Tet2 Deficiency in Macrophages Undermines Heart Repair after Infarction
Authors: Fang Shaohai , Xiao Yang , Li Jia , Li Tingting , Zeng Hongxiang , Han Wei , Zhou Yubin , Sun Deqiang , Martin James M. , Huang Yun 
Published: October 2019

Abstract
Background: Clonal hematopoiesis of indeterminate potential (CHIP) is often observed during aging[1]. CHIP is characterized by a clonal expansion of subset blood-cell clones without other hematological abnormalities. Recent studies reported a strong connection between CHIP and cardiovascular disease (CVD). Individuals with mutations in epigenetic regulators (e.g., DNMT3A, TET2, ASXL1 and JAK2) have a higher risk for CVD[2]. In vivo studies using mouse models confirmed that Tet2-deficient HSPCs exhibited clonal expansion. Furthermore, mice transferred with Tet2-deficient HSPCs showed increased risk of atherosclerosis and worse outcome after permanent left anterior descending artery (LAD) ligation induced myocardial infarction (MI)[3,4]. Macrophages were found to be one of the most affected cell types in Tet2 deficient hematopoietic system associated with increased CVD risk[3,4]. Tet2 deficiency in macrophages is known to cause aberrant innate immune response[5]. Tet2 knockout (KO) macrophages provide a protective microenvironment to prevent melanoma progression[6], suggesting the pivotal role of Tet2 in regulating macrophage function in different context. In this study, we aim to dissect the molecular mechanism on how Tet2 deficiency disrupts normal macrophage function during heart repair.
Methods: We crossed Tet2f/f mice with lysMCre mice to yield macrophage specific Tet2 deficient mice (Tet2f/f-lysMCre). We performed LAD ligation in Tet2f/f-lysMCre mice to induce MI. Age and gender matched lysMCre mice were used as controls. Cardiac function was monitored by echocardiogram every week after MI for 4 weeks. Then we sacrificed mice and performed histological analysis to evaluate heart damage and repairs in lysMCre and Tet2f/f-lysMCre mice. During the course of the experiments, we collected peripheral blood and bone marrows to examine the impact of Tet2 loss on macrophages in response to heart damage and repair. In parallel, we also collected heart tissue from lysMCre and Tet2f/f-lysMCre mice at 1 and 4 weeks after LAD ligation followed by single-cell RNA-seq analysis to further dissect the underlying molecular mechanism.
Results: Prior to MI, no significant difference in heart function and macrophage numbers were observed between lysMCre and Tet2f/f-lysMCre mice at the age of 6-8 weeks old. Upon LAD-induced MI, we observed worse heart function in Tet2f/f-lysMCre mice compared to lysMCre mice. Tet2f/f-lysMCre mice showed ~40% reduction in ejection fraction and ~50% decrease in fraction shortening compared to lysMCre mice (n = 15). Further histological analysis revealed >2-fold increase in scar areas and infarcted areas in Tet2f/f-lysMCre compared to lysMCre mice. Single cell analysis confirmed a substantial increase of the fibroblast population in Tet2f/f-lysMCre mice upon LAD ligation. Furthermore, we also observed altered expression of a large fraction of genes related to macrophage activation and tissue repair capability, suggesting that Tet2 plays important roles in regulating macrophages function within damaged heart tissues. Further epigenomic analysis on sorted cardiac-specific macrophages is anticipated provide more valuable mechanistic information.
Conclusion: Taken together, our data suggest that Tet2 deficient macrophages play an important role during heart damage and repair. Inactivation mutations of TET2 detected in CHIP patients might lead to impaired macrophage function during heart damage and therefore increase the CVD risk.
References
1. Jaiswal, S., Fontanillas, P., Flannick, J. et al. (2014). N Engl J Med 371, 2488-2498.
2. Jaiswal, S., Natarajan, P., Silver, A. J. et al. (2017). N Engl J Med 377, 111-121.
3. Fuster, J. J., MacLauchlan, S., Zuriaga, M. A. et al. (2017). Science 355, 842-847.
4. Sano, S., Oshima, K., Wang, Y. et al. (2018). J Am Coll Cardiol 71, 875-886.
5. Zhang, Q., Zhao, K., Shen, Q. et al. (2015). Nature 525, 389-393.
6. Pan, W., Zhu, S., Qu, K. et al. (2017). Immunity 47, 284-297 e285.

Disclosures
No relevant conflicts of interest to declare.