An essential role for the circadian-regulated gene nocturnin in osteogenesis: the importance of local timekeeping in skeletal homeostasis - PubMed (original) (raw)

Comparative Study

An essential role for the circadian-regulated gene nocturnin in osteogenesis: the importance of local timekeeping in skeletal homeostasis

Anyonya R Guntur et al. Ann N Y Acad Sci. 2011 Nov.

Abstract

The role of circadian proteins in regulating whole-body metabolism and bone turnover has been studied in detail and has led to the discovery of an elemental system for timekeeping involving the core genes Clock, Bmal1, Per, and Cry. Nocturnin (Noc; Ccrn4l), a peripheral circadian-regulated gene has been shown to play a very important role in regulating adipogenesis by deadenylation of key mRNAs and intracytoplasmic transport of PPARγ. The role that it plays in osteogenesis has previously not been studied in detail. In this report we examined in vitro and in vivo osteogenesis in the presence and absence of Noc and show that loss of Noc enhances bone formation and can rescue rosiglitazone-induced bone loss in mice. The circadian rhythm of Noc is likely to be an essential element of marrow stromal cell fate.

© 2011 New York Academy of Sciences.

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Conflict of interest statement

Conflicts of interest

The authors declare no conflicts of interests

Figures

Figure 1

Figure 1

(A) Effect of Nocturnin on osteoblastogenesis. This figure shows effect of overexpression of (a) Noc on osteoblast gene marker expression as can be observed, there is a significant suppression of osteoblastogeneis, which is evident from the decrease in (b) ATF4 and (c) Osteocalci ; (d) Osterix we also saw a trend towards suppression in (e) CYP51 when Noc is overexpressed, in MC3T3E1 cells compared to GFP cells. (B) The increase in Noc is confirmed by the Flag tag Western blot along with a NOC protein levels in cells, Actin was used as the loading control. (C) (c’)The long term (20 days with change in media every two days) osteoblast differentiation assay on cells that have Noc knocked down show that there is a significant increase in nodule formation compared to control cells. (c’’) Osteoblast differentiation assay for 7 days showed decreased alkaline phosphatase staining in Noc overexpressed cells compared to control cells (n = 3, * indicates P < 0.05). (D) Alizarin red and Alcian blue staining showing the tibial and fibula bones from Noc control +/− and Noc null.

Figure 2

Figure 2

Effect of rosiglitazone treatment on bone in the absence of Nocturnin. Graphical representation of the data from mice that were on control diet and rosiglitazone diet. (a) Trabecular BV/TV, (b) trabecular connectivity density, (c) trabecular number, and (d) trabecular space. MicroCT evaluation of femurs from mice that were on rosiglitazone diet and compared to mice on control diet showed that there are increased trabecular parameters in the Noc null mice, suggesting that there is a protection effect of rosiglitazone treatment on bone in the absence of Noc. (n = 4 animals per group, _P_-values are indicated on the chart)

Figure 3

Figure 3

Model showing the effect rosiglitazone treatment has on bone in the presence and absence of Nocturnin. The model illustrates the salient points of the paper: in a wild-type (WT) pre-osteoblast in the presence of rosiglitazone, Nocturnin helps PPARγ translocate in to the nucleus where it can help facilitate adipogenesis potentially over osteogenesis; and in the cytoplasm, Nocturnin can potentially bind to the mRNA’s of ATF4, Osterix, and CYP51 and negatively regulate them using its deadenylase function. In the absence of Nocturnin (Nocturnin−/−) there is less of PPARγ in the nucleus, along with loss of deadenylase regulation of the osteoblast marker transcripts, which results in protection from bone loss on rosiglitazone treatment.

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