Biology subjects

Simmons, D. D.

Publications and source records attributed to Simmons, D. D..

7 recordsLinked to original sources

bioRxiv2026

Cochlear Innate Immune Homeostasis is altered in the Oncomodulin-Deficient Mouse Model

As part of cochlear innate immunity, cochlear resident macrophages regulate different aspects of tissue maturation, cochlear homeostasis, and injury response. Cochlear resident macrophages exhibit dynamic changes in morphology, distribution, and abundance after cochlear injury. However, in the absence of pathology, regulation of cochlear innate immunity is poorly understood. Since loss of cochlear outer hair cells (OHCs) are indicators of cochlear pathology, we hypothesize that cochlear innate immunity might be sensitive to changes in OHC function. Calcium homeostasis in OHCs is necessary for auditory function, and its dysregulation is associated with hearing loss. However, it is unknown if changes in OHC Ca2+ homeostasis are sufficient to alter cochlear innate immunity. Here, we investigate alterations in cochlear innate immunity in a mouse model lacking oncomodulin (OCM), an OHC-specific calcium buffer. Our study focused on the osseous spiral lamina (OSL), a region adjacent to cochlear hair cells. At 1 month, wild-type (WT) mice and Ocm knockout (KO) mice have similar hearing thresholds and no evidence of cochlear damage. However, in KO mice, OSL resident macrophages show increased density, altered morphology, and increased spatial segregation closer to the sensory epithelium. Despite these changes in OSL resident macrophages, cytokine profiling revealed no remarkable differences. At 5 months, Ocm KO mice show a progressive hearing loss with a frequency dependent loss of OHCs and inner hair cell ribbon synapses, but the density of OSL macrophages remained unchanged. Prior to hearing onset, there was no significant difference in immune cell numbers between Ocm WT and KO mice. These findings suggest that cochlear innate immunity is sensitive to OHC calcium buffering following hearing onset.

neuroscience↗

bioRxiv2024

Lack of Oncomodulin Increases ATP-Dependent Calcium Signaling and Susceptibility to Noise in Adult Mice

Tight regulation of Ca2+ is crucial for the function of cochlear outer hair cells (OHCs). Dysregulation of Ca2+ homeostasis in OHCs is associated with impaired hearing and contributes to increased vulnerability to insults such as noise exposure. Ca2+ signaling in developing OHCs is modulated by oncomodulin (OCM), an EF-hand calcium-binding protein. Here, we investigated whether the lack of OCM disrupts the control of intracellular Ca2+ in mature OHCs, and influences vulnerability to acoustic injury. Using young adult CBA/CaJ mice, we found that OHCs from Ocm-knockout (Ocm-/-) mice showed normal biophysical profiles, electromotile responses, and synaptic innervation compared to littermate controls. Moderate noise exposure (95 dB SPL, 2 hrs) caused temporary threshold shifts in Ocm+/+ and Ocm-/- mice. However, while Ocm+/+ fully recovered thresholds 2 weeks after noise exposure, Ocm-/- mice showed permanent threshold shifts. Additionally, Ocm-/- mice had auditory brainstem responses with highly variable latencies and amplitudes both before and after noise exposure compared to Ocm+/+ mice. Using a genetically encoded Ca2+ sensor (GCaMP6s) expressed in Ocm+/+ and Ocm-/- OHCs, we found that prolonged noise exposure (95 dB SPL, 9 hrs) significantly increased GCaMP6s fluorescence, ATP-induced Ca2+ signaling and also caused greater threshold shifts in Ocm-/- compared to Ocm+/+ OHCs. However, prolonged noise exposure had no significant change in the number of presynaptic OHC ribbons in either Ocm+/+ or Ocm-/- mice. We assessed whether the ATP-induced responses were due to changes in P2X2 receptor expression. Prior to noise exposure, P2X2 expression was higher in the cochlea of Ocm-/- mice compared to Ocm+/+ mice. Following prolonged noise, P2X2 receptors were upregulated in the cochlea of Ocm+/+ but not in the Ocm-/- mice, which retained their pre-noise expression level. We propose that the lack of OCM increases susceptibility to cochlear pathology and that purinergic signaling and dysregulation of cytosolic Ca2+ homeostasis likely contribute to early onset hearing loss in the Ocm-/- mice.

neuroscience↗

bioRxiv2023

Oncomodulin Regulates Spontaneous Calcium Signaling and Maturation of Afferent Innervation in Cochlear Outer Hair Cells

Cochlear outer hair cells (OHCs) are responsible for the exquisite frequency selectivity and sensitivity of mammalian hearing. During development, the maturation of OHC afferent connectivity is refined by coordinated spontaneous Ca2+ activity in both sensory and non-sensory cells. Calcium signaling in neonatal OHCs can be modulated by Oncomodulin (OCM, {beta}-parvalbumin), an EF-hand calcium-binding protein. Here, we investigated whether OCM regulates OHC spontaneous Ca2+ activity and afferent connectivity during development. Using a genetically encoded Ca2+ sensor (GCaMP6s) expressed in OHCs in wild-type (Ocm+/+) and Ocm knockout (Ocm-/-) littermates, we found increased spontaneous Ca2+ activity and upregulation of purinergic receptors in OHCs from GCaMP6s Ocm-/- cochlea immediately following birth. The afferent synaptic maturation of OHCs was delayed in the absence of OCM, leading to an increased number of ribbon synapses and afferent fibers on GCaMP6s Ocm-/- OHCs before hearing onset. We propose that OCM regulates the spontaneous Ca2+ signaling in the developing cochlea and the maturation of OHC afferent innervation.

developmental biology↗

bioRxiv2022

Oncomodulin (OCM) uniquely regulates calcium signaling in neonatal cochlear outer hair cells.

In cochlear outer hair cells (OHCs), a network of Ca2+ channels, pumps and Ca2+-binding proteins (CaBPs) regulates the localization, spread, and magnitude of free Ca2+ ions. During early postnatal development, OHCs express three prominent mobile EF-hand CaBPs: oncomodulin (OCM), -parvalbumin (APV) and sorcin. We have previously shown that deletion of Ocm (Ocm-/-) gives rise to progressive cochlear dysfunction in young adult mice. Here, we show that changes in Ca2+ signaling begin early in postnatal development of Ocm-/- mice. While mutant OHCs exhibit normal electrophysiological profiles compared to controls, their intracellular Ca2+ signaling is altered. The onset of OCM expression at postnatal day 3 (P3) causes a developmental change in KCl-induced Ca2+ transients in OHCs and leads to slower KCl-induced Ca2+ transients than those elicited in cells from Ocm-/- littermates. We compared OCM buffering kinetics with other CaBPs in animal models and cultured cells. In a double knockout of Ocm and Apv (Ocm-/-;Apv-/-), mutant OHCs show even faster Ca2+ kinetics, suggesting that APV may also contribute to early postnatal Ca2+ signaling. In transfected HEK293T cells, OCM slows Ca2+ kinetics more so than either APV or sorcin. We conclude that OCM controls the intracellular Ca2+ environment by lowering the amount of freely available [Ca2+]i in OHCs and in transfected HEK293T cells. We propose that OCM plays an important role in shaping the development of early OHC Ca2+ signals through its inimitable Ca2+ buffering capacity.

developmental biology↗

bioRxiv2021

Diminished GAD67 Terminals and Ambient GABA Inhibition Associated with Reduced Motor Neuron Recruitment Threshold in the SOD1G93A ALS mouse

Pre-symptomatic studies in mouse models of the neurodegenerative motor neuron (MN) disease, Amyotrophic Lateral Sclerosis (ALS) highlight early alterations in intrinsic and synaptic excitability and have supported an excitotoxic theory of MN death. However, a role for synaptic inhibition in disease development is not sufficiently explored among other mechanisms. Since inhibition plays a role in both regulating motor output and in neuroprotection, we examined the age-dependent anatomical changes in inhibitory presynaptic terminals on MN cell bodies using fluorescent immunohistochemistry for GAD67 (GABA) and GlyT2 (glycine) presynaptic proteins comparing ALS-vulnerable trigeminal jaw closer (JC) motor pools with the ALS-resistant extraocular (EO) MNs in the SOD1G93A mouse model for ALS. Our results indicate differential patterns of temporal changes of these terminals in vulnerable versus resilient MNs and relative differences between SOD1G93A and wild-type (WT) MNs. Notably, we found pre-symptomatic up-regulation in inhibitory terminals in the EO MNs while the vulnerable JC MNs mostly showed a decrease in inhibitory terminals. Specifically, there was a statistically significant decrease in the GAD67 somatic abuttal in the SOD1G93A JC MNs compared to WT around P12. Using in vitro patch-clamp electrophysiology, we found a parallel decrease in the ambient GABA-dependent tonic inhibition in the SOD1G93A JC MNs. While it is unclear if the two mechanisms are directly related, pharmacological blockade of specific subtype of GABAA-5 receptors suggests that tonic inhibition can control MN recruitment threshold. Furthermore, reduction in tonic GABA current as observed here in the mutant, identifies a putative molecular mechanism explaining our observations of hyperexcitable shifts in JC MN recruitment threshold in the SOD1G93A mouse. Lastly, we showcase non-parametric resampling-based bootstrap statistics for data analyses, and provide the Python code on GitHub for wider reuse.

neuroscience↗

bioRxiv2021

Oncomodulin Delays Age-Related Hearing Loss in C57 and CBA Mice

Ca2+ signaling is a major contributor to sensory hair cell function in the cochlea. Oncomodulin (OCM) is a Ca2+ binding protein preferentially expressed in outer hair cells of the cochlea and few other specialized cell types. Here, we expand on our previous reports and show that OCM prevents early progressive hearing loss in mice of two different genetic backgrounds: CBA/CaJ and C57BI/6J. In both backgrounds, genetic disruption of Ocm leads to early progressive hearing loss as measured by auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE). In both strains, loss of Ocm reduced hearing across lifetime (hearing span) by more than 50% relative to wild type (WT). Even though the two WT strains have very different hearing spans, OCM plays a considerable and similar role within their genetic environment to regulate hearing function. The accelerated ARHL of the Ocm KO illustrates the importance of Ca2+ signaling in maintaining hearing health.

neuroscience↗

bioRxiv2018

Spontaneous and coordinated Ca2+ activity of cochlear sensory and non-sensory cells drives the maturation of OHC afferent innervation

Outer hair cells (OHCs) are highly specialized sensory cells conferring the fine tuning and high sensitivity of the mammalian cochlea to acoustic stimuli. Here, by genetically manipulating spontaneous Ca2+ signalling in vivo, through a period of early postnatal development, we find that the refinement of OHC afferent innervation is regulated by complementary spontaneous Ca2+ signals originating in OHCs and non-sensory cells. OHCs fire spontaneous Ca2+ spikes during a narrow period of immature development. Simultaneously, waves of Ca2+ activity in the non-sensory greater epithelial ridge act, via ATP-induced activation of P2X receptors, to synchronize OHC firing, resulting in the refinement of their afferent innervation. In the absence of connexin channels Ca2+ waves are impaired, leading to a reduction in the number of ribbon synapses and afferent fibres on OHCs. We propose that the correct maturation of the afferent connectivity in OHCs requires experience-independent Ca2+ signals from sensory and non-sensory cells.

neuroscience↗