The application of monitoring real-time analysis to reveal the secret of lysosomal hydrogen ion channels for the first time in Cell

At 23:00 on June 23, 2022, Beijing time, in a study published in the journal Cell, the team of Haoxing Xu from the University of Michigan in Ann Arbor identified the first hydrogen ion channel TMEM175 on the lysosomal membrane.

This study was inspired by an early discovery made by Professor Xu Haoxin's team: when they directly recorded electrophysiological recordings of the intracellular lysosomal membrane, as long as there was a pH difference between the inside and outside of the lysosomal membrane following physiological conditions (the pH outside the membrane was = 7.

In order to find this "predicted" lysosomal hydrogen ion channel protein, the authors overexpressed a series of possible lysosomal membrane proteins one by one, and finally, after excluding dozens of proteins, found that when the membrane protein When TMEM175 was overexpressed, the recorded "hydrogen ion current" was as much as 20 times higher than that of the control group; at the same time, after knocking out the TMEM175 gene using CRISPR-Cas9 technology, even if the lysosome was set No current signal was recorded at the more acidic pH of 3.

After comparison, they noticed an essential difference in the experimental conditions used by the two: when the previous literature studied TMEM175, the regulation of pH on channel function was ignored, and they believed that TMEM175 mainly permeated potassium ions; Hu Meiqin et al.

Even more exciting, they also identified for the first time small molecule compounds DCPIB and ML 67-33 that can activate the TMEM175 channel

In order to further explore the regulatory mechanism of the ion channel TMEM175, the authors adjusted the interior of the lysosome to a neutral pH and the exterior of the lysosome to an acidic pH, and found that even if there was a hydrogen ion concentration gradient, the hydrogen ion current could not be recorded.

Although TMEM175 potassium currents could be recorded in some cells in the presence of overexpression, endogenous TMEM175 did not show recordable potassium currents, while the agonists DCPIB and arachidonic acid could activate significantly Therefore, TMEM175 is not a naturally open potassium ion channel as previously thought, but a new type of hydrogen ion channel with a gating mechanism that operates in neutral or alkaline environments and in the presence of agonists.