Increased Bone Mass in Mice Lacking the Adipokine Apelin

Authors

Lalita Wattanachanya, Wei-Dar Lu, Ramendra K. Kundu, Liping Wang, Marcia J. Abbott, Dylan O'Carroll, Thomas Quertermous and Robert A. Nissenson

Abstract

Adipose tissue plays an important role in skeletal homeostasis, and there is interest in identifying adipokines that influence bone mass. One such adipokine may be apelin, a ligand for the Gi-G protein-coupled receptor APJ, which has been reported to enhance mitogenesis and suppress apoptosis in MC3T3-E1 cells and primary human osteoblasts (OBs). However, it is unclear whether apelin plays a physiological role in regulating skeletal homeostasis in vivo. In this study, we compared the skeletal phenotypes of apelin knockout (APKO) and wild-type mice and investigated the direct effects of apelin on bone cells in vitro. The increased fractional cancellous bone volume at the distal femur was observed in APKO mice of both genders at 12 weeks of age and persisted until the age of 20. Cortical bone perimeter at the femoral midshaft was significantly increased in males and females at both time points. Dynamic histomorphometry revealed that APKO mice had increased rates of bone formation and mineral apposition, with evidences of accelerated OB proliferation and differentiation, without significant alteration in osteoclast activity. An in vitro study showed that apelin increased proliferation of primary mouse OBs as well as suppressed apoptosis in a dose-dependent manner with the maximum effect at 5nM. However, it had no effect on the formation of mineralized nodules. We did not observed significantly altered in osteoclast parameters in vitro. Taken together, the increased bone mass in mice lacking apelin suggested complex direct and paracrine/endocrine effects of apelin on bone, possibly via modulating insulin sensitivity. These results indicate that apelin functions as a physiologically significant antianabolic factor in bone in vivo.

Link to Article

http://dx.doi.org/10.1210/en.2012-2034

Immediately Placed Implants in Periodontally Compromised Patients: A Prospective Clinical Study

Authors

Rehab Elsharkawy and Hala El-Menoufy

Abstract

Purpose: This study was done to compare the outcome of implants placed immediately in partially edentulous periodontally compromised to periodontally healthy patients clinically and radiographically. Material and methods: Twenty immediately placed implants were followed up one year after loading clinically and radiographically. Patients were divided into 2 groups: 10 implants in group H (healthy, n=9) and 10 implants in group PD (moderate to severe chronic periodontitis, n=7). Clinical (modified bleeding index mBI, modified plaque index mPI, probing pocket depth PPD and degree of mobility using Periotest device) and radiographic parameters (Bone implant contact ratio BICR and vertical bone resorption) were assessed. Results: There were no significant differences in implant success rate between the 2 groups. Since the time of loading till the end of follow up period all implants were immobile, there was no pain or suppuration around the implants and there were no evidence of peri-implant radiolucency in the x-rays. Through all periods; there was no statistically significant difference between the two groups in the mPI or PPD, at any time point. At loading and 3 months post-loading; PD group showed statistically significantly higher mean mBI than healthy group. PD group showed statistically significantly lower mean PTVs (more stability) at time of loading (-1±2.1) and at 3 months PL (-1 ±1.8) than the H group at loading (0.5±0.7) and 3 ms PL (0.6±2) where P was 0.022 and 0.031for L and 3 ms PL respectively. Regarding the radiographic measures, there were no statistically significant differences between the two groups in the BICR and the VBL at any time point, through all the follow up periods P value ≤ 0.05. Conclusion: Immediate implants may be successful treatment modality in partially edentulous patients suffering from moderate to severe chronic periodontitis, provided that careful debridement of the extraction sockets is done and a good maintenance protocol is followed.

Link to Article

http://www.jofamericanscience.org/journals/am-sci/am0903/067_16822am0903_426_434.pdf

The Ras-GTPase activity of neurofibromin restrains ERK-dependent FGFR signaling during endochondral bone formation

Authors

Koichiro Ono, Matthew R. Karolak, Jean de la Croix Ndong, Weixi Wang, Xiangli Yang and Florent Elefteriou

Abstract

The severe defects in growth plate development caused by chondrocyte extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) gain or loss-of-function suggest that tight spatial and temporal regulation of mitogen-activated protein kinase signaling is necessary to achieve harmonious growth plate elongation and structure. We provide here evidence that neurofibromin, via its Ras guanosine triphosphatase -activating activity, controls ERK1/2-dependent fibroblast growth factor receptor (FGFR) signaling in chondrocytes. We show first that neurofibromin is expressed in FGFR-positive prehypertrophic and hypertrophic chondrocytes during growth plate endochondral ossification. Using mice lacking neurofibromin 1 (Nf1) in type II collagen-expressing cells, (Nf1col2−/− mutant mice), we then show that lack of neurofibromin in post-mitotic chondrocytes triggers a number of phenotypes reminiscent of the ones observed in mice characterized by FGFR gain-of-function mutations. Those include dwarfism, constitutive ERK1/2 activation, strongly reduced Ihh expression and decreased chondrocyte proliferation and maturation, increased chondrocytic expression of Rankl, matrix metalloproteinase 9 (Mmp9) and Mmp13 and enhanced growth plate osteoclastogenesis, as well as increased sensitivity to caspase-9 mediated apoptosis. Using wildtype (WT) and Nf1−/− chondrocyte cultures in vitro, we show that FGF2 pulse-stimulation triggers rapid ERK1/2 phosphorylation in both genotypes, but that return to the basal level is delayed in Nf1−/− chondrocytes. Importantly, in vivo ERK1/2 inhibition by daily injection of a recombinant form of C-type natriuretic peptide to post-natal pups for 18 days was able to correct the short stature of Nf1col2−/− mice. Together, these results underscore the requirement of neurofibromin and ERK1/2 for normal endochondral bone formation and support the notion that neurofibromin, by restraining RAS-ERK1/2 signaling, is a negative regulator of FGFR signaling in differentiating chondrocytes.

Link to Article

http://dx.doi.org/10.1093/hmg/ddt162

Histomorphologic Changes of the Long Head of the Biceps Tendon in Common Shoulder Pathologies

Authors

Augustus D. Mazzocca, M.S., M.D., Mary Beth R. McCarthy, B.S., Felicia A. Ledgard, M.S., David M. Chowaniec, B.S., William J. McKinnon Jr., B.A., Steven Delaronde, M.P.H., M.S.W., Louis J. Rubino, M.D., John Apolostakos, B.S., Anthony A. Romeo, M.D., Robert A. Arciero, M.D., Knut Beitzel, M.A., M.D.

Abstract

We used 32 LHB tendons of patients undergoing tenodesis (mean age, 54.7 ± 10.1 years) and 9 harvested tissue donors. Tendons were divided according to 4 diagnostic groups: (1) biceps instability, (2) tendinosis, (3) DJD, and (4) normal control. After sectioning, tendons were fixed in formalin and stained with H&E and alcian blue for histologic analysis. Measurements of collagen organization by use of polarized light microscopy was then performed, and protein expression for type I and type III collagen, tenascin C, and decorin was determined. There were no statistical differences found for protein expression of type I or type III collagen, tenascin C, or decorin. The proximal and distal regions of the tendons had statistically significant differences in alcian blue staining, with the proximal portion containing a higher amount of proteoglycan (instability, P = .001; tendinosis, P = .005; DJD, P = .008; control, P = .011). When compared with the nonpathologic control tendons, a significant increase in alcian blue staining for the proximal region was seen in all 3 groups. Total polarized light analysis showed that the distal tendon had a significantly higher intensity (organization) compared with the proximal tendon (P < .001); this was also seen in all of the diagnostic groups (instability, P = .010; tendinosis, P = .013; DJD, P = .07; control, P = .028). This study showed a greater degree of degeneration of the proximal (intra-articular) regions of the LHB tendon when compared with the distal regions in all pathologic groups. However, no major differences at the cellular level were found among groups. The pathomechanisms of the various forms of known LHB diagnoses are not yet fully understood and basic science studies may help in understanding their etiology and therefore optimizing treatment options.

Link to Article

http://dx.doi.org/10.1016/j.arthro.2013.02.002

Constitutive protein kinase A activity in osteocytes and late osteoblasts produces an anabolic effect on bone

Authors

Richard S. Kao, Marcia J. Abbott, Alyssa Louie, Dylan O'Carroll, Weidar Lu, Robert Nissenson

Abstract

Osteocytes have been implicated in the control of bone formation. However, the signal transduction pathways that regulate the biological function of osteocytes are poorly defined. Limited evidence suggests an important role for the Gs/cAMP pathway in osteocyte function. In the present study, we explored the hypothesis that cAMP-dependent kinase A (PKA) activation in osteocytes plays a key role in controlling skeletal homeostasis. To test this hypothesis, we mated mice harboring a Cre-conditional, mutated PKA catalytic subunit allele that encodes a constitutively active form of PKA (CαR) with mice expressing Cre under the control of the osteocyte-specific promoter, DMP1. This allowed us to direct the expression of CαR to osteocytes in double transgenic progeny. Examination of Cre expression indicated that CαR was also expressed in late osteoblasts. Cortical and trabecular bone parameters from 12-week old mice were determined by μCT. Expression of CαR in osteocytes and late osteoblasts altered the shape of cortical bone proximal to the tibia-fibular junction (TFJ) and produced a significant increase in its size. In trabecular bone of the distal femur, fractional bone volume, trabecular number, and trabecular thickness were increased. These increases were partially the results of increased bone formation rates (BFRs) on the endosteal surface of the cortical bone proximal to the TFJ as well as increased BFR on the trabecular bone surface of the distal femur. Mice expressing CαR displayed a marked increase in the expression of osteoblast markers such as osterix, runx2, collagen 1α1, and alkaline phosphatase (ALP). Interestingly, expression of osteocyte marker gene, DMP1, was significantly up-regulated but the osteocyte number per bone area was not altered. Expression of SOST, a presumed target for PKA signaling in osteocytes, was significantly down-regulated in females. Importantly, no changes in bone resorption were detected. In summary, constitutive PKA signaling in osteocytes and late osteoblasts led to a small expansion of the size of the cortical bone proximal to the TFJ and an increase in trabecular bone in female mice. This was associated with down-regulation of SOST and up-regulation of several osteoblast marker genes. Activation of the PKA pathway in osteocytes and late osteoblasts is sufficient for the initiation of an anabolic skeletal response.

Link to Article

http://dx.doi.org/10.1016/j.bone.2013.04.001

C/EBPα regulates osteoclast lineage commitment

Authors

Wei Chen1, Guochun Zhu, Liang Hao, Mengrui Wu, Hongliang Ci, and Yi-Ping Li

Abstract

Despite recent insights gained from the effects of targeted deletion of the Finkel-Biskis-Jinkins osteosarcoma oncogene (c-fos), Spleen focus-forming virus (SFFV) proviral integration 1 (PU.1), microphthalmia-associated transcription factor, NF-κB, and nuclear factor of activated cells cytoplasmic 1 (NFATc1) transcription factor genes, the mechanism underlying transcription factors specifying osteoclast (OC) lineage commitment from monocyte/macrophage remains unclear. To characterize the mechanism by which transcription factors regulate OC lineage commitment, we mapped the critical cis-regulatory element in the promoter of cathepsin K (Ctsk), which is expressed specifically in OCs, and found that CCAAT/enhancer binding protein α (C/EBPα) is the critical cis-regulatory element binding protein. Our results indicate that C/EBPα is highly expressed in pre- OCs and OCs. The combined presence of macrophage colony-stimulating factor and receptor activator of NF-κB ligand significantly induces high C/EBPα expression. Furthermore, C/EBPα−/− newborn mice exhibited impaired osteoclastogenesis, and a severe osteopetrotic phenotype, but unaffected monocyte/macrophage development. Impaired osteoclastogenesis of C/EBPα−/− mouse bone marrow cells can be rescued by c-fos overexpression. Ectopic expression of C/EBPα in mouse bone marrow cells and monocyte/macrophage cells, in the absence of receptor activator of NF-κB ligand, induces expression of receptor activator of NF-κB, c-fos, Nfatc1, and Ctsk, and it reprograms monocyte/macrophage cells to OC-like cells. Our results demonstrate that C/EBPα directly up-regulates c-fos expression. C/EBPα+/− mice exhibit an increase in bone density compared with C/EBPα+/+ controls. These discoveries establish C/EBPα as the key transcriptional regulator of OC lineage commitment, providing a unique therapeutic target for diseases of excessive bone resorption, such as osteoporosis and arthritis.

Link to Article

http://dx.doi.org/10.1073/pnas.1211383110