Role of Fas and Treg Cells in Fracture Healing as Characterized in the Fas-Deficient (lpr) Mouse Model of Lupus

Previous studies showed that loss of tumor necrosis factor α (TNFα) signaling delayed fracture healing by delaying chondrocyte apoptosis and cartilage resorption. Mechanistic studies showed that TNFα induced Fas expression within chondrocytes; however, the degree to which chondrocyte apoptosis is mediated by TNFα alone or dependent on the induction of Fas is unclear. This question was addressed by assessing fracture healing in Fas-deficient B6.MRL/Faslpr/J mice. Loss of Fas delayed cartilage resorption but also lowered bone fraction in the calluses. The reduced bone fraction was related to elevated rates of coupled bone turnover in the B6.MRL/Faslpr/J calluses, as evidenced by higher osteoclast numbers and increased osteogenesis. Analysis of the apoptotic marker caspase 3 showed fewer positive chondrocytes and osteoclasts in calluses of B6.MRL/Faslpr/J mice. To determine if an active autoimmune state contributed to increased bone turnover, the levels of activated T cells and Treg cells were assessed. B6.MRL/Faslpr/J mice had elevated Treg cells in both spleens and bones of B6.MRL/Faslpr/J but decreased percentage of activated T cells in bone tissues. Fracture led to ∼30% to 60% systemic increase in Treg cells in both wild-type and B6.MRL/Faslpr/J bone tissues during the period of cartilage formation and resorption but either decreased (wild type) or left unchanged (B6.MRL/Faslpr/J) the numbers of activated T cells in bone. These results show that an active autoimmune state is inhibited during the period of cartilage resorption and suggest that iTreg cells play a functional role in this process. These data show that loss of Fas activity specifically in chondrocytes prolonged the life span of chondrocytes and that Fas synergized with TNFα signaling to mediate chondrocyte apoptosis. Conversely, loss of Fas systemically led to increased osteoclast numbers during later periods of fracture healing and increased osteogenesis. These findings suggest that retention of viable chondrocytes locally inhibits osteoclast activity or matrix proteolysis during cartilage resorption

Diminished Bone Formation During Diabetic Fracture Healing Is Related to the Premature Resorption of Cartilage Associated with Increased Osteoclast Activity

Histological and molecular analysis of fracture healing in normal and diabetic animals showed significantly enhanced removal of cartilage in diabetic animals. Increased cartilage turnover was associated with elevated osteoclast numbers, a higher expression of genes that promote osteoclastogenesis, and diminished primary bone formation. Introduction Diminished bone formation, an increased incidence of nonunions, and delayed fracture healing have been observed in animal models and in patients with diabetes. Fracture healing is characterized by the formation of a stabilizing callus in which cartilage is formed and then resorbed and replaced by bone. To gain insight into how diabetes affects fracture healing, studies were carried out focusing on the impact of diabetes on the transition from cartilage to bone. Materials and Methods A low-dose treatment protocol of streptozotocin in CD-1 mice was used to induce a type 1 diabetic condition. After mice were hyperglycemic for 3 weeks, controlled closed simple transverse fractures of the tibia were induced and fixed by intramedullary pins. Histomorphometric analysis of the tibias obtained 12, 16, and 22 days after fracture was performed across the fracture callus at 0.5 mm proximal and distal increments using computer-assisted image analysis. Another group of 16-day samples were examined by μCT. RNA was isolated from a separate set of animals, and the expression of genes that reflect the formation and removal of cartilage and bone was measured by real-time PCR. Results Molecular analysis of collagen types II and X mRNA expression showed that cartilage formation was the same during the initial period of callus formation. Histomorphometric analysis of day 12 fracture calluses showed that callus size and cartilage area were also similar in normoglycemic and diabetic mice. In contrast, on day 16, callus size, cartilage tissue, and new bone area were 2.0-, 4.4-, and 1.5-fold larger, respectively, in the normoglycemic compared with the diabetic group (p \u3c 0.05). Analysis of μCT images indicated that the bone volume in the normoglycemic animals was 38% larger than in diabetic animals. There were 78% more osteoclasts in the diabetic group compared with the normoglycemic group (p \u3c 0.05) on day 16, consistent with the reduction in cartilage. Real-time PCR showed significantly elevated levels of mRNA expression for TNF-α, macrophage-colony stimulating factor, RANKL, and vascular endothelial growth factor-A in the diabetic group. Similarly, the mRNA encoding ADAMTS 4 and 5, major aggrecanases that degrade cartilage, was also elevated in diabetic animals. Conclusions These results suggest that impaired fracture healing in diabetes is characterized by increased rates of cartilage resorption. This premature loss of cartilage leads to a reduction in callus size and contributes to decreased bone formation and mechanical strength frequently reported in diabetic fracture healing

Experimental fracture healing in Fas Mutant Mice (B6.MRL/FasLPR/J)

PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact [email protected] (D.Sc.D.)--Boston University, Goldman School of Dental Medicine, 2007 (Oral and Maxillofacial Surgery).Includes bibliography: leaves 111-130.Introduction: The term "osteoimmunology" is a new concept that has received much attention in the recent years. It refers to the relationship between the immune system and skeletal system. lt is based on observations that bone destruction is caused by an abnormaI activation of the immune system in rheumatoid arthritis, and that mice lacking immunomoduIatory molecules often exhibit an unexpected bone phenotype. Fas, an important memberoOf the TNF superfamily and death receptor provides apoptosis for many key cell types which participate in normaI bone remodeling as well as the endochondral healing process. Fas is a critical receptor in regulating the life cycle of osteoclasts. Osteoclastogenesis has been implicated in many disease processes such as osteoporosis. Studies on fracture healing in TNFR1 and TNRR2 knock-out mice have shown that chondrocyte apoptosis through TNF[alpha] is an essential step in endochondraI bone formation (Gerstenfeld et al, 2003). Furthermore; TNF[alpha] was demonstrated to upregulate Fas expression (Cho et al, 2003). Since both receptors mediate apoptosis of essential cells involved in the fracture healing process (chondrocytes and osteoclasts), the functional inter-relationship between the TNF[alpha] receptors and Fas must be defined. Materials and Methods: Experimental closed femur fractures were generated in 8-10 week oId male B6.MRL/Fas[lpr]/J mice and their control, C57BL/B6 mice. These mice exhibit Fas receptor mutation and are a well-established modeI for systemic lupus erythematosus (SLE). The mice were sacrificed and bones were harvested for both strains on days 0, 3, 5, 10, 14, 21, 28 for molecular analysis by RPA and RT-PCR, on days 21 and 35 for microcomputed tomography and mechanical testing and on days 14 and 21 for histomorphometry. Results: Calluses in the B6.MRL/Fas[lpr]/J showed a lower ratio of bone volume to total callus volume than in the controIs on day 35 (P[less than]0.05). Trabecular number and thickness on day 35 were lower in the B6.MRL/Fas[lpr]/J calluses (P=0.001 and p=0.024) whiIe trabecular spacing was higher (P=0.0089). The fractured control femurs sustained a higher maximum torque than the B6.MRL/Fas[lpr]/J strain (P=0.005). Histomorphometric analysis demonstrated a higher TRAP-positive cell count per area of bone and cartilage in the day 21 B6.MRL/Fas[lpr]/J sections as well as a higher total calIus area in days 14 and 21. The extracellular matrix RPA demonstrated that there was no difference in cartilage marker expression (type ll and X collagen). An over-expression of ECM proteins (OPN, BSP, OC and type I collagen) was observed in the B6.MRL/Fas[lpr]/J fractures at later time-points during secondary bone formation (d14 - 28). Osteoclastic markers and key osteoclastic regulators which were assayed by RT-PCR showed a trend toward increased osteoclastogenesis. Conclusion: In conclusion, our data shows that the B6.MRL/Fas[lpr]/J bones are weaker on mechanical testing and exhibit less bone volume fraction. The trabeculae are thinner, Iess in number and more porous. The number of TRAP-positive cells per area of bone and cartilage was greater in the B6.MRL/Fas[lpr]/J day 21 histological sections and this corresponded to a higher ratio of RANKL/OPG at days 21 and 28. An examination of initial endochondral bone formation requires the coupling between bone formation and resorption through a balance between osteoblasts and osteoclasts. From these data, we determined that there is a higher osteoclast activity in the B6.MRL/Fas[lpr]/J yet more expression of extracellular matrix proteins at later stages in the fracture repair. We conclude that there is a state of high turnover osteopenia occurring in the B6.MRL/Fas[lpr]/J mouse

Evaluating the use of role-play simulations in teaching management of medical emergencies in the dental clinic

Abstract Background Practical hands-on training is necessary for clinical competence in managing medical emergencies in the dental setting. Therefore, the King Abdulaziz University Faculty of Dentistry developed a role-play simulation-based clinical module for training clinical years (Years 4, 5, and 6) dental students in medical emergency management between 2016 and 2020. This study aimed to assess the knowledge and skills of years 4, 5, and 6 dental students before and after the completion of the role-play simulation-based medical emergency training module. Methods A mandatory four-hour annual training module was designed consisting of a 45-minute lecture on the medical emergency basic action plan and overview, four hands-on stations, and six role-play simulation-based medical emergency stations. A 16-item multiple choice test was used to assess the knowledge of the students before and after the training module every academic year. An objective structured clinical exam (OSCE) on a medical emergency scenario was administered to the students graduating each year. The difference between the pre- and post-module test scores and the one-time OSCE pass/fail rate were analyzed statistically using appropriate tests. Results A total of 846 students participated in the study between 2017 and 2020: 275 once, 483 twice, 87 thrice, and one participated four times; in total, 1,506 assessments were conducted. Overall, the pre-test and post-test mean scores were 9.4 ± 3.0 and 13.5 ± 1.6, respectively. All students showed significant improvements in the post-test scores compared to the pre-test scores. Year 4 students showed the highest improvement, followed by Year 5 and Year 6. There was a statistically significant association between the pass/fail rate of the OSCE station and the number of times the module was taken. Conclusions The significant improvement in the scores of clinical year students in this study supports an annual mandate for all dental students to undergo simulation-based competency training in their clinical years. Teaching institutions are recommended to utilize simulation and hands-on instruction to teach medical emergency management

Surgical Orthodontic Treatment of Severe Skeletal Class II

This paper describes an adult Saudi male patient who presented with a severe skeletal class II deformity. The case was managed with a combination of presurgical orthodontic treatment followed by a double jaw orthognathic surgery and then another phase of orthodontic treatment for final occlusal detailing. Extraction of the four first premolars was done during the presurgical orthodontic phase of treatment to decompensate upper and lower incisors and to give room for surgical setback of the maxillary anterior segment. Double jaw surgery was performed: bilateral sagittal split ramus osteotomy for 8 mm mandibular advancement combined with three-piece Le Fort I maxillary osteotomy, 6 mm setback of the anterior segment, 8 mm impaction of the maxilla, and 5 mm advancement genioplasty. Although the anteroposterior discrepancy and the facial convexity were so severe, highly acceptable results were obtained, both esthetically as well as occlusally

Variation of pediatric and adolescents head and neck pathology in the city of Jeddah: A retrospective analysis over 10 years

AbstractThis study was conducted to present a comprehensive view of the most common head and neck pathologies among the pediatric and adolescent population of the city of Jeddah, Saudi Arabia. Data were collected from the oral and maxillofacial surgery (OMFS) records at King Abdulaziz University Hospital and King Fahad Hospital Jeddah (KFHJ) from the period 1998 to 2009. All patients who were 18years of age and younger were included in the study. Identified lesions were classified into four categories: cystic, neoplastic, vascular and fibro-osseous. Age and sex distribution of the lesions were also calculated. A total of 155 patients were included in this study. Of all the lesions, 143 (92.26%) were benign and 12 (7.74%) were malignant; 63 (40.65%) were cysts; 48 (30.97%) were neoplasms; 23 (14.84%) were vascular and 21 (13.55%) were fibro-osseous tumors. The most common lesions were hemangioma (20 cases; 12.9%) followed by retention cyst (19 cases; 12.26%) and dentigerous cyst (15 cases; 9.68%). The most common benign odontogenic neoplasm was odontoma (7 cases; 4.52%), of which central giant cell granuloma (6 cases; 3.87%) was the most frequent benign nonodontogenic tumor and lymphoma (6 cases; 3.87%) was the most common malignant one. Although this study might benefit clinicians in guiding them through differential diagnosis of pediatric and adolescent head and neck pathology in reference to their sex and age groups, governmental efforts are badly needed to establish a Saudi childhood pathology registry