Extrarenal Functions of Polycystin-1

描述(申请人提供)：PKD1编码PC1，一种跨膜受体样蛋白，而PKD2编码PC2，一种钙通道，它们相互作用形成功能性多囊蛋白复合体，在许多组织和细胞类型中广泛表达。PKD1或PKD2基因失活突变可导致常染色体显性遗传性多囊肾病(ADPKD)。对ADPKD的研究已经阐明了多囊蛋白在肾上皮细胞中的功能及其对初级纤毛的相互依赖；然而，它们仅提供了一个有限的窗口，揭示了多囊蛋白/初级纤毛复合体在其他组织中潜在的更广泛的功能，如骨。我们发现PKD1和PKD2以及初级纤毛存在于成骨细胞和骨细胞中，来自PKD1基因缺失的小鼠的原代成骨细胞在体外具有成骨细胞分化能力和向脂肪细胞分化的倾向，并且在小鼠成熟成骨细胞中有条件地缺失PKD1会由于成骨细胞介导的骨形成受损而导致骨量减少，这也与体内骨髓脂肪生成的增加有关。这些发现表明，多囊藻毒素和初生纤毛在骨骼中具有重要的生物学功能。为了进一步研究多囊蛋白的骨骼功能，我们将利用成骨细胞系特异性启动子-CRE小鼠选择性地删除成骨细胞系内不同阶段的PKD1和PKD2，包括成骨前细胞、成熟成骨细胞和骨细胞。为了探索多囊蛋白和初级纤毛在骨中的潜在相互依赖关系，我们将研究骨特异性Kif3a缺失对成骨细胞系中初级纤毛形成的影响。我们提出的假设是，多囊蛋白的丢失导致成骨前细胞、成熟成骨细胞和骨细胞无法维持其分化和存活阶段，导致细胞恢复到增殖、分化较低的状态，并对影响骨骼发育和出生后骨形成的众多环境线索做出异常反应。总之，我们的研究将多囊蛋白/初级纤毛复合体定义为骨骼中一种新的合成代谢途径，并可能为开发合成代谢药物治疗骨质疏松疾病提供新的靶点。此外，更多地了解多囊蛋白在骨骼中的具体功能将有助于澄清它们的整体功能，这些功能将被翻译回肾脏和其他组织。 公共卫生相关性：通过在体内有条件地从成骨细胞谱系中删除PKD1和Kif3a的小鼠遗传学研究，我们发现多囊蛋白和初级纤毛在骨骼发育和出生后骨功能中发挥重要作用。这些发现表明，初级纤毛/多囊蛋白复合体作为感知环境线索的枢纽，并将其转化为多种信号通路，支持成骨细胞的发育和成熟成骨细胞的分化状态，从而对骨量产生净的积极影响；因此，代表了骨生物学的一个新领域，并为设计骨量减少症的合成代谢治疗提供了一个新的分子靶点。此外，更多地了解多囊蛋白和初级纤毛在不同细胞环境中的功能可以转化为对它们在肾脏中的功能的更广泛的理解。

DESCRIPTION (provided by applicant): Pkd1 encodes PC1, a transmembrane receptor-like protein, and Pkd2 encodes PC2, a calcium channel, which interact to form functional polycystin complexes that are widely expressed in many tissues and cell types. Inactivating mutations of PKD1 or PKD2 genes cause Autosomal Dominant Polycystic Kidney Disease (ADPKD). Studies of ADPKD have elucidated the functions of polycystins and their interdependence on primary cilia in renal epithelial cells; however, they have provided only a limited window into the potential broader functions of polycystins/primary cilia complexes in other tissues, such as bone. We have found that Pkd1 and Pkd2, as well as primary cilia are present in osteoblasts and osteocytes, that primary osteoblasts derived from Pkd1 null mice have impaired osteoblast differentiation capacity and a propensity to differentiate in to adipocytes in vitro, and that conditional deletion of Pkd1 in mature osteoblasts of mice results in osteopenia due to impaired osteoblast-mediated bone formation that is also associated with increased bone marrow adipogenesis in vivo. These findings suggest that polycystins and primary cilia have important biological function in bone. To further examine the skeletal functions of polycystins, we will use osteoblast-lineage specific promoter-Cre mice to selectively delete Pkd1 and Pkd2 from different stages within the osteoblastic lineage, including pre-osteoblasts, mature osteoblasts and osteocytes. To explore potential interdependence of polycystin and primary cilia in bone, we will examine the effect of bone-specific deletion of Kif3a to disrupt primary cilia formation in the osteoblastic lineage. We propose the hypothesis that the loss of polycystins results in the inability of pre-osteoblasts, mature osteoblasts, and osteocytes to maintain their stage of differentiation and survival, resulting in cells reverting to a proliferative, less differentiated state and responding abnormally to the multitude of environmental clues affecting skeletal development and bone formation postnatally. Overall, our studies will define the polycystin/primary cilium complex as a new anabolic pathway in bone as well as possibly provide a new target for developing anabolic agents to treat osteoporotic disorders. In addition, a greater knowledge of specific functions of polycystins in bone will help clarify their overall functions that will translate back to the kidney and other tissues. PUBLIC HEALTH RELEVANCE: We have discovered that polycystins and primary cilia play important roles in skeletal development and postnatal bone function through mouse genetic studies that conditionally deleted Pkd1 and Kif3a from the osteoblast lineage in vivo. These findings suggest that the primary cilium/polycystin complex acts as a hub to sense environmental clues and translate them into multiple signaling pathways that sustain osteoblastic development and sustain the differentiated state of mature osteoblast, which lead to a net positive effect on bone mass; and as such, represent a new area of bone biology and an identification of a novel molecular target to design anabolic treatments for osteopenic disorders. In addition, a greater knowledge of polycystins and primary cilia functions in a different cellular context could translate into a broader understanding of their functions in the kidney.