The role of monocytes and macrophages in the dynamic permeability of the blood-perilymph barrier

• Published in: Hearing research Vol. 374; pp. 49 - 57
• Main Authors: Hirose, Keiko, Li, Song-Zhe
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15-03-2019
• Subjects: Blood perilymph barrier; CCR2; CX3CR1; Endocochlear potential; Lipopolysaccharide; Macrophage; Monocyte; CX3CR1; Blood perilymph barrier; Monocyte; Lipopolysaccharide; Endocochlear potential; Macrophage; CCR2
• ISSN: 0378-5955; 1878-5891
• DOI: 10.1016/j.heares.2019.01.006

The blood-perilymph barrier serves a critical role by separating the components of blood from inner ear fluids, limiting traffic of cells, proteins and other solutes into the labyrinth, and allowing gas (O2-CO2) exchange. Inflammation produces changes in the blood-perilymph barrier resulting in increased vascular permeability. It is commonly thought that compromise of the blood-inner ear barrier would lead to hearing impairment through loss of the endocochlear potential (EP). In fact, the effect of increasing cochlear vascular permeability on hearing function and EP is poorly understood. We used a novel method to measure the integrity of the blood-perilymph barrier and demonstrated the effects of barrier compromise on ABR threshold and EP. We also investigated the contribution of CX3CR1 cochlear macrophages and CCR2 inflammatory monocytes to barrier function after systemic exposure to lipopolysaccharide (LPS). We found that systemic LPS induced a profound change in vascular permeability, which correlated with minimal change in ABR threshold and EP. Macrophage depletion using CX3CR1-DTR mice did not alter the baseline permeability of cochlear vessels and resulted in preservation of barrier function in LPS-treated animals. We conclude that cochlear macrophages are not required to maintain the barrier in normal mice and activated macrophages are a critical factor in breakdown of the barrier after LPS. CCR2 null mice demonstrated that LPS induction of barrier leakiness occurs in the absence of CCR2 expression. Thus, enhanced aminoglycoside ototoxicity after LPS can be linked to the expression of CCR2 in inflammatory monocytes, and not to preservation of the blood-perilymph barrier in CCR2 knockout mice.
•The blood perilymph barrier is dynamic, and systemic inflammation causes changes in inner ear vessel permeability.•Macrophages and monocytes contribute to opening of the barrier, and CX3CR1 expressing cells influence this change while CCR2 expression does not.•The EP and ABR are maintained despite major changes in vascular permeability.•Elimination of macrophages, including strial and lateral wall macrophages, does not result in loss of EP or ABR threshold.