The protective effects of systemic dexamethasone on sensory epithelial damage and hearing loss in targeted Cx26-null mice

Activating transcription factor 6 contributes to cisplatin‑induced ototoxicity via regulating the unfolded proteins response

As a broad-spectrum anticancer drug, cisplatin is widely used in the treatment of tumors in various systems. Unfortunately, several serious side effects of cisplatin limit its clinical application, the most common of which are nephrotoxicity and ototoxicity. Studies have shown that cochlear hair cell degeneration is the main cause of cisplatin-induced hearing loss. However, the mechanism of cisplatin-induced hair cell death remains unclear. The present study aimed to explore the potential role of activating transcription factor 6 (ATF6), an endoplasmic reticulum (ER)-localized protein, on cisplatin-induced ototoxicity in vivo and in vitro. In this study, we observed that cisplatin exposure induced apoptosis of mouse auditory OC-1 cells, accompanied by a significant increase in the expression of ATF6 and C/EBP homologous protein (CHOP). In cell or cochlear culture models, treatment with an ATF6 agonist, an ER homeostasis regulator, significantly ameliorated cisplatin-induced cytotoxicity. Further, our in vivo experiments showed that subcutaneous injection of an ATF6 agonist almost completely prevented outer hair cell loss and significantly alleviated cisplatin-induced auditory brainstem response (ABR) threshold elevation in mice. Collectively, our results revealed the underlying mechanism by which activation of ATF6 significantly improved cisplatin-induced hair cell apoptosis, at least in part by inhibiting apoptosis signal-regulating kinase 1 expression, and demonstrated that pharmacological activation of ATF6-mediated unfolded protein response is a potential treatment for cisplatin-induced ototoxicity.

In Utero Gene Therapy and its Application in Genetic Hearing Loss

For monogenic genetic diseases, in utero gene therapy (IUGT) shows the potential for early prevention against irreversible and lethal pathological changes. Moreover, animal models have also demonstrated the effectiveness of IUGT in the treatment of coagulation disorders, hemoglobinopathies, neurogenetic disorders, and metabolic and pulmonary diseases. For major alpha thalassemia and severe osteogenesis imperfecta, in utero stem cell transplantation has entered the phase I clinical trial stage. Within the realm of the inner ear, genetic hearing loss significantly hampers speech, cognitive, and intellectual development in children. Nowadays, gene therapies offer substantial promise for deafness, with the success of clinical trials in autosomal recessive deafness 9 using AAV-OTOF gene therapy. However, the majority of genetic mutations that cause deafness affect the development of cochlear structures before the birth of fetuses. Thus, gene therapy before alterations in cochlear structure leading to hearing loss has promising applications. In this review, addressing advances in various fields of IUGT, the progress, and application of IUGT in the treatment of genetic hearing loss are focused, in particular its implementation methods and unique advantages.

Injectable dexamethasone-loaded peptide hydrogel for therapy of radiation-induced ototoxicity by regulating the mTOR signaling pathway

Radiation-induced ototoxicity is associated with inflammation response and excessive reactive oxygen species in the cochlea. However, the effectiveness of many drugs in clinical settings is limited due to anatomical barriers in the inner ear and pharmacokinetic instability. To address this issue, we developed an injectable hydrogel called RADA32-HRN-dexamethasone (RHD). The RHD hydrogel possesses self-anti-inflammatory properties and can self-assemble into nanofibrous structures, ensuring controlled and sustained release of dexamethasone in the local region. Flow cytometry analysis revealed that the uptake of FITC-conjugated RHD gel by hair cells increased in a time-dependent manner. Compared to free dexamethasone solutions, dexamethasone-loaded RHD gel achieved a longer and more controlled release profile of dexamethasone. Additionally, RHD gel effectively protected against the inflammatory response, reduced excessive reactive oxygen species production, and reversed the decline in mitochondrial membrane potentials induced by ionizing radiation, leading to attenuation of apoptosis and DNA damage. Moreover, RHD gel promoted the recovery of outer hair cells and partially restored auditory function in mice exposed to ionizing radiation. These findings validated the protective effects of RHD gel against radiation-induced ototoxicity in both cell cultures and animal models. Furthermore, RHD gel enhanced the activity of the mammalian target of rapamycin (mTOR) signaling pathway, which was inhibited by ionizing radiation, thereby promoting the survival of hair cells. Importantly, intratympanic injections of RHD gel exhibited excellent biosafety and do not interfere with the anti-tumor effects of radiotherapy. In summary, our study demonstrates the therapeutic potential of injectable dexamethasone-loaded RHD hydrogel for the treatment of radiation-induced hearing loss by regulating the mTOR signaling pathway.

Effects of maternal hypothyroidism on postnatal cardiomyocyte proliferation and cardiac disease responses of the progeny

Maternal hypothyroidism (MH) could adversely affect the cardiac disease responses of the progeny. This study tested the hypothesis that MH reduces early postnatal cardiomyocyte (CM) proliferation so that the adult heart of MH progeny has a smaller number of larger cardiac myocytes, which imparts adverse cardiac disease responses following injury. Thyroidectomy (TX) was used to establish MH. The progeny from mice that underwent sham or TX surgery were termed Ctrl (control) or MH (maternal hypothyroidism) progeny, respectively. MH progeny had similar heart weight (HW) to body weight (BW) ratios and larger CM size consistent with fewer CMs at postnatal day 60 (P60) compared with Ctrl (control) progeny. MH progeny had lower numbers of EdU+, Ki67+, and phosphorylated histone H3 (PH3)+ CMs, which suggests they had a decreased CM proliferation in the postnatal timeframe. RNA-seq data showed that genes related to DNA replication were downregulated in P5 MH hearts, including bone morphogenetic protein 10 (Bmp10). Both in vivo and in vitro studies showed Bmp10 treatment increased CM proliferation. After transverse aortic constriction (TAC), the MH progeny had more severe cardiac pathological remodeling compared with the Ctrl progeny. Thyroid hormone (T4) treatment for MH mothers preserved their progeny's postnatal CM proliferation capacity and prevented excessive pathological remodeling after TAC. Our results suggest that CM proliferation during early postnatal development was significantly reduced in MH progeny, resulting in fewer CMs with hypertrophy in adulthood. These changes were associated with more severe cardiac disease responses after pressure overload.NEW & NOTEWORTHY Our study shows that compared with Ctrl (control) progeny, the adult progeny of mothers who have MH (MH progeny) had fewer CMs. This reduction of CM numbers was associated with decreased postnatal CM proliferation. Gene expression studies showed a reduced expression of Bmp10 in MH progeny. Bmp10 has been linked to myocyte proliferation. In vivo and in vitro studies showed that Bmp10 treatment of MH progeny and their myocytes could increase CM proliferation. Differences in CM number and size in adult hearts of MH progeny were linked to more severe cardiac structural and functional remodeling after pressure overload. T4 (synthetic thyroxine) treatment of MH mothers during their pregnancy, prevented the reduction in CM number in their progeny and the adverse response to disease stress.

Peroxisome Deficiency in Cochlear Hair Cells Causes Hearing Loss by Deregulating BK Channels

The peroxisome is a ubiquitous organelle in rodent cells and plays important roles in a variety of cell types and tissues. It is previously indicated that peroxisomes are associated with auditory function, and patients with peroxisome biogenesis disorders (PBDs) are found to have hearing dysfunction, but the specific role of peroxisomes in hearing remains unclear. In this study, two peroxisome-deficient mouse models (Atoh1-Pex5^-/- and Pax2-Pex5^-/- ) are established and it is found that peroxisomes mainly function in the hair cells of cochleae. Furthermore, peroxisome deficiency-mediated negative effects on hearing do not involve mitochondrial dysfunction and oxidative damage. Although the mammalian target of rapamycin complex 1 (mTORC1) signaling is shown to function through peroxisomes, no changes are observed in the mTORC1 signaling in Atoh1-Pex5^-/- mice when compared to wild-type (WT) mice. However, the expression of large-conductance, voltage-, and Ca2⁺ -activated K⁺ (BK) channels is less in Atoh1-Pex5^-/- mice as compared to the WT mice, and the administration of activators of BK channels (NS-1619 and NS-11021) restores the auditory function in knockout mice. These results suggest that peroxisomes play an essential role in cochlear hair cells by regulating BK channels. Hence, BK channels appear as the probable target for treating peroxisome-related hearing diseases such as PBDs.

Injectable Poloxamer Hydrogel Formulations for Intratympanic Delivery of Dexamethasone

BACKGROUND

In this study, we prepared and evaluated an injectable poloxamer (P407) hydrogel formulation for intratympanic (IT) delivery of dexamethasone (DEX).

METHODS

DEX-loaded P407 hydrogels were characterized in terms of thermogelation, drug loading capacities, particle size, and drug release. The in vivo toxicity and drug absorption of the DEX-loaded P407 formulation after IT injection were evaluated using an animal model by performing histopathological analysis and drug concentration measurements.

RESULTS

The P407 hydrogel effectively solubilized hydrophobic DEX and demonstrated a sustained release compared to the hydrophilic DEX formulation. The in vivo study showed that the hydrogel formulation delivered considerable drug concentrations to the inner ear and displayed a favorable safety profile without apparent cytotoxicity or inflammation.

CONCLUSION

P407 hydrogel can be useful as an injectable inner ear delivery formulation for hydrophobic drugs due to their biocompatibility, drug-solubilizing capacity, thermogelation, and controlled release.

Combining three independent pathological stressors induces a heart failure with preserved ejection fraction phenotype

Heart failure (HF) with preserved ejection fraction (HFpEF) is defined as HF with an ejection fraction (EF) ≥ 50% and elevated cardiac diastolic filling pressures. The underlying causes of HFpEF are multifactorial and not well-defined. A transgenic mouse with low levels of cardiomyocyte (CM)-specific inducible Cavβ2a expression (β2a-Tg mice) showed increased cytosolic CM Ca2+, and modest levels of CM hypertrophy, and fibrosis. This study aimed to determine if β2a-Tg mice develop an HFpEF phenotype when challenged with two additional stressors, high-fat diet (HFD) and Nω-nitro-l-arginine methyl ester (l-NAME, LN). Four-month-old wild-type (WT) and β2a-Tg mice were given either normal chow (WT-N, β2a-N) or HFD and/or l-NAME (WT-HFD, WT-LN, WT-HFD-LN, β2a-HFD, β2a-LN, and β2a-HFD-LN). Some animals were treated with the histone deacetylase (HDAC) (hypertrophy regulators) inhibitor suberoylanilide hydroxamic acid (SAHA) (β2a-HFD-LN-SAHA). Echocardiography was performed monthly. After 4 mo of treatment, terminal studies were performed including invasive hemodynamics and organs weight measurements. Cardiac tissue was collected. Four months of HFD plus l-NAME treatment did not induce a profound HFpEF phenotype in FVB WT mice. β2a-HFD-LN (3-Hit) mice developed features of HFpEF, including increased atrial natriuretic peptide (ANP) levels, preserved EF, diastolic dysfunction, robust CM hypertrophy, increased M2-macrophage population, and myocardial fibrosis. SAHA reduced the HFpEF phenotype in the 3-Hit mouse model, by attenuating these effects. The 3-Hit mouse model induced a reliable HFpEF phenotype with CM hypertrophy, cardiac fibrosis, and increased M2-macrophage population. This model could be used for identifying and preclinical testing of novel therapeutic strategies.NEW & NOTEWORTHY Our study shows that three independent pathological stressors (increased Ca2+ influx, high-fat diet, and l-NAME) together produce a profound HFpEF phenotype. The primary mechanisms include HDAC-dependent-CM hypertrophy, necrosis, increased M2-macrophage population, fibroblast activation, and myocardial fibrosis. A role for HDAC activation in the HFpEF phenotype was shown in studies with SAHA treatment, which prevented the severe HFpEF phenotype. This "3-Hit" mouse model could be helpful in identifying novel therapeutic strategies to treat HFpEF.

4-octyl itaconate improves the viability of D66H cells by regulating the KEAP1-NRF2-GCLC/HO-1 pathway

As a novel nuclear factor E2-related factor 2 (NRF2) activator, the itaconate has shown significant therapeutic potential for oxidative stress diseases. However, its role in Vohwinkel syndrome in relation to the gap junction protein beta 2 (GJB2) mutation is still unclear. This study aimed at investigating the effect of 4-octyl itaconate (OI) on HaCaT and D66H cells and clarify its potential mechanism in vitro. The optimal concentration and treatment time of OI on HaCaT cells and D66H cells were determined by CCK-8 and LDH experiments. The effect of OI on cell proliferation was detected by EdU staining and FACS analysis of PI, while the apoptosis was evaluated by TUNEL staining and FACS analysis of Annexin V. The ROS staining was performed, and the levels of SOD, MDA, GSH and GSH/GSSG were detected to evaluate the effect of OI on oxidative damage induced by D66H-type mutation. CO-IP, Western blot, immunofluorescence and qPCR analyses were employed to detect the activation of KEAP1-NRF2-GCLC/HO-1 pathway by OI. Finally, sh-NRF2 was used to confirm the activation of this pathway by OI. Results showed that OI could improve the cell viability decreased by GJB2 gene mutation by regulating the balance between cell growth and apoptosis induced by oxidative damage. Furthermore, this alleviation process was regulated by the KEAP1-NRF2-HO-1/GCLC pathway. In conclusion, OI could improve the viability of HaCaT and D66H cells via regulating the KEAP1-NRF2-GCLC/HO-1 pathway, which provided a wide spectrum of potential targets for effective therapeutic treatments of Vohwinkel syndrome in the clinic.

The NLRP3 inflammasome as a target for sensorineural hearing loss

Sensorineural hearing loss is the most common type of hearing loss in adults and occurs due to damage of the inner ear caused by a range of factors including ageing, excessive noise, toxins, and cancer. Auto-inflammatory disease is also a cause of hearing loss and there is evidence that inflammation could contribute to hearing loss in other conditions. Within the inner ear there are resident macrophage cells that respond to insults and whose activation correlates with damage. The NLRP3 inflammasome is a multi-molecular pro-inflammatory protein complex that forms in activated macrophages and may contribute to hearing loss. The aim of this article is to discuss the evidence for the NLRP3 inflammasome and associated cytokines as potential therapeutic targets for sensorineural hearing loss in conditions ranging from auto-inflammatory disease to tumour-induced hearing loss in vestibular schwannoma.

Pathological mechanisms of connexin26-related hearing loss: Potassium recycling, ATP-calcium signaling, or energy supply?

Hereditary deafness is one of the most common human birth defects. GJB2 gene mutation is the most genetic etiology. Gap junction protein 26 (connexin26, Cx26) encoded by the GJB2 gene, which is responsible for intercellular substance transfer and signal communication, plays a critical role in hearing acquisition and maintenance. The auditory character of different Connexin26 transgenic mice models can be classified into two types: profound congenital deafness and late-onset progressive hearing loss. Recent studies demonstrated that there are pathological changes including endocochlear potential reduction, active cochlear amplification impairment, cochlear developmental disorders, and so on, in connexin26 deficiency mice. Here, this review summarizes three main hypotheses to explain pathological mechanisms of connexin26-related hearing loss: potassium recycling disruption, adenosine-triphosphate-calcium signaling propagation disruption, and energy supply dysfunction. Elucidating pathological mechanisms underlying connexin26-related hearing loss can help develop new protective and therapeutic strategies for this common deafness. It is worthy of further study on the detailed cellular and molecular upstream mechanisms to modify connexin (channel) function.