An Unbiased Approach to Search for the Cause of the Reduced Osteogenic Differentiation Potential of NF1-Deficient Osteoprogenitors
Abstract
Our laboratory was one of the first to tackle the underlying causes of a debilitating and challenging orthopaedic manifestation of NF1, called NF1 pseudarthrosis. This condition is characterized by tibia bowing, fracture, and recalcitrant healing and affects mostly children with NF1, who can go through several surgeries without successful bone healing, leading to pain, risk of infection, long hospitalization, and in some cases amputation of the limb at an early age. We have previously used modeling of this manifestation in mice to identify the cell of origin (a skeletal progenitor stem cell) to characterize a failure of bone mineralization and cortical porosity that likely lead to bowing and poor mechanical resistance of this bone, as well as to propose the idea that Asfotase alpha, developed by Alexion Pharmaceutical for another pediatric bone disease, could be repurposed to prevent fracture of the NF1 bowed tibia. Until this can be tested clinically, children with NF1 will still break their bowed tibia; hence we must also spend effort in identifying a treatment that will promote bone union in cases of recalcitrant tibia healing. We know what cell is at fault, but not why mutations in NF1 in these cells leads them to a state where they cannot become bone-forming cells and build up bone at the fracture site, like bone cells from children without NF1 do. We and others have used an “educated guess” strategy to address this question. Although a few targets were identified, and potential drug treatments were successful in mouse models, none of those translated to the clinic yet. This can be explained in part by the potential negative side effects of the proposed drugs that preclude transition to a trial, but also by the fact that the mechanism of action of these drugs is likely not targeting the right cells (the ones with NF1 double-hit mutations). Therefore, the goal of the proposed research project is twofold. First, we are driven by evidence that the almost “generic” focus on blocking activation of ERK signaling in cells with NF1-inactivating mutations is not going to work to correct the reduced ability of NF1-deficient skeletal progenitors to differentiate into bone-forming cells and heal bone. Hence, we aim at identifying, via a non-candidate and state-of-the-art approach (RNA-Seq), the ERK-independent pathway/genes blocking the osteogenic differentiation of skeletal stem cells with NF1-inactivating mutations and their contribution to normal bone healing. This will be performed in both mouse and human cells previously prepared from two patients with NF1 pseudarthrosis, thus raising clinical relevance of the findings and promoting faster transition to future trials. The second goal of this work is to use mouse and human bone progenitor cells deficient for NF1 to functionally test the contribution of identified top candidates to the defect of these cells. This research goes against the mainstay in NF1 research, i.e., activation of ERK signaling as the root of most NF1 manifestations, but has the potential of identifying the correct pathway or genes involved in the most morbid and challenging orthopedic manifestations associated with NF1. If this is accomplished, we and others will “bark at the right tree,” redirect our efforts on new target(s), and design an efficient pharmacological approach to promote bone healing in these children. This is critical to support the orthopaedic management of this condition and related ones, such as NF1 dystrophic scoliosis. With a bit of luck, the newly identify pathway can be targeted with existing drugs, as we have done before, hence reducing time to achieve patient-related outcomes.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 19, 2019
- Source ID
- W81XWH1910574
Entities
People
- Florent Elefteriou
Organizations
- Baylor College of Medicine
- United States Army