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Abstract
PRIP (phospholipase C-related, but catalytically inactive protein) is a novel protein isolated in this laboratory. PRIP-deficient mice showed increased serum gonadotropins, but decreased gonadal steroid hormones. This imbalance was similar to that for the cause of bone disease, such as osteoporosis. In the present study, therefore, we analyzed mutant mice with special reference to the bone property. We first performed three-dimensional analysis of the femur of female mice. The bone mineral density and trabecular bone volume were higher in mutant mice. We further performed histomorphometrical assay of bone formation parameters: bone formation rate, mineral apposition rate, osteoid thickness, and osteoblast number were up-regulated in the mutant, indicating that increased bone mass is caused by the enhancement of bone formation ability. We then cultured primary cells isolated from calvaria prepared from both genotypes. In mutant mice, osteoblast differentiation, as assessed by alkaline phosphatase activity and the expression of osteoblast differentiation marker genes, was enhanced. Moreover, we analyzed the phosphorylation of Smad1/5/8 in response to bone morphogenetic protein, with longer phosphorylation in the mutant. These results indicate that PRIP is implicated in the negative regulation of bone formation.
Highlights
Phospholipase C-related, but catalytically inactive protein (PRIP)4 was first identified as a novel D-myo-inositol-1,4,5-trisphosphate-binding protein and tentatively named p130 based on molecular size [1]
Bone mineral density at the metaphysis of femurs isolated from each genotype of females at the ages of 6 and 12 months is shown in Fig. 1, A–C; the parameters of total bone and trabecular bone were higher in KO mice at both ages, but statistical significance was only seen in mice at 6 months, while cortical bone was not different
We examined the expression, by real-time PCR, of the transcription factor induced by bone morphogenetic protein 4 (BMP4) and osteoblast differentiation marker genes induced by L-ascorbic acid and -glycerophosphate using cultures of primary cells isolated calvaria from wild type (WT) and KO mice
Summary
Phospholipase C-related, but catalytically inactive protein (PRIP) was first identified as a novel D-myo-inositol-1,4,5-trisphosphate-binding protein and tentatively named p130 based on molecular size [1]. The molecular mechanisms underlying the inhibition of exocytosis by PRIP are currently being studied in the laboratory; gonadal steroid hormones were not up-regulated in response to increased gonadotropins, but were rather lower in KO mice; the serum level of progesterone in KO mice was about half that in control mice, while estradiol appeared to be lower, albeit with no statistical significance [21]. Three-dimensional analysis of the femurs of female mice was performed, as well as a histomorphometrical assay of bone formation parameters, including the bone formation rate, mineral apposition rate, osteoid thickness, and osteoblast number. All these results indicated that the increased bone mass seen in mutant mice is caused by enhanced bone formation. These results indicated that PRIP is implicated in the regulation of bone formation in a negative manner, partly through the regulation of Smad phosphorylation
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