ABSTRACT
Congenital pseudarthrosis of the tibia (CPT) is a severe pathology marked by spontaneous bone fractures that fail to heal, leading to fibrous nonunion. Half of patients with CPT are affected by the multisystemic genetic disorder neurofibromatosis type 1 (NF1) caused by mutations in the NF1 tumor suppressor gene, a negative regulator of RAS-mitogen-activated protein kinase (MAPK) signaling pathway. Here, we analyzed patients with CPT and Prss56-Nf1 knockout mice to elucidate the pathogenic mechanisms of CPT-related fibrous nonunion and explored a pharmacological approach to treat CPT. We identified NF1-deficient Schwann cells and skeletal stem/progenitor cells (SSPCs) in pathological periosteum as affected cell types driving fibrosis. Whereas NF1-deficient SSPCs adopted a fibrotic fate, NF1-deficient Schwann cells produced critical paracrine factors including transforming growth factor-ß and induced fibrotic differentiation of wild-type SSPCs. To counteract the elevated RAS-MAPK signaling in both NF1-deficient Schwann cells and SSPCs, we used MAPK kinase (MEK) and Src homology 2 containing protein tyrosine phosphatase 2 (SHP2) inhibitors. Combined MEK-SHP2 inhibition in vivo prevented fibrous nonunion in the Prss56-Nf1 knockout mouse model, providing a promising therapeutic strategy for the treatment of fibrous nonunion in CPT.
Subject(s)
Mice, Knockout , Neurofibromin 1 , Protein Tyrosine Phosphatase, Non-Receptor Type 11 , Pseudarthrosis , Schwann Cells , Animals , Female , Humans , Male , Mice , Cell Differentiation/drug effects , Fibrosis , Mitogen-Activated Protein Kinase Kinases/metabolism , Mitogen-Activated Protein Kinase Kinases/antagonists & inhibitors , Neurofibromatosis 1/pathology , Neurofibromatosis 1/metabolism , Neurofibromatosis 1/complications , Neurofibromin 1/metabolism , Neurofibromin 1/genetics , Protein Tyrosine Phosphatase, Non-Receptor Type 11/metabolism , Protein Tyrosine Phosphatase, Non-Receptor Type 11/antagonists & inhibitors , Pseudarthrosis/pathology , Pseudarthrosis/metabolism , Pseudarthrosis/congenital , Schwann Cells/metabolism , Schwann Cells/drug effects , Schwann Cells/pathology , Stem Cells/metabolism , Stem Cells/drug effects , Tibia/pathologyABSTRACT
The 'cough network' exhibits plasticity at the sensor and integration levels leading to modulation of the strength or pattern of the cough reflex. Little is known about the interactions between cough and human activities, especially during exercise. The present study was designed to determine whether exercise, mimicked by electrically induced muscle contractions, can modify the incidence and/or strength of cough following mechanical stimulation of the trachea in anesthetized rabbits. Thirteen anesthetized, tracheotomized rabbits were studied by a total of 311 tracheal stimulations: 196 at rest and 115 during exercise. During muscle contractions, the incidence of the cough reflex (CR) decreased and the expiration reflex (ER) increased (p < 0.0001). The sensitivity of the CR and ER both decreased during exercise compared to the sensitivity of the CR at rest (p < 0.02), while the strength of the expulsive response remained unchanged. These results indicate that adjustments occurring during muscle contractions likely downregulate tracheal defensive reflexes in anesthetized rabbits.
