Prof. Dr. med. Thomas Lenarz PD Dr. med. Timo Stöver
Department of Otolaryngology MHH
0049-511-532-3808 Fax: 0049-511-532-5558
The overall focus of our research activities is the development of a therapy to prevent and treat hearing loss. Thus we aim a) to prevent spiral ganglion cell loss and b) initiate the regrowth of their peripheral processes following deafness. Both aspects are of major importance to reach improvement of the cochlear implant performance. Our work is funded by the European Union (EU) as a part of the EU-BioEar project (http://www.uta.fi/projektit/eubioear/).
The cochlear implant (CI) has been the "success story" of neuroprosthetic devices. Through the development of this device we reach high levels of speech discrimination in most implanted patients. Especially in deaf born children, meanwhile cochlear implant is the therapy of choice to treat deafness. However, speech understanding is individually variable. A significant part of these differences depends on the state of survival and excitability of the auditory nerve cell bodies locating in the spiral ganglion (spiral ganglion cells, SGC). Following the loss of hair cells of the inner ear, the auditory nerve degenerates. The SGC death appears to be due to apoptosis from loss of neurotrophic factors (NTF) provided by the normal inner ear, including activity in the nerve. The latter directly influencing intracellular ion homeostasis and inducing the expression of NTFs that can support nerve survival in a paracrine or autocrine-like manner.
The specific goal of our research is to identify survival factors (largely neurotrophins, NTF, but also electrical stimulation) that will improve the benefits of the cochlear implant to the deaf. Thus our research will provide an intervention that may yield interventions to prevent deafness, will likely effect the development and application of other neuroprostheses, as well as a local intervention that may prevent the degeneration of other cranial nerves and sites in the central nervous system (CNS).
It is well known that substantial changes occur in the afferent neuron following deprivation and sensory experience. The mechanisms that regulate these changes, however, are largely unknown and only very brief information is available regarding the underlying molecular mechanisms of deafness and electrical stimulation. In the auditory system, deafening in neonates and adults produces degenerative changes in the peripheral and central pathways. The expression of these changes can manifest itself as rapid atrophy of dendrites. Such changes are more striking when deafness is induced in neonates compared with adults.
We have reported that early administration of NTF in vivo can protect the SGCs from degeneration following deafness. These findings support studies conducted by others in the auditory system and studies on other peripheral nervous systems which demonstrate that immediate administration of various NTF in vivo reduces neuronal death after injury and the deafferentation.
At this time data indicates SGC survival-effectiveness of brain derived neurotrophic factor (BDNF), neurotrophin - 3 (NT-3) and glial cell line-derived neurotrophic factor (GDNF). These factors and their receptors have been demonstrated in the inner ear. Ciliary neurotrophic factor (CNTF) and acidic fibroblast growth factor (FGF1) have been shown to interact with these NTF in SGC survival and regrowth. However, it is largely unknown how these factors unfold their protective effects on SGC and what common mechanisms underlay their NTF's effects.
Because there are a large number of factors that may be effective in the prevention of apoptosis and to promote regrowth of the peripheral process (and more being discovered daily), an efficient model for surveying the effectiveness of these agents for clinical application must be available. A organ culture of spiral ganglion cells permits such assessments and reduces the use of animals in these studies. In these studies different NTFs, and their dose response function can be evaluated. One approach to this model is the use of cultured spiral ganglions for our approach.
a) Expression changes related to deafness: To determine time dependant gene expression changes in rat, related to deafness. Rats will be deafened chemically and inner ear tissue will be generated at different time points. This project will lead to the discovery of deafness induced gene regulation using gene array techniques as well as conventional molecular biology methods as Northern Blotting and RT-PCR. The results will help to understand the underlying mechanisms of hearing loss and will be used to specifically focus NTF therapy.
b) Expression changes related to electrical stimulation: To determine changes in gene expression induced by electrical stimulation following deafness. Rats will be implanted with a stimulating electrode following deafening. After variable periods of electrical stimulation of the auditory nerve, inner ear tissue will be harvested and used to investigate electrically induced gene expression. The results will help to understand the protective mechanisms induced by elctrical stimulation following deafness and optimize the combined therapy of electrical stimultation and NTF's.
c) Cell culture NTF and ES, identification of gene expression To determine the effects on gene expression of SGC following exposure of different NTF, electrical stimulation and knock out animals. Mice and rat tissue will be used from wild type stems and knock out / in stems to determine differences in effectiveness of NTF in regard to the molecular configuration of the tested tissue. This project will help to elucidate the underlying mechanisms of protective effects on SGC as well as the regrowth inducing stimuli.
d) Gene transfer identified gene To evaluate the effectiveness of overexpressing genes previously determined for protecting SGC from trauma or inducing regrowth of SGC processes. Using either liposomes or viral vector techniques, constructs will be designed to allow gene specific overexpression in organ culture of SCG being used in protection and regrowth assays. This project will test candidate genes for protection and regrowth effectiveness on the auditory nerve in vitro.
Immunohistochemistry, Western Blotting, RNA-Isolation, Northern Blotting, RT-PCR, Cell culture, Gene-Array technique, Gene transfer tehniques
Kanzaki S, Stöver T, Kawamoto K, Prieskorn DM, Altschuler RA, Miller JM, Raphael Y. Glial cell line-derived neurotrophic factor and chronic electrical stimulation prevent VIII cranial nerve degeneration following denervation. J Comp Neurol. 2002 Dec 16;454(3):350-60.
Cho Y, Gong TW, Stöver T, Lomax MI, Altschuler RA. Gene expression profiles of the rat cochlea, cochlear nucleus, and inferior colliculus. J Assoc Res Otolaryngol. 2002 Mar;3(1):54-67.
Kanzaki S, Kawamoto K, Oh SH, Stöver T, Suzuki M, Ishimoto S, Yagi M, Miller JM, Lomax MI, Raphael Y. From gene identification to gene therapy. Audiol Neurootol. 2002 May-Jun;7(3):161-4.
Stöver T, Kawamoto K, Kanzaki S, Raphael Y. Feasibility of inner ear gene transfer after middle ear administration of an adenovirus vector. Laryngorhinootologie. 2001 Aug;80(8):431-5.
Stöver T, Nam Y, Gong TL, Lomax MI, Altschuler RA. Glial cell line-derived neurotrophic factor (GDNF) and its receptor complex are expressed in the auditory nerve of the mature rat cochlea. Hear Res. 2001 May;155(1-2):143-51.
Nam YJ, Stöver T, Hartman SS, Altschuler RA. Upregulation of glial cell line-derived neurotrophic factor (GDNF) in the rat cochlea following noise. Hear Res. 2000 Aug;146(1-2):1-6.
Stöver T, Gong TL, Cho Y, Altschuler RA, Lomax MI. Expression of the GDNF family members and their receptors in the mature rat cochlea. Brain Res Mol Brain Res. 2000 Mar 10;76(1):25-35.
Stöver T, Yagi M, Raphael Y. Transduction of the contralateral ear after adenovirus-mediated cochlear gene transfer. Gene Ther. 2000 Mar;7(5):377-83. Stöver T, Yagi M, Raphael Y. Cochlear gene transfer: round window versus cochleostomy inoculation. Hear Res. 1999 Oct;136(1-2):124-30.