Investigating the role for Utrophin in age-related decline of the Merkel lineage

我们的触觉使许多行为成为人类生存的基础，让我们吃， 沟通和生存。触觉反应的缺陷被认为有助于姿势性的下降， 稳定性和抓地力，以及由此产生的下降频率增加，这是一个主要因素决定 老年人的生活质量和独立生活的能力。在哺乳动物中， （曲率、纹理和振动）由驻留在皮肤中的触觉感受器编码，具有不同的生理特性。 性质和形态学终末器官;然而，这背后的细胞和分子机制 多样性基本上是未知的。此外，调节皮肤干细胞，负责 维持感知轻柔触摸的细胞机械感受器（如默克尔细胞）的周转， 未知我们的实验室以前的特点是一个人口的上皮干细胞，居住在表皮 皮肤中的触摸圆顶，称为触摸圆顶干细胞（TDSC），负责维持皮肤的功能。 默克尔血统在稳态。这项提案的长期目标是定义细胞和分子 TDSC维持默克尔血统的基础。我们的初步数据记录了一个戏剧性的年龄相关的 人（40 - 90岁）和鼠（2 - 32月龄）皮肤中默克尔细胞数量下降。 然而，TDSC数字保持不变。我们证实，与年龄相关的默克尔细胞丢失不是由于 成熟默克尔细胞的早熟退出或感觉传入神经支配的缺陷，但由于TDSC减少 补充默克尔血统的能力。利用TDSC祖细胞中这种与年龄相关的缺陷 能力，我们进行了蛋白质组学和mRNA分析的TDSC从年轻与老年小鼠皮肤， 确定了粘着斑相关蛋白Utrn（Utrn）在老年人中显著下调， TDSC。出生后第20天，Utrn敲除（Utrn-/-）小鼠与Wt小鼠相比，显示出相同数量的默克尔细胞 小鼠，排除Utrn在默克尔细胞发育中的作用。然而，默克尔的细胞数量减少了， 在2个月大的Utrn-/-小鼠中为50%，为Utrn在年龄相关性免疫缺陷中的功能作用提供了遗传证据。 通过TDSC维持默克尔谱系。我们确定了Nrg 1-Erbb 2信号轴作为一个调节器， Utrn在体外小鼠和人上皮角质形成细胞以及体内TDSC中的表达。这些初步 研究结果支持我们的中心假设：TDSC需要Nrg 1-Erbb 2调节Utrn表达 维持默克尔细胞内稳态。为了验证我们的假设，我们将采用小鼠模型， 破坏或挽救Utrn表达并评估其对默克尔细胞稳态的影响。使用体内谱系 追踪工具和Nrg 1条件等位基因，我们将研究TDSC的细胞机制 默克尔谱系的维持和TD小生境中Nrg 1表达的上游调节。最后我们将 询问TDSC中Utrn调节的分子机制和Utrn功能的下游效应物。 我们的目标是首次揭示默克尔谱系干细胞调控的遗传机制。

Our sense of touch enables numerous behaviors fundamental to human existence, allowing us to eat, communicate and survive. Deficits in tactile responsiveness are thought to contribute to the decline of postural stability and hand grip, and the resulting increase in falling frequency, which is a major factor determining quality of life and the ability to live independently for the elderly. In mammals, different tactile qualities (curvature, texture and vibration) are encoded by touch receptors residing in the skin with distinct physiological properties and morphological end-organs; however, the cellular and molecular mechanisms underlying this diversity are largely unknown. Furthermore, the regulation of skin stem cells that are responsible for maintaining the turnover of cellular mechanoreceptors that perceive gentle touch, such as Merkel cells, is unknown. Our laboratory previously characterized a population of epithelial stem cells that reside in epidermal touch domes in the skin, termed touch dome stem cells (TDSCs), that are responsible for maintaining the Merkel lineage during homeostasis. The long-term goal of this proposal is to define the cellular and molecular basis for TDSC maintenance of the Merkel lineage. Our preliminary data chronicles a dramatic age-related decline in Merkel cell numbers in human (40 – 90 years of age) and murine (2 – 32 months of age) skin. However, TDSC numbers remain unchanged. We confirmed that age-related loss of Merkel cells is not due to precocious exit of mature Merkel cells or defects in sensory afferent innervation but is due to diminished TDSC progenitor capacity to replenish the Merkel lineage. Leveraging this age-related deficit in TDSC progenitor capacity, we performed proteomics and mRNA profiling of TDSCs from young versus aged mouse skin and identified the focal adhesion-associated protein Utrophin (Utrn) to be dramatically downregulated in aged TDSCs. Utrn null (Utrn-/-) mice at postnatal day 20 displayed equal numbers of Merkel cells compared to Wt mice, excluding a role for Utrn in Merkel cell development. However, Merkel cell numbers were reduced by 50% in 2-month-old Utrn-/- mice providing genetic evidence for a functional role for Utrn in age-related maintenance of the Merkel lineage by TDSCs. We identified the Nrg1-Erbb2 signaling axis as a regulator of Utrn expression in mouse and human epithelial keratinocytes in vitro and TDSCs in vivo. These preliminary findings support our central hypothesis: Nrg1-Erbb2 regulation of Utrn expression is required for TDSC maintenance of Merkel cell homeostasis. To test our hypothesis, we will employ mouse models to genetically disrupt or rescue Utrn expression and assess its impact on Merkel cell homeostasis. Using in vivo lineage tracing tools and a Nrg1 conditional allele we will investigate the cellular mechanisms underlying TDSC maintenance of the Merkel lineage and upstream regulation of Nrg1 expression in the TD niche. Finally, we will interrogate the molecular mechanisms for Utrn regulation and downstream effectors of Utrn function in TDSCs. Our goal is to uncover first of its kind genetic mechanisms for stem cell regulation of the Merkel lineage.