Mitochondrial cytochrome oxidase immunolabeling in aged human temporal bones

[Changes in the type and amount of bone collagens in chronic suppurative otitis media]

OBJECTIVE

Comparative assessment of the collagen-tissue interaction in the bone tissue of the middle ear structures in patients with chronic suppurative otitis media (CSOM).

MATERIAL AND METHODS

A prospective study of 42 patients aged 16-60 years with CSOM admitted for reconstructive sanitizing surgery was performed. To study the collagen-tissue interaction, intraoperative samples of the bone tissue of the middle ear were used. A software calculation of vascular-stromal areas and ratios of various types of bone tissue collagen was carried out during histomorphological examination.

RESULTS AND DISCUSSION

The quantitative and qualitative parameters of bone tissue collagen obtained intraoperatively in patients with CSOM were studied. The cavities of the middle ear are in the phase of a chronic purulent process, when the bone structures are morphologically disorganized according to the pathological type, and sclerosis with overgrowth of the cellular structure of the mastoid process is considered a favorable outcome for delimiting the focus of inflammation in the pyramid of the temporal bone.

CONCLUSIONS

Changes in the processes of collagen remodeling of bone structures contribute to the maintenance of inflammation of the middle ear in all clinical forms of CSOM. Pathological osteogenesis can serve as an indicator of the progressive course of a purulent-destructive process in the cavities of the middle ear, which makes it possible to reliably determine the rate of bone tissue transformation to predict relapse after reconstructive and sanitizing surgery.

Pathology and mechanisms of cochlear aging

Presbycusis, or age-related hearing loss (ARHL), occurs in most mammals with variations in the age of onset, rate of decline, and magnitude of degeneration in the central nervous system and inner ear. The affected cochlear structures include the stria vascularis and its vasculature, spiral ligament, sensory hair cells and auditory neurons. Dysfunction of the stria vascularis results in a reduced endocochlear potential. Without this potential, the cochlear amplification provided by the electro-motility of the outer hair cells is insufficient, and a high-frequency hearing-loss results. Degeneration of the sensory cells, especially the outer hair cells also leads to hearing loss due to lack of amplification. Neuronal degeneration, another hallmark of ARHL, most likely underlies difficulties with speech discrimination, especially in noisy environments. Noise exposure is a major cause of ARHL. It is well-known to cause sensory cell degeneration, especially the outer hair cells at the high frequency end of the cochlea. Even loud, but not uncomfortable, sound levels can lead to synaptopathy and ultimately neuronal degeneration. Even in the absence of a noisy environment, aged cells degenerate. This pathology most likely results from damage to mitochondria and contributes to degenerative changes in the stria vascularis, hair cells, and neurons. The genetic underpinnings of ARHL are still unknown and most likely involve various combinations of genes. At present, the only effective strategy for reducing ARHL is prevention of noise exposure. If future strategies can improve mitochondrial activity and reduce oxidative damage in old age, these should also bring relief.

Hearing impairment in MELAS: new prospective in clinical use of microRNA, a systematic review

AIM

To evaluate the feasibility of microRNAs (miR) in clinical use to fill in the gap of current methodology commonly used to test hearing impairment in MELAS patients.

MATERIAL AND METHOD

A literature review was performed using the following keywords, i.e., MELAS, Hearing Loss, Hearing Impairment, Temporal Bone, Otoacustic Emission (OTOAE), Auditory Brain Response (ABR), and microRNA. We reviewed the literature and focused on the aspect of the temporal bone, the results of electrophysiological tests in human clinical studies, and the use of miR for detecting lesions in the cochlea in patients with MELAS.

RESULTS

In patients with MELAS, Spiral Ganglions (SG), stria vascularis (SV), and hair cells are damaged, and these damages affect in different ways various structures of the temporal bone. The function of these cells is typically investigated using OTOAE and ABR, but in patients with MELAS these tests provide inconsistent results, since OTOAE response is absent and ABR is normal. The normal ABR responses are unexpected given the SG loss in the temporal bone. Recent studies in humans and animals have shown that miRs, and in particular miRs 34a, 29b, 76, 96, and 431, can detect damage in the cells of the cochlea with high sensitivity. Studies that focus on the temporal bone aspects have reported that miRs increase is correlated with the death of specific cells of the inner ear. MiR - 9/9* was identified as a biomarker of human brain damage, miRs levels increase might be related to damage in the central auditory pathways and these increased levels could identify the damage with higher sensitivity and several months before than electrophysiological testing.

CONCLUSION

We suggest that due to their accuracy and sensitivity, miRs might help monitor the progression of SNHL in patients with MELAS.

Immunohistochemical techniques for the human inner ear

In this review, we provide a description of the recent methods used for immunohistochemical staining of the human inner ear using formalin-fixed frozen, paraffin and celloidin-embedded sections. We also show the application of these immunohistochemical methods in auditory and vestibular endorgans microdissected from the human temporal bone. We compare the advantages and disadvantages of immunohistochemistry (IHC) in the different types of embedding media. IHC in frozen and paraffin-embedded sections yields a robust immunoreactive signal. Both frozen and paraffin sections would be the best alternative in the case where celloidin-embedding technique is not available. IHC in whole endorgans yields excellent results and can be used when desiring to detect regional variations of protein expression in the sensory epithelia. One advantage of microdissection is that the tissue is processed immediately and IHC can be made within 1 week of temporal bone collection. A second advantage of microdissection is the excellent preservation of both morphology and antigenicity. Using celloidin-embedded inner ear sections, we were able to detect several antigens by IHC and immunofluorescence using antigen retrieval methods. These techniques, previously applied only in animal models, allow for the study of numerous important proteins expressed in the human temporal bone potentially opening up a new field for future human inner ear research.

Major arc mitochondrial DNA deletions in cytochrome c oxidase-deficient human cochlear spiral ganglion cells

CONCLUSIONS

This study suggests that cytochrome c oxidase subunit 3 (COX 3) expression is diminished in spiral ganglion cells from individuals with presbycusis. In addition to the mitochondrial DNA (mtDNA) common deletion (CD), other deletions involving the mtDNA major arc contribute to the observed deficit in COX 3 expression.

OBJECTIVES

To assess COX 3 deficiency in spiral ganglion cells from individuals with presbycusis and to determine whether deletions other than the CD contribute to this deficiency.

METHODS

COX 3 immunofluorescence staining of archival human temporal bone tissue sections from individuals with presbycusis and from age-matched normal-hearing individuals was performed and the intensity of spiral ganglion cell immunostaining was measured. Single COX 3-deficient spiral ganglion cells were isolated by laser microdissection (LMD) and the DNA was analyzed with duplex real-time PCR assays to assess the CD level and the total mtDNA major arc deletion level.

RESULTS

A statistically significant difference (p = 0.021) in the mean intensity of COX 3 immunofluorescence staining of spiral ganglion cells was observed between individuals with presbycusis and normal-hearing controls. The total mtDNA major arc deletion level was greater than the CD level in COX 3-deficient spiral ganglion cells.

Somatic mtDNA mutations cause progressive hearing loss in the mouse

Mitochondrial dysfunction has been implicated in the commonly occurring age-associated hearing loss (presbyacusis). We have previously generated mtDNA mutator mice with increased levels of somatic mtDNA point mutations causing phenotypes consistent with premature ageing. We have now utilized these mice to investigate whether elevated levels of somatic mtDNA mutations affect the auditory system. The mtDNA mutator mice develop a progressive impairment of hearing (ABR thresholds). Quantitative assessment of hair cell loss in the cochlea did not show any significant difference between the mutator and wild-type mice. The mtDNA mutator mice showed progressive apoptotic cell loss in the spiral ganglion and increased pathology with increasing age in the stria vascularis. The neurons in the cochlear nucleus showed an accelerated progressive degeneration with increasing age in the mutator mice compared to the wild-type mice. Both physiological and histological characterization thus reveals a striking resemblance between the auditory system pathology of mtDNA mutator mice and humans with presbyacusis. Somatic mtDNA mutations accumulate during normal ageing and further studies in humans are now warranted to investigate whether presbyacusis can be linked to mitochondrial dysfunction.

Role of mitochondrial dysfunction and mitochondrial DNA mutations in age-related hearing loss

Mitochondrial DNA (mtDNA) mutations/deletions are considered to be associated with the development of age-related hearing loss (AHL). We assessed the role of accumulation of mtDNA mutations in the development of AHL using Polg(D257A) knock-in mouse, which exhibited increased spontaneous mtDNA mutation rates during aging and showed accelerated aging primarily due to increased apoptosis. They exhibited moderate hearing loss and degeneration of the hair cells, spiral ganglion cells and stria vascularis by 9 month of age, while wild-type animals did not. We next examined if mitochondrial damage induced by systemic application of germanium dioxide caused progressive hearing loss and cochlear damage. Guinea pigs and mice given germanium dioxide exhibited degeneration of the muscles and kidney and developed hearing loss due to degeneration of cochlear tissues, including the stria vascularis. Calorie restriction, which causes a metabolic shift toward increased energy metabolism in some organs, has been shown to attenuate AHL and age-related cochlear degeneration and to lower quantity of mtDNA deletions in the cochlea of mammals. Together these findings indicate that decreased energy metabolism due to accumulation of mtDNA mutations/deletions and decline of respiratory chain function play an important role in the manifestation of AHL.

Unbiased stereological estimation of the spiral ligament and stria vascularis volumes in aging and Ménière's disease using archival human temporal bones

The present study applies the unbiased stereological technique-Cavalieri principle to measure the volumes of the stria vascularis (SV) and the spiral ligament (SL) using postmortem archival human temporal bones from normal young and older subjects and subjects with Ménière's disease. Normative data was obtained from subjects without ages ranging from 15 to 84 years old who had no history of audiovestibular disease (N=25). For comparison purposes, the normative specimens were divided into three groups: group 1 (n=8) had ages ranging from 15 to 38 years old, average age=23.9; group 2 (n=8) had ages ranging from 51 to 59 years old, average age=55.1; group 3 (n=9) had ages ranging from 64 to 84 years old, average age=74.3. The average SV volume of group 3 (0.479 mm3) was significantly lower than that of group 1 (0.705 mm3) (p<0.0005) and was significantly lower than that of group 2 (0.603 mm3) (p=0.01). The average SL volume of group 3 (8.42 mm3) was significantly lower than that of group 1 (9.54 mm3) (p<0.05), but was not significantly lower than that of group 2 (8.58 mm3). Five subjects with Ménière's disease, confirmed by histopathological examination (ages ranging from 63 to 91 years old, average age=73.4), were studied. The average SV volume in Ménière's subjects (0.378 mm3) was significantly lower than age-matched controls (p<0.05). The average SL volume in Ménière's subjects (7.01 mm3) was also significantly lower than age-matched controls (p<0.05). The SV and SL volumes were unaffected by gender. The present study demonstrates for the first time the use of the unbiased stereological technique-Cavalieri principle-as a reliable and efficient method to obtain volumetric estimates of the SV and the SL by using archival human temporal bone specimens.

Mutation in Mitochondrial DNA as a Cause of Presbyacusis

Much of the hearing loss that occurs in old age is likely to be due to the long-term deterioration of the mitochondria in the different structures of the cochlea. The current review surveys some of the basic information on mitochondria and mitochondrial DNA, as a background to their possible involvement in presbyacusis. It is likely that oxygen radicals damage mitochondrial DNA and other components of the mitochondria, such as their proteins and lipids. This further compromises both oxidative phosphorylation and the repair processes in mitochondria, setting up a vicious cycle of degradation. Evidence is presented from inherited point mutations on the possibly most critical sites for mutations in mitochondrial DNA associated with hearing loss. It is suggested that random sorting and clonal expansion of mutations both maintain the integrity of the pool of mitochondrial DNA molecules and give rise to the apoptosis that leads to loss of vulnerable cells, and hence to deafness. It is moreover suggested that apoptosis of the vulnerable cells of the inner ear may to some extent be preventable, or at least delayed.

Effects of age and cochlear damage on the metabolic activity of the avian cochlear nucleus

Most aging commercially raised broiler chickens display a progressive loss of cochlear hair cells in a pattern similar to the cochlear degeneration found in aging humans: basal (high frequency) hair cells are affected first, followed by apical (low frequency) hair cells [Durham et al., Hear. Res. 166 (2002) 82-95]. Here, cochlear anatomy was assessed from scanning electron micrographs. Then, the metabolic activity of cochlear nucleus (nucleus magnocellularis, NM) neurons in 15-19, 30, 39, 40, and 65-66 week old broiler chickens was examined using cytochrome oxidase histochemistry and compared to the degree of cochlear abnormality. Cochleae of 15-19 week old birds are largely normal; therefore the level of NM metabolic activity is considered the baseline. Cochleae of the 30 week old group display mild damage and hair cell regeneration in the base. Metabolic activity in rostral (high frequency) NM is increased relative to the baseline, while activity remains unchanged in caudal (low frequency) NM. The 39 and 65-66 week old groups display severe and total damage extending into the apex of the cochlea. Metabolic activity is decreased in rostral and caudal NM at these ages. These results suggest that auditory central nervous system metabolism (cytochrome oxidase activity) is affected by changes in the aging chicken cochlea.