P063 Optogenetics for Obstructive Sleep Apnea

Introduction We propose a novel sleep apnea therapy whereby a viral vector construct induces opsin expression and therefore light sensitivity to the upper airway muscles. Pulsed light to these muscles during sleep will enhance muscle contractions resulting in airway dilation and apnea prevention. Here we investigate the therapy’s feasibility, and determine whether a muscle-specific promotor induces superior expression and light-evoked EMG responses compared to a non-specific promotor. Superiority will be determined by the strength and specificity of opsin expression as restricting expression to the tongue minimises the likelihood of immune responses and unwanted sensation, movement or pain with light application. Methods 10 rats received an intramuscular injection of a viral vector construct to induce opsin expression in the tongue. 4 rats received a non-specific construct and 6 received a muscle-specific construct. Pulsed light was applied directly to the tongue, and genioglossus EMG activity was recorded. Confocal imaging of the brainstem and tongue quantified the strength and specificity of opsin expression. Results Despite the greater titer of the non-specific construct, the muscle-specific construct consistently drove stronger expression in the tongue and subsequently greater light-evoked EMG activity. Additionally, whilst the non-specific construct drove retrograde gene expression in hypoglossal motor neurons, no retrograde expression was induced by the muscle-specific construct. Conclusions This study provides proof-of-concept of a non-invasive optogenetic stimulation-based therapy for OSA. The superior expression and light induced EMG activity generated by the muscle-specific promotor indicates that it is the preferred promotor for future studies employing direct optogenetic stimulation of skeletal muscle.

In vivo analysis of onset and progression of retinal degeneration in the Nr2e3rd7/rd7 mouse model of enhanced S-cone sensitivity syndrome

The photoreceptor-specific nuclear receptor Nr2e3 is not expressed in Nr2e3rd7/rd7 mice, a mouse model of the recessively inherited retinal degeneration enhanced S-cone sensitivity syndrome (ESCS). We characterized in detail C57BL/6J Nr2e3rd7/rd7 mice in vivo by fundus photography, optical coherence tomography and fluorescein angiography and, post mortem, by histology and immunohistochemistry. White retinal spots and so-called ‘rosettes’ first appear at postnatal day (P) 12 in the dorsal retina and reach maximal expansion at P21. The highest density in ‘rosettes’ is observed within a region located between 100 and 350 µM from the optic nerve head. ‘Rosettes’ disappear between 9 to 12 months. Non-apoptotic cell death markers are detected during the slow photoreceptor degeneration, at a rate of an approximately 3% reduction of outer nuclear layer thickness per month, as observed from 7 to 31 months of age. In vivo analysis of Nr2e3rd7/rd7 Cx3cr1gfp/+ retinas identified microglial cells within ‘rosettes’ from P21 on. Subretinal macrophages were observed in vivo and by confocal microscopy earliest in 12-months-old Nr2e3rd7/rd7 retinas. At P21, S-opsin expression and the number of S-opsin expressing dorsal cones was increased. The dorso-ventral M-cone gradient was present in Nr2e3rd7/rd7 retinas, but M-opsin expression and M-opsin expressing cones were decreased. Retinal vasculature was normal.

Developmental and environmental plasticity in opsin gene expression in Lake Victoria cichlid fish

In many organisms, sensory abilities develop and evolve according to the changing demands of navigating, foraging and communication across different environments and life stages. Teleost fish inhabit heterogeneous light environments and exhibit a large diversity in visual system properties among species. Cichlids are a classic example of this diversity, generated by different tuning mechanisms that involve both genetic factors and phenotypic plasticity. Here, we document the developmental progression of visual pigment gene expression in Lake Victoria cichlids and test if these patterns are influenced by variation in light conditions. We reared two sister species of Pundamilia to adulthood in two distinct visual conditions that resemble the two light environments that they naturally inhabit in Lake Victoria. We also included interspecific first-generation hybrids. We then quantified (using RT-qPCR) the expression of the four Pundamilia opsins (SWS2B, SWS2A, RH2A and LWS) at 14 time points. We find that opsin expression profiles progress from shorter-wavelength sensitive opsins to longer-wavelength sensitive opsins with increasing age, in both species and their hybrids. The developmental trajectories of opsin expression also responded plastically to the visual conditions. Finally, we found subtle differences between reciprocal hybrids, possibly indicating parental effects and warranting further investigation. Developmental and environmental plasticity in opsin expression may provide an important stepping stone in the evolution of cichlid visual system diversity.Research highlightsIn Lake Victoria cichlid fish, expression levels of opsin genes (encoding visual pigments) differ between developmental stages and between experimental light treatments. This plasticity may contribute to the evolution of cichlid visual system diversity.

Evolutionary ecology of the visual opsin gene sequence and its expression in turbot (Scophthalmus maximus)

Background As flatfish, turbot undergo metamorphosis as part of their life cycle. In the larval stage, turbot live at the ocean surface, but after metamorphosis they move to deeper water and turn to benthic life. Thus, the light environment differs greatly between life stages. The visual system plays a great role in organic evolution, but reports of the relationship between the visual system and benthic life are rare. In this study, we reported the molecular and evolutionary analysis of opsin genes in turbot, and the heterochronic shifts in opsin expression during development. Results Our gene synteny analysis showed that subtype RH2C was not on the same gene cluster as the other four green-sensitive opsin genes (RH2) in turbot. It was translocated to chromosome 8 from chromosome 6. Based on branch-site test and spectral tuning sites analyses, E122Q and M207L substitutions in RH2C, which were found to be under positive selection, are closely related to the blue shift of optimum light sensitivities. And real-time PCR results indicated the dominant opsin gene shifted from red-sensitive (LWS) to RH2B1 during turbot development, which may lead to spectral sensitivity shifts to shorter wavelengths. Conclusions This is the first report that RH2C may be an important subtype of green opsin gene that was retained by turbot and possibly other flatfish species during evolution. Moreover, E122Q and M207L substitutions in RH2C may contribute to the survival of turbot in the bluish colored ocean. And heterochronic shifts in opsin expression may be an important strategy for turbot to adapt to benthic life.

Maternal Hypothyroidism Delayed Retinal Opsin-Development in the Neonatal Period: Analysis of TRH-Deficient Mice

Introduction: Retinal cone photoreceptor cells contain short (S) and medium (M) wavelength opsins, which are light-sensitive substances involved in color vision and visual acuity by sensing lights of different wavelengths. Thyroid hormones promote M-opsin expression and suppress S-opsin expression during the differentiation of cone photoreceptors. It was previously reported that M-opsin expression was delayed and S-opsin expression increased in TSH receptor-deficient mice and methimazole-induced hypothyroid mice. In addition, no M-opsin expression and increased S-opsin expression were observed in thyroid hormone receptor (TR) β2-deficient mice (Ng L et al, Nature Genetics. 2001; 27(1): 94-98.). This suggested that impaired thyroid function affects opsin development. We therefore examined retinal development in TRH-deficient mice, which are a model of central hypothyroidism established in our laboratory. Methods: We performed HE staining of the retina at postnatal 30 days and electroretinography at postnatal 10 weeks using TRH-/- and wild-type (WT) mice. We also examined expression levels of S/M opsin mRNA in WT, TRH-/- and TRH-/- pups born from TRH-/- dams at postnatal 12,17 and 30 days, and TRβΔ337T knock-in mice (TRβmut/mut) at postnatal 30 days. Furthermore, we performed immunohistochemistry to examine S/M opsin protein expression in these mice. Results: The retinal structures by HE staining and retinal functions by electroretinography in TRH-/- mice were unchanged compared with those in WT mice. Although M-opsin expression was not detected and S-opsin expression was higher in TRβmut/mut mice than in WT mice, the mRNA and protein expression levels of S/M-opsin did not significantly differ between TRH-/- pups born from TRH+/- dams and WT pups at all postnatal days. TRH-/- pups born from TRH-/- dams exposed to maternal hypothyroidism had similar serum total T4 levels to TRH-/- pups born from TRH+/- with normal maternal thyroid function. In contrast, the mRNA expression level of M-opsin was significantly lower (1.00±0.06 vs 0.64±0.05: mean ± SE, p<0.01) and the protein expression level was lower in TRH-/- pups born from TRH-/- dams than in WT pups at postnatal 12 days. However, these differences disappeared after postnatal 17 days, and there was no difference in M-opsin expression in TRH-/- pups born from TRH-/- dams compared with WT pups. Conclusions: Although no delay in opsin development was observed in TRH-/- pups born from TRH+/- dams, TRH-/- pups born from central hypothyroid dams exhibited delayed opsin development, suggesting that maternal hypothyroidism affects the development of retinal opsin in the neonatal period.