Modeling Hemifacial Spasm in Mice

PROJECT SUMMARY/ABSTRACT Hemifacial spasm (HFS) is a chronic neuromuscular disorder characterized by involuntary facial muscle contractions, typically affecting one side of the face. It significantly impairs the quality of life of patients by causing social embarrassment, functional blindness, and psychological distress. The current treatments for HFS, such as Botulinum neurotoxin Type A (BoNT/A) injections and microvascular decompression (MVD) surgery, provide symptom relief but do not address the underlying pathophysiological mechanisms, resulting in recurring symptoms for many patients. One of the primary challenges in advancing the understanding of HFS is the lack of an animal model that accurately replicates the clinical features of the disorder. Evidence suggests that hyperactivity of the facial nerve due to demyelination is associated with HFS. However, no existing rodent model has successfully imitated the spontaneous and involuntary nature of facial muscle contractions seen in HFS patients. This proposal aims to develop a novel rodent model of HFS using lysophosphatidic acid (LPA)-induced demyelination of the facial nerve roots, closely replicating the clinical manifestations of HFS. We hypothesize that demyelination of the facial nerve root at the root entry/exit zone (REZ) leads to hyperactivity of the facial nucleus, which drives HFS-like behavior in mice. Preliminary data strongly support this hypothesis, demonstrating that LPA injection into the facial nerve roots leads to robust HFS-like behavior, including asymmetrical eyelid twitching, whisker pad twitching with lip pulling, ear retraction, and forced eyelid closure. Additionally, electromyography (EMG) revealed increased burst activity in the facial muscles, and microelectrode array (MEA) recordings confirmed heightened activity in the facial nucleus of LPA-injected mice. To rigorously validate the facial spasm behavior and investigate the neural mechanisms underlying HFS, we propose three specific aims: Aim 1: Validate the HFS rodent model by employing DeepLabCut machine learning to accurately quantify facial muscle dynamics and assess facial spasm behavior with high precision. Aim 2: Assess the dynamics of cholinergic neurons in the facial nucleus using a viral strategy and intravital calcium imaging in Chat- Cre mice following facial nerve root demyelination. Aim 3: Investigate the effects of optogenetic and chemogenetic manipulation of facial nucleus activity on HFS-like behavior, determining whether modulating neuronal hyperactivity can alleviate the neuromuscular disorder. This approach will provide mechanistic insights into the role of the facial nucleus in HFS and identify potential therapeutic targets. Collectively, this project aims to validate a rodent model of HFS, elucidate the underlying neural mechanisms, and pave the way for the development of novel therapeutic strategies targeting the neural substrate involved in HFS. The insights gained from this study could significantly impact the treatment of HFS and contribute to improving HFS patient outcomes.