Wild-type and engineered adeno-associated viral vectors produce comparable opsin expression and light-evoked responses in rat skeletal muscle

Optogenetics offers a minimally invasive, low-fatigue, and temporally precise alternative to electrical stimulation for skeletal muscle control. After opsin expression in muscle cells, contraction can be stimulated with light. Obstructive sleep apnea, characterized by repeated airway collapse during sleep, suits this approach, as upper airway muscles are readily accessible via the oral cavity, and require stimulation synchronized to respiration. This study compared wild-type (adeno-associated virus 9 [AAV9]) and engineered (AAVMYO) viral vectors for the delivery of identical muscle-specific optogenetic constructs in rats. Three weeks after intramuscular injections, both vectors produced comparable opsin expression in the tongue (<i>p</i> = 0.54) and near-zero expression in non-target tissues. AAVMYO-treated animals had greater light-evoked increases in muscle activation than those treated with AAV9 (8.5-fold vs. 2.0-fold; <i>p</i> < 0.0001). Conversely, AAV9-treated animals had greater light-evoked airway dilation (2.1 mm² vs. 0.3 mm²; <i>p</i> = 0.02). By 12 weeks, opsin expression declined to near-zero (vs. 3 weeks; <i>p</i> < 0.0001), light stimulation no longer increased muscle activation (<i>p</i> > 0.05), and anti-AAV antibodies had significantly increased (<i>p</i> < 0.0001). Unlike in mice, AAVMYO did not consistently outperform AAV9 in delivering gene therapy to rat muscles. Despite this, these data support optogenetics for obstructive sleep apnea, although sustained efficacy requires a better understanding of host immune responses and potentially transient immune suppression.