Hair Follicle Neogenesis in Response to Wounding

描述（由申请人提供）：通常情况下，皮肤愈合后不会再生其先前的正常结构，包括毛囊和汗腺。疤痕会导致挛缩和发病。没有皮肤再生的损伤愈合导致慢性伤口。了解皮肤在受伤后不能再生的原因，将为治疗急性和慢性伤口带来新的方法，这些都是我们卫生系统面临的主要医学问题。损伤后毛囊新生（HFN）是哺乳动物皮肤再生的一个范例。我们发现，在小鼠背部皮肤全层切除后，在愈合的伤口中重新形成了毛囊。毛囊形成区域的皮肤看起来正常，没有疤痕，并且有新的毛囊，皮脂腺和脂肪组织的存在。根据先前的报告，人类也可能出现类似的再生水平，尽管要弱得多。本研究的目的是表征受伤后与HFN相关的细胞和分子事件。我们利用基因表达阵列研究了皮肤这种非凡的再生能力。成纤维细胞生长因子9 （Fgf9）在表皮再上皮化后上调，但在毛胚形成之前上调。利用毛囊新生损伤模型，我们发现抑制Fgf9导致新毛囊形成的统计学显著减少。在诱导的K14/Fgf9转基因小鼠中，过表达Fgf9导致伤口愈合过程中毛囊形成显著增加。值得注意的是，我们发现γ / δ T细胞是表皮中Fgf9的主要来源。这一发现建立了皮肤再生和免疫系统之间的潜在联系，并启动了上皮干细胞专家George Cotsarelis博士和宾夕法尼亚大学病理学和实验室医学系T细胞免疫学专家Avinash Bhandoola博士之间的拟议合作。表皮γ / δ T细胞先前与小鼠的伤口修复有关，但它们在毛囊再生中的可能作用尚未被研究。有趣的是，这些细胞在人类表皮中不存在，尽管它们存在于真皮层中。这是否可以解释为什么人类皮肤再生与老鼠相比如此有限？我们建议：1。确定缺乏γ / δ T细胞的小鼠是否发生毛囊再生。2. 使用Lck-Cre/floxedFgf9小鼠删除T细胞中的Fgf9，以测试Fgf9缺失对毛囊损伤后新生的影响。定义不同类型的γ / δ T细胞在制造Fgf9和诱导毛囊新生能力方面的差异，4。确定小鼠和人类γ / δ T细胞在伤口愈合反应（产生Fgf9和其他生长因子的能力）方面的差异。这些研究有助于皮肤生物学家和免疫学家之间的跨学科努力，将皮肤再生研究推向新的方向。这里产生的初步结果将为一个更大的关于T细胞亚群在皮肤再生和发育中的作用的互动研究项目奠定基础。Avinash Bhandoola博士在T细胞发育方面的专业知识与Cotsarelis博士在上皮干细胞和毛发生物学方面的知识相结合，将为解剖免疫系统在皮肤再生中的作用提供强有力的合作。最终，这些发现可能会影响与伤口愈合、疤痕形成、衰老和其他退行性疾病相关的医学问题。

DESCRIPTION (provided by applicant): Typically, skin heals with a scar without regenerating its previous normal structure that includes hair follicles and sweat glands. Scarring causes contractures and morbidity. Impaired healing without skin regeneration leads to chronic wounds. Understanding why skin does not regenerate after wounding would lead to new approaches for treating both acute and chronic wounds, which are major medical problems facing our health system. Hair follicle neogenesis (HFN) after wounding serves as a paradigm for mammalian skin regeneration. We found that following full-thickness excision of mouse skin on the back, hair follicles formed de novo in the healed wound. The skin in the area of hair follicle formation appeared normal without a scar and with the presence of new hair follicles, sebaceous glands and adipose tissue. Based on prior reports, it is possible that similar, albeit much less robust levels of regeneration also occur in humans. The goal of the parent grant is to characterize the cellular and molecular events associated with HFN following wounding. We have studied this remarkable regenerative capacity of the skin using gene expression arrays. Fibroblast growth factor 9 (Fgf9) was upregulated in the epidermis after reepithelialization, but prior to hair germ formation. Using a wounding model for hair follicle neogenesis, we showed that inhibiting Fgf9 resulted in a statistically significant decrease in new hair follicle formation. Over expression of Fgf9 in inducible K14/Fgf9 transgenic mice resulted in marked increases in hair follicle formation during wound healing. Remarkably, we discovered that gamma/delta T cells are the major source of Fgf9 in the epidermis. This finding established a potential connection between skin regeneration and the immune system, and initiated the proposed collaboration between Dr. George Cotsarelis, an expert in epithelial stem cells and PI of the parent grant, and Dr. Avinash Bhandoola, an expert in T cell immunology in the Department of Pathology and Laboratory Medicine at Penn. Epidermal gamma/delta T cells were previously implicated in wound repair in the mouse, but their possible role in hair follicle regeneration has not been studied. Intriguingly, these cells are absent in human epidermis, although they are present in the dermis. Could this explain why human skin regeneration is so severely limited compared to the mouse? We propose to: 1. Determine if hair follicle regeneration occurs in mice lacking gamma/delta T cells. 2. Delete Fgf9 in T cells using Lck-Cre/floxedFgf9 mice to test the effect of loss of Fgf9 on hair follicle neogenesis following wounding, 3. Define differences between different types of gamma/delta T cells in their ability to make Fgf9 and induce hair follicle neogenesis, 4. Determine differences between mouse and human gamma/delta T cells with respect to their wound healing response (ability to produce Fgf9 and other growth factors). These studies lend themselves to interdisciplinary efforts between cutaneous biologists and immunologists that will push research of skin regeneration into new directions. The preliminary results generated here would form a nidus for a larger interactive research project on the role of T cell subsets in skin regeneration and development. Dr. Avinash Bhandoola's expertise in T cell development combined with Dr. Cotsarelis's knowledge of epithelial stem cells and hair biology will provide a strong collaborative effort for the dissection of the role(s) of the immune system in skin regeneration. Ultimately, the findings could impact on medical problems related to wound healing, scar formation, aging and other degenerative conditions.