Sakamoto Akio, Chen Min, Kobayashi Tatsuya, Kronenberg Henry M, Weinstein Lee S
Metabolic Diseases Branch, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
J Bone Miner Res. 2005 Apr;20(4):663-71. doi: 10.1359/JBMR.041210. Epub 2004 Dec 6.
G(s)alpha is a ubiquitously expressed G protein alpha-subunit that couples receptors to adenylyl cyclase. Mice with chondrocyte-specific ablation of the G(s)alpha gene had severe epiphyseal and growth plate abnormalities and ectopic cartilage formation within the metaphyseal region of the tibia. These results show that G(s)alpha negatively regulates chondrocyte differentiation and is the critical signaling mediator of the PTH/PTH-rP receptor in growth plate chondrocytes.
G(s)alpha is a ubiquitously expressed G protein alpha-subunit that mediates signaling through G protein-coupled receptors to activate the cAMP/protein kinase A signaling pathway. Although studies suggest an important role for G(s)alpha in regulating growth plate development, direct in vivo results examining this role are lacking.
The G(s)alpha gene was ablated in murine cartilage by mating mice with loxP sites surrounding the G(s)alpha promoter and first exon with collagen 2a1 promoter-Cre recombinase transgenic mice. Skeletal tissues were studied by gross and microscopic pathology, and gene expression was determined by in situ hybridization.
Mice with complete chondrocyte-specific G(s)alpha deficiency (homozygotes) died within minutes after birth and had severe epiphyseal and growth plate defects with shortening of the proliferative zone and accelerated hypertrophic differentiation of growth plate chondrocytes, a phenotype similar to that of PTH/PTH-related peptide (PTHrP) receptor knockout mice. Indian hedgehog and PTH/PTHrP receptor expression in prehypertrophic chondrocytes was unaffected in mutant mice. PTHrP expression in periarticular cartilage was increased in the mutant mice, probably because of the closer proximity of Ihh-secreting chondrocytes to the periarticular zone. In addition, these mice developed ectopic cartilage at the anterior side of the metaphyseal region in the tibia. Mice with partial G(s)alpha deficiency (heterozygotes) exhibited no phenotype. These results show that G(s)alpha negatively regulates chondrocyte differentiation and is the critical signaling mediator of the PTH/PTHrP receptor in epiphyseal and growth plate chondrocytes.
G(s)α是一种广泛表达的G蛋白α亚基，它将受体与腺苷酸环化酶偶联。软骨细胞特异性敲除G(s)α基因的小鼠出现严重的骨骺和生长板异常，以及胫骨干骺端区域的异位软骨形成。这些结果表明，G(s)α负向调节软骨细胞分化，并且是生长板软骨细胞中甲状旁腺激素/甲状旁腺激素相关肽（PTH/PTH-rP）受体的关键信号转导介质。
G(s)α是一种广泛表达的G蛋白α亚基，它通过G蛋白偶联受体介导信号传导，以激活环磷酸腺苷/蛋白激酶A信号通路。尽管研究表明G(s)α在调节生长板发育中起重要作用，但缺乏直接研究这一作用的体内实验结果。
通过将在G(s)α启动子和第一个外显子周围带有loxP位点的小鼠与胶原2a1启动子-Cre重组酶转基因小鼠交配，在小鼠软骨中敲除G(s)α基因。通过大体和显微镜病理学研究骨骼组织，并通过原位杂交确定基因表达。
完全缺乏软骨细胞特异性G(s)α的小鼠（纯合子）在出生后几分钟内死亡，具有严重的骨骺和生长板缺陷，增殖区缩短，生长板软骨细胞肥大分化加速，这一表型与甲状旁腺激素/甲状旁腺激素相关肽（PTHrP）受体敲除小鼠相似。在突变小鼠中，前肥大软骨细胞中印度刺猬蛋白（Ihh）和PTH/PTHrP受体的表达未受影响。突变小鼠关节周围软骨中的PTHrP表达增加，可能是因为分泌Ihh的软骨细胞更靠近关节周围区域。此外，这些小鼠在胫骨干骺端区域前侧出现异位软骨。部分缺乏G(s)α的小鼠（杂合子）未表现出表型。这些结果表明，G(s)α负向调节软骨细胞分化，并且是骨骺和生长板软骨细胞中PTH/PTHrP受体的关键信号转导介质。
