Epigenetic Mechanisms of Methamphetamine Addiction / 生物化学与生物物理进展

ABSTRACT

Methamphetamine (METH) is a powerful stimulant drug that can cause addiction and serious health problems. It is one of the most widely abused drugs in the world. However, the mechanisms of how METH affects the brain and leads to addiction are still unclear, and there are no effective treatments for METH addiction in clinical practice. Therefore, it is important to explore the new addiction mechanisms and treatment strategies of METH. METH addiction is a complex and chronic brain disorder that involves multiple brain regions and neurotransmitter systems. Neurotransmitters are chemical messengers that transmit signals between neurons (nerve cells) in the brain. Some of the main neurotransmitters involved in METH addiction are dopamine (DA), glutamate (Glu), norepinephrine (NE), and serotonin (SNRIS). These neurotransmitters regulate various aspects of brain function, such as reward, reinforcement, motivation, cognition, emotion, and behavior. When a person takes METH, it causes a surge of these neurotransmitters in the brain, especially in the prefrontal cortex (mPFC), ventral tegmental area (VTA), and nucleus accumbens (NAc). These brain regions form a circuit called the mesocorticolimbic system, which is responsible for mediating the rewarding and reinforcing effects of drugs and natural stimuli. The increased levels of neurotransmitters in this circuit make the person feel euphoric, alert, confident, and energetic. However, repeated or chronic use of METH can also cause negative effects, such as anxiety, paranoia, psychosis, depression, and cognitive impairment. The effects of METH on the brain are not only due to the changes in neurotransmitter levels, but also to the changes in gene expression. Gene expression is the process by which genes are turned on or off to produce proteins that perform various functions in the cells. Gene expression can be influenced by environmental factors, such as drugs, stress, diet, etc. One way that environmental factors can affect gene expression is through epigenetic mechanisms. Epigenetics is a branch of genetics that studies the heritable changes in gene expression that are not caused by changes in DNA sequence. Epigenetic mechanisms include histone modifications, DNA methylation, and non-coding RNA regulation. These mechanisms can modulate the chromatin structure and accessibility, thereby affecting the transcriptional activity of genes. Chromatin is a complex of DNA and proteins that forms the chromosomes in the nucleus of the cell. The chromatin structure can be altered by adding or removing chemical groups to histones (proteins that wrap around DNA) or DNA itself. These chemical groups can either activate or repress gene expression by changing the affinity of transcription factors (proteins that bind to DNA and initiate transcription) or other regulatory molecules. Non-coding RNAs are RNA molecules that do not code for proteins but can regulate gene expression by interacting with DNA, RNA, or proteins. Epigenetic mechanisms provide a link between environmental stimuli and gene expression, and play an important role in various physiological and pathological processes, including drug addiction. Recent studies have shown that epigenetic mechanisms are involved in the regulation of neurotransmitter systems and neural plasticity in response to METH exposure. Neural plasticity is the ability of neurons to change their structure and function in response to experience or injury. Neural plasticity is essential for learning, memory, adaptation, and recovery. The expression of some genes related to METH addiction is altered by epigenetic modifications, such as histone acetylation, methylation, ubiquitination, and non-coding RNA regulation. These epigenetic changes may affect the synaptic function and morphology, neuronal connectivity, and circuitry formation in the brain regions implicated in METH addiction. Moreover, some epigenetic modifications may persist for a long time after METH withdrawal, suggesting that they may contribute to the development and maintenance of METH addiction. In this article, we review the current literature on the epigenetic mechanisms of METH addiction. We will first introduce METH and its pharmacological effects, and then discuss the epigenetic regulation of neurotransmitter systems and neural plasticity by METH. We will focus on the changes of histone, DNA, and RNA during METH addiction, and the possible causes and consequences of their relationship with METH addiction. We will also provide some perspectives on the potential applications of epigenetic interventions for METH addiction treatment.