Association between the mitochondrial DNA 4977 common deletion in the hair shaft and hearing loss in presbycusis

Induced Pluripotent Stem Cells, a Stepping Stone to In Vitro Human Models of Hearing Loss

Hearing loss is the most prevalent sensorineural impairment in humans. Yet despite very active research, no effective therapy other than the cochlear implant has reached the clinic. Main reasons for this failure are the multifactorial nature of the disorder, its heterogeneity, and a late onset that hinders the identification of etiological factors. Another problem is the lack of human samples such that practically all the work has been conducted on animals. Although highly valuable data have been obtained from such models, there is the risk that inter-species differences exist that may compromise the relevance of the gathered data. Human-based models are therefore direly needed. The irruption of human induced pluripotent stem cell technologies in the field of hearing research offers the possibility to generate an array of otic cell models of human origin; these may enable the identification of guiding signalling cues during inner ear development and of the mechanisms that lead from genetic alterations to pathology. These models will also be extremely valuable when conducting ototoxicity analyses and when exploring new avenues towards regeneration in the inner ear. This review summarises some of the work that has already been conducted with these cells and contemplates future possibilities.

Analyses of Mitochondrial DNA and Immune Phenotyping Suggest Accelerated T-Cell Turnover in Treated HIV

BACKGROUND

HIV infection is associated with premature aging, and mitochondrial integrity is compromised during the aging process. Because mitochondrial toxicity is a consequence of antiretroviral therapies (ARTs), we hypothesized HIV and long-term ART would correlate with immunosenescence and mitochondrial DNA (mtDNA) pathology.

SETTING

Thirteen older HIV-infected individuals (aged >40 years) with virologic suppression (stratified by duration of ART) were compared with 10 uninfected controls well-matched for age.

METHODS

Peripheral blood T-cells were immunophenotyped to measure immune activation, proliferation, and immunosenescence in subsets. mtDNA copies per cell and the relative abundance of mtDNA carrying the "common deletion" (RACD) were quantified by droplet digital polymerase chain reaction.

RESULTS

Immune activation was higher in HIV-infected individuals than HIV-uninfected individuals in mature CD4 T-cell subsets (CD4TTM P = 0.025, CD4TEM P = 0.0020) regardless of ART duration. Cell populations from uninfected individuals were more likely to be more senescent populations in mature CD4 T-cell subsets (TTM P = 0.017), and CD8 (CD8TEMRA+ P = 0.0026). No differences were observed in mtDNA or RACD levels in any CD4 T-cell subsets, while CD8TSCM of infected individuals trended to have more mtDNA (P = 0.057) and reduced RACD (P = 0.0025).

CONCLUSIONS

HIV-infected individuals demonstrated increased immune activation, but reduced senescence in more mature T-cell subsets. Increased mtDNA content and lower RACD in CD8TSCM suggest immune activation driven turnover of these cells in HIV-infected persons.

Correlation between mitochondrial DNA 4977 bp deletion and presbycusis: A system review and meta-analysis

OBJECTIVE

Researchers have evaluated the associations between mitochondrial DNA (mtDNA) 4977 bp deletion and presbycusis. This study aimed to assess the differences of mtDNA 4977 bp deletion between presbycusis patients and controls by conducting a meta-analysis of published studies.

METHODS

Databases, including PubMed, Embase, Web of Science, China National Knowledge Infrastructure (CNKI), and Wanfang Data were searched to collect case-control studies on the correlation between mitochondrial DNA 4977 bp deletion and presbycusis. The research findings of related articles were collected according to the inclusion criteria. Pooled odds ratios (ORs) and corresponding confidence intervals (CIs) were calculated. Meanwhile, subgroup analysis was performed to examine the source of heterogeneity. Revman 5.3 and Stata 12.0 software were used for data synthesis.

RESULTS

Eight English and Chinese studies were included in the meta-analysis, the results of which showed that mitochondrial DNA 4977 bp deletion could increase the risk of presbycusis (OR = 8.16, 95% CI: 3.51-18.99), and the difference was statistically significant (P <. 01). Analysis of the polled OR showed the incidence of mtDNA 4977 bp deletion was 8.50 times higher in Asians with presbycusis than in the control group. And the OR in the studies of occidentals was 7.24. Sample source analysis was also performed with the sample source divided by temporal bone source and other sources (hair and blood). The OR was 4.18 and 22.36 for the temporal bone and other sources, respectively.

CONCLUSION

Mitochondrial DNA 4977 bp deletion could increase the risk of presbycusis.

Association of genetic variations in the mitochondrial DNA control region with presbycusis

Background

The prominent role of mitochondria in the generation of reactive oxygen species, cell death, and energy production contributes to the importance of this organelle in the intracellular mechanism underlying the progression of the common sensory disorder of the elderly, presbycusis. Reduced mitochondrial DNA (mtDNA) gene expression and coding region variation have frequently been reported as being associated with the development of presbycusis. The mtDNA control region regulates gene expression and replication of the genome of this organelle. To comprehensively understand of the role of mitochondria in the progression of presbycusis, we compared variations in the mtDNA control region between subjects with presbycusis and controls.

Methods

A total of 58 presbycusis patients and 220 control subjects were enrolled in the study after examination by the otolaryngologist and audiology tests. Variations in the mtDNA control region were investigated by polymerase chain reaction and Sanger sequencing.

Results

A total of 113 sequence variants were observed in mtDNA, and variants were detected in 100% of patients, with 84% located in hypervariable regions. The frequencies of the variants, 16,223 C>T, 16,311 T>C, 16,249 T>C, and 15,954 A>C, were significantly different between presbycusis and control subjects.

Conclusion

The statistically significant difference in the frequencies of four nucleotide variants in the mtDNA control region of presbycusis patients and controls is in agreement with previous experimental evidence and supports the role of mitochondria in the intracellular mechanism underlying presbycusis development. Moreover, these variants have potential as diagnostic markers for individuals at a high risk of developing presbycusis. The data also suggest the possible presence of changes in the mtDNA control region in presbycusis, which could alter regulatory factor binding sites and influence mtDNA gene expression and copy number.