The discovery of Lin Sheng Cai's team first outlined the roadmap of metformin's functional exercise from the molecular perspective, which is crucial for improving the safety and efficacy of drug targets. It provides a new idea for the treatment of diabetes, and the development and application of anti-tumor and anti-aging drugs. Li Xiaoying Director of Endocrinology and metabolism Department of Zhongshan Hospital Affiliated to Fudan University Metformin is the most commonly used drug for diabetes and is no stranger to the public. In recent years, some clinical studies have found that in addition to reducing blood glucose, metformin also has certain effects in alleviating fatty liver, protecting cardiovascular system, inhibiting tumor growth and alleviating the symptoms of neurodegenerative diseases. Where do these effects come from? Metformin has been used clinically for more than 60 years, and countless patients have benefited from it, but people have never been able to find out its specific mechanism of action, which greatly limits the understanding and application of this good medicine in the medical community. Recently, this "scientific puzzle" has been answered. Lin Shengcai, academician of the Chinese Academy of Sciences and professor of the school of life sciences of Xiamen University, after seven years of scientific research, successfully found the direct action target of metformin, and outlined the road map of metformin from the molecular perspective for the first time, laying a foundation for further expanding its application scope. The relevant research results were published in the journal Nature. "Find another way" to produce effect Metformin was isolated from the plant goat bean in the 1920s. Later, scientists found that it has hypoglycemic effect, and modified and optimized its structure. Metformin, which was launched in 1957, is widely used in the treatment of diabetes. It is generally believed that metformin acts directly on the liver, kidney and intestine. After being transported into cells, it mainly plays important biological functions such as reducing fat content and blood glucose by activating the protein kinase (AMPK) signal pathway activated by adenosine monophosphate. AMPK is known as the master switch of human metabolism. When the cell energy level decreases, it is activated by elevated adenosine phosphate (AMP), which plays an important role in maintaining the regulation function of material and energy homeostasis. So how exactly does metformin control this switch? Previous experiments have found that metformin can increase AMP level and activate AMPK by inhibiting the function of mitochondrial electron transport chain complex. However, it is worth noting that these experiments used extremely high concentrations of metformin that exceeded the clinical concentration and far exceeded the clinical dosage. Therefore, this effect result is difficult to truly reflect the physiological effect. It is worth mentioning that when studying the mechanism of metformin activating AMPK, scientists also found a strange phenomenon. Compared with metformin, other synthetic AMPK activators do not have all the effects of metformin, and clinical doses of metformin have no effect on the increase of AMP level. Intuitively, when patients were treated with metformin, the level of AMP in cells that activated AMPK did not increase, but the drug still worked. Lin Shengcai's team, who has long been committed to the study of metabolic homeostasis and the mechanism of metabolic diseases, believes that various signs suggest that the activation of AMPK by metformin may be "another way", which is likely to activate AMPK with a new and amp independent pathway. In 2016, the team published the preliminary conclusion that metformin may activate AMPK through a pathway called lysosomal pathway used by the body when sensing hunger and falling blood glucose levels, which pointed out the rough direction for the exercise of metformin's efficacy. "The research at that time was equivalent to tracking the thief into the building, but he didn't know which room he was in." Lin Shengcai explained vividly. Based on the above research direction, after more than five years of exploration, the team found the molecular target of metformin - PEN2, and confirmed that the lysosomal pathway is the correct pathway for metformin to activate AMPK. A target caught with a "fishhook" In this work, Lin Shengcai team first cooperated with Deng Xianming team of Xiamen University. Through a series of exploration, the latter broke through many problems in chemical synthesis and synthesized the chemical probe of metformin. In short, the working principle of this probe is similar to fishing. The "fishing hook" at the front end is metformin, and the "fishing rod" at the back end is a label called biotin. After the front-end metformin molecule meets the protein it binds, that is, the target, researchers can "catch" metformin together with its target through the back-end label, and then through analysis, they can accurately know what the target of metformin binding is. Through this method, the research team "fished" more than 2000 proteins that may bind to metformin from the cells, and screened 317 proteins on lysosomes for further verification. By verifying the interaction between metformin and these proteins one by one, the researchers again narrowed the scope to 113 proteins that specifically bind to metformin. Subsequently, the research team successively inhibited the expression of these 113 proteins through gene silencing, and finally found that metformin could not activate AMPK when the expression of a distinctive protein, PEN2, was inhibited. This result shows that PEN2 can mediate the activation of AMPK by metformin, that is, PEN2 is the key target for metformin to start lysosomal pathway and activate AMPK. Subsequently, the researchers further confirmed the identity of PEN2 in animal experiments. They knocked out PEN2 from mice and Caenorhabditis elegans and found that metformin could no longer activate AMPK, and the effects of metformin on reducing glucose levels and liver fat content disappeared. All experimental results show that PEN2 is an indispensable signal molecule in the mechanism of metformin. In this regard, the researchers also specially stressed that this pathway does not depend on amp and will not disturb the intracellular AMP level, which may explain why metformin will not cause damage to cells due to reducing energy level while playing its therapeutic role. Or it will bring benefits to the treatment of more diseases Academic circles generally believe that based on the action mechanism of metformin, safer new alternative drugs may be developed in the future. For example, at present, metformin can only act on a few tissues such as liver and intestine, and its efficacy is still limited. If people want to use metformin to reduce fat while retaining strong muscles, rather than reducing them together, they should be particularly careful. After finding the molecular target of metformin, it is very likely to design metformin target drugs that specifically target adipose tissue, which undoubtedly brings benefits to the treatment of various metabolic diseases such as increasingly serious malnutrition. In addition, the role of PEN2 in tumor formation, aging and dementia has been gradually revealed. Studies have found that many Alzheimer's patients have mutations in PEN2 gene. Therefore, metformin targeting PEN2 may play a role in the prevention and treatment of Alzheimer's disease. Li Xiaoying, director of Endocrinology and metabolism Department of Zhongshan Hospital Affiliated to Fudan University, said, "the discovery of Lin Shengcai team has outlined the roadmap of metformin exercise function from the molecular perspective for the first time, which is very important for improving the safety and efficacy of drug targets, and provides a new idea for the treatment of diabetes, and the development and application of anti-tumor and anti-aging drugs." The research team said that at present, analyzing the interaction between small molecules such as metformin and proteins is still a very cutting-edge or immature field. Based on their experience in discovering the target of metformin this time, there are countless water-soluble protein molecules that can bind to metformin, just like various salt ions in aqueous solution, and it is like looking for a needle in a haystack to "fish" PEN2 from these massive water-soluble protein molecules. For this situation, there is no better screening means, and the only way is to take the trouble to screen one by one. In addition, whether the PEN2 target can fully explain the different effects of metformin and whether there are other targets need to be invested in more research in the future. (outlook new era)