How do Olfactory Reserve Stem Cells Differentiate into Neuronal Cells? – A Combined in vitro/in vivo Approach

嗅觉相关的嗅觉功能障碍影响高达70%的80岁以上的人群。嗅上皮具有独特的再生潜力，这是由于两种干细胞：（1）球状基底细胞，其是再生的第一水平，并且经历恒定的神经发生以更新嗅上皮;和（2）水平基底细胞，其是休眠的储备干细胞，并且仅在嗅上皮严重损伤时激活。 在老年嗅觉症中，嗅觉感觉神经元和球状基底细胞的丧失导致神经源性衰竭。然而，休眠的水平基底细胞群未能激活。因此，有意激活水平基底细胞原位是一个有吸引力的治疗目标，在年龄相关的嗅觉功能障碍。 先前的研究表明，水平基底细胞可以通过下调转录因子p63来激活。这可以通过外源性给予视黄酸来实现。然而，即使成功激活后，激活的HBC也可以采取四种不同的命运。其中，只有一个导致神经元分化为球状基底细胞和嗅神经元细胞。因此，这种激活水平基底细胞的治疗方法也需要将干细胞储备推向神经元谱系。神经元随后分化为球状基底细胞和嗅神经元细胞的潜在机制在很大程度上仍然是难以捉摸的。这应该在以下结合体外/体内方法中阐明：首先，将使用免疫组织化学在培养的鼠水平基底细胞中评估不同因素对分化的影响。在第二步中，将这种神经分化的嗅觉组织移植到鼠宿主嗅觉上皮中。结果也将使用免疫组织化学进行评估。目的是建立最佳的培养条件，在体外再生嗅上皮，然后可以移植到受损的宿主嗅上皮。

Age-related olfactory dysfunction affects up to 70% of the population over the age of 80 years. The olfactory epithelium has a distinctive potential to regenerate due to two kinds of stem cells: (1) Globose basal cells which are the first level of regeneration and undergo constant neurogenesis to renew the olfactory epithelium, and (2) horizontal basal cells which are dormant reserve stem cells and only activated in severe damage of the olfactory epithelium. In presbyosmia, the loss of olfactory sensory neurons and globose basal cells leads to a neurogenic exhaustion. However, the population of dormant horizontal basal cells fails to activate. Hence, the deliberate activation of horizontal basal cells in situ is an attractive therapeutic goal in age-related olfactory dysfunction. Previous studies have showed that horizontal basal cells can be activated by downregulation of the transcription factor p63. This can be achieved by the exogenous administration of retinoic acid. However, even after successful activation, the activated HBCs can adopt four different fates. Of them, only one leads to neuronal differentiation into globose basal cells and olfactory neuronal cells. Thus, this therapeutic approach to activate horizontal basal cells also necessitates driving the stem cell reserve toward a neuronal lineage. The underlying mechanisms of the subsequent neuronal differentiation into globose basal cells and olfactory neuronal cells are still largely elusive. This should be elucidated in the following combined in vitro/in vivo approach: First, the effect of different factors on the differentiation will be assessed in cultured murine horizontal basal cells using immunohistochemistry. In a second step this neurogenically differentiated olfactory tissue will be transplanted into a murine host olfactory epithelium. The outcome will also be assessed using immunohistochemistry, too. The aim is to establish optimal culture conditions to regenerate olfactory epithelium in vitro which then can be transplanted into a damaged host olfactory epithelium.