Vascular regeneration in adult mouse cochlea stimulated by VEGF-A165 and driven by NG2-derived cells ex vivo

Predicting Atrophy of the Cochlear Stria Vascularis from the Shape of the Threshold Audiogram

Several lines of evidence have suggested that steeply sloping audiometric losses are caused by hair cell degeneration, while flat audiometric losses are caused by strial atrophy, but this concept has never been rigorously tested in human specimens. Here, we systematically compare audiograms and cochlear histopathology in 160 human cases from the archival collection of celloidin-embedded temporal bones at the Massachusetts Eye and Ear. The dataset included 106 cases from a prior study of normal-aging ears, and an additional 54 cases selected by combing the database for flat audiograms. Audiogram shapes were classified algorithmically into five groups according to the relation between flatness (i.e., SD of hearing levels across all frequencies) and low-frequency pure-tone average (i.e., mean at 0.25, 0.5, and 1.0 kHz). Outer and inner hair cell losses, neural degeneration, and strial atrophy were all quantified as a function of cochlear location in each case. Results showed that strial atrophy was worse in the apical than the basal half of the cochlea and was worse in females than in males. The degree of strial atrophy was uncorrelated with audiogram flatness. Apical atrophy was correlated with low-frequency thresholds and basal atrophy with high-frequency thresholds, and the former correlation was higher. However, a multivariable regression with all histopathological measures as predictors and audiometric thresholds as the outcome showed that strial atrophy was a significant predictor of threshold shift only in the low-frequency region, and, even there, the contribution of outer hair cell damage was larger.SIGNIFICANCE STATEMENT Cochlear pathology can only be assessed postmortem; thus, human cochlear histopathology is critical to our understanding of the mechanisms of hearing loss. Dogma holds that relative damage to sensory cells, which transduce mechanical vibration into electrical signals, versus the stria vascularis, the cellular battery that powers transduction, can be inferred by the shape of the audiogram, that is, down-sloping (hair cell damage) versus flat (strial atrophy). Here we quantified hair cell and strial atrophy in 160 human specimens to show that it is the degree of low-frequency hearing loss, rather than the audiogram slope, that predicts strial atrophy. Results are critical to the design of clinical trials for hearing-loss therapeutics, as current drugs target only hair cell, not strial, regeneration.

Systemic gene therapy rescues retinal dysfunction and hearing loss in a model of Norrie disease

Deafness affects 5% of the world's population, yet there is a lack of treatments to prevent hearing loss due to genetic causes. Norrie disease is a recessive X-linked disorder, caused by NDP gene mutation. It manifests as blindness at birth and progressive sensorineural hearing loss, leading to debilitating dual sensory deprivation. To develop a gene therapy, we used a Norrie disease mouse model (Ndptm1Wbrg ), which recapitulates abnormal retinal vascularisation and progressive hearing loss. We delivered human NDP cDNA by intravenous injection of adeno-associated viral vector (AAV)9 at neonatal, juvenile and young adult pathological stages and investigated its therapeutic effects on the retina and cochlea. Neonatal treatment prevented the death of the sensory cochlear hair cells and rescued cochlear disease biomarkers as demonstrated by RNAseq and physiological measurements of auditory function. Retinal vascularisation and electroretinograms were restored to normal by neonatal treatment. Delivery of NDP gene therapy after the onset of the degenerative inner ear disease also ameliorated the cochlear pathology, supporting the feasibility of a clinical treatment for progressive hearing loss in people with Norrie disease.

Research advances in cochlear pericytes and hearing loss

Pericytes are specialized mural cells surrounding endothelial cells in microvascular beds. They play a role in vascular development, blood flow regulation, maintenance of blood-tissue barrier integrity, and control of angiogenesis, tissue fibrosis, and wound healing. In recent decades, understanding of the critical role played by pericytes in retina, brain, lung, and kidney has seen significant progress. The cochlea contains a large population of pericytes. However, the role of cochlear pericytes in auditory pathophysiology is, by contrast, largely unknown. The present review discusses recent progress in identifying cochlear pericytes, mapping their distribution, and defining their role in regulating blood flow, controlling the blood-labyrinth barrier (BLB) and angiogenesis, and involvement in different types of hearing loss.

The cochlea is built to last a lifetime

Orchestration of protein production and degradation and the regulation of protein lifetimes play a central role in many basic biological processes. Nearly all mammalian proteins are replenished by protein turnover in waves of synthesis and degradation. Protein lifetimes in vivo are typically measured in days, but a small number of extremely long-lived proteins (ELLPs) persist for months or even years. ELLPs are rare in all tissues but are enriched in tissues containing terminally differentiated post-mitotic cells and extracellular matrix. Consistently, emerging evidence suggests that the cochlea may be particularly enriched in ELLPs. Damage to ELLPs in specialized cell types, such as crystallin in the lens cells of the eye, causes organ failure such as cataracts. Similarly, damage to cochlear ELLPs is likely to occur with many insults, including acoustic overstimulation, drugs, anoxia, and antibiotics, and may play an underappreciated role in hearing loss. Furthermore, hampered protein degradation may contribute to acquired hearing loss. In this review, I highlight our knowledge of the lifetimes of cochlear proteins with an emphasis on ELLPs and the potential contribution that impaired cochlear protein degradation has on acquired hearing loss and the emerging relevance of ELLPs.

Integrative Functional Transcriptomic Analyses Implicate Shared Molecular Circuits in Sensorineural Hearing Loss

Sensorineural hearing loss (SNHL) is referred to as the most common type of hearing loss and typically occurs when the inner ear or the auditory nerve is damaged. Aging, noise exposure, and ototoxic drugs represent three main causes of SNHL, leading to substantial similarities in pathophysiological characteristics of cochlear degeneration. Although the common molecular mechanisms are widely assumed to underlie these similarities, its validity lacks systematic examination. To address this question, we generated three SNHL mouse models from aging, noise exposure, and cisplatin ototoxicity, respectively. Through constructing gene co-expression networks for the cochlear transcriptome data across different hearing-damaged stages, the three models are found to significantly correlate with each other in multiple gene co-expression modules that implicate distinct biological functions, including apoptosis, immune, inflammation, and ion transport. Bioinformatics analyses reveal several potential hub regulators, such as IL1B and CCL2, both of which are verified to contribute to apoptosis accompanied by the increase of (ROS) in in vitro model system. Our findings disentangle the shared molecular circuits across different types of SNHL, providing potential targets for the broad effective therapeutic agents in SNHL.

Hearing Function, Degeneration, and Disease: Spotlight on the Stria Vascularis

The stria vascularis (SV) is a highly vascularized tissue lining the lateral wall of the cochlea. The SV maintains cochlear fluid homeostasis, generating the endocochlear potential that is required for sound transduction. In addition, the SV acts as an important blood-labyrinth barrier, tightly regulating the passage of molecules from the blood into the cochlea. A healthy SV is therefore vital for hearing function. Degeneration of the SV is a leading cause of age-related hearing loss, and has been associated with several hearing disorders, including Norrie disease, Meniere's disease, Alport syndrome, Waardenburg syndrome, and Cytomegalovirus-induced hearing loss. Despite the SV's important role in hearing, there is still much that remains to be discovered, including cell-specific function within the SV, mechanisms of SV degeneration, and potential protective or regenerative therapies. In this review, we discuss recent discoveries elucidating the molecular regulatory networks of SV function, mechanisms underlying degeneration of the SV, and otoprotective strategies for preventing drug-induced SV damage. We also highlight recent clinical developments for treating SV-related hearing loss and discuss future research trajectories in the field.

17β-Estradiol promotes angiogenesis of stria vascular in cochlea of C57BL/6J mice

It is widely accepted that the stria vascularis (SV) in cochlea plays a critical role in the generation of endocochlear potential (EP) and the secretion of the endolymph. 17β-estradiol (E2) is the most potent and abundant endogenous estrogen during the premenopausal period, thus, considered as the reference estrogen. This study aimd to investigate the protective effect of E2 by promoting the expression of vascular endothelial growth factor (VEGF) and thus promoting the vascular regeneration of the SV in elderly mice. After being treated with E2 either in vivo or in vitro, the hearing threshold changes of C57BL/6J elder mice continuously reduced, endothelial cell morphology improved, the number of endothelial cells (ECs) tubular nodes increased significantly, the ability of tubular formation enhanced significantly and the expression of VEGF increased. In vitro, cell model in conjunction with in vivo ovariectomized model was established to demonstrate for the first time that E2 promotes angiogenesis by promoting the secretion of VEGF through the phosphatidylinositol 3-kinase (PI3K)/AKT pathway (PI3K/AKT). In conclusion, E2 demonstrated potent angiogenesis properties with significant protection against Age-Related Hearing Loss (ARHL), which provides a new idea for the improvement of ARHL.

VEGFA165 gene therapy ameliorates blood-labyrinth barrier breakdown and hearing loss

Millions of people are affected by hearing loss. Hearing loss is frequently caused by noise or aging and often associated with loss of pericytes. Pericytes populate the small vessels in the adult cochlea. However, their role in different types of hearing loss is largely unknown. Using an inducible and conditional pericyte depletion mouse model and noise-exposed mouse model, we show that loss of pericytes leads to marked changes in vascular structure, in turn leading to vascular degeneration and hearing loss. In vitro, using advanced tissue explants from pericyte fluorescence reporter models combined with exogenous donor pericytes, we show that pericytes, signaled by VEGF isoform A165 (VEGFA165), vigorously drive new vessel growth in both adult and neonatal mouse inner ear tissue. In vivo, the delivery of an adeno-associated virus serotype 1-mediated (AAV1-mediated) VEGFA165 viral vector to pericyte-depleted or noise-exposed animals prevented and regenerated lost pericytes, improved blood supply, and attenuated hearing loss. These studies provide the first clear-cut evidence that pericytes are critical for vascular regeneration, vascular stability, and hearing in adults. The restoration of vascular function in the damaged cochlea, including in noise-exposed animals, suggests that VEGFA165 gene therapy could be a new strategy for ameliorating vascular associated hearing disorders.

Postnatal Changes of Neural Stem Cells in the Mammalian Auditory Cortex

Our previous study reported neural stem cells (NSCs) in the auditory cortex (AC) of postnatal day 3 (P3) mice in vitro. It is unclear whether AC-NSCs exist in vivo. This study aims to determine the presence and changes of AC-NSCs during postnatal development and maturation both in vitro and in vivo. P3, postnatal day 14 (P14), 2-month-old (2M), and 4-month-old (4M) mouse brain tissues were fixed and cryosectioned for NSC marker immunostaining. In vitro, P3, P14, and 2M AC tissues were dissected and cultured in suspension to study NSCs. NSC proliferation was examined by EdU incorporation and cell doubling time assays in vitro. The results show that Nestin and Sox2 double expressing NSCs were observed in the AC area from P3 to 4M in vivo, in which the number of NSCs remarkably reduced with age. In vitro, the neurosphere forming capability, cell proliferation, and percentage of Nestin and Sox2 double expressing NSCs significantly diminished with age. These results suggest that AC-NSCs exist in the mouse AC area both in vitro and in vivo, and the percentage of AC-NSCs decreases during postnatal development and maturation. The results may provide important cues for the future research of the central auditory system.

Acoustic Trauma Causes Cochlear Pericyte-to-Myofibroblast-Like Cell Transformation and Vascular Degeneration, and Transplantation of New Pericytes Prevents Vascular Atrophy

Acoustic trauma disrupts cochlear blood flow and damages sensory hair cells. Damage and regression of capillaries after acoustic trauma have long been observed, but the underlying mechanism of pathology has not been understood. We show herein that loud sound causes change of phenotype from neural/glial antigen 2 positive/α-smooth muscle actin negative to neural/glial antigen 2 positive/α-smooth muscle actin positive in some pericytes (PCs) on strial capillaries that is strongly associated with up-regulation of transforming growth factor-β1. The acoustic trauma also reduced capillary density and increased deposition of matrix proteins, particularly in the vicinity of transformed PCs. In a newly established in vitro three-dimensional endothelial cell (EC) and PC co-culture model, transformed PCs induced thicker capillary-like branches in ECs and increased collagen IV and laminin expression. Transplantation of exogenous PCs derived from neonatal day 10 mouse cochleae to acoustic traumatized cochleae, however, significantly attenuated the decreased vascular density in the stria. Transplantation of PCs pretransfected with adeno-associated virus 1-vascular endothelial growth factor-A165 under control of a hypoxia-response element markedly promotes vascular volume and blood flow, increased proliferation of PCs and ECs, and attenuated loud sound-caused loss in endocochlear potential and hearing. Our results indicate that loud sound-triggered PC transformation contributes to capillary wall thickening and regression, and young PC transplantation effectively rehabilitates the vascular regression and improves hearing.

Tendon explant models for physiologically relevant invitro study of tissue biology - a perspective

Background: Tendon disorders increasingly afflict our aging society but we lack the scientific understanding to clinically address them. Clinically relevant models of tendon disease are urgently needed as established small animal models of tendinopathy fail to capture essential aspects of the disease. Two-dimensional and three-dimensional cell and tissue culture models are similarly limited, lacking many physiological extracellular matrix cues required to maintain tissue homeostasis or guide matrix remodeling. These cues reflect the biochemical and biomechanical status of the tissue, and encode information regarding the mechanical and metabolic competence of the tissue. Tendon explants overcome some of these limitations and have thus emerged as a valuable tool for the discovery and study of mechanisms associated with tendon homeostasis and pathophysiology. Tendon explants retain native cell-cell and cell-matrix connections, while allowing highly reproducible experimental control over extrinsic factors like mechanical loading and nutritional availability. In this sense tendon explant models can deliver insights that are otherwise impossible to obtain from in vivo animal or in vitro cell culture models. Purpose: In this review, we aimed to provide an overview of tissue explant models used in tendon research, with a specific focus on the value of explant culture systems for the controlled study of the tendon core tissue. We discuss their advantages, limitations and potential future utility. We include suggestions and technical recommendations for the successful use of tendon explant cultures and conclude with an outlook on how explant models may be leveraged with state-of-the-art biotechnologies to propel our understanding of tendon physiology and pathology.