NF1 Gene Expression in Mouse Fracture Healing and in Experimental Rat Pseudarthrosis

Abstract

(PP) S U M M A R Y Neurofibromatosis type 1 (NF1) is an inherited disease with an incidence of about 1:3000 worldwide. Approximately half of all patients with NF1 present osseous manifestations, which can vary from mild to severely debilitating changes such as congenital pseudarthrosis. In the present study, fracture healing of mouse tibia was followed and specimens were collected 5, 9, 14, and 22 days postoperatively. Experimental pseudarthrosis of rat was followed up to 15 weeks postoperatively. In situ hybridization and immunohistochemistry were used to demonstrate expression of NF1 tumor suppressor and phosphorylated p44/42 mitogen-activated protein kinase (MAPK), an indicator of the Ras-MAPK pathway. The results showed that ossified callus was formed in mouse fracture 22 days after the operation. The final outcome of rat pseudarthrosis was detected 9 weeks after the operation, presenting abundant cartilaginous callus at the pseudarthrosis. NF1 gene expression was noted in the maturing and in the hypertrophic cartilages during normal mouse fracture healing, and in rat pseudarthrosis. Phosphorylated p44/42 MAPK was detected in a subpopulation of the hypertrophic chondrocytes in both models. Furthermore, positive labeling for NF1 mRNA and protein was detected in endothelium in both the pseudarthrosis and in the fracture. In conclusion, NF1 gene expression and function are needed for normal fracture healing, possibly restraining excessive Ras-MAPK pathway activation.

Identification of Novel Gene Expression in Healing Fracture Callus Tissue by DNA Microarray

“…Multiple studies have used a "gene-by-gene" approach to examine the temporal expression of the gene or genes of interest [16][17][18][19][20][21]. This process reveals the spatial distribution of expression, but is not useful in isolating novel genes involved in fracture healing.…”

Modeling bone morphogenetic protein and bisphosphonate combination therapy in wild‐type and Nf1 haploinsufficient mice

“…7 Neurofibromin is expressed in a wide variety of cell types, including osteoblasts, osteoclasts, chondrocytes, and endothelial cells found in healing fractures. 8 Neurofibromin functions as a GTPase activating protein (GAP) that negatively regulates the activity of p21 ras (Ras). 9,10 In some settings, increased Ras activity has been shown to antagonize osteogenic differentiation.…”

Biologic Characteristics of Fibrous Hamartoma from Congenital Pseudarthrosis of the Tibia Associated with Neurofibromatosis Type 1

“…Nf1 is expressed in many types of cells, including maturing chondrocytes, hypertrophic chondrocytes, osteoblasts, osteocytes, and osteoclasts 11 . Furthermore, its expression has been reported at fracture sites in a mouse model and at pseudarthrosis sites in a rat model 12 , suggesting the involvement of mutant Nf1 in the development of pseudarthrosis.…”