Pericyte abnormalities precede strial capillary basement membrane thickening in Alport mice

A critical evaluation of "leakage" at the cochlear blood-stria-barrier and its functional significance

The blood-labyrinth-barrier (BLB) is a semipermeable boundary between the vasculature and three separate fluid spaces of the inner ear, the perilymph, the endolymph and the intrastrial space. An important component of the BLB is the blood-stria-barrier, which shepherds the passage of ions and metabolites from strial capillaries into the intrastrial space. Some investigators have reported increased "leakage" from these capillaries following certain experimental interventions, or in the presence of inflammation or genetic variants. This leakage is generally thought to be harmful to cochlear function, principally by lowering the endocochlear potential (EP). Here, we examine evidence for this dogma. We find that strial capillaries are not exclusive, and that the asserted detrimental influence of strial capillary leakage is often confounded by hair cell damage or intrinsic dysfunction of the stria. The vast majority of previous reports speculate about the influence of strial vascular barrier function on the EP without directly measuring the EP. We argue that strial capillary leakage is common across conditions and species, and does not significantly impact the EP or hearing thresholds, either on evidentiary or theoretical grounds. Instead, strial capillary endothelial cells and pericytes are dynamic and allow permeability of varying degrees in response to specific conditions. We present observations from mice and demonstrate that the mechanisms of strial capillary transport are heterogeneous and inconsistent among inbred strains.

The Stria Vascularis in Mice and Humans Is an Early Site of Age-Related Cochlear Degeneration, Macrophage Dysfunction, and Inflammation

Age-related hearing loss, or presbyacusis, is a common degenerative disorder affecting communication and quality of life for millions of older adults. Multiple pathophysiologic manifestations, along with many cellular and molecular alterations, have been linked to presbyacusis; however, the initial events and causal factors have not been clearly established. Comparisons of the transcriptome in the lateral wall (LW) with other cochlear regions in a mouse model (of both sexes) of "normal" age-related hearing loss revealed that early pathophysiological alterations in the stria vascularis (SV) are associated with increased macrophage activation and a molecular signature indicative of inflammaging, a common form of immune dysfunction. Structure-function correlation analyses in mice across the lifespan showed that the age-dependent increase in macrophage activation in the stria vascularis is associated with a decline in auditory sensitivity. High-resolution imaging analysis of macrophage activation in middle-aged and aged mouse and human cochleas, along with transcriptomic analysis of age-dependent changes in mouse cochlear macrophage gene expression, support the hypothesis that aberrant macrophage activity is an important contributor to age-dependent strial dysfunction, cochlear pathology, and hearing loss. Thus, this study highlights the SV as a primary site of age-related cochlear degeneration and aberrant macrophage activity and dysregulation of the immune system as early indicators of age-related cochlear pathology and hearing loss. Importantly, novel new imaging methods described here now provide a means to analyze human temporal bones in a way that had not previously been feasible and thereby represent a significant new tool for otopathological evaluation.SIGNIFICANCE STATEMENT Age-related hearing loss is a common neurodegenerative disorder affecting communication and quality of life. Current interventions (primarily hearing aids and cochlear implants) offer imperfect and often unsuccessful therapeutic outcomes. Identification of early pathology and causal factors is crucial for the development of new treatments and early diagnostic tests. Here, we find that the SV, a nonsensory component of the cochlea, is an early site of structural and functional pathology in mice and humans that is characterized by aberrant immune cell activity. We also establish a new technique for evaluating cochleas from human temporal bones, an important but understudied area of research because of a lack of well-preserved human specimens and difficult tissue preparation and processing approaches.

The timing of auditory sensory deficits in Norrie disease has implications for therapeutic intervention

Norrie disease is caused by mutation of the NDP gene, presenting as congenital blindness followed by later onset of hearing loss. Protecting patients from hearing loss is critical for maintaining their quality of life. This study aimed to understand the onset of pathology in cochlear structure and function. By investigating patients and juvenile Ndp-mutant mice, we elucidated the sequence of onset of physiological changes (in auditory brainstem responses, distortion product otoacoustic emissions, endocochlear potential, blood-labyrinth barrier integrity) and determined the cellular, histological, and ultrastructural events leading to hearing loss. We found that cochlear vascular pathology occurs earlier than previously reported and precedes sensorineural hearing loss. The work defines a disease mechanism whereby early malformation of the cochlear microvasculature precedes loss of vessel integrity and decline of endocochlear potential, leading to hearing loss and hair cell death while sparing spiral ganglion cells. This provides essential information on events defining the optimal therapeutic window and indicates that early intervention is needed. In an era of advancing gene therapy and small-molecule technologies, this study establishes Ndp-mutant mice as a platform to test such interventions and has important implications for understanding the progression of hearing loss in Norrie disease.

Role of the Stria Vascularis in the Pathogenesis of Sensorineural Hearing Loss: A Narrative Review

Sensorineural hearing loss is a common sensory impairment in humans caused by abnormalities in the inner ear. The stria vascularis is regarded as a major cochlear structure that can independently degenerate and influence the degree of hearing loss. This review summarizes the current literature on the role of the stria vascularis in the pathogenesis of sensorineural hearing loss resulting from different etiologies, focusing on both molecular events and signaling pathways, and further attempts to explore the underlying mechanisms at the cellular and molecular biological levels. In addition, the deficiencies and limitations of this field are discussed. With the rapid progress in scientific technology, new opportunities are arising to fully understand the role of the stria vascularis in the pathogenesis of sensorineural hearing loss, which, in the future, will hopefully lead to the prevention, early diagnosis, and improved treatment of sensorineural hearing loss.

Endothelin receptor antagonists for the treatment of diabetic and nondiabetic chronic kidney disease

PURPOSE OF REVIEW

To summarize new clinical findings of endothelin receptor antagonists (ERA) in various etiologies of kidney disease targeted in clinical trials.

RECENT FINDINGS

Endothelin-1 is a multifunctional peptide with potential relevance to glomerular and tubulointerstitial kidney diseases. The phase 3 SONAR trial demonstrated a significant reduction in clinically relevant kidney outcomes for patients with diabetic kidney disease (DKD) after long-term treatment with the ERA, atrasentan, in addition to blockade of the renin-angiotensin-aldosterone system. Promising preclinical disease models and small clinical trials in non-DKD resulted in the initiation of phase 3 trials investigating the effects of long-term treatment with ERA in patients with immunoglobulin A (IgA) nephropathy and focal segmental glomeruloscelerosis (FSGS). The mechanisms by which ERA protects the kidneys have been extensively studied with evidence for the protection of tubule cells, podocytes, mesangial cells, the endothelial glycocalyx, and a reduction in glomerular perfusion pressure. The occurrence of fluid retention during ERA treatment, particularly in susceptible populations, necessitates strategies to support safe and effective treatment.

SUMMARY

Treatment with ERA induces long-term kidney protection in DKD. Phase 3 trials are underway to investigate ERA effects in patients with IgA nephropathy and FSGS.