The nucleocytoplasmic shuttling protein CIZ reduces adult bone mass by inhibiting bone morphogenetic protein–induced bone formation

Abstract

Osteoporosis is a major health problem; however, the mechanisms regulating adult bone mass are poorly understood. Cas-interacting zinc finger protein (CIZ) is a nucleocytoplasmic shuttling protein that localizes at cell adhesion plaques that form where osteoblasts attach to substrate. To investigate the potential role of CIZ in regulating adult bone mass, we examined the bones in CIZ-deficient mice. Bone volume was increased and the rates of bone formation were increased in CIZ-deficient mice, whereas bone resorption was not altered. CIZ deficiency enhanced the levels of mRNA expression of genes encoding proteins related to osteoblastic phenotypes, such as alkaline phosphatase (ALP) as well as osterix mRNA expression in whole long bones. Bone marrow cells obtained from the femora of CIZ-deficient mice revealed higher ALP activity in culture and formed more mineralized nodules than wild-type cells. CIZ deficiency enhanced bone morphogenetic protein (BMP)–induced osteoblastic differentiation in bone marrow cells in cultures, indicating that BMP is the target of CIZ action. CIZ deficiency increased newly formed bone mass after femoral bone marrow ablation in vivo. Finally, BMP-2–induced bone formation on adult mouse calvariae in vivo was enhanced by CIZ deficiency. These results establish that CIZ suppresses the levels of adult bone mass through inhibition of BMP-induced activation of osteoblasts.

Nmp4/CIZ Suppresses the Parathyroid Hormone Anabolic Window by Restricting Mesenchymal Stem Cell and Osteoprogenitor Frequency

“…This is consistent with the observed equivalent addition of bone during the first 2 weeks of treatment, but the divergence in both serum osteocalcin and bone formation in the null mice at 3 weeks [7 and the present work]. Finally, the Nmp4/CIZ-KO osteoblast exhibits a modest, but significant, enhanced response to numerous anabolic stimuli, including PTH, BMP2, and mechanical loading [24,[33][34][35]; therefore, an expanded population of such cells is certainly consistent with the augmented skeletal bone mineral density and bone mineral content of the null animals.…”

“…The Nmp4-null BM yielded 4-fold more of these colonies than did the WT BM. In an earlier study, Noda and colleagues observed that BM cultures from null mice yielded about 3-fold more mineralized nodules than WT mice [24], which is equivalent to measuring CFUosteoblast colonies [25]. In the present study, we also determined that the total number of CFU-F colonies obtained from the null mice was significantly elevated as was the% CFU-F Alkphos + /total CFU-F.…”

“…To address this issue, a combination of genetic-, drug-, and transplantation-based approaches will be required, because all of these methods have strengths and drawbacks, yet their intersection reveals complementary aspects of the phenomenon under study. However, the previously observed heightened PTH-responsiveness and osteogenic capacity of Nmp4-KO BMSCs and osteoblasts in culture [24,33,35] and the enhanced number of the progenitors of these cells (present study) likely make a substantial contribution to the extended anabolic window. Additionally, Nmp4/CIZ deficiency augmented newly formed trabecular bone mass after femoral BM ablation as compared to WT mice [24], confirming the enhanced osteogenic capacity of the reconstituted KO BM.…”

Nanogel‐based scaffold delivery of prostaglandin E2 receptor–specific agonist in combination with a low dose of growth factor heals critical‐size bone defects in mice

“…Calvarial defects were made as previously described (22). After 4 weeks, microfocal computed tomography (micro-CT) (14,15,22), histologic analysis (23,24), and alkaline phosphatase assay in serum were conducted (15). Calvariae from neonatal mice were cultured in vehicle (0.01% DMSO) or 10 Ϫ7 M EP4A for 24 hours (25) before RNA extraction and reverse transcription-polymerase chain reaction were performed (26).…”

“…Osteoblastic MC3T3-E1 cells were treated with BMP-2 (50 ng/ml), with or without EP4A (10 Ϫ7 M), or with vehicle (DMSO), and then were subjected to serum alkaline phosphatase assay (23) and luciferase assay, as described elsewhere (27).…”