<i>Tet2</i> and <i>Jak2</i> clonal hematopoiesis do not modify murine tauopathy

Background Clonal hematopoiesis (CH) increases with age and elevates the risk of numerous age-associated diseases. However, the association between CH and neurodegenerative diseases has remained unclear. Objective We tested the association between the presence of CH and tauopathy in a murine model. Methods We established novel models of Tet2 loss-of-function and Jak2 gain-of-function (V617F) CH in CD45.1-expressing PS19 tauopathy mice using unconditioned bone marrow (BM) cell transfer, thereby maintaining brain integrity, clonal expansion, and enabling mutant cell tracking. Results In CD45.1- PS19 mice, Tet2 -/- cells (CD45.2) started at a fraction of &lt;2% and clonally expanded in all BM cavities and the blood over 5 months. Tet2 mutant and WT immune cells, however, displayed equivalently low capacity to infiltrate the brain of PS19 mice even with advanced tau deposition. While Tet2 mutant microglia displayed elevated IL1-β production, they comprised a small fraction (3.49 ± 1.35%) relative to the high frequency of mutant monocytes in the blood (26.36 ± 4.33%) of aged CD45.1- PS19 mice after clonal expansion. Jak2 V617F cells (CD45.2) also expanded clonally in the BM and blood over time and had a modestly increased capacity to infiltrate the brain of aged CD45.1- PS19 mice but their proportion among brain microglia remained low (1.12 ± 0.28%) relative to blood monocytes (28.91 ± 4.66%). Critically, Tet2 or Jak2 CH did not alter tau accumulation in the hippocampus or cortex, nor did they influence brain atrophy. Conclusions Our findings suggest that CH mutant cells do not influx the murine tauopathy brain in large proportions and that CH does not modify neurodegeneration or tau accumulation in mice.