No Effect of Ppm1d-Mutant Clonal Hematopoiesis on Atherosclerosis Development in Mice.

BACKGROUND

Clonal hematopoiesis driven by somatic mutations is an emerging cardiovascular risk factor, and the DNA damage response gene PPM1D is among the most frequently mutated genes. Mutations in PPM1D are enriched in cancer patients and survivors, where cytotoxic therapies promote the expansion of mutant clones, a condition termed therapy-related clonal hematopoiesis. Although PPM1D-mutant clonal hematopoiesis has been associated with increased risk and poorer prognosis of atherosclerotic cardiovascular disease in humans, it remains unclear whether these mutations, or their expansion under cytotoxic stress, causally contribute to atherosclerosis.

METHODS

We modeled PPM1D-mutant clonal hematopoiesis in Ldlr-/- mice through bone marrow transplantation strategies. Conventional transplantation approaches were used to generate mice with complete or partial hematopoietic reconstitution by cells carrying monoallelic or biallelic gain-of-function Ppm1dR451X mutations. To mimic therapy-related clonal hematopoiesis, we used a nonconditioned adoptive transfer model in which a small fraction of mutant hematopoietic cells was introduced into recipients, followed by fractionated low-dose γ-radiation to promote clonal expansion. All mice were fed a Western diet to induce atherosclerosis. Clonal dynamics, plaque size and characteristics, and macrophage functions were evaluated using flow cytometry, histopathology, and in vitro assays.

RESULTS

Ppm1d-mutant cells expanded in blood and bone marrow after low-dose radiation, but not in nonirradiated mice. Across all transplantation strategies, Ppm1d mutations did not affect plasma cholesterol, atherosclerotic plaque size, or composition. In vitro, mutant macrophages showed no alterations in proliferation, cytokine expression, or cholesterol handling, although apoptosis in response to genotoxic stress was modestly reduced (≈20%).

CONCLUSIONS

Ppm1d-mutant hematopoietic cells expand predominantly under genotoxic stress and do not promote atherosclerosis in mice under the conditions tested. These findings raise the possibility that the association of PPM1D mutations with atherosclerotic cardiovascular disease may, at least in part, reflect exposure to DNA damage response-activating stressors that independently promote clonal expansion and atherosclerosis, rather than direct causality.