CIZ regulates anabolic action of PTH on bone

我们分析了BMP抑制因子CIZ在甲状旁腺激素信号转导中的作用。CapPR小鼠在成骨细胞和成牙本质细胞中表达具有结构性活性的PTH/PTHrP受体(CapPR)，并表现出骨体积的增加。CIZKO小鼠也显示出骨量增加。在我们的初步实验中，我们将CapPR小鼠与CIZKO小鼠杂交，并且CapPR-CIZKO小鼠表现出进一步的骨体积增加。我们在扩大CapPR-CIZKO小鼠数量方面遇到了困难，因为CapPR小鼠身体虚弱，而且由于CIZKO小鼠存在精子发生缺陷。在细胞培养体系中，我们使用了成骨样细胞系MC-3T3E1细胞。为了分析cAMP反应元件(cAMP Response Element，CRE)的转录活性，我们用pCre-Luc载体转染细胞，并进行荧光素酶活性检测。当CIZ过表达时，CapPR诱导的Cre-活性增加没有变化。据报道，CIZ抑制BMP信号，PTH增强BMP信号。因此，我们推测CIZ不是直接抑制PTH诱导的骨量增加，而是通过抑制BMP信号途径影响PTH诱导的骨量增加。

We analyzed the involvement of CIZ, a BMP-inhibitory factor, in PTH-signaling. The caPPR mice express constitutively active PTH/PTHrP receptor (caPPR) in osteoblasts and in odontoblasts, and exhibit increased bone volume. The CIZKO mice also show increased bone volume. We crossed caPPR mice with CIZKO and caPPR-CIZKO mice exhibited further increased bone volume in our preliminary experiments.We had difficulties in expanding the number of caPPR-CIZKO mice, because caPPR mice are weak and because CIZKO mice have defect in spermatogenesis as reported. However, we finally got 6-10 mice in each group of 4 genotypes x 2 sex.In cell culture system, we used MC-3T3E1 cells, a osteoblast-like cell line. In order to analyze the transcriptional activity of CRE (cAMP response element), we transfected cellswith pCre-Luc vector and performed luciferase assays. When CIZ was overexpressed, caPPR-induced increase of CRE-activity did not show changes. CIZ inhibits BMP signal and PTH are reported to enhance BMP signals. Therefore we speculate that CIZ does not directly inhibit PTH-induced bone increase but that CIZ affects PTH-induced bone increase by way of inhibiting BMP signaling.