Mutant Samd9l expression impairs hematopoiesis and induces bone marrow failure in mice
Sherif Abdelhamed, Melvin E. Thomas III, Tamara Westover, Masayuki Umeda, Emily Xiong, Chandra Rolle, Michael P. Walsh, Huiyun Wu, Jason R. Schwartz, Virginia Valentine, Marcus Valentine, Stanley Pounds, Jing Ma, Laura J. Janke, Jeffery M. Klco
Sherif Abdelhamed, Melvin E. Thomas III, Tamara Westover, Masayuki Umeda, Emily Xiong, Chandra Rolle, Michael P. Walsh, Huiyun Wu, Jason R. Schwartz, Virginia Valentine, Marcus Valentine, Stanley Pounds, Jing Ma, Laura J. Janke, Jeffery M. Klco
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Research Article Hematology

Mutant Samd9l expression impairs hematopoiesis and induces bone marrow failure in mice

Abstract

SAMD9 and SAMD9L germline mutations have recently emerged as a new class of predispositions to pediatric myeloid neoplasms. Patients commonly have impaired hematopoiesis, hypocellular marrows, and a greater risk of developing clonal chromosome 7 deletions leading to MDS and AML. We recently demonstrated that expressing SAMD9 or SAMD9L mutations in hematopoietic cells suppresses their proliferation and induces cell death. Here, we generated a mouse model that conditionally expresses mutant Samd9l to assess the in vivo impact on hematopoiesis. Using a range of in vivo and ex vivo assays, we showed that cells with heterozygous Samd9l mutations have impaired stemness relative to wild-type counterparts, which was exacerbated by inflammatory stimuli, and ultimately led to bone marrow hypocellularity. Genomic and phenotypic analyses recapitulated many of the hematopoietic cellular phenotypes observed in patients with SAMD9 or SAMD9L mutations, including lymphopenia, and pinpointed TGF-β as a potential targetable pathway. Further, we observed nonrandom genetic deletion of the mutant Samd9l locus on mouse chromosome 6, mimicking chromosome 7 deletions observed in patients. Collectively, our study has enhanced our understanding of mutant Samd9l hematopoietic phenotypes, emphasized the synergistic role of inflammation in exaggerating the associated hematopoietic defects, and provided insights into potential therapeutic options for patients.

Authors

Sherif Abdelhamed, Melvin E. Thomas III, Tamara Westover, Masayuki Umeda, Emily Xiong, Chandra Rolle, Michael P. Walsh, Huiyun Wu, Jason R. Schwartz, Virginia Valentine, Marcus Valentine, Stanley Pounds, Jing Ma, Laura J. Janke, Jeffery M. Klco

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Figure 3

Impaired ex vivo and in vivo fitness of Samd9l-mutant cells.

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Impaired ex vivo and in vivo fitness of Samd9l-mutant cells. (A and B) S...
(A and B) Serial colony-forming unit cell (CFU-C) analysis of Lin– cells from C57BL/6, Samd9l-KO, Samd9l-WT, and Samd9l-Mut mice. (A) Cells were plated (3,000 cells/plate) in methylcellulose media. One week later, colonies were counted and serially replated (10,000 cells/plate) for a total of 3 rounds. (B) The number of colonies in the weekly replates. (C) Schematic illustration of the competitive transplantation model. Lin– cells from CD45.2 (C57BL/6, Samd9l-KO, Samd9l-WT, or Samd9l-Mut cells) and CD45.1 (wild-type competitor) were injected i.v. at a 1:1 ratio via tail vein into lethally irradiated CD45.1/CD45.2 mice. (D) CD45.2 chimerism in the PB of recipient animals (n ≥ 12 per group) from 0 to 8 weeks. (E) Intrafemoral (i.f.) competitive transplantation scheme. Lin– cells from CD45.2 (Samd9l-WT or Samd9l-Mut cells) and CD45.1 (wild-type competitor) were injected at a 1:1 ratio into the femurs of lethally irradiated CD45.1/CD45.2 mice. (F) CD45.2 chimerism in the PB of recipient animals in E (n ≥ 8 per group). Time is denoted in weeks after injections. A longitudinal mixed-effects regression model was used for statistical analysis. Initially, a global test of whether all 4 groups had the same longitudinal trend was performed. A significant result from this global test was followed by pairwise tests evaluating the equality of trends over time for the 2 groups. ***P < 0.001. Error bars indicate the SEM for biological replicates. Gray, C57BL/6; blue, Samd9l-KO, black, Samd9l-WT; red, Samd9l-Mut.