P092 Infantile osteopetrosis: a case report Traduction en Anglais

Background Infantile osteopetrosis is a rare genetic disorder characterized by increased bone density due to defective osteoclastic resorption. Case report We report the case of a 6 years old girl, born of a consanguineous marriage, hospitalized in our department for bone deformations and visual disturbances. On clinical examination, there was conjunctival pallor, thoracic deformity, genu-valgum and dentigenesis disorder as well as nystagmus and severe loss of visual acuity. The complete blood count showed regenerative normochromic normocytic anaemia as well as thrombocytopenia. Assessment for infectious disorders was negative. The skeletal X-ray revealed diffuse osteocondensation of the skeleton. The CT scan of the rock bones of cranial bases revealed bilateral segmental stenosis of the facial canal with densification of the ossicular chain and thickening of the stapes. Cranio-orbital MRI revealed bilateral optic duct stenosis with atrophy of the optic nerves and chiasma. The diagnosis of osteopetrosis was retained according to this set of clinical and radiological arguments. Unfortunately, the genetic study could not be performed. Histocompatible bone marrow transplant may be curative but was not available for our patient. Genetic counseling was offered for the family as well as dental and orthopedic care. Conclusion Infantile osteopetrosis is a rare but serious pathology that can have severe functional repercussion and even be life-threatening, requiring early diagnosis and management.

Controversial technologies in intramedullary osteosynthesis of rats femur fractures

The aim: to conduct a comparative study of osteoreparative regeneration, namely in the periosteal and intermediate areas of the cortex, during intramedullary osteosynthesis of the femur of rats with and without reaming of the bone marrow canal. Materials and methods. The work is based on the results of an experimental study conducted on 56 white mature laboratory rats, which simulated diaphyseal fracture of the femur and performed stable nail osteosynthesis with reaming of the bone marrow canal in the first series and without reaming in the second series of the experiment. Histological examination of the specimens was performed on the 7th, 14th, 28th and 90th day after surgery. Results. The procedure of reaming the bone marrow canal reduces the potential reparative capacity of bone tissue in the endosteal area and leads to “distorted” activation of the process of the cortex restructuring. There is a significant activation of osteoclastic resorption. Conclusions. Bone fusion is more active with the use of intramedullary fixator without reaming of the bone marrow canal, because its reaming reduces the manifestations of reparative potentials in the endosteal region and leads to excessive activation of the resorptive process of restructuring the cortex of both endosteal and central part

Deficiency of Lipin2 Results in Enhanced NF-κB Signaling and Osteoclast Formation in RAW-D Murine Macrophages

Lipin2 is a phosphatidate phosphatase that plays critical roles in fat homeostasis. Alterations in Lpin2, which encodes lipin2, cause the autoinflammatory bone disorder Majeed syndrome. Lipin2 limits lipopolysaccharide (LPS)-induced inflammatory responses in macrophages. However, little is known about the precise molecular mechanisms underlying its anti-inflammatory function. In this study, we attempted to elucidate the molecular link between the loss of lipin2 function and autoinflammatory bone disorder. Using a Lpin2 knockout murine macrophage cell line, we showed that lipin2 deficiency enhances innate immune responses to LPS stimulation through excessive activation of the NF-κB signaling pathway, partly because of TAK1 signaling upregulation. Lipin2 depletion also enhanced RANKL-mediated osteoclastogenesis and osteoclastic resorption activity accompanied by NFATc1 dephosphorylation and increased nuclear accumulation. These results suggest that lipin2 suppresses the development of autoinflammatory bone disorder by fine-tuning proinflammatory responses and osteoclastogenesis in macrophages. Therefore, this study provides insights into the molecular pathogenesis of monogenic autoinflammatory bone disorders and presents a potential therapeutic intervention.

How to Get Them off?—Assessment of Innovative Techniques for Generation and Detachment of Mature Osteoclasts for Biomaterial Resorption Studies

The fusion process of mononuclear monocytes into multinuclear osteoclasts in vitro is an essential process for the study of osteoclastic resorption of biomaterials. Thereby biomaterials offer many influencing factors such as sample shape, material composition, and surface topography, which can have a decisive influence on the fusion and thus the entire investigation. For the specific investigation of resorption, it can therefore be advantageous to skip the fusion on samples and use mature, predifferentiated osteoclasts directly. However, most conventional detachment methods (cell scraper, accutase), lead to a poor survival rate of osteoclasts or to a loss of function of the cells after their reseeding. In the present study different conventional and novel methods of detachment in combination with different culture surfaces were investigated to obtain optimal osteoclast differentiation, yield, and vitality rates without loss of function. The innovative method—using thermoresponsive surfaces for cultivation and detachment—was found to be best suited. This is in particular due to its ability to maintain osteoclast activity, as proven by TRAP 5b-, CTSK-activity and resorption pits on dentin discs and decellularized osteoblast-derived matrix plates. In conclusion, it is shown, that osteoclasts can be predifferentiated on cell culture dishes and transferred to a reference biomaterial under preservation of osteoclastic resorption activity, providing biomaterial researchers with a novel tool for material characterization.

Microporosities in 3D-Printed Tricalcium-Phosphate-Based Bone Substitutes Enhance Osteoconduction and Affect Osteoclastic Resorption

Additive manufacturing is a key technology required to realize the production of a personalized bone substitute that exactly meets a patient’s need and fills a patient-specific bone defect. Additive manufacturing can optimize the inner architecture of the scaffold for osteoconduction, allowing fast and reliable defect bridging by promoting rapid growth of new bone tissue into the scaffold. The role of scaffold microporosity/nanoarchitecture in osteoconduction remains elusive. To elucidate this relationship, we produced lithography-based osteoconductive scaffolds from tricalcium phosphate (TCP) with identical macro- and microarchitecture, but varied their nanoarchitecture/microporosity by ranging maximum sintering temperatures from 1000 °C to 1200 °C. After characterization of the different scaffolds’ microporosity, compression strength, and nanoarchitecture, we performed in vivo studies that showed that ingrowth of bone as an indicator of osteoconduction significantly decreased with decreasing microporosity. Moreover, at the 1200 °C peak sinter temperature and lowest microporosity, osteoclastic degradation of the material was inhibited. Thus, even for wide-open porous TCP-based scaffolds, a high degree of microporosity appears to be essential for optimal osteoconduction and creeping substitution, which can prevent non-unions, the major complication during bone regeneration procedures.

Cranial bone flap resorption—pathological features and their implications for clinical treatment

Cranioplasty following decompressive craniectomy (DC) has a primary complication when using the autologous bone: aseptic bone resorption (ABR). So far, risk factors such as age, number of fragments, and hydrocephalus have been identified but a thorough understanding of the underlying pathophysiology is still missing. The aim of this osteopathological investigation was to gain a better understanding of the underlying processes. Clinical data of patients who underwent surgical revision due to ABR was collected. Demographics, the time interval between craniectomy and cranioplasty, and endocrine serum parameters affecting bone metabolism were collected. Removed specimens underwent qualitative and quantitative histological examination. Two grafts without ABR were examined as controls. Compared to the controls, the typical layering of the cortical and cancellous bone was largely eliminated in the grafts. Histological investigations revealed the coexistence of osteolytic and osteoblastic activity within the necrosis. Bone appositions were distributed over the entire graft area. Remaining marrow spaces were predominantly fibrotic or necrotic. In areas with marrow cavity fibrosis, hardly any new bone tissue was found in the adjacent bone, while there were increased signs of osteoclastic resorption. Insufficient reintegration of the flap may be due to residual fatty bone marrow contained in the bone flap which seems to act as a barrier for osteogenesis. This may obstruct the reorganization of the bone structure, inducing aseptic bone necrosis. Following a path already taken in orthopedic surgery, thorough lavage of the implant to remove the bone marrow may be a possibility, but will need further investigation.

P0872EFFECT OF PARATHYROID HORMONE OSCILLATIONS ON BONE HEALTH: FROM OSTEO-ANABOLISM TO CATABOLISM

Background and Aims In patients with chronic kidney disease or primary hyperparathyroidism, chronically elevated parathyroid hormones (PTH) levels exert catabolic effects on the bone. In contrast, PTH oscillations (as seen in healthy subjects) or daily application of teriparatide (a form of PTH consisting of the N-terminal 34 amino acids; it is used to treat osteoporosis) promote bone formation. These differential responses have important clinical and therapeutic implications. Although the anabolic effects of PTH (and teriparatide) cycling are widely accepted, the underlying osteo-anabolic dynamics are not well understood. Method A recently developed mechanistic physiology-based model quantitating the interrelations of osteoclasts, osteoblasts and osteocytes on bone remodeling is used (Cherif et al., ΝΔΤ 2018, 33 (συππλ. 1): 165–166). The model incorporates cell-to-cell signaling pathways (i.e., RANK-RANKL-OPG), intracellular pathways, cytokines (i.e. TGFβ), PTH, sclerostin, and endocrine and paracrine feedbacks. Using the validated model, we explore the effect of altered PTH (teriparatide) administration regimen (e.g., dosing frequency and amplitude) on bone catabolism and anabolism, respectively. Results As in previous studies, the model accurately predicts differential responses of osteo-anabolic and catabolic effects of continuously and intermittently elevated PTH (teriparatide) levels, respectively. In addition, we observe that intermittent administration of PTH with a high frequency and amplitude induces bone catabolism similar to that seen in pathologies with continuously elevated PTH (i.e. primary or secondary hyperparathyroidism). We see a more than 3-fold change from baseline in osteoclastic over osteoblastic activities, resulting in a bone efflux of calcium and phosphate. Low PTH frequency with high dosing amplitude induces both osteoclastic and osteoblastic activities, but the net result is bone anabolism. Further, Fig. 1 shows a nonlinear region where high osteoblastic activities exceed osteoclastic resorption. These findings suggest the existence of optimal PTH (teriparatide) frequency-amplitude combinations that enhance anabolic gains, beyond which there can be a detrimental effect on bone. Conclusion Our results suggest that both frequency and amplitude of PTH (teriparatide) cycling affect the balance of osteo-catabolic and -anabolic effects. Understanding the underlying mechanism of differential osteo-anabolic and -catabolic responses induced by intermittent and continuous levels of PTH, respectively, may provide new therapeutic options for patients and minimize unintended consequences of intervention protocols.

Cortical bone maturation in mice requires SOCS3 suppression of gp130/STAT3 signalling in osteocytes

Bone strength is determined by its dense cortical shell, generated by unknown mechanisms. Here we use the Dmp1Cre:Socs3f/f mouse, with delayed cortical bone consolidation, to characterise cortical maturation and identify control signals. We show that cortical maturation requires a reduction in cortical porosity, and a transition from low to high density bone, which continues even after cortical shape is established. Both processes were delayed in Dmp1Cre:Socs3f/f mice. SOCS3 (suppressor of cytokine signalling 3) inhibits signalling by leptin, G-CSF, and IL-6 family cytokines (gp130). In Dmp1Cre:Socs3f/f bone, STAT3 phosphorylation was prolonged in response to gp130-signalling cytokines, but not G-CSF or leptin. Deletion of gp130 in Dmp1Cre:Socs3f/f mice suppressed STAT3 phosphorylation in osteocytes and osteoclastic resorption within cortical bone, leading to rescue of the corticalisation defect, and restoration of compromised bone strength. We conclude that cortical bone development includes both pore closure and accumulation of high density bone, and that these processes require suppression of gp130-STAT3 signalling in osteocytes.