Ppm1d Clonal Hematopoiesis Does Not Promote Atherosclerosis in Murine Models

Clonal hematopoiesis (CH) is an age-associated condition common in the elderly that arises when hematopoietic stem cells acquire somatic mutations in an assortment of genes, most commonly DNMT3A, TET2, ASXL1, PPM1D, and JAK2. CH is associated with increased coronary artery disease and all-cause mortality. Epidemiological studies have revealed that different CH driver mutations are associated with unique outcomes. PPM1D CH is more prevalent in patients following radiation and cytotoxic therapy. PPM1D CH has been strongly associated with coronary artery disease, peripheral artery disease, and all-cause mortality. However, it is unclear if this relationship is causative.

We tested the ability of Ppm1d mutations to promote atherosclerosis in mice. To model Ppm1d CH, we transplanted a mixture of 20% bone marrow from mice expressing Ppm1d T476* truncation mutation under the control of an Scl-Cre and 80% wild-type bone marrow into Ldlr^-/- recipient mice and subjected them to atherosclerosis studies. In parallel, Scl-Cre-driven Ppm1d T476* mutations were introduced into Apoe^-/- mice for atherosclerosis studies. To examine the interaction between DNA damage and Ppm1d, we transplanted bone marrow with Ppm1d mutations restricted to monocyte/macrophage or pan-hematopoietic expression of Ppm1d T476* into Ldlr^-/- mice. Cisplatin was administered after the establishment of atherosclerosis, and lesion burden and inflammasome activation were quantified.

We found that in vitro Ppm1d mutant macrophages have increased AIM2 (absent in melanoma 2) inflammasome activation and increased inflammasome activation in response to cisplatin. However, in vivo, we found no evidence of elevated inflammasome activation in plaques. Across both Ldlr and Apoe knockout models, hematopoietic Ppm1d mutations did not promote atherosclerosis. Furthermore, Ppm1d mutations did not exacerbate atherosclerosis following administration of cisplatin.

These findings indicate that in murine models, Ppm1d mutations are not sufficient to promote atherosclerosis, suggesting that the epidemiological association between PPM1D CH and coronary artery disease may not be due to changes in plaque development.