The reduced osteogenic potential of Nf1-deficient osteoprogenitors is EGFR-independent

Abstract

Neurofibromatosis type 1 (NF1) is a common genetic disorder caused by mutations in the NF1 gene. Recalcitrant bone healing following fracture (i.e. pseudarthrosis) is one of the most problematic skeletal complications associated with NF1. The etiology of this condition is still unclear; thus, pharmacological options for clinical management are limited. Multiple studies have shown the reduced osteogenic potential of Nf1-deficient osteoprogenitors. A recent transcriptome profiling investigation revealed that EREG and EGFR, encoding epiregulin and its receptor Epidermal Growth Factor Receptor 1, respectively, were among the top over-expressed genes in cells of the NF1 pseudarthrosis site. Because EGFR stimulation is known to inhibit osteogenic differentiation, we hypothesized that increased EREG and EGFR expression in NF1-deficient skeletal progenitors may contribute to their reduced osteogenic differentiation potential. In this study, we first confirmed via single-cell mRNA sequencing that EREG over-expression was associated with NF1 second hit somatic mutations in human bone cells, whereas Transforming Growth Factor beta 1 (TGFβ1) expression was unchanged. Second, using ex-vivo recombined Nf1-deficient mouse bone marrow stromal cells (mBMSCs), we show that this molecular signature is conserved between mice and humans, and that epiregulin generated by these cells is overexpressed and active, whereas soluble TGFβ1 expression and activity are not affected. However, blocking either epiregulin function or EGFR signaling by EGFR1 or pan EGFR inhibition (using AG-1478 and Poziotinib respectively) did not correct the differentiation defect of Nf1-deficient mBMSCs, as measured by the expression of Alpl, Ibsp and alkaline phosphatase activity. These results suggest that clinically available drugs aimed at inhibiting EGFR signaling are unlikely to have a significant benefit for the management of bone non-union in children with NF1 PA.

The neurofibromatosis type I gene promotes autophagy via mTORC1 signalling pathway to enhance new bone formation after fracture

“…Previous study conducted by Kuorilehto et al associated the NF1 gene expression with mouse fracture healing and rat pseudarthrosis, 14 and reported normal NF1 function was needed to achieve a normal bone fracture healing. When NF1 function is impaired, reduced osteogenic activity is seen in NF1 ‐deficient model 15 . In our current study, we found reduced NF1 expression in non‐union bones as compared to normal fracture bones, supporting the theory that NF1 is critical in bone fracture healing process.…”

“…When NF1 function is impaired, reduced osteogenic activity is seen in NF1-deficient model. 15 In our current study, we found reduced NF1 expression in non-union bones as compared to normal fracture bones, supporting the theory that NF1 is critical in bone fracture healing process. Autophagy is the process that allows cells to recycle damaged cellular components, and it plays an essential role in multiple tissue functions such as liver 16 and bone, 17 as well as in diseases such as cancers.…”

Unilateral Creeping Destruction of Deformed Mandibular Ramus and Angle Associated with Extensive Facial Plexiform Neurofibroma in Neurofibromatosis Type 1: A Case Report with Analysis of the Literature for Diagnosing Osteolytic Events of the Mandible in Tumor-suppressor Gene Syndrome

“…However, the residual ramus had been resorbed. regeneration and bone repair of patients with NF1 (11). This condition may be involved in bone malformations of these patients.…”

Targeting Super-Enhancer–Associated Oncogenes in Osteosarcoma with THZ2, a Covalent CDK7 Inhibitor

“…In addition to coding RNAs, these super-enhancers have been reported to drive the expression of long non-coding RNAs such as MALAT1 (39), and microRNAs such as MIR663B (40) and MIR21 (41), which have been reported to contribute to osteosarcoma malignancy. In addition, some lineage-specific transcription factors which regulate skeletal development, such as GLI2 (42), LIF (43), MDM2 (44), RUNX2 (45), and EGFR (46), were found to be associated with super-enhancers ( Fig. 1A and C).…”