Brain-derived neurotrophic factor overexpression in taste buds diminishes chemotherapy induced taste loss.

Vismodegib is used in patients suffering from advanced basal cell carcinoma (BCC), but 100% of the patients taking it report dysgeusia and 50% discontinue the treatment. Treatment with neurotrophic factors can stimulate neuronal survival and functional improvement in injured organs. Here, we analysed novel transgenic mouse lines in which brain-derived neurotrophic factor (BDNF) is overexpressed in taste buds, to examine whether higher levels of BDNF would reduce or prevent negative side effects of vismodegib in the taste system. BDNF plays crucial roles for development, target innervation, and survival of gustatory neurons and taste buds. The behavioural test in this study showed that vehicle-treated wild-type mice prefered 10 mM sucrose over water, whereas vismodegib treatment in wild-type mice caused total taste loss. Gustducin-BDNF mice had a significantly increased preference for low concentration of sucrose solution over water compared to wild-type mice, and most importantly the transgenic mice were able to detect low concentrations of sucrose following vismodegib treatment. We evaluated taste cell morphology, identity, innervation and proliferation using immunohistochemistry. All drug-treated mice exhibited deficits, but because of a possible functional upcycled priming of the peripheral gustatory system, GB mice demonstrated better morphological preservation of the peripheral gustatory system. Our study indicates that overexpression of BDNF in taste buds plays a role in preventing degeneration of taste buds. Counteracting the negative side effects of vismodegib treatment might improve compliance and achieve better outcome in patients suffering from advanced BCC.

Targeted taste cell-specific overexpression of brain-derived neurotrophic factor in adult taste buds elevates phosphorylated TrkB protein levels in taste cells, increases taste bud size, and promotes gustatory innervation.

Brain-derived neurotrophic factor (BDNF) is the most potent neurotrophic factor in the peripheral taste system during embryonic development. It is also expressed in adult taste buds. There is a lack of understanding of the role of BDNF in the adult taste system. To address this, we generated novel transgenic mice in which transgene expression was driven by an α-gustducin promoter coupling BDNF expression to the postnatal expression of gustducin in taste cells. Immunohistochemistry revealed significantly stronger BDNF labeling in taste cells of high BDNF-expressing mouse lines compared with controls. We show that taste buds in these mice are significantly larger and have a larger number of taste cells compared with controls. To examine whether innervation was affected in Gust-BDNF mice, we used antibodies to neural cell adhesion molecule (NCAM) and ATP receptor P2X3. The total density of general innervation and specifically the gustatory innervation was markedly increased in high BDNF-expressing mice compared with controls. TrkB and NCAM gene expression in laser capture microdissected taste epithelia were significantly up-regulated in these mice. Up-regulation of TrkB transcripts in taste buds and elevated taste cell-specific TrkB phosphorylation in response to increased BDNF levels indicate that BDNF controls the expression and activation of its high affinity receptor in taste cells. This demonstrates a direct taste cell function for BDNF. BDNF also orchestrates and maintains taste bud innervation. We propose that the Gust-BDNF transgenic mouse models can be employed to further dissect the specific roles of BDNF in the adult taste system.

Oral cancer: enduring characteristics and emerging trends.

Oral cancer is arguably the most serious condition that dental providers may encounter in their practice. The relatively poor prognosis associated with oral cancer highlights the importance of the dental team's awareness of the disease. While many characteristics of oral cancer have endured over time, new research is revealing trends that are changing the way we approach its screening, diagnosis and treatment. In this report, we provide a translational overview of oral cancer, including risk factors, signs and symptoms, clinical management, as well as our recent findings on the role of chronic inflammation in the development of the disease. In addition, our recent genetic profiling approach in both cancer cell lines and in patients has identified potential biomarkers, molecular pathways and therapeutic drugs for oral squamous cell carcinomas. This comprehensive review should be of interest to all dental professionals.

Pro-inflammatory genes as biomarkers and therapeutic targets in oral squamous cell carcinoma.

Oral squamous cell carcinoma (OSCC) is a major health problem worldwide, and patients have a particularly poor 5-year survival rate. Thus, identification of the molecular targets in OSCC and subsequent innovative therapies are greatly needed. Prolonged exposure to alcohol, tobacco, and pathogenic agents are known risk factors and have suggested that chronic inflammation may represent a potential common denominator in the development of OSCC. Microarray analysis of gene expression in OSCC cell lines with high basal NF-κB activity and OSCC patient samples identified dysregulation of many genes involved in inflammation, wound healing, angiogenesis, and growth regulation. In particular IL-8, CCL5, STAT1, and VEGF gene expression was up-regulated in OSCC. Moreover, IL-8 protein levels were significantly higher in OSCC cell lines as compared with normal human oral keratinocytes. Targeting IL-8 expression by siRNA significantly reduced the survival of OSCC cells, indicating that it plays an important role in OSCC development and/or progression. Inhibiting the inflammatory pathway by aspirin and the proteasome/NF-κB pathway by bortezomib resulted in marked reduction in cell viability in OSCC lines. Taken together our studies indicate a strong link between inflammation and OSCC development and reveal IL-8 as a potential mediator. Treatment based on prevention of general inflammation and/or the NF-κB pathway shows promise in OSCCs.

Oral cancer: enduring characteristics and emerging trends.

Oral cancer is arguably the most serious condition that dental providers may encounter in their practice. The relatively poor prognosis associated with oral cancer highlights the importance of the dental team's awareness of the disease. While many characteristics of oral cancer have endured over time, new research is revealing trends that are changing the way we approach its screening, diagnosis and treatment. In this report, we provide a translational overview of oral cancer, including risk factors, signs and symptoms, clinical management, as well as our recent findings on the role of chronic inflammation in the development of the disease. In addition, our recent genetic profiling approach in both cancer cell lines and in patients has identified potential biomarkers, molecular pathways and therapeutic drugs (Velcade and Aspirin) for oral squamous cell carcinomas. This comprehensive review should be of interest to all dental professionals.

Gustatory papillae and taste bud development and maintenance in the absence of TrkB ligands BDNF and NT-4.

Taste buds and the peripheral nerves innervating them are two important components of the peripheral gustatory system. They require appropriate connections for the taste system to function. Neurotrophic factors play crucial roles in the innervation of peripheral sensory organs and tissues. Both brain-derived neurotrophic factor (BDNF) null-mutated and neurotrophin-4 (NT-4) null-mutated mice exhibit peripheral gustatory deficits. BDNF and NT-4 bind to a common high affinity tyrosine kinase receptor, TrkB (NTRK-2), and a common p75 neurotrophin receptor (NGFR). We are currently using a transgenic mouse model to study peripheral taste system development and innervation in the absence of both TrkB ligands. We show that taste cell progenitors express taste cell markers during early stages of taste bud development in both BDNF(-/-)xNT-4(-/-) and wild-type mice. At early embryonic stages, taste bud progenitors express Troma-1, Shh, and Sox2 in all mice. At later stages, lack of innervation becomes a prominent feature in BDNF(-/-)xNT-4(-/-) mice leading to a decreasing number of fungiform papillae and morphologically degenerating taste cells. A total loss of vallate taste cells also occurs in postnatal transgenic mice. Our data indicate an initial independence but a later permissive and essential role for innervation in taste bud development and maintenance.

Taste cell formation does not require gustatory and somatosensory innervation.

Dependency of taste buds and taste papillae on innervation has been debated for a long time. Previous research showed neurotrophins, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), play an important role for the establishment of the lingual gustatory and somatosensory innervation. BDNF null mutant mice showed severe deficits in gustatory innervation and loss of taste buds while NT-3 null mutation reduced lingual somatosensory innervation to tongue papillae. These results proved BDNF or NT-3 null mutations affected different sensory modalities (i.e. gustatory and somatosensory, respectively). In this study, we analyzed taste bud development in BDNFxNT-3 double knockout mice to examine the relationship between taste bud development and gustatory/somatosensory innervation. Our results demonstrate that, at the initial stage, before nerve fibers reached the appropriate areas in the papilla, taste bud formation did not require innervation. However, at the synaptogenic stage, after nerve fibers ramified into the apical epithelium, innervation was required and played an essential role in the development of taste buds/papillae.

Expression patterns of neurotrophic factor mRNAs in developing human teeth.

Neurotrophic factors regulate survival, differentiation, growth and plasticity in the nervous system. In addition, based on their specific and shifting temporospatial expression patterns, neurotrophic factors have been implicated in morphogenetic events during tooth development in rodents. To determine whether these findings in rodents could be related to humans, we have now studied nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), glial cell-line derived neurotrophic factor (GDNF), and neurturin (NTN) mRNA expression patterns in developing human teeth during gestational weeks 6.5-11. Using in situ hybridization histochemistry, we found distinct and specific patterns of neurotrophin and GDNF mRNA expression in the developing human teeth. NGF mRNA labeling was weak and confined predominantly to the dental papilla. BDNF mRNA labeling was stronger than NGF mRNA and was seen in the mesenchyme located lateral to the dental organ, as well as in epithelial structures (inner dental epithelium and enamel knot). NT-3 mRNA was observed in the dental papilla and in the area of the cervical loop. NT-4 mRNA was expressed in both oral and dental epithelia in all stages studied. GDNF mRNA was found in the dental follicle and at different sites in the inner dental epithelium. Weak NTN mRNA labeling was also found in the developing teeth. Based on these findings, we suggest that neurotrophins, GDNF and NTN might be involved in morphogenetic events during early stages of tooth development in humans. Protein gene product (PGP) 9.5-immunoreactive nerve fibers were observed in the dental follicle by 11 weeks coinciding with the labeling for neurotrophic factor mRNAs in this structure. This suggests that these neurotrophic factors might be involved in the innervation of dental structures. The rich expression of neurotrophic factors in developing dental tissues suggests that developing, or possibly adult, dental tissue might be used as an allograft source of trophic support for diseases of the nervous system.

Dental pulp cells provide neurotrophic support for dopaminergic neurons and differentiate into neurons in vitro; implications for tissue engineering and repair in the nervous system.

Glial cell line-derived neurotrophic factor (GDNF) mRNA is highly expressed by dental pulp cells (DPCs) prior to the initiation of dental pulp innervation. We show that radioactively labelled exogenous GDNF is retrogradely transported from neonatal teeth and vibrissae to the trigeminal neurons, indicating that GDNF acts as a classical neurotrophic factor in the trigeminal system. We also show that DPCs from both rats and humans produce nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and GDNF mRNAs in vitro, promote the survival and phenotypic characteristics of embryonic dopaminergic (DA) neurons and protect DA neurons against the neurotoxin 6-hydroxy-dopamine (6-OHDA) in vitro. By using inhibitory antibodies to NGF, BDNF and GDNF, we show that the promotion of DA neuron survival relates to the production and release of neurotrophic proteins by DPCs in vitro. We suggest that in vivo production of neurotrophic factors by DPCs play roles in tooth innervation. However, continued production of neurotrophic factors by the DPCs might have wider implications. We propose that the dental pulp is a viable source of easily attainable cells with possible potential for development of autologous cell transplantation therapies. We also show that a population of neural crest-derived dental pulp cells acquire clear neuronal morphology and protein expression profile in vitro, indicating the presence of a cell population in the dental pulp with neuronal differentiation capacity that might provide additional benefits when grafted into the CNS.

Lingual deficits in neurotrophin double knockout mice.

Brain-derived neurotrophic factor (BDNF) and Neurotrophin 3 (NT-3) are members of the neurotrophin family and are expressed in the developing and adult tongue papillae. BDNF null-mutated mice exhibit specific impairments related to innervation and development of the gustatory system while NT-3 null mice have deficits in their lingual somatosensory innervation. To further evaluate the functional specificity of these neurotrophins in the peripheral gustatory system, we generated double BDNF/NT-3 knockout mice and compared the phenotype to BDNF(-/-) and wild-type mice. Taste papillae morphology was severely distorted in BDNF(-/-) xNT-3(-/-) mice compared to single BDNF(-/-) and wild-type mice. The deficits were found throughout the tongue and all gustatory papillae. There was a significant loss of fungiform papillae and the papillae were smaller in size compared to BDNF(-/-) and wild-type mice. Circumvallate papillae in the double knockouts were smaller and did not contain any intraepithelial nerve fibers. BDNF(-/-) xNT-3(-/-) mice exhibited additive losses in both somatosensory and gustatory innervation indicating that BDNF and NT-3 exert specific roles in the innervation of the tongue. However, the additional loss of fungiform papillae and taste buds in BDNF(-/-) xNT-3(-/-) mice compared to single BDNF knockout mice indicate a synergistic functional role for both BDNF-dependent gustatory and NT-3-dependent somatosensory innervations in taste bud and taste papillae innervation and development.