Local scientists believe they have created a new approach toward anti-inflammatory therapy.
Earlier this semester, Boston University cell biology students spent time studying RNA interference (RNAi), a process by which small snippets of RNA can be used to stop the translation of certain genes. While these students were learning about this procedure in an effort to do well on an upcoming test, researchers in Boston and Cambridge were working on implementing the same procedure into action in an effort to cure illnesses such as heart disease and cancer.
A new study published in Nature Biotechnology reports results that show how RNAi can be used to prevent inflammation in cells to prevent the aforementioned diseases, among others. Researchers from the Centers for Systems Biology at Massachusetts General Hospital, Harvard-MIT Division of Health Sciences and Technology, Harvard Medical School, Brigham and Women’s Hospital, Alnylam Pharmaceuticals, Harrison School of Pharmacy, and Seoul National University in South Korea all participated in the study.
“Researchers may have struck upon an effective novel anti-inflammatory treatment by manipulating the molecular navigation system used by inflammatory immune cells to reach sites of tissue damage,” the abstract for the study says. “Given that inflammation [exacerbates] almost all major diseases, this therapy could potentially have wide-spread benefit.”
RNAi is a cellular mechanism used to silence genes after they have been translated from DNA to RNA, explains Gabriel Courties, a researcher in the lab at the Centers for Systems Biology where the research was conducted.
“Since its discovery in plants, RNAi machinery has been shown to be conserved in many species including fish, flies, worms, fungi, and mammals. In all these species, RNAi represents an important host defense mechanism that has evolved to protect against harmful RNAs produced by viral infections or genetic mobile elements,” Courties said in an e-mail interview. “It is also a cellular process [that plays] important roles in gene regulation in all the biological processes investigated so far.”
Cells translate DNA code to functioning proteins through the help of messenger RNA, or mRNA, the abstract notes. The mRNA copies protein-coding portions of DNA and carries a message from the nucleus to the cytoplasm. It travels to the ribosomes, where proteins are made, and is translated into molecules such as proteins.
The small non-coding RNAs (siRNAs) can control gene expression by targeting mRNAs for degradation or translational repression by binding to them and preventing their translation into proteins.
SWELL DRUGS FOR THE SWOLLEN
RNAi has the potential not only to act as a gene-silencing tool, but also as a novel class of drugs, Courties explained. It can be used to shut down any potential gene of interest linked to human diseases. RNAi based therapies have been successfully applied to stop different diseases including cancers, infectious, neurogenerative and autoimmune diseases.
“RNAi is [so great because it is] a technique that can be used in patients. It overcomes hurdles of unspecific effects and the limited efficacy of drugs by ‘surgically’ targeting one protein, which is knocked down,” Matthias Nahrendorf, the senior author of the study, said in an e-mail interview.
Scientists studied cells called inflammatory monocytes, which are the key cells in inflammation and repair, Nahrendorf said. Although some types of these cells are necessary for defense and wound healing, other types can be harmful if they are out of control.
“In good times, these cells defend, eat bacteria, and promote early stages of wound healing, but in disease, they can be harmful,” Nahrendorf said. “These cells cause atherosclerosis, myocardial infarction and are involved in virtually all diseases with inflammatory components.”
During illness or injury, distressed cells release a cocktail of chemicals to attract immune cells to the damaged site, the abstract says.
“Like a chemical GPS, immune cells follow these signals which navigate them to the right place,” the abstract further explains. “Researchers have developed a way to manipulate this navigation system by selectively silencing the protein that inflammatory cells use to detect these signals.”
SWEATING THE SMALL STUFF
Inflammatory monocytes use a receptor, CCR2, that directs them to the sites of injury, infection, and inflammation. This recruitment of monocytes usually has a negative effect, and so researchers sought a way to turn it off.
“We were able to use RNAi to stop these inflammatory monocytes from traveling to the site of inflammation. To do this, [we needed to know] the mRNA that encodes the target protein CCR2, so we could then design and test the complementary silencing RNA,” Nahrendorf said.
Nahrendorf wrote in the abstract that the hardest part of using RNAi to prevent protein expression was delivering the siRNA’s to the right place.
“It [the siRNA] not only needs to go to the cell of interest but it needs to reach the right compartment within that cell of interest,” he said. “To do this, packaging the right siRNA sequence in the right delivery vehicle is critical.”
The researchers worked on finding the correct siRNA sequences against the CCR2 receptor. They then labeled it with a fluorescent tag and encapsulated it into a nanoparticle delivery system designed by Robert Lander and Daniel Anderson at MIT.
The prepared nanoparticle was then injected into mice, and by imaging the fluorescent tags, the researchers were able to determine whether the siRNA had reached the target monocytes or not.
After determining whether the siRNA reached the target monocytes, the researchers also had to ensure that the siRNA reached the correct location within the cells to block the production of CCR2. To do this, they ensured that the CCR2 production in cells had gone down and they looked for specific cleavage products because the siRNA is supposed to cleave the mRNA.
The researchers found that after treatment with siRNA, the monocytes were not able to travel to the sites of injury, infection and inflammation.
The abstract states that the researchers tested effect of blocking CCR2 production in a variety of animal disease models, mainly atherosclerpsis, heart failure, cancer and transplant rejection. They found that siRNA was effective in all of these models, and the “number of monocytes reduced anywhere from 50-80 percent.”
“For example, tumors in mice weren’t growing as fast, in fact sizes in mice with myocardial infarction were smaller and atherosclerotic plaques were smaller and less inflamed,” the abstract says.
INVENTIONS FOR THE INFLAMED
“I believe we created a completely new class of cell specific anti-inflammatory therapy,” Nahrendorf said. “The interesting aspect is that this treatment should only target inflammatory monocytes, the bad guys, while not harming other protective immune cells, the good guys.”
The next step in this research, Nahrendorf said, is to test siRNA in large animals and conduct toxicity studies in human beings.
BU students said they are impressed by the impact siRNA could potentially have on disease treatment.
“I think it’s interesting to hear about how the things we are learning about in class can actually be put into use,” said Sonal Jain, a sophomore in the College of Arts and Sciences.
CAS sophomore Devi Moody said she hopes the study can have an impact on students who want to effect scientific change beyond college.
“Hopefully news like this gets students more motivated to become a part of research and use what they learn at BU to make a real difference,” she said.