Mechanisms Underlying Excitability Regulation of Motoneuron Types in ALS

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Project Summary/Abstract Multifarious pathologies of amyotrophic lateral sclerosis (ALS) have been studied, yet effective treatments remain elusive. Abnormalities in motoneuron (MN) excitability remain the most tightly linked to disease path- ogenesis. The central hypothesis of this proposal is that these abnormalities are not an epiphenomenon of ALS, but rather an early pathophysiologic event that initiates the events leading to MN death. Paradoxically, both MN HYPER- and HYPO-excitability changes have been seen at various disease stages, in multiple lines of ALS mice. The lack of clarity on what roles hyper- and hypo-excitability changes play (i.e., neuropro- tective or detrimental), and which ion channels underlie these changes, represents a critical barrier to the development of more effective treatments. The rationale for this proposal is that understanding how hypo- excitability mechanisms also contribute to the increasingly unstable MN environment will fill an important gap in knowledge. The working hypotheses of this proposal are that: 1) Hyper- and hypo-excitable changes in MN properties are not mutually exclusive, but can concurrently exist; 2) they represent fluctuations be- tween disease and compensatory mechanisms; 3) their opposing effects cause excitability fluctuations that are initially manageable; but then escalate in magnitude, eventually leading to MN death; and 4) under- standing the ionic mechanisms underlying both hyper- and hypo-excitability changes can lead to drug tar- gets for stabilization of MN excitability to prevent MN death. The hypotheses will be tested via these Aims: Aim 1: Determine the form of motoneuronal excitability dysregulation at symptom onset, A large array of electrical and anatomical cell properties that modulate excitability will be measured in G93A ALS mouse MNs vs. wild-type (WT) MNs. Aim 2: Identify the cellular mechanisms mediating MN hypo-excitability via computational modeling. High- fidelity computer models will analyze interactions of excitability properties; then predict likely mechanisms. Aim 3: Empirically verify model predictions of reduced Kv2.1 channel activation in MNs and cortical neurons. Electrophysiology, immunohistochemistry, and Western blot experiments will assess the activation and ex- pression levels of ion channels in ALS vs. WT MNs at four key disease stages. If verified, these data would provide the first evidence of concurrent hypo- and hyper-excitability within MNs in ALS, thereby providing a novel mechanism of excitability dysregulation in ALS and frontotemporal lobar degeneration dementia (FTD).