Chemoreceptor Cell Development in the Carotid Body

描述（由申请人提供）：颈动脉体（CB）是一种主要的缺氧化学感受器官，可诱导许多重要器官的反射反应。个体间的低氧反应是可变的，遗传差异可能是一个潜在的机制。例子可以在人类以及近交系小鼠中看到。我们已经表明，在DBA/2 J小鼠中，大CB和强烈的缺氧反应，而在A/J小鼠中，小CB和弱反应。我们的初步数据表明，这些差异在出生后发展。（1）GDNF mRNA在DBA/2 J小鼠CB中的表达高于A/J小鼠CB。(2)GDNF基因表达与DBA/2 J、A/J及其子代小鼠的球细胞（GC）数目指数相关。(3)DBA/2 J小鼠从1日龄到4周龄GC数量增加，而A/J小鼠则没有。(4)在1-2周龄时，DBA/2 J小鼠中GC的增殖比A/J小鼠中更稳健。(4)BK通道的表达和活性在DBA/2 J小鼠中较高，而在A/J小鼠中较低。(5)当用GDNF培养幼年A/J小鼠的CB时，BK通道的mRNA和通道活性变得与DBA/2 J小鼠相似。(6)通过GC中的电压依赖性K通道活性和CB中的细胞内Ca 2+监测，DBA/2 J小鼠的低血糖敏感性高于A/J小鼠。基于这些观察和文献检索，我们假设：（1）GDNF对GC的出生后生存和生长起着关键作用。(2)GDNF促进BK通道的表达，其支持GC的出生后存活和缺氧敏感性。该提议的具体目的是确定：（1）GDNF对于GC的出生后存活和生长的作用;（2）GDNF是否促进BK通道在发育中的GC中的表达;（3）BK通道对于GC的出生后存活的作用;（4）GDNF介导的BK通道表达是否支持出生后发育期间GC的缺氧敏感性。将应用新开发的全CB培养系统以及膜片钳、Ca 2+成像、RT-PCR（使用全CB和单个GC）、形态计量学和免疫组织化学。研究生后CB成熟的遗传基础可能为低氧化学感受和化学传导通路提供一些见解。此外，可以开发用于CB相关疾病的治疗措施，例如婴儿猝死综合征、先天性低通气综合征、Prader-Willi综合征中的呼吸问题、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.