A cellular basis for age-related impaired tactile acuity

描述（由申请人提供）：众所周知，触觉感知随着年龄的增长而恶化，这种现象伴随着皮肤中的许多结构缺陷，包括默克尔细胞神经突复合物，其他触觉传入和触觉敏感性的急剧丧失。触觉感知缺陷被认为是导致体位稳定性和握力下降的原因，并导致跌倒频率增加，这是决定老年人生活质量和独立生活能力的主要因素。技术障碍阻碍了理解与年龄相关的触觉丧失的细胞和分子基础：1)体感受体的多样性；2)机械感受末端器官分散在皮肤各处的事实。此外，关于负责维持感知轻触的细胞机械感受器（如默克尔细胞）更新的假定皮肤祖细胞群的信息非常缺乏。默克尔细胞代表了一种成熟的神经内分泌谱系，它存在于啮齿类动物和人类毛状皮肤表皮的独特结构中，称为触觉丘（TDs）。我们的实验室先前发现了一种新的角化细胞祖细胞群，该细胞定位于TD中的默克尔细胞，称为TD祖细胞（TDPCs），我们证明了TDPCs可以在再生条件和稳态下产生默克尔谱系。为了进一步探索TDPCs在默克尔细胞稳态中的作用，我们在实验室建立了BAC转基因小鼠模型Krt17CreERT2，该模型选择性地靶向表皮中的TDPCs，表达他莫昔芬诱导的Cre重组酶，同时排除成熟的默克尔细胞。将Krt17CreERT2小鼠与其他可诱导的报告等位基因结合使用，我们证明了i) TDPCs是皮肤的永久居民，仅负责维持默克尔血统；ii)在年轻成人皮肤中，TD内的整个成熟默克尔细胞池每两个月轮换一次。这些初步发现确立了Krt17CreERT2小鼠作为一个很好的平台来研究衰老皮肤中默克尔细胞稳态是如何被扰乱的。本研究的主要目的是确定TDPCs祖细胞能力的下降是否导致了默克尔细胞-神经突复合体的衰老和触觉的减弱。为了实现我们的目标，我们将使用Krt17CreERT2小鼠来测定衰老皮肤中默克尔细胞的发生和凋亡率。我们还将从衰老皮肤中纯化TDPCs，并在体外评估其克隆生成能力。最后，我们将对年轻成人和老年TDPCs进行移植，并直接评估其在体内再生默克尔细胞和恢复触觉敏锐度的能力。这些研究对于理解我们的触觉的细胞调控是至关重要的，触觉是我们感知周围环境的能力的基本要素，随着年龄的增长，这种能力会严重减弱。

DESCRIPTION (provided by applicant): It is well established that touch perception deteriorates with age and this phenomenon is accompanied by a number of structural defects in the skin including a dramatic loss of Merkel cell-neurite complexes, other tactile afferents and touch sensitivity. Deficits in touch perception are thought to contribute to the decline of postura stability and handgrip, 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. Technical hurdle that have hindered efforts to understand the cellular and molecular basis of age-related losses in touch perception are i) the variety of somatosensory receptors and ii) the fact that mechanoreceptive end organs are scattered throughout the skin. Furthermore, information regarding putative skin progenitor populations that are responsible for maintaining the turnover of cellular mechanoreceptors that perceive light touch, such as Merkel cells, is sorely lacking. Merkel cells represent a mature neuroendocrine lineage that resides in unique structures in the epidermis of hairy skin in rodents and humans termed touch domes (TDs). Our laboratory previously identified a novel keratinocyte progenitor population localized with Merkel cells in TDs termed TD progenitor cells (TDPCs) and we demonstrated that TDPCs could give rise to the Merkel lineage both under regenerative conditions and homeostasis. To further explore the role of TDPCs in Merkel cell homeostasis, we generated a BAC transgenic mouse model in our laboratory, Krt17CreERT2 that selectively targets TDPCs in the epidermis for expression of a tamoxifen-inducible Cre recombinase while excluding mature Merkel cells. Using Krt17CreERT2 mice in combination with other Cre-inducible reporter alleles we demonstrated that i) TDPCs are permanent residents of the skin that are solely responsible for maintaining the Merkel lineage and ii) the entire pool of mature Merkel cells within the TD is turned over every two months in young adult skin. These preliminary findings establish Krt17CreERT2 mice as an excellent platform to examine how Merkel cell homeostasis may be perturbed in aged skin. The main objective of this proposal is to determine whether a decline in progenitor capacity of TDPCs underlies the age-related loss in Merkel cell-neurite complexes and diminished touch sensation. To accomplish our objective, we will employ Krt17CreERT2 mice to determine the rate of Merkel cell genesis and apoptosis in aged skin. We will also purify TDPCs from aged skin and assess their clonogenic capacity in vitro. Finally, we will transplant young adult and aged TDPCs and directly assess their ability to regenerate Merkel cells in vivo and restore tactile acuity. These studies will be critical to understanding the cellular regulation of our sense of touch, an essentil element of our ability to perceive our surroundings that is severely diminished as we age.