Regulation of Parathyroid Functions By G-Protein Coupled Receptors

甲状旁腺（PTGs）通过调节甲状旁腺功能来控制矿物质、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。据文献记载， 同型细胞外钙敏感受体（CaSR）通过升高血清[Ca 2 +]抑制PTH分泌。 然而，促进PTH分泌的机制在低钙和各种高甲状旁腺激素（HPT） 由于CaSR缺乏的状态尚未被探索。我们的试验数据提出了一个新的假设， GABA和GABAB 1 R调节CaSR的G蛋白信号以促进PTH的自分泌机制 分泌物多学科方法将由两个高度互补的团队在大学进行 匹兹堡大学和加州大学旧金山弗朗西斯科将通过3个具体的 目标。目的1将首先证明在功能性相互作用之间的生理病理学相关性， 通过研究甲状旁腺细胞（PTC）特异性GABAB 1 R和/或CaSR敲除小鼠， 在低钙血症和不同形式的HPT挑战的情况下（即，CaSR缺乏或慢性肾脏 疾病）和从患有原发性和继发性HPT的患者中切除的人PTG。目标2将定义 通过研究PTC特异性Gad 1和Gad 2的作用，探讨Gad 1/2在调节PTG功能中的生物学作用 在小鼠中Ca 2+缺乏和各种HPT状态的条件下进行双敲除，并评估Gad 1/2和 从原发性和继发性HPT患者中切除的人PTG中的GABA表达。目标3将描述 CaSR/GABAB 1 R异聚体改变G-蛋白激活的分子机制， CaSR及其对培养甲状旁腺源性PTH-C1分泌PTH和产生GABA的影响 细胞光学（FRET，TIRF，BiFC）和生物化学技术将用于测试PTH释放的理论， 和GABA的合成是通过涉及GABAB 1 R对CaSR的变构作用的机制来控制的 通过受体异聚化的信号传导，抑制Ca 2+介导的Gq/11和Gi信号转导，并促进 甲状旁腺激素分泌。该项目的成功完成将有助于开发新的治疗方案，以管理PTH低， 或分泌过多和相关的内分泌和骨骼疾病，并防止GABAB 1 R的不良副作用 用于神经系统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.