Our goal is to use the mechanisms that generate neuronal networks to create neurons from stem cells, to either replace diseased and damaged tissue or as a source of material to study disease mechanisms. A key focus of such regenerative studies is to restore function to the spinal cord, which is particularly vulnerable to damage. However, although considerable progress has been made in understanding how to direct stem cells towards motor neurons that control coordinated movement, little progress has been made so far directing stem cells to form the sensory neurons that allow us to experience the environment around us.
Our proposed research will use insights from the mechanisms known to generate the sensory neurons during the development of the spinal cord, to derive these neurons from stem cells. We will initially use mouse embryonic stem cells in these studies, to accelerate the experimental progress. We will then apply our findings to human embryonic stem cells, and assess whether these cells are competent to repopulate the spinal cord. These studies will significantly advance our understanding of how to generate the full repertoire of neural subtypes necessary to repair the spinal cord after injury, specifically permitting patients to recover sensations such as pain and temperature. Moreover, they also represent a source of therapeutically beneficial cells for modeling debilitating diseases, such as the chronic insensitivity to pain.
Millions of Californians live with compromised nervous systems, damaged by either traumatic injury or disease. These conditions can be devastating, stripping patients of their ability to move, feel and think, and currently have no cure. As well as being debilitating for patients, living with these diseases is also extremely expensive, costing both Californians and the state of California many billions of dollars. For example, the estimated lifetime cost for a single individual managing spinal paralysis is estimated to be up to $3 million.
Stem cell technology offers tremendous hope for reversing or ameliorating both disease and injury states. Stem cells can be used to replenish any tissue damaged by injury or disease, including the spinal cord, which is particularly vulnerable to physical damage. Our proposed studies will develop the means to produce the spinal sensory neurons that permit us to perceive the environment. We will also determine whether these in vitro derived sensory neurons are suitable for transplantation back into the spinal cord. The generation of these neurons will constitute an important step towards reversing or ameliorating spinal injuries, and thereby improve the productivity and quality of life of many Californians. Moreover, progress in this field will solidify the leadership role of California in stem cell research and stimulate the future growth of the biotechnology and pharmaceutical industries within the state.
A promising strategy to treat neurodegenerative diseases is to use embryonic stem cell (ESC)-derived neurons to replace damaged or diseased populations of neurons. In our CIRM-funded studies, we proposed to establish a protocol that will derive spinal sensory interneurons (INs) from ESCs. These INs are required to reestablish the sensory connections that would allow an injured patient to perceive external stimuli, such as pain and temperature. The existence of in vitro derived spinal sensory INs would also accelerate studies examining the basis of debilitating spinal dysfunctions, such as congenital pain insensitivity.
We have made significant progress towards this goal in year 1. We have identified that specific members of the Bone Morphogenetic Protein (BMP) family can direct mouse ESCs towards specific classes of spinal INs. These signals appear to be evolutionally conserved: our preliminary results suggest that BMPs have the same activity directing human ESCs towards spinal sensory IN fates. We are thus well poised to initiate our proposed studies in year 2: assessing whether stem cell derived INs can integrate in the spinal cord.
Recovering sensation after spinal cord injury or disease is both an urgent unmet medical need and an objective that would immeasurably improve the quality of patients’ lives. Although important progress has been made towards rewiring the motor circuits that will permit paralyzed patients to walk, very little progress had been made reestablishing the sensory circuits that permit patients to experience their environment. Sensory circuits are established by spinal interneurons, there are distinct classes of interneurons which permit us to position our bodies in space, touch our children, and detect and avoid the painful stimuli that can result in serious physical damage. This award has permitted us to make progress on this problem: we have established protocols to derive spinal interneurons from human stem cells for the first time, as well as gaining a deep understanding into the molecular mechanisms that generate spinal interneurons during development. We are now poised to start assessing whether the stem cell derived sensory interneurons are functionally identical to their in vivo counterparts.