Globins - on the hunt to protect your liver

Anti-fibrotic therapy remains an unmet medical need in human chronic liver diseases. A research team led by Professor Norifumi Kawada, Osaka City University (OCU), reported the anti-fibrotic function of globin family members in hepatic stellate cells (HSCs), the main cell type involved in liver fibrosis. In mice with advanced liver fibrosis, myoglobin (MB), (neuroglobin) NGB and (cytoglobin) CYGB injection can suppress liver inflammation and fibrosis.

The functions of globin family members have been extensively studied, focusing primarily on the specific tissues in which these proteins are expressed: hemoglobin (HB) in erythrocytes, MB in muscle cells, NGB in nervous tissues, and CYGB in pericytes and fibroblasts. Beyond the well-established oxygen-binding respiratory functions of heme-containing proteins, all globins are also known to be involved in the regulation of harmful reactive oxygen species (ROS), protecting cells from oxidative stress.

“Liver fibrosis occurs after repetitive and long-lasting injury or inflammation in the liver. These injuries are accompanied with the accumulation of ROS that activate HSCs, followed by collagen production,” explains Dr. Kawada.

Along with Dr. Le Thi Thanh Thuy, PhD fellow Vu Ngoc Hieu, and colleagues, Dr. Kawada observed that when they culture human HSCs under globin treatments, MB, NGB, and CYGB enter the cellular organelles, hunt the intracellular harmful ROSs, and reduce the direct signal regulating the production of collagen. “Results showed the antioxidant capacity of the globins to be greater than the well-documented glutathione and even vitamin C,” continues Dr. Kawada. 

This is great news for three members of the globin family, but what happened to HB? “We noticed that hemoglobin did not enter the cell,” explains Dr. Thuy, “we speculate this is due to size as HB is 4 times the size of its monomer siblings.”

In the next set of experiments, Dr. Kawada and his group generated a mouse model of advanced liver fibrosis using chemical agents and applied MB, NGB, and CYGB by intravenous injection. Interestingly, the therapeutic protein dramatically suppressed liver inflammation and fibrosis without any side effects. PhD fellow Hieu points out, “in addition to the liver, we focused on possible side effects with the neighboring kidney. Creatinine levels remained normal throughout the treatment.”

With this discovery, that was published in the journal Redox Biology, the research team hopes to establish a foothold to a potential therapy for liver fibrosis in the near future.

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Glossary

1. Liver fibrosis

Liver fibrosis is a wound-healing response to chronic liver injury and often results in cirrhosis, liver failure, portal hypertension, and hepatocellular carcinoma.

2. Hepatic stellate cells

Hepatic stellate cells reside in the space of Disse, between hepatocytes and the sinusoidal endothelial cells, in the liver.  Hepatic stellate cells are the major collagen-producing cells, and activation of hepatic stellate cells is a key issue in liver fibrosis.

3. Reactive oxygen species  

Reactive oxygen species (ROS) include several chemically reactive molecules derived from oxygen. State of excessive quantity of ROS call oxidative stress, which may result in significant damage to cell structures.

4. COL1A1 promoter

The COL1A1 promoter region is a segment of DNA located upstream of a gene coding for COL1A1. This region controls the initiation of transcription from DNA to mRNA, which is ultimately translated into COL1A1 protein.

5. Cell-free system

Cell-free system is referred to as platforms that enable testing biological systems in an environment without cells.

6. Glutathione

Glutathione is well-known antioxidant which is capable of preventing damage to important cellular components caused by reactive oxygen species such as free radicals, peroxides, lipid peroxides, and heavy metals

7. Human globins

The globins are a superfamily of heme-containing globular proteins, involved in binding and/or transporting oxygen. Prominent members include Hemoglobin, Myoglobin, Neuroglobin, Cytoglobin.

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