Myosin light chain kinase regulates hearing in mice by influencing the F-actin cytoskeleton of outer hair cells and cochleae

Abstract

Myosin light chain kinase (MLCK) phosphorylates myosin regulatory light chains to facilitate its interaction with actin filaments and produce contractile activity. The outer hair cells (OHCs) in the ear contain large amounts of actin and a variety myosins. The stereociliary and somatic motility of OHCs are closely related to hearing. It appears likely that MLCK may play an important role in acoustic trans-duction. In this study, we analyzed, both in vivo and in vitro, the OHCs of mice bearing a specific deletion of the MLCK gene and the OHCs of control mice. The phenotype was assessed by auditory function [acoustic brainstem responses (ABRs) and distortion product otoacoustic emissions (DPOAEs)], inner ear morphology and histology. MLCK-deficient mice aged 6-7 months showed impaired hearing, a 5- to 10-dB sound pressure level (SPL) increase in the ABR thresholds, when responding to clicks and tones of different frequencies (8 and 16 kHz) (P<0.05). The DPOAE amplitudes of 3-month-old MLCK-deficient mice decreased significantly (>10 dB SPL) at low frequencies (4, 5 and 6 kHz). The OHCs in the MLCK-deficient mice increased with abnormal stereocilia. The staining of F-actin and the phosphorylation of the regulatory light chain in MLCK-deficient OHCs was weak. Our results indicate that MLCK may regulate the structure and the motility of stereocilia through F-actin polymerization.

Influence of myosin regulatory light chain and myosin light chain kinase on hair cells of the inner ear

“…The experiments demonstrated dose dependency and effects over a broad range of stimulus frequencies. Previous evidence also supports a role of MLCK activity in hearing: mice exhibiting a specific deletion of MLCK in either inner or outer hair cells display increased ABR thresholds (19,20). The phosphorylation of MYL12 is therefore important in normal hearing, perhaps by affecting an adaptation motor such as MYO7A.…”

“…Both RLC and MLCK occur in distinct isoforms in various cell types; for example, the organ of Corti expresses RLCs such as MYL9 and MYL12 as well as MYLK1 (also known as smooth-muscle MLCK or smMLCK). The phosphorylation of MYL12 by MYLK1 regulates shape changes in outer hair cells (Oya et al, 2021); moreover, deletion of the gene MYLK1 in cochlear hair cells causes hearing loss (Zhu et al, 2012; Yang et al, 2014).…”

High glucose upregulates myosin light chain kinase to induce microfilament cytoskeleton rearrangement in hippocampal neurons

“…MLCK is the primary regulator of various forms of eukaryotic motility. MLCK serves a role in numerous functions of non-muscle cells, including cytoskeletal clustering, platelet shape alterations, transepithelial permeability and cytoskeletal arrangements, stress fiber formation, cell spreading and migration, cytokinesis, secretion and neurite growth cone advancement, which affect ion exchange or ion currents at the plasma membrane ( 27 – 29 ). In synapses, MLCK and its downstream substrate myosin, regulate different stages of neurotransmitter release ( 30 ), including refilling of readily releasable pools following tetanus stimulation, vesicle mobility ( 31 , 32 ), supply of fast-releasing vesicles ( 33 ) and vesicle mobilization ( 34 ).…”