Changes in MAP2 and tyrosinated alpha-tubulin expression in cochlear inner hair cells after amikacin treatment in the rat

Microtubule and auditory function - an underestimated connection

The organ of Corti, located in the cochlea within the inner ear is the receptor organ for hearing. It converts auditory signals into neuronal action potentials that are transmitted to the brain for further processing. The mature organ of Corti consists of a variety of highly differentiated sensory cells that fulfil unique tasks in the processing of auditory signals. The actin and microtubule cytoskeleton play essential function in hearing, however so far, more attention has been paid to the role of actin. Microtubules play important roles in maintaining cellular structure and intracellular transport in virtually all eukaryotic cells. Their functions are controlled by interactions with a large variety of microtubule-associated proteins (MAPs) and molecular motors. Current advances show that tubulin posttranslational modifications, as well as tubulin isotypes could play key roles in modulating microtubule properties and functions in cells. These mechanisms could have various effects on the stability and functions of microtubules in the highly specialised cells of the cochlea. Here, we review the current understanding of the role of microtubule-regulating mechanisms in the function of the cochlea and their implications for hearing, which highlights the importance of microtubules in the field of hearing research.

Neuronal development in the cochlea of a nonhuman primate model, the common marmoset

Precise cochlear neuronal development is vital to hearing ability. Understanding the developmental process of the spiral ganglion is useful for studying hearing loss aimed at aging or regenerative therapy. Although interspecies differences have been reported between rodents and humans, to date, most of our knowledge about the development of cochlear neuronal development has been obtained from rodent models because of the difficulty in using human fetal samples in this field. In this study, we investigated cochlear neuronal development in a small New World monkey species, the common marmoset (Callithrix jacchus). We examined more than 25 genes involved in the neuronal development of the cochlea and described the critical developmental steps of these neurons. We also revealed similarities and differences between previously reported rodent models and this primate animal model. Our results clarified that this animal model of cochlear neuronal development is more similar to humans than rodents and is suitable as an alternative for the analysis of human cochlear development. The time course established in this report will be a useful tool for studying primate‐specific neuronal biology of the inner ear, which could eventually lead to new treatment strategies for human hearing loss.

A mutation in MAP2 is associated with prenatal hair follicle density

Hairlessness is usually a rare trait in pigs; however, in this study, we found hairless (HR) pigs at a relatively high frequency in 1 pig herd. We observed that, the lower hair shaft density of HR pigs could be mainly attributed to the lower hair follicle density, and during the embryonic period, d 39-45 were a critical stage for the formation of the hair follicle. In this regard, d 41 during gestation was a particularly important point. Hair follicle morphogenesis occurring at an early stage of embryo development is similar to humans and mice. Further analyses of association studies based on single-nucleotide polymorphism chip as well as sequence data, mRNA sequencing, immunohistochemistry, and comparative genomics demonstrated that microtubule-associated protein 2 (MAP2) is a key gene responsible for hair follicle density and 1 missense mutation of A-to-G at rs328005415 in MAP2, causing a valine-to-methionine substitution leads to the HR phenotype. Considering the high homology between pigs and humans, our research has some significance for the study of the mechanisms of skin development, hair morphogenesis, and hair loss in humans by showing that the pig may be a more appropriate model in which to study these processes.-Jiang, Y., Jiang, Y., Zhang, H., Mei, M., Song, H., Ma, X., Jiang, L., Yu, Z., Zhang, Q., Ding, X. A mutation in MAP2 is associated with prenatal hair follicle density.

Role of nonlinear localized Ca(2+) pulses along microtubules in tuning the mechano-sensitivity of hair cells

This paper aims to provide an overview of the polyelectrolyte model and the current understanding of the creation and propagation of localized pulses of positive ions flowing along cellular microtubules. In that context, Ca(2+) ions may move freely on the surface of microtubule along the protofilament axis, thus leading to signal transport. Special emphasis in this paper is placed on the possible role of this mechanism in the function of microtubule based kinocilium, a component of vestibular hair cells of the inner ear. We discuss how localized pulses of Ca(2+) ions play a crucial role in tuning the activity of dynein motors, which are involved in mechano-sensitivity of the kinocilium. A prevailing notion holds that the concentration of Ca(2+) ions around the microtubules within the kinocilium represents the control parameter for Hopf bifurcation. Therefore, a key feature of this mechanism is that the velocities of these Ca(2+) pulses be sufficiently high to exert control at acoustic frequencies.

Tinnitus: pathology of synaptic plasticity at the cellular and system levels

Despite being more and more common, and having a high impact on the quality of life of sufferers, tinnitus does not yet have a cure. This has been mostly the result of limited knowledge of the biological mechanisms underlying this adverse pathology. However, the last decade has witnessed tremendous progress in our understanding on the pathophysiology of tinnitus. Animal models have demonstrated that tinnitus is a pathology of neural plasticity, and has two main components: a molecular, peripheral component related to the initiation phase of tinnitus; and a system-level, central component-related to the long-term maintenance of tinnitus. Using the most recent experimental data and the molecular/system dichotomy as a framework, we describe here the biological basis of tinnitus. We then discuss these mechanisms from an evolutionary perspective, highlighting similarities with memory. Finally, we consider how these discoveries can translate into therapies, and we suggest operative strategies to design new and effective combined therapeutic solutions using both pharmacological (local and systemic) and behavioral tools (e.g., using tele-medicine and virtual reality settings).

Truncated Tau with the Fyn-binding domain and without the microtubule-binding domain hinders the myelinating capacity of an oligodendrocyte cell line

The mechanisms underlying developmental myelination have therapeutic potential following CNS injury and degeneration. We report that transplanted central glial (CG)-4 cells had a diminished myelinating capacity in myelin-deficient (md) rats when cells express a mutated form of Tau (Tau [688]), which binds Fyn but not the microtubules. In the brain of the md rats, Tau [688]-transfected CG-4 cells displayed a decrease in cellular process outgrowth and myelination; in the spinal cord the extent of myelination rostral and caudal to the injection site was decreased. In contrast, control Tau [605]-transfected CG-4 cells formed long cellular processes and substantial areas of myelin both in the brain and spinal cord. In culture, Tau [688]-transfected CG-4 cells displayed a decrease in cellular process outgrowth, and Fyn localized largely in the cell body, not the processes. Thus, Tau in oligodendrocytes plays a key role in myelination, and a functional Tau-Fyn interaction might have therapeutic potential during demyelination and myelin repair following CNS injury and degeneration.

Calpain activity in the amikacin-damaged rat cochlea

The principal aim of this study was to investigate the involvement of calpain in the degeneration of hair cells and ganglion neurons in the amikacin-poisoned rat cochlea. An antibody designed against fodrin-breakdown products (FBDP), which result exclusively from cleavage by calpain, was used. In addition, the involvement of both caspases and protein kinase C (PKC) was studied using, respectively, antibodies against activated caspase 3 and PKCgamma. The results demonstrate the accumulation of FBDP in the degenerating hair cells, in some supporting cells such as Deiters cells, and, later, in the affected ganglion neurons that had been deprived of their sensory targets. Activated caspase 3 was evidenced in a few dying hair cells and ganglion neurons. PKCgamma was highly expressed in all ganglion neurons, sometimes after the loss of hair cells. We conclude that calpain plays a role in the degradation of both the sensory cells and neurons after amikacin ototoxicity. In the poisoned hair cells, calpain and caspase 3 may have synergistic effects in the process of apoptosis. In the ganglion neurons deprived of their sensory elements, calpain may have a prominent role in cell degradation. By contrast, in these ganglion neurons PKCgamma may be implicated in a survival process. Finally, we suggest that calpain is involved in the remodeling of Deiters cells during the scarring process that follows hair cell loss.

Fate of neural stem cells grafted into injured inner ears of mice

Loss of sensory hair cells in the inner ear is a major cause of permanent hearing loss, since regeneration of hair cells rarely occurs in mammals. The aim of this study was to examine the potential of neural stem cell transplantation to restore inner ear hair cells in mice. Fetal neural stem cells were transplanted into the mouse inner ear after drug-induced injury. Histological analysis demonstrates that the majority of grafted cells differentiated into glial or neural cells in the inner ear. Strikingly, however, we show that grafted cells integrate in vestibular sensory epithelia and express specific markers for hair cells. This finding suggests that transplanted neural stem cells have the potential to differentiate and restore inner ear hair cells.