The regulation of melanocyte stem cells by Wnt signaling

描述(申请人提供)：黑素细胞干细胞(McSCs)在一生中维持健康的黑素细胞种群。了解它们的行为和调节与黑素细胞丧失引起的疾病有关，如炎症后色素减退、白癜风和头发变白，以及黑色素瘤的生物学。目前，对控制McSCs的细胞和分子机制知之甚少。这项资助的目的是了解Wnt信号的功能及其在毛囊中的McSCs中的调节。在毛囊的周期性再生过程中，McSCs与毛囊上皮干细胞(EpSCs)协同激活。它们为毛球提供分化的黑素细胞，以产生头发色素。我们发现，在生长期开始时，McSCs在相邻EPSCs分泌Wnt配体后激活Wnt信号。通过在McSCs中删除或激活Wnt信号的关键调节因子2-catenin，我们已经证明了Wnt信号在MCSC分化过程中起着至关重要的作用。我们假设Wnt信号是MCSC分化所必需的，并且EPSCs在毛囊周期中协调调节McSCs和EPSCs自身的Wnt信号。为了解决这一假设，我们将追求以下具体目标。在Aim1中，我们将通过在黑素细胞中表达分泌的Wnt信号抑制物Dkk1或Wnt信号的核介质显性-阴性形式Lef1来抑制McSCs中的Wnt信号。我们将研究这如何影响他们在毛发周期中产生功能性黑素细胞的能力。在AIM2中，为了确定EPSCs分泌的Wnt配体(S)是否能够激活邻近的McSCs中的Wnt信号并促进其分化，我们利用遗传的小鼠模型，缺失了毛囊EPSCs中Wnt配体分泌所必需的Wnless基因或强制EPSCs表达Wnt配体。在AIM3中，我们将测试Wnt抑制剂是否可以促进MCSC在衰老过程中的维持，这一过程已知会导致MCSC在异常分化后耗尽和丢失。具体地说，我们将利用转基因小鼠模型在McSCs中过度表达Dkk1或显性-阴性形式的Lef1，以检查这是否促进了未分化的McSCs在衰老过程中的维持。我们还将测试Wnt抑制是否可以逆转MCSC的分化，这一过程预示着它们随后的丧失。我们的研究将为我们提供对McSCs调控的分子机制以及黑素细胞行为如何与毛发再生相协调的新的理解，为了解黑素细胞不适当地丢失(如头发变白和白癜风)或经历黑色素瘤等细胞生长失控的疾病提供科学基础。

DESCRIPTION (provided by applicant): Melanocyte stem cells (McSCs) sustain a healthy population of melanocytes throughout life. Understanding their behavior and regulation is relevant to disorders resulting from melanocyte loss such as post inflammatory hypopigmentation, vitiligo, and hair graying, as well as to the biology of melanoma. Currently, little is known about the cellular and molecular mechanisms that govern McSCs. The goal of this grant is to understand the function of Wnt signaling and its regulation in McSCs residing in the hair follicle. McSCs are coordinately activated with follicular epithelial stem cells (EpSCs) during the cyclical regeneration of the hair follicle. They provide differentiated melanocytes to the hair bulb for the production of hair pigment. We discovered that McSCs activate Wnt signaling following Wnt ligand secretion from adjacent EpSCs at the onset of anagen. By transgenically deleting or activating 2-catenin, a key mediator of Wnt signaling in McSCs, we have shown that Wnt signaling is crucial for McSC differentiation. We hypothesize that Wnt signaling is required for McSC differentiation and that EpSCs coordinately regulate Wnt signaling in McSCs and EpSCs themselves during the hair follicle cycle. To address this hypothesis, we will pursue the following specific aims. In Aim1, we will inhibit Wnt signaling in McSCs by expressing either a secreted inhibitor of Wnt signaling, Dkk1, or a dominant- negative form of a nuclear mediator of Wnt signaling, Lef1, in melanocytes. We will examine how this influences their ability to give rise to functional melanocytes during the hair cycle. In Aim2, to determine if Wnt ligand(s) secreted by EpSCs can activate Wnt signaling in neighboring McSCs and promote their differentiation, we will delete the Wntless gene, which is necessary for Wnt ligand secretion, in follicular EpSCs or force expression of a Wnt ligand by EpSCs, using genetic mouse models. In Aim3, we will test if Wnt inhibitors can promote McSC maintenance during aging, a process known to result in McSC exhaustion and loss following their aberrant differentiation. Specifically, we will utilize transgenic mouse models to overexpress either Dkk1 or a dominant-negative form of Lef1 in McSCs to examine if this promotes the maintenance of undifferentiated McSCs during aging. We will also test if Wnt inhibition can reverse McSC differentiation, a process that presages their ensuing loss. Our study will provide us with a novel understanding of the molecular mechanisms regulating McSCs and how melanocyte behavior is coordinated with hair regeneration, providing a scientific foundation for understanding diseases in which melanocytes are either inappropriately lost such as hair graying and vitiligo or undergo uncontrolled cell growth as in melanoma.