New genetic discoveries offer hope for targeted lupus therapies

Lupus is a lifelong, often painful and occasionally fatal autoimmune disease. Few treatments exist today beyond powerful steroids to knock down the patient’s immune system -; a therapy that has its own serious risks.

The good news is that new and promising treatments are in clinical trials. But the term lupus belies the fact that the disease has a variety of causes, meaning that treatments will have to be highly personalized to ensure that each patient is given the drug that targets the specific genetic mutation responsible for their lupus variety. .

Researchers are just beginning to link specific genetic mutations to subgroups of lupus patients, allowing doctors to target therapies to those who will benefit the most. In the latest advance, researchers at the University of California, Berkeley, report in a new paper the discovery of two groups of patients with genetic mutations that are nearly identical to mutations that researchers had previously identified in mouse and cell lines as linked with autoimmune. disease.

These two genetic links are among several dozen mutations that the UC Berkeley team recently discovered and linked to lupus, all in a gene that regulates a prime suspect in a subset of lupus patients -; proteins called toll-like receptors (TLRs), which enable immune cells to recognize foreign DNA and RNA.

According to study leader Gregory Barton, professor of molecular and cellular biology at UC Berkeley, identifying these mutations could help doctors provide a personalized treatment for patients with hypersensitive TLRs and, in particular, hypersensitive TLR7 receptors. .

“We basically have a map now,” said Barton, who is also an investigator at the Howard Hughes Medical Institute. “It’s not like everyone who has lupus has a mutation in the gene that causes overactivation of TLRs and TLR7. But there are drugs coming online that specifically inhibit TLR7. As we sequence more and more people, it will become more it’s easy to identify those patients and put them on these drugs, which is much better than the current course of therapy for lupus, which is brutal.

“This is exciting because the drug will be available orally and is in clinical trials now,” said Victoria Rael, a UC Berkeley graduate student who, with fellow graduate student Julian Yano, is co-first author of the paper.

The results of the genetic screens and details of the patients’ mutations were published today (May 23) in the Journal of Experimental Medicine.

A problem with knowing “self”

Autoimmune diseases, which range from rheumatoid arthritis and Crohn’s disease to scleroderma and many thyroid conditions, result from the immune system’s attacks on the body’s cells that destroy normal, healthy tissue.

Many studies have linked at least two types of autoimmune diseases, lupus and psoriasis, to TLRs, which are part of the innate immune system that initially detects foreign invaders, such as viruses and bacteria, and stimulates the first line of attack. Normally, TLRs are finely tuned to react only to foreign DNA and RNA, but if this tuning is off, they can react to nucleic acids and the body’s proteins bound to nucleic acids, which look a lot like those of pathogens.

What makes this autoimmune reaction so deadly is that TLRs also activate the body’s second line of defense, the most powerful adaptive immune response, by mobilizing T and B cells, macrophages, and other cells. These cells then mount a sustained attack that destroys healthy body tissue and causes chronic inflammation.

The most common form, systemic lupus erythematosus (SLE), for example, is initially characterized by skin rashes -; in particular, a butterfly-shaped rash on the face -; but later from damage to joints, muscles, organs and skin, causing pain and fatigue. It is most commonly seen in women, often starting during the teenage years. Lupus, in general, is two to three times more common in women from many ethnic and racial minority groups than in white women.

“We think the way the system works is that if the nucleic acids find these receptors, it’s very likely they’re from a virus,” Barton said. “But in some people, the receptor is more responsive, so now levels of self-nucleic acids that wouldn’t otherwise stimulate the receptor in a normal person activate the receptor. We think one of the ways these mutations work is that they’re create levels of self-nucleic acids that would not normally be stimulatory, stimulatory.”

Barton and his lab colleagues have been investigating the role of TLRs that are dysregulated in lupus, and in particular, one of the key proteins that regulates them: UNC93B1, or UNC for short. A few years ago, a team of postdoctoral and graduate students in his lab screened in cell culture more than 100 genetic mutations in the UNC gene to see which ones overstimulated TLRs and would be good targets for studies of further. While they published some details in previous papers, they did not publish the full list because there seemed to be a few points -; there was almost no genomic sequencing data from lupus patients to compare mutations that overstimulated TLRs.

But that has changed in recent years, thanks to a drop in the cost of genome sequencing. That’s how the mother of a young daughter with severe autoimmune disease found Barton. Her daughter’s DNA was sequenced and showed a mutation in a region of UNC that Barton’s team had noted in previous work.

Lupus in the family

Rael and graduate student Madeleine Weiss used the same cell culture screening technique to test the new mutation from the young girl and found that it had a hyperstimulatory effect, similar to the effect of other mutations in that region of the UNC gene. Surprisingly, the patient had the genetic mutation in only one of the two UNC alleles, meaning she had a normal UNC gene, but she still suffered severe autoimmune symptoms.

Barton and his team also connected with a family of five affected by lupus. All had mutations in a UNC allele in a different region of the UNC protein that Barton’s team had previously identified. This mutation, when examined in cell lines, also produced overactive TLRs.

We were skeptical that just one copy of a gene would be enough to cause a disease. It wasn’t until we put the patients’ mutations into cell lines and saw that they led to a very convincing TLR hyper-response that we realized they had the potential to be sufficient to cause disease.”

Victoria Rael, graduate student at UC Berkeley

Rael and Yano then repeated the screening work previously performed in the laboratory and confirmed that 32 distinct mutations in the UNC gene -; about a third of the mutations tested -; increased the sensitivity of TLR7 to nucleic acids at least twofold. About five other mutants increased TLR7 sensitivity, but to a lesser degree. Before these screens, only two mutations in the UNC protein had been linked to increased TLR7 sensitivity in mice, although three more human mutations were reported within the past two months.

Barton hopes that by publishing the full list of TLR hypersensitivity mutations, doctors can identify other lupus patients who may benefit from anti-TLR drugs now in clinical trials. One drug, M5049, or Enpatoran, appears to work by binding to two human receptors, TLR7 and TLR8, and preventing them from binding nucleic acids.

Rael, Yano and other members of Barton’s lab are further investigating how these unique UNC mutations affect how a patient manifests the disease. They have recreated these patients’ mutations in mice so they can model human lupus.

“With mouse models, you can start to think about how, even though the mutations are in the same protein, different mechanisms of TLR regulation are disrupted, which immune cells are activated as a result, and how this can lead to changes in symptoms. . patients suffer”, said Rael.

The lab is also trying to understand how UNC tunes TLRs, which may be regulating the number and regulation of TLRs on immune cells. More TLRs can make a person more sensitive to the small number of self-nucleic acids circulating in the body.

“UNC93B1 is important for getting the receptors to where they can function, but it’s also important for regulating them once they get there,” Barton said. “The protein is a very baroque way of trying to make decisions about whether the nucleic acid you’ve just bound to a TLR is from a virus or from one of your own cells.”

He hopes doctors will add this gene to the list of genes associated with lupus, “so if they see a mutation like this, even a heterozygous mutation, they will investigate further.”

Other senior authors of the paper are Bo Liu of the Chinese Academy of Sciences in Shanghai and Olivia Majer of the Max Planck Institute for Infection Biology in Berlin, Germany. Co-authors also include doctors from UC San Francisco, Stanford University and hospitals in Missouri, North Carolina and Washington.

The work was funded in part by the Lupus Research Institute, the Lupus Research Alliance, and the National Institutes of Health (R01AI072429).