Contributions
Abstract: S246
Type: Oral Presentation
Session title: Stem cell biology and microenvironment
Background
Hematopoietic stem cells (HSCs) are responsible for maintaining blood cell production throughout the lifetime of an organism. In the unperturbed state, they mainly remain quiescent, although they do occasionally enter the cell cycle to meet homeostatic demands of the mature blood cell production. Upon stress, such as inflammation, severe blood loss or chemotherapy, HSCs mount a massive proliferative response to enable elevated production of peripheral blood cells. Previously, our group has linked inflammatory-stress induced exit from dormancy with a decrease in the HSC functional potential (Walter et al, 2015, Nature).
Aims
We wanted to investigate if the HSC attrition was specific to the inflammatory challenge used in our previous research or there was a general link between dormancy and functional potential regardless of the stress-stimuli used. Therefore, we used alternative inflammatory and non-inflammatory stimuli that have been shown to promote HSC cycling.
Methods
We used the ScltTA H2B-GFP mouse model to facilitate tracking of the HSC divisional history. Mice were either repeatedly treated with lipopolysaccharide (LPS); fluorouracil (5-FU); or were serially bled. Mice were then allowed to recover for 4 weeks prior to end point analysis, in which we assessed HSC divisional history as well as its relationship to the self-renewal, differentiation and engraftment potency via in vitro proliferation and differentiation assay as well as via transplantation of the FACS sorted HSCs into lethally irradiated recipient mice.
Results
None of the treatment regimens led to sustained suppression of peripheral blood cell counts, indicating a remarkable capability of the hematopoietic system to sustain mature blood production. The bleeding protocol did not lead to an increase in HSC divisional history despite previous reports on upregulation of Ki67 staining in the HSC pool of the serially bled mice. LPS treatment, on the other hand, led to an increase in HSC exit from dormancy and 5-FU challenge resulted in the activation of the entire HSC pool. In the case of all three treatments, HSCs which have divided extensively exerted decreased functional potency in the in vitro assay as well as in vivo in transplantation studies.
Conclusion
Our data reveals a remarkable capability of HSCs to sustain mature blood cell production under conditions of severe stress imposed by inflammation, repetitive loss of large blood volumes and recurring exposure to cytotoxic chemotherapeutic agents. The HSCs that have engaged into the cell cycle showed loss of functional potency providing further evidence that dormancy indeed protects HSC’s potency and that this is irrespective of the type of stimuli used. We would also suggest that this outcome suggests that HSCs do not undergo self-renewal divisions following exposure to such stimuli. In contrast to LPS and 5-FU treatment, and despite the fact that more than 70% of the total blood volume was removed on three separate occasions, the bleeding protocol did not cause dormant label-retaining HSCs into cycle. This could be explained by blood cell production being sustained under these conditions by either non-label retaining “active HSCs, or more differentiated progenitors. We are currently further investigating the effect that serial bleeding has on hematopoietic progenitor cells as well as HSC dormancy and the relationship between dormancy and functional potential after applying doses of 5-FU that do not activate the entire HSC pool.
Keyword(s): Activation, Hematopoiesis, Hematopoietic stem and progenitor cells, Self-renewal
Abstract: S246
Type: Oral Presentation
Session title: Stem cell biology and microenvironment
Background
Hematopoietic stem cells (HSCs) are responsible for maintaining blood cell production throughout the lifetime of an organism. In the unperturbed state, they mainly remain quiescent, although they do occasionally enter the cell cycle to meet homeostatic demands of the mature blood cell production. Upon stress, such as inflammation, severe blood loss or chemotherapy, HSCs mount a massive proliferative response to enable elevated production of peripheral blood cells. Previously, our group has linked inflammatory-stress induced exit from dormancy with a decrease in the HSC functional potential (Walter et al, 2015, Nature).
Aims
We wanted to investigate if the HSC attrition was specific to the inflammatory challenge used in our previous research or there was a general link between dormancy and functional potential regardless of the stress-stimuli used. Therefore, we used alternative inflammatory and non-inflammatory stimuli that have been shown to promote HSC cycling.
Methods
We used the ScltTA H2B-GFP mouse model to facilitate tracking of the HSC divisional history. Mice were either repeatedly treated with lipopolysaccharide (LPS); fluorouracil (5-FU); or were serially bled. Mice were then allowed to recover for 4 weeks prior to end point analysis, in which we assessed HSC divisional history as well as its relationship to the self-renewal, differentiation and engraftment potency via in vitro proliferation and differentiation assay as well as via transplantation of the FACS sorted HSCs into lethally irradiated recipient mice.
Results
None of the treatment regimens led to sustained suppression of peripheral blood cell counts, indicating a remarkable capability of the hematopoietic system to sustain mature blood production. The bleeding protocol did not lead to an increase in HSC divisional history despite previous reports on upregulation of Ki67 staining in the HSC pool of the serially bled mice. LPS treatment, on the other hand, led to an increase in HSC exit from dormancy and 5-FU challenge resulted in the activation of the entire HSC pool. In the case of all three treatments, HSCs which have divided extensively exerted decreased functional potency in the in vitro assay as well as in vivo in transplantation studies.
Conclusion
Our data reveals a remarkable capability of HSCs to sustain mature blood cell production under conditions of severe stress imposed by inflammation, repetitive loss of large blood volumes and recurring exposure to cytotoxic chemotherapeutic agents. The HSCs that have engaged into the cell cycle showed loss of functional potency providing further evidence that dormancy indeed protects HSC’s potency and that this is irrespective of the type of stimuli used. We would also suggest that this outcome suggests that HSCs do not undergo self-renewal divisions following exposure to such stimuli. In contrast to LPS and 5-FU treatment, and despite the fact that more than 70% of the total blood volume was removed on three separate occasions, the bleeding protocol did not cause dormant label-retaining HSCs into cycle. This could be explained by blood cell production being sustained under these conditions by either non-label retaining “active HSCs, or more differentiated progenitors. We are currently further investigating the effect that serial bleeding has on hematopoietic progenitor cells as well as HSC dormancy and the relationship between dormancy and functional potential after applying doses of 5-FU that do not activate the entire HSC pool.
Keyword(s): Activation, Hematopoiesis, Hematopoietic stem and progenitor cells, Self-renewal