Ectodermal-Neural Cortex 1 Isoforms Have Contrasting Effects on MC3T3-E1 Osteoblast Mineralization and Gene Expression.

The importance of Wnt pathway signaling in development of bone has been well established. Here we investigated the role of a known Wnt target, ENC1 (ectodermal-neural cortex 1; NRP/B), in osteoblast differentiation. Enc1 expression was detected in mouse osteoblasts, chondrocytes, and osteocytes by in situ hybridization, and osteoblastic expression was verified in differentiating primary cultures and MC3T3-E1 pre-osteoblast cells, with 57 kDa and 67 kDa ENC1 protein isoforms detected throughout differentiation. Induced knockdown of both ENC1 isoforms reduced alkaline phosphatase staining and virtually abolished MC3T3-E1 mineralization. At culture confluence, Alpl (alkaline phosphatase liver/bone/kidney) expression was markedly reduced compared with control cells, and there was significant and coordinated alteration of other genes involved in cellular phosphate biochemistry. In contrast, with 67 kDa-selective knockdown mineralized nodule formation was enhanced and there was a two-fold increase in Alpl expression at confluence. There was enhanced expression of Wnt/ß-catenin target genes with knockdown of both isoforms at this time-point and a five-fold increase in Frzb (Frizzled related protein) with 67 kDa-selective knockdown at mineralization, indicating possible ENC1 interactions with Wnt signaling in osteoblasts. These results are the first to demonstrate a role for ENC1 in the control of osteoblast differentiation. Additionally, the contrasting mineralization phenotypes and transcriptional patterns seen with coordinate knockdown of both ENC1 isoforms vs selective knockdown of 67 kDa ENC1 suggest opposing roles for the isoforms in regulation of osteoblastic differentiation, through effects on Alpl expression and phosphate cellular biochemistry. This study is the first to report differential roles for the ENC1 isoforms in any cell lineage. J. Cell. Biochem. 118: 2141-2150, 2017. © 2016 Wiley Periodicals, Inc.

Transient disturbance in physeal morphology is associated with long-term effects of nitrogen-containing bisphosphonates in growing rabbits.

UNLABELLED: Bisphosphonates have clinical benefit in children with severe osteogenesis imperfecta or osteoporosis and potential benefit in children with Perthes disease or undergoing distraction osteogenesis. However, there is concern about the effects of bisphosphonates on the physis and bone length. In 44 growing rabbits, zoledronic acid caused a transient disruption of physeal morphology, retention of cartilaginous matrix in trabeculae and cortical bone of the metaphysis, and a minor decrement in tibial bone length at maturity. INTRODUCTION: Data from growing animal models suggest that bisphosphonates cause retention of longitudinal cartilaginous septa at the chondro-osseous junction, extension of trabeculae to the metaphyseal-diaphyseal junction, and varying dose-dependent effects on longitudinal growth. However, there is a lack of data regarding effects of intermittent use of nitrogen-containing bisphosphonates on the physis and on tibial length in models reaching maturity. MATERIALS AND METHODS: Contralateral tibias of juvenile rabbits were examined after right tibial distraction osteogenesis from two previous studies. Animals were randomized to receive 0.1 mg/kg zoledronic acid (ZA) IV at 8 weeks of age (ZA*1) or 8 and 10 weeks of age (ZA*2) or saline. Body mass was analyzed from 5 to 44 weeks of age; tibial length and proximal physeal-metaphyseal histology and histomorphometry were analyzed at 8-52 weeks of age. RESULTS: Tibial length was 3% less at 14 weeks of age in the ZA*2-treated versus saline group (p<0.05) in both studies, and this difference persisted at maturity in the long-term study group (26 weeks of age, p<0.05). Total body mass gain from 5 to 26 weeks of age was 14% less in ZA*2-treated than saline animals (p<0.05). Rate of weight gain from 8 to 10 weeks of age was 76% less in ZA*2 compared with saline animals (p<0.05). Radiographs showed radiodense lines in the metaphyses of ZA-treated bones, corresponding to the number of doses. Histologically, lines resulting from the first dose of ZA contained longitudinal cartilaginous matrix cores surrounded by bone, whereas those from the second dose contained spherical cores of matrix caused by transient disruption of physeal morphology after the first dose of ZA. Resorption of these lines at later times was radiographically and histologically evident, but remnants of cartilaginous matrix remained in the cortical bone of ZA-treated animals. CONCLUSIONS: ZA treatment within the final 13.5% of the rabbit tibial growth period caused a transient disruption in physeal morphology and resorption associated with retention of cartilaginous matrix and coinciding with a persistent 3% decrement in tibial length. Disruption of physeal morphology and potential loss of bone length should be considered when administering nitrogen-containing bisphosphonates to children before closure of the major physes.

Zoledronic acid prevents osteopenia and increases bone strength in a rabbit model of distraction osteogenesis.

UNLABELLED: Prolonged healing times and stress-shielding osteopenia remain problematic in distraction osteogenesis. In this study of 30 rabbits, zoledronic acid increased regenerate volume, mineralization, and tibial strength and prevented osteopenia over a 6-week period. Translation to the clinical setting, if safe, could improve outcomes in distraction osteogenesis in children. INTRODUCTION: Because the external fixators for limb lengthening and reconstruction are designed to control the positions of bone fragments accurately, they also produce stress-shielding effects on the forming regenerate and surrounding bone. Osteopenia, leading to refracture and limitations on rehabilitation, are common consequences, potentially increasing morbidity and detracting from final clinical outcome. MATERIALS AND METHODS: We examined the effect of zoledronic acid on distraction osteogenesis in 42 immature male NZW rabbits. The model chosen results in reliable regenerate formation and stress-shielding osteopenia. Fourteen animals received either Saline, zoledronic acid 0.1 mg/kg at surgery (ZOL), or another dose 2 weeks postoperatively (Redosed ZOL). Rabbits underwent DXA for bone mineral content and bone mineral density in regenerate and surrounding segments of operated and contralateral tibias. After death at 6 weeks, 30 pairs of tibias underwent quantitative computerized tomography (QCT) and four-point bend testing, and 12 were examined by histomorphometry. The study was powered at 0.8 to show differences of 1.3 SDs for mineral and mechanical parameters. RESULTS: Osteopenia observed in tibias of the Saline group was absent in ZOL and Redosed ZOL tibias, the latter exhibiting higher bone mineral density and bone mineral content over contralateral regions (p < 0.01). Regenerate bone mineral content was higher in ZOL and Redosed ZOL versus Saline groups at 4 and 6 weeks (p < 0.01). Cross-sectional area was 49% and 59% greater at 6 weeks in ZOL and Redosed ZOL regenerates compared with the Saline group (p < 0.01). ZOL and Redosed ZOL tibias were 29% and 89% stronger by four-point bending than the Saline group (p < 0.01). Histomorphometry in the regenerate of ZOL and Redosed ZOL groups revealed higher trabecular bone volume and trabecular number compared with the Saline group (p < 0.001). CONCLUSIONS: Zoledronic acid administration led to significantly greater bone area, mineral content, strength, and trabecular number with reduced stress-shielding osteopenia in this model of distraction osteogenesis. These data suggest that intraoperative and postoperative zoledronic acid administration could improve outcomes in children undergoing limb lengthening.

Zoledronic acid treatment results in retention of femoral head structure after traumatic osteonecrosis in young Wistar rats.

UNLABELLED: Osteonecrosis (ON) of the femoral head in childhood can lead to loss of femoral head architecture and subsequent deformity. When femoral head ON was surgically induced in 24 rats, zoledronic acid treatment and prophylaxis improved sphericity and maintenance of architecture at 6 weeks. This preliminary experiment supports the use of bisphosphonates in childhood ON. INTRODUCTION: We hypothesized that the bisphosphonate zoledronic acid could preserve femoral head structure while allowing bone repair. MATERIALS AND METHODS: Osteonecrosis (ON) was surgically induced in the right femoral head of 24 female Wistar rats. The rats were randomized into three treatment groups and dosed subcutaneously with saline, zoledronic acid (0.1 mg/kg) at 1 and 4 weeks postoperation (ZA post), or zoledronic acid (0.1 mg/kg) given 2 weeks preoperation and at 1 and 4 weeks postoperation (ZA pre-post). After death at 6 weeks postoperation, undecalcified specimens were analyzed by DXA and standardized histomorphometric analysis. RESULTS: Seventy-one percent of saline-operated femoral heads were aspherical (Mose score > 1), whereas only 13% and 0% of operated heads in the ZA-treated groups were aspherical (p < 0.05). DXA-measured bone mineral density in saline-treated femoral heads was reduced by 34% and 43% compared with the ZA-treated groups (p < 0.01). Histomorphometry showed decreases of 12% and 17% in bone volume (BV/TV) in saline groups compared with ZA post and ZA pre-post (p < 0.05), and a decrease in trabecular number (Tb.N) of 18% and 14% (p < 0.05), respectively. Bone formation rate (BFR) was increased by 56% in saline-treated operated heads over ZA post and was 4.8 times increased over the ZA pre-post group (p < 0.05). The differences in BV/TV and Tb.N in treated groups must therefore be caused by a reduction in bone turnover. Observational histology confirmed the retention of necrotic architecture in treated groups. CONCLUSIONS: Zoledronic acid treatment and prophylaxis preserved femoral head architecture after traumatic ON in this rat model at 6 weeks. These data indicate that, by conserving femoral head architecture, bone repair may occur in conjunction with improved femoral head shape.

Transient retention of endochondral cartilaginous matrix with bisphosphonate treatment in a long-term rabbit model of distraction osteogenesis.

UNLABELLED: Bisphosphonates induce major increases in strength of callus in distraction osteogenesis in the short term. Poor understanding of the underlying mechanism, however, raises concerns about long-term consequences. In this long-term study in 32 rabbits, zoledronic acid transiently increased trabeculae by delayed temporal progression of endochondral bone remodeling but did not prevent radiographic completion of bone repair. INTRODUCTION: We hypothesized that bisphosphonate inhibition of osteoclast-mediated resorption would retain bone during repair, producing a larger callus in the short term. However, if remodeling was not restored, completion of the bone repair process in the long term could be jeopardized. MATERIALS AND METHODS: Juvenile rabbits underwent right tibial osteotomy and 2 weeks of distraction, followed by a period of consolidation. Animals received saline (controls) or zoledronic acid (ZA; 0.1 mg/kg at surgery and again 2 weeks later), and distracted tibias were examined by radiograph, DXA, histology, and histomorphometry at 2, 4, 6, 18, and 44 weeks after surgery. RESULTS: Regenerated bone in ZA-treated animals was denser than controls on radiographs at 6 weeks and had more distinct radiodense trabeculae and retention of original cortices at 18 weeks. By 44 weeks, controls and ZA-treated animals were radiographically healed and indistinguishable. Regenerate BMD and BMC increased between 2 and 4 weeks in all animals, with a greater effect in ZA. At 6 weeks, BMD and BMC in ZA-treated animals were 1.6- and 2-fold greater, respectively, than controls (p < 0.01). From 6 to 44 weeks, the control values gradually increased and approached the ZA-treated values. Regenerate bone volume and trabecular number by histomorphometry were from 1.6- to 2-fold greater in ZA-treated animals at 6 and 18 weeks (p < 0.05). Endochondral cartilaginous matrix volume was up to 2.4-fold greater in ZA-treated animals at 2 and 4 weeks (p < 0.05). TRACP+ cells in ZA-treated animals were larger with more nuclei. Mineral apposition rate and osteoblast number and surface were lower in ZA-treated animals at 6 weeks (p < 0.01) but not at later times. CONCLUSIONS: Disruption of TRACP+ cell function by ZA during bone regeneration seems to lead to an accretion of cancellous bone built on a larger endochondral cartilaginous matrix and increased bone mass, consistent with reported increases in short-term callus strength. This increase in bone mass, caused by a delay in remodeling, provided a transient advantage without preventing radiographic completion of the bone repair process in the long term. Noncontinuous treatment with nitrogen-containing bisphosphonates thus can have short-term beneficial effects without preventing long-term bone repair.

Clinical, Molecular, and Genetic Characteristics of PAPA Syndrome: A Review.

PAPA syndrome (Pyogenic Arthritis, Pyoderma gangrenosum, and Acne) is an autosomal dominant, hereditary auto-inflammatory disease arising from mutations in the PSTPIP1/CD2BP1 gene on chromosome 15q. These mutations produce a hyper-phosphorylated PSTPIP1 protein and alter its participation in activation of the "inflammasome" involved in interleukin-1 (IL-1ß) production. Overproduction of IL-1ß is a clear molecular feature of PAPA syndrome. Ongoing research is implicating other biochemical pathways that may be relevant to the distinct pyogenic inflammation of the skin and joints characteristic of this disease. This review summarizes the recent and rapidly accumulating knowledge on these molecular aspects of PAPA syndrome and related disorders.

Low-intensity ultrasound stimulation in distraction osteogenesis in rabbits.

Low-intensity pulsed ultrasound has been shown to accelerate fracture healing. This experiment investigated its possible role in distraction. Thirty-four New Zealand White rabbits had distraction osteogenesis, followed by low-intensity pulsed ultrasound therapy. Seventeen animals had the ultrasound transducer switched off (controls). Four and 6 weeks postoperatively, tibiae were analyzed using quantitative computed tomography and four-point mechanical testing. Two tibiae from each group had histologic analysis at 4 weeks. No significant differences were identified between regenerates of ultrasound-treated and control groups with respect to bone mineral content, cross-sectional area, and strength. No significant reductions in osteopenia proximal and distal to the regenerate were observed. Histologic observation showed no differences in bone volume fraction, but ultrasound-treated regenerates appeared to have fewer trabeculae of increased thickness, and fewer osteoclasts. The modulation by ultrasound may occur by accelerating endochondral ossification through action on chondrocytes, yet distraction osteogenesis is largely intramembranous. Although ultrasound is proven to be effective in unconstrained systems such as plaster, the current study does not support the role of low-intensity pulsed ultrasound as an adjunct for patients having distraction osteogenesis in a rigid fixator. Additional research is needed to definitively support the use of low-intensity pulsed ultrasound in such situations.