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MAT mediates metabolic stress in HSPC
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Figure 4. High-fat diet (HFD)-stressed hematopoiesis in control and Adipoq-Cre+;Kitlfl/fl male mice. (A and B) Kitlfl/fl and Adipoq-Cre+;Kitlfl/fl male mice at the age of eight weeks were fed with normal chow (NC) or HFD (n=3-4) for another eight weeks. (A) Representative images of femur sections. (B) Quantification of adipocyte numbers in the BM from the growth plate to 4.5 mm away distally. (C-I) 8-week old Kitlfl/fl (n=6 for each diet) and Adipoq-Cre+;Kitlfl/fl (n=8 for NC and n=6 for HFD) male mice were fed with NC or HFD for eight weeks. BM cellularity (C), LSK number (D), GMP number (E), CLP number (F), CMP number (G), MEP number (H), and the MEP/GMP ratio (I) were determined by flow cytometry. (J-N) Complete blood count of NC- and HFD-fed Kitlfl/fl (n=16 and 13, respectively) and Adipoq-Cre+;Kitlfl/fl (n=12 and 6, respectively) male mice showing granulocyte number (J), monocyte number (K), lymphocyte number (L), megakaryocyte-erythrocyte (MkE) to granulo- cyte-monocyte (GrMo) ratio (M), and the ratio of lymphocyte to all myeloid cells including MkE and GrMo (N). Data are presented as mean±Standard Deviation. *P<0.05; **P<0.01; ***P<0.001 by two-way ANOVA followed by multiple comparison using Tukey's correction (B) or Sidak correction (C-N).
strate that adipocyte-derived niche factor SCF is essential for the maintenance of hematopoietic stem and myeloid progenitor cells.
We then performed the complete blood count test of the peripheral blood. Levels of red blood count (RBC), hemo- globin concentration (HGB), and hematocrit were all decreased in both male and female Adipoq-Cre+;Kitlfl/fl mice when compared to Kitlfl/fl controls (Table 1). The mean cor- puscular volume (MCV) and the count of reticulocytes were both significantly increased in Adipoq-Cre+;Kitlfl/fl mice (Table 1), showing that Adipoq-Cre+;Kitlfl/fl mice devel- oped the typical macrocytic anemia that is observed in animals and patients with loss-of-function mutations in the SCF/KIT pathway.35,36,43 Meanwhile, Adipoq-Cre+;Kitlfl/fl mice also had less platelets compared to control mice (Table 1). Within white blood cells, neutrophils, mono- cytes, and lymphocytes reduced their number in both sexes, while eosinophils and basophils were significantly
declined in male Adipoq-Cre+;Kitlfl/fl mice and showed a trending reduction in female Adipoq-Cre+;Kitlfl/fl mice (Table 1). Taken together, these data from both male and female mice indicate that adipocytes compose a niche that pro- duce SCF to maintain unperturbed hematopoiesis.
Ablation of stem cell factor in Osterix+ cells impairs hematopoiesis
Adipoq-Cre-mediated ablation deleted SCF in all adipose tissues. To exclude the potential confounding effect of SCF from peripheral adipose tissues, we then conditional- ly deleted the Kitl gene in BM stroma cells using the Osterix (Osx1)-Cre, which marks progenitor cells that can be differentiated into MAT.24-26 Loss of SCF in Osx1+ cells resulted in lower BM cellularity (Figure 3A) and drastically reduced populations of LSK, phenotypic LT-HSC, MP, CMP, GMP, MEP, and CLP in Osx1-Cre+;Kitlfl/fl mice (Figure 3B). Such reductions were much larger than those
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