Optogenetic Stimulation of the Auditory Nerve

Direct electrical stimulation of spiral ganglion neurons (SGNs) by cochlear implants (CIs) enables open speech comprehension in the majority of implanted ...

University Medical Center Goettingen

Suppressor of cytokine signaling 3 (SOCS3) expression in bone marrow cells (BMC) was up-regulated upon exposure to interleukin 6, lipopolysaccharide, or tumor-associated factors. But, how the up-regulated SOCS3 affects differentiation of BMCs is incompletely characterized. Here, we showed that SOCS3 promoted BMCs to intently differentiate into CD8 T cells. Importantly, lung can be as one athymus tissue for the BMCs to differentiate into CD8(+) T cells. Notch1 plays a critical role in the differentiation from SOCS3-transfected BMCs to CD8(+) T cells. We conclude that the up-regulated SOCS3 in some pathologic conditions, such as tumor and inflammation, might promote BMCs to differentiate into CD8(+) T lymphocytes in lung tissue via up-regulating Notch1 expression. This may represent a new mechanism against diseases such as tumor.

Suppressor of cytokine signaling 3 promotes bone marrow cells to differentiate into CD8+ T lymphocytes in lung tissue via up-regulating Notch1 expression.

Tumor-associated dendritic cells (DCs) often induce T cell anergy or deletion and regulatory T cells instead of antitumor immunity. Although many tumor-associated Ags have been found, there is still no effective vaccine for cancer. Thus, novel rational strategies to enhance the immunogenicity of cancer-specific Ags are needed. Chromosome 1 open reading frame 190 (c1orf190), a gene that encodes a 239-aa hypothetical protein and contains multiple kinase phosphorylation sites, has a wide relationship with multiple signaling pathway molecules and can be regulated by multiple factors, such as TLR ligands. In this study, we demonstrate that c1orf190 can activate NF-κB, drive the production of cytokines, and promote the Ag-presenting function and the priming ability of DCs. Furthermore, c1orf190 can promote resistance of DCs to tumor-associated inhibition not only in the Ag-presenting function but also in the priming ability to induce Ag-specific T lymphocytes. Thus, c1orf190, an NF-κB activator, may be a candidate gene for regulating the function of DCs to resist tumor-associated factor-mediated dysfunction. We also found that c1orf190-mediated cytokine release is achieved by activating the canonical but not the noncanonical NF-κB pathway.

Chromosome 1 open reading frame 190 promotes activation of NF-κB canonical pathway and resistance of dendritic cells to tumor-associated inhibition in vitro.

Inner hair cells (IHCs) of the cochlea use ribbon synapses to transmit auditory information faithfully to spiral ganglion neurons (SGNs). In the present study, we used genetic disruption of the presynaptic scaffold protein bassoon in mice to manipulate the morphology and function of the IHC synapse. Although partial-deletion mutants lacking functional bassoon (Bsn(ΔEx4/5)) had a near-complete loss of ribbons from the synapses (up to 88% ribbonless synapses), gene-trap mutants (Bsn(gt)) showed weak residual expression of bassoon and 56% ribbonless synapses, whereas the remaining 44% had a loosely anchored ribbon. Patch-clamp recordings and synaptic CaV1.3 immunolabeling indicated a larger number of Ca(2+) channels for Bsn(gt) IHCs compared with Bsn(ΔEx4/5) IHCs and for Bsn(gt) ribbon-occupied versus Bsn(gt) ribbonless synapses. An intermediate phenotype of Bsn(gt) IHCs was also found by membrane capacitance measurements for sustained exocytosis, but not for the size of the readily releasable vesicle pool. The frequency and amplitude of EPSCs were reduced in Bsn(ΔEx4/5) mouse SGNs, whereas their postsynaptic AMPA receptor clusters were largely unaltered. Sound coding in SGN, assessed by recordings of single auditory nerve fibers and their population responses in vivo, was similarly affected in Bsn(gt) and Bsn(ΔEx4/5) mice. Both genotypes showed impaired sound onset coding and reduced evoked and spontaneous spike rates. In summary, reduced bassoon expression or complete lack of full-length bassoon impaired sound encoding to a similar extent, which is consistent with the comparable reduction of the readily releasable vesicle pool. This suggests that the remaining loosely anchored ribbons in Bsn(gt) IHCs were functionally inadequate or that ribbon independent mechanisms dominated the coding deficit.

Disruption of the presynaptic cytomatrix protein bassoon degrades ribbon anchorage, multiquantal release, and sound encoding at the hair cell afferent synapse.

Hearing over a wide range of sound intensities is thought to require complementary coding by functionally diverse spiral ganglion neurons (SGNs), each changing activity only over a subrange. The foundations of SGN diversity are not well understood but likely include differences among their inputs: the presynaptic active zones (AZs) of inner hair cells (IHCs). Here we studied one candidate mechanism for causing SGN diversity-heterogeneity of Ca(2+) influx among the AZs of IHCs-during postnatal development of the mouse cochlea. Ca(2+) imaging revealed a change from regenerative to graded synaptic Ca(2+) signaling after the onset of hearing, when in vivo SGN spike timing changed from patterned to Poissonian. Furthermore, we detected the concurrent emergence of stronger synaptic Ca(2+) signals in IHCs and higher spontaneous spike rates in SGNs. The strengthening of Ca(2+) signaling at a subset of AZs primarily reflected a gain of Ca(2+) channels. We hypothesize that the number of Ca(2+) channels at each IHC AZ critically determines the firing properties of its corresponding SGN and propose that AZ heterogeneity enables IHCs to decompose auditory information into functionally diverse SGNs.

Concurrent maturation of inner hair cell synaptic Ca2+ influx and auditory nerve spontaneous activity around hearing onset in mice.

Endbulb of Held terminals of auditory nerve fibers (ANF) transmit auditory information at hundreds per second to bushy cells (BCs) in the anteroventral cochlear nucleus (AVCN). Here, we studied the structure and function of endbulb synapses in mice that lack the presynaptic scaffold bassoon and exhibit reduced ANF input into the AVCN. Endbulb terminals and active zones were normal in number and vesicle complement. Postsynaptic densities, quantal size and vesicular release probability were increased while vesicle replenishment and the standing pool of readily releasable vesicles were reduced. These opposing effects canceled each other out for the first evoked EPSC, which showed unaltered amplitude. We propose that ANF activity deprivation drives homeostatic plasticity in the AVCN involving synaptic upscaling and increased intrinsic BC excitability. In vivo recordings from individual mutant BCs demonstrated a slightly improved response at sound onset compared to ANF, likely reflecting the combined effects of ANF convergence and homeostatic plasticity. Further, we conclude that bassoon promotes vesicular replenishment and, consequently, a large standing pool of readily releasable synaptic vesicles at the endbulb synapse.

Bassoon-disruption slows vesicle replenishment and induces homeostatic plasticity at a CNS synapse.

Auditory prostheses can partially restore speech comprehension when hearing fails. Sound coding with current prostheses is based on electrical stimulation of auditory neurons and has limited frequency resolution due to broad current spread within the cochlea. In contrast, optical stimulation can be spatially confined, which may improve frequency resolution. Here, we used animal models to characterize optogenetic stimulation, which is the optical stimulation of neurons genetically engineered to express the light-gated ion channel channelrhodopsin-2 (ChR2). Optogenetic stimulation of spiral ganglion neurons (SGNs) activated the auditory pathway, as demonstrated by recordings of single neuron and neuronal population responses. Furthermore, optogenetic stimulation of SGNs restored auditory activity in deaf mice. Approximation of the spatial spread of cochlear excitation by recording local field potentials (LFPs) in the inferior colliculus in response to suprathreshold optical, acoustic, and electrical stimuli indicated that optogenetic stimulation achieves better frequency resolution than monopolar electrical stimulation. Virus-mediated expression of a ChR2 variant with greater light sensitivity in SGNs reduced the amount of light required for responses and allowed neuronal spiking following stimulation up to 60 Hz. Our study demonstrates a strategy for optogenetic stimulation of the auditory pathway in rodents and lays the groundwork for future applications of cochlear optogenetics in auditory research and prosthetics.

Zhizi Jing

Auditory Systems Physiology Group,
Department of Otolaryngology,
Auditory Systems Physiology Group, Department of Otolaryngology

University Medical Center Goettingen

Optogenetic Stimulation of the Auditory Nerve

Zhizi Jing

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University Medical Center Goettingen

Optogenetic Stimulation of the Auditory Nerve

Auditory Systems Physiology Group,
Department of Otolaryngology,
Auditory Systems Physiology Group, Department of Otolaryngology