A cellular basis for age-related impaired tactile acuity

描述(申请人提供)：众所周知，触觉会随着年龄的增长而恶化，这一现象伴随着皮肤的一些结构性缺陷，包括默克尔细胞-轴突复合体、其他触觉传入细胞和触摸敏感性的急剧丧失。触觉缺陷被认为是导致后遗症稳定性和握力下降的原因，以及由此导致的跌倒频率的增加，这是决定老年人生活质量和独立生活能力的主要因素。阻碍人们努力了解与年龄相关的触觉丧失的细胞和分子基础的技术障碍是：i)体感受体的多样性和ii)机械感受性末端器官散布在皮肤各处的事实。此外，有关负责维持感知光接触的细胞力感受器(如默克尔细胞)周转的假定皮肤祖细胞群体的信息严重缺乏。默克尔细胞代表一种成熟的神经内分泌谱系，存在于啮齿动物和人类被称为触摸穹顶(TDS)的多毛皮肤的表皮中的独特结构中。我们实验室以前在TDS中发现了一种新的定位于Merkel细胞的角质形成细胞祖细胞群体，称为TD前体细胞(TDPC)，我们证明了TDPC在再生条件和动态平衡条件下都可以产生Merkel血统。为了进一步探索TDPC在Merkel细胞动态平衡中的作用，我们在实验室建立了一个BAC转基因小鼠模型Krt17CreERT2，该模型选择性地针对表皮中的TDPC表达他莫昔芬诱导的Cre重组酶，同时排除成熟的Merkel细胞。使用Krt17CreERT2小鼠和其他Cre诱导的报告等位基因，我们证明了i)TDPC是皮肤的永久居民，仅负责维持Merkel血统，ii)TD内的整个成熟Merkel细胞池每两个月在年轻成人皮肤中翻转一次。这些初步发现使Krt17CreERT2小鼠成为研究老化皮肤中默克尔细胞动态平衡可能受到干扰的极佳平台。这项建议的主要目的是确定TDPC祖细胞能力的下降是否是与年龄相关的Merkel细胞-轴突复合体丧失和触觉减弱的基础。为了实现我们的目标，我们将使用Krt17CreERT2小鼠来测定老年皮肤中Merkel细胞的生成率和凋亡率。我们还将从老化皮肤中提纯TDPC，并在体外评估其克隆形成能力。最后，我们将移植年轻的成人和老年的TDPC，并直接评估它们在体内再生默克尔细胞和恢复触觉敏感度的能力。这些研究将对理解我们触觉的细胞调节至关重要，触觉是我们感知周围环境能力的基本要素，随着我们年龄的增长，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.