Cell Rep: A novel mechanism by which copper ions regulate fatty acid metabolism

Macronutrients (including glucose, lipids, and amino acids) and micronutrients (including metals) are essential for
maintaining metabolic balance.
The relationship between glucose and lipid metabolism disorders and the onset of metabolic diseases is well known; However, the role of trace elements in the occurrence and development of metabolic diseases is poorly
understood.

Copper is an important trace element involved in the assembly
of a variety of enzymes (SOD1, COX, etc.
).
The outer electron cloud of copper atoms has a high density and can accommodate the transport of multiple electrons, so copper ions are the catalytic center
of a variety of metabolic enzymes.
Although copper ions are crucial in life activities, how changes in copper ions in cells are perceived and how copper ions participate in the regulation of glycolipid metabolism have been rarely reported
.
The liver is the most important copper storage organ, and the liver copper is maintained in a stable range under
physiological conditions.
Ceruliplasmin (CP) is synthesized and secreted mainly by the liver, which secretes copper from the liver into the blood and transports it to other tissues
.
The global prevalence of non-alcoholic fatty liver disease (NAFLD) has reached 25% of the population, but there is no clinically approved specific drug
.

Therefore, there is an urgent need to explore the pathogenesis of MAFLD and new pathogenic factors
.
In recent years, clinical studies have found that hepatic copper deficiency is closely related to the pathogenesis of NAFLD; Feeding copper-containing feed to fatty liver rabbits effectively alleviated the symptoms of
NAFLD.
However, the mechanism of copper and lipid metabolism and NAFLD development has been poorly studied
.

Under the leadership and strong support of Academician Jia Weiping, on October 18, 2022, the research group of Liu Junli of the Institute of Diabetes, Sixth People's Hospital Affiliated to Shanghai Jiao Tong University School of Medicine and Professor Miao He of Harvard Medical School jointly published a report entitled "Downregulation of hepatic Ceruloplasmin ameliorates NAFLD via SCO1-AMPK-LKB1" in Cell Reports magazine complex", elucidating the role of copper and ceruloplasmin in the development of NAFLD and its molecular mechanisms
.
Academician Jia and Teacher Liu's doctoral student Xie Liping, Teacher Liu's postdoctoral Yuan Yanmei and doctoral student Lu Sijia, and Miao's student Xu Simiao are the joint works
of this article.

The researchers measured the changes of copper ions in the liver of different populations by mass spectrometry, and found that the content of copper ions in the liver of NAFLD patients was significantly reduced, and the content of copper ions in the liver of ob/ob mice and DIO mice was also significantly reduced
.
The researchers studied all genes involved in copper ion transport and metabolism in clinical samples of NAFLD liver, and found that ceruloplasmin (CP) and other genes were significantly upregulated.
Then, siRNA was used to knock out the relevant genes in hepatocytes one by one, and the screening found that the downknock CP led to a significant increase in the concentration of copper ions in hepatocytes, while the effect of knocking out other genes was not obvious
.
These results suggest that the decrease in copper ions in the liver of patients with NAFLD may be caused
by upregulation of CP expression.
The researchers constructed liver-specific CP knockout mice and performed high-fat feeding, and found that CP knockout led to the inhibition of high-fat feed-induced reduction of liver copper ions, and then alleviated the occurrence
of fatty liver caused by high-fat induction.

Mitochondria are the main organelles
for fatty acid oxidation.
High-fat feeding led to swelling of mitochondria and loss
of mitochondrial crest damage in mouse hepatocytes.
The investigators found that liver-specific knockout CP inhibited mitochondrial damage caused by high-fat feeding and increased the number
of healthy mitochondria.
Seahorse experiments also showed that hepatocyte knockout CP increased cell oxidative capacity
.
The improvement of mitochondrial function further promotes the oxidation
of fatty acids in hepatocytes.

The researchers found that liver knockout led to the activation of AMPK signaling pathway through RNA-seq studies, and based on AMPK inhibitors, AMPK gene knockout and other means, it was also proved that CP knockout to promote liver fatty acid oxidation depends on the AMPK-PGC1α-PPARα signaling pathway
.

After CP knockout, did the upward regulation of copper ion concentration mediate the activation of AMPK? Removal of intracellular copper ions by copper ion-specific chelators significantly weakened the AMPK activation and fatty acid oxidation gene expression mediated by CP deletion.
In contrast, iron-specific chelators do not have these effects
.
The upregulation of copper ions plays an important role
in activating AMPK and inhibiting fatty liver.

How do copper ions activate AMPK? AMPK is not copper-containing protein, but the researchers found that silencing copper-containing protein SCO1 effectively inhibited CP knockout-mediated AMPK activation and fatty acid oxidation gene increase.
Moreover, SCO1 forms a complex with AMPKa/β/γ and LKB1 to promote AMPK activation
.
Removing copper ions from cells with BCS disrupts SCO1's binding to AMPKa; Consistent with this, the binding ability of SCO1 mutants with copper binding site deletion to AMPKa was significantly inhibited
.
These experiments proved that only SCO1, loaded with copper ions, can effectively form complexes with AMPKa and LKB1 and promote AMPK activation and upregulation of fatty acid oxidation
.

Finally, by injecting mice with copper chelating agent (BCS), the researchers reversed the enhancement of fatty acid oxidation and excessive fat accumulation in hepatocytes caused by CP knockout, further proving that restoring liver copper levels is the main reason for
CP knockout-mediated improvement in fatty liver symptoms.

In summary, starting from clinical research, this study has discovered a new cause that induces the occurrence of NAFLD; In addition, a novel mechanism
by which trace element copper ions regulate the metabolism of macronutrient lipids through the SCO1-LKB1-AMPK complex was revealed.
This study brings new enlightenment to the future study of the physiological effects of copper ions, and also provides a new theoretical basis
for the prevention and treatment of NAFLD and drug development.

Liu Junli's research group is recruited

Liu Junli's research group focuses on glycolipid metabolism and related diseases, and has published many research papers in Cell Metabolism (2), Science Translation Medicine, Cell Reports and Metabolism in recent years, and their series of research work has received extensive attention from domestic and foreign peers, international authoritative journals Nature Medicine and Nature Reviews Endocrinology and other journals have published a number of positive reviews
of Research Highlights.
Due to the needs of work, Liu Junli's research group is open to recruit 2 postdoctoral fellows, welcome to contact the doctor who is interested in joining as soon as possible (daoyangzi@aliyun.
com), for detailed recruitment information, please refer to the laboratory website: www.
junliliu-lab.
com.