Page 60 - 2019_09-HaematologicaMondo-web

Z. Zhang et al.
observed in Adipoq-Cre+;Kitlfl/fl mice (Figure 2), suggesting that SCF from non-MAT, Osx1-Cre-derived niche cells also contributed to HSPC defects in Osx1-Cre+;Kitlfl/fl mice. Interestingly, heterozygous Osx1-Cre+;Kitlfl/+ mice also had decreased BM cellularity and frequencies of all HSPC (Figure 3A and B), suggesting the haploinsufficiency of SCF in hematopoietic regulation. Similar to findings in Adipoq-Cre+;Kitlfl/fl mice, the MEP/GMP ratio was reduced (Figure 3C) and the CMP/CLP ratio showed a trending decrease (Figure 3D). As a result, Osx1-Cre+;Kitlfl/fl mice suf- fered macrocytic anemia (Figure 3E). Furthermore, there were fewer platelets, neutrophils, and monocytes in Osx1- Cre+;Kitlfl/fl mice (Figure 3E). Counts of eosinophils, basophils, and lymphocytes were similar between control and Osx1-Cre+;Kitlfl/fl mice (Figure 3E). BM cells from Osx1- Cre+;Kitlfl/fl KO mice could efficiently form CFU as wild- type controls (Figure 3F). suggesting defects in the niche environment not intrinsically in HSPC as a result of loss of adipose SCF. However, splenomegaly and profoundly increased CFU formation of splenic cells were observed in Osx1-Cre+;Kitlfl/fl mice (Figure 3G and H), demonstrating a shift of hematopoiesis toward the spleen. Taking data from Adipoq-Cre- and Osx1-Cre-mediated knockout mice, we argue that, in the steady-state, SCF from MAT is essential for homeostasis of hematopoietic progenitors.
MAT-derived stem cell factor contributes to stressed hematopoiesis in obesity
Obesity is associated with increased MAT mass and altered hematopoietic and immune functions. We then asked whether MAT-derived SCF mediates the effect of high-fat diet (HFD) on hematopoiesis. Male Kitlfl/fl and Adipoq-Cre+;Kitlfl/fl mice gained similar body weight after HFD feeding for eight weeks (Online Supplementary Figure S6A). HFD significantly increased BM adiposity and cellu- larity, which could be slightly diminished by the loss of adipose SCF (Figure 4A-C). We did not observe any changes in Kitl gene expression or SCF secretion after HFD in the BM (Online Supplementary Figure S6B and C), indicat- ing a potential compensation from non-adipocytes. Future experiments are required to determine SCF expression by different stroma cells during HFD. Flow cytometric assess- ment of HSPC showed that numbers of LSK, GMP, and CLP progenitors in wild-type male mice were increased after HFD (Figure 4D-F). Such induction was completely blunted in Adipoq-Cre+;Kitlfl/fl males (Figure 4D-F). It is pos- sible that other yet-to-be defined factors mediate the expansion of HSPC in response to HFD, but their com- plete function requires MAT-secreted SCF. Even though HFD did not affect numbers of CMP or MEP (Figure 4G and H), there was a reduction in the ratio of MEP to GMP (Figure 4I). The MEP/GMP ratio was lower in Adipoq- Cre+;Kitlfl/fl males and could not be further reduced by HFD (Figure 4I). Consistent with the changes of HSPC in the BM, there was an increase in the number of granulocytes, monocytes, and lymphocytes in the peripheral blood of wild-type males after HFD (Figure 4J-L). The ratio of megakaryocyte (represented by platelet)-erythrocyte (MkE) to granulocyte-monocyte (GrMo) was down-regu- lated (Figure 4M), while the ratio of lymphocytes to all myeloid cells was up-regulated by HFD (Figure 4N). These data suggest that HFD preferentially promotes the hematopoietic differentiation toward the GrMo and lym- phoid lineages, which may contribute to the development of inflammation and insulin resistance in obesity. In the
peripheral blood of Adipoq-Cre+;Kitlfl/fl male mice, however, HFD could not increase the number of granulocytes, monocytes or lymphocytes to the extent observed in Kitlfl/fl males (Figure 4J-L). HFD-induced downregulation of MkE/GrMo ratio and upregulation of lymphoid/myeloid lineage ratio were both ablated in Adipoq-Cre+;Kitlfl/fl male mice (Figure 4M and N). Other peripheral blood parame- ters including RBC count, HGB, MCV, and platelet count were either not affected by HFD or were similarly regulat- ed between Kitlfl/fl and Adipoq-Cre+;Kitlfl/fl males (Online Supplementary Figure S6D). These results indicate that SCF from MAT is required for the skewed hematopoietic dif- ferentiation toward GrMo and lymphoid lineages during HFD.
Sexual dimorphism is observed in obesity-associated inflammation and immune dysfunction, which is partially attributable to difference in hematopoiesis.44,45 We then sought to determine the effect of MAT-derived SCF on obesity-stressed hematopoiesis in females. HFD-induced gain in body weight was similar between Kitlfl/fl and Adipoq-Cre+;Kitlfl/fl female mice (Online Supplementary Figure S7A). We found that, compared to males, HFD feeding in wild-type females did not affect BM cellularity (Online Supplementary Figure S7B) but LSK and all myeloid progen- itors including CMP, MEP and GMP were all expanded (Online Supplementary Figure S7C-F), without a change in the relative ratio of MEP to GMP (Online Supplementary Figure S7G). The increase in the frequency of LSK, CMP, and MEP by HFD in females was abolished when SCF was deleted in adipocytes (Online Supplementary Figure S7C-E). However, the increase in GMP frequency after HFD in females seemed to be independent of adipocyte- derived SCF (Online Supplementary Figure S7F). In the peripheral blood, HFD feeding significantly augmented the red blood cell count and hemoglobin concentration in both Kitlfl/fl and Adipoq-Cre+;Kitlfl/fl female mice (Online Supplementary Figure S7H and I). Mean corpuscular volume (MCV), platelet count, and lymphocyte count were not affected by HFD in either Kitlfl/fl or Adipoq-Cre+;Kitlfl/fl female mice (Online Supplementary Figure S7J-L). Despite the increased frequency of GMP in the BM, there was a declining trend in peripheral granulocytes and significant downregulation of monocytes in HFD wild-type females, which was absent in Adipoq-Cre+;Kitlfl/fl female mice (Online Supplementary Figure S7M and N). Reasons causing these discrepancies between the BM and the periphery are unclear, but may involve the production and turnover of mature cells, their release into the circulation, and recruit- ment to target tissues. Taken all these data from male and female mice, we conclude that MAT niche factor SCF is required for HFD-induced changes in HSPC maintenance and differentiation, despite the sex differences observed in such responses.
Adipocyte-derived stem cell factor partially mediates the β3-adrenergic regulation of hematopoietic stem and progenitor cells
The BM is extensively innervated by the SNS.23,46 β-adrenoceptors are expressed in Nestin+ SSC and their activation by the SNS mediates the circadian mobilization of HSC,47,48 while the neuropathy of the BM niche con- tributes to the pathogenesis of myeloproliferative neo- plasms.49,50 In addition, MAT, particularly the rMAT, expresses all three β-adrenoceptors and undergoes remod- eling when the sympathetic tone is elevated by cold or
1738
haematologica | 2019; 104(9)