Recent research, published in the journal Sciences Advances and carried out by CONICET researchers and Spanish colleagues, shows that the protein known as galectin-1 (Gal-1) prevents the development of pathological vascular remodeling that underlies atherosclerosis and AAA. This was proven, on the one hand, by comparing the expression levels of Gal-1 in samples from patients with atherosclerosis and abdominal aortic aneurysm (AAA) with control tissues, and, on the other, by performing different assays. in vivo.
The collaborative work made it possible to articulate the expertise in cardiology and cardiovascular diseases (CVD) of the group led by José Luis Martín-Ventura at the Network Biomedical Research Center for Cardiovacular Diseases (CIBERCV) and the Autonomous University of Madrid (UAM), with the extensive experience that the team led by Gabriel Rabinovich , CONICET researcher at the Institute of Biology and Experimental Medicine (IBYME, CONICET – F-IBYME), has in the study of the role of Gal-1 in different pathological scenarios, such as cancer, autoimmune diseases and infections.
CVDs are the leading cause of death in the world. According to figures from the World Health Organization (WHO), around 18 million people die annually as a result of this type of pathology. Atherosclerosis and AAA are CVDs whose underlying cause is pathological vascular remodeling.
Atherosclerosis is characterized by the formation of what is known as atheromatous plaques, which when destabilized release their contents and promote the formation of thrombi that block blood flow. AAA is distinguished by the dilation of the abdominal aorta, which can progress to rupture of the artery, causing, in most cases, death. As it is an asymptomatic disease, it is very difficult to diagnose it before it has a fatal outcome.
Until today, most of the drugs used to treat these types of diseases aim to lower cholesterol and other lipid levels, or to reduce blood glucose. But once these pathologies are advanced, they are very difficult to treat . That is why it is very important that research be carried out with the ultimate goal of designing drugs that can counteract both atherosclerosis and AAA.
Gal-1 and pathological vascular remodeling
"We knew, from previous research, that Gal-1 plays a very important role in the regulation of the immune system -by operating as an immunomodulator-, and that, in addition, it modulates certain vascular programs. In this way, in cancer, Gal-1 helps tumors escape the immune response, as well as create new blood vessels –angiogenesis– that favor the migration of tumor cells and the formation of metastasis,” indicated Dr. Gabriel. Rabinovich, from IBYME-CONICET.
“On the other hand, in situations of autoimmunity – in which the immune system is exacerbated and attacks functional tissues, recognizing its own antigens as foreign –, Gal-1 makes it possible to restore the functioning of the tolerogenic circuits and inhibit inflammation. The role of Gal-1 in the modulation of both immunological and vascular programs led us to think that this protein could play some role in atherosclerosis, where these two components are highly marked. But we had very little experience in cardiology, so when Martín-Ventura proposed to work together, it seemed like an excellent idea,” he added.
Gal-1 expression in healthy human aortas, in atherosclerosis and in AAA
The first step of the research was to compare the levels of Gal-1 in human atheroma plaques with what happened in samples of healthy aortic walls.
“This first study allowed us to see that in the plaques of patients with atherosclerosis, the expression of Gal-1 was greatly reduced compared to what occurred in the control samples. "Although we still did not know through what mechanisms, this gave us an indication that the development of atherosclerosis could be linked to the decrease in Gal-1 ," says Rabinovich.
Subsequently, the research team wanted to study what happened to the expression of Gal-1 in human AAA, and they saw that, as occurred in atherosclerosis, the levels decreased drastically ; which indicated that the loss of this galectin favors the development of mechanisms linked to the pathological vascular remodeling that underlies both cardiovascular pathologies.
“In the case of AAA, which is a disease that progresses silently and without warning, deregulation in Gal-1 expression could even serve as a biomarker of phantom progression. That is, Gal 1 could be a window to detect the pathology in time,” indicates Sebastián Maller , one of the authors of the work, who did his doctorate at IBYME between 2014 and 2019.
The formation of atheroma plaques in Gal-1-deficient mice and their reversal through the administration of recombinant Gal-1
After observing that in human aortas from patients with atherosclerosis, the expression of Gal-1 was greatly decreased, the research team wanted to see what happens if mice genetically modified to not express Gal-1 are induced with atherosclerosis, in relation to what happens if wild genotype mice are subjected to the same process.
“When atherosclerosis was induced, Gal-1-deficient mice exhibited larger and larger atheromatous plaques than wild-type mice. The difference was even more noticeable than we expected. This confirmed what we had seen in humans,” says Juan Manuel Pérez-Sáez , CONICET researcher at IBYME and one of the protagonists of the work.
One of the most interesting aspects of the research was when Gal-1-deficient mice, which were induced to form atherosclerotic plaques, were administered recombinant Gal-1 to analyze whether the pathological condition could be reversed. The results were “ surprisingly successful ,” according to a CONICET statement.
The treatment resulted in a 34 percent reduction in lesion area in the aorta compared to vehicle control delivery. The size of the plates was also noticeably reduced. Similar effects were found when Gal-1-deficient AAA mice were treated with recombinant Gal-1.
“Treatment with Gal-1 decreased the size of the necrotic core, a marker of instability of advanced atherosclerotic plaques, which could prevent plaque rupture and associated complications such as infarction or stroke,” said Dr. José Luis . Martín-Ventura, from CIBERCV and the Autonomous University of Madrid.
“These results are very encouraging if we consider that there is a gap in the availability of treatments for these cardiovascular pathologies. Although there is still a long way to go before this can be applied in patients, our goal is that this research can have therapeutic continuity ,” Rabinovich added.
The mechanisms of action of Gal-1 in the prevention of atherosclerosis
Once it was possible to determine, based on what was observed in humans and animal models, the existence of a link between the decrease in Gal-1 levels and the development of atherosclerosis, the research team aimed to elucidate how –through what mechanisms– this protein is involved in the prevention of pathological vascular remodeling.
Three fundamental mechanisms can be recognized in the development of atherosclerosis. An early mechanism is linked to what is known as the formation of foam cells. This process takes place from an injury to the walls of the endothelium, which allows a series of lipids, mainly cholesterol, to begin to permeate into the artery; To which a response is produced by cells of the immune system – macrophages – that begin to phagocytize the released lipids and take a foamy form. These foam cells deposit on the walls of the arteries, producing an inflammatory process.
A second mechanism is linked to the phenotypic change of the so-called smooth muscle cells, which are vascular cells that line the arteries. In the development of atherosclerosis, these cells change their program, they stop being contractile and begin to become less plastic, more fibrous and proliferative. Upon changing phenotype, smooth muscle cells surround foam cells and further reduce the caliber of the aorta. This is how atheroma plaques form. A third mechanism, the most late, occurs when, in response to the previous two, necrosis begins to occur, that is, significant cell death, and to generate instability in the plaques, with the possibility of them breaking and their contents obstructing other blood vessels.
“The first thing we wanted to study was how Gal-1 could intervene in the prevention of atherosclerosis through modulation of the immune system. Contrary to what we expected, we did not find that there were greater numbers of macrophages in the plaques of Gal-1-deficient mice. However, we observed that the macrophages present were more efficient and phagocytosed more lipids. That is, Gal-1 does not modulate the number of macrophages that respond to the injury, but it does modulate their functionality,” said Rabinovich.
“As we know that Gal-1 plays an immunosuppressive role, we assumed that in its absence the immune system would be more active and recruit more macrophages. But it turned out that the number of cells recruited to respond to the injury was the same, but their capacity to become foam cells was greater,” Pérez-Sáez explained.
Secondly, the researchers wanted to know if Gal-1 also plays a role in atherosclerosis through the modulation of vascular programs, and they were able to determine that Gal-1 has a key role in the phenotypic change experienced by smooth muscle cells.
Through the proteomic study of the aorta of Gal-1-deficient mice, which allows us to detect all the proteins that are deregulated when a gene is deleted (in this case, Gal-1), they saw that the proteins that were most modulated were mitochondrial proteins. “Mitochondria are organelles on which the energy and metabolism of the cell depend, whose function is greatly altered in atherosclerosis,” explained Rabinovich. From this study, it was determined that, through the mitochondrial respiration program, Gal-1 modulates changes in the metabolic functionality of smooth muscle cells.
“This means that Gal 1 plays a dual role in atherosclerosis. On the one hand, it acts as an immunomodulator by preventing the formation of foam cells, but it also inhibits the phenotypic change of smooth muscle cells,” said Rabinovich.
The research also managed to determine the effects that the administration of recombinant Gal-1 has on these mechanisms. “Administration of recombinant Gal-1 to Gal-1-deficient atherosclerotic mice prevented macrophages from phagocytosing lipids and, therefore, the formation of foam cells, but also restored contractility to smooth muscle cells that had changed their phenotype. In other words, the administration of recombinant Gal-1 can reverse, in mice, the atherosclerotic mechanisms that are triggered by the endogenous absence of this protein,” Rabinovich concluded.
When observing what happens in mice with AAA, a pathology whose mechanisms are similar to those of atherosclerosis, although they involve greater protein breakdown (proteolysis), the results were similar.
