Long-term in vivo application of a potassium channel-based optogenetic silencer in the healthy and epileptic mouse hippocampus

Suppression of epileptic seizures by transcranial activation of K+-selective channelrhodopsin

Optogenetics is a valuable tool for studying the mechanisms of neurological diseases and is now being developed for therapeutic applications. In rodents and macaques, improved channelrhodopsins have been applied to achieve transcranial optogenetic stimulation. While transcranial photoexcitation of neurons has been achieved, noninvasive optogenetic inhibition for treating hyperexcitability-induced neurological disorders has remained elusive. There is a critical need for effective inhibitory optogenetic tools that are highly light-sensitive and capable of suppressing neuronal activity in deep brain tissue. In this study, we developed a highly sensitive moderately K+-selective channelrhodopsin (HcKCR1-hs) by molecular engineering of the recently discovered Hyphochytrium catenoides kalium (potassium) channelrhodopsin 1. Transcranial activation of HcKCR1-hs significantly prolongs the time to the first seizure, increases survival, and decreases seizure activity in several status epilepticus mouse models. Our approach for transcranial optogenetic inhibition of neural hyperactivity may be adapted for cell type-specific neuromodulation in both basic and preclinical settings.

Low frequency stimulation for seizure suppression: Identification of optimal targets in the entorhinal-hippocampal circuit

BACKGROUND

Mesial temporal lobe epilepsy (MTLE) with hippocampal sclerosis (HS) is a common form of drug-resistant focal epilepsy in adults. Treatment for pharmacoresistant patients remains a challenge, with deep brain stimulation (DBS) showing promise for alleviating intractable seizures. This study explores the efficacy of low frequency stimulation (LFS) on specific neuronal targets within the entorhinal-hippocampal circuit in a mouse model of MTLE.

OBJECTIVE

Our previous research demonstrated that LFS of the medial perforant path (MPP) fibers in the sclerotic hippocampus reduced seizures in epileptic mice. Here, we aimed to identify the critical neuronal population responsible for this antiepileptic effect by optogenetically stimulating presynaptic and postsynaptic compartments of the MPP-dentate granule cell (DGC) synapse at 1 Hz. We hypothesize that specific targets for LFS can differentially influence seizure activity depending on the cellular identity and location within or outside the seizure focus.

METHODS

We utilized the intrahippocampal kainate (ihKA) mouse model of MTLE and targeted specific neural populations using optogenetic stimulation. We recorded intracranial neuronal activity from freely moving chronically epileptic mice with and without optogenetic LFS up to 3 h.

RESULTS

We found that LFS of MPP fibers in the sclerotic hippocampus effectively suppressed epileptiform activity while stimulating principal cells in the MEC had no impact. Targeting DGCs in the sclerotic septal or non-sclerotic temporal hippocampus with LFS did not reduce seizure numbers but shortened the epileptiform bursts.

CONCLUSION

Presynaptic stimulation of the MPP-DGC synapse within the sclerotic hippocampus is critical for seizure suppression via LFS.

Evaluating the Potential of Light Exposure on Reducing the Frequency of Epileptic Seizures

Epilepsy is one of the most common and devastating neurological disorders that causes unprovoked, recurrent seizures arising from excessive synchronized neuronal discharging. Although antiepileptic drugs (AEDs) reduce the frequency of epilepsy seizures, drug-refractory epileptic patients exert resistance to AEDs, resulting in treatment difficulty. Moreover, pharmacological treatments do not show satisfactory results in response to photosensitive epilepsy. In the recent era, light therapy emerged as a potential non-pharmacological approach for treating various diseases, including depression, seasonal affective disorders, migraine, pain, and others. Several studies have also shown the potential of light therapy in treating epilepsy. In addition, Red light evokes epilepsy seizures. Blue lenses filter the red light and significantly suppress the frequency of epilepsy seizures. However, the effects of green light on the frequency of epileptic seizures are not studied yet. In addition, light-activated gene therapy or optogenetics also emerged as a possible option for epilepsy treatment. Animal models have shown the therapeutic possibilities of optogenetics and light therapy; however, human studies addressing this possibility are still vague. This review provides the beneficial effects of light in reducing seizure frequency in epilepsy patients. A limited number of studies have been reported so far; therefore, light therapy for treating epilepsy requires more studies on animal models to provide precise results of light effects on seizures.

Time-resolved study on signaling pathway of photoactivated adenylate cyclase and its nonlinear optical response

Photoactivated adenylate cyclases (PACs) are multidomain BLUF proteins that regulate the cellular levels of cAMP in a light-dependent manner. The signaling route and dynamics of PAC from Oscillatoria acuminata (OaPAC), which consists of a light sensor BLUF domain, an adenylate cyclase domain, and a connector helix (α3-helix), were studied by detecting conformational changes in the protein moiety. Although circular dichroism and small-angle X-ray scattering measurements did not show significant changes upon light illumination, the transient grating method successfully detected light-induced changes in the diffusion coefficient (diffusion-sensitive conformational change (DSCC)) of full-length OaPAC and the BLUF domain with the α3-helix. DSCC of full-length OaPAC was observed only when both protomers in a dimer were photoconverted. This light intensity dependence suggests that OaPAC is a cyclase with a nonlinear light intensity response. The enzymatic activity indeed nonlinearly depends on light intensity, that is, OaPAC is activated under strong light conditions. It was also found that both DSCC and enzymatic activity were suppressed by a mutation in the W90 residue, indicating the importance of the highly conserved Trp in many BLUF domains for the function. Based on these findings, a reaction scheme was proposed together with the reaction dynamics.

Aion is a bistable anion-conducting channelrhodopsin that provides temporally extended and reversible neuronal silencing

Optogenetic silencing allows to reveal the necessity of selected neuronal populations for various neurophysiological functions. These range from synaptic transmission and coordinated neuronal network activity to control of specific behaviors. An ideal single-component optogenetic silencing tool should be switchable between active and inactive states with precise timing while preserving its activity in the absence of light until switched to an inactive state. Although bistable anion-conducting channelrhodopsins (ACRs) were previously engineered to reach this goal, their conducting state lifetime was limited to only a few minutes and some ACRs were not fully switchable. Here we report Aion, a bistable ACR displaying a long-lasting open state with a spontaneous closing time constant close to 15 min. Moreover, Aion can be switched between the open and closed state with millisecond precision using blue and orange light, respectively. The long conducting state enables overnight silencing of neurons with minimal light exposure. We further generated trafficking-optimized versions of Aion, which show enhanced membrane localization and allow precisely timed, long-lasting all-optical control of nociceptive responses in larvae of Drosophila melanogaster. Thus, Aion is an optogenetic silencing tool for inhibition of neuronal activity over many hours which can be switched between an active and inactive state with millisecond precision.

Aion is an anion-conducting, bistable channelrhodopsin that enables long-term silencing of neuronal networks, as demonstrated in organotypic hippocampal cultures and Drosophila melanogaster larvae.

Rare KCND3 Loss-of-Function Mutation Associated With the SCA19/22

Spinocerebellar ataxia 19/22 (SCA19/22) is a rare neurodegenerative disorder caused by mutations of the KCND3 gene, which encodes the Kv4. 3 protein. Currently, only 22 KCND3 single-nucleotide mutation sites of SCA19/22 have been reported worldwide, and detailed pathogenesis remains unclear. In this study, Sanger sequencing was used to screen 115 probands of cerebellar ataxia families in 67 patients with sporadic cerebellar ataxia and 200 healthy people to identify KCND3 mutations. Mutant gene products showed pathogenicity damage, and the polarity was changed. Next, we established induced pluripotent stem cells (iPSCs) derived from SCA19/22 patients. Using a transcriptome sequencing technique, we found that protein processing in the endoplasmic reticulum was significantly enriched in SCA19/22-iPS-derived neurons and was closely related to endoplasmic reticulum stress (ERS) and apoptosis. In addition, Western blotting of the SCA19/22-iPS-derived neurons showed a reduction in Kv4.3; but, activation of transcription factor 4 (ATF4) and C/EBP homologous protein was increased. Therefore, the c.1130 C>T (p.T377M) mutation of the KCND3 gene may mediate misfold and aggregation of Kv4.3, which activates the ERS and further induces neuron apoptosis involved in SCA19/22.