Periodic Reporting for period 3 - EXPLOSIA (EXpansion and Phenotype Loss Of SMCs In Atherosclerosis: Causal effects and therapeutic possibilities)
Reporting period: 2023-08-01 to 2025-01-31
Atherosclerosis is a major constraint to living long and healthy lives in modern societies. It is a chronic disease caused by the accumulation of low-density lipoproteins (LDLs) in the arterial intima, which induces plaque development with progressive accumulation of macrophages, smooth muscle cells (SMCs), fibrous tissue, calcifications, and necrotic debris. After decades of silent development, plaques with necrosis that reach the luminal surface may suddenly rupture, precipitate thrombosis, and cause heart attack or stroke. These complications underlie almost 1/3 of all deaths in the world, and this number is projected to increase as increasing life span puts larger parts of the global population at risk.
Current therapies against atherosclerosis lower LDL and blood pressure, but even optimal current medical therapy is insufficient to completely halt the disease. There is therefore an urgent need to identify alternative targets for anti-atherosclerotic therapy.
In EXPLOSIA, we explore disease mechanisms carried by smooth muscle cells (SMCs) in atherosclerosis. We and others have uncovered a large population of SMCs in plaques, which has escaped detection because the cells completely lose the conventional SMC phenotype. Strikingly, we have found that the entire plaque SMC population derives from only a few founder SMCs that undergo massive clonal expansion and phenotypic modulation during lesion formation. We hypothesize that the balance between the different modulated SMC subtypes and the functions they carry are central to lesion progression.
We address this hypothesis in 3 steps. First, we determine links between SMC subtypes, their gene expression programs, and atherosclerotic disease activity by combining single-cell transcriptomics with novel techniques to alter atherosclerotic disease activity in gene-modified mice and minipigs. Second, we will develop techniques for manipulating genes in modulated plaque SMCs and test the causal role of perturbing SMC subtypes and function for lesion progression. Third, we conduct a comparative analysis of clonal structure in mice, minipigs, and humans.
Current therapies against atherosclerosis lower LDL and blood pressure, but even optimal current medical therapy is insufficient to completely halt the disease. There is therefore an urgent need to identify alternative targets for anti-atherosclerotic therapy.
In EXPLOSIA, we explore disease mechanisms carried by smooth muscle cells (SMCs) in atherosclerosis. We and others have uncovered a large population of SMCs in plaques, which has escaped detection because the cells completely lose the conventional SMC phenotype. Strikingly, we have found that the entire plaque SMC population derives from only a few founder SMCs that undergo massive clonal expansion and phenotypic modulation during lesion formation. We hypothesize that the balance between the different modulated SMC subtypes and the functions they carry are central to lesion progression.
We address this hypothesis in 3 steps. First, we determine links between SMC subtypes, their gene expression programs, and atherosclerotic disease activity by combining single-cell transcriptomics with novel techniques to alter atherosclerotic disease activity in gene-modified mice and minipigs. Second, we will develop techniques for manipulating genes in modulated plaque SMCs and test the causal role of perturbing SMC subtypes and function for lesion progression. Third, we conduct a comparative analysis of clonal structure in mice, minipigs, and humans.
During the first part of EXPLOSIA, we have obtained a comprehensive map of associations between disease activity and gene expression profiling in SMCs in mice and minipig models (see attached image). This has been achieved using techniques (scRNA-seq) that can measure the expression level of thousands of genes concurrently in single cells harvested from murine and porcine plaques. By integrating public data from human atherosclerosis, we have confirmed that many genes regulated with disease activity in SMCs in our experimental models are also expressed in human plaque SMCs. We have also found that disease-associated activity differs between different SMC subtypes opening avenues for selected targeting of specific types of SMCs and their function. Some of these data have been published as an abstract and they are under preparation for publication and sharing in open data repositories.
Furthermore, we are currently targeting several candidate genes in SMCs stemming from our analysis to explore their causal role in disease development and whether they can function as targets for therapy. This is explored in mouse models where we can selectively delete selected genes in SMCs and SMC-derived cells and study the impact on atherosclerotic lesion development. Finally, we are developing new tools for interrogating clonal relationships among cells in human tissues. If they stand final validation, they will offer new possibilities to understand differences and similarities between SMC behavior in our experimental and human atherosclerosis.
Furthermore, we are currently targeting several candidate genes in SMCs stemming from our analysis to explore their causal role in disease development and whether they can function as targets for therapy. This is explored in mouse models where we can selectively delete selected genes in SMCs and SMC-derived cells and study the impact on atherosclerotic lesion development. Finally, we are developing new tools for interrogating clonal relationships among cells in human tissues. If they stand final validation, they will offer new possibilities to understand differences and similarities between SMC behavior in our experimental and human atherosclerosis.
The project delivers data sets and insights into SMCs that will be important for therapeutic strategies to target SMCs in atherosclerosis and potentially other types of SMC-driven disease. In the second part of EXPLOSIA, we test several such targets for therapy in SMCs that can potentially ameliorate disease. Furthermore, we study whether different risk factors (LDL and blood pressure) induce different types of disease activity in plaques. The goal is to deliver a list of potential targets for therapy in plaque SMCs.
Furthermore, we expect the project to deliver new tools for biomedical research in atherosclerosis and beyond. One is an experimental model in mice allowing genes to be deleted across the entire SMC population in established plaques, which is not currently possible. Another is a new analysis technique to understand clonal relationships between cells in human tissues. Apart from providing new insight into the mechanisms by which SMCs accumulate in human atherosclerosis, this method could have applications in other medical fields, such as cancer.
Finally, the project is the training ground for several upcoming and talented young scientists.
Furthermore, we expect the project to deliver new tools for biomedical research in atherosclerosis and beyond. One is an experimental model in mice allowing genes to be deleted across the entire SMC population in established plaques, which is not currently possible. Another is a new analysis technique to understand clonal relationships between cells in human tissues. Apart from providing new insight into the mechanisms by which SMCs accumulate in human atherosclerosis, this method could have applications in other medical fields, such as cancer.
Finally, the project is the training ground for several upcoming and talented young scientists.