Chemoreceptor Cell Development in the Carotid Body

描述（由申请人提供）：颈动脉体（CB）是一个主要的缺氧化学感觉器官，可诱导许多重要器官的反射反应。个体之间的缺氧反应是不同的，遗传差异可能是一个潜在的机制。在人类和近亲繁殖的老鼠身上都可以看到这样的例子。我们已经证明DBA/2J小鼠有大的CB和强的缺氧反应，而a /J小鼠有小的CB和弱的缺氧反应。我们的初步数据显示，这些CBs差异是在出生后形成的。我们的其他重要发现是：(1)DBA/2J小鼠的CB中GDNF mRNA的表达高于A/J小鼠的CB。(2) GDNF基因在DBA/2J、A/J及子代小鼠中表达与glomus cell （GC）数量指数相关。(3) DBA/2J小鼠1 ~ 4周龄GCs数量增加，而A/J小鼠无此现象。(4) 1 ~ 2周龄时，GCs在DBA/2J小鼠体内的增殖比A/J小鼠更强。(4) GCs中BK通道的表达和活性在DBA/2J小鼠中较高，在A/J小鼠中较低。(5) GDNF培养幼龄A/J小鼠CBs后，BK通道mRNA和通道活性与DBA/2J小鼠相似。(6)通过GCs中电压依赖性K通道活性和CBs中细胞内Ca2+监测的缺氧敏感性，DBA/2J小鼠比A/J小鼠更高。基于这些观察和文献检索，我们假设：(1)GDNF在GCs的出生后存活和生长中起关键作用。(2) GDNF促进BK通道的表达，支持GCs的产后存活和缺氧敏感性。本提案的具体目的是确定：(1)GDNF在GCs出生后存活和生长中的作用；(2) GDNF是否促进了GCs中BK通道的表达；(3) BK通道在GCs出生后存活中的作用；(4) gdnf介导的BK通道表达是否支持出生后发育过程中GCs的缺氧敏感性。将采用新开发的全CB培养系统，包括膜片钳，Ca2+成像，RT-PCR（使用全CB和单GC），形态测定法和免疫组织化学。研究出生后脑脊液成熟的遗传基础可能为缺氧化学接受和化学转导途径提供一些见解。此外，可能会开发出治疗措施来治疗与cb相关的疾病，如婴儿猝死综合征、先天性低通气综合征、普瑞德-威利综合征中的通气问题、慢性心力衰竭和原发性高血压。

DESCRIPTION (provided by applicant): The carotid body (CB), a major hypoxic chemosensory organ, induces reflex responses in many vital organs. The hypoxic responses among individuals are variable, and genetic differences may be an underlying mechanism. Examples can be seen in humans as well as inbred strains of mice. We have shown that a large CB and robust hypoxic responses in DBA/2J mice, and a small CB and weak responses in A/J mice. Our preliminary data show that these differences in the CBs develop after birth. Our other important findings are: (1) The expression of GDNF mRNA in the CB of DBA/2J mice was higher than in the CB of A/J mice. (2) GDNF gene expression correlated to glomus cell (GC) number index in the DBA/2J, A/J and offspring mice. (3) The number of GCs increased from 1-day to 4-week-old in DBA/2J mice, but not in A/J mice. (4) Proliferation of GCs was more robust in DBA/2J than in A/J mice at 1-2 weeks of age. (4) Expression and activity of BK channels in GCs were high in DBA/2J mice and low in A/J mice. (5) When CBs of young A/J mice were cultured with GDNF, BK channel mRNA and channel activity became similar to that of DBA/2J mice. (6) Hypoxic sensitivity, monitored by voltage-dependent K channel activity in GCs and intracellular Ca2+ in CBs, was higher in DBA/2J than in A/J mice. Based on these observations and literature search, we have hypothesized: (1) GDNF plays a critical role for postnatal survival and growth of GCs. (2) GDNF promotes the expression of BK channels, which support postnatal survival and hypoxic sensitivity of GCs. Specific aims of this proposal are to determine: (1) the role of GDNF for postnatal survival and growth of GCs; (2) if GDNF promotes the expression of BK channels in developing GCs; (3) the role of BK channels for postnatal survival of GCs; (4) if the GDNF-mediated BK channel expression supports hypoxic sensitivity of GCs during postnatal development. A newly developed whole CB culture system together with patch clamp, Ca2+ imaging, RT-PCR (using whole CB and single GC), morphometry, and immunohistochemistry will be applied. Studying genetic bases of postnatal maturation of the CB may provide some insights into hypoxic chemoreception and chemotransduction pathways. Further, therapeutic measures may be developed for CB-related diseases such as sudden infant death syndrome, congenital hypoventilation syndrome, ventilatory problems in Prader-Willi syndrome, chronic heart failure, and primary hypertension.