Inflammatory Signaling Mediated By Gasdermin D Underlies Tet2-Mutant Clonal Hematopoiesis-Associated Tissue Dysfunction

Aging is characterized by the progressive accumulation of somatic mutations. Acquisition of certain somatic mutations in hematopoietic stem cells (HSCs) confers on them a fitness advantage enabling them to outcompete other HSCs by clonal expansion in a phenomenon called clonal hematopoiesis (CH). CH is associated with a 40% increase in all-cause mortality linked to elevated risk for aging-associated morbidities such as cardiovascular disease (CVD), chronic kidney disease, COPD, and chronic liver disease. However, the mechanism by which CH exerts its adverse effects on disparate tissues is poorly understood. Here, we use CH-associated cardiac dysfunction as a paradigm to uncover general principles by which CH leads to the decline of tissue function.

CH was modeled in mice by transplanting whole bone marrow (WBM) cells deficient for Tet2, a frequently mutated CH gene, into irradiated WT mice. We observed an elevated incidence of atrial fibrillation (AF) in Tet2^–/– WBM recipients relative to WT WBM recipients without any surgical or dietary intervention (Fig. A). The Tet2^–/– WBM recipients also had reduced left ventricular ejection fraction (LVEF), an indicator of heart failure. Mice exhibiting elevated incidence of AF and reduced LVEF are defined as having cardiac dysfunction. In addition, we observed that Tet2^–/– WBM recipients had increased systemic inflammation compared to controls, as evidenced by elevated levels of proinflammatory cytokines in the serum. Furthermore, their cardiac tissue exhibited upregulation of the inflammasome signaling pathway including the activation of Gasdermin D, the effector of pyroptotic cell death. Inflammation in the cardiac tissue was concomitantly associated with increased cardiac fibrosis in Tet2^–/– WBM recipients.

Since inflammation is a known driver of CVD, we hypothesized that abrogating Gasdermin D-mediated inflammatory signaling could ameliorate CH-induced cardiac dysfunction. Indeed, Gsdmd^–/– recipient mice were protected from cardiac dysfunction upon transplantation with Tet2^–/– WBM cells (Fig. A). Importantly, expansion of mutant hematopoietic cells was also mitigated in the absence of GSDMD: transplantation of Tet2^–/– WBM cells along with either WT or Gsdmd^–/– WBM cells revealed that GSDMD deficiency restrained the rate of clonal expansion of Tet2^–/– cells (Fig. B). This suggests that instead of being mere bystanders, WT cells in the environment may play an active role in regulating the rate of mutant cell expansion via intercellular communication mediated by GSDMD.

Identification of proinflammatory factors mediating clonal expansion and cardiac dysfunction is of significant interest for potential therapeutic intervention. Thus, we sought to determine factors that were upregulated in CH mouse models while being downregulated in Gsdmd^–/– mice. Luminex multiplexed assay enabled us to identify several understudied proinflammatory cytokines present in serum satisfying the above criteria. In addition to elevated levels in the serum, some of these cytokines were upregulated in the cardiac tissue of Tet2^–/– WBM recipient mice but not in WT WBM recipients. Furthermore, some are reported to induce inflammasome signaling.

CH, even in the absence of known drivers, is associated with higher CVD-associated mortality, suggesting the existence of pathways common to multiple forms of CH; systemic inflammation is one potential common mechanism. We tested whether aged WT WBM, which has low levels of mutant clone expansion but exhibits several features of CH, could cause cardiac dysfunction. We transplanted either aged or young WT WBM into young WT recipients and found that the aged WT WBM recipients exhibited elevated AF and reduced LVEF. These data suggest that aging-associated systemic inflammation may be sufficient for cardiac dysfunction.

Importantly, one of the cytokines we uncovered was also upregulated in aged WT mice and has been associated with inflammation and fibrosis in multiple tissues. This cytokine is being further investigated as a top candidate for therapeutic intervention since it is a common feature of CH with and without identified drivers.

Overall, our findings demonstrate the critical role of Gasdermin D-mediated inflammatory signaling in the pathogenesis of Tet2-mutant CH-induced cardiac dysfunction. We have also uncovered a cytokine that has emerged as a promising therapeutic target for CH-associated pathologies.