Effects of adenoviral vector-mediated BDNF expression on the bulbectomy-induced apoptosis of olfactory receptor neurons

Basal cells express functional TRPV4 channels in the mouse nasal epithelium

Basal cells in the nasal epithelium (olfactory and airway epithelia) are stem/progenitor cells that are capable of dividing, renewing and differentiating into specialized cells. These stem cells can sense their biophysical microenvironment, but the underlying mechanism of this process remains unknown. Here, we demonstrate the prominent expression of the transient receptor potential vanilloid type 4 (TRPV4) channel, a Ca²⁺-permeable channel that is known to act as a sensor for hypo-osmotic and mechanical stresses, in the basal cells of the mouse nasal epithelium. TRPV4 mRNA was expressed in the basal portions of the prenatal mouse nasal epithelium, and this expression continued into adult mice. The TRPV4 protein was also detected in the basal layers of the nasal epithelium in wild-type but not in TRPV4-knockout (TRPV4-KO) mice. The TRPV4-positive immunoreactions largely overlapped with those of keratin 14 (K14), a marker of basal cells, in the airway epithelium, and they partially overlapped with those of K14 in the olfactory epithelium. Ca²⁺ imaging analysis revealed that hypo-osmotic stimulation and 4α-phorbol 12,13 didecanoate (4α-PDD), both of which are TRPV4 agonists, caused an increase in the cytosolic Ca²⁺ concentration in a subset of primary epithelial cells cultured from the upper parts of the nasal epithelium of the wild-type mice. This response was barely noticeable in cells from similar parts of the epithelium in TRPV4-KO mice. Finally, there was no significant difference in BrdU-labeled proliferation between the olfactory epithelia of wild-type and TRPV4-KO mice under normal conditions. Thus, TRPV4 channels are functionally expressed in basal cells throughout the nasal epithelium and may act as sensors for the development and injury-induced regeneration of basal stem cells.

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TRPV4 is expressed in basal stem cells of the nasal airway and olfactory epithelium.

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TRPV4 expression appears in the nasal epithelium during the late prenatal stages.

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TRPV4 activation causes an increase in cytosolic Ca²⁺ concentration.

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TRPV4 may be involved in a variety of cellular functions in progenitor/stem cells.

BDNF expression in olfactory bulb and epithelium during regeneration of olfactory epithelium

To further understand the roles of growth factors in the olfactory neurogenesis, we studied the mRNA levels of diverse genes in olfactory bulb (OB) and olfactory epithelium (OE) during the regeneration process of OE. mRNA expression levels of various genes in the OB and OE during the regeneration processes of OE from damage induced by methimazole administration were studied by DNA microarray analysis. The results were confirmed by quantitative real-time RT-PCR and immunohistochemistry. Expression levels of various genes dramatically changed during the observation period. Among them, mRNA expression of BDNF dramatically increased in OE during the first 7 days and then decreased. In contrast, mRNA expression of BDNF in OB significantly decreased during the first 7 days after administration and then gradually increased. The changes in the mRNA levels of OMP in OB precisely followed those of OMP in OE and OB. The present results suggest that BDNF in OE contributes to the early stage of regeneration, and BDNF in OB has its role in the late stage of regeneration of olfactory receptor neurons (ORNs).

Bone marrow stem cell transplantation to olfactory epithelium

OBJECTIVES

We sought to develop a new therapeutic strategy for degeneration of olfactory receptor neurons (ORNs).

METHODS

We transplanted into Balb/C mice, locally by transnasal injection and systemically via the tail vain, BrdU-labeled bone marrow stem cells, also known as NRGs, which have the ability to differentiate into neural cells. Bone marrow stem cells engrafted into the olfactory epithelium were examined immunohistochemically.

RESULTS

Compared with previous studies, in which bone marrow was transplanted rather than bone marrow stem cells, migration of transplanted bone marrow stem cells into the olfactory epithelium was observed earlier, and engraftment rates were significantly higher. However, migrated bone marrow stem cells were positive for GAP43 but not for olfactory marker protein.

CONCLUSIONS

These results suggest that engrafted cells had differentiated into premature, but not mature, ORNs. Further experiments using autologous bone marrow stem cells in combination with various growth factors and/or neurotrophic factors should aid the development of new therapeutic methods for degenerated ORNs.

The proto-oncogene BCL6 promotes survival of olfactory sensory neurons

For the mammalian olfactory epithelium to continually detect odorant, neuronal survival, apoptosis, and regeneration must be coordinated. Here, we showed that the proto-oncogene BCL6, which encodes a transcriptional repressor required for lymphocyte terminal differentiation, contributes to the survival of olfactory sensory neurons (OSNs). In the olfactory epithelia of the BCL6 null mutant mice, many OSNs were positive for both OMP and GAP43. The epithelium was relatively thinner, showing many apoptotic signals. These characters were phenotypically similar to those of the wild-type mice treated with nasal lectin irrigation, which acutely induces apoptosis of OSNs. Odorant receptors were expressed normally in the epithelia of the mutant mice, and their overall expression profile based on DNA microarray analyses was roughly similar to that of the apoptosis-induced olfactory epithelia of the wild-type mice. Experimental increase of BCL6 together with green fluorescent protein in OSNs using adenovirus-mediated gene transfer made the epifluorescence last longer than the control fluorescence without exogenous BCL6 after the nasal lectin irrigation, indicating that BCL6 made the infected neurons survive longer. We conclude that BCL6 plays an active role in the survival of OSNs as an anti-apoptotic factor and confers immature OSNs enough time to fully differentiate into mature ones.

Amphibian larvae and zinc sulphate: a suitable model to study the role of brain-derived neurotrophic factor (BDNF) in the neuronal turnover of the olfactory epithelium

The vertebrate olfactory system has fascinated neurobiologists over the last six decades because of its ability to replace its neurons and synaptic connections continuously throughout adult life, under both physiological and pathological conditions. Among the factors that are proposed to be involved in this regenerative potential, brain-derived neurotrophic factor (BDNF) is a candidate for having an important role in the neuronal turnover in the olfactory epithelium (OE) because of its well-documented neurogenic and trophic effects throughout the nervous system. The aim of the present study was to generate a suitable model to study the participation of BDNF in the recovery of the OE after injury in vivo. We developed an experimental design in which the OE of Rhinella arenarum tadpoles could be easily and selectively damaged by immersing the animals in ZnSO(4) solutions of various concentrations for differing time periods. Image analysis of histological sections showed that different combinations of each of these conditions produced statistically different degrees of injury to the olfactory tissue. We also observed that the morphology of the OE was restored within a few days of recovery after ZnSO(4) treatment. Immunohistochemical analysis of BDNF was performed with an antiserum whose specificity was confirmed by Western blotting, and which showed drastic changes in the abundance and distribution pattern of this neurotrophin in the damaged olfactory system. Our results thus suggest that BDNF is involved in the regeneration of the OE of amphibian larvae, and that our approach is suitable for further investigations of this topic.

Effect of Ninjin-yoei-to (Rensheng-Yangrong-Tang) on olfactory behavior after olfactory nerve transection

Ninjin-yoei-to (NYT), a Japanese traditional medicine, is used to treat athrepsia due to surgery, anorexia, cold constitution, and anemia. There are reports of the effects of NYT on the nervous system; however, there have been no behavioral studies of the effect of NYT on olfactory function. The olfactory system undergoes continuous replacement of sensory neurons. Morphologic and behavioral studies have shown that the olfactory system recovers after bilateral olfactory nerve transection (BNX). However, in the humans, olfactory function does not always recover. In this study, we examined the effect of oral NYT on behavioral recovery after BNX. Fourteen mice were subjected to BNX. The regular diet was mixed with 2% NYT (NYT diet). Mice were separated into two groups; seven mice were fed the regular diet (control group), and seven mice were fed the NYT diet (NYT group). NYT was administered beginning 7 days prior to BNX and continuing for 35 days after BNX. Mice in both groups had free access to food and water. Olfactory function was evaluated by testing each mouse's ability to avoid cotton balls treated with acetic acid. After BNX, mice lost their ability to avoid cotton balls treated with acetic acid. In the control group, the time for behavioral recovery after BNX was 28 days. In the NYT group, the time for behavioral recovery after BNX was 21 days. NYT hastened behavioral recovery after BNX. NYT may have therapeutic benefits for patients with olfactory disorders.

Bidirectional changes in water-maze learning following recombinant adenovirus-associated viral vector (rAAV)-mediated brain-derived neurotrophic factor expression in the rat hippocampus

Alterations in hippocampal brain-derived neurotrophic factor (BDNF) expression have been implicated in the pathogenesis of emotional and cognitive dysfunction. Here, we induced BDNF overexpression in the rat hippocampus using recombinant adenovirus-associated viral (rAAV) vectors, and studied its long-term (2 months postinduction) effects on anxiety-related behaviour, exploration in the open field, and spatial learning in the water maze. Although the treatment successfully led to substantial elevation of hippocampal BDNF levels, its effect on spatial learning was bidirectional: a subset of rAAV-induced BDNF-overexpressing rats performed well above control level, whereas the rest were clearly impaired. This behavioural distinction corresponded to two markedly different levels of BDNF overexpression. The increase in dorsal hippocampal BDNF content achieved in the 'water-maze-impaired' subgroup was twice that attained in the 'water-maze-improved' rats. Although neither subgroup of rAAV-induced BDNF-overexpressing rats differed from controls in the open field, the 'water-maze-impaired' subgroup also showed a significant anxiolytic effect. Our results suggest that hippocampal BDNF elevation significantly affects cognitive and emotional behaviours, but the direction and magnitude of the effects critically depend on the precise levels of overexpression. This factor must be taken into account in future studies examining the functional consequences of hippocampal BDNF overexpression.

Bcl-2 expression mediated by Cre/loxP system in olfactory epithelium

To study the Bcl-2 expression mediated by the Cre/loxP recombination system and its effect on prevention of apoptosis in olfactory epithelium. Adenoviral vectors with cassette for Bcl-2 (AxCALNLBcl-2) and Cre recombinase (AxCANCre) were applied to mouse olfactory epithelium by intranasal instillation. The effect of exogenous Bcl-2 expression on prevention of apoptosis of olfactory receptor neurons was investigated using an apoptosis model induced by bulbectomy. The Bcl-2 product was expressed not only in the olfactory receptor neurons but also in the supporting cells. Although statistical analysis did not show significant difference, the number of apoptotic cells in the infected olfactory epithelium on post-bulbectomy day 2 was lower than that of control and the number of survived mature olfactory receptor neurons in the infected olfactory epithelium on post-bulbectomy day 5 was higher than that of control. Although further studies are required for clinical application, the results of our study suggest that this strategy may be able to deliver exogenous Bcl-2 for the treatment of degeneration of olfactory receptor neurons.

Adenovirus-mediated gene transfer in olfactory epithelium and olfactory bulb: a long-term study

OBJECTIVES

We sought to study the spatiotemporal gene expression mediated by adenoviral vector in the olfactory pathways.

METHODS

The replication-defective adenoviral vector AxCALacZ, which encodes the enzyme Escherichia coli beta-galactosidase, was applied to mouse olfactory epithelium by intranasal instillation.

RESULTS

The LacZ gene product, beta-galactosidase, was expressed not only in the olfactory receptor neurons and their axons, but also in the olfactory bulbs. The first evidence of anterograde labeling was observed at postinfection day (PID) 2. At PID 3, beta-galactosidase was strongly expressed in olfactory nerve axons, as well as their terminal glomeruli, in the olfactory bulbs. beta-Galactosidase expression persisted up to PID 90, and there was a significant decrease in the number of labeled neurons at PID 30.

CONCLUSIONS

These results suggest possible long-term effects of adenovirus-mediated gene transfer on the olfactory neurons, as well as the olfactory bulbs.