Rac/Rho pathway regulates actin depolymerization induced by aminoglycoside antibiotics.

Prior research has shown that stress stimuli can alter the actin cytoskeleton, affecting cell adhesion and permeation. It was already known that aminoglycoside antibiotics can cause sensory cell loss in the inner ear. However, the specific pathways involved in this process remain unclear. No prior work had resolved how redox-dependent Rho GTPase pathways might be involved. This gap motivated investigations into how Rho GTPase activity might influence actin dynamics in response to aminoglycosides. The inner ear is particularly sensitive to such drugs, but the underlying mechanisms are not fully understood. This uncertainty drove the need to explore the role of Rac1 and RhoA in actin depolymerization. Understanding these mechanisms could help clarify how ototoxicity occurs at the cellular level.

The study aimed to determine how aminoglycoside antibiotics affect actin cytoskeleton dynamics in the inner ear. The researchers focused on redox-dependent Rho GTPase pathways as potential regulators of these changes. They used the CBA mouse model to examine the effects of kanamycin on sensory cells. The specific problem addressed was the lack of clarity regarding the molecular mechanisms behind actin depolymerization in response to aminoglycosides. The motivation was to identify the role of Rac1 and RhoA in this process. By using in vivo and in vitro approaches, the study sought to clarify the sequence of events leading to hair cell loss. The goal was to determine whether Rac1 activation mediates actin depolymerization and contributes to ototoxicity.

The study used a CBA mouse model to assess the effects of kanamycin on the inner ear. Researchers examined changes in F-actin and beta-actin arrangements in outer hair cells. They also analyzed adherens junction and tight junction complexes between hair cells and supporting cells. In vivo experiments were complemented by in vitro studies using inner-ear-derived cell lines. The expression of mutated Rac1 was evaluated to determine its impact on actin structure. Immunoreactivity of p140mDia was measured to assess RhoA activity. The formation of Rac1/p67phox and RhoA/p140mDia complexes was monitored to evaluate signaling dynamics. These methods allowed the team to link Rac1 activation to actin depolymerization and superoxide formation.

Kanamycin treatment in vivo disrupted F-actin formation and altered beta-actin arrangement in outer hair cell stereocilia. Adherens and tight junction complexes between hair cells and supporting cells were also affected. The drug activated Rac1 and promoted the formation of the Rac1/p67phox complex. At the same time, RhoA activity was reduced, and the RhoA/p140mDia complex formation decreased. In cell lines, mutated Rac1 altered F-actin structure and reduced p140mDia immunoreactivity. These findings suggest that Rac1 activation leads to superoxide formation via NADPH oxidase. The changes in actin structure and junctional complexes are linked to hair cell loss. These results indicate a direct role for Rac1 in mediating aminoglycoside-induced ototoxicity.

The authors propose that Rac1 activation mediates actin depolymerization in response to aminoglycosides. This depolymerization is followed by superoxide formation via NADPH oxidase. The disruption of actin structures and junctional complexes contributes to hair cell loss. These findings suggest a specific pathway by which kanamycin causes ototoxicity. The study highlights the role of redox-dependent Rho GTPase pathways in this process. The results support the idea that Rac1 is central to the sequence of events leading to sensory cell damage. The findings may help identify potential targets for mitigating aminoglycoside-induced hearing loss. The authors emphasize the importance of understanding these mechanisms for future therapeutic approaches.