Pathophysiology of the cochlear intrastrial fluid-blood barrier (review)

Abstract

The blood-labyrinth barrier (BLB) in the stria vascularis is a highly specialized capillary network that controls exchanges between blood and the intrastitial space in the cochlea. The barrier shields the inner ear from blood-born toxic substances and selectively passes ions, fluids, and nutrients to the cochlea, playing an essential role in the maintenance of cochlear homeostasis. Anatomically, the BLB is comprised of endothelial cells (ECs) in the strial microvasculature, elaborated tight and adherens junctions, pericytes (PCs), basement membrane (BM), and perivascular resident macrophage-like melanocytes (PVM/Ms), which together form a complex “cochlear-vascular unit” in the stria vascularis. Physical interactions between the ECs, PCs, and PVM/Ms, as well as signaling between the cells, is critical for controlling vascular permeability and providing a proper environment for hearing function. Breakdown of normal interactions between components of the BLB is seen in a wide range of pathological conditions, including genetic defects and conditions engendered by inflammation, loud sound trauma, and ageing. In this review, we will discuss prevailing views of the structure and function of the strial cochlear-vascular unit (also referred to as the “intrastrial fluid-blood barrier”). We will also discuss the disrupted homeostasis seen in a variety of hearing disorders. Therapeutic targeting of the strial barrier may offer opportunities for improvement of hearing health and amelioration of auditory disorders.

Bilateral cochlear ossification in a patient with Takayasu arteritis

“…For example, human temporal bone studies of hearing loss in Sjogren's syndrome revealed immunoglobulin G deposition in the basement membrane of the stria vascularis [16]. Disrupted vascular integrity in the stria vascularis changes the blood barrier permeability in the stria vascularis [15]. In our case, noncontrast FLAIR revealed high signal intensity in the whole cochlea and vestibule (Figure 1), which might reflect an increased concentration of protein passing through blood vessels with increased permeability [17].…”

“…Circulating immune complexes have been reported in cases of SNHL associated with TAK [5,14]. There is evidence suggesting that strial capillaries may be a target of autoimmune hearing disorders [15]. For example, human temporal bone studies of hearing loss in Sjogren's syndrome revealed immunoglobulin G deposition in the basement membrane of the stria vascularis [16].…”

Culture media-based selection of endothelial cells, pericytes, and perivascular-resident macrophage-like melanocytes from the young mouse vestibular system

“…The physical blood-tissue barrier is comprised of ECs in the strial microvasculature, elaborated tight and adherens junctions, and accessory cells such as PCs, basement membrane (BM), and PVM/Ms, which together form a complex blood-tissue barrier with region-specific features(Shi, 2016). …”

Inner ear delivery: Challenges and opportunities

“…The BLB divides the vascular compartment of the inner ear from the inner ear fluid spaces. The BLB consists of a network of vascular endothelial cells coupled together by tight junctions, basement membrane, pericytes, and perivascular resident macrophage‐like melanocytes that, combined, regulate exchange between the blood and surrounding perivascular space . In addition to maintaining normal fluid and ion physiology and preventing pathogens from entering the inner ear, the BLB also prevents therapeutic agents in systemic circulation from accessing the inner ear.…”