Regulation of Parathyroid Functions By G-Protein Coupled Receptors

甲状旁腺(PTG)通过调节甲状旁腺调节矿物质、激素和骨骼的动态平衡 激素(PTH)分泌对血清[Ca~(2+)]变化的反应有充分的证据表明，激活 同源胞外钙敏感受体(CaSR)通过升高血清[Ca~(2+)]来抑制PTH的分泌。 然而，在低钙和各种甲状旁腺功能亢进症(HPT)时促进PTH分泌的机制 由于CaSR缺乏而导致的状态还没有被探索。我们的先导数据提出了一种新的小说假设 GABA和GABAB1R调节CASR G蛋白信号促进甲状旁腺激素的自分泌机制 分泌物。多学科方法将由两个互补性很强的团队在牛津大学实施 匹兹堡大学和加州大学旧金山分校将通过3个具体的项目来检验这一假设 目标。目标1将首先证明生理病理相关性之间的功能相互作用 研究甲状旁腺细胞(PTC)特异性GABAB1R和/或CaSR基因敲除小鼠在PTG中的CaSR和GABAB1R 在低钙血症和不同形式的HPT挑战(即CaSR缺乏或慢性肾脏)的情况下 疾病)和从原发和继发性HPT患者身上摘除的人类PTG。目标2将定义 通过研究PTC特异性Gad1和Gad2的作用研究Gad1/2在调节PTG功能中的生物学作用 小鼠钙缺乏和不同HPT状态下的双基因敲除及Gad1/2和Gad1/2的检测 原发性和继发性HPT患者PTG中GABA的表达。目标3将描述 CaSR/GABAB1R异构体改变G蛋白激活效应的分子机制 钙调素受体及其对甲状旁腺来源的甲状旁腺细胞分泌和GABA产生的影响 细胞。将使用光学(FRET、TIRF、BIFC)和生化技术来测试PTH释放的理论 和GABA的合成是通过GAB1R在CaSR上的变构作用来调控的 通过受体异构化抑制钙介导的Gq/11和Gi信号转导并促进 甲状旁腺素分泌。该项目的顺利完成将有助于开发新的治疗甲状旁腺激素低水平的方案。 或高分泌及相关的内分泌和骨骼疾病，预防GAB1R的不良副作用 开给神经疾病患者的激动剂和拮抗剂。

Parathyroid glands (PTGs) control mineral, hormonal, and skeletal homeostasis by adjusting parathyroid hormone (PTH) secretion in response to changes in serum [Ca2+]. It is well documented that activation of homomeric extracellular calcium-sensing receptor (CaSR) by raising serum [Ca2+] suppresses PTH secretion. However, the mechanisms promoting PTH secretion at hypocalcemic and various hyperparathyroidism (HPT) states due to CaSR-deficiency have not been explored. Our pilot data raise a novel hypothesis of a novel autocrine mechanism by which GABA and GABAB1R regulate G protein signaling of the CaSR to promote PTH secretion. Multi-disciplinary approaches to be performed by two highly complementary teams at University of Pittsburgh and University of California San Francisco will be employed to test this hypothesis through 3 specific aims. Aim 1 will first demonstrate the physiopathological relevance of the functional interaction between the CaSR and GABAB1R in PTGs by studying parathyroid cell (PTC)-specific GABAB1R and/or CaSR knockout mice in the contexts of hypocalcemia and different forms of HPT challenges (i.e., CaSR-deficiency or chronical kidney disease) in vivo and human PTGs excised from patients with primary and secondary HPT. Aim 2 will define the biological actions of Gad1/2 in regulating PTG functions by studying the effects of PTC-specific Gad1 and Gad2 double knockout in conditions of Ca2+ deficiency and various HPT states in mice and assessing Gad1/2 and GABA expression in human PTGs excised from patients with primary and secondary HPT. Aim 3 will delineate molecular mechanisms by which the CaSR/GABAB1R heteromers alter efficacy of G-protein activation of the CaSR and its consequence for PTH secretion and GABA production in cultured parathyroid-derived PTH-C1 cells. Optical (FRET, TIRF, BiFC) and biochemical techniques will be used to test the theory that PTH release and GABA synthesis are controlled through mechanisms involving the allosteric action of GABAB1R on CaSR signaling via receptor heteromerization that inhibits Ca2+-mediated Gq/11 and Gi signal transduction and promote PTH secretion. Successful completion of this project will help to develop new regimens to manage PTH hypo- or hyper-secretion and related endocrine and skeletal diseases and prevent unwanted side-effects of GABAB1R agonists and antagonists prescribed to patients with neurological disorders.