acid-phosphatase and Neurofibromatosis-1

Neurofibromatosis type 1 (NF1) is a common genetic condition caused by mutations in the NF1 gene. Patients often suffer from tissue-specific lesions associated with local double-inactivation of NF1. In this study, we generated a novel fracture model to investigate the mechanism underlying congenital pseudarthrosis of the tibia (CPT) associated with NF1. We used a Cre-expressing adenovirus (AdCre) to inactivate Nf1 in vitro in cultured osteoprogenitors and osteoblasts, and in vivo in the fracture callus of Nf1(flox/flox) and Nf1(flox/-) mice. The effects of the presence of Nf1(null) cells were extensively examined. Cultured Nf1(null)-committed osteoprogenitors from neonatal calvaria failed to differentiate and express mature osteoblastic markers, even with recombinant bone morphogenetic protein-2 (rhBMP-2) treatment. Similarly, Nf1(null)-inducible osteoprogenitors obtained from Nf1 MyoDnull mouse muscle were also unresponsive to rhBMP-2. In both closed and open fracture models in Nf1(flox/flox) and Nf1(flox/-) mice, local AdCre injection significantly impaired bone healing, with fracture union being <50% that of wild type controls. No significant difference was seen between Nf1(flox/flox) and Nf1(flox/-) mice. Histological analyses showed invasion of the Nf1(null) fractures by fibrous and highly proliferative tissue. Mean amounts of fibrous tissue were increased upward of 10-fold in Nf1(null) fractures and bromodeoxyuridine (BrdU) staining in closed fractures showed increased numbers of proliferating cells. In Nf1(null) fractures, tartrate-resistant acid phosphatase-positive (TRAP+) cells were frequently observed within the fibrous tissue, not lining a bone surface. In summary, we report that local Nf1 deletion in a fracture callus is sufficient to impair bony union and recapitulate histological features of clinical CPT. Cell culture findings support the concept that Nf1 double inactivation impairs early osteoblastic differentiation. This model provides valuable insight into the pathobiology of the disease, and will be helpful for trialing therapeutic compounds.

Topics: Acid Phosphatase; Animals; Bone Morphogenetic Protein 2; Cell Differentiation; Cell Lineage; Cell Proliferation; Disease Models, Animal; Female; Fibrosis; Fracture Healing; Gene Deletion; HEK293 Cells; Humans; Integrases; Isoenzymes; Mice; Mice, Inbred C57BL; Mice, Knockout; Muscles; Neurofibromatosis 1; Neurofibromin 1; Osteoblasts; Osteoclasts; Osteogenesis; Pseudarthrosis; Recombinant Proteins; Reproducibility of Results; Tartrate-Resistant Acid Phosphatase; Tibia; Transforming Growth Factor beta

Patients with neurofibromatosis 1 (NF1) are shorter than expected and often have low bone mineral density (BMD), but the pathogenesis of these bony problems is poorly understood.. We performed an exploratory study of BMD, 18 laboratory measures of bone metabolism, and fracture history in 72 adult NF1 patients.. Eight of the 18 clinical biochemical measures of bone health had at least 10% of NF1 patients outside the standard reference range. Serum 25-hydroxy-vitamin D concentrations were low in 56% of the NF1 patients, serum parathyroid hormone (PTH) concentrations were high in 34%, and urine deoxypyridinoline cross-link concentrations were high in 50%. Mean serum 25-hydroxy-vitamin D concentrations were significantly lower in people with NF1 than in season matched controls in both summer (p = 0.008) and winter (p<0.001). 36 (50%) of the 72 people with NF1 studied had BMD consistent with osteopenia, and 14 (19%) had BMD consistent with osteoporosis. High serum PTH concentration, high serum bone tartrate resistant acid phosphatase concentration, and high serum calcium concentration were associated with lower BMD among the NF1 patients. Males were more likely than females to have low BMD. The reported frequency of fractures in individuals with NF1 was much higher than in their unaffected siblings and spouses (p<0.001), and pathological fractures were reported only in NF1 patients.. People with NF1 often have a generalised abnormality of bone metabolism. Further studies are needed to determine the biochemical and molecular basis of this abnormality.

Topics: Acid Phosphatase; Adult; Aged; Amino Acids; Animals; Bone Density; Bone Diseases, Metabolic; Calcium; Female; Fractures, Bone; Humans; Isoenzymes; Logistic Models; Male; Middle Aged; Multivariate Analysis; Neurofibromatosis 1; Osteoporosis; Parathyroid Hormone; Phosphates; Tartrate-Resistant Acid Phosphatase; Vitamin D; Young Adult

The melanin macroglobule (MMG), formerly called "macromelanosome," is a cytoplasmic spherical granule formed in the melanocyte, varying in size from one to several microns, much larger than normal ellipsoidal melanosomes. Although ultrastructural features of MMG have been adequately described in the past, there has been a disagreement about the formation process of MMG. In order to further elucidate the nature and origin of MMG, electron microscopic studies were conducted in several pigmentary disorders. Our findings included: (1) The most remarkable characteristics of MMG are (a) the pleomorphism of their internal structure and (b) the variation of their size. (2) MMG do not represent true melanosomes but unique forms of autolysosomes resulting from the fusion of autophagosomes (containing various numbers of melanosomes) with primary and/or secondary lysosomes. (3) MMG are retained within melanocytes or transferred to keratinocytes and to Langerhans cells in the epidermis, and to macrophages in the dermis in any of their developmental stages. After transfer, MMG can fuse with other heterolysosomes and probably increase in size in these cells. We regard melanosome complexes as but one step in an autophagic process within melanocytes which can, on occasion, produce MMG as residual bodies.

Topics: Acid Phosphatase; Albinism; Autophagy; Biopsy; Eye Diseases; Histocytochemistry; Humans; Melanocytes; Microscopy, Electron; Microscopy, Electron, Scanning; Monophenol Monooxygenase; Neurofibromatosis 1; Nevus, Pigmented; Skin Neoplasms; Terminology as Topic