MANF supports the inner hair cell synapse and the outer hair cell stereocilia bundle in the cochlea.

Failure in the structural maintenance of the hair cell stereocilia bundle and ribbon synapse causes hearing loss. Here, we have studied how ER stress elicits hair cell pathology, using mouse models with inactivation of Manf (mesencephalic astrocyte-derived neurotrophic factor), encoding an ER-homeostasis-promoting protein. From hearing onset, Manf deficiency caused disarray of the outer hair cell stereocilia bundle and reduced cochlear sound amplification capability throughout the tonotopic axis. In high-frequency outer hair cells, the pathology ended in molecular changes in the stereocilia taper region and in strong stereocilia fusion. In high-frequency inner hair cells, Manf deficiency degraded ribbon synapses. The altered phenotype strongly depended on the mouse genetic background. Altogether, the failure in the ER homeostasis maintenance induced early-onset stereociliopathy and synaptopathy and accelerated the effect of genetic causes driving age-related hearing loss. Correspondingly, MANF mutation in a human patient induced severe sensorineural hearing loss from a young age onward. Thus, we present MANF as a novel protein and ER stress as a mechanism that regulate auditory hair cell maintenance in both mice and humans.

Stress and Tinnitus; Transcutaneous Auricular Vagal Nerve Stimulation Attenuates Tinnitus-Triggered Stress Reaction.

INTRODUCTION: Tinnitus can become a strong stressor for some individuals, leading to imbalance of the autonomous nervous system with reduction of parasympathetic activity. It can manifest itself as sleep disturbances, anxiety and even depression. This condition can be reversed by bioelectrical vagal nerve stimulation (VNS). Conventional invasive VNS is an approved treatment for epilepsy and depression. Transcutaneous VNS (taVNS) stimulating the auricular branch of the vagus nerve has been shown to activate the vagal pathways similarly as an implanted VNS. Therefore, taVNS might also be a therapeutic alternative in health conditions such as tinnitus-related mental stress (TRMS). This retrospective study in 171 TRMS patients reports the clinical features, psychophysiological characteristics, and results of the heart rate variability (HRV) tests before and after test-taVNS. This study also reports the therapy outcomes of 113 TRMS patients treated with taVNS, in combination with standard tinnitus therapy. METHODS: Diagnostic tinnitus and hearing profiles were defined. To detect possible cardiac adverse effects, test-taVNS with heart rate monitoring as well as pre- and post-stimulation HRV tests were performed. Daily taVNS home therapy was prescribed thereafter. To assess therapeutic usefulness of taVNS, 1-year follow-up outcome was studied. Results of HRV tests were retrospectively analyzed and correlated to diagnostic data. RESULTS: The large majority of patients with TRMS suffer from associated symptoms such as sleep disturbances and anxiety. Baseline HRV data showed that more than three quarters of the 171 patients had increased sympathetic activity before test-taVNS. Test-taVNS shifted mean values of different HRV parameters toward increased parasympathetic activity in about 80% of patients. Test-taVNS did not cause any cardiac or other side effects. No significant adverse effects were reported in follow-up questionnaires. CONCLUSION: TRMS is an example of a stress condition in which patients may benefit from taVNS. As revealed by HRV, test-taVNS improved parasympathetic function, most efficiently in patients with a low starting HRV level. Our tinnitus treatment program, including taVNS, effectively alleviated tinnitus stress and handicap. For wider clinical use, there is a great need for more knowledge about the optimal methodology and parameters of taVNS.

Deficiency of the ER-stress-regulator MANF triggers progressive outer hair cell death and hearing loss.

The non-conventional neurotrophic factor mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER)-resident protein that promotes ER homeostasis. MANF has a cytoprotective function, shown in the central nervous system neurons and pancreatic beta cells. Here, we report that MANF is expressed in the hair cells and neurons and in selected non-sensory cells of the cochlea and that Manf inactivation triggers upregulation of the ER chaperones in these cells. However, Manf inactivation resulted in the death of only outer hair cells (OHCs), the cells responsible for sound amplification in the cochlea. All OHCs were formed in Manf-inactivated mice, but progressive OHC death started soon after the onset of hearing function. The robust OHC loss was accompanied by strongly elevated hearing thresholds. Conditional Manf inactivation demonstrated that MANF has a local function in the cochlea. Immunostainings revealed the upregulation of CHOP, the pro-apoptotic component of the unfolded protein response (UPR), in Manf-inactivated OHCs, linking the UPR to the loss of these cells. The phenotype of Manf-inactivated OHCs was distinctly dependent on the mouse strain, such that the strains characterized by early-onset age-related hearing loss (C57BL/6J and CD-1) were affected. These results suggest that Manf deficiency becomes detrimental when accompanied by gene mutations that predispose to hearing loss, by intensifying ER dyshomeostasis. Together, MANF is the first growth factor shown to antagonize ER stress-mediated OHC death. MANF might serve as a therapeutic candidate for protection against hearing loss induced by the ER-machinery-targeting stressors.

The Stress Response in the Non-sensory Cells of the Cochlea Under Pathological Conditions-Possible Role in Mediating Noise Vulnerability.

Various stressors, such as loud sounds and the effects of aging, impair the function and viability of the cochlear sensory cells, the hair cells. Stressors trigger pathophysiological changes in the cochlear non-sensory cells as well. We have here studied the stress response mounted in the lateral wall of the cochlea during acute noise stress and during age-related chronic stress. We have used the activation of JNK/c-Jun, ERK, and NF-κB pathways as a readout of the stress response, and the expression of the FoxO3 transcription factor as a possible additional player in cellular stress. In the aging cochlea, NF-κB transcriptional activity was strongly induced in the stria vascularis of the lateral wall. This induction was linked with the atrophy of the stria vascularis, suggesting a role for NF-κB signaling in mediating age-related strial degeneration. Acutely following noise exposure, the JNK/c-Jun, ERK, and NF-κB pathways were activated in the spiral ligament of the lateral wall of CBA/Ca mice. This activation was concomitant with the morphological transformation of macrophages, suggesting that the upregulation of stress signaling leads to macrophage activation. In contrast, C57BL/6J mice lacked these responses. Only the combination of noise exposure and a systemic stressor, lipopolysaccharide, exceeded the threshold for the activation of stress signaling in the lateral wall of C57BL/6J mice. In addition, we found that, at the young adult age, outer hair cells of CBA/Ca mice are much more vulnerable to loud sounds compared to these cells of C57BL/6J mice. These results suggest that the differential stress response in the lateral wall of the two mouse strains underlies, in part, the differential noise vulnerability of their outer hair cells. Together, we propose that the molecular stress response in the lateral wall modulates the outcome of the stressed cochlea.

Hearing disorder from music; a neglected dysfunction.

CONCLUSION: Music-induced acute acoustic trauma is not inevitably linked to hearing dysfunction as validated by conventional pure tone audiometry. Tinnitus is often in combination with hyperacusis. Our results point at 'silent hearing loss' as the underlying pathology, having afferent nerve terminal damage rather than hair cell loss as the structural correlate. OBJECTIVES: Exposure to loud music is one of the most common causes of acute acoustic trauma, which adolescents and teenagers experience by voluntary exposure to loud music of sound levels up to 110 dB(A). METHODS: The clinical and psychophysical data of 104 consecutive patients with music-induced hearing disorder (MIHD) were analyzed to construct individual hearing and tinnitus profiles. In all cases, tinnitus was the presenting symptom. RESULTS: Hearing abilities were normal in about two-thirds of the tinnitus patients. Tinnitus was experienced most often as a high-frequency tone (83%). The Tinnitus Handicap Inventory (THI) scores ranged from 0 to 94 with an average score of 43.1. Visual analog scales (VAS) were used to assess tinnitus loudness (average 42.4) and annoyance (average 54.2), and tinnitus awareness was estimated (average 60.3). All VAS values correlated strongly with the THI. Hyperacusis was present in 65% and 71% of the patients reported sleeping disorders.

Cytoskeletal Stability in the Auditory Organ In Vivo: RhoA Is Dispensable for Wound Healing but Essential for Hair Cell Development.

Wound healing in the inner ear sensory epithelia is performed by the apical domains of supporting cells (SCs). Junctional F-actin belts of SCs are thin during development but become exceptionally thick during maturation. The functional significance of the thick belts is not fully understood. We have studied the role of F-actin belts during wound healing in the developing and adult cochlea of mice in vivo. We show that the thick belts serve as intracellular scaffolds that preserve the positions of surviving cells in the cochlear sensory epithelium. Junctions associated with the thick F-actin belts did not readily disassemble during wound healing. To compensate for this, basolateral membranes of SCs participated in the closure of surface breach. Because not only neighboring but also distant SCs contributed to wound healing by basolateral protrusions, this event appears to be triggered by contact-independent diffusible signals. In the search for regulators of wound healing, we inactivated RhoA in SCs, which, however, did not limit wound healing. RhoA inactivation in developing outer hair cells (OHCs) caused myosin II delocalization from the perijunctional domain and apical cell-surface enlargement. These abnormalities led to the extrusion of OHCs from the epithelium. These results demonstrate the importance of stability of the apical domain, both in wound repair by SCs and in development of OHCs, and that only this latter function is regulated by RhoA. Because the correct cytoarchitecture of the cochlear sensory epithelium is required for normal hearing, the stability of cell apices should be maintained in regenerative and protective interventions.

Non-invasive vagus nerve stimulation reduces sympathetic preponderance in patients with tinnitus.

CONCLUSION: Transcutaneous vagal nerve stimulation (tVNS) might offer a targeted, patient-friendly, and low-cost therapeutic tool for tinnitus patients with sympathovagal imbalance. OBJECTIVES: Conventionally, VNS has been performed to treat severe epilepsy and depression with an electrode implanted to the cervical trunk of vagus nerve. This study investigated the acute effects of tVNS on autonomic nervous system (ANS) imbalance, which often occurs in patients with tinnitus-triggered stress. METHODS: This study retrospectively analysed records of 97 patients who had undergone ANS function testing by heart rate variability (HRV) measurement immediately before and after a 15-60 min tVNS stimulation. RESULTS: The pre-treatment HRV recording showed sympathetic preponderance/reduced parasympathetic activity in about three quarters (73%) of patients. Active tVNS significantly increased variability of R-R intervals in 75% of patients and HRV age was decreased in 70% of patients. Either the variability of R-R intervals was increased or the HRV age decreased in 90% of the patients. These results indicate that tVNS can induce a shift in ANS function from sympathetic preponderance towards parasympathetic predominance. tVNS caused no major morbidity, and heart rate monitoring during the tVNS treatment showed no cardiac or circulatory effects (e.g. bradycardia) in any of the patients.

c-Jun N-Terminal Phosphorylation: Biomarker for Cellular Stress Rather than Cell Death in the Injured Cochlea.

Prevention of auditory hair cell death offers therapeutic potential to rescue hearing. Pharmacological blockade of JNK/c-Jun signaling attenuates injury-induced hair cell loss, but with unsolved mechanisms. We have characterized the c-Jun stress response in the mouse cochlea challenged with acoustic overstimulation and ototoxins, by studying the dynamics of c-Jun N-terminal phosphorylation. It occurred acutely in glial-like supporting cells, inner hair cells, and the cells of the cochlear ion trafficking route, and was rapidly downregulated after exposures. Notably, death-prone outer hair cells lacked c-Jun phosphorylation. As phosphorylation was triggered also by nontraumatic noise levels and none of the cells showing this activation were lost, c-Jun phosphorylation is a biomarker for cochlear stress rather than an indicator of a death-prone fate of hair cells. Preconditioning with a mild noise exposure before a stronger traumatizing noise exposure attenuated the cochlear c-Jun stress response, suggesting that the known protective effect of sound preconditioning on hearing is linked to suppression of c-Jun activation. Finally, mice with mutations in the c-Jun N-terminal phosphoacceptor sites showed partial, but significant, hair cell protection. These data identify the c-Jun stress response as a paracrine mechanism that mediates outer hair cell death.

The Rho GTPase Cdc42 regulates hair cell planar polarity and cellular patterning in the developing cochlea.

Hair cells of the organ of Corti (OC) of the cochlea exhibit distinct planar polarity, both at the tissue and cellular level. Planar polarity at tissue level is manifested as uniform orientation of the hair cell stereociliary bundles. Hair cell intrinsic polarity is defined as structural hair bundle asymmetry; positioning of the kinocilium/basal body complex at the vertex of the V-shaped bundle. Consistent with strong apical polarity, the hair cell apex displays prominent actin and microtubule cytoskeletons. The Rho GTPase Cdc42 regulates cytoskeletal dynamics and polarization of various cell types, and, thus, serves as a candidate regulator of hair cell polarity. We have here induced Cdc42 inactivation in the late-embryonic OC. We show the role of Cdc42 in the establishment of planar polarity of hair cells and in cellular patterning. Abnormal planar polarity was displayed as disturbances in hair bundle orientation and morphology and in kinocilium/basal body positioning. These defects were accompanied by a disorganized cell-surface microtubule network. Atypical protein kinase C (aPKC), a putative Cdc42 effector, colocalized with Cdc42 at the hair cell apex, and aPKC expression was altered upon Cdc42 depletion. Our data suggest that Cdc42 together with aPKC is part of the machinery establishing hair cell planar polarity and that Cdc42 acts on polarity through the cell-surface microtubule network. The data also suggest that defects in apical polarization are influenced by disturbed cellular patterning in the OC. In addition, our data demonstrates that Cdc42 is required for stereociliogenesis in the immature cochlea.

How to bury the dead: elimination of apoptotic hair cells from the hearing organ of the mouse.

Hair cell death is a major cause of hearing impairment. Preservation of surface barrier upon hair cell loss is critical to prevent leakage of potassium-rich endolymph into the organ of Corti and to prevent expansion of cellular damage. Understanding of wound healing in this cytoarchitecturally complex organ requires ultrastructural 3D visualization. Powered by the serial block-face scanning electron microscopy, we penetrate into the cell biological mechanisms in the acute response of outer hair cells and glial-like Deiters' cells to ototoxic trauma in vivo. We show that Deiters' cells function as phagocytes. Upon trauma, their phalangeal processes swell and the resulting close cellular contacts allow engulfment of apoptotic cell debris. Apical domains of dying hair cells are eliminated from the inner ear sensory epithelia, an event thought to depend on supporting cells' actomyosin contractile activity. We show that in the case of apoptotic outer hair cells of the organ of Corti, elimination of their apices is preceded by strong cell body shrinkage, emphasizing the role of the dying cell itself in the cleavage. Our data reveal that the resealing of epithelial surface by junctional extensions of Deiters' cells is dynamically reinforced by newly polymerized F-actin belts. By analyzing Cdc42-inactivated Deiters' cells with defects in actin dynamics and surface closure, we show that compromised barrier integrity shifts hair cell death from apoptosis to necrosis and leads to expanded hair cell and nerve fiber damage. Our results have implications concerning therapeutic protective and regenerative interventions, because both interventions should maintain barrier integrity.

DNA damage signaling regulates age-dependent proliferative capacity of quiescent inner ear supporting cells.

Supporting cells (SCs) of the cochlear (auditory) and vestibular (balance) organs hold promise as a platform for therapeutic regeneration of the sensory hair cells. Prior data have shown proliferative restrictions of adult SCs forced to re-enter the cell cycle. By comparing juvenile and adult SCs in explant cultures, we have here studied how proliferative restrictions are linked with DNA damage signaling. Cyclin D1 overexpression, used to stimulate cell cycle re-entry, triggered higher proliferative activity of juvenile SCs. Phosphorylated form of histone H2AX (γH2AX) and p53 binding protein 1 (53BP1) were induced in a foci-like pattern in SCs of both ages as an indication of DNA double-strand break formation and activated DNA damage response. Compared to juvenile SCs, γH2AX and the repair protein Rad51 were resolved with slower kinetics in adult SCs, accompanied by increased apoptosis. Consistent with thein vitro data, in a Rb mutant mouse model in vivo, cell cycle re-entry of SCs was associated with γH2AX foci induction. In contrast to cell cycle reactivation, pharmacological stimulation of SC-to-hair-cell transdifferentiation in vitro did not trigger γH2AX. Thus, DNA damage and its prolonged resolution are critical barriers in the efforts to stimulate proliferation of the adult inner ear SCs.

Coupling the cell cycle to development and regeneration of the inner ear.

Cell cycle exit and acquirement of a postmitotic state is essential for the proper development of organs. In the present review, we examine the role of the cell cycle control in the sensory epithelia of the mammalian inner ear. We describe the roles of the core cell cycle regulators in the proliferation of prosensory cells and in the initiation and maintenance of terminal mitosis of the sensory epithelia. We also discuss how other intracellular signalling may influence the cell cycle. Finally, we address the question of whether manipulations of the cell cycle may have the potential to create replacement cells for the damaged inner sensory epithelia.

Transcutaneous vagus nerve stimulation in tinnitus: a pilot study.

CONCLUSIONS: This pilot study shows that transcutaneous vagus nerve stimulation (tVNS), if combined with sound therapy (ST), reduces the severity of tinnitus and tinnitus-associated distress. Our magnetoencephalography (MEG) results show that auditory cortical activation can be modulated by the application of tVNS. Thus, tVNS might offer a new avenue to treat tinnitus and tinnitus-associated distress. OBJECTIVES: Recent studies suggest that tinnitus can be improved by tailored ST or by VNS plus ST. Our aims were to study whether tVNS has therapeutic effects on patients with tinnitus and, additionally, if tVNS has effects on acoustically evoked neuronal activity of the auditory cortex. METHODS: The clinical efficacy was studied by a short-term tVNS plus ST trial in 10 patients with tinnitus using disease-specific and general well-being questionnaires. tVNS was delivered to the left tragus. The acute effects of tVNS were evaluated in eight patients in the MEG study in which the N1m response was analyzed in terms of source level amplitude and latency in the presence or absence of tVNS. RESULTS: The treatment with tVNS plus ST produced improved mood and decreased tinnitus handicap scores, indicating reduced tinnitus severity. The application of tVNS decreased the amplitude of auditory N1m responses in both hemispheres.

Cdc42-dependent structural development of auditory supporting cells is required for wound healing at adulthood.

Cdc42 regulates the initial establishment of cytoskeletal and junctional structures, but only little is known about its role at later stages of cellular differentiation. We studied Cdc42's role in vivo in auditory supporting cells, epithelial cells with high structural complexity. Cdc42 inactivation was induced early postnatally using the Cdc42(loxP/loxP);Fgfr3-iCre-ER(T2) mice. Cdc42 depletion impaired elongation of adherens junctions and F-actin belts, leading to constriction of the sensory epithelial surface. Fragmented F-actin belts, junctions containing ectopic lumens and misexpression of a basolateral membrane protein in the apical domain were observed. These defects and changes in aPKCλ/ι expression suggested that apical polarization is impaired. Following a lesion at adulthood, supporting cells with Cdc42 loss-induced maturational defects collapsed and failed to remodel F-actin belts, a process that is critical to scar formation. Thus, Cdc42 is required for structural differentiation of auditory supporting cells and this proper maturation is necessary for wound healing in adults.

Restrictions in cell cycle progression of adult vestibular supporting cells in response to ectopic cyclin D1 expression.

Sensory hair cells and supporting cells of the mammalian inner ear are quiescent cells, which do not regenerate. In contrast, non-mammalian supporting cells have the ability to re-enter the cell cycle and produce replacement hair cells. Earlier studies have demonstrated cyclin D1 expression in the developing mouse supporting cells and its downregulation along maturation. In explant cultures of the mouse utricle, we have here focused on the cell cycle control mechanisms and proliferative potential of adult supporting cells. These cells were forced into the cell cycle through adenoviral-mediated cyclin D1 overexpression. Ectopic cyclin D1 triggered robust cell cycle re-entry of supporting cells, accompanied by changes in p27(Kip1) and p21(Cip1) expressions. Main part of cell cycle reactivated supporting cells were DNA damaged and arrested at the G2/M boundary. Only small numbers of mitotic supporting cells and rare cells with signs of two successive replications were found. Ectopic cyclin D1-triggered cell cycle reactivation did not lead to hyperplasia of the sensory epithelium. In addition, a part of ectopic cyclin D1 was sequestered in the cytoplasm, reflecting its ineffective nuclear import. Combined, our data reveal intrinsic barriers that limit proliferative capacity of utricular supporting cells.

Differential sensitivity of the inner ear sensory cell populations to forced cell cycle re-entry and p53 induction.

Previous studies have shown that the maintenance of post-mitotic state is critical for the life-long survival of the inner ear mechanosensory cells, the hair cells. A general concept is that differentiated, post-mitotic cells rapidly die following cell cycle re-entry. Here we have compared the response of postnatal cochlear (auditory) and utricular (balance) hair cells to forced cell cycle reactivation and p53 up-regulation. Forced S-phase entry was triggered through the human papillomavirus-16 E7 oncogene misexpression in explant cultures. It induced DNA damage and p53 induction in cochlear outer hair cells and these cells were rapidly lost, before entry into mitosis. The death was attenuated by p53 inactivation. In contrast, despite DNA damage and p53 induction, utricular hair cells showed longer term survival and a proportion of them progressed into mitosis. Consistently, pharmacological elevation of p53 levels by nutlin-3a led to a death-prone phenotype of cochlear outer hair cells, while other hair cell populations were death-resistant. These data have important clinical implications as they show the importance of p53 in sensory cells that are essential in hearing function.

Cell cycle regulation in the inner ear sensory epithelia: role of cyclin D1 and cyclin-dependent kinase inhibitors.

Sensory hair cells and supporting cells of the mammalian cochlea and vestibular (balance) organs exit the cell cycle during embryogenesis and do not proliferate thereafter. Here, we have studied the mechanisms underlying the maintenance of the postmitotic state and the proliferative capacity of these cells. We provide the first evidence of the role of cyclin D1 in cell cycle regulation in these cells. Cyclin D1 expression disappeared from embryonic hair cells as differentiation started. The expression was transiently upregulated in cochlear hair cells early postnatally, paralleling the spatiotemporal pattern of unscheduled cell cycle re-entry of cochlear hair cells from the p19(Ink4d)/p21(Cip1) compound mutant mice. Cyclin D1 misexpression in vitro in neonatal vestibular HCs from these mutant mice triggered S-phase re-entry. Thus, cyclin D1 suppression is important for hair cell's quiescence, together with the maintained expression of cyclin-dependent kinase inhibitors. In contrast to hair cells, cyclin D1 expression was maintained in supporting cells when differentiation started. The expression continued during the neonatal period when supporting cells have been shown to re-enter the cell cycle upon stimulation with exogenous mitogens. Thereafter, the steep decline in supporting cell's proliferative activity paralleled with cyclin D1 downregulation. Thus, cyclin D1 critically contributes to the proliferative plasticity of supporting cells. These data suggest that targeted cyclin D1 induction in supporting cells might be an avenue for proliferative regeneration in the inner ear.

Prox1 interacts with Atoh1 and Gfi1, and regulates cellular differentiation in the inner ear sensory epithelia.

Inner ear hair cells and supporting cells arise from common precursors and, in mammals, do not show phenotypic conversion. Here, we studied the role of the homeodomain transcription factor Prox1 in the inner ear sensory epithelia. Adenoviral-mediated Prox1 transduction into hair cells in explant cultures led to strong repression of Atoh1 and Gfi1, two transcription factors critical for hair cell differentiation and survival. Luciferase assays showed that Prox1 can repress transcriptional activity of Gfi1 independently of Atoh1. Prox1 transduction into cochlear outer hair cells resulted in degeneration of these cells, consistent with the known phenotype of Gfi1-deficient mice. These results together with the widespread expression of endogenous Prox1 within the population of inner ear supporting cells point to the role for Prox1 in antagonizing the hair cell phenotype in these non-sensory cells. Further, in vivo analyses of hair cells from Gfi1-deficient mice suggest that the cyclin-dependent kinase inhibitor p57(Kip2) mediates the differentiation- and survival-promoting functions of Gfi1. These data reveal novel gene interactions and show that these interactions regulate cellular differentiation within the inner ear sensory epithelia. The data point to the tight regulation of phenotypic characteristics of hair cells and supporting cells.

CD2-associated protein is widely expressed and differentially regulated during embryonic development.

CD2-associated protein (CD2AP) is an adapter protein that is involved in various signaling and vesicular trafficking processes and also functions as a linker between plasma membrane proteins and the actin cytoskeleton. The protein is known to have important functions in T cells and glomerular podocytes, but it is also expressed by many other adult-type tissues and cells. Here we analyzed the expression of the protein during early embryonic development and organogenesis of the mouse. The results showed differential tissue-specific regulation of CD2AP in developing and maturing organs. In oocytes and pre-implantation embryos, CD2AP was located diffusely in the cytoplasm, whereas in late blastocysts it was concentrated to the intercellular contacts. During organogenesis, CD2AP was distinctly upregulated upon, e.g., the pretubular aggregation of metanephric mesenchyme cells and the appearance of the osteoblastic rim around cartilages during endochondral ossification. High CD2AP expression was also observed during epithelial-like conversion of some highly specialized secretory cell types such as the odontoblasts, the cells of the choroid plexus and the decidualized cells of the endometrial stroma. In other instances, such as the development of the proximal tubuli of the kidney and the flat alveolar epithelium of the lung, the protein was downregulated upon differentiation and maturation of the cells. Finally, certain cells, e.g., glomerular podocytes, those forming the collecting ducts of the kidney, and the urothelium of the kidney pelvis, expressed CD2AP throughout their differentiation and maturation. Multiple molecules and complex pathways regulate embryogenesis, and scaffolding proteins apparently have pivotal roles in targeting and finetuning, e.g., growth factor- or hormone-induced processes. The cell-type specific spatio-temporal regulation of CD2AP during development suggests that this adapter protein is a key regulatory partner in many signaling pathways and cellular processes governing differentiation and morphogenesis.

Occupational noise-induced hearing loss reports and tinnitus in Finland.

CONCLUSION: In occupational noise-induced hearing loss (NIHL) reports, many tinnitus sufferers probably remain undetected and untreated at present. Attention should be focused on tinnitus, as well as threshold shifts resulting from NIHL. OBJECTIVES: Occupational NIHL is frequent among workers in industrialized countries and it is one of the greatest occupational health hazards. Hearing conservation programs have led to a reduction in the numbers of severe occupational NIHL. Our objectives were to analyze the severity of occupational NIHL reported in Finland, identify risk occupations, and investigate the occurrence of tinnitus among the reported cases. MATERIALS AND METHODS: We examined the records of 857 NIHL cases with an identifiable disability category of the total 858 NIHL cases reported in 2000. We sent tinnitus questionnaires to 366 of these NIHL cases. RESULTS: The degree of speech-frequency hearing loss was generally low, and a mention of tinnitus was reported in only 34 cases (4.0%). However, 88.7% of the patients actually had unreported tinnitus.