Expression of Msx-1 is suppressed in bisphosphonate associated osteonecrosis related jaw tissue-etiopathology considerations respecting jaw developmental biology-related unique features

<p>Abstract</p> <p>Background</p> <p>Bone-destructive disease treatments include bisphosphonates and antibodies against the osteoclast differentiator, RANKL (aRANKL); however, osteonecrosis of the jaw (ONJ) is a frequent side-effect. Current models fail to explain the restriction of bisphosphonate (BP)-related and denosumab (anti-RANKL antibody)-related ONJ to jaws. Msx-1 is exclusively expressed in craniofacial structures and pivotal to cranial neural crest (CNC)-derived periodontal tissue remodeling. We hypothesised that Msx-1 expression might be impaired in bisphosphonate-related ONJ. The study aim was to elucidate Msx-1 and RANKL-associated signal transduction (BMP-2/4, RANKL) in ONJ-altered and healthy periodontal tissue.</p> <p>Methods</p> <p>Twenty ONJ and twenty non-BP exposed periodontal samples were processed for RT-PCR and immunohistochemistry. An automated staining-based alkaline phosphatase-anti-alkaline phosphatase method was used to measure the stained cells:total cell-number ratio (labelling index, Bonferroni adjustment). Real-time RT-PCR was performed on ONJ-affected and healthy jaw periodontal samples (n = 20 each) to quantitatively compare Msx-1, BMP-2, RANKL, and GAPDH mRNA levels.</p> <p>Results</p> <p>Semi-quantitative assessment of the ratio of stained cells showed decreased Msx-1 and RANKL and increased BMP-2/4 (all p < 0.05) expression in ONJ-adjacent periodontal tissue. ONJ tissue also exhibited decreased relative gene expression for Msx-1 (p < 0.03) and RANKL (p < 0.03) and increased BMP-2/4 expression (p < 0.02) compared to control.</p> <p>Conclusions</p> <p>These results explain the sclerotic and osteopetrotic changes of periodontal tissue following BP application and substantiate clinical findings of BP-related impaired remodeling specific to periodontal tissue. RANKL suppression substantiated the clinical finding of impaired bone remodelling in BP- and aRANKL-induced ONJ-affected bone structures. Msx-1 suppression in ONJ-adjacent periodontal tissue suggested a bisphosphonate-related impairment in cellular differentiation that occurred exclusively jaw remodelling. Further research on developmental biology-related unique features of jaw bone structures will help to elucidate pathologies restricted to maxillofacial tissue.</p

Second permanent molars: embryological origin, development and eruption. Role of the RANK/RANKL/OPG pathway

Craniofacial skeleton formation, and more specifically alveolar bone development, follow a finely regulated controlled genetic program. A spatial and temporal combination of molecular signals determines the type and inter- and intra-maxillary position of each dental-alveolar unit. The volumetric growth and movement of tooth germs depend on a coordinated adaptive peripheral alveolar bone modeling process which is supported by signaling pathways between cells of the dental epithelium, dental follicle and alveolar bone. These signaling pathways involve transcription factors, proto-oncogenes and diffusible factors called “growth factors”. Transient impairment of these signals during time windows corresponding to the development of the various dental types could explain specific localized eruption deficits in a given dental type, as observed for second molars. Ongoing studies show that disturbances of bone resorption related to disruption of the RANKL/RANK/OPG signaling pathway affect tooth eruption and root morphogenesis, with a clear relationship between the time window of onset of disruption and the affected dental type

Deuxièmes molaires permanentes : origine embryologique, développement et éruption. Rôle de la triade RANK/RANKL/OPG

La formation du squelette cranio-facial et plus particulièrement le développement alvéolo-dentaire suivent un programme génétique finement régulé et contrôlé. En effet, une combinatoire spatiale et temporelle de signaux moléculaires détermine la typologie et la position intraet inter-maxillaires de chaque unité alvéolo-dentaire. La croissance volumétrique ainsi que les déplacements des germes dentaires dépendent d’un processus de modelage adaptatif et coordonné de l’os alvéolaire périphérique supporté par des voies de signalisation entre les cellules de l’épithélium dentaire, du sac folliculaire et de l’alvéole osseuse. Ces voies de signalisation impliquent des facteurs de transcription, des proto-oncogènes et des facteurs diffusibles dits « de croissance ». Des altérations transitoires de ces signalisations, au cours des fenêtres de temps correspondant à la formation des différents types dentaires, pourraient expliquer les atteintes localisées et spécifiques de l’éruption d’un type dentaire comme cela peut être observé pour les deuxièmes molaires. Des travaux en cours montrent que les perturbations de la résorption osseuse en relation avec des atteintes de la signalisation RANKL/RANK/OPG ont des répercussions sur l’éruption dentaire et sur la morphogenèse des racines avec une relation claire entre la fenêtre temporelle de survenue des perturbations et le type de dent atteint

Preclinical evidence of potential craniofacial adverse effect of zoledronic acid in pediatric patients with bone malignancies

High doses of zoledronic acid (ZOL), one of the most potent inhibitors of bone resorption, are currently evaluated in phase III clinical trials in Europe for the treatment of malignant pediatric primary bone tumors. The impact of such an intensive treatment on the craniofacial skeleton growth is a critical question in the context of patients with actively growing skeleton; in particular, in light of our previous studies evidencing that endochondral bone formation was transiently disturbed by high doses of ZOL. Two protocols adapted from pediatric treatments were developed for newborn mice (a total of 5 or 10 injections of ZOL 50 μg/kg every two days). Their impact on skull bones and teeth growth was analyzed by X-rays, microCT and histology up to 3 months after the last injection. ZOL administrations induced a transient delay of skull bone growth and an irreversible delay in incisor, first molar eruption and root elongation. Other teeth were affected, but most were erupted by 3 months. Root histogenesis was severely impacted for all molars and massive odontogenic tumor-like structures were observed in all mandibular incisors. High doses of ZOL irreversibly disturbed teeth eruption and elongation, and delayed skull bone formation. These preclinical observations are essential for the follow-up of onco-pediatric patients treated with ZOL

Cephalometric assessment of craniofacial dysmorphologies in relation with Msx2 mutations in mouse

To determine the role of Msx2 in craniofacial morphology and growth, we used a mouse model and performed a quantitative morphological characterization of the Msx2 (-/-) and the Msx2 (+/-) phenotype using a 2D cephalometric analysis applied on micrographs.status: publishe

Skeletal consequences of RANKL-blocking antibody (IK22-5) injections during growth: Mouse strain disparities and synergic effect with zoledronic acid

High doses of bone resorption inhibitors are currently under evaluation in pediatric oncology. Previous works have evidenced transient arrest in long bone and skull bone growth and tooth eruption blockage when mice were treated with zoledronic acid (ZOL). The question of potential similar effects with a RANKL-blocking antibody (IK22.5) was raised. Sensitivity disparities in these inhibitors between mouse strains and synergic effects of zoledronic acid and a RANKL-blocking antibody were subsidiary questions. In order to answer these questions, newborn C57BL/6J and CD1 mice were injected every two or three days (4 injections in total so 7 or 10 days of treatment length) with high doses of a RANKL-blocking antibody. The consequences on the tibia, craniofacial bones and teeth were analyzed by μCT and histology at the end of the treatment and one, two and three months later. The results obtained showed that RANKL-blocking antibody injections induced a transient arrest of tibia and skull bone growth and an irreversible blockage of tooth eruption in C57BL/6J mice. In CD1 mice, tooth eruption defects were also present but only at much higher doses. Similar mouse strain differences were obtained with zoledronic acid. Finally, a synergic effect of the two inhibitors was evidenced. In conclusion as previously observed for bisphosphonates (ZOL), a RANKL-blocking antibody induced a transient arrest in long bone and skull bone growth and a blockage of tooth eruption with however disparities between mouse strains with regard to this last effect. A synergic effect of both bone resorption inhibitors was also demonstrated