Dissecting intrinsic and extrinsic mechanisms in the clonal expansion of the hematopoietic stem cells in del(5q) MDS
Final Report Abstract
During my postdoctoral research fellowship, I aimed to answer a crucial question: Why do hematopoietic stem cells with a large chromosomal deletion gain a clonal advantage in del(5q) Myelodysplastic Syndrome? To contribute to a better understanding of the disease pathogenesis in del(5q) MDS and to find out how the malignant clone gains an advantage in the bone marrow, represses healthy hematopoiesis and transforms into acute leukemia. I investigated cell intrinsic effects in hematopoietic stem cells (HSC) with haploinsufficiency for candidate genes and cell extrinsic effects through contribution of the bone marrow microenvironment to permitting or driving clonal expansion and leukemic transformation. I used mouse models with conditional haploinsufficiency (~50% downregulation of gene dosage) to systematically investigate haploinsufficiency for genes commonly deleted in del(5q) MDS (Apc, Csnk1a1, Egr1) for their competitive advantage. This was performed in direct competition in one mouse and in co-deletion, using a genetic barcoding approach and validated by classical competitive transplantation assay. This approach led to the following observations on the effect of genetic haploinsufficiency on a clonal level: 1) Csnk1a1 haploinsufficiency provides the greatest clonal advantage of all candidate genes tested, 2) combined Csnk1a1/Egr1 haploinsufficiency does not contribute to further clonal expansion, and 3) inflammation increases the competitive advantage of Csnk1a1 haploinsufficient HSCs. Csnk1a1 haploinsufficiency seems to drive a robust pro-proliferative phenotype by upregulation of Myc targets and Wnt/b-catenin-signaling, which surpasses the clonal expansion potential of Egr1 and Apc haploinsufficiency and is enhanced under environmental stress providing selective pressure. As we and others have hypothesized, this seems to be dependent on hitting the perfect Wnt-signaling dosage. We hypothesized that this proproliferative drive predisposes HSCs to malignant transformation, which is guarded by p53 unless it loses its function in a second-hit event. We modeled the clonal evolution of p53 mutated clones by targeting Trp53 by CRISPR-Cas9 in the background of Csnk1a1 haploinsufficiency. We observed leukemic transformation of murine Csnk1a1 haploinsufficient HSCs with Trp53 mutation, recapitulating a genetical murine model of secondary/therapyrelated AML with del(5q) and Trp53 mutation. Our findings therefore support the crucial role of CSNK1A1 in myeloid disease with del(5q) and its potential as a targetable vulnerability. We observed that Csnk1a1-/+ immature non-committed progenitors showed a characteristic downregulation of HSC-extrinsic mechanisms, such as immune response and inflammatory stress response. We thus hypothesized that Csnk1a1-/+ HSCs are more robust to inflammatory stress, providing a selection advantage over WT cells. We further demonstrated this as Csnk1a1-/+ HSPCs, in direct competition with WT HSPCs, gained a considerable advantage over WT HSPCs under systemic low-dose inflammatory stress over time. We investigated inflammatory stress induced in the microenvironment through alarmin molecules S100A8/S100A9 in other mouse models for Del(5q) MDS, haploinsufficient for Rps14 and miR-145/miR-146a. Furthermore, we observed striking upregulation of S100A8/S100A9 also in murine models for myeloproliferative neoplasms (MPN), other clonal myeloid malignancies of the bone marrow. In summary, I investigated and reported in this project on how cell-intrinsic and extrinsic inflammatory signaling drives pathogenesis in myeloid malignancy, including MDS and MPN.
Publications
- (2021) Heterogeneous bone-marrow stromal progenitors drive myelofibrosis via a druggable alarmin axis. Cell Stem Cell
Leimkühler NB, Gleitz HFE, Ronghui L, Snoeren IAM, Fuchs SNR, Nagai JS, Banjanin B, Lam KH, Vogl T, Kuppe C, Stalmann USA, Büsche G, Kreipe H, Gütgemann I, Krebs P, Banz Y, Boor P, Tai EW, Brümmendorf TH, Koschmieder S, Crysandt M, Bindels E, Kramann R, Costa IG, Schneider RK
(See online at https://doi.org/10.1016/j.stem.2020.11.004) - (2022) Genetic barcoding systematically comparing genes in del(5q) MDS reveals a central role for CSNK1A1 in clonal expansion. Blood Adv.
Stalmann USA, Ticconi F, Snoeren IAM, Li R, Gleitz H, Cowley G, McConkey ME, Wong AB, Schmitz S, Fuchs SNR, Sood S, Leimkühler NB, Martinez-Høyer S, Banjanin B, Root DE, Brümmendorf TH, Pearce J, Schuppert A, Bindels E, Essers M, Heckl D, Stiehl TP, Costa IG, Ebert BL, Schneider RK
(See online at https://doi.org/10.1182/bloodadvances.2021006061) - (2022) Single cell analysis of cultured bone marrow stromal cells reveals high similarity to fibroblasts in situ. Exp. Hematology
Stalmann USA, Banjanin B, Snoeren IAM, Nagai JS, Leimkühler NB, Li R, Benabid A, Pritchard J, Malyaran H, Neuss S, Bindels E, Costa IG, Schneider RK
(See online at https://doi.org/10.1016/j.exphem.2022.03.010)
