Sox9 Inhibits Cochlear Hair Cell Fate by Upregulating Hey1 and HeyL Antagonists of Atoh1.

peer reviewedIt is widely accepted that cell fate determination in the cochlea is tightly controlled by different transcription factors (TFs) that remain to be fully defined. Here, we show that Sox9, initially expressed in the entire sensory epithelium of the cochlea, progressively disappears from differentiating hair cells (HCs) and is finally restricted to supporting cells (SCs). By performing ex vivo electroporation of E13.5-E14.5 cochleae, we demonstrate that maintenance of Sox9 expression in the progenitors committed to HC fate blocks their differentiation, even if co-expressed with Atoh1, a transcription factor necessary and sufficient to form HC. Sox9 inhibits Atoh1 transcriptional activity by upregulating Hey1 and HeyL antagonists, and genetic ablation of these genes induces extra HCs along the cochlea. Although Sox9 suppression from sensory progenitors ex vivo leads to a modest increase in the number of HCs, it is not sufficient in vivo to induce supernumerary HC production in an inducible Sox9 knockout model. Taken together, these data show that Sox9 is downregulated from nascent HCs to allow the unfolding of their differentiation program. This may be critical for future strategies to promote fully mature HC formation in regeneration approaches

Gene transfer in inner ear cells: a challenging race

Recent advances in human genomics led to the identification of numerous defective genes causing deafness, which represent novel putative therapeutic targets. Future gene-based treatment of deafness resulting from genetic or acquired sensorineural hearing loss may include strategies ranging from gene therapy to antisense delivery. For successful development of gene therapies, a minimal requirement involves the engineering of appropriate gene carrier systems. Transfer of exogenous genetic material into the mammalian inner ear using viral or non-viral vectors has been characterized over the last decade. The nature of inner ear cells targeted, as well as the transgene expression level and duration, are highly dependent on the vector type, the route of administration and the strength of the promoter driving expression. This review summarizes and discusses recent advances in inner ear gene-transfer technologies aimed at examining gene function or identifying new treatment for inner ear disorders

Oxidative Stress in the Cochlea: An Update.

This paper will focus on understanding the role and action of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in the molecular and biochemical pathways responsible for the regulation of the survival of hair cells and spiral ganglion neurons in the auditory portion of the inner ear. The pivotal role of ROS/RNS in ototoxicity makes them potentially valuable candidates for effective otoprotective strategies. In this review, we describe the major characteristics of ROS/RNS and the different oxidative processes observed during ototoxic cascades. At each step, we discuss their potential as therapeutic targets because an increasing number of compounds that modulate ROS/RNS processing or targets are being identified

In vivo protection of spiral ganglion neurons by bryostatin 1: preliminary results

Background: We aim to demonstrate the effect of bryostatin 1, a macrocyclic lactone that activates protein kinase C, on spiral ganglion neurons (SGNs) of adult guinea pigs deafened by aminoglycoside. Methodology: Twenty-one guinea pigs were deafened by the aminoglycoside gentamicin and then treated by continuous infusion of experimental molecule for 1 month. The experimental molecule was bryostatin 1, artificial perilymph (negative control), or neurotrophins and an apoptosis inhibitor (positive control). Neuronal density in the spiral ganglia was quantified. Results: Bryostatin 1 protected SGNs after a gentamicin challenge. Conclusions: Bryostatin 1 has a neuroprotective effect when administered continuously at low doses in adult guinea pigs

Behavioural phenotyping of SV2A lox/lox mice: Motor and anxiety-like features

Background: Epilepsy is one of the most common neurological disorders (Alexopoulos, 2004). Current anti-epileptic drugs, such as Levetiracetam (Keppra®) or Brivaracetam, mainly target the trans-membrane Synaptic Vesicle Protein 2A (Hamann et al., 2008). Studies on homozygous SV2A KO mice phenotype, prove the mice to suffer severe seizures and die within 3 weeks (Crowder et al., 1999), establishing a link between this protein and the epilepsy. In 2009, the availability of heterozygous SV2A (+/-) mice as research tool enabled shedding light on the role of protein SV2A, revealing no motor differences but anxiety-like features in these mice compared with the WT (Lamberty et al., 2009), and a pro-epileptic phenotype (Crowder et al., 1999; Kaminski et al., 2008). Recently, a floxed SV2A mouse model has been produced with the Cre/loxP recombination system, this model allows invalidating the protein in CA3 hippocampal region, not followed by epileptic seizures (Menten-Dedoyart et al., 2016). Objectives: Perform a first behavioural phenotyping of SV2A lox/lox mice. Methodology: Two experiments were conducted in parallel to evaluate the effect of 3 different genotypes in the phenotype: WT (Grik4-/-, SV2A lox/lox), HZ (Grik4 +/-, SV2A lox/+) and cKO (Grik4 +/-, SV2A lox/lox) in male (n = 42) and female (n = 33) separately . Mice were housed individually along the experiment, with standard food and water ad libitum. After an acclimatization period of 2 weeks, anxiety-like features as well as exploration abilities were evaluated in an elevated plus-maze (EPM) single session of 5 minutes). 3 days later, spontaneous locomotor activity and habituation to the environment were measured during 1 hour, 3 consecutive days, in the activity chambers (ACT). Results: One-way ANOVA in EPM data presented no significant differences between groups, either in males or in females. A significant difference was found, between time spent in close arms vs open arms (p0.05). Statistical significant differences were found between the 3 days (p<0.01; η2p = 0.716 males; η2p = 0.663 females). Conclusion: Results indicate that a decrease in the hippocampal expresion of SV2A protein does not lead to major behavioral changes. Regarding locomotor activity, the results found in heterozygous SV2A (+/-) mice are in line with (Lamberty et al., 2009), however, our mice did not present anxiety-like features, being necessary a global decrease in brain SV2A levels and not only a partial loss in a restricted region of the brain. Further analyses increasing the number of mice per group, will allow us to intensify our power value from 50-60% (females-males) up to 80%, with large effect size and a signification of p<0.05. An additional test to evaluate the spatial memory may help us better understand the effect a specific reduction in SV2A hippocampal expression has on the phenotype of mice.ARC 13/17 - 07 (SYNAP - SV2A