Abstract：
Intracellular phosphoinositide 3-kinase (PI3K) signaling is activated by multiple bone-active receptors. Genetic mutations activating PI3K signaling are associated with clinical syndromes of tissue overgrowth in multiple organs, often including the skeleton. Bone formation is increased by removing the PI3K inhibitor PTEN, but the effect of direct PI3K in the osteoblast lineage has not been reported. We introduced a known gain-of-function mutation in Pik3ca, the gene encoding the p110α catalytic subunit of PI3K, in osteocytes and late osteoblasts using the dentin matrix protein-1 Cre (Dmp1Cre) mouse and assessed the skeletal phenotype. Femur shape was grossly normal, but cortical thickness was significantly greater in both male and female Dmp1Cre.Pik3caH1047R mice, leading to almost doubled bone strength at 12 weeks of age. Both sexes had smaller marrow areas from 6 weeks of age. Female mice also exhibited greater cross sectional area, which continued to increase until 24 weeks of age, resulting in a further increase in bone strength. While both male and female mice had increased endocortical mineralizing surface, only female mice had increased periosteal mineralizing surface. The bone formed in the Dmp1Cre.Pik3caH1047R mice showed no increase in intracortical remodeling nor any defect in cortical bone consolidation. In contrast, on both endocortical and periosteal surfaces, there was a greater extent of lamellar bone formation with highly organized osteocyte networks extending along the entire surface at a greater thickness than in control mice. In conclusion, direct activation of PI3Kα in cells targeted by Dmp1Cre leads to high cortical bone mass and strength with abundant lamellar cortical bone in female and male mice with no increase in intracortical remodeling. This differs from the effect of PTEN deletion in the same cells, suggesting that activating PI3Kα in osteoblasts and osteocytes may be a more suitable target to promote formation of lamellar bone.
Patients with genetic activation of an enzyme called phosphoinositide-3 kinase (PI3K) have tissue overgrowth syndromes, where parts of the body become enlarged, sometimes including the skeleton. There are two types of mutations that cause these problems: one that directly causes the PI3K enzyme to be more active, or one that removes the normal brake on PI3K signaling (called PTEN). We studied the effect of directly activating PI3K enzyme specifically in osteoblasts (the cells that form bone) and osteocytes (osteoblasts that make a network inside the bone tissue itself). We found mice with these mutations formed normally shaped bones that were very strong because the outer shell was thicker than usual. In both male and female mice, it became thicker on the inside of the shell, but in female mice it also became thicker on the outside, making the bones even stronger over time. The new bone was well-organized bone, which likely helped make the increase in bone strength so profound. This is very different to what has previously been shown in mice with the other type of mutation in their bone forming cells; those mice had a shell that contained many large holes (pores). This indicates that directly stimulating PI3K enzyme is more beneficial for bone than removing the PTEN brake.
Patients with genetic activation of an enzyme called phosphoinositide-3 kinase (PI3K) have tissue overgrowth syndromes, where parts of the body become enlarged, sometimes including the skeleton. There are two types of mutations that cause these problems: one that directly causes the PI3K enzyme to be more active, or one that removes the normal brake on PI3K signaling (called PTEN). We studied the effect of directly activating PI3K enzyme specifically in osteoblasts (the cells that form bone) and osteocytes (osteoblasts that make a network inside the bone tissue itself). We found mice with these mutations formed normally shaped bones that were very strong because the outer shell was thicker than usual. In both male and female mice, it became thicker on the inside of the shell, but in female mice it also became thicker on the outside, making the bones even stronger over time. The new bone was well-organized bone, which likely helped make the increase in bone strength so profound. This is very different to what has previously been shown in mice with the other type of mutation in their bone forming cells; those mice had a shell that contained many large holes (pores). This indicates that directly stimulating PI3K enzyme is more beneficial for bone than removing the PTEN brake.
摘要：
细胞内磷酸肌醇3-激酶(PI3K)信号由多种骨活性受体激活。激活PI3K信号的基因突变与多器官组织过度生长的临床综合征有关，通常包括骨架。通过去除PI3K抑制剂PTEN增加骨形成，但直接PI3K在成骨细胞谱系中的感化还没有报导。我们在Pik3ca中引入了一个已知的功能增益突变，编码PI3K的p110α催化亚基的基因，使用牙本质基质蛋白-1Cre（Dmp1Cre）小鼠在骨细胞和晚期成骨细胞中进行骨骼表型评估。股骨形状非常正常，但男性和女性Dmp1Cre的皮质厚度明显更大。Pik3caH1047R小鼠,导致12周龄时的骨强度几乎翻了一番。从6周龄开始，两种性别的骨髓面积都较小。雌性小鼠还表现出更大的横截面积，一直增加到24周龄，导致骨强度进一步增加。虽然雄性和雌性小鼠的皮质内矿化表面都增加，只有雌性小鼠骨膜矿化表面增加。骨在Dmp1Cre中形成。Pik3caH1047R小鼠显示皮质内重塑没有增加，皮质骨巩固也没有任何缺陷。相比之下,在皮质内和骨膜表面，与对照小鼠相比，板层骨形成的程度更高，骨细胞网络高度组织化，沿着整个表面延伸的厚度更大。总之,在Dmp1Cre靶向的细胞中，PI3Kα的直接激活导致雌性和雄性小鼠的高皮质骨量和强度以及丰富的层状皮质骨，而皮质内重塑没有增加。这与相同细胞中PTEN缺失的效果不同，提示激活成骨细胞和骨细胞中的PI3Kα可能是更合适的促进板层骨形成的靶标。
患有一种叫做磷酸肌醇-3激酶（PI3K）的基因激活的患者有组织过度生长综合征，身体的各个部分变得扩大，有时包括骷髅。有两种类型的突变导致这些问题：一种直接导致PI3K酶更活跃，或移除PI3K信号上的正常制动(称为PTEN)。我们研究了直接激活PI3K酶在成骨细胞（形成骨的细胞）和骨细胞（在骨组织本身内部形成网络的成骨细胞）中的作用。我们发现具有这些突变的小鼠形成了非常坚固的正常形状的骨骼，因为外壳比平常厚。在雄性和雌性小鼠中，它在外壳的内部变得更厚，但是在雌性老鼠中，它的外部也变得更厚，让骨头随着时间的推移变得更强壮。新的骨头是组织良好的骨头，这可能有助于使骨骼强度的增加如此深远。这与先前在骨骼形成细胞中具有其他类型突变的小鼠中所显示的非常不同；那些小鼠的外壳包含许多大孔（孔）。这表明直接刺激PI3K酶比去除PTEN制动对骨更有益。
患有一种叫做磷酸肌醇-3激酶（PI3K）的基因激活的患者有组织过度生长综合征，身体的各个部分变得扩大，有时包括骷髅。有两种类型的突变导致这些问题：一种直接导致PI3K酶更活跃，或移除PI3K信号上的正常制动(称为PTEN)。我们研究了直接激活PI3K酶在成骨细胞（形成骨的细胞）和骨细胞（在骨组织本身内部形成网络的成骨细胞）中的作用。我们发现具有这些突变的小鼠形成了非常坚固的正常形状的骨骼，因为外壳比平常厚。在雄性和雌性小鼠中，它在外壳的内部变得更厚，但是在雌性老鼠中，它的外部也变得更厚，让骨头随着时间的推移变得更强壮。新的骨头是组织良好的骨头，这可能有助于使骨骼强度的增加如此深远。这与先前在骨骼形成细胞中具有其他类型突变的小鼠中所显示的非常不同；那些小鼠的外壳包含许多大孔（孔）。这表明直接刺激PI3K酶比去除PTEN制动对骨更有益。
