Developing a neuron replacement therapy to improve breathing, motor function and survival in neurodegenerative disease
Developing a neuron replacement therapy to improve breathing, motor function and survival in neurodegenerative disease. Respiratory failure is the leading cause of death in patients with the neurodegenerative disease Amyotrophic Lateral Sclerosis (ALS), yet there are currently no effective therapies to improve breathing outside of mechanical ventilation. Some human ALS patients use accessory respiratory muscles (ARMs) to help improve ventilation as the diaphragm becomes progressively weaker and those patients breathe better, sleep better, and have a better prognosis than patients with similar diaphragm dysfunction that do not recruit ARMs for breathing. It is not known why some patients recruit ARMs and others do not. Based on our work using the SOD1G 93 mouse model of ALS, we hypothesize that degeneration of spinal V2a neurons prevents accessory respiratory muscles from being recruited for breathing at late stages of disease and accelerates motor neuron degeneration. Thus, we propose that replacing degenerated V2a neurons with embryonic (or stem cell-derived) V2a neurons will restore ARM activity, slow or prevent motor neuron degeneration, and improve breathing and survival of ALS patients. The proposed studies will gauge the potential benefits and identify the greatest barriers to V2a replacement therapy using ALS model mice. We will assess the ability of embryonic V2a neurons implanted into the cervical spinal cords of symptomatic SOD1G 93 mice to integrate into circuits controlling respiratory muscles and restore function. This process requires multiple steps measured by our studies. Cell counts will be used to assess short-term and long-term survival of fluorescently labeled transplanted neurons. Pseudorabies virus tracing will be used to assess synaptic connectivity between transplanted neurons and motor neurons controlling ARMs. A custom physiological system to simultaneously measure ARM activity and ventilation in the same mouse throughout the course of disease progression will be used to assess whether transplanted neurons form functional connections that are able to restore ARM activity and/or improve ventilation. To facilitate our studies, we will implant V2a neurons from transgenic mice that express DREADD receptors to allow us to increase (or decrease) their excitability with a drug-like molecule. This tool will allow us to excite V2a neurons to determine whether transplanted neurons are able to drive ARM activity even in the absence of appropriate upstream connections. We will also assess ARM and diaphragm innervation and phrenic motor neuron survival to determine whether transplanted neurons improve motor neuron survival in ALS model mice. These studies will test the feasibility of using embryonic or stem cell derived V2a neurons to maintain respiratory and motor function in ALS patients.
Dr. Crone was awarded $100,000 over 2 years from L.I.F.E. for his research project.
Steven Crone, PhD
Dr. Steven Crone is an assistant professor in the Division of Pediatric Neurosurgery at Cincinnati Children’s Hospital Medical Center where his laboratory investigates how respiratory circuits are altered by disease and injury. Dr. Crone earned a B.S. (1995) in Molecular and Cellular Biology (with honors) from the Pennsylvania State University and a Ph.D. (2003) from the University of California at San Diego, performing his thesis research at the Salk Institute for Biological Studies. His thesis research demonstrated that the ErbB2 receptor tyrosine kinase is essential for preventing dilated cardiomyopathy and for maintenance of the enteric nervous system, with important implications for the treatment of Hirschsprung’s disease, heart disease and ErbB2/Her2 dependent breast cancer. Dr. Crone performed his postdoctoral work at the University of Chicago where he developed transgenic tools to label, ablate, or alter the activity or function of one particular developmental neuron class (the V2a class) in order to assess its function in motor behaviors. His work established that V2a neurons are important for the speed dependent recruitment of circuits controlling locomotor pattern and gait. He applied the same tools to studying brainstem respiratory circuits to show that V2a neurons provide excitatory drive required to maintain a regular breathing pattern in neonatal mice. Since joining Cincinnati Children’s Hospital Medical Center in 2012, Dr. Crone’s interest in improving breathing in patients with amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), and spinal cord injury led him to investigate the circuits that control accessory respiratory muscles (ARMs), which may be used to augment ventilation when diaphragm function is impaired. As this was a largely unexplored area of research, his laboratory developed a novel physiological system to investigate ARM recruitment as well as transgenic and viral tools to identify neurons that comprise these circuits and test their function. Dr. Crone investigates respiratory circuits from a basic science as well as a translational perspective, with the ultimate goal of developing strategies to augment or repair respiratory circuits to improve breathing in patients with neurodegenerative disease or spinal cord injury.