Molecular and Genetic Mechanisms of Abnormal Cold Sensing – Implication for Thermoregulation, Obesity and Pain Research

皮肤中的冷伤害感受器和热感受器致力于检测冷和有害的冷温度。它们的功能与体温稳态密切相关。虽然冷敏感皮肤神经末梢的分子特化已经被认识到，与冷传感器瞬时受体电位M8和A1通道，我们仍然对更复杂的生理功能知之甚少，例如遗传和性别特异性机制，导致冷hypo和超敏反应。使用一个大的筛选研究的基础上定制设计的热梯度测定，我们确定了，在25个近交系小鼠品系，冷低和冷过敏株和品系有和没有性别差异的舒适温度选择。对避冷特性的品系和性别差异的遗传作图分析使我们找到了在参与体温调节和代谢的四个不同系统中表达的候选基因：初级传入神经、下丘脑、肌肉和棕色脂肪组织。后者，由于其在体内能量平衡调节中的关键作用，正在成为肥胖研究的兴趣越来越大。除了在舒适温度选择和避冷方面的基本差异外，哺乳动物还通过各种调节手段对环境寒冷做出反应，从而延长耐寒性，改善舒适性并降低能量消耗。到目前为止，这些冷适应机制的分子本质还没有被揭示，但我们的初步数据表明，TRPC 5受体可能是一个有前途的候选人介导冷适应，导致，在TRPC 5的存在下，以改善冷舒适或，没有TRPC 5，以增加避冷通过初级传入冷敏感性的调整。TRPC 5在三叉神经感觉系统中也有作用，其中我们的电生理数据暗示了TRPM 8和TRPA 1在牙齿中作为冷换能器的功能。转基因小鼠线，缺乏组合的三个冷传感器连同最近开发的技术，使我们能够记录传播的动作电位从牙髓伤害性感受器通过小鼠牙槽神经颌骨准备将为我们提供洞察冷转导如何在牙齿中工作。此外，两个新的小鼠线与荧光TRPA1和TRPC5结合逆行标记从磨牙将使我们能够解决的重叠的三个冷传感器在正常和发炎的神经支配磨牙和三叉神经节。当寒冷变得疼痛时，除了保持核心体温外，生理功能是保护组织免受损伤和冻伤，但在神经病变或神经损伤中，正常的寒冷被认为是烧灼痛。使用基于冷异常性疼痛的药理学模型的遗传作图方法，我们将Adra2b受体中的SNP鉴定为控制冷异常性疼痛的严重程度的潜在遗传因子，这将被验证。

Cold nociceptors and thermoreceptors in the skin are dedicated to detect cold and noxious cold temperatures. Their function is tightly connected to body temperature homeostasis. Although the molecular specialization of the cold sensitive cutaneous nerve endings has been recognized, with the cold transducer Transient Receptor Potential M8 and A1 channels, we still have little knowledge about more complex physiological functions, for example the genetic and sex-specific mechanisms that lead to cold hypo- and hypersensitivity. Using a large screening study based on a custom-designed thermal gradient assay, we identified, among 25 inbred mouse strains, cold hypo- and cold hypersensitive strains and strains with and without sex difference in comfort temperature selection. Genetic mapping analysis of the strain and sex differences in the cold avoidance trait led us to candidate genes expressed in four different systems that are involved in thermoregulation and metabolism: primary afferents, hypothalamus, muscle and brown adipose tissue. The latter one, due to its critical role in body energy balance regulation, is becoming of increasing interest in obesity research. In addition to basic differences in comfort temperature selection and cold avoidance, mammals react to environmental cold by various means of adjustment leading to extended cold tolerance, improved comfort and decreased energy expenditure. So far, the molecular nature of these cold acclimation mechanism has not been revealed, but our preliminary data show that the TRPC5 receptor could be a promising candidate to mediate cold acclimation that leads, in presence of TRPC5, to improved cold comfort or, without TRPC5, to increased cold avoidance via adjustments of primary afferent cold sensitivity. TRPC5 has also a role in the trigeminal sensory system where our electrophysiological data imply a function as cold transducer in teeth together with TRPM8 and TRPA1. Transgenic mouse lines that lack combinations of the three cold transducers together with a recently developed technique that allows us to record propagated action potentials from tooth pulp nociceptors via mouse alveolar nerve-jaw preparations will provide us insight into how cold transduction works in teeth. Additionally, two new mouse lines with fluorescent TRPA1 and TRPC5 in combination with retrograde labeling from molar teeth will allow us to resolve the overlap of the three cold transducers in normal and inflamed nerves innervating molar teeth and in the trigeminal ganglia. When cold becomes painful, apart from core body temperature preservation, the physiological function is to protect from tissue damage and freeze injury, but in neuropathy or nerve injury, normal cold is perceived as burning pain. Using a genetic mapping approach based on a pharmacological model of cold allodynia, we identified a SNP in the Adra2b receptor as potential heritable factor that controls the severity of cold allodynia which will be validated.