Progress Report on Grants Awarded in 2011
Establishing a Two-Step Protocol for Hair Cell and Auditory Neuron Regeneration
Most cases of deafness involve the death of the sound-sensing cells in the inner ear or the neurons that carry the information to the brain. One strategy to regenerate these cells is to purify the progenitor cells that give rise to them and to understand how these progenitors normally develop into either sensory cells or neurons.
The two laboratories involved in this project have worked with a new type of progenitor cell that can grow and multiply in a dish, allowing researchers to learn which genes allow the cells to continue to multiply and which genes allow the cells to retain the flexibility to develop into multiple kinds of inner-ear cells. They explored how the progenitors change with different growth conditions and have engineered the cells to turn different colors when they changed into one or another kind of cell. Future research will be aimed at identifying specific molecules that can cause progenitors to become either sensory cells or neurons. This work lays the foundation for efforts to engineer these progenitors to repair the damaged cochlea.
Lisa Goodrich, Harvard Medical School
Matthias Lütolf, École Polytechnique Fédérale de Lausanne
Gene Therapy in Mouse Models of Human Deafness
For many years, hopes have been pinned on gene therapy to correct inherited disorders of the nervous system. Gene therapy typically uses engineered viruses to carry corrective genes into those cells specifically damaged by a mutant gene. There are over 300 distinct inherited forms of deafness, and some might be treated in this way. A problem for gene therapy in the inner ear, however, is that there are few viruses known to enter the sensory cells of the inner ear.
In this project, two laboratories—expert in using viruses for experimental physiology of hearing and in using gene therapy for humans—collaborated to explore new viruses to carry genes into sensory cells. Researchers successfully identified an adeno-associated virus type 1 (AAV1) as effective at entering sensory cells, and they tested this virus using a mouse missing a critical gene for hearing. In a dish, the AAV1 could carry a corrective gene into sensory cells from that mouse and repair function; thus proving the basic concept. Injected into ears of deaf mice, the AAV1 was able to enter many, but not all, sensory cells to restore function. Overall, mice carrying a corrective gene that were treated with AAV1 showed some restoration of hearing, an important milestone on the way to gene therapy for human deafness. This work will be continued in the Bertarelli Program in Translational Neuroscience and Neuroengineering, to optimize the efficiency of the technique.
Jeffrey R. Holt, HMS and Boston Children’s Hospital
Patrick Aebischer, EPFL
Biomolecular Therapeutic Delivery into the Inner Ear for Hair Cell Regeneration and Reinnervation
To treat hearing loss caused by the death of the sound-sensing cells in the inner ear, researchers are working to identify factors that might convert other cells into sensory cells and to develop methods of delivering those factors in a specific and controlled manner. For this project, a pioneer in sensory cell regeneration worked with a bioengineer specializing in regenerative factor delivery to develop new ways of delivering regenerative factors to the inner ear, forming research teams. One team worked to discover factors that would induce the conversion into sensory cells. The second team then used engineered proteins or submicroscopic nanoparticles to bind these factors so that they could be injected into a mouse inner ear for slow release. The efficacies of the factors and the delivery system were tested in mice that had lost their sensory cells.
The research identified a set of two factors that shows promise in converting cells to sensory cells, and it showed that nanoparticles are a promising delivery technology. In further work, the group will test the new factors with the nanoparticles. This may lead to treatments to restore hearing, especially in older humans.
Zheng-Yi Chen, HMS and Massachusetts Eye and Ear
Jeffrey Hubbell, Institute of Bioengineering at EPFL
Functional Neural Repair of Sensory and Motor Systems Using Complementary Training, Pharmacological, Genetic and Neurostimulation Strategies
Spinal cord injuries are among the most serious of traumatic injuries in humans, resulting in untreatable paralysis for about half of all cases. For this project, a consortium of four laboratories combined electrical, physical, pharmacological and gene therapy in a rodent model of complete spinal cord injury. Significant progress was made in the following areas:
- A robotic postural neuroprosthesis, developed for training rats that have spinal cord injury, has been miniaturized to work with mice. While mice are ten times smaller, they have significant advantages for research because there are many genetically engineered variants that can be used to understand recovery from injury at a molecular level.
- Miniature, flexible electrode arrays were developed that could be surgically implanted in the spinal cord and could stimulate the cord to promote recovery. Testing shows some improvement following stimulation, which will be repeated with a larger number of test animals. In addition, synchronized electrical stimulation was used together with the robotic walking training to enhance the recovery from injury.
- Earlier studies showed that two genes (PTEN and SOCS3) appear to inhibit the recovery from spinal cord injury, so methods have been developed to prevent the inhibition by those genes. Gene therapy vectors based on adeno-associated virus were found to work to suppress PTEN and to promote regrowth of nerves from the brain to the spinal cord. In parallel work, mice lacking both PTEN and SOCS3 were genetically engineered, and it is expected that the mice will show significantly more recovery from spinal cord injury.
Zhigang He and Clifford Woolf, HMS and Boston Children's
Stéphanie P. Lacour and Grégoire Courtine, EPFL
New Generation Auditory Brain-Stem Implant with Flexible Optoelectronic Arrays for Neurostimulation
The cochlear implant, a device that bypasses a damaged inner ear and conveys electrical signals directly to the auditory nerve, has been an extremely successful neural prosthesis over the past few decades. However, some patients cannot be fitted with cochlear implant because of nerve damage. Instead, a similar prosthesis might be introduced further up the nervous system, specifically in the cochlear nucleus of the brain stem. But existing brain-stem implants have been only moderately effective.
This team of five investigators, with complementary expertise in the auditory brain stem and in electrode and optical design, is designing the next generation of brain-stem implant. Flexible stimulating arrays have been developed that combine both electrical and optical stimulation and can conform to the brain tissue more effectively. These have been tested in mice to show that the signals generated by sound are carried up to higher centers in the nervous system. These promising results will drive a new round of experiments in the second phase of the Bertarelli Program.
Daniel J. Lee and M. Christian Brown, HMS and Mass Eye and Ear
Stéphanie P. Lacour, Philippe Renaud and Nicolas Grandjean, EPFL
Optical Imaging of the Inner Ear for Cellular Diagnosis and Therapy: Cochlear Implants and Beyond
One of the great challenges in diagnosing hearing problems is that the physician cannot see the tissues and cells of the inner ear. In contrast, simple optical methods allow inspection of the retina of the eye. In this project, a physicist specializing in nonlinear optics has collaborated with an otologic surgeon skilled in the anatomy of the human inner ear to develop new imaging methods for the human inner ear.
The team has used new nonlinear optical methods—including optical coherence tomography, second-harmonic generation and excitation of autofluorescence—to look deep into the inner ear in order to assess the health of the individual sensory cells. In initial experiments, these methods were optimized for inner ear cells in a dish, and later experiments applied the new techniques to assess damage in live rodents. For use in humans, microendoscopes will be needed to carry the light out of the ear, and further experiments will optimize the endoscope technology. This will lead to new instruments for diagnosing the health of the inner ear, so the new therapies can be applied more appropriately to different kinds of hearing loss.
Konstantina Stankovic, HMS and Mass Eye and Ear
Demetri Psaltis, EPFL