Expression of apoptosis-related genes in the organ of Corti, modiolus and stria vascularis of newborn rats

[Molecular networks of hypoxia and neuronal apoptosis in the cochlea]

BACKGROUND

In organotypic cultures, the modiolus (MOD) region of newborn rats shows a fourfold higher rate of cell death than the organ of Corti (OC). The differing vulnerability of OC and MOD cells is related to differential expression of numerous genes (DEG).

MATERIALS AND METHODS

Organotypic cultures of OC and MOD of 3-5-day-old rats were exposed to a normoxic or a hypoxic (pO₂ 10-20 mmHg; 5 h) atmosphere. Cell death rate and gene expression as detected by c‑DNA microarray analysis were determined 24 h after the culture was created. Genes with modified expression (n = 60) were analyzed for biological processes according to the DAVID Gene Ontology Database (GO). Molecular networks were created using the STRING and ConsensusPathDB databases.

RESULTS

The network of the GO annotations "hypoxia", "inflammation", and "mechanical stimulus" indicates the existence of two gene clusters: a cluster with pro-inflammatory genes (Ccl3, Cxcl2, Cxcr4, Ccl20) and a cluster with hypoxia-associated genes (e.g., c-Jun, Hif1a, and Vegfa). The network of the GO annotations "positive and negative regulation of neuron apoptotic process" suggests that the differential expression of c-Jun, Ngfr, and Casp3 is important for regulation of programmed cell death in neuronal cells of the OC and MOD.

CONCLUSION

While c‑JUN acts as an important modulator of the balance between cell death and survival, the associations of NGFR and CASP3 seem to be significant for the initiation of cell death. The evaluation and application of findings from biostatistical databases is important for understanding the function of individual genes and gene clusters in medically relevant biological processes.

Acute Noise Exposure Is Associated With Intrinsic Apoptosis in Murine Central Auditory Pathway

Noise that is capable of inducing the hearing loss (NIHL) has a strong impact on the inner ear structures and causes early and most obvious pathophysiological changes in the auditory periphery. Several studies indicated that intrinsic apoptotic cell death mechanisms are the key factors inducing cellular degeneration immediately after noise exposure and are maintained for days or even weeks. In addition, studies demonstrated several changes in the central auditory system following noise exposure, consistent with early apoptosis-related pathologies. To clarify the underlying mechanisms, the present study focused on the noise-induced gene and protein expression of the pro-apoptotic protease activating factor-1 (APAF1) and the anti-apoptotic B-cell lymphoma 2 related protein a1a (BCL2A1A) in the cochlear nucleus (CN), inferior colliculus (IC) and auditory cortex (AC) of the murine central auditory pathway. The expression of Bcl2a1a mRNA was upregulated immediately after trauma in all tissues investigated, whereas the protein levels were significantly reduced at least in the auditory brainstem. Conversely, acute noise has decreased the expression of Apaf1 gene along the auditory pathway. The changes in APAF1 protein level were not statistically significant. It is tempting to speculate that the acoustic overstimulation leads to mitochondrial dysfunction and induction of apoptosis by regulation of proapoptotic and antiapoptotic proteins. The inverse expression pattern on the mRNA level of both genes might reflect a protective response to decrease cellular damage. Our results indicate the immediate presence of intrinsic apoptosis following noise trauma. This, in turn, may significantly contribute to the development of central structural deficits. Auditory pathway-specific inhibition of intrinsic apoptosis could be a therapeutic approach for the treatment of acute (noise-induced) hearing loss to prevent irreversible neuronal injury in auditory brain structures and to avoid profound deficits in complex auditory processing.

Exposure of Wistar rats to 24-h psycho-social stress alters gene expression in the inferior colliculus

Recently, we have demonstrated that the exposure of Wistar rats to psycho-social stress results in a transient auditory hypersensitivity. Here, to learn more about modifications occurring in auditory brainstem, we have analyzed gene expression pattern in inferior colliculus using quantitative RT-PCR. As targets, we have chosen genes associated with: neural activity (FBJ osteosarcoma viral oncogene, cFos), hypoxia (nitric oxide synthase inducible, iNos; superoxide dismutase 2, Sod2), neuroprotection (nerve growth factor beta, Ngfb; heat shock factor 1, Hsf1; heat shock protein 70, Hsp70) and inflammation (tumor necrosis factor alpha, Tnfa; tumor necrosis factor alpha receptor, Tnfar; substance P, Sp; cyclooxygenase 2, Cox2). We found that the expression of all genes was modified following stress, as compared to the controls. Immediately after stress, the number of transcripts encoding iNos, Sod2, Hsf1, Ngfb, Tnfa, Tnfar and Sp was significantly increased, suggesting possible modulation during exposure to stressor. Interestingly, we found that expression of Hsf1 and Ngfb at this particular time was left-right asymmetrical: there were more transcripts of both genes found in the left colliculi, as compared to the right colliculi. Three hours post-stress, iNos, Hsf1, Tnfa and Tnfar were still upregulated, Sod2, Ngfb and Sp went back to baseline and Cox2 was upregulated. Six hours post-stress, cFos mRNA became downregulated. The number of Hsp70 mRNA increased 24h post-stress. Except for the reduced number of cFos transcripts, expression of all other genes tested reached the baseline seven days post-stress. Presented results corroborate the concept of auditory system responding to the psycho-social stress. Post-stress changes in the IC gene expression could likely indicate shift from allostasis to homeostasis in the auditory brainstem.

Occlusal disharmony increases amyloid-β in the rat hippocampus

Amyloid-β plays a causative role in Alzheimer's disease. Occlusal disharmony causes chronic psychological stress, and psychological stress increases amyloid-β accumulation. The purpose of the present study was to investigate whether occlusal disharmony-induced psychological stress affects the accumulation of amyloid-β and its related gene expressions in the rat hippocampus. Eight-week-old male Wistar rats (n = 18) were divided into three groups of six rats each: (1) a control group that received no treatment for 8 weeks; (2) an occlusal disharmony group that underwent cutoff maxillary molar cusps for 8 weeks; and (3) a recovered group that underwent cutoff maxillary molar cusps for 4 weeks followed by recovery for 4 weeks. Occlusal disharmony increased plasma corticosterone levels in a time-dependent manner. Levels of amyloid-β 40 and 42, glucocorticoid receptor (Gr) protein, and cleaved caspase 3 (Casp3) as well as gene expressions of amyloid precursor protein, beta-secretase, Casp3, and Gr in the hippocampus in the occlusal disharmony group were significantly higher than those in the control group (P < 0.016). These findings were significantly improved by recovery of occlusion (P < 0.016). These results indicate that psychological stress induced by occlusal disharmony reversibly induces amyloid-β 40 and 42 in the rat hippocampus through the glucocorticoid signal.

Expression analysis of prestin and selected transcription factors in newborn rats

Transcription factors (TFs) have a central role to play in regulating gene expression. To analyze the co-expression patterns of selected TFs with the motor protein prestin of the outer hair cells, we applied an real-time PCR approach combining several kinds of information: (i) expression changes during postnatal development, (ii) expression changes by exposure of organotypic cultures of the organ of Corti to factors which significantly affect prestin expression [thyroid hormone (T4), retinoic acid (RA), butyric acid (BA), increased KCl concentration] and (iii) changes along the apical-basal gradient. We found that the mRNA levels of the TF Brn-3c (Pou4f3), a member of the POU family, are significantly associated with the regulation of prestin during postnatal development and in cultures supplemented with T4 (0.5 μM), BA (0.5-2.0 mM), and high KCl (50 mM) concentration. The mRNA level of the constitutively active TF C/ebpb (CCAAT/enhancer binding protein beta) correlates positively with the prestin expression during postnatal development and in cultures exposed to T4 and RA (50-100 μM). The mRNA levels of the calcium-dependent TF CaRF correlates significantly with the prestin expression in cultures exposed to T4 and high KCl concentration. The observed coexpression patterns may suggest that the TFs Brn-3c, C/ebpb, and Carf contribute to regulating the expression of prestin under the investigated conditions.

Decrease of prestin expression by increased potassium concentration in organotypic cultures of the organ of Corti of newborn rats

Prestin is the motor protein of the outer hair cells of the organ of Corti and a key factor in ensuring a high sensitivity level of mammalian hearing. In the present study, we examined the effects of increased extracellular potassium (K(+)) concentration on the expression of prestin mRNA and the transcription factors Gata-3 and Carf in the organotypic culture of the organ of Corti of newborn rats. Mannitol and NaCl were used to analyze possible effects of hyperosmotic stress or ion-specific changes, respectively. An increase in prestin expression by a factor of 1.5-2.0 was seen in cultures grown in the presence of 5mM K(+). Potassium concentration of 35 and 55 mM induced a parallel decrease in prestin and Carf expression, but Gata-3 expression increased. Mannitol had no effect on gene expression whereas increased NaCl concentrations decreased prestin, but not Carf expression. The data suggest that chronic depolarization might decrease the prestin expression and possibly contribute to hearing loss and tinnitus.

Neurofibromin (Nf1) is required for skeletal muscle development

Neurofibromatosis type 1 (NF1) is a multi-system disease caused by mutations in the NF1 gene encoding a Ras-GAP protein, neurofibromin, which negatively regulates Ras signaling. Besides neuroectodermal malformations and tumors, the skeletal system is often affected (e.g. scoliosis and long bone dysplasia) demonstrating the importance of neurofibromin for development and maintenance of the musculoskeletal system. Here, we focus on the role of neurofibromin in skeletal muscle development. Nf1 gene inactivation in the early limb bud mesenchyme using Prx1-cre (Nf1(Prx1)) resulted in muscle dystrophy characterized by fibrosis, reduced number of muscle fibers and reduced muscle force. This was caused by an early defect in myogenesis affecting the terminal differentiation of myoblasts between E12.5 and E14.5. In parallel, the muscle connective tissue cells exhibited increased proliferation at E14.5 and an increase in the amount of connective tissue as early as E16.5. These changes were accompanied by excessive mitogen-activated protein kinase pathway activation. Satellite cells isolated from Nf1(Prx1) mice showed normal self-renewal, but their differentiation was impaired as indicated by diminished myotube formation. Our results demonstrate a requirement of neurofibromin for muscle formation and maintenance. This previously unrecognized function of neurofibromin may contribute to the musculoskeletal problems in NF1 patients.

Expression of genes implicated in oxidative stress in the cochlea of newborn rats

Oxidative stress is an important mechanism inducing ototoxicity-, age- and noise-induced hearing loss. To better understand this phenomenon, we examined cochlear tissues for the expression of following genes involved directly or indirectly in the oxidative stress response: glyceraldehyde-3-phosphate dehydrogenase (Gapdh); solute carrier family-2 (facilitated glucose transporter), member-1 (Slc2a1); heme oxygenase-1 (Hmox1); heme oxygenase-2 (Hmox2); inducible nitric oxide synthase-2 (Nos2); transferrin (Tf); transferrin receptor (Tfrc); glutathione S-transferase A3 (Gsta3) and metallothionein-1a (Mt1a). Cochlear tissues were dissected from the p3-p5 Wistar rats, divided into the organ of Corti (OC), modiolus (MOD) and stria vascularis together with spiral ligament (SV + SL) and processed immediately or cultured under normoxic conditions or a short-term, mild hypoxia followed by re-oxygenation. After 24 h, explants were collected and total RNA isolated, transcribed and amplified in the real time RT-PCR. We found all genes listed above expressed in the freshly isolated cochlear tissues. In the OC and MOD, Slc2a1, Tf, and Mt1a were expressed on a lower level than in the SV + SL. In the OC, Hmox1 was expressed on a lower level than in the MOD and SV + SL. Hypoxic and normoxic cultures increased the transcript number of Gapdh, Slc2a1 and Hmox1 in all cochlear tissues. The expression of Nos2, Tf, Gsta3 and Mt1a increased in a tissue-specific manner. In the SV + SL, Mt1a expression decreased after normoxic and hypoxic conditions. Taken together, using real time RT-PCR, our results imply that oxidative stress may be an important component of cochlear injury during the developing period. In spite of the immaturity of the tissue, a differential response of antioxidant enzymes/proteins with respect to the pathway, the expression levels and regions was observed.

Role of mitochondrial uncoupling protein 4 in rat inner ear

The uncoupling protein 4 (UCP4) belongs to the mitochondrial anion transporter family. Protein tissue distribution and functions are still a matter of debate. Using an antibody we have previously shown that UCP4 appears in neurons and to a lesser extent in astrocytes of murine neuronal tissue as early as days 12-14 of embryonic development (Smorodchenko et al., 2009). Here we demonstrated for the first time that neurosensory cells such as hair cells of the inner ear and mechanosensitive Merkel cells in skin also express a significant amount of UCP4. We tested the hypothesis about whether UCP4 contributes to the regulation of oxidative stress using the model of oxygen deprivation. For this we compared the protein expression level in freshly isolated explants of organ of Corti, modiolus and stria vascularis from neonatal rats with explants cultured under hypoxia. Western blot analysis revealed that the UCP4 level was not increased under hypoxic conditions, when compared to the mitochondrial outer membrane protein VDAC or to the anti-oxidative enzyme SOD2. We moreover demonstrated that UCP4 expression is differently regulated during postnatal stages and is region-specific. We hypothesized that UCP4 may play an important role in functional maturation of the rat inner ear.

Involvement of calpain-I and microRNA34 in kanamycin-induced apoptosis of inner ear cells

Inner ear cells, including hair cells, spiral ganglion cells, stria vascularis cells and supporting cells on the basilar membrane, play a major role in transducing hearing signals and regulating inner ear homoeostasis. However, their functions are often damaged by antibiotic-induced ototoxicity. Apoptosis is probably involved in inner ear cell injury following aminoglycoside treatment. Calpain, a calcium-dependent protease, is essential for mediating and promoting cell death. We have therefore investigated the involvement of calpain in the molecular mechanism underlying ototoxicity induced by the antibiotic kanamycin in mice. Kanamycin (750 mg/kg) mainly induced cell death of cochlear cells, including stria vascularis cells, supporting cells and spiral ganglion cells, but not hair cells within the organ of Corti. Cell death due to apoptosis occurred in a time-dependent manner with concomitant up-regulation of calpain expression. Furthermore, the expression levels of two microRNAs, mir34a and mir34c, were altered in a dose-dependent manner in cochlear cells. These novel findings demonstrated the involvement of both calpain and microRNAs in antibiotic-induced ototoxicity.

Novel avenues of drug discovery and biomarkers for diabetes mellitus

Globally, developed nations spend a significant amount of their resources on health care initiatives that poorly translate into increased population life expectancy. As an example, the United States devotes 16% of its gross domestic product to health care, the highest level in the world, but falls behind other nations that enjoy greater individual life expectancy. These observations point to the need for pioneering avenues of drug discovery to increase life span with controlled costs. In particular, innovative drug development for metabolic disorders such as diabetes mellitus becomes increasingly critical given that the number of diabetic people will increase exponentially over the next 20 years. This article discusses the elucidation and targeting of novel cellular pathways that are intimately tied to oxidative stress in diabetes mellitus for new treatment strategies. Pathways that involve wingless, β-nicotinamide adenine dinucleotide (NAD(+)) precursors, and cytokines govern complex biological pathways that determine both cell survival and longevity during diabetes mellitus and its complications. Furthermore, the role of these entities as biomarkers for disease can further enhance their utility irrespective of their treatment potential. Greater understanding of the intricacies of these unique cellular mechanisms will shape future drug discovery for diabetes mellitus to provide focused clinical care with limited or absent long-term complications.

Diabetes mellitus: channeling care through cellular discovery

Diabetes mellitus (DM) impacts a significant portion of the world's population and care for this disorder places an economic burden on the gross domestic product for any particular country. Furthermore, both Type 1 and Type 2 DM are becoming increasingly prevalent and there is increased incidence of impaired glucose tolerance in the young. The complications of DM are protean and can involve multiple systems throughout the body that are susceptible to the detrimental effects of oxidative stress and apoptotic cell injury. For these reasons, innovative strategies are necessary for the implementation of new treatments for DM that are generated through the further understanding of cellular pathways that govern the pathological consequences of DM. In particular, both the precursor for the coenzyme beta-nicotinamide adenine dinucleotide (NAD(+)), nicotinamide, and the growth factor erythropoietin offer novel platforms for drug discovery that involve cellular metabolic homeostasis and inflammatory cell control. Interestingly, these agents and their tightly associated pathways that consist of cell cycle regulation, protein kinase B, forkhead transcription factors, and Wnt signaling also function in a broader sense as biomarkers for disease onset and progression.

Expression of the proinflammatory cytokines in cochlear explant cultures: influence of normoxia and hypoxia

Hearing loss can be induced by a variety of factors including hypoxia and inflammation. Here, we investigated in vitro the effect of hypoxia on the expression of proinflammatory cytokines in the explanted cochlear tissues. Using RT-PCR, we determined the expression of genes encoding IL-1beta, IL-6 and TNF in the organ of Corti (OC), modiolus (MOD) and stria vascularis together with spiral ligament (SV+SL). In addition, using ELISA, we determined the concentration of IL-1beta and IL-6 in the supernatants of explant cultures. We found that the dissection, explanting and consecutive 24-h normoxic culture results in highly increased expression of IL-1beta and IL-6, as compared to the freshly isolated tissues. TNFalpha was upregulated only in the MOD. Interestingly, 24h of hypoxia decreased the number of mRNA encoding IL-1beta and IL-6 and increased the number of mRNA encoding TNFalpha in the SV+SL as compared to normoxia. The concentration of IL-6 measured in the explant tissue culture supernatants was significantly lower in hypoxic than in the normoxic cultures. Our results show that tissue dissection and explanting as well as hypoxia can influence the expression and secretion of proinflammatory cytokines. This implies the presence of tissue-specific regulatory pathways between hypoxia and inflammation in the inner ear.

The vitamin nicotinamide: translating nutrition into clinical care

Nicotinamide, the amide form of vitamin B(3) (niacin), is changed to its mononucleotide compound with the enzyme nicotinic acide/nicotinamide adenylyltransferase, and participates in the cellular energy metabolism that directly impacts normal physiology. However, nicotinamide also influences oxidative stress and modulates multiple pathways tied to both cellular survival and death. During disorders that include immune system dysfunction, diabetes, and aging-related diseases, nicotinamide is a robust cytoprotectant that blocks cellular inflammatory cell activation, early apoptotic phosphatidylserine exposure, and late nuclear DNA degradation. Nicotinamide relies upon unique cellular pathways that involve forkhead transcription factors, sirtuins, protein kinase B (Akt), Bad, caspases, and poly (ADP-ribose) polymerase that may offer a fine line with determining cellular longevity, cell survival, and unwanted cancer progression. If one is cognizant of the these considerations, it becomes evident that nicotinamide holds great potential for multiple disease entities, but the development of new therapeutic strategies rests heavily upon the elucidation of the novel cellular pathways that nicotinamide closely governs.

Evaluation of vardenafil for the treatment of subjective tinnitus: a controlled pilot study

Background

Vardenafil (Levitra^®) represents a potent and highly selective phosphodiesterase type 5 (PDE5) inhibitor, which is established for treatment of various diseases. There are several unpublished reports from patients stating that vardenafil has a considerable therapeutic effect on their concomitant tinnitus. This pilot study was conducted to specifically assess the effect of vardenafil in patients with chronic tinnitus.

Methods

This trial was based on a prospective, randomized, double-blind, placebo-controlled, parallel group design. Fourty-two consecutive subjects with mon- or binaural chronic tinnitus received 10 mg vardenafil (N = 21) or matching placebo tablets (N = 21) administered orally twice a day over a period of 12 weeks. Clinical examination and data acquisition took place at each visit: at baseline, after 4 weeks, after 12 weeks (end of treatment with study medication), and at non-medicated follow-up after 16 weeks. Assessment of clinical effectiveness was based on a standardized tinnitus questionnaire (TQ), the Short Form 36 health survey (SF-36), audiometric measurements (mode, pitch and loudness of tinnitus; auditory thresholds) and biomarkers of oxidative stress in patients' blood (malondialdehyde, protein carbonyl, homocysteine and total antioxidative status). Therapeutic efficacy was evaluated by comparison of subjective and objective parameters with baseline data between both treatment groups (ANCOVA).

Results

Vardenafil had no superior efficacy over placebo in the treatment of chronic tinnitus during this study. The primary efficacy criterion 'TQ total score' failed to demonstrate significant improvement compared to placebo. Subjective reports of TQ subscales and general quality of life areas (SF-36), objective audiometric examinations as well as investigated biomarkers for oxidative stress did not reveal any significant treatment effects. The safety profile was favorable and consistent with that in other vardenafil studies.

Conclusion

Although hypoxia and ischemia play a special role in the pathogenesis of tinnitus, the PDE5-inhibitor-induced increase of nitric oxide-mediated vasodilatation exerted no specific influence on tinnitus symptomatology. Considering the unclear risk of rarely associated hearing impairment, systemic application of vardenafil or other PDE5 inhibitors prove to be not appropriate for therapy of chronic tinnitus.

MRNA expression of members of the IGF system in the organ of Corti, the modiolus and the stria vascularis of newborn rats

We analyzed the mRNA expression of the insulin-like growth factor (IGF) family genes and of selected downstream pathway genes using the Affymetrix microarray system and confirmatory RT-PCR in the freshly prepared organ of Corti (OC), modiolus (MOD) and stria vascularis (SV) from neonatal rats (3-5 days old) and after 24h in culture. Among the seven members of the IGF family analyzed in this paper, IGF1, IGF2 and IGF-binding protein (IGFBP2) had the highest basal expression in all regions. Preparatory stress and culture increased the expression of IGF2, IGFBP2, IGFBP3, IGFBP5, glucose transporterl (GLUT1), signal transducer, and activator of transcription3 (STAT3), phosphoinositide-3-kinase regulatory subunit (Pik3r1), Jun oncogene (c-jun) and decreased that of mitogen-activated protein kinases MAPK3 and MAPK14 in all regions. Region-specific changes were observed in OC (GLUT1), MOD (IGFBP3 and c-jun) and SV (IGF2 and IGFBP2).