Program: Oral and Poster Abstracts
Type: Oral
Session: 506. Hematopoiesis and Stem Cells: Microenvironment, Cell Adhesion and Stromal Stem Cells: Hematopoietic Stem Cells on Stress
We have shown that Akt-activated endothelial cells (ECs) within the hematopoietic microenvironment, are indispensable for supporting HSC self-renewal during both steady-state and regenerative hematopoiesis and that EC-specific Mapk signaling drives the differentiation of HSCs into lineage-committed progeny. Here, we demonstrate that young BMECs maintain high levels of Akt signaling, whereas aged ECs exhibit preferential signaling through Mapk. Utilizing a novel HSC/EC co-culture system, we demonstrate that aged BMECs co-cultured with hematopoietic stem and progenitor cells (HSPCs) isolated from young mice inhibit the expansion of repopulating HSCs and are unable to expand aged HSPCs that give rise to long-term, multilineage engraftment. Of note, when we co-cultured aged HSPCs with young BMECs we found that we were able to maintain their functional capacity when assessed by competitive repopulation assays. These data suggest that BMECs play an important role in regulating HSC function.
Based on these observations, we set out to test if endothelial Mapk inhibits the vascular niche from supporting functional hematopoiesis. We generated a mouse model in which Mapk was selectively overexpressed in ECs (Mapk VCC) and demonstrated that these mice exhibit a defect in phenotypic and functional HSCs, resembling phenotypes similar to aged HSCs. In particular, transplanted HSCs from Mapk VCC mice lead to diminished engraftment ability with an in increase in myeloid contribution at the expense of B and T cells. To directly test if the functional defects in the HSCs were due to the Mapk-activated vascular niche, we isolated BMECs from these mice and found that Mapk-activated ECs have a decreased ability to support the ex vivo expansion of functional HSCs, with less HSCs in quiescence and more differentiation into granulocytic myeloid cells. Transcriptome and proteomic analyses revealed that aged and Mapk-activated BMECs have similar defects in their pro-HSC angiocrine repertoire, suggesting a possible mechanism for their diminished capacity to instruct and maintain a balanced and healthy hematopoietic system. Furthermore, we utilized an endothelial-based cellular therapy approach to rejuvenate the BM microenvironment and demonstrated that transplantation of young BMECs can enhance hematopoietic recovery and restore HSC function following myeloablative injury in aged mice.
Taken together, our in vivo animal model and EC/HSC co-culture system will allow us to screen for angiocrine factors that support the functional attributes of the HSC. Additionally, we have unlocked a potential therapeutic application for the transplantation of ECs following myeloablative treatment. Transplantation of BMECs may create a more permissive microenvironment that promotes an increase in the number of engrafted HSPCs following BM transplantation and accelerates the rate of hematopoietic recovery following radiation or chemotherapeutic regimens decreasing the morbidity/mortality associated with life threatening pancytopenias in the elderly.
Disclosures: No relevant conflicts of interest to declare.
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