Biology subjects

Joffrois, C.

Publications and source records attributed to Joffrois, C..

7 recordsLinked to original sources

bioRxiv2025

Ectopic expression of two cone opsins in mouse RGCs results in opposite responses to light stimulation, likely due to differential G protein activation

Retinitis pigmentosa, a leading cause of inherited blindness, results in photoreceptor degeneration that current optogenetic approaches aim to address through microbial opsin expression in retinal ganglion cells (RGCs). While these microbial proteins restore light sensitivity, their clinical potential remains limited by low light sensitivity and immunogenicity risks. Recent efforts have focused on vertebrate opsins as safer alternatives, with mid-wavelength cone opsin (MW-opsin) demonstrating RGC depolarization via endogenous G-protein signaling. In this study, we reveal a surprising divergence in signaling outcomes of expressing short-wavelength mouse cone opsin (Opn1sw) in RGCs of blind mice. Using multielectrode array recordings and whole-cell patch clamping, we demonstrate that Opn1sw induces membrane hyperpolarization in RGCs - a stark contrast to MW-opsins depolarizing effects. This unexpected inversion suggests differential engagement of intracellular signaling pathways, potentially stemming from distinct G-protein coupling preferences. Comparative analysis of native G-protein expression profiles in RGCs versus cone photoreceptors supports this hypothesis, revealing mismatches that may explain ectopic opsin behavior. Our findings challenge the assumption of conserved opsin signaling across spectral subtypes and cell types, highlighting critical gaps in understanding vertebrate opsin-G protein interactions in non-native cellular environments. This discovery points to the necessity of systematic characterization of opsin signaling networks in target retinal cells, a prerequisite for engineering optimized optogenetic tools that reliably produce desired electrophysiological outcomes. By establishing spectral subtype-dependent signaling divergence, our work redefines parameters for developing next-generation vision restoration therapies.

neuroscience↗

bioRxiv2024

A flexible high-precision photoacoustic retinal prosthesis

Retinal degenerative diseases of photoreceptors are a leading cause of blindness with no effective treatment. Retinal prostheses aim to restore sight by stimulating residual retinal cells. Here, we present a photoacoustic retinal stimulation technology. We designed a polydimethylsiloxane and carbon-based flexible film that converts near-infrared laser pulses into a localized acoustic field with 56-{micro}m lateral resolution, allowing precise stimulation of mechanosensitive retinal cells. This photoacoustic stimulation robustly and locally modulated retinal ganglion cell activity in both wild-type and degenerated ex vivo rat retinae. In animals subretinally implanted with a millimeter-sized photoacoustic film, pulsed laser stimulation generated neural modulation along the visual pathway to the superior colliculus, as measured by functional ultrasound imaging. The biosafety of the film was confirmed by the absence of short-term adverse effects , while local thermal increases were measured below 1 {degrees}C. These findings demonstrate the potential of photoacoustic stimulation for high-acuity visual restoration in blind patients.

neuroscience↗

bioRxiv2022

Inducible non-human primate models of retinal degeneration for testing end stage therapies and understanding disease mechanisms

The anatomical differences between the retinas of humans and most animal models pose a challenge for testing novel therapies. Non-human primate (NHP) retina is anatomically closest to the human retina with the presence of a high acuity region called the fovea. However, there is a lack of relevant NHP models for retinal degeneration that can be used for preclinical studies of vision restoration. To address this unmet need we aimed to generate inducible NHP models of photoreceptor degeneration. We generated three cynomolgus macaque models using distinct strategies. We used two genetically targeted strategies using optogenetics and Crispr-Cas9 to ablate specifically rods to mimic rod-cone dystrophy. Additionally, we created an acute model by physical separation of the photoreceptors and retinal pigment epithelium using a polymer patch. Retinal degeneration was evaluated in all three models by in-life exams such as fundus imaging, optical coherence tomography, adaptive optics and electroretinography. In the genetic models we observed punctuate areas of degeneration in the injected area marked by disorganization of outer segments, loss of rod photoreceptors and thinning of the outer nuclear layer. In the acute model, the degeneration was faster and involved both rods and cones. Among the three distinct NHP models, the Crispr-Cas9 based approach was the most advantageous model in view of recapitulating disease specific features and its ease of implementation. The acute model however resulted in the fastest degeneration making it the most relevant model for testing end-stage vision restoration therapies such as stem cell transplantation.

bioengineering↗

bioRxiv2022

Encoding surprise by retinal ganglion cells

The efficient coding hypothesis posits that early sensory neurons transmit maximal information about sensory stimuli, given internal constraints. A central prediction of this theory is that neurons should preferentially encode stimuli that are most surprising. Previous studies suggest this may be the case in early visual areas, where many neurons respond strongly to rare or surprising stimuli. For example, previous research showed that when presented with a rhythmic sequence of full-field flashes, many retinal ganglion cells (RGCs) respond strongly at the instance the flash sequence stops, and when another flash would be expected. This phenomenon is called the omitted stimulus response. However, it is not known whether the responses of these cells varies in a graded way depending on the level of stimulus surprise. To investigate this, we presented retinal neurons with extended sequences of stochastic flashes. With this stimulus, the surprise associated with a particular flash/silence, could be quantified analytically, and varied in a graded manner depending on the previous sequences of flashes and silences. Interestingly, we found that RGC responses could be well explained by a simple normative model, which described how they optimally combined their prior expectations and recent stimulus history, so as to encode surprise. Further, much of the diversity in RGC responses could be explained by the model, due to the different prior expectations that different neurons had about the stimulus statistics. These results suggest that even as early as the retina many cells encode surprise, relative to their own, internally generated expectations.

neuroscience↗

bioRxiv2021

In vivo optogenetic stimulation of the primate retina activates the visual cortex after long-term transfection

Over the last 15 years, optogenetics has changed fundamental research in neuroscience, and is now reaching toward therapeutic applications. Vision restoration strategies using optogenetics are now at the forefront of these new clinical opportunities. But applications to human patients suffering from retinal diseases leading to blindness rise important concerns on the long-term functional expression of optogenes and the efficient signal transmission to higher visual centers. Here we demonstrate in non-human primates, continued expression and functionality at the retina level [~]20 months after delivery of our construct. We also performed in-vivo recordings of visually evoked potentials in the primary visual cortex of anaesthetized animals. Using synaptic blockers, we isolated the in-vivo cortical activation resulting from the direct optogenetic stimulation of primate retina. In conclusion, our work indicates long-term transgene expression and transmission of the signal generated in the macaque retina to the visual cortex, two important features for future clinical applications.

neuroscience↗

bioRxiv2021

Functional ultrasound imaging of the spreading activity following optogenetic stimulation of the rat visual cortex

Optogenetic stimulation of the primary visual cortex (V1) is a promising therapy for sight restoration, but it remains unclear what total cerebral volume is activated after surface stimulation. In this study, we expressed the red-shifted opsin ChrimsonR in excitatory neurons within V1 in rats, and used the fine spatial resolution provided by functional ultrasound imaging (fUS) over the whole depth of the brain to investigate the brain response to focal surface stimulation. We observed optogenetic activation of a high proportion of the volume of V1. Extracellular recordings confirmed the neuronal origin of this activation. Moreover, neuronal responses were even located in deep layers under conditions of low irradiance, spreading to the LGN and V2, consistent with a normal visual information process. This study paves the way for the use of optogenetics for cortical therapies, and highlights the value of coupling fUS with optogenetics.

neuroscience↗

bioRxiv2018

Modeling the Electro-chemical Properties of Microbial Opsin ChrimsonR for Application to Optogenetics-based Vision Restoration

Optogenetic activation of neurons [1] have greatly contributed to our understanding of how neural circuits operate, and holds huge promise in the field of neural prosthetics, particularly in sensory restoration. The discovery of new channelrhodopsins, Chrimson -- which is 45 nm more red-shifted than any previously discovered or engineered channelrhodopsin -- and its mutant ChrimsonR with faster kinetics [2] made this technology available for medical applications. However, a detailed model that would be able to accurately reproduce the membrane potential dynamics in cells transfected with ChrimsonR under light stimulation is missing. We address this issue by developing the first model for the electrochemical behavior of ChrimsonR that predicts its conductance in response to arbitrary light stimulation. Our model captures ON and OFF dynamics of the protein for stimuli with frequencies up to 100 Hz and their relationship with the brightness, as well as its activation curve, the steady-state amplitude of the response as a function of light intensity. Additionally, we capture a slow adaptation mechanism at a timescale at the order of minutes. Our model holds for light intensities covering the whole dynamic range of the channel (from response onset to saturation) and for timescales in the order of up to several minutes. This model is a new step towards modeling the spiking activity of ChrimsonR-expressing neurons, required for the precise control of information transmission in optogenetics-based Brain-Computer Interfaces, and will inform future applications of ChrimsonR based optogenetics.

neuroscience↗