Non-preferential, but detrimental accumulation of macrophages with clonal hematopoiesis-driver mutations in cardiovascular tissues
Authors: Dederichs T , Yerdenova A , Horstmann H , Nuebling S , Kohl P , Wolf D , Westermann D , Hilgendorf I 
Published: November 2023

Abstract

Background
Clonal hematopoiesis of indeterminate potential (CHIP) is an acquired genetic risk factor of cardiovascular (CV) disease transmitted by myeloid cells. Harboring CHIP is associated with higher risk of coronary artery disease and worse prognosis of congestive heart failure. Studies show that circulating monocytes of CHIP carriers are more pro-inflammatory than those of non-carriers, but to what extend mutant monocytes and their progenies accumulate in the tissue of CV lesions remains unknown. First, we aimed to identify the frequencies of mutant macrophages in human carotid plaque and heart tissues relative to those of mutant monocytes in the patients’ blood. Second, we compared the gene expression profiles of circulating and tissue myeloid cells of CHIP carriers with those from non-carriers.

Methods
We recruited patients undergoing carotid endarterectomy and aortic valve replacement. Blood and CV tissue (carotid plaque or right atrium appendix) of patients who provided study consents were retrieved during the surgeries and immediately processed for the isolation of lymphocytes and myeloid cells. Whole blood DNA was subjected to CHIP mutation screening.
DNA and RNA of eight DNMT3A or TET2 mutation carriers and eight matched non-carriers were isolated from sorted cells. We measured the frequencies of CHIP mutations in each sorted cell type using a droplet-digital PCR method. RNA of the sorted myeloid cells from the carriers and matched non-carriers were subjected to RNA sequencing.

Results
Our data showed that CHIP-mutant monocytes in the blood is similar to that of CHIP-mutant macrophages in both the plaque (ratio versus monocytes =1.2, p=0.44) and the heart (ratio versus monocytes=0.89, p=0.47), suggesting a comparable ability of mutant and non-mutant monocytes to accumulate in the cardiovascular lesions. Near absence of CHIP clones in lymphocytes (ratio versus monocytes=0.06, p&lt;0.0001) confirmed the myeloid skewing driven by DNMT3A or TET2 mutations. Unexpectedly, we detected similar size of CHIP clones in CCR2-positive and CCR2-negative cardiac macrophages (ratio=0.95, p=0.77), challenging the current paradigm that CCR2-negative cardiac macrophages represent a resident population with minimal monocyte contribution.
Transcriptomic profiles of blood and tissue monocytes/macrophages from these carriers were distinct from those of eight matched non-carriers, featuring differentially up-regulated cytokines (eg. IL1B, S100A9) and chemokines (eg. CXCL1, CCL3) in cells from the carriers. Myeloid cells from the carriers up-regulated genes enriching pathways related to immune activation and inflammation.

Conclusion
Our study manifested the presence of pro-inflammatory CHIP-mutant myeloid cells in human plaque and heart tissues. The equivalent size of CHIP clones in the circulation and tissue suggests a comparable ability of mutant and non-mutant monocytes to accumulate in CV lesions, but inflammation may mediate CHIP-associated CV diseases.