Study paves the way to a novel treatment for bone loss

Researchers at the University of São Paulo prove that increased levels of chemerin observed in patients with diseases involving chronic inflammation can cause damage to bone tissue.

By Karina Toledo, in Ribeirão Preto  |  Agência FAPESP – Experiments with mice conducted at the University of São Paulo (USP) in Ribeirão Preto, Brazil, suggest that inhibiting the action of a protein called chemerin can be an effective strategy for avoiding the bone loss that is associated with inflammatory diseases such as obesity, diabetes and rheumatoid arthritis. 

Results of the research project, which was supported by FAPESP, have been published in the Journal of Bone and Mineral Research.

“Chemerin is a molecule produced mainly by adipocytes [fat cells], but it’s also expressed in several organs. There’s evidence that this protein is augmented in the bloodstream of people with obesity, type 2 diabetes, dyslipidemia, osteoporosis, rheumatoid arthritis, psoriasis and Crohn’s disease,” said Sandra Yasuyo Fukada, a professor at USP’s Ribeirão Preto School of Pharmaceutical Sciences (FCFRP) and the principal investigator for the project.

Recent research has also shown that obese individuals with dyslipidemia are more likely to suffer from bone fractures, osteoporosis and periodontal disease, a range of inflammatory gum conditions that may eventually lead to the loss of the soft tissue and bone that support the teeth.

According to Fukada, the correlations among chronic inflammation, bone loss and augmented chemerin are well established, but it was not previously understood whether chemerin was merely a marker or whether it played an active role in processes that culminate in bone loss.

“Previous research showed a reduction in oral cavity chemerin levels after removal of tartar from the teeth of patients with periodontal disease. When the inflammation decreased, chemerin levels also fell,” she said. “However, it still wasn’t clear which was the cause and which was the effect. We were the first group to show that chemerin does indeed play an active role in periodontal disease.” 

First, the researchers needed to demonstrate that both chemerin and CMKLR1, the cell receptor that chemerin activates, are expressed in osteoclasts, which are cells that specialize in bone resorption. Second, the group conducted an in vitro investigation to find out exactly how chemerin affects osteoclasts and bone. 

To do this, they isolated hematopoietic stem cells, which differentiate into osteoclasts, from the bone marrow of mice. For bones to stay healthy, these cells must be balanced with osteoblasts, which make bone tissue by producing a matrix that then becomes mineralized.

“When we placed the precursor cells on a conventional culture plate to differentiate, we found that chemerin didn’t induce any changes,” Fukada said. “The number of osteoclasts formed was the same with or without chemerin in the medium. However, when we repeated the experiment on a plate with artificial bone matrix at the bottom, we found that the osteoclasts’ bone resorption capacity increased in the presence of chemerin. The hole made in the bone matrix was three times greater in the presence of chemerin.”

Through other in vitro experiments, the group discovered that when chemerin binds to its cell receptor, it induces the production of cathepsin K, an enzyme that breaks down bone collagen. The study also showed that this effect depends on a protein called ERK-5, which acts as an intermediary in the process.

“We found that chemerin boosts the phosphorylation [activation] of ERK-5 and that the increase in cathepsin K doesn’t occur when chemerin is blocked,” Fukada said.

Preventing damage

To test the effect of chemerin in vivo, the researchers used two different models of dyslipidemia. One involved mice that had been genetically modified not to express the gene that codes for the satiety hormone leptin and that therefore became obese while young, developing metabolic disorders such as insulin resistance and dyslipidemia.

In the second model, mice were fed a hyperlipidic diet for 16 weeks. They did not become as obese as the leptin-deficient mice, but their abdominal fat increased significantly, and metabolic disorders appeared as a result.

“Both groups displayed high cholesterol levels, especially the group fed a hyperlipidic diet, as well as augmented levels of blood chemerin compared with the control,” Fukada said. “In addition, expression of chemerin and its receptor increased in the gums of the dyslipidemic mice [in both models] compared with the control.”

When they compared subgingival bone loss, the researchers found that it was 60% greater in the mice fed a hyperlipidic diet than in the control group and about 20% greater in the leptin-deficient mice.

In another experiment, leptin-deficient mice were treated with a chemerin receptor antagonist (a molecule that binds to the receptor and prevents the chemerin from acting).

An analysis performed when the mice reached adulthood showed significantly reduced bone loss, with final results that were similar to those of the control. The researchers also showed that the treatment prevented an increase in gingival cathepsin K.

“Our hypothesis is that although the dyslipidemic mice produced more chemerin than the control, its action was blocked by the treatment, and bone loss was therefore minimized,” Fukada said.

The molecule tested as a chemerin receptor antagonist is still for experimental use only. “We now need to study the effect of chemerin in human osteoclasts to find out whether we can produce the same results,” she said.

Fukada presented the findings to date on June 23 during the Third International Symposium on Inflammatory Diseases (INFLAMMA III), organized by the Center for Research on Inflammatory Diseases (CRID), one of FAPESP’s Research, Innovation and Dissemination Centers (RIDCs), and the Brazilian Inflammation Society (SBIn).

Part of the research was done during Giselle de Angelo Carbonaro Guerreiro’s PhD research for the Graduate Studies in Pediatric Dentistry Program at USP’s Ribeirão Preto Dentistry School (FORP), and part was completed during Erivan Schnaider Ramos Junior’s postdoctoral research, supported by a scholarship from FAPESP. The project was conducted with CRID’s support.

The article “Adipokine chemerin bridges metabolic dyslipidemia and alveolar bone loss in mice” can be retrieved from: onlinelibrary.wiley.com/doi/10.1002/jbmr.3072/full.