Reindeer Antler Velvet: a unique model to study cellular and molecular mechanisms underlying tissue regeneration

哺乳动物的进化选择了加速伤口闭合，代价是产生纤维性瘢痕。为了使未来能够开发出改善皮肤愈合的治疗方法，全面了解促进再生和纤维化愈合反应的分子信号将是必不可少的。我们目前对这些不同过程的理解很差，部分原因是我们缺乏一个强大的哺乳动物组织再生模型。鹿角是唯一能够完全再生的哺乳动物器官。生长中的鹿角覆盖着皮肤(天鹅绒)，含有毛囊、腺体、密集的神经和血管供应。在令人兴奋的前期工作中，我们发现鹿茸在受伤后能够无疤痕再生，这一现象以前只归因于胚胎皮肤。再生的天鹅绒伤口含有新形成的毛囊、腺体、密集的神经和色素沉着。相比之下，(同一动物的)背部皮肤相同的伤口会导致纤维性瘢痕，由无序的细胞外基质组成，没有附属物、神经或色素。我们将利用这个强大的比较模型来研究哺乳动物皮肤修复的这些不同模式下的基本细胞和分子动力学。我们将测试这一假说，即再生是由天鹅绒真皮成纤维细胞内独特的基因表达程序实现的。*目标1-描述使皮肤再生与纤维瘢痕形成之间的分子调节因素。我们将使用RNAseq对受伤的鹿茸和鹿茸背部进行比较转录分析，以确定使鹿茸再生的分子机制。*目的2-对鹿茸再生过程中唯一激活或抑制的基因进行功能评估。小分子和慢病毒载体旨在激活或抑制识别的基因或相关的信号通路，将应用于天鹅绒和背部伤口，以确定它们在促进再生或疤痕形成方面的作用。*目标3-从鹿茸中分离和鉴定真皮祖细胞。我们假设天鹅绒富含能够再生的真皮祖细胞。我们将从鹿茸或背皮真皮/间充质中分离出祖细胞，并进行表型鉴定和移植实验，以比较它们的内在功能能力。*目的4-表征静息鹿茸内以及纤维皮肤修复和再生期间的巨噬细胞动力学。巨噬细胞是组织再生的重要贡献者。我们假设巨噬细胞对绒毛损伤表现出独特的反应，从而改变了真皮成纤维细胞修复程序。使用免疫染色、细胞分类和细胞术，我们将记录留存巨噬细胞的组成以及背皮和天鹅绒对损伤的反应。**

Mammalian evolution has selected for accelerated wound closure at the expense of generating fibrotic scar. To enable future development of therapies that improve skin healing, a comprehensive understanding of the molecular signals that promote a regenerative versus fibrotic healing response will be essential. Our current understanding of these divergent processes is poor, partly because we lack a robust mammalian model of tissue regeneration.******Deer antlers are the only mammalian organ capable of complete regeneration. Growing antlers are covered in skin (velvet) that contains hair follicles, glands, dense innervation and vascular supply. In exciting preliminary work, we discovered that after injury, antler velvet is capable of scarless regeneration, a phenomenon previously ascribed only to embryonic skin. Regenerated velvet wounds contain newly formed hair follicles, glands, dense innervation and pigmentation. In contrast, identical wounds in backskin (of the same animal) resulted in fibrotic scar, consisting of disorganized extracellular matrix and an absence of appendages, innervation or pigment. We will exploit this powerful comparative model to study the basic cellular and molecular dynamics that underlie these divergent modes of mammalian skin repair. We will test the hypothesis that regeneration is enabled by a unique gene expression program within velvet dermal fibroblasts.******Aim 1- To characterize the molecular regulators that enable skin regeneration versus formation of fibrotic scar. We will use RNAseq to perform a comparative transcriptomic analysis of injured antler velvet and backskin to identify the molecular mechanisms that enable velvet regeneration.******Aim 2 – Functional evaluation of genes that are exclusively activated or repressed during velvet regeneration. Small molecules and lentiviral vectors designed to activate or inhibit identified genes or associated signaling pathways, will be applied to velvet and backskin wounds to ascertain their role in promoting regeneration or scar formation. ******Aim 3 - To isolate and characterize dermal progenitors from antler velvet. We hypothesize that velvet is enriched with dermal progenitors that enable regeneration. We will isolate progenitors from antler velvet or backskin dermis/mesenchyme and perform phenotypic characterization and transplantation experiments to compare their intrinsic functional capacities.******Aim 4 – To characterize macrophage dynamics within resting antler velvet and during fibrotic skin repair versus regeneration. Macrophage are essential contributors to tissue regeneration. We hypothesize that macrophage exhibit a unique response to velvet injury which consequently modifies the dermal fibroblast repair program. Using immunostaining, cell sorting and cytometry we will document the composition of resident macrophages as well as the response to injury in backskin versus velvet.**