A novel KCNQ4 mutation and a private IMMP2L-DOCK4 duplication segregating with nonsyndromic hearing loss in a Brazilian family

Autosomal Dominant Non-Syndromic Hearing Loss (DFNA): A Comprehensive Narrative Review

Autosomal dominant non-syndromic hearing loss (HL) typically occurs when only one dominant allele within the disease gene is sufficient to express the phenotype. Therefore, most patients diagnosed with autosomal dominant non-syndromic HL have a hearing-impaired parent, although de novo mutations should be considered in all cases of negative family history. To date, more than 50 genes and 80 loci have been identified for autosomal dominant non-syndromic HL. DFNA22 (MYO6 gene), DFNA8/12 (TECTA gene), DFNA20/26 (ACTG1 gene), DFNA6/14/38 (WFS1 gene), DFNA15 (POU4F3 gene), DFNA2A (KCNQ4 gene), and DFNA10 (EYA4 gene) are some of the most common forms of autosomal dominant non-syndromic HL. The characteristics of autosomal dominant non-syndromic HL are heterogenous. However, in most cases, HL tends to be bilateral, post-lingual in onset (childhood to early adulthood), high-frequency (sloping audiometric configuration), progressive, and variable in severity (mild to profound degree). DFNA1 (DIAPH1 gene) and DFNA6/14/38 (WFS1 gene) are the most common forms of autosomal dominant non-syndromic HL affecting low frequencies, while DFNA16 (unknown gene) is characterized by fluctuating HL. A long audiological follow-up is of paramount importance to identify hearing threshold deteriorations early and ensure prompt treatment with hearing aids or cochlear implants.

Immp2l Mutation Induces Mitochondrial Membrane Depolarization and Complex III Activity Suppression after Middle Cerebral Artery Occlusion in Mice

OBJECTIVE

We previously reported that mutations in inner mitochondrial membrane peptidase 2-like (Immp2l) increase infarct volume, enhance superoxide production, and suppress mitochondrial respiration after transient cerebral focal ischemia and reperfusion injury. The present study investigated the impact of heterozygous Immp2l mutation on mitochondria function after ischemia and reperfusion injury in mice.

METHODS

Mice were subjected to middle cerebral artery occlusion for 1 h followed by 0, 1, 5, and 24 h of reperfusion. The effects of Immp2l^+/- on mitochondrial membrane potential, mitochondrial respiratory complex III activity, caspase-3, and apoptosis-inducing factor (AIF) translocation were examined.

RESULTS

Immp2l^+/- increased ischemic brain damage and the number of TUNEL-positive cells compared with wild-type mice. Immp2l^+/- led to mitochondrial damage, mitochondrial membrane potential depolarization, mitochondrial respiratory complex III activity suppression, caspase-3 activation, and AIF nuclear translocation.

CONCLUSION

The adverse impact of Immp2l^+/- on the brain after ischemia and reperfusion might be related to mitochondrial damage that involves depolarization of the mitochondrial membrane potential, inhibition of the mitochondrial respiratory complex III, and activation of mitochondria-mediated cell death pathways. These results suggest that patients with stroke carrying Immp2l^+/- might have worse and more severe infarcts, followed by a worse prognosis than those without Immp2l mutations.

The Pathological Mechanisms of Hearing Loss Caused by KCNQ1 and KCNQ4 Variants

Deafness-associated genes KCNQ1 (also associated with heart diseases) and KCNQ4 (only associated with hearing loss) encode the homotetrameric voltage-gated potassium ion channels Kv7.1 and Kv7.4, respectively. To date, over 700 KCNQ1 and over 70 KCNQ4 variants have been identified in patients. The vast majority of these variants are inherited dominantly, and their pathogenicity is often explained by dominant-negative inhibition or haploinsufficiency. Our recent study unexpectedly identified cell-death-inducing cytotoxicity in several Kv7.1 and Kv7.4 variants. Elucidation of this cytotoxicity mechanism and identification of its modifiers (drugs) have great potential for aiding the development of a novel pharmacological strategy against many pathogenic KCNQ variants. The purpose of this review is to disseminate this emerging pathological role of Kv7 variants and to underscore the importance of experimentally characterizing disease-associated variants.

Genetic etiology of non-syndromic hearing loss in Latin America

Latin America comprises all countries from South and Central America, in addition to Mexico. It is characterized by a complex mosaic of regions with heterogeneous genetic profiles regarding the geographical origin of the ancestors and proportions of admixture between the Native American, European and African components. In the first years following the findings of the role of the GJB2/GJB6 genes in the etiology of hearing loss, most scientific investigations about the genetics of hearing loss in Latin America focused on assessing the frequencies of pathogenic variants in these genes. More recently, modern techniques allowed researchers in Latin America to make exciting contributions to the finding of new candidate genes, novel mechanisms of inheritance in previously known genes, and characterize a wide diversity of variants, many of them unique to Latin America. This review aimed to provide a general landscape of the genetic studies about non-syndromic hearing loss in Latin America and their main scientific contributions. It allows the conclusion that, although there are similar contributions of some genes, such as GJB2/GJB6, when compared to European and North American countries, Latin American populations revealed some peculiarities that indicate the need for tailored strategies of screening and diagnosis to specific geographic regions.

USP36-Mediated Deubiquitination of DOCK4 Contributes to the Diabetic Renal Tubular Epithelial Cell Injury via Wnt/β-Catenin Signaling Pathway

Diabetic kidney disease (DKD) has become the leading cause of end-stage renal disease but the efficacy of current treatment remains unsatisfactory. The pathogenesis of DKD needs a more in-depth research. Ubiquitin specific proteases 36 (USP36), a member of deubiquitinating enzymes family, has aroused wide concerns for its role in deubiquitinating and stabilizing target proteins. Nevertheless, the role of USP36 in diabetes has never been reported yet. Herein, we identified an increased expression of USP36 both in vitro and in vivo in diabetic renal tubular epithelial cells (TECs), and its overexpression is related to the enhanced epithelial-to-mesenchymal transition (EMT). Further investigation into the mechanisms proved that USP36 could directly bind to and mediate the deubiquitination of dedicator of cytokinesis 4 (DOCK4), a guanine nucleotide exchange factor (GEF) that could activate Wnt/β-catenin signaling pathway and induce EMT. Our study revealed a new mechanism that USP36 participates in the pathogenesis of DKD, and provided potential intervening targets accordingly.

Molecular basis and restoration of function deficiencies of Kv7.4 variants associated with inherited hearing loss

Deafness non-syndromic autosomal dominant 2 (DFNA2) is characterized by symmetric, predominantly high-frequency sensorineural hearing loss that is progressive across all frequencies. The disease is associated with variants of a potassium voltage-gated channel subfamily Q member 4 gene, KCNQ4 (Kv7.4). Here, we studied nine recently identified Kv7.4 variants in DFNA2 pedigrees, including V230E, E260K, D262V, Y270H, W275R, G287R, P291L, P291S and S680F. We proved that the variant S680F did not alter the channel function while the other eight variants resulted in function deficiencies. We further proved that the two variants E260K and P291S showed reduced cell membrane expressions while the other seven variants showed moderate cell surface expressions. Thus, trafficking deficiency is not a common mechanism underlying channel dysfunction. Next, we studied two variants, V230E and G287R, using molecular dynamics simulation. We showed that V230E stabilized Kv7.4 channel in the closed state by forming an additional hydrogen bond with a basic residue K325, while G287R distorted the selectivity filter and blocked the pore region of Kv7.4 channel. Moreover, by co-expressing wild-type (WT) and variant proteins in vitro, we demonstrated that the heterogeneous Kv7.4 channel currents were reduced compared to the WT channel currents and the reduction could be rescued by a Kv7.4 opener retigabine. Our study provided the underlying mechanisms and suggested a potential alternative therapeutic approach for DFNA2.

Genes important for otoneurological diagnostic purposes - current status and future prospects

SUMMARY

This review focuses on the current knowledge of the genes responsible for non-syndromic hearing loss that can be useful for otoneurological diagnostic purposes. From among a large number of genes that have been associated with non-syndromic hearing impairment, we selected several best-known genes, including the COCH gene, GJB2, GJB6 and SLC26A4, and we describe their role and effects of mutations and prevalence of mutations in various populations. Next, we focus on genes associated with tinnitus. Important areas for further research include assessment of genes potentially involved in pathophysiology of tinnitus and vertigo, which have traditionally been considered as being of otological aetiology, while advances in neuroimaging techniques have increasingly shifted studies toward neurological correlations.