Extrarenal Functions of Polycystin-1

描述（由申请人提供）：Pkd 1编码PC 1（一种跨膜受体样蛋白），Pkd 2编码PC 2（一种钙通道），它们相互作用形成功能性多囊蛋白复合物，在许多组织和细胞类型中广泛表达。PKD 1或PKD 2基因的失活突变导致常染色体显性多囊肾病（ADPKD）。ADPKD的研究已经阐明了多囊蛋白的功能及其对肾上皮细胞中初级纤毛的相互依赖性;然而，它们仅提供了一个有限的窗口，以了解多囊蛋白/初级纤毛复合物在其他组织（如骨）中的潜在更广泛功能。我们已经发现，Pkd 1和Pkd 2以及初级纤毛存在于成骨细胞和骨细胞中，来自Pkd 1缺失小鼠的初级成骨细胞具有受损的成骨细胞分化能力和体外分化为脂肪细胞的倾向，以及小鼠成熟成骨细胞中Pkd 1的条件性缺失导致由于成骨细胞受损而引起的骨质减少，介导的骨形成，其也与体内骨髓脂肪生成增加相关。这些结果表明，多囊蛋白和初级纤毛在骨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，我们将使用成骨细胞谱系特异性启动子-Cre小鼠选择性地删除成骨细胞谱系内不同阶段的Pkd 1和Pkd 2，包括前成骨细胞、成熟成骨细胞和骨细胞。为了探索骨中多囊蛋白和初级纤毛的潜在相互依赖性，我们将研究骨特异性Kif 3a缺失对破坏成骨细胞谱系中初级纤毛形成的影响。我们提出的假设是，多囊蛋白的损失导致前成骨细胞，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，分化程度较低的状态，并对出生后影响骨骼发育和骨形成的众多环境线索做出异常反应。总体而言，我们的研究将多囊蛋白/初级纤毛复合物定义为骨中的新合成代谢途径，并可能为开发合成代谢药物以治疗骨质疏松症提供新靶点。此外，更多地了解多囊蛋白在骨骼中的特定功能将有助于阐明它们的整体功能，这些功能将转化回肾脏和其他组织。 公共卫生相关性：我们已经发现，多囊蛋白和初级纤毛在骨骼发育和出生后的骨功能中发挥重要作用，通过小鼠遗传学研究，有条件地删除体内成骨细胞谱系中的Pkd 1和Kif 3a。这些发现表明，初级纤毛/多囊蛋白复合体作为一个枢纽，感知环境线索，并将其转化为多个信号通路，维持成骨细胞的发育和维持成熟成骨细胞的分化状态，这导致对骨量的净正效应;因此，代表了骨生物学的一个新领域，并确定了一个新的分子靶点，以设计骨质疏松症的合成代谢治疗方法。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，可以更广泛地理解它们在肾脏中的功能。

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.