BI-ANNUAL C-CEBH/NIDCD JOINT MEETING Sept. 19, 2024
Danielle Powell
Hearing loss amidst complex care needs or dementia: Identifying public health approaches for support and intervention
Utilizing a public health approach, Dr. Powell will bridge biological study of hearing systems in older adults with person-centered care needs and implementation sciences. CEBH research programs and NIDCD strategic initiatives are fundamental to understanding the health impacts of hearing loss on individuals and inform how we approach health care strategies to address communication needs. As an audiologist, epidemiologist, gerontologist and health services researcher working outside of the traditional CEBH disciplines, Dr. Powell will present a snapshot of her research on understanding the impacts of hearing loss in older adults with complex care needs like that of dementia, and the challenges faced by this unique population in accessing hearing rehabilitation education or hearing management. Attention will be paid to the unique challenges faced in translation biological and lab research into accessible and scalable service delivery models for implementation in mainstream care.
Christopher Shults
Transcription Factor Helios is Required for Outer Hair Cell Maturation and Function
Background: The transcriptional cascade that drives outer hair cell (OHC) maturation is still heavily under investigation. Our lab has identified the transcription factor Helios, which is encoded by the Ikzf2 gene, as an essential regulator for hair cells to reach a mature OHC fate. Mice deficient for Helios suffer from early onset hearing loss secondary to dysfunction of the OHCs, including a reduction in prestin-dependent electromotility. Additionally, the ectopic expression of Ikzf2 in inner hair cells results in the downregulation of IHC-specific genes and a transcriptomic shift towards OHC genetic markers. These findings provide insight into the regulatory power of Helios in OHCs; however, little is still understood concerning the mechanism in which Helios acts. Furthermore, the role of Helios post-OHC maturation has not been determined. In this study, we assess the requirement of Helios in fully differentiated mature OHCs and outline major transcriptional shifts in Helios-deficient OHCs.
Methods: Ikzf2 floxed mice were crossed separately with either Gfi1-Cre (onset of cre-recombinase expression in cochlear HCs at ~E16.5) or prestin-CreERT2 (tamoxifen-induced at P12/13/14) lines to conditionally deplete Helios from hair cells. The auditory function of these Ikzf2 cKO mice was determined using auditory brain response (ABR) tests and measuring distortion product otoacoustic emissions (DPOAEs) at both four and six weeks of age. To evaluate OHC loss, whole mount cochlear immunohistochemistry was performed at six weeks of age utilizing phalloidin and an anti-Prestin antibody. Transcriptional changes in Helios-deficient OHCs were determined using bulk and single-cell RNA sequencing of isolated OHCs from P8 Ikzf2 floxed; Gfi1-Cre mice.
Results: Both the Gfi1-Cre and the prestin-CreERT2 driven Ikzf2 cKO mice demonstrate a decrease in auditory function as assessed by ABR and DPOAE testing. Interestingly, both conditionally deleted lines exhibit elevated ABR thresholds by 4-weeks of age compared to their normal hearing littermate controls. Histological analyses identify that in the Gfi1-Cre driven Ikzf2 cKO mice there is a profound decrease in OHC number. However, in the prestin-CreERT2 driven Ikzf2 cKO mice revealed no OHC loss at 6-weeks of age. Transcriptional studies of the Helios deficient OHCs indicated a decrease in OHC-specific gene expression and a shift towards an inner hair cell-like state. Additionally, many deafness-related genes were dysregulated in the OHCs of this mouse model.
Conclusions: Our data reveal that Helios is required both for OHC development, as well as OHC functional maintenance. To better describe the role of Helios in regulating OHC maturation, we will further apply epigenetic techniques including CUT&RUN and ATAC-Seq to verify the downstream target genes of Helios and distinguish the biological pathways controlled by Helios.
Zachary Stoner
Mechanisms Regulating Organization of the Vestibular Ganglion
The vestibular system of the inner ear, comprised of five sensory end organs as well as their innervating neurons, is derived from a common primordium, the otic placode. During early otic development, neuronal fate determination is orchestrated by a cascade of proneural basic helix-loop-helix (bHLH) gene expression beginning with Neurogenin1 (Neurog1). Transient expression of Neurog1 in a small subset of otic precursors leads to commitment towards the neuronal lineage and subsequent delamination from the otic epithelium to form the cochleovestibular ganglion (CVG). Developmental patterning leads to populations within the CVG adopting either a vestibular or auditory fate and the eventual rise of two anatomically distinct ganglia. Unlike the auditory system where the first order neurons have well-defined topographic maps, the organization of neurons within the vestibular ganglion (VG) does not appear to be spatially organized based on their peripheral or central targets. The mechanism underlying vestibular ganglion neuron (VGN) identity and organization is unknown. To address this, our study investigates whether sequential and spatial delamination of neuroblasts from the otic epithelium determines the fate and position of individual VGNs. Using Neurog1-creERT2 transgenic mice to lineage-trace the neuronal-fated cells and EdU labeling to determine neuronal birthdates, we uncover distinct temporally regulated neuronal lineages within the VG. Our results indicate that the temporal sequence of neuron production regulates the organization of VGNs, with the earliest born neurons occupying restricted regions within the VG. Additionally, temporally distinct VGN populations appear to innervate specific regions within the vestibular end organs. Currently, we are working to determine the molecular signatures of spatially distinct VGN populations using scRNA-seq and investigating the underlying mechanism regulating VGN identity.
Cathy Yea Won Sung
Macrophage Ablation Protects Against Cisplatin-induced Hearing Loss without affecting the Tumor Efficacy of Cisplatin in Mice
Cisplatin is a widely used anti-cancer drug that leads to the death of mechanosensory hair cells in the cochlea, resulting in permanent hearing loss. Macrophages, the major resident immune cells in the cochlea, play an important role in driving both inflammatory and tissue repair responses. We have used a clinically relevant mouse model of cisplatin-induced ototoxicity coupled with selective macrophage ablation using PLX3397, an inhibitor of colony-stimulating factor 1 receptor. To determine the effect of PLX3397 in cisplatin-induced ototoxicity, mice underwent three cycles of cisplatin treatment, each cycle consisting of a once-daily cisplatin injection for 4 days followed by a 10-day recovery period. Selective macrophage ablation was achieved by treating subsets of mice with PLX3397 seven days prior to and throughout the cisplatin treatment. Hearing sensitivity was assessed using auditory brainstem responses (ABR). Remarkably, we found that macrophage ablation via PLX3397 treatment provided complete protection against cisplatin-induced hearing loss and outer hair cell (OHC) death.
As PLX3397 was recently approved by the FDA to treat tenosynovial giant cell tumor, this raises the possibility of repurposing PLX3397 to prevent cisplatin-induced ototoxicity in cancer patients receiving cisplatin. To examine the feasibility of using PLX3397 to reduce cisplatin-induced ototoxicity in the clinic, we further determined whether PLX3397 altered the chemotherapeutic efficacy of cisplatin in tumor-bearing mice. To establish the tumor-bearing mouse model, TC-1 tumor cells were subcutaneously injected into the hind flank of adult mice. Simultaneously, mice received control or PLX3397 chow to ablate macrophages. Seven days later, when palpable tumors were detected, mice were administered either saline or cisplatin while continuing to receive PLX3397. Tumor volume was measured daily. The four experimental groups employed were Saline/Vehicle, Saline/PLX3397, Cisplatin/Vehicle, and Cisplatin/PLX3397 in wild-type mice or mice implanted with TC-1 tumor cells. Cisplatin/Vehicle treatment significantly reduced tumor volume by approximately 63% (25 days after tumor implantation) compared with the Saline/Vehicle-treated group. Importantly, no significant difference in tumor volume was observed between mice receiving Cisplatin/PLX3397 versus those treated with Cisplatin/Vehicle, indicating that PLX3397 did not compromise the anti-tumor efficacy of cisplatin.
Our data indicate that macrophage ablation using PLX3397 provides robust protection against cisplatin-induced hearing loss. Importantly, in a tumor-bearing mouse model, we observed no reduction in the anti-tumor efficacy of cisplatin in mice that were also treated with PLX3397. As PLX3397 was approved by the FDA to treat tenosynovial giant cell tumor, our present study provides evidence that PLX3397 can likely be repurposed to prevent cisplatin-induced hearing loss in cancer patients receiving cisplatin.
Wing Ng
Cortical Responses to Speech Mixtures in a Ferret Cocktail Party
Segregation of complex sounds such as speech, music, and animal vocalizations as they simultaneously emanuate from multiple sources (referred to as the cocktail party problem) is a remarkable ability that is common in humans and animals alike. This study combines the insights from animal single-unit physiology with segregation of speech-like mixtures to study the neural underpinnings of this phenomonon. Ferrets were trained to attend to a female voice and detect a target word, both in presence or absence of a concurrent, equally salient male voice. Single neuron recordings were obtained from primary and secondary ferret auditory cortical fields, as well as frontal cortex. During task performance, representation of the female words became more enhanced relative to those of the (distractor) male in all cortical regions, especially in the higher auditory cortical field. Analysis of the temporal and spectral response characteristics during task performance reveals how speech segregation gradually emerges in the auditory cortex.
Paul Mayo
Two Cues Are Better Than One: Adding Interaural Time Differences Improves Spatial Hearing For Bilateral Cochlear-Implant Users
Bilateral cochlear-implant (BI-CI) listeners show limited sensitivity to interaural time differences (ITDs), the dominant localization cue for acoustic-hearing listeners, and mainly rely on interaural level differences (ILDs) for localization. Studies utilizing bilaterally synchronized direct stimulation capable of conveying ITDs have investigated sensitivity to ITDs or ILDs in isolation. It is, however, unclear how these two cues interact in controlled and bilaterally synchronized electrical stimulation. Therefore, this study performed an ITD-ILD cue-weighting lateralization experiment with BI-CI listeners using direct stimulation of single electrodes. Preliminary results show that BI-CI listeners display sensitivity only to ILDs with unsynchronized stimulation and equal sensitivity to both ITDs and ILDs with synchronized stimulation. Additionally, providing ITDs and ILDs together via bilaterally synchronized stimulation resulted in increased lateralization ranges and slopes, thus improved spatial hearing acuity compared to either cue alone. These results suggest providing both ITDs and ILDs via bilaterally synchronized sound processors has the potential to improve spatial hearing in BI-CI listeners. The data have implications for clinical sound processor design and stimulation strategies.
Nina Benway
Examining Vocal Tract Coordination in Childhood Apraxia of Speech with Acoustic-to-Articulatory Speech Inversion Feature Sets
Childhood apraxia of speech is a genetically driven, neurodevelopmental speech sound disorder with speech deficits theorized to reflect difficulty in the spatiotemporal programming of speech movements. Therefore, this work examined how well articulatory coordination features generated from audio-estimated kinematic data distinguished speakers with childhood apraxia of speech versus non-apraxic speech sound disorder. Two correlation-based feature sets motivated by recent literature demonstrated high performance in replicated 6-fold nested cross validated studies, with no statistically significant difference between feature sets (mean AUROC = .90, σ = .04). An ablation study emphasized the importance of source-filter coordination in this population of apraxic speakers, with the source-ablated feature set performing significantly worse than the lip-ablated, the tongue-ablated, and full feature set (ΔAUROC = -.19, SE = 0.01, p < .001).
Vrishab Commuri
Physiological Functional Connectivity and Altered Auditory Processing
Listening in difficult, noisy conditions affects the cortical neural circuits that underlie speech comprehension. These directional circuits convey neural signals between cortical regions, encode information related to processing of the stimulus, and are characterized by their dominant frequency band, e.g., delta band or theta band. Here we elucidate how these circuits change as listening conditions become increasingly adverse, and we reveal differences in regional recruitment between individuals. We utilize the Network Localized Granger Causality (NLGC) framework applied to magnetoencephalography (MEG) data to simultaneously estimate neural currents in cortex and the graph network that connects current sources to one another. This directional connectivity is analyzed in multiple non-overlapping regions that span the entire cortex. Additionally, a Temporal Response Function (TRF) analysis is performed on the estimated current sources to probe hierarchical processing of speech features among network-connected current sources and to determine to what extent these circuits convey signals that temporally track the stimulus. Broadly, we estimate the connectivity of the cortical neural circuits in physiological frequency bands that are involved in processing speech, and we examine how the circuits change with listening difficulty. We also demonstrate how to combine these circuits with established TRF analysis to localize hierarchical processing of speech. We present results on a listening data set, but note that the methods are widely applicable to most MEG data sets.
Sayaka Inagaki
Interaction between TBC1D24 and KIBRA is disrupted by two epilepsy-associated TBC1D24 missense variants
Human TBC1D24 variants are associated with either deafness, epilepsy or DOORS syndrome. The relationships between TBC1D24 variants and its different clinical phenotypes are not understood. Currently, three proteins have been reported as binding partners of TBC1D24 orthologues, however, the clinically heterogeneous disorders caused by TBC1D24 variants remain unexplained. Biological functions are rarely embodied solely in individual proteins, but rather result from interactions and complexes among proteins, DNA, RNA and/or small molecules in cells. We hypothesized that the phenotypic heterogeneity of missense variants of TBC1D24 result, in part, from perturbed binding of protein partners yet to be discovered. In this study, we performed a yeast two-hybrid (Y2H) screen using mouse TBC1D24 as bait and a mouse inner ear library as prey to discover novel protein partners. As a result, KIBRA, a scaffold protein encoded by the Wwc1 gene, was suggested as a partner of TBC1D24. KIBRA is involved in the Hippo signaling pathway and is also important for memory and cognition. Further validation assays indicated that the TLDc domain of TBC1D24 binds to the KIBRA C2 domain. Two epilepsy-associated recessive missense variants in the TLDc domain of human TBC1D24 disrupt the interaction with the human KIBRA C2 domain. The mRNAs encoded by TBC1D24 and KIBRA in mouse are co-expressed in a subset of brain hippocampal cells indicating the likely availability of KIBRA and TBC1D24 proteins to interact in vivo. This study uncovered a pathogenic mechanism of TBC1D24-associated epilepsy and also linked together the TBC1D24 and KIBRA pathways.
Jason Putnam
Neural correlates of Pitch perception in Mouse Auditory cortex
Pitch perception is a fundamental component of hearing that is critical for everyday listening tasks, such as speech comprehension and music appreciation. Temporal periodicity is an acoustic cue for pitch perception, yet it is poorly understood how the auditory system transforms temporal periodicity into ‘periodicity pitch’—a percept that is heard in-common across sounds with the same temporal periodicity but different spectral profiles. Here, we used mice as an animal model to study the neural basis of periodicity pitch in auditory cortex. Because mice have poor hearing below 2 kHz, and their auditory filters above 2 kHz blur spectral profiles, we hypothesized that pitch perception in mice may largely derive from temporal periodicity in sound and is represented in auditory cortex as periodotopy. To investigate periodicity pitch perception, we trained a cohort of mice on a go/no-go auditory operant conditioning task in which they were rewarded for licking a waterspout after hearing sounds with a low fundamental frequency (F0), and punished with a time-out after licking in response to a high F0. The stimulus set included 4 kinds of periodic broadband sounds (2-45 kHz), each with different spectral profiles: harmonic stacks (HS), click trains (CT), iterated ripple noise (IRN), and amplitude modulated noise (AMN). Each type of sound was presented in randomized order, and with F0=55 Hz (go-signal) or F0=330 Hz (no-go signal). We used in vivo widefield imaging of auditory cortex in awake transgenic thy1-GCaMP6s mice to study cortical periodotopy in response to HS, CT, AMN, and IRN stimuli. Results: Our preliminary behavioral data show that mice learned to correctly discriminate F0 (d’ greater than 1) for each type of sound, except IRN. However, we found that mice could learn to correctly discriminate IRNs when spectral cues were made available by increasing F0. Importantly, our results suggest that mice initially trained only with HS immediately generalized the task to HS, CT, and AMN stimuli. Our widefield imaging results show that HS, CT, and AMN each have similar periodotopy in cortical space, though the exact spatial pattern differed across individual mice. In contrast, IRN showed weak periodotopy that was often spatially inconsistent and more variable compared to the other stimuli. Our results suggest that mice may perceive periodicity pitch. Furthermore, the robustness of periodotopy for a given sound may correlate with how well mice hear periodicity pitch.
Jennifer Chisholm
Effects of Propofol Sedation on the ABR in Patients with CLN3/Batten Disease
CLN3 (Batten Disease) is a rare and fatal autosomal recessive, lysosomal storage disorder characterized by rapidly progressive vision loss with typical onset between 4 -7 years old, behavioral issues, cognitive decline, seizures, and neurodegeneration. The purpose of this study is to describe auditory brainstem response (ABR) latency prolongations observed when testing was performed under propofol sedation versus a wakeful state. Individuals with CLN3/Batten Disease enrolled in NIH protocol were seen for an auditory evaluation that included and standard hearing evaluation and neurodiagnostic auditory brainstem response (ABR) testing. The ABR was conducted while the patients were relaxed and awake (or in natural sleep) and anesthetized with propofol, and a comparison was made to investigate the effects of propofol on the ABR. Additionally, for patients seen longitudinally, comparisons are made over time to assess for changes within individuals. Interpretation of the neurodiagnostic ABR was based on a 1-4 grading scale that considers wave presence and morphology, absolute and interpeak latencies, and the wave V/I amplitude ratio. Grades 1 and 2 represent normal to near normal findings, and grades 3 and 4 indicating retrocochlear involvement. There is a significant effect of sedation (propofol) on ABR latencies in this group, which sometimes changes the ABR’s clinical interpretation. The average amount of latency prolongations under sedation in our group are greater than previous reports in the literature. Longitudinal comparisons may determine if there are changes over time that parallel CLN3 disease progression.