Dekel Shilo

Amelogenin in cranio-facial development: the tooth as a model to study the role of amelogenin during embryogenesis

The amelogenins comprise 90% of the developing extracellular enamel matrix proteins and play a major role in the biomineralization and structural organization of enamel. Amelogenins were also detected, in smaller amounts, in postnatal calcifying mesenchymal tissues, and in several nonmineralizing tissues including brain. Low molecular mass amelogenin isoforms were suggested to have signaling activity; to produce ectopically chondrogenic and osteogenic-like tissue and to affect mouse tooth germ differentiation in vitro. Recently, some amelogenin isoforms were found to bind to the cell surface receptors; LAMP-1, LAMP-2 and CD63, and subsequently localize to the perinuclear region of the cell. The recombinant amelogenin protein (rHAM(+)) alone brought about regeneration of the tooth supporting tissues: cementum, periodontal ligament and alveolar bone, in the dog model, through recruitment of progenitor cells and mesenchymal stem cells. We show that amelogenin is expressed in various tissues of the developing mouse embryonic cranio-facial complex such as brain, eye, ganglia, peripheral nerve trunks, cartilage and bone, and is already expressed at E10.5 in the brain and eye, long before the initiation of tooth formation. Amelogenin protein expression was detected in the tooth germ (dental lamina) already at E13.5, much earlier than previously reported (E19). Application of amelogenin (rHAM(+)) beads together with DiI, on E13.5 and E14.5 embryonic mandibular mesenchyme and on embryonic tooth germ, revealed recruitment of mesenchymal cells. The present results indicate that amelogenin has an important role in many tissues of the cranio-facial complex during mouse embryonic development and differentiation, and might be a multifunctional protein.

The induction of tuftelin expression in PC12 cell line during hypoxia and NGF-induced differentiation

The tuftelin protein isoforms undergo post‐translation modifications, and are ubiquitously expressed in various tissues in embryos, adults, and tumors. Developmental and pathological studies suggested an apparent correlation between oxygen deprivation and tuftelin expression. The aim of the study was therefore to investigate the effect of a pathological insult (hypoxia) and a physiological growth factor (NGF), which antagonistically regulate HIF1 expression, on tuftelin expression using the neuronal PC12 cell model. In the present study, we first demonstrated the expression of tuftelin in PC12 cells, providing an experimental system to investigate the pathophysiological role of tuftelin. Furthermore, we demonstrated the induction of tuftelin during hypoxia by oxygen deprivation and during chemical hypoxia by cobalt chloride. Down‐regulation of HIF1α mRNA blocked hypoxia‐induced HIF1α expression, and reduced by 89% hypoxia‐induced tuftelin expression. In mice, intraperitoneal injection of cobalt chloride significantly induced tuftelin mRNA and protein expression in the brain. During NGF‐mediated PC12 differentiation, tuftelin expression was significantly induced in correlation with neurite outgrowth. This induction was partially blocked by K252a, a selective antagonist of the NGF receptor TrkA, indicating the involvement of the TrkA‐signaling pathways in tuftelin induction by NGF. Revealing the physiological role of tuftelin will clarify mechanisms related to the “hypoxic genome,” and NGF‐induced neurotrophic and angiogenic effects. J. Cell. Physiol. 226: 165–172, 2010.

Biphasic influence of hypoxia on tuftelin expression in mouse mesenchymal C3H10T1/2 stem cells.

Tuftelin, an acidic protein, thought to play a role in the initial stages of ectodermal enamel mineralization, has since been detected in mesenchymal-derived tissues. During bone/cartilage development and regeneration, mesenchymal stem cells (MSCs) undergo an avascular period in a hypoxic environment, involving induction of hypoxia-inducible factor 1-alpha (HIF-1-alpha), a key component in this process. In the present study we investigated, in a mouse mesenchymal C3H10T1/2 stem cell model, the hypothesis that oxygen stress modulates tuftelin 1 expression in relation to HIF-1-alpha (Hif1a), in a mouse mesenchymal C3H10T1/2 stem cell model. The results of the present study showed a biphasic induction of tuftelin, similar to the pattern of HIF-1-alpha expression, in MSCs subjected to a hypoxic insult of 1% O(2) through a period of 2-24 h. Immunocytochemistry analysis of the cells exposed to hypoxic insult for 2-24 h revealed the same biphasic pattern of tuftelin protein expression. Tuftelin localization appears to be mainly in the cytoplasm, and concentrated at the perinuclear region of the cells by 24 h of hypoxic insult. Based on our previous studies using the neuronal PC12 cell model, in which tuftelin induction was mediated by Hif1a, we propose that tuftelin is a member of oxygen-sensitive genes and implicated in the adaptive mechanisms regulating MSC function.

Functional Reconstruction in Mandibular Avulsion Injuries

AbstractThe present report describes the planning and surgery as well as pitfalls and management of a patient with a near total mandibular avulsion injury that was rehabilitated using three-dimensional (3D) laser printing of a titanium lower jaw. Laser-sintering involves zapping layers of powdered metal to recreate a 3D implantable skeletal defect. The process involves using either mirror imaging of the unaffected side or using archival image database of healthy individuals. A 25-year-old man presented with a gunshot injury that left him with a near total avulsed mandible. The patient received state-of-the-art treatment using a laser 3D printed mandible which was connected to the muscles of mastication for functionality. The inner side of the titanium jaw was filled with the patients comminuted fractured bones in addition to harvested iliac crest bone graft that was covered with the patients remaining periosteal tissue. The implantation of a near total mandible using 3D laser printing is a fast and predictable process that in selected patients can result in aesthetically as well as functionally excellent results. The authors believe that the future of craniofacial reconstruction will employ these methods for facial bony reconstruction.

Skeletal ligament healing using the recombinant human amelogenin protein

Injuries to ligaments are common, painful and debilitating, causing joint instability and impaired protective proprioception sensation around the joint. Healing of torn ligaments usually fails to take place, and surgical replacement or reconstruction is required. Previously, we showed that in vivo application of the recombinant human amelogenin protein (rHAM+) resulted in enhanced healing of the tooth‐supporting tissues. The aim of this study was to evaluate whether amelogenin might also enhance repair of skeletal ligaments. The rat knee medial collateral ligament (MCL) was chosen to prove the concept. Full thickness tear was created and various concentrations of rHAM+, dissolved in propylene glycol alginate (PGA) carrier, were applied to the transected MCL. 12 weeks after transection, the mechanical properties, structure and composition of transected ligaments treated with 0.5 μg/μl rHAM+ were similar to the normal un‐transected ligaments, and were much stronger, stiffer and organized than control ligaments, treated with PGA only. Furthermore, the proprioceptive free nerve endings, in the 0.5 μg/μl rHAM+ treated group, were parallel to the collagen fibres similar to their arrangement in normal ligament, while in the control ligaments the free nerve endings were entrapped in the scar tissue at different directions, not parallel to the axis of the force. Four days after transection, treatment with 0.5 μg/μl rHAM+ increased the amount of cells expressing mesenchymal stem cell markers at the injured site. In conclusion application of rHAM+ dose dependently induced mechanical, structural and sensory healing of torn skeletal ligament. Initially the process involved recruitment and proliferation of cells expressing mesenchymal stem cell markers.

Applications of Distraction Osteogenesis in Oral and Maxillofacial Surgery

Distraction osteogenesis (DO) of facial bones provides an excellent system of membranous bone formation. The bone is generated by stretching a callus that develops following corticotomy or an osteotomy of the facial bones. The use of DO in oral and maxillofacial surgery (OMS) has increased enormously in the last two decades especially for severe bone deficiency. DO is used in the hypoplastic retruded maxilla and midface, such as in cleft palate or Crouzon patients and in the mandible for the treatment of facial asymmetries or in patients with a hypoplastic mandible which may cause airway obstruction associated with obstructive sleep apnea (OSA). In addition, alveolar distraction osteogenesis (ADO) is used for augmentation in patients with severe deficient alveolar bone, prior to dental implantation. The aim of this chapter is to review the current application of distraction osteogenesis in oral and maxillofacial surgery upon the authors experience and based on the literature.

Solitary Frontal Sinus Fractures Compared to Multiple Facial Fractures, Energy Impact Dependency

Abstract Frontal sinus fractures account for 2% to 15% of maxillofacial injuries. Up to 66% to 87% of the patients with frontal sinus fractures experience associated facial fractures. The majority of classifications used today categorize frontal sinus fractures depending on the integrity of the anterior table, posterior table, and the nasofrontal outflow. A retrospective study was performed, which included 24 patients diagnosed with frontal sinus fractures. Treatment in all patients consisted of open reduction and bone fixation. We analyzed population variables, injury etiology, fracture site, associated craniofacial injuries, surgical technique employed, handling of the nasofrontal duct, and postoperative complications. The most frequent etiology was falling accidents. Fifty-eight percent of the fractures involved both the anterior and posterior tables. Sixty-six percent experienced associated facial fractures. Fifty percent of frontal sinus fractures were treated by open reduction internal fixation as the only treatment, 33.3% underwent sinus obliteration, and 16.6% were treated with cranialization. Frontal sinus fractures resulting from high-energy impact exhibited additional facial bone fractures in 100% of the cases, whereas fractures following low-energy impact showed involvement of additional facial fractures in only 27% of the cases. In this report, we suggest a modification to the anteroposterior classification of frontal sinus fractures. In addition to the involvement of the anterior and posterior walls and the degree of dislocation, high and low energy impact can direct us to the involvement of additional facial fractures and influence the surgical strategy.