Highlights • Optogenetic stimulation of the auditory pathway promises unprecedented research opportunities and a fundamental advance for hearing restoration. • Feasibility and improved frequency ...resolution of optogenetic stimulation of the cochlea have been demonstrated in rodents. • Major efforts toward developing efficient, reliable and safe optogenetics as well as optical stimulation technology remain to be undertaken.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) where immunopathology is thought to be mediated by myelin-reactive CD4+ T helper (TH) cells. The ...TH cells most commonly implicated in the pathogenesis of the disease are of TH1 and TH17 lineage, which are defined by the production of interferon-γ and interleukin-17, respectively. Moreover, there is emerging evidence for the involvement of TH17.1 cells, which share the hallmarks of TH1 and TH17 subsets. In this review, we summarise current knowledge about the potential role of TH17 subsets in the initiation and progression of the disease and put a focus on their response to approved immunomodulatory MS drugs. In this regard, TH17 cells are abundant in peripheral blood, cerebrospinal fluid and brain lesions of MS patients, and their counts and inflammatory mediators are further increased during relapses. Fingolimod and alemtuzumab induce a paramount decrease in central memory T cells, which harbour the majority of peripheral TH17 cells, while the efficacy of natalizumab, dimethyl fumarate and importantly hematopoietic stem cell therapy correlates with TH17.1 cell inhibition. Interestingly, also CD20 antibodies target highly inflammatory TH cells and hamper TH17 differentiation by IL-6 reductions. Moreover, recovery rates of TH cells best correlate with long-term efficacy after therapeutical immunodepletion. We conclude that central memory TH17.1 cells play a pivotal role in MS pathogenesis and they represent a major target of MS therapeutics.
•TH17 cells are abundant in patients with MS and further increase during relapses.•TH17.1 cells appear to have a pathogenic advantage over other TH cells.•Cells from the TH17 axis represent major targets of MS therapeutics.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Spontaneous excitatory postsynaptic currents (sEPSCs) measured from the first synapse in the mammalian auditory pathway reach a large mean amplitude with a high level of variance (CV between 0.3 and ...1). This has led some to propose that each inner hair cell (IHC) ribbon-type active zone (AZ), on average, releases ∼6 synaptic vesicles (SVs) per sEPSC in a coordinated manner. If true, then the predicted change in membrane capacitance (Cm) for such multivesicular fusion events would equate to ∼300 attofarads (aF). Here, we performed cell-attached Cm measurements to directly examine the size of fusion events at the basolateral membrane of IHCs where the AZs are located. The frequency of events depended on the membrane potential and the expression of Cav1.3, the principal Ca2+-channel type of IHCs. Fusion events averaged 40 aF, which equates to a normal-sized SV with an estimated diameter of 37 nm. The calculated SV volumes showed a high degree of variance (CV > 0.6). These results indicate that SVs fused individually with the plasma membrane during spontaneous and evoked release and SV volume may contribute more variability in EPSC amplitude than previously assumed.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Cochlear implants (CIs) are considered the most successful neuroprosthesis as they enable speech comprehension in the majority of half a million CI users suffering from sensorineural hearing loss. By ...electrically stimulating the auditory nerve, CIs constitute an interface re‐connecting the brain and the auditory scene, providing the patient with information regarding the latter. However, since electric current is hard to focus in conductive environments such as the cochlea, the precision of electrical sound encoding—and thus quality of artificial hearing—is limited. Recently, optogenetic stimulation of the cochlea has been suggested as an alternative approach for hearing restoration. Cochlear optogenetics promises increased spectral selectivity of artificial sound encoding, hence improved hearing, as light can conveniently be confined in space to activate the auditory nerve within smaller tonotopic ranges. In this review, we discuss the latest experimental and technological developments of cochlear optogenetics and outline the remaining challenges on the way to clinical translation.
In this review, A. Dieter, D. Keppeler and T. Moser summarize the state of the art and progresses made in optical cochlear implantation using ontogenetic technology and discuss the challenges for translation into patients with hearing loss.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Rod photoreceptors (PRs) use ribbon synapses to transmit visual information. To signal ‘no light detected’ they release glutamate continually to activate post-synaptic receptors. When light is ...detected glutamate release pauses. How a rod’s individual ribbon enables this process was studied here by recording evoked changes in whole-cell membrane capacitance from wild-type and ribbonless (
Ribeye
-ko) mice. Wild-type rods filled with high (10 mM) or low (0.5 mM) concentrations of the Ca
2+
-buffer EGTA created a readily releasable pool (RRP) of 87 synaptic vesicles (SVs) that emptied as a single kinetic phase with a τ<0.4 ms. The lower concentration of EGTA accelerated Ca
v
channel opening and facilitated release kinetics. In contrast, ribbonless rods created a much smaller RRP of 22 SVs, and they lacked Ca
v
channel facilitation; however, Ca
2+
channel-release coupling remained tight. These release deficits caused a sharp attenuation of rod-driven scotopic light responses. We conclude that the synaptic ribbon facilitates Ca
2+
-influx and establishes a large RRP of SVs.
Neural sound encoding in the mammalian cochlea faces the challenge of representing audible sound pressures that vary over six orders of magnitude. The cochlea meets this demand through the use of ...active micromechanics as well as the diversity and adaptation of afferent neurons and their synapses. Mechanisms underlying neural diversity likely include heterogeneous presynaptic input from inner hair cells (IHCs) to spiral ganglion neurons (SGNs) as well as differences in the molecular profile of SGNs and in their efferent control. Here, we tested whether glutamate release from IHCs, previously found to be critical for maintaining different molecular SGN profiles, is required for establishing heterogeneity of active zones (AZs) in IHCs. We analyzed structural and functional heterogeneity of IHC AZs in mouse mutants with disrupted glutamate release from IHCs due to lack of a vesicular glutamate transporter (Vglut3) or impaired exocytosis due to defective otoferlin. We found the variance of the voltage-dependence of presynaptic Ca
2+
influx to be reduced in exocytosis-deficient IHCs of otoferlin mutants. Yet, the spatial gradients of maximal amplitude and voltage-dependence of Ca
2+
influx along the pillar-modiolar IHC axis were maintained in both mutants. Further immunohistochemical analysis showed an intact spatial gradient of ribbon size in Vglut3
–/–
mice. These results indicate that IHC exocytosis and glutamate release are not strictly required for establishing the heterogeneity of IHC AZs.
Normal hearing and synaptic transmission at afferent auditory inner hair cell (IHC) synapses require otoferlin. Deafness DFNB9, caused by mutations in the OTOF gene encoding otoferlin, might be ...treated by transferring wild‐type otoferlin cDNA into IHCs, which is difficult due to the large size of this transgene. In this study, we generated two adeno‐associated viruses (AAVs), each containing half of the otoferlin cDNA. Co‐injecting these dual‐AAV2/6 half‐vectors into the cochleae of 6‐ to 7‐day‐old otoferlin knock‐out (Otof−/−) mice led to the expression of full‐length otoferlin in up to 50% of IHCs. In the cochlea, otoferlin was selectively expressed in auditory hair cells. Dual‐AAV transduction of Otof−/− IHCs fully restored fast exocytosis, while otoferlin‐dependent vesicle replenishment reached 35–50% of wild‐type levels. The loss of 40% of synaptic ribbons in these IHCs could not be prevented, indicating a role of otoferlin in early synapse maturation. Acoustic clicks evoked auditory brainstem responses with thresholds of 40–60 dB. Therefore, we propose that gene delivery mediated by dual‐AAV vectors might be suitable to treat deafness forms caused by mutations in large genes such as OTOF.
Synopsis
Gene delivery of large genes exceeding the packing capacity of a single adeno‐associated virus (AAV) is challenging. Split‐AAV vectors can bypass this problem. This work offers the first application of split‐AAV gene therapy to the inner ear to restore hearing in a genetically deaf mouse model.
The 6 kb‐long otoferlin coding sequence was split into two fragments and packaged into two separate AAV2/6 viruses which were co‐injected into cochleae of otoferlin knock‐out mice.
Both the dual‐AAV trans‐splicing and the hybrid strategy led to re‐assembly of the two otoferlin cDNA fragments and expression of full‐length otoferlin.
Otoferlin expression from dual‐AAVs was restricted to hair cells and reached ˜30% of wild type otoferlin protein levels in inner hair cells.
In inner hair cells, fast exocytosis of the readily releasable pool of vesicles was fully recovered, and vesicle replenishment was restored to 35–50% of wild‐type controls.
Auditory brainstem responses were present albeit with reduced wave amplitudes in dual‐AAV transduced otoferlin knock‐out mice and indicated hearing thresholds of 40–60 dB.
Gene delivery of large genes exceeding the packing capacity of a single adeno‐associated virus (AAV) is challenging. Split‐AAV vectors can bypass this problem. This work offers the first application of split‐AAV gene therapy to the inner ear to restore hearing in a genetically deaf mouse model.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Multiple sclerosis (MS) is a chronic inflammatory demyelinating and neurodegenerative disease of the central nervous system (CNS). In recent years, vitamin D has gained attention, as low serum levels ...are suspected to increase the risk for MS. Cholecalciferol supplementation has been tested in several clinical trials, since hypovitaminosis D was linked to higher disease activity and may even play a role in long-term outcome. Here, we review the current understanding of the molecular effects of vitamin D beyond calcium homeostasis, the potential beneficial action in MS and hazards including complications of chronic and high-dose therapy. In clinical trials, doses of up to 40,000 IU/day were tested and appeared safe as add-on therapy for short-term periods. A recent meta-analysis of a randomized, double-blind, placebo-controlled clinical trial investigating vitamin D as add-on therapy in MS, however, suggested that vitamin D had no therapeutic effect on disability or relapse rate. We recognize a knowledge gap for chronic and high-dose therapy, which can lead to life-threatening complications related to vitamin D toxicity including renal failure, cardiac arrythmia and status epilepticus. Moreover, vitamin D toxicity may manifest as fatigue, muscle weakness or urinary dysfunction, which may mimic the natural course of progressive MS. Given these limitations, vitamin D supplementation in MS is a sensitive task which needs to be supervised by physicians. While there is strong evidence for vitamin D deficiency and the development of MS, the risk-benefit profile of dosage and duration of add-on supplementation needs to be further clarified.
Cochlear implants (CIs) electrically stimulate spiral ganglion neurons (SGNs) and partially restore hearing to half a million CI users. However, wide current spread from intracochlear electrodes ...limits spatial selectivity (i.e. spectral resolution) of electrical CIs. Optogenetic stimulation might become an alternative, since light can be confined in space, promising artificial sound encoding with increased spectral selectivity. Here we compare spectral selectivity of optogenetic, electric, and acoustic stimulation by multi-channel recordings in the inferior colliculus (IC) of gerbils. When projecting light onto tonotopically distinct SGNs, we observe corresponding tonotopically ordered IC activity. An activity-based comparison reveals that spectral selectivity of optogenetic stimulation is indistinguishable from acoustic stimulation for modest intensities. Moreover, optogenetic stimulation outperforms bipolar electric stimulation at medium and high intensities and monopolar electric stimulation at all intensities. In conclusion, we demonstrate better spectral selectivity of optogenetic over electric SGN stimulation, suggesting the potential for improved hearing restoration by optical CIs.
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