The University of Hong Kong’s Department of Chemistry, led by Professor Hongzhe Sun, recently published a paper titled “Mitochondrial ATP synthase as a direct molecular target of chromium(III) to ameliorate hyperglycaemia stress” in the journal Nature Communications.
The study’s findings suggest that chromium(III) (Cr(III)), a common nutritional supplement, can improve the metabolism of glucose in cells by regulating ATP synthase activity. This process can mitigate mitochondrial deformation caused by high glucose levels and significantly enhance glucose metabolism in type 2 diabetic mice.
To better understand the molecular mechanism underlying Cr(III)’s effects and identify its protein targets, the research team developed a fluorescent probe capable of detecting transient metal-protein interactions. This allowed them to track the Cr(III) proteome within HepG2 cells with high spatiotemporal resolution, leading to the discovery of Cr(III)-binding proteins within the cells.
The team’s subsequent investigations revealed that Cr(III) replaces magnesium ions (Mg2+) in ATP synthase, reducing the enzyme’s activity and activating the downstream AMPK pathway. These processes ultimately result in improved glucose metabolism. This study introduces a novel concept for hypoglycemic research.
“Despite being used for decades as a nutritional supplement for diabetes treatment, weight loss, and muscle development, the protein target and mechanism of action of Cr(III) have remained unknown. By utilizing a novel fluorescent probe and other chemical biology techniques, we were able to uncover the longstanding scientific mystery of the biological chemistry of Cr(III) and demonstrate its ability to regulate glucose by targeting ATP synthase,” explained Professor Sun.
With over 500 million patients worldwide, diabetes is a chronic metabolic disease that causes nearly 2 million direct deaths each year. Type 2 diabetes mellitus (T2DM) affects over 95% of diabetic patients and poses a serious threat to human health. Chromium (Cr(III)) has been extensively studied for its effect on anti-type 2 diabetes in animal models. Its supplementation in rat diets was found to increase blood sugar removal rates, leading to its widespread use in nutritional supplements for diabetes treatment, weight loss, and muscle development. In fact, it is the second best-selling supplement in the U.S., right after calcium.
Despite its significance in food and nutritional science, chromium remains one of the least understood transition metals in the periodic table. The importance, pharmacological properties, and mechanisms of action of Cr(III) in human physiology have been debated for more than half a century. Chromodulin, the originally conceived low-molecular-weight chromium(III)-binding peptide, has never been reproducibly identified. However, Cr(III) is widely believed to improve glucose metabolism, regulate carbohydrate and lipid metabolism, maintain normal blood sugar levels, and enhance insulin signaling.
Despite this, the underlying molecular mechanism remains unknown due to the difficulty in identifying Cr(III)’s molecular targets in cells. These biomolecules are crucial for understanding Cr(III)’s physiological and pharmacological effects, and are often referred to as the “Holy Grail” of chromium biochemistry.
To date, no proteins that directly bind Cr(III) have been identified in cells or tissues. Controversial separation and detection methods often produce weak Cr(III) signals, which may be due to the dissociation of Cr(III) from its bound proteins. There is currently no suitable method for tracking Cr(III)-binding proteins in living cells. Labeling metalloproteins with a small molecule fluorescent probe is beneficial for understanding their spatiotemporal distribution and functional regulation in living cells, particularly for metals that bind weakly or transiently to proteins.
Key findings
The research team has made significant progress in understanding how Cr(III) improves hyperglycemic stress at a molecular level, building on their previous work. They synthesized a fluorescent probe that can track and recognize Cr(III)-binding proteins in living cells, consisting of a fluorophore (coumarin derivative), a metal chelating group (nitrilotriacetate), and a photoactive crosslinking group (arylazide). The probe enters the cell, binds to target proteins, and forms a covalent bond upon ultraviolet light irradiation, which fixes the proteins in cells for downstream purification.
The team used these probes to monitor the distribution of Cr(III)-binding proteins in living cells and found that they were concentrated in the cells’ mitochondria. They identified these proteins through two-dimensional gel electrophoresis and mass spectrometry and discovered that Cr(III) binds to Thr213 and Glu242 residues in the active site of ATP synthase, replacing magnesium ion (Mg2+), reducing ATP synthase activity, and activating the AMPK pathway. This pathway then reduces mitochondrial damage caused by high glucose and improves glucose metabolism, as confirmed in a mouse model of type II diabetes.
This groundbreaking study is highly praised by reviewers for its important implications for human health and the identification of molecular targets, a task that has been challenging for the past 70 years. Chromium supplements are widely sold for weight loss and muscle building, but their mode of action has been controversial. Therefore, this research addresses a major health issue that needs careful evaluation for the protection or benefit of large populations concerning anti-diabetic actions of chromium(III). The authors use a new approach of chemical biology and a vast number of experiments to shed light on chromium biology.
Source: The University of Hong Kong