379-80.
5. Sun, L.M., K.H. Wang, and Y.C. Lee, Keloid incidence in Asian people and its comorbidity with other fibrosis-related diseases: a nationwide population-based study. Arc Dermatol Res, 2014. 306(9): p. 803-8.
6. Hochman, B., F.C. Isoldi, F. Furtado, and L.M. Ferreira, New approach to the understanding of keloid: psychoneuroimmune-endocrine aspects. Clin Cosmet and Invest Dermatol, 2015. 8: p. 67-73.
7. Babatunde, O.P. and A.E. Oyeronke, Scarification practice and scar complications among the Nigerian Yorubas. Indian J Dermatol Venereol Leprol, 2010. 76(5): p. 571-2.
8. Choi, Y.-J., Y.H. Lee, H.J. Lee, G.-Y. Lee, and W.-S. Kim, Auricular keloid management in Asian skin: Clinical outcome of intralesional excision and postoperative triamcinolone acetonide intralesional injection. J Cosmet Dermatol, 2020. 00: p. 1-7.
9. Verhaegen, P.D., P.P. van Zuijlen, N.M. Pennings, et al., Differences in collagen architecture between keloid, hypertrophic scar, normotrophic scar, and normal skin: An objective histopathological analysis. Wound Repair Regen, 2009. 17(5): p. 649-56.
10. Lee, J.Y., C.C. Yang, S.C. Chao, and T.W. Wong, Histopathological differential diagnosis of keloid and hypertrophic scar. Am J Clin Dermatol, 2004. 26(5): p. 379-84.
11. Gauglitz, G.G., H.C. Korting, T. Pavicic, T. Ruzicka, and M.G. Jeschke, Hypertrophic scarring and keloids: pathomechanisms and current and emerging treatment strategies. Mol Med, 2011. 17(1-2): p. 113-25.
12. Wang, Z., K.D. Fong, T.T. Phan, I.J. Lim, M.T. Longaker, and G.P. Yang, Increased transcriptional response to mechanical strain in keloid fibroblasts due to increased focal adhesion complex formation. J Cell Physiol, 2006. 206(2): p. 510-7.
13. Hsu, C.K., H.H. Lin, H.I. Harn, et al., Caveolin-1 Controls Hyperresponsiveness to Mechanical Stimuli and Fibrogenesis-Associated RUNX2 Activation in Keloid Fibroblasts. J Invest Dermatol, 2018. 138(1): p. 208-18.
14. Bran, G.M., U.R. Goessler, C. Schardt, K. Hormann, F. Riedel, and H. Sadick, Effect of the abrogation of TGF-beta1 by antisense oligonucleotides on the expression of TGF-beta-isoforms and their receptors I and II in isolated fibroblasts from keloid scars. Int J Mol Med, 2010. 25(6): p. 915-21.
15. Nangole, F.W. and G.W. Agak, Keloid pathophysiology: fibroblast or inflammatory disorders? JPRAS Open, 2019. 22: p. 44-54.
16. Rockwell, W.B., I.K. Cohen, and H.P. Ehrlich, Keloids and hypertrophic scars: a comprehensive review. Plast Reconstr Surg, 1989. 84(5): p. 827-37.
17. Roques, C. and L. Teot, The use of corticosteroids to treat keloids: a review. Int J Low Extrem Wounds, 2008. 7(3): p. 137-45.
18. Ogawa, R., S. Akita, S. Akaishi, et al., Diagnosis and Treatment of Keloids and Hypertrophic Scars—Japan Scar Workshop Consensus Document 2018. Burns & Trauma, 2019. 7: p. 1-40.
19. Jones, C.D., L. Guiot, M. Samy, M. Gorman, and H. Tehrani, The Use of Chemotherapeutics for the Treatment of Keloid Scars. Dermatol Reports, 2015. 7: p. 15-9.
20. Park, T.H., C.W. Kim, J.S. Choi, et al., PARP1 Inhibition as a Novel Therapeutic Target for Keloid Disease. Adv Wound Care (New Rochelle), 2019. 8(5): p. 186-94.
21. Fanous, A., A. Bezdjian, D. Caglar, et al., Treatment of Keloid Scars with Botulinum Toxin Type A versus Triamcinolone in an Athymic Nude Mouse Model. Plast Reconstr Surg, 2019. 143(3): p. 760-7.
22. Zhao, Y., J. Shi, and L. Lyu, Critical role and potential therapeutic efficacy of interleukin-37 in the pathogenesis of keloid scarring. J Cosm Dermatol, 2020. 19(7): p. 1805-6.
23. Al-Attar, A., S. Mess, J.M. Thomassen, C.L. Kauffman, and S.P. Davison, Keloid pathogenesis and treatment. Plast Reconstr Surg, 2006. 117(1): p. 286-300.
24. Wang, R., J. Chen, Z. Zhang, and Y. Cen, Role of chymase in the local renin-angiotensin system in keloids: inhibition of chymase may be an effective therapeutic approach to treat keloids. Drug Des Devel Ther, 2015. 9: p. 4979-88.
25. Kilmister, E.J., C. Paterson, H.D. Brasch, P.F. Davis, and S.T. Tan, The Role of the Renin-Angiotensin System and Vitamin D in Keloid Disorder-A Review. Front Surg, 2019. 6: p. 67-78.
26. Bao, Y., S. Xu, Z. Pan, et al., Comparative Efficacy and Safety of Common Therapies in Keloids and Hypertrophic Scars: A Systematic Review and Meta-analysis. Aesthet Plast Surg, 2020. 44(1): p. 207-18.
27. Diaz, A., K. Tan, H. He, et al., Keloid lesions show increased IL-4/IL-13 signaling and respond to Th2-targeting dupilumab therapy. J Eur Acad Dermatol Venereol, 2020. 34(4): p. e161-e4.
28. Darzi, M.A., N.A. Chowdri, S.K. Kaul, and M. Khan, Evaluation of various methods of treating keloids and hypertrophic scars: a 10-year follow-up study. Br J Plast Surg, 1992. 45(5): p. 374-9.
29. Jfri, A. and A. Alajmi, Spontaneous Keloids: A Literature Review. Dermatology, 2018. 234(3-4): p. 127-30.
30. Murray, J.C., Keloids and hypertrophic scars. Clin Dermatol, 1994. 12(1): p. 27-37.
31. Nakashima, M., S. Chung, A. Takahashi, et al., A genome-wide association study identifies four susceptibility loci for keloid in the Japanese population. Nat Genet, 2010. 42(9): p. 768-71.
32. Clark, J.A., M.L. Turner, L. Howard, H. Stanescu, R. Kleta, and J.B. Kopp, Description of familial keloids in five pedigrees: evidence for autosomal dominant inheritance and phenotypic heterogeneity. BMC Dermatol, 2009. 9(8): p. 1-8.
33. Tsai, C.-H. and R. Ogawa, Keloid research: current status and future directions. Scars, burns & healing, 2019. 5: p. 1-8.
34. Hsu, C.K., H.H. Lin, H.I. Harn, M.W. Hughes, M.J. Tang, and C.C. Yang, Mechanical forces in skin disorders. J Dermatol Sci, 2018. 90(3): p. 232-40.
35. Ogawa, R., Keloid and Hypertrophic Scars Are the Result of Chronic Inflammation in the Reticular Dermis. Int J Mol Sci, 2017. 18(3): p. 606-15.
36. Ghazawi, F.M., R. Zargham, M.S. Gilardino, D. Sasseville, and F. Jafarian, Insights into the Pathophysiology of Hypertrophic Scars and Keloids: How Do They Differ? Adv Skin Wound Care, 2018. 31(1): p. 582-95.
37. Lynch, M.D. and F.M. Watt, Fibroblast heterogeneity: implications for human disease. J Clin Invest, 2018. 128(1): p. 26-35.
38. Funayama, E., T. Chodon, A. Oyama, and T. Sugihara, Keratinocytes Promote Proliferation and Inhibit Apoptosis of the Underlying Fibroblasts: An Important Role in the Pathogenesis of Keloid. J Invest Dermatol, 2003. 121(6): p. 1326-31.
39. Shook, B.A., R.R. Wasko, G.C. Rivera-Gonzalez, et al., Myofibroblast proliferation and heterogeneity are supported by macrophages during skin repair. Science, 2018. 362(6417): p. e2971-8.
40. Ogawa, R. and S. Akaishi, Endothelial dysfunction may play a key role in keloid and hypertrophic scar pathogenesis – Keloids and hypertrophic scars may be vascular disorders. Med Hypotheses, 2016. 96: p. 51-60.
41. Shang, T., B. Yao, D. Gao, J. Xie, X. Fu, and S. Huang, A novel model of humanised keloid scarring in mice. Int Wound J, 2018. 15(1): p. 90-4.
42. Marttala, J., J.P. Andrews, J. Rosenbloom, and J. Uitto, Keloids: Animal models and pathologic equivalents to study tissue fibrosis. Matrix Biol, 2016. 51: p. 47-54.
43. Theoret, C.L. and J.M. Wilmink, Aberrant wound healing in the horse: naturally occurring conditions reminiscent of those observed in man. Wound Repair Regen, 2013. 21(3): p. 365-71.
44. Supp, D.M., Animal Models for Studies of Keloid Scarring. Adv Wound Care, 2019. 8(2): p. 77-89.
45. Silver, I.A., Basic physiology of wound healing in the horse. Equine Vet J, 1982. 14(1): p. 7-15.
46. Cheng, L., X. Sun, J. Yu, et al., A facilely fabricated in vivo hypertrophic scar model through continuous gradient elastic tension. RSC Adv, 2015. 5: p. 107430-44.
47. Zomer, H.D. and A.G. Trentin, Skin wound healing in humans and mice: Challenges in translational research. J Dermatol Sci, 2018. 90(1): p. 3-12.
48. Nuutila, K., S. Katayama, J. Vuola, and E. Kankuri, Human Wound-Healing Research: Issues and Perspectives for Studies Using Wide-Scale Analytic Platforms. Adv Wound Care (New Rochelle), 2014. 3(3): p. 264-71.
49. Ito, M. and G. Cotsarelis, Is the hair follicle necessary for normal wound healing? J Invest Dermatol, 2008. 128(5): p. 1059-61.
50. Vandamme, T.F., Use of rodents as models of human diseases. J Pharm Bioallied Sci, 2014. 6(1): p. 2-9.
51. Aarabi, S., K.A. Bhatt, Y. Shi, et al., Mechanical load initiates hypertrophic scar formation through decreased cellular apoptosis. FASEB J, 2007. 21(12): p. 3250-61.
52. Wang, H. and S. Luo, Establishment of an animal model for human keloid scars using tissue engineering method. J Burn Care Res, 2013. 34(4): p. 439-46.
53. Sunaga, A., H. Kamochi, S. Sarukawa, et al., Reconstitution of Human Keloids in Mouse Skin. Plast Reconstr Surg Glob Open, 2017. 5(4): p. e1304-10.
54. Limandjaja, G.C., L.J. van den Broek, T. Waaijman, et al., Reconstructed human keloid models show heterogeneity within keloid scars. Arch Dermatol Res, 2018. 310(10): p. 815-26.
55. Lee, Y.S., T. Hsu, W.C. Chiu, et al., Keloid-derived, plasma/fibrin-based skin equivalents generate de novo dermal and epidermal pathology of keloid fibrosis in a mouse model. Wound Repair Regen, 2016. 24(2): p. 302-16.
56. Park, T.H., D.K. Rah, C.H. Chang, and S.Y. Kim, Establishment of Patient-Derived Keloid Xenograft Model. J Craniofac Surg, 2016. 27(7): p. 1670-3.
57. Mandal, A., D. Imran, and G.S. Rao, Spontaneous keloids in siblings. Ir Med J, 2004. 97(8): p. 250-1.
58. Bleasdale, B., S. Finnegan, K. Murray, S. Kelly, and S.L. Percival, The Use of Silicone Adhesives for Scar Reduction. Adv Wound Care (New Rochelle), 2015. 4(7): p. 422-30.
59. Ogawa, R., Keloid and Hypertrophic Scars Are the Result of Chronic Inflammation in the Reticular Dermis. 2017. 18(3): p. 606-15.
60. Huang, C., K. Miyazaki, S. Akaishi, A. Watanabe, H. Hyakusoku, and R. Ogawa, Biological effects of cellular stretch on human dermal fibroblasts. J Plast Reconstr Aesthet Surg, 2013. 66(12): p. e351-61.
61. Wong, V.W., K.C. Rustad, S. Akaishi, et al., Focal adhesion kinase links mechanical force to skin fibrosis via inflammatory signaling. Nat Med, 2011. 18(1): p. 148-52.
62. Aoki, M., A. Kondo, N. Matsunaga, and R. Ogawa, The Immunosuppressant Fingolimod (FTY720) for the Treatment of Mechanical Force-Induced Abnormal Scars. Hindawi, 2020. 2020: p. 1-11.
63. Ye, X., Z. Pang, and N. Zhu, Dihydromyricetin attenuates hypertrophic scar formation by targeting activin receptor-like kinase 5. Eur J Pharmacol, 2019. 852: p. 58-67.
64. Wang, Z., X. Huang, T. Zan, Q. Li, and H. Li, A modified scar model with controlled tension on secondary wound healing in mice. Burns & Trauma, 2020. 8: p. 13-7.
65. Park, S.A., J. Covert, L. Teixeira, et al., Importance of defining experimental conditions in a mouse excisional wound model. Wound Repair Regen, 2015. 23(2): p. 251-61.
66. Dohi, T., J. Padmanabhan, S. Akaishi, et al., The Interplay of Mechanical Stress, Strain, and Stiffness at the Keloid Periphery Correlates with Increased Caveolin-1/ROCK Signaling and Scar Progression. Plast Reconstr Surg, 2019. 144(1): p. 58e-67e.
67. Yamada, E., The fine structure of the gall bladder epithelium of the mouse. J Biophys Biochem Cytol, 1955. 1(5): p. 445-58.
68. Sinha, B., D. Koster, R. Ruez, et al., Cells respond to mechanical stress by rapid disassembly of caveolae. Cell, 2011. 144(3): p. 402-13.
69. Kruglikov, I.L. and P.E. Scherer, Caveolin-1 as a target in prevention and treatment of hypertrophic scarring. NPJ Regen Med, 2019. 4(9): p. 1-7.
70. Navarro, A., B. Anand-Apte, and M.O. Parat, A role for caveolae in cell migration. FASEB J, 2004. 18(15): p. 1801-11.
71. Lin, H.H., H.K. Lin, I.H. Lin, et al., Mechanical phenotype of cancer cells: cell softening and loss of stiffness sensing. Oncotarget, 2015. 6(25): p. 20946-58.
72. Zhang, G.-Y., Q. Yu, T. Cheng, et al., Role of caveolin-1 in the pathogenesis of tissue fibrosis by keloid-derived fibroblasts in vitro. Br J Dermatol, 2011. 164(3): p. 623-7.
73. Del Galdo, F., F. Sotgia, C.J. de Almeida, et al., Decreased expression of caveolin 1 in patients with systemic sclerosis: crucial role in the pathogenesis of tissue fibrosis. Arthritis Rheum, 2008. 58(9): p. 2854-65.
74. Castello-Cros, R., D. Whitaker-Menezes, A. Molchansky, et al., Scleroderma-like properties of skin from caveolin-1-deficient mice: implications for new treatment strategies in patients with fibrosis and systemic sclerosis. Cell Cycle, 2011. 10(13): p. 2140-50.
75. Drab, M., P. Verkade, M. Elger, et al., Loss of caveolae, vascular dysfunction, and pulmonary defects in caveolin-1 gene-disrupted mice. Science, 2001. 293(5539): p. 2449-52.
76. Razani, B., J.A. Engelman, X.B. Wang, et al., Caveolin-1 null mice are viable but show evidence of hyperproliferative and vascular abnormalities. J Biol Chem, 2001. 276(41): p. 38121-38.
77. Williams, F.N., D.N. Herndon, and L.K. Branski, Where we stand with human hypertrophic and keloid scar models. Exp Dermatol, 2014. 23(11): p. 811-2.
78. Perlman, R.L., Mouse models of human disease: An evolutionary perspective. Evol Med Public Health, 2016(1): p. 170-6.
79. Wang, Y., S.M. Mithieux, Y. Kong, et al., Tropoelastin incorporation into a dermal regeneration template promotes wound angiogenesis. Adv Healthc Mater, 2015. 4(4): p. 577-84.
80. Huang, S.-Y., X. Xiang, R.-Q. Guo, S. Cheng, L.-Y. Wang, and L. Qiu, Quantitative assessment of treatment efficacy in keloids using high-frequency ultrasound and shear wave elastography: a preliminary study. Sci Rep, 2020. 10(1375): p. 1-7.
81. Schuetzenberger, K., M. Pfister, A. Messner, et al., Comparison of optical coherence tomography and high frequency ultrasound imaging in mice for the assessment of skin morphology and intradermal volumes. Sci Rep, 2019. 9(13643): p. 1-7.
82. Bran, G., U. Goessler, K. Hormann, F. Riedel, and H. Sadick, Keloids: Current concepts of pathogenesis (Review). Int J Mol Med, 2009. 24: p. 283-93.
83. Chesnoy, S., P.Y. Lee, and L. Huang, Intradermal injection of transforming growth factor-beta1 gene enhances wound healing in genetically diabetic mice. Pharm Res, 2003. 20(3): p. 345-50.
84. Wells, R.G., The role of matrix stiffness in hepatic stellate cell activation and liver fibrosis. J Clin Gastroenterol, 2005. 39(4 Suppl 2): p. S158-61.
85. Watanabe, N., S. Hanabuchi, V. Soumelis, et al., Human thymic stromal lymphopoietin promotes dendritic cell-mediated CD4+ T cell homeostatic expansion. Nat Immunol, 2004. 5(4): p. 426-34.
86. Wynn, T.A., Fibrotic disease and the T(H)1/T(H)2 paradigm. Nat Rev Immunol, 2004. 4(8): p. 583-94.
87. Chambert, J., T. Lihoreau, S. Joly, et al., Multimodal investigation of a keloid scar by combining mechanical tests in vivo with diverse imaging techniques. J Mech Behav Biomed Mater, 2019. 99: p. 206-15.
88. Langton, A.K., S.E. Herrick, and D.J. Headon, An extended epidermal response heals cutaneous wounds in the absence of a hair follicle stem cell contribution. J Invest Dermatol, 2008. 128(5): p. 1311-8.
89. Ademola, S.A., A.I. Michael, and O.A. Olawoye, Temporoparietal scalp keloid: an unusual occurrence. Int J Dermatol, 2015. 54(9): p. 1066-7.