Chemoreceptor Cell Development in the Carotid Body

描述(申请人提供)：颈动脉小体(CB)，一个主要的缺氧性化学感受器，在许多重要器官中诱导反射反应。个体之间的低氧反应是不同的，遗传差异可能是一个潜在的机制。在人类和近亲繁殖的小鼠身上都可以看到这样的例子。我们发现在DBA/2J小鼠中有一个大的CB和强烈的低氧反应，在A/J小鼠中有一个小的CB和弱的反应。我们的初步数据显示，CBS的这些差异是在出生后发展起来的。我们的另一个重要发现是：(1)DBA/2J小鼠脐带血中GDNF mRNA的表达高于A/J小鼠脐带血。(2)DBA/2J、A/J及子代小鼠GDNF基因表达与球体细胞(GC)数量指数相关。(3)DBA/2J小鼠GCs数量从1日龄至4周龄逐渐增多，而A/J小鼠则无明显变化。(4)1-2周龄DBA/2J小鼠的GCs增殖能力强于A/J小鼠。(4)BK通道在GCs中的表达和活性在DBA/2J小鼠中高表达，在A/J小鼠中低表达。(5)幼龄A/J小鼠CBS与GDNF共同培养后，BK通道mRNA和通道活性与DBA/2J小鼠相似。(6)DBA/2J小鼠的低氧敏感性高于A/J小鼠，由GCs的电压依赖性K通道活性和CBS的细胞内钙离子活动监测。基于这些观察和文献检索，我们假设：(1)GDNF对GCs的出生后存活和生长起关键作用。(2)GDNF促进BK通道的表达，BK通道支持GCs的出生后存活和低氧敏感性。本研究的具体目的是确定：(1)GDNF在GCs出生后存活和生长中的作用；(2)GDNF是否促进发育中的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GCs在出生后发育过程中的缺氧敏感性。新开发的全脐血培养系统将与膜片钳、钙成像、RT-PCR(使用全脐血和单个GC)、形态计量学和免疫组织化学一起应用。研究脐带血出生后成熟的遗传学基础可能会为了解低氧化学感受和化学转导途径提供一些启示。此外，还可以开发治疗与CB相关的疾病的措施，如婴儿猝死综合征、先天性低通气综合征、Prader-Willi综合征的呼吸问题、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.