Localization of nitric oxide synthase isoforms in the human cochlea

Zika virus infection causes widespread damage to the inner ear

Zika virus (ZIKV) has been recently recognized as a causative agent of newborn microcephaly, as well as other neurological consequences. A less well recognized comorbidity of prenatal ZIKV infection is hearing loss, but cases of hearing impairment following adult ZIKV infection have also been recognized. Diminished hearing following prenatal ZIKV infection in a mouse model has been reported, but no cellular consequences were observed. We examined the effects of ZIKV infection on inner ear cellular integrity and expression levels of various proteins important for cochlear function in type I interferon receptor null (Ifnar1^-/-) mice following infection at 5-6 weeks of age. We show that ZIKV antigens are present in cells within the cochlear epithelium, lateral wall, spiral limbus and spiral ganglion. Here we show that ZIKV infection alters cochlear expression of genes that signal cell damage (S100B), transport fluids (AQP1), are gaseous transmitters (eNOs) and modulate immune response (F4/80). Morphological analyses shows that not only are cochlear structures compromised by ZIKV infection, but damage also occurs in vestibular end organs. ZIKV produces a graded distribution of cellular damage in the cochlea, with greatest damage in the apex similar to that reported for cytomegalovirus (CMV) infection. The graded distribution of damage may indicate a differential susceptibility to ZIKV along the cochlear tonotopic axis. Collectively, these data are the first to show the molecular and morphological damage to the inner ear induced by ZIKV infection in adults and suggests multiple mechanisms contributing to the hearing loss reported in the human population.

eNOS gene Glu298Asp variant confer risk in sudden sensorineural hearing loss

BACKGROUND

Sudden sensorineural hearing loss (SSNHL) causes the loss of hearing of 30 dB or greater on at least three contiguous frequencies. It is known to be a multifactorial disease which the exact cause is unknown, rendering it as an idiopathic disorder of patients.

AIMS/OBJECTIVES

This study aims to shed further light on pathogenesis of this disease by studying the association between eNOS gene Glu298Asp polymorphism and VDR gene FokI polymorphism with SSNHL in Iranian population.

MATERIAL AND METHODS

This study involves a total of 77 cases and 100 controls, with patients inflicted with SSNHL categorized in case group and healthy subjects as control group. Genotyping of the VDR and eNOS genes was conducted by the polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) method.

RESULTS

Our results showed a statistically significant association between genotype frequencies of eNOS gene Glu298Asp polymorphism in case group compared to healthy individuals in the control group (p = .01). Also, TT genotype was significantly the most prevalent genotype in case group in comparison to control group (TT vs GT + GG, OR = 3.5; 95% CI = 1.18-11.79). On the other hand, analysis of VDR gene FokI polymorphism frequencies showed no statistically significant association with SSNHL.

CONCLUSIONS AND SIGNIFICANCE

Our findings showed a significant association between the eNOS gene Glu298Asp polymorphism and SSNHL in the Iranian population; and "TT" genotype might be considered as a risk factor for SSNHL.

Oxidative Stress in the Blood Labyrinthine Barrier in the Macula Utricle of Meniere's Disease Patients

The blood labyrinthine barrier (BLB) is critical in the maintenance of inner ear ionic and fluid homeostasis. Recent studies using imaging and histopathology demonstrate loss of integrity of the BLB in the affected inner ear of Meniere's disease (MD) patients. We hypothesized that oxidative stress is involved in the pathogenesis of BLB degeneration, and to date there are no studies of oxidative stress proteins in the human BLB. We investigated the ultrastructural and immunohistochemical changes of the BLB in the vestibular endorgan, the macula utricle, from patients with MD (n = 10), acoustic neuroma (AN) (n = 6) and normative autopsy specimens (n = 3) with no inner ear disease. Each subject had a well-documented clinical history and audiovestibular testing. Utricular maculae were studied using light and transmission electron microscopy and double labeling immunofluorescence. Vascular endothelial cells (VECs) were identified using isolectin B4 (IB4) and glucose-transporter-1 (GLUT-1). Pericytes were identified using alpha smooth muscle actin (αSMA) and phalloidin. IB4 staining of VECS was consistently seen in both AN and normative. In contrast, IB4 was nearly undetectable in all MD specimens, consistent with the significant VEC damage confirmed on transmission electron microscopy. GLUT-1 was present in MD, AN, and normative. αSMA and phalloidin were expressed consistently in the BLB pericytes in normative, AN specimen, and Meniere's specimens. Endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), and nitrotyrosine were used as markers of oxidative stress. The VECs of the BLB in Meniere's had significantly higher levels of expression of iNOS and nitrotyrosine compared with normative and AN specimen. eNOS-IF staining showed similar patterns in normative and Meniere's specimens. Microarray-based gene expression profiling confirmed upregulation of iNOS mRNA from the macula utricle of Meniere's patients compared with AN. Nitrotyrosine, a marker recognized as a hallmark of inflammation, especially when seen in association with an upregulation of iNOS, was detected in the epithelial and stromal cells in addition to VECs in MD. Immunohistochemical and ultrastructural degenerative changes of the VEC suggest that these cells are the primary targets of oxidative stress, and pericyte pathology including degeneration and migration, likely also plays a role in the loss of integrity of the BLB and triggering of inflammatory pathways in MD. These studies advance our scientific understanding of oxidative stress in the human inner ear BLB and otopathology.

Hearing impairment, cochlear morphology, and peroxynitrite (ONOO(-)) formation in adult and aging NOS II knockout mice

CONCLUSION

Nitric oxide synthase (NOS) II induction is a protective mechanism against age-related degeneration of the cochlea.

OBJECTIVES

An induction of NOS II has been described in different inner ear pathologies. The objective was to examine the role of NOS II in age-related degeneration of the cochlea.

METHODS

The hearing ability in adult and aging NOS II knockout mice (KO) and their wildtype (WT) littermates was explored via auditory brainstem response (ABR) measurements. Inner ear morphological differences were studied with scanning electron microscopy (SEM). Immunohistochemistry was used to examine the induction of NOS II in the inner ear of aging WT mice. Expression of nitrotyrosin, a marker protein for the reactive oxygen species peroxynitrite, was compared between KO and WT mice using immunohistochemistry.

RESULTS

Adult KO mice exhibited a mild hearing impairment. WT mice showed an induction of NOS II after 6 months of age. Age-related hearing deterioration was accelerated in KO mice, which was accompanied by increased nitrotyrosin formation and outer hair cell loss.

Nitric oxide--a versatile key player in cochlear function and hearing disorders

Nitric oxide (NO) is a signaling molecule which can generally be formed by three nitric oxide synthases (NOS). Two of them, the endothelial nitric oxide synthase (eNOS) and the neural nitric oxide synthase (nNOS), are calcium/calmodulin-dependent and constitutively expressed in many cell types. Both isoforms are found in the vertebrate cochlea. The inducible nitric oxide synthase (iNOS) is independent of calcium and normally not detectable in the un-stimulated cochlea. In the inner ear, as in other tissues, NO was identified as a multitask molecule involved in various processes such as neurotransmission and neuromodulation. In addition, increasing evidence demonstrates that the NO-dependent processes of cell protection or, alternatively, cell destruction seem to depend, among other things, on changes in the local cochlear NO-concentration. These alterations can occur at the cellular level or within a distinct cell population both leading to an NO-imbalance within the hearing organ. This dysfunction can result in hearing loss or even in deafness. In cases of cochlear malfunction, regulatory systems such as the gap junction system, the blood vessels or the synaptic region might be affected temporarily or permanently by an altered NO-level. This review discusses potential cellular mechanisms how NO might contribute to different forms of hearing disorders. Approaches of NO-reduction are evaluated and the transfer of results obtained from experimental animal models to human medication is discussed.

Lack of Tff3 peptide results in hearing impairment and accelerated presbyacusis

Tff peptides are secreted mainly by the gastrointestinal epithelial cells and their primary role is maintaining normal structure and function of mucous epithelia. Ongoing studies on their expression pattern have disclosed other sites of their synthesis thus revealing additional physiological functions in the organism. Here we present new data about Tff3 expression in the cochlea of the rodent inner ear. On the basis of RT-PCR we describe the presence of Tff3 transcripts in both, a mouse cDNA library isolated from whole cochleae from postnatal days 3-15 (P3-P15), and also in cochlear tissue. By using a riboprobe for the fragment containing exon 1, 2 and 3 of Tff3, in situ hybridization, localized Tff3 signals in neurons of spiral ganglion and vestibular organ. We did not observe any abnormalities in the middle ear of Tff3 knock-out mice, neither did histological examination of the inner ear indicate any gross morphological changes in the cochlea. However, ABR (auditory evoked brain stem responses) audiograms revealed that the Tff3 knock-out animals show an accelerated presbyacusis and a hearing loss of about 15 dB at low frequencies increasing to 25 dB loss at higher frequencies. These findings suggest that Tff3 could play a role in neurosensory signaling. Further studies are needed to clarify this new function in the auditory system.

Probable function of Boettcher cells based on results of morphological study: localization of nitric oxide synthase

Boettcher cells lie on the basilar membrane beneath Claudius cells. The cells are considered supporting cells for the organ of Corti, and present only in the lower turn of the cochlea, which responds to high-frequency sound. Boettcher cells interdigitate with each other, and project microvilli into the intercellular space. Their structural specialization suggests that Boettcher cells may play a significant role in the function of the cochlea. Nitric oxide synthase (NOS) has previously been detected in substructures of the cochlea. In the cochlea, it is believed that nitric oxide plays an important role in neurotransmission, blood flow regulation, and induction of cytotoxicity under pathological conditions. Findings concerning detection of NOS on Boettcher cells are rare. We demonstrated here the localization of NOS on Boettcher cells of the rat by immunohistochemistry using polyclonal antibody to NOS. On observation with the light microscope using DAB staining, positive immunostaining to NOS was observed in Boettcher cells. In immunoelectron micrographs, NOS was detected abundantly in the cytoplasm of the interdigitations. This suggests that the interdigitations may play significant roles by using NOS. It follows from this that the nitric oxide (NO) on Boettcher cells may influences neighboring Boettcher cells. The ultrastructure of Boettcher cells suggests that they may be active cells, which perform both secretory and absorptive functions.

Candidate???s Thesis: Platelet-Activating Factor???Induced Hearing Loss: Mediated by Nitric Oxide?

OBJECTIVES/HYPOTHESIS

Platelet-activating factor (PAF)in middle ear effusion is thought to induce hearing loss. The purpose of this study is to investigate the role of nitric oxide (NO) in the mechanism of PAF-induced hearing loss by studying the effects of PAF application on the round window membrane (RWM) with and without PAF-antagonist NO-blocker.

STUDY DESIGN

Longitudinal study on randomized guinea pigs using PAF to induce hearing loss. METHODS Guinea pigs were divided into four groups: PBS, PAF, PAF-antagonist, and L-NAME. The PBS group received phosphate buffered saline (PBS) and the PAF groups received 10, 20, and 40 microg of PAF soaked into gelfoam and placed on the RWM. PAF-antagonist (WEB 2170) and NOS inhibitor NG-nitro-l-arginine-methylester (L-NAME) were injected intraperitoneally prior to PAF 20 microg application on the RWM. The following three tests were performed on each animal group: Hearing was tested with an auditory brainstem response (ABR) test over 24 hours. At the end of 24 hours, cochlear hair cells were examined by scanning electron microscopy (SEM) and immunohistochemistry was carried out on the cochlea to test the expression of inducible nitric oxide synthase (iNOS).

RESULTS

The PAF group developed significant elevation of ABR threshold and cochlear hair cell damage in the SEM group as compared with the PBS control group. The PAF-antagonist (WEB 2170) and the L-NAME groups did not show significant elevation of ABR threshold and cochlear hair cell damage compared with the group administered PAF 20 microg, but in the PAF-antagonist group, the elevation of ABR threshold was significant compared with that of the PBS control group, whereas it was not significant compared with the PBS group in the L-NAME group. Strong expression of iNOS on cochlea was observed in the PAF group and lighter expression was seen in PBS, WEB 2170, and L-NAME groups.

CONCLUSIONS

This study demonstrated that PAF placed on the RWM induced hearing loss and cochlear hair cell damage. The PAF-antagonists and L-NAME prevented the PAF-induced hearing loss and inhibited iNOS expression in the cochlea. These findings suggest that the PAF-induced hearing loss caused by cochlear hair cell damage may have been mediated by NO. PAF-antagonists and L-NAME may have future therapeutic implications in preventing sensorineural hearing loss associated with chronic otitis media. The results of this study have significant potential clinical application.

Ebselen attenuates cochlear damage caused by acoustic trauma

Ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one), a seleno-organic compound, mimics glutathione peroxidase and reacts with peroxynitrite. It is reported to protect against gentamicin- and cisplatin-induced ototoxicity. We investigated whether it protects the cochlea from acoustic trauma. Male pigmented guinea pigs (250-300 g) with normal auditory brainstem response (ABR) thresholds were exposed for 5 h to 125 dB sound pressure level octave band noise centered at 4 kHz. One hour before and 18 h after exposure, they received orally 0.25 ml chloroform solution containing 0, 10, or 30 mg/kg ebselen (n=6, 5 and 5, respectively). The protective effect of ebselen was evaluated by ABR measurement and quantitative hair cell assessment. Treatment significantly (P<0.01) reduced the extent of permanent threshold shifts and outer hair cell loss. Interestingly, the protective effect of a 30 mg/kg dose was less than that of a 10 mg/kg dose. There were no adverse systemic or auditory function effects in three unexposed control subjects given 30 mg/kg ebselen. These findings indicate that ebselen attenuates noise-induced cochlear damage. The concentration that provides optimal protection against such damage has now to be determined.

Altered expression of inducible nitric oxide synthase (iNOS) in the cochlea

Using immunohistochemistry and Western blot, the expression of inducible nitric oxide synthase (iNOS) in the lateral wall and organ of Corti was examined in normal (unstimulated) and stimulated mice and guinea pigs. The stimuli were: (1). injection of bacterial lipopolysaccharide (LPS, 5 mg/ml) into the middle ear through the tympanic membrane and (2). exposure to a 110 dB SPL (A-weighted) broadband noise, 3 h/day, for three consecutive days. For the unstimulated condition, weak iNOS expression was found in the vascular endothelium, marginal cells, nerve fibers, stereocilia of hair cells and Hensen's cells of the organ of Corti. More intense iNOS fluorescence signals were observed in cochlear tissues (particularly in hair cells and stria vascularis marginal cells) in animals exposed to loud sound or treated with LPS. Although the precise roles of iNOS expression in normal cochlear function have yet to be determined, enhanced iNOS expression following noise exposure and LPS suggests its participation in cochlear pathophysiology, including noise- and inflammatory factor-induced hearing loss.