Daniel Toben

Zfp521 controls bone mass by HDAC3-dependent attenuation of Runx2 activity

Zfp521 regulates osteoblast development during lineage commitment and osteoblast maturation by suppressing Runx2 transcriptional activity.

Deterioration of fracture healing in the mouse model of NF1 long bone dysplasia

Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic disease resulting from inactivating mutations in the gene encoding the protein neurofibromin. NF1 manifests as a heritable susceptibility to tumours of neural tissue mainly located in the skin (neurofibromas) and pigmented skin lesions. Besides these more common clinical manifestations, many NF1 patients (50%) have abnormalities of the skeleton. Long bones are often affected (usually the tibia) and the clinical signs range from bowing to spontaneous fractures and non-unions. Here we present the analysis of bone fracture healing in the Nf1(Prx1)-knock-out mouse, a model of NF1 long bone dysplasia. In line with previously reported cortical bone injury results, fracture healing was impaired in Nf1(Prx1) mice. We showed that the defective fracture healing in Nf1(Prx1) mice is characterized by diminished cartilaginous callus formation and a thickening of the periosteal bone. These changes are paralleled by fibrous tissue accumulation within the fracture site. We identify a population of fibrous tissue cells within the Nf1 deficient fracture as alpha-smooth muscle actin positive myofibroblasts. Additionally, histological and in-situ hybridization analysis reveal a direct contact of the fracture site with muscle fascia, suggesting a possible involvement of muscle derived cells in the fracture deterioration.

An easily reproducible and biomechanically standardized model to investigate bone healing in rats, using external fixation / Ein leicht reproduzierbares und biomechanisch standardisiertes Modell zur Untersuchung der Knochenheilung in der Ratte unter Verwendung eines Fixateur Externe

Abstract We have established a new small animal model to investigate the process of bone regeneration. A total of 42 male Sprague-Dawley rats received an osteotomy of the left femur, stabilized with a custom-made external fixator. The fixation method was chosen to create an easily reproducible, biomechanically well-defined model with minimized interference of the implant with the healing zone. At 14 or 56 days post-operation, the animals were sacrificed and examined biomechanically, histologically and radiologically. Radiologically, the femurs of all animals were anatomically positioned directly post-operation and remained in that position throughout the examination period. At 14 days post-operation, a typical periosteal callus formation could be observed both histologically and radiologically. At 56 days post-operation, the osteotomy was almost completely bridged by periosteal callus and the biomechanical competence of the bones was fully restored. Relative to the intact contralateral femur, the torsional stiffness median was 130.3% (interquartile range 118.9–157.7%) and the maximum torsional failure moment median was 135.6% (interquartile range 69.5–208.7%). As this model provides standardized conditions, it is suitable for a wide range of investigations and is particularly valuable for investigations of locally applied therapies, such as osteoconductive materials or osteoinductive factors. Zusammenfassung Wir haben ein neues Kleintiermodell zur Untersuchung der Prozesse der Knochenregeneration etabliert. Bei 42 männlichen Sprague-Dawley-Ratten wurde das linke Femur osteotomiert und mittels eines speziell gefertigten Fixateur Externe stabilisiert. Diese Fixierungsmethode wurde gewählt, um ein leicht reproduzierbares, biomechanisch gut definiertes Modell mit minimaler Beeinflussung der Heilungszone durch das Implantat zu schaffen. 14 bzw. 56 Tage postoperativ wurden die Tiere getötet und biomechanisch, histologisch und radiologisch untersucht. Radiologisch zeigten alle Tiere sowohl direkt postoperativ als auch über den Verlauf des Untersuchungszeitraums eine anatomisch korrekte Reposition des Knochens. 14 Tage postoperativ zeigte sich histologisch wie radiologisch die typische Bildung von periostalem Kallus. 56 Tage postoperativ war die Osteotomie zumeist komplett durch periostalen Knochen überbrückt und die biomechanische Kompetenz des Knochens vollständig wieder hergestellt. Bezogen auf das jeweils intakte kontralaterale Os femoris lag die Torsionssteifigkeit im Median bei 130,3% (Inter-Quartilsabstand= 118,9–157,7%) und das maximale Torsionsmoment im Median bei 135,6% (Inter-Quartilsabstand=69,5– 208,7%). Aufgrund der sehr gut standardisierbaren Bedingungen des Modells eignet es sich für unterschiedlichste Untersuchungen, insbesondere für die Erforschung lokal angewandter Therapien, wie z.B. osteokonduktiver Materialien oder osteoinduktiver Faktoren.