Scientists uncover previously unknown target of alcohol in the brain: the TMEM132B-GABAA receptor complex

What happens in the brain when we drink alcohol? Scientists have taken a significant step toward answering this question by identifying a protein called TMEM132B as a key regulator of alcohol’s effects. This protein not only amplifies alcohol’s action on GABA_A receptors—key players in neural inhibition—but also influences behaviors like anxiety reduction and alcohol consumption. The findings have been published in the journal Cell.

Alcohol is one of the most widely consumed and abused psychoactive substances globally, contributing to approximately 3 million deaths annually and a substantial burden on public health and society. Beyond the immediate risks associated with excessive consumption, alcohol use disorders are highly prevalent, causing chronic health issues and social consequences.

Despite its widespread use, the precise ways in which alcohol alters brain function at the molecular level remain poorly understood. Previous studies have shown that alcohol influences GABA_A receptors—a type of receptor in the brain that plays a critical role in the central nervous system by mediating the effects of gamma-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in the brain. However, the complexity of these receptors has made it challenging to pinpoint how alcohol’s actions translate into its behavioral and physiological effects.

To address this, researchers at the National Institute of Neurological Disorders and Stroke focused on auxiliary proteins—molecules that interact with GABA_A receptors to modify their function and distribution. These proteins could provide broader insights into alcohol’s effects than traditional genetic studies targeting individual receptor subunits.

“Alcohol is the most consumed and abused psychoactive drug globally, but the molecular mechanisms underlying its action in the brain and leading to alcohol use disorders remain largely unknown. We wish to make some contributions here,” said study author Wei Lu, a senior investigator at the National Institute of Neurological Disorders and Stroke.

The researchers conducted a series of experiments involving human brain tissues, animal models, and cellular assays. They began by analyzing postmortem brain samples from individuals with alcohol use disorder to identify molecular changes associated with chronic alcohol exposure. Using mass spectrometry, they compared protein levels in the hippocampus—a brain region involved in learning, memory, and emotion regulation—between individuals with and without alcohol use disorder. This analysis revealed a reduction in the levels of TMEM132B, a transmembrane protein with a previously unknown function, in the brains of individuals with alcohol use disorder.

The researchers then used animal models to explore the role of TMEM132B. They generated genetically modified mice that either completely lacked the TMEM132B gene (knockout mice) or carried a mutation that specifically disrupted TMEM132B’s interaction with GABA_A receptors (knock-in mice). These models were used to examine how the absence or alteration of TMEM132B affected brain activity, receptor function, and alcohol-related behaviors.

In normal mice, TMEM132B was found to interact with GABA_A receptors, increasing their abundance on the surface of neurons and slowing their deactivation. These changes make neurons more sensitive to inhibitory signals, which help to regulate and calm neural activity. When alcohol was introduced, it acted as a positive modulator of GABA_A receptors, enhancing their inhibitory effects. TMEM132B amplified this modulation, making the neurons even more responsive to alcohol.

However, in mice genetically engineered to lack TMEM132B, this enhancement was diminished. Electrophysiological measurements from hippocampal neurons showed that alcohol-induced potentiation of GABA_A receptor activity was significantly reduced in these mice.

Behaviorally, the absence of TMEM132B profoundly affected how mice responded to alcohol. When normal mice were given alcohol, they displayed reduced anxiety, as measured by their willingness to explore open spaces in an elevated plus maze. They also experienced sedation, demonstrated by their loss of the righting reflex (a measure of sedation). In contrast, mice lacking TMEM132B showed markedly reduced responses to alcohol in these tests. They did not exhibit the same levels of anxiety reduction, and their sedative response was weaker, with fewer mice losing their righting reflex after alcohol administration.

These findings suggest that TMEM132B is essential for alcohol’s calming and sedative effects. Without this protein, alcohol’s ability to enhance GABA_A receptor function is diminished, leading to weaker behavioral responses.

Interestingly, despite experiencing diminished behavioral effects from alcohol, TMEM132B knockout mice consumed more alcohol compared to normal mice. In two-bottle choice experiments, where mice could choose between water and alcohol at varying concentrations, knockout mice consistently drank more alcohol. This tendency was even more pronounced in binge-like drinking tests, where the mice consumed large quantities of alcohol in short periods.

This increased consumption appears to reflect a compensatory mechanism. Because TMEM132B knockout mice experienced reduced calming and sedative effects from alcohol, they seemed to consume more in an attempt to achieve the same effects. This pattern mirrors certain aspects of alcohol use disorders in humans, where tolerance to alcohol’s effects can lead to increased consumption.

The compulsive nature of alcohol consumption in TMEM132B knockout mice was further demonstrated in tests that introduced an aversive component. In these tests, a bitter substance (quinine) was added to the alcohol to discourage drinking. While normal mice reduced their alcohol intake when quinine was present, the knockout mice continued to drink large amounts despite the bitter taste. This behavior indicates a loss of control over alcohol consumption, a hallmark of compulsive drinking.

The knock-in mice exhibited deficits similar to those seen in the knockout mice: reduced potentiation of GABA_A receptor activity by alcohol, diminished behavioral responses to alcohol, and increased alcohol consumption. This finding underscores that TMEM132B’s role in alcohol’s effects is directly tied to its interaction with GABA_A receptors.

The researchers also explored the specific molecular interactions between TMEM132B and GABA_A receptor subtypes. TMEM132B was shown to interact with a broad range of GABA_A receptor subunits, including those found in both synaptic and extrasynaptic locations. This broad interaction likely explains why its absence has such a pronounced effect on alcohol-related behaviors. TMEM132B’s influence on receptor dynamics is not limited to a specific subtype, making it a key regulator of alcohol’s effects on inhibitory signaling throughout the brain.

“The key take-home message is that we have identified the key target of alcohol in the brain: the TMEM132B-GABA_A receptor complex,” Lu told PsyPost. “Genetic disruption of this complex increases alcohol consumption and reduces anxiolytic and hypnotic effects of alcohol in the brain in mice. Thus, approaches that can strengthen the interaction between TMEM132B and GABA_A receptors might be useful in developing therapeutics to treat alcohol use disorders.”

This discovery is significant because it bridges findings from both human brain tissue and animal models, allowing for a translational approach to understanding alcohol’s effects. The inclusion of human tissue highlights that chronic alcohol consumption reduces TMEM132B expression in both humans and mice, suggesting a shared mechanism across species.

“Although human and mice have differences in brain structure and receptor dynamics, we found that chronic alcohol consumption led to reduced expression of TMEM132B in both human and mouse brain tissues, indicating a common mechanism operated in both human and mice in response to chronic alcohol drinking,” Lu explained.

“Thus, TMEM132B-dependent mechanisms we have characterized in mice likely also function in human brain. Based on our findings, approaches to maintain the expression of TMEM132B in the brain or strengthen the interaction between TMEM132B and GABA_A receptors might be an effective strategy for development of treatment for alcohol use disorders.”

However, there is still much to learn about the the TMEM132B-GABA_A receptor complex. The researchers are interested in pursuing three different lines of research, starting with the molecular basis of the TMEM132B-GABA_A receptor interaction. “We plan to map amino acid domains in GABA_A receptor subunits that mediate the binding to TMEM132B,” Lu said. “These molecular details will enable us to design sophisticated knockin mouse lines to genetically manipulate the TMEM132B-GABA_A receptor interaction in vivo, so that the roles of GABA_A receptor subunit-specific interaction with TMEM132B in psychoactive effects of alcohol in vivo can be determined.”

“The second question we are interested is to determine the mechanisms underlying the involvement of TMEM132B in alcoholism,” Lu said. “As discussed above, we have already found that TMEM132B expression is significantly reduced in postmortem human alcoholic brains. However, it remains unknown whether the reduced expression of TMEM132B contributes to development of alcoholism. We wish to investigate how TMEM132B expression is reduced in the human alcoholic brain and whether/how reduced expression of TMEM132B contributes to development of alcoholism in mouse models.

“The third one is to identify which population(s) of neurons in the brain are critical for the effects of TMEM132B in the regulation of alcohol-related behaviors.”

“These studies will deepen our understanding of the role of TMEM132B in both acute and long-term effects of alcohol in the brain and will uncover the region-specific role of TMEM132B in modulating alcohol action in the brain,” Lu explained. “Our long-term goal is to develop pharmacotherapies for alcohol use disorders.”

The study, “The TMEM132B-GABAA receptor complex controls alcohol actions in the brain,” was authored by Guohao Wang, Shixiao Peng, Miriam Reyes Mendez, Angelo Keramidas, David Castellano, Kunwei Wu, Wenyan Han, Qingjun Tian, Lijin Dong, Yan Li, and Wei Lu.