Hdac3-Deficiency Increases Marrow Adiposity and Induces Lipid Storage and Glucocorticoid Metabolism in Osteo-Chondroprogenitor Cells

Authors

Meghan E. McGee-Lawrence, Lomeli R. Carpio, Ryan J. Schulze, Jessica L. Pierce, Mark A. McNiven, Joshua N. Farr, Sundeep Khosla, Merry Jo Oursler, and Jennifer J. Westendorf

Abstract

Bone loss and increased marrow adiposity are hallmarks of aging skeletons. Conditional deletion of histone deacetylase (Hdac) 3 in murine osteo-chondroprogenitor cells causes osteopenia and increases marrow adiposity, even in young animals, but the origins of the increased adiposity are unclear. To explore this, bone marrow stromal cells (BMSCs) from Hdac3-depleted and control mice were cultured in osteogenic medium. Hdac3-deficient cultures accumulated lipid droplets in greater abundance than control cultures and expressed high levels of genes related to lipid storage (Fsp27/Cidec, Plin1) and glucocorticoid metabolism (Hsd11b1) despite normal levels of Pparγ2. Approximately 5% of the lipid containing cells in the wildtype cultures expressed the master osteoblast transcription factor Runx2, but this population was 3-fold greater in the Hdac3-depleted cultures. Adenoviral expression of Hdac3 restored normal gene expression, indicating that Hdac3 controls glucocorticoid activation and lipid storage within osteoblast lineage cells. HDAC3 expression was reduced in bone cells from postmenopausal as compared to young women, and in osteoblasts from aged as compared to younger mice. Moreover, phosphorylation of S424 in Hdac3, a posttranslational mark necessary for deacetylase activity, was suppressed in osseous cells from old mice. Thus, concurrent declines in transcription and phosphorylation combine to suppress Hdac3 activity in aging bone, and reduced Hdac3 activity in osteo-chondroprogenitor cells contributes to increased marrow adiposity associated with aging.

Link To Article

http://dx.doi.org/10.1002/jbmr.2602

RAP-011 augments callus formation in closed fractures in rats

Authors

Alyson Morse, Tegan Cheng, Lauren Peacock, Kathy Mikulec, David Little, and Aaron Schindeler

Abstract

ACE-011 is a bone anabolic agent generated by fusing the extracellular domain of the Activin Type 2A receptor (ActRIIA) to an IgG-Fc. The orthopedic utility of ACE-011 was investigated using a murine analogue, RAP-011. Initially, a rat closed fracture model was tested using bi-weekly (biw) 10 mg/kg RAP-011. RAP-011 significantly increased callus length and callus bone volume (BV, +43% at 6w, p < 0.01). The polar moment of inertia was calculated to be substantively increased (+80%, p < 0.01), however mechanical bending tests showed a more modest increase in maximum load to failure (+24%, p < 0.05). Histology indicated enhanced appositional bone growth, but it was hypothesized that reduced remodeling, evidenced by decreased serum CTX (-16% at 6w, p < 0.01), could be compromising bone quality in the callus. A second closed fracture study was performed to examine lower ‘pulse’ [RAP-011(p)] and ‘sustained’ [RAP-011(s)] regimens of biw 0.6mg/kg × 2, 0.35mg/kg × 3 and 0.18mg/kg × 2, 0.1mg/kg × 7 respectively, compared with PTH(1-34) (25µg/kg/d) and vehicle controls. RAP-011 treatments gave modest increases in callus length and callus BV at 6w (p < 0.01), but did not achieve an increase in maximum load over vehicle. In summary, RAP-011 is effective in promoting bone formation during repair, but optimizing callus bone quality will require further investigation.

Link To Article

http://dx.doi.org/10.1002/jor.22985

Intravenous Immunoglobulin (IVIG) Attenuates TNF-Induced Pathologic Bone Resorption and Suppresses Osteoclastogenesis by Inducing A20 Expression

Authors

Min Joon Lee, Elisha Lim, Sehwan Mun, Seyeon Bae, Koichi Murata, Lionel B. Ivashkiv, and Kyung-Hyun Park-Min

Abstract

Investigations on the therapeutic effects of intravenous immunoglobulin (IVIG) have focused on the suppression of autoantibody- and immune complex-mediated inflammatory pathogenesis. Inflammatory diseases such as rheumatoid arthritis are often accompanied by excessive bone erosion but the effect of IVIG on osteoclasts, bone-resorbing cells, has not been studied. Here, we investigate whether IVIG directly regulates osteoclast differentiation and has therapeutic potential for suppressing osteoclast-mediated pathologic bone resorption. IVIG or cross-linking of Fcγ receptors with plate-bound IgG suppressed receptor activator of nuclear factor-kappa B ligand (RANKL)-induced osteoclastogenesis and expression of osteoclast-related genes such as integrin β3 and cathepsin K in a dose-dependent manner. Mechanistically, IVIG or plate-bound IgG suppressed osteoclastogenesis by downregulating RANKL-induced expression of NFATC1, the master regulator of osteoclastogenesis. IVIG suppressed NFATC1 expression by attenuating RANKL-induced NF-κB signaling, explained in part by induction of the inflammatory signaling inhibitor A20. IVIG administration attenuated in vivo osteoclastogenesis and suppressed bone resorption in the tumor necrosis factor (TNF)-induced calvarial osteolysis model. Our findings show that, in addition to suppressing inflammation, IVIG directly inhibits osteoclastogenesis through a mechanism involving suppression of RANK signaling. Direct suppression of osteoclast differentiation may provide beneficial effects on preserving bone mass when IVIG is used to treat rheumatic disorders.

Link To Article

http://dx.doi.org/10.1002/jcp.25091

Riboflavin crosslinked high-density collagen gel for the repair of annular defects in intervertebral discs: An in vivo study

Authors

Peter Grunert, Brandon H. Borde, Sara B. Towne, Yu Moriguchi, Katherine D. Hudson, Lawrence J. Bonassar, Roger Härtl

Abstract

Open annular defects compromise the ability of the annulus fibrosus to contain nuclear tissue in the disc space, and therefore lead to disc herniation with subsequent degenerative changes to the entire intervertebral disc. This study reports the use of riboflavin crosslinked high-density collagen gel for the repair of annular defects in a needle-punctured rat-tail model. High-density collagen has increased stiffness and greater hydraulic permeability than conventional low-density gels; riboflavin crosslinking further increases these properties. This study found that treating annular defects with crosslinked high-density collagen inhibited the progression of disc degeneration over 18 weeks compared to untreated control discs. Histological sections of FITC-labeled collagen gel revealed an early tight attachment to host annular tissue. The gel was subsequently infiltrated by host fibroblasts which remodeled it into a fibrous cap that bridged the outer disrupted annular fibers and partially repaired the defect. This repair tissue enhanced retention of nucleus pulposus tissue, maintained physiological disc hydration, and preserved hydraulic permeability, according to MRI, histological, and mechanical assessments. Degenerative changes were partially reversed in treated discs, as indicated by an increase in nucleus pulposus size and hydration between weeks 5 and 18. The collagen gel appeared to work as an instant sealant and by enhancing the intrinsic healing capabilities of the host tissue.

Link To Article

http://dx.doi.org/10.1016/j.actbio.2015.06.006

Alternative NF-κB Regulates RANKL-Induced Osteoclast Differentiation and Mitochondrial Biogenesis via Independent Mechanisms

Authors

Rong Zeng, Roberta Faccio, and Deborah V Novack

Abstract

Mitochondrial biogenesis, the generation of new mitochondrial DNA and proteins, has been linked to osteoclast (OC) differentiation and function. In this study we used mice with mutations in key alternative NF-κB pathway proteins, RelB and NIK, to dissect the complex relationship between mitochondrial biogenesis and osteoclastogenesis. OC precursors lacking either NIK or RelB, RANKL were unable to increase mitochondrial DNA or OxPhos protein expression, associated with lower oxygen consumption rates. Transgenic OC precursors expressing constitutively active NIK showed normal RANKL-induced mitochondrial biogenesis (OxPhos expression and mitochondria copy number) compared to controls, but larger mitochondrial dimensions and increased oxygen consumption rates, suggesting increased mitochondrial function. To deduce the mechanism for mitochondrial biogenesis defects in NIK- and RelB-deficient precursors, we examined expression of genes known to control this process. PGC-1β (Ppargc1b) expression, but not PGC-1α, PPRC1 or ERRα, was significantly reduced in RelB-/- and NIK-/- OCs. Because PGC-1β has been reported to positively regulate both mitochondrial biogenesis and differentiation in OCs, we retrovirally overexpressed PGC-1β in RelB-/- cells, but surprisingly found that it did not affect differentiation, nor restore RANKL-induced mitochondrial biogenesis. To determine whether the blockade in osteoclastogenesis in RelB-deficient cells precludes mitochondrial biogenesis, we rescued RelB-/- differentiation via overexpression of NFATc1. Mitochondrial parameters in neither WT nor RelB-deficient cultures were affected by NFATc1 overexpression, and bone resorption in RelB -/- was not restored. Furthermore, NFATc1 co-overexpression with PGC-1β, while allowing OC differentiation, did not rescue mitochondrial biogenesis or bone resorption in RelB-/- OCs, by CTX-I levels. Thus, our results indicate that the alternative NF-κB pathway plays dual, but distinct roles in controlling the independent processes of OC differentiation and OC mitochondrial biogenesis. Furthermore, the inability of PGC-1β to drive mitochondrial biogenesis in OCs without RelB indicates a cell-type specificity in mitochondria regulation.

Link To Article

http://dx.doi.org/10.1002/jbmr.2584

S-EQUOL PREVENTS LOSS OF BONE STRENGTH IN RAT OSTEOPOROSIS MODEL

Authors

J.A. Yu-Yahiro, C.B. Ruff, B.G. Parks, V.S. Sinkov, I. Merchenthaler

Abstract

Background: To investigate the effect of S-equol, a selective estrogen receptor ß agonist produced in certain individuals by biotransformation of the soy isoflavone daidzein, on bone structure, bone strength, and metabolism in overiectomized rats. Design: Controlled animal study. Participants: Total of 75 female rats. Intervention: Animals were divided into 5 groups: ovariectomized (OVX), OVX+17-beta estradiol benzoate (EB), OVX+S-equol (30 mg/kg), OVX+S-equol (100 mg/kg), and SHAM. Animals received drug or vehicle for 60 days. At sacrifice, right femora and vertebrae (L3 and L4) were excised. Measurements: Bone density and structural parameters were measured by pQCT. Mechanical testing and quantitative histomorphometry were done. Blood markers of bone metabolism and uterine weights were measured. Results: Higher dose S-equol preserved mechanical strength of bone. Vertebral compressive strength, femoral bending strength, and femoral cortical thickness were not different between the S- equol (100 mg/kg) , SHAM, and EB groups and all were significantly higher than OVX and S-equol (30 mg/kg) groups. No differences were found in osteoclast numbers or vertebral bone mineral composition, and serum markers of bone metabolism did not follow the pattern of strength measures differences. Uterine weight in the higher dose S-equol group was significantly lower than in SHAM and EB groups. Conclusions: Treatment of OVX rats with S-equol (100 mg/kg) resulted in preservation of vertebral and femoral bone strength and volume not different from that in SHAM or EB rats. Higher dose S-equol caused less uterine stimulation than did endogenous or synthetic estrogen. These results suggest that S-equol warrants further study as a possible alternative to estrogen replacement for treatment of osteoporosis.

Link To Article

http://www.jarcp.com/498-s-equol-prevents-loss-of-bone-strength-in-rat-osteoporosis-model.html