Overexpressions of nerve growth factor and its tropomyosin-related kinase A receptor on chordoma cells

Chordoma: To know means to recognize

Chordoma is a rare type of bone cancer characterized by its locally aggressive and destructive behavior. Chordoma is located in one of the three primary regions: skull base/clivus, sacrum or mobile spine. Chordoma grows slowly, therefore its insidious onset leads to delayed diagnosis, accounting for the low survival rates. Treatment centers around successful en bloc resection with negative margins, though, considering the anatomically constrained site of growth, it frequently requires adjuvant radiotherapy. This article analyzes the existing literature with the aim to provide a better insight in the current state of research in chordoma classification, characteristics, and management.

Genetic aberrations and molecular biology of skull base chordoma and chondrosarcoma

Chordomas and chondrosarcomas are two major malignant bone neoplasms located at the skull base. These tumors are rarely metastatic, but can be locally invasive and resistant to conventional chemotherapies and radiotherapies. Accordingly, therapeutic approaches for the treatment of these tumors can be difficult. Additionally, their location at the skull base makes them problematic. Although accurate diagnosis of these tumors is important because of their distinct prognoses, distinguishing between these tumor types is difficult due to overlapping radiological and histopathological findings. However, recent accumulation of molecular and genetic studies, including extracranial location analysis, has provided us clues for accurate diagnosis. In this report, we review the genetic aberrations and molecular biology of these two tumor types. Among the abundant genetic features of these tumors, brachyury immunohistochemistry and direct sequencing of IDH1/2 are simple and useful techniques that can be used to distinguish between these tumors. Although it is still unclear why these tumors, which have such distinct genetic backgrounds, show similar histopathological findings, comparison of their genetic backgrounds could provide essential information.

Otoprotective effects of mouse nerve growth factor in DBA/2J mice with early-onset progressive hearing loss

As it displays progressive hair-cell loss and degeneration of spiral ganglion neurons (SGNs) characterized by early-onset progressive hearing loss (ePHL), DBA/2J is an inbred mouse strain widely used in hearing research. Mouse nerve growth factor (mNGF), as a common exogenous nerve growth factor (NGF), has been studied extensively for its ability to promote neuronal survival and growth. To determine whether mNGF can ameliorate progressive hearing loss (PHL) in DBA/2J mice, saline or mNGF was given to DBA/2J mice of either sex by daily intramuscular injection from the 1st to the 9th week after birth. At 5, 7, and 9 weeks of age, in comparison with vehicle groups, mNGF groups experienced decreased auditory-evoked brainstem response (ABR) thresholds and increased distortion product otoacoustic emission (DPOAE) amplitudes, the prevention of hair cell loss, and the inhibition of apoptosis of SGNs. Downregulation of Bak/Bax and Caspase genes and proteins in cochleae of mice receiving the mNGF treatment was detected by real-time PCR, Western blot, and immunohistochemistry. This suggests that the Bak-dependent mitochondrial apoptosis pathway may be involved in the otoprotective mechanism of mNGF in progressive hearing loss of DBA/2J mice. Our results demonstrate that mNGF can act as an otoprotectant in the DBA/2J mice for the early intervention of PHL and, thus, could become of great value in clinical applications. © 2017 Wiley Periodicals, Inc.

Effect of RNA Interference-Mediated Suppression of p75 on the Viability of Rat Notochordal Cells

Study Design

In vitro cell culture model.

Purpose

To investigate the effects of RNA interference (RNAi) on p75 expression and viability of rat notochordal cells treated with serum deprivation.

Overview of Literature

RNAi enables the inhibition of specific genes by sequence-specific gene silencing using a double-stranded RNA.

Methods

Notochordal cells were isolated, cultured, and placed in 10% (control) or 0% (apoptosis-promoting) fetal bovine serum (FBS) for 48 hours. The expression of p75, apoptosis, and cell proliferation were determined. To suppress p75 expression, a small interfering RNA (siRNA) was synthesized against p75 (p75 siRNA) and transfected into cells. The suppression of p75 mRNA expression was investigated using the reverse transcription-polymerase chain reaction. The degree of p75 suppression was semiquantitatively analyzed using densitometry. The effect of p75 siRNA on apoptosis and proliferation of cells was determined. Solutions of an unrelated siRNA and transfection agent alone served as controls.

Results

Serum deprivation significantly increased apoptosis by 40.3%, decreased proliferation of notochordal cells by 45.3% (both, p<0.001), and upregulated p75 expression. The p75 siRNA suppressed p75 expression in cells cultured in 0% FBS. The rate of suppression by p75 siRNA of p75 mRNA was 72.9% (p<0.001). Suppression of p75 expression by p75 siRNA inhibited apoptosis by 7% and increased proliferation by 14% in cells cultured in 0% FBS (both, p<0.05).

Conclusions

siRNA-mediated suppression of p75 inhibited apoptosis and increased proliferation of notochordal cells under conditions of serum deprivation, suggesting that RNAi might serve as a novel therapeutic approach for disc degeneration caused by insufficient viability of disc cells through the suppression of the expression of harmful genes.

The molecular aspects of chordoma

Chordomas are one of the rarest bone tumors, and they originate from remnants of embryonic notochord along the spine, more frequently at the skull base and sacrum. Although they are relatively slow growing and low grade, chordomas are highly recurrent, aggressive, locally invasive, and prone to metastasize to the lungs, bone, and the liver. Chordomas highly and generally show a dual epithelial-mesenchymal differentiation. These tumors resist chemotherapy and radiotherapy; therefore, radical surgery and high-dose radiation are the most used treatments, although there is no standard way to treat the disease. The molecular biology process behind the initiation and progression of a chordoma needs to be revealed for a better understanding of the disease and to develop more effective therapies. Efforts to discover the mysteries of these molecular aspects have delineated several molecular and genetic alterations in this tumor. Here, we review and describe the emerging insights into the molecular landscape of chordomas.

Chordoma: the entity

Chordomas are malignant tumors of the axial skeleton, characterized by their locally invasive and slow but aggressive growth. These neoplasms are presumed to be derived from notochordal remnants with a molecular alteration preceding their malignant transformation. As these tumors are most frequently observed on the skull base and sacrum, patients suffering from a chordoma present with debilitating neurological disease, and have an overall 5-year survival rate of 65%. Surgical resection with adjuvant radiotherapy is the first-choice treatment modality in these patients, since chordomas are resistant to conventional chemotherapy. Even so, management of chordomas can be challenging, as chordoma patients often present with recurrent disease. Recent advances in the understanding of the molecular events that contribute to the development of chordomas are promising; the most novel finding being the identification of brachyury in the disease process. Here we present an overview of the current paradigms and summarize relevant research findings.

Dose- and time-dependent effect of high glucose concentration on viability of notochordal cells and expression of matrix degrading and fibrotic enzymes

PURPOSE

Diabetes mellitus is an important aetiological factor in intervertebral disc degeneration. The disappearance of notochordal cells in the nucleus pulposus is thought to be the starting point for intervertebral disc degeneration. A cellular effect of diabetes mellitus on apoptosis of notochordal cells and intervertebral disc degeneration has been recently reported. However, how the duration and severity of diabetes mellitus affects viability of notochordal cells and intervertebral disc degeneration is still unknown .

METHODS

Rat notochordal cells were isolated, cultured, and placed in either 10 % foetal bovine serum (FBS) (normal control) or 10 % FBS plus three different high glucose concentrations (0.1 M, 0.2 M, and 0.4 M) (experimental conditions) for one, three, five and seven days, respectively. We identified and quantified the degree of proliferation and apoptosis, caspase activities, and cleavages of Bid and cytochrome-c. In addition, we examined the cells for expression of matrix metalloproteinases (MMPs) and their tissue inhibitors of metalloproteinases (TIMPs).

RESULTS

Each three high glucose concentrations significantly decreased proliferation and increased apoptosis of notochordal cells from culture days one to seven in a dose-dependent manner. Compared with those of 10 % FBS, caspase-9 and -3 activities and cleavage of Bid and cytochrome-c were significantly increased in each three high glucose concentrations, accompanied by increased expression of MMP-1, -2, -3, -7, -9, and -13 and TIMP-1 and -2.

CONCLUSIONS

High glucose concentration significantly decreased proliferation and increased apoptosis of notochordal cells via the intrinsic pathway with dose- and time-dependent effects. We also found that expression of MMPs and TIMPs was increased with dose- and time-dependent effects. Therefore, these results suggest that aggressive glucose control from an early stage of diabetes mellitus should be recommended to prevent or limit intervertebral disc degeneration.

Effect of nerve growth factor and its transforming tyrosine kinase protein and low-affinity nerve growth factor receptors on apoptosis of notochordal cells

PURPOSE

The disappearance of notochordal cells by apoptosis is thought to be the starting point of intervertebral disc degeneration. The aim of this study was to determine the apoptotic pathway of notochordal cells as well as the anti-apoptotic potential of caspase inhibitors.

METHODS

Rat notochordal cells were isolated, cultured, and placed in either 0 % (apoptosis-promoting condition) or 10 % (normal control) foetal bovine serum (FBS). We identified and quantified apoptotic cell deaths and caspase activities. In addition, we examined the cells for expression of nerve growth factor (NGF) and its two receptors--TrkA (survival signal) and p75 (apoptotic signal)--and downstream pathways. Finally, we analysed the degree of anti-apoptotic effects of caspase inhibitors on the cells.

RESULTS

The apoptotic rate and expressions of caspase-8 (extrinsic pathway), -9 (intrinsic pathway), and -3 (common executioner) of notochordal cells were increased in 0 % FBS compared with those in 10 % FBS. Expressions of NGF, p75 receptor and JNK downstream pathways were also increased in 0 % FBS. In contrast, expressions of the TrkA receptor and Akt and MAPK downstream pathways were decreased in 0 % FBS. Pancaspase, capase-9 and capase-8 inhibitors significantly reduced apoptotic cell death.

CONCLUSIONS

Our results suggest that notochordal cells undergo apoptosis through both the intrinsic and extrinsic pathways by activation of NGF, p75 receptor, and the JNK downstream pathway. We also found that apoptosis of notochordal cells can be attenuated by caspase inhibitors. Caspase inhibitors may play a therapeutic role in delaying the starting point of disc degeneration that is due to inappropriate or premature excessive apoptosis of notochordal cells.

The biological basis for modern treatment of chordoma

Chordomas are rare malignant tumors arising in bone of the spheno-occiput, sacrum, and vertebral column which can cause neurological deficit. Current management of chordoma involves safe resection followed by radiation therapy. However, surgical resection is often subtotal and chordoma often recurs despite optimal therapy. Despite years of effort, effective adjuvant therapy for denovo, recurrent and metastatic chordoma are absent and 5-year survival is at best 65%. While no chemotherapeutic agent has been demonstrated to be effective against chordoma in vivo, a greater understanding of the genetics and molecular biology of chordoma is opening up avenues of investigation towards the rational development of targeted therapies. Although enthusiasm for the use of already established or new investigational agents will increase with greater understanding of chordoma biology, laboratory studies of these agents are important prior to incorporation into clinical human trials. The authors review the current state of knowledge regarding chordoma and offer insight into potential new therapies for this rare and challenging tumor.

Analysis of the fibroblastic growth factor receptor-RAS/RAF/MEK/ERK-ETS2/brachyury signalling pathway in chordomas

Chordomas are rare primary malignant bone tumours that derive from notochord precursor cells and express brachyury, a molecule involved in notochord development. Little is known about the genetic events responsible for driving the growth of this tumour, but it is well established that brachyury is regulated through fibroblastic growth factor receptors (FGFRs) through RAS/RAF/MEK/ERK and ETS2 in ascidian, Xenopus and zebrafish, although little is known about its regulation in mammals. The aim of this study was to attempt to identify the molecular genetic events that are responsible for the pathogenesis of chordomas with particular focus on the FGFR signalling pathway on the basis of the evidence in the ascidian and Xenopus models that the expression of brachyury requires the activation of this pathway. Immunohistochemistry showed that 47 of 50 chordomas (94%) expressed at least one of the FGFRs, and western blotting showed phosphorylation of fibroblast growth factor receptor substrate 2 alpha (FRS2alpha), an adaptor signalling protein, that links FGFR to the RAS/RAF/MEK/ERK pathway. Screening for mutations in brachyury (all coding exons and promoter), FGFRs 1-4 (previously reported mutations), KRAS (codons 12, 13, 51, 61) and BRAF (exons 11 and 15) failed to show any genetic alterations in 23 chordomas. Fluorescent in situ hybridisation analysis on FGFR4, ETS2 and brachyury failed to show either amplification of these genes, although there was minor allelic gain in brachyury in three tumours, or translocation for ERG and ETS2 loci. The key genetic events responsible for the initiation and progression of chordomas remain to be discovered.