A Force-Sensitive Adhesion GPCR is Required for Equilibrioception

Neurology Biophysics Life Sciences Cell Biology Medicine
equilibrioception force-sensitive GPCR mechanoelectrical transduction vestibular hair cells Lphn2

Academic Background

Equilibrioception is a crucial ability for mammals to perceive and navigate the three-dimensional world. This ability relies on the rapid mechanoelectrical transduction (MET) response of vestibular hair cells (VHCs), which detects the position and motion of the head. Although previous studies have shown that transmembrane channel-like proteins (TMCs) are key components of MET channels, the molecular mechanisms underlying equilibrioception remain largely unknown. In recent years, G protein-coupled receptors (GPCRs) have gained attention as mechanosensors, particularly in sensory systems such as vision, olfaction, and touch. However, the role of GPCRs in the vestibular system has not been thoroughly investigated. Therefore, this study aims to explore the role of GPCRs in equilibrioception, focusing specifically on the force-sensitive GPCR Lphn2 (also known as ADGRL2) in vestibular hair cells.

Source of the Paper

This research was conducted by a collaborative team from several top research institutions in China, including Qilu Hospital of Shandong University, Southeast University, and Huazhong University of Science and Technology. The research team was led by 15 co-first authors, including Zhao Yang, Shu-Hua Zhou, and Qi-Yue Zhang, with corresponding authors Wei Yang, Fan Yi, Ren-Jie Chai, Xiao Yu, and Jin-Peng Sun. The paper was published online on February 18, 2025, in the journal Cell Research, under the title A force-sensitive adhesion GPCR is required for equilibrioception.

Research Process and Results

1. Screening of Mechanosensitive GPCRs in the Vestibular System

The research team first analyzed the expression of 30 GPCRs in mouse vestibular hair cells using single-cell RNA sequencing (scRNA-seq), identifying 12 GPCRs expressed in more than 20% of the hair cells. Subsequently, the team developed a high-throughput mechanical stimulation assay using a magnetic tweezer system and a GPCR biosensor platform to detect the activation of these GPCRs under mechanical force. The results showed that five GPCRs—Lphn2, Gpr133, Gpr126, Lphn3, and Vlgr1—activated Gi or Gs signaling pathways in response to mechanical force, indicating their mechanosensitivity.

2. Expression and Function of Lphn2 in Vestibular Hair Cells

Through immunostaining and RNA in situ hybridization, the research team confirmed that Lphn2 is expressed on the apical membrane of mouse vestibular hair cells but is absent in the stereocilia. By constructing a conditional Lphn2 knockout mouse model, the team found that the loss of Lphn2 led to abnormal balance behaviors in mice, including significant impairments in circling behavior and swimming ability. Additionally, Lphn2 deficiency resulted in a significant reduction in the MET currents of vestibular hair cells.

3. Lphn2 Regulates the MET Process in Vestibular Hair Cells

To further investigate the role of Lphn2 in the MET process, the research team used a fluid jet system to mechanically stimulate vestibular hair cells and recorded the MET currents. The results showed that the MET currents were significantly reduced in Lphn2-deficient hair cells or after treatment with the Lphn2-specific inhibitor D11. Interestingly, Lphn2 deficiency did not affect the stiffness of the stereocilia or the tip-link-mediated MET currents, indicating that Lphn2 regulates a tip-link-independent MET process.

4. Functional Coupling of Lphn2 with Tmc1

Using co-immunoprecipitation and confocal microscopy, the research team found that Lphn2 co-localizes with Tmc1 on the apical membrane of vestibular hair cells. Further experiments in a heterologous expression system demonstrated that Lphn2 could convert mechanical force stimulation into an increased open probability of the Tmc1 channel. Additionally, the team developed a Tmc1-specific inhibitor, C14, which was found to inhibit Lphn2-mediated MET currents, further supporting the functional coupling between Lphn2 and Tmc1 in the MET process.

5. Lphn2-Mediated Neurotransmitter Release and Calcium Signaling

The research team also discovered that Lphn2 could induce glutamate release and trigger calcium signaling in vestibular hair cells under mechanical force stimulation. Using a glutamate sensor and a calcium fluorescent probe, the team confirmed that Lphn2 deficiency or D11 treatment significantly reduced glutamate release and calcium signaling in response to mechanical stimulation.

6. Re-expression of Lphn2 Restores Balance Function

Finally, the research team re-expressed Lphn2 in the vestibular hair cells of Lphn2-deficient mice using an adeno-associated virus (AAV). They found that the re-expression of Lphn2 significantly improved the balance behaviors of the mice and restored the MET currents in vestibular hair cells. These results indicate that Lphn2 directly participates in the regulation of equilibrioception in the vestibular system.

Conclusions and Significance

This study reveals that the force-sensitive GPCR Lphn2 is expressed on the apical membrane of vestibular hair cells and, through functional coupling with Tmc1, regulates a tip-link-independent MET process. The loss of Lphn2 leads to abnormal balance behaviors and a significant reduction in MET currents in vestibular hair cells, while the re-expression of Lphn2 restores these functions. This research highlights the important role of GPCRs in the vestibular system and provides new insights into the molecular mechanisms of equilibrioception.

Research Highlights

  1. First to reveal the mechanosensory function of GPCRs in the vestibular system: Lphn2, as a force-sensitive GPCR, participates in equilibrioception by regulating the MET process in vestibular hair cells.
  2. Discovery of a tip-link-independent MET process: The MET currents regulated by Lphn2 are independent of tip-links, indicating greater complexity in the MET process of vestibular hair cells.
  3. Development of specific inhibitors for Lphn2 and Tmc1: The inhibitors D11 and C14 provide powerful tools for studying the functions of Lphn2 and Tmc1.
  4. Restoration of balance function through AAV-mediated re-expression: This finding offers a potential therapeutic strategy for treating vestibular dysfunction.

Other Valuable Information

The research team also found that the expression pattern of Lphn2 in vestibular hair cells differs from that in cochlear hair cells, suggesting that the functions of Lphn2 may vary across different sensory systems. Additionally, the team proposed an interaction model between Lphn2 and Tmc1, providing new insights for future studies on the functional coupling of GPCRs and ion channels.

This study not only deepens our understanding of the molecular mechanisms of equilibrioception but also provides a theoretical foundation for developing new treatments for vestibular dysfunction. By revealing the role of GPCRs in the vestibular system, this research opens new directions in the field of sensory biology.