Hematopoietic mutations in epigenetic regulators like DNA methyltransferase 3 alpha (DNMT3A), play a pivotal role in driving clonal hematopoiesis of indeterminate potential (CHIP), and are associated with unfavorable outcomes in patients suffering from heart failure (HF). However, the precise interactions between CHIP-mutated cells and other cardiac cell types remain unknown. Here, we identify fibroblasts as potential partners in interactions with CHIP-mutated monocytes. We used combined transcriptomic data derived from peripheral blood mononuclear cells of HF patients, both with and without CHIP, and cardiac tissue. We demonstrate that inactivation of DNMT3A in macrophages intensifies interactions with cardiac fibroblasts and increases cardiac fibrosis. DNMT3A inactivation amplifies the release of heparin-binding epidermal growth factor-like growth factor, thereby facilitating activation of cardiac fibroblasts. These findings identify a potential pathway of DNMT3A CHIP-driver mutations to the initiation and progression of HF and may also provide a compelling basis for the development of innovative anti-fibrotic strategies.

Both fatty bone marrow (FBM) and somatic mutations in hematopoietic stem cells (HSCs), also termed clonal hematopoiesis (CH) accumulate with human aging. However it remains unclear whether FBM can modify the evolution of CH. To address this question, we herein present the interaction between CH and FBM in two preclinical male mouse models: after sub-lethal irradiation or after castration. An adipogenesis inhibitor (PPARγ inhibitor) is used in both models as a control. A significant increase in self-renewal can be detected in both human and rodent DNMT3A^Mut-HSCs when exposed to FBM. DNMT3A^Mut-HSCs derived from older mice interacting with FBM have even higher self-renewal in comparison to DNMT3A^Mut-HSCs derived from younger mice. Single cell RNA-sequencing on rodent HSCs after exposing them to FBM reveal a 6-10 fold increase in DNMT3A^Mut-HSCs and an activated inflammatory signaling. Cytokine analysis of BM fluid and BM derived adipocytes grown in vitro demonstrates an increased IL-6 levels under FBM conditions. Anti-IL-6 neutralizing antibodies significantly reduce the selective advantage of DNMT3A^Mut-HSCs exposed to FBM. Overall, paracrine FBM inflammatory signals promote DNMT3A-driven clonal hematopoiesis, which can be inhibited by blocking the IL-6 pathway.

Microglia are established in embryogenesis forming a self-containing cellular compartment resisting seeding with cells derived from adult definitive hematopoiesis. We report that monocyte-derived macrophages (MoMΦ) accumulate in the brain of aging mice with distinct topology, including the nigrostriatum and medulla, but not the frontal cortex. Parenchymal MoMΦ adopt bona fide microglia expression profiles. Unlike microglia, these monocyte-derived microglia (MoMg) are due to their hematopoietic origin targets of clonal hematopoiesis (CH). Using a chimeric transfer model, we show that hematopoietic expression of DNMT3A ^R822H , a prominent mutation in human CH, renders MoMg pathogenic promoting motor deficits resembling atypical Parkinsonian disorders. Collectively, these data establish in a mouse model that MoMg progressively seed the brains of aging healthy mice, accumulate in selected areas, and, when carrying a somatic mutation associated with CH, can contribute to brain pathology.

The limbus of the eye is the location of the corneal epithelial stem cell niche. These cells are necessary for continuous renewal of the corneal epithelium. In the case of limbal stem cell deficiency, these cells are damaged, and the whole cornea becomes opaque. It is important to be able to identify stem cells that could be applied for new therapeutic strategies. There are various known markers to characterize these cells, including p63, Nanog, oct4 and FGFR2. However, none of these markers are exclusively expressed in these stem cells (they are also expressed in transient amplified cells). It seems likely that a combination of stem cell markers will be necessary for corneal stem cell identification. The aim of this study was to detect IRF8 in limbal epithelial stem cells and to determine its function. In a mouse model, IRF8 could be detected in limbal and basal epithelial cells of the cornea by histological and immunohistological staining of wild-type mouse eyes. Furthermore, the limbus of the eye was significantly smaller in IRF8-knockout mice than in wild-type mice, and the expression of Nanog was lower in IRF8-knockout mice. This suggests that IRF8 has an influence on the maintenance of stem cell properties in the limbus, possibly by affecting the expression of Nanog. Furthermore, IRF8 has an impact on E-cadherin and N-cadherin expression in the mouse eye.