Amyotrophic lateral sclerosis (ALS) is characterized by the progressive and selective loss of motor neurons (MNs) in the motor cortex, brainstem, and spinal cord, resulting in death of patients 2-5 years after diagnosis. Glutamate-mediated excitotoxicity in the CNS has been implicated as a major contributor to the manifestation of ALS. It is thought that glutamate-mediated excitotoxicity in ALS is due to diminished capacity of motor neurons to handle excessive Ca2+ influx, which serves as a trigger for neurodegeneration. Therefore, the development of drugs which lower Ca2+ influx associated with excitatory activity in CNS is widely considered as an important focal point in the search for therapeutics for ALS. Ionotropic AMPA receptors are glutamate-activated ion channels that are key regulators of Ca2+ influx and the excitatory state of the CNS. We propose to develop novel steric block nucleic acid agents called antisense oligomers (AOs) that will lead to the production of more desensitizable AMPA receptors. AMPA receptors are pentamers composed of 4 subunits termed GluR1-4, present in various homomeric and heteromeric combinations. Two alternatively spliced variants of all GluRs called """"""""flip"""""""" and """"""""flop"""""""" are normally expressed in the CNS. The AMPA """"""""flip"""""""" variants are more resistant to desentization, whereas the """"""""flop"""""""" variants are readily desensitized. Thus, when the flip/flop ratio of GluR1, GluR3 and GluR4 is elevated, the AMPA receptors are resistant to desensitization, and neurons are more excitable and permit greater influx of calcium. In this proposal, we will develop novel AOs that function to specifically lower GluR flip isoform expression, and thus decrease flip/flop ratio. We will evaluate AO efficacy in vitro, including assessment of their functional affects on AMPA currents and also test their efficacy in normal mice after intracerebroventricular (ICV) delivery. We propose that the optimized AOs could lead to a novel therapeutic strategy to treat ALS by increasing GluR subunit-specific AMPA desentization, resulting in neuroprotection. Also, there is evidence that the number of Ca2+-permeable AMPA receptors and the flip/flop ratio may be abnormally high in ALS, further supporting our rationale to develop compounds that increase AMPA channel desensitization. Also, our AOs may be applicable to other disorders where modulating AMPA receptor activity is a focus of current drug discovery, including epilepsy, Parkinsonism, traumatic brain injury, neuropathic pain, and stroke.
We propose to develop and validate compounds called steric block oligomers in pre-clincal studies that could ultimately lead to a novel therapeutic strategy to treat Amyotrophic lateral sclerosis (ALS) in humans, by normalizing synaptic function in spinal motor neurons.
