Contributions
Abstract: S139
Type: Oral Presentation
Presentation during EHA22: On Friday, June 23, 2017 from 12:15 - 12:30
Location: Room N104
Background
Some studies show that a high-fat diet (HFD) induces major perturbations in murine hematopoietic stem cells (HSC) and hematopoietic system homeostasis. However, it is currently difficult to say whether these alterations are related to direct effects such as changes in lipid metabolism in HSC or indirect 'side effects' on HSC, such as pathophysiology related to obesity or inflammation observed after an extended diet over several months or a diet very rich in fat (>60 kJ% of fat). For example, HFD-induced obesity significantly alters hematopoiesis in bone marrow (BM), with a decreased proliferation of HSC, a general suppression of progenitors, an enhancement of lymphopoiesis, and an activation of myeloid cell production from BM progenitors. Inflammation also affects HSC homeostasis, as Interferon alpha is well-known to activate dormant HSC in vivo.
Aims
Our strategy is to characterize the impact of a short-term HFD on HSC and hematopoiesis in non-obese C57BL/6J mice.
Methods
In a prospective study, C57BL/6J mice were fed a control diet (4 kJ% of fat) or HFD (42 kJ% of fat), over a short period of 4 weeks, to investigate the direct-impact of such a diet on hematopoiesis.
Results
While fat intake leaded to an increase in plasma cholesterol levels, mice did not develop obesity, and no inflammatory monocytes and no modulation of pro-/anti-inflammatory cytokine levels were detected in blood and BM, respectively. No significant impact was observed on the total number of cells in blood and BM. However, we noted an increase in the number of progenitors and a loss of more than 50% of the most primitive HSC (SLAM). We validated this loss via transplantation of BM isolated from HFD-fed mice (Ly.1) in competition with control BM (Ly.2), in lethally irradiated recipient mice which only reconstitute 20% of the recipient hematopoiesis from HFD HSC. To further investigate lipid metabolism in HSC, we quantified the major lipid constituents in control and HFD HSC. Among altered lipids, cholesterol was the most affected in HFD HSC. These changes might alter the structure of the HSC plasma membrane such as lipid rafts (LR), which are important for signal transduction in hematopoiesis, driving the retention/dormancy of HSC in BM. To determine if fat intake may affect LR quantity in hematopoietic cell membrane, we stained Lineage-negative (Lin-) cells with the cholera toxin subunit B (CTB) and analyzed the distribution of different populations of hematopoietic cells, expressing either high (CTBhi) or low (CTBlo) levels of LR. Fat intake disrupts CTBhi cells in the Lin- Sca-1+ c-Kit+ (LSK) and LSK-CD34- compartments, while no variation was detectable among progenitors (Lin- c-Kit+ and Lin-). Importantly, we discovered that CTBhi cells were enriched with SLAM HSC (46%, versus 2% for the CTBlo). While we found ~50% of CTBhi cells among LSK-CD34- HSC in control diet-fed mice, a HFD has led to a loss of the CTBhi population. Using the proliferation marker Ki67, we observed a decrease in the proportion of LSK-CD34- primitive HSC in G0, meaning that HSC quiescence state was affected by a HFD. Transforming growth factor (TGF)-β signaling has long been known to be involved in modulating HSC quiescence, partly by preventing HSC re-entry into the cell cycle. As a HFD induced a loss of LR on HSC, we looked at the localization of TGF-β receptor 1 (TR1) on the LSK-CD34- cell surface. While TR1 strongly colocalized with LR in macrodomains on HSC, we observed that LR were more organized in microdomains and the delocalization of TR1 among LR was furthermore detected when mice were fed a HFD. Moreover, reduced phospho-Smad2/3 indicated lower activation of the TGF-β pathway in HSC purified from HFD-fed mice. Finally, injection of recombinant TGF-β1 led to the rescue of the 4 week HFD-dependent SLAM HSC depletion, which clearly highlights that a HFD affects TGF-β signaling on HSC.
Conclusion
In conclusion, HFD markedly and rapidly affects primitive hematopoiesis and impairs the maintenance of primitive HSC in non-obese mice. Not only our results uncover the impact of HFD independently of obesity but they also identify the disturbance of LR/TGF-β signaling-mediated quiescence as its main molecular mechanism of action.
Session topic: 23. Hematopoiesis, stem cells and microenvironment
Keyword(s): Hematopoietic Stem Cell, Transforming growth factor-, Lipid rafts, Lipid metabolism
Abstract: S139
Type: Oral Presentation
Presentation during EHA22: On Friday, June 23, 2017 from 12:15 - 12:30
Location: Room N104
Background
Some studies show that a high-fat diet (HFD) induces major perturbations in murine hematopoietic stem cells (HSC) and hematopoietic system homeostasis. However, it is currently difficult to say whether these alterations are related to direct effects such as changes in lipid metabolism in HSC or indirect 'side effects' on HSC, such as pathophysiology related to obesity or inflammation observed after an extended diet over several months or a diet very rich in fat (>60 kJ% of fat). For example, HFD-induced obesity significantly alters hematopoiesis in bone marrow (BM), with a decreased proliferation of HSC, a general suppression of progenitors, an enhancement of lymphopoiesis, and an activation of myeloid cell production from BM progenitors. Inflammation also affects HSC homeostasis, as Interferon alpha is well-known to activate dormant HSC in vivo.
Aims
Our strategy is to characterize the impact of a short-term HFD on HSC and hematopoiesis in non-obese C57BL/6J mice.
Methods
In a prospective study, C57BL/6J mice were fed a control diet (4 kJ% of fat) or HFD (42 kJ% of fat), over a short period of 4 weeks, to investigate the direct-impact of such a diet on hematopoiesis.
Results
While fat intake leaded to an increase in plasma cholesterol levels, mice did not develop obesity, and no inflammatory monocytes and no modulation of pro-/anti-inflammatory cytokine levels were detected in blood and BM, respectively. No significant impact was observed on the total number of cells in blood and BM. However, we noted an increase in the number of progenitors and a loss of more than 50% of the most primitive HSC (SLAM). We validated this loss via transplantation of BM isolated from HFD-fed mice (Ly.1) in competition with control BM (Ly.2), in lethally irradiated recipient mice which only reconstitute 20% of the recipient hematopoiesis from HFD HSC. To further investigate lipid metabolism in HSC, we quantified the major lipid constituents in control and HFD HSC. Among altered lipids, cholesterol was the most affected in HFD HSC. These changes might alter the structure of the HSC plasma membrane such as lipid rafts (LR), which are important for signal transduction in hematopoiesis, driving the retention/dormancy of HSC in BM. To determine if fat intake may affect LR quantity in hematopoietic cell membrane, we stained Lineage-negative (Lin-) cells with the cholera toxin subunit B (CTB) and analyzed the distribution of different populations of hematopoietic cells, expressing either high (CTBhi) or low (CTBlo) levels of LR. Fat intake disrupts CTBhi cells in the Lin- Sca-1+ c-Kit+ (LSK) and LSK-CD34- compartments, while no variation was detectable among progenitors (Lin- c-Kit+ and Lin-). Importantly, we discovered that CTBhi cells were enriched with SLAM HSC (46%, versus 2% for the CTBlo). While we found ~50% of CTBhi cells among LSK-CD34- HSC in control diet-fed mice, a HFD has led to a loss of the CTBhi population. Using the proliferation marker Ki67, we observed a decrease in the proportion of LSK-CD34- primitive HSC in G0, meaning that HSC quiescence state was affected by a HFD. Transforming growth factor (TGF)-β signaling has long been known to be involved in modulating HSC quiescence, partly by preventing HSC re-entry into the cell cycle. As a HFD induced a loss of LR on HSC, we looked at the localization of TGF-β receptor 1 (TR1) on the LSK-CD34- cell surface. While TR1 strongly colocalized with LR in macrodomains on HSC, we observed that LR were more organized in microdomains and the delocalization of TR1 among LR was furthermore detected when mice were fed a HFD. Moreover, reduced phospho-Smad2/3 indicated lower activation of the TGF-β pathway in HSC purified from HFD-fed mice. Finally, injection of recombinant TGF-β1 led to the rescue of the 4 week HFD-dependent SLAM HSC depletion, which clearly highlights that a HFD affects TGF-β signaling on HSC.
Conclusion
In conclusion, HFD markedly and rapidly affects primitive hematopoiesis and impairs the maintenance of primitive HSC in non-obese mice. Not only our results uncover the impact of HFD independently of obesity but they also identify the disturbance of LR/TGF-β signaling-mediated quiescence as its main molecular mechanism of action.
Session topic: 23. Hematopoiesis, stem cells and microenvironment
Keyword(s): Hematopoietic Stem Cell, Transforming growth factor-, Lipid rafts, Lipid metabolism