PI3K alpha and delta promote hematopoietic stem cell activation
Shayda Hemmati, Taneisha Sinclair, Meng Tong, Boris Bartholdy, Rachel O. Okabe, Kristina Ames, Leanne Ostrodka, Tamanna Haque, Imit Kaur, Taylor S. Mills, Anupriya Agarwal, Eric M. Pietras, Jean J. Zhao, Thomas M. Roberts, Kira Gritsman
Shayda Hemmati, Taneisha Sinclair, Meng Tong, Boris Bartholdy, Rachel O. Okabe, Kristina Ames, Leanne Ostrodka, Tamanna Haque, Imit Kaur, Taylor S. Mills, Anupriya Agarwal, Eric M. Pietras, Jean J. Zhao, Thomas M. Roberts, Kira Gritsman
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Research Article Hematology

PI3K alpha and delta promote hematopoietic stem cell activation

Abstract

Many cytokines and chemokines that are important for hematopoiesis activate the PI3K signaling pathway. Because this pathway is frequently mutated and activated in cancer, PI3K inhibitors have been developed for the treatment of several malignancies and are now being tested in the clinic in combination with chemotherapy. However, the role of PI3K in adult hematopoietic stem cells (HSCs), particularly during hematopoietic stress, is still unclear. We previously showed that the individual PI3K catalytic isoforms p110α and p110β have dispensable roles in HSC function, suggesting redundancy between PI3K isoforms in HSCs. We now demonstrate that simultaneous deletion of p110α and p110δ in double-knockout (DKO) HSCs uncovers their redundant requirement in HSC cycling after 5-fluorouracil (5-FU) chemotherapy administration. In contrast, DKO HSCs were still able to exit quiescence in response to other stress stimuli, such as LPS. We found that DKO HSCs and progenitors had impaired sensing of inflammatory signals ex vivo, and that levels of IL-1β and MIG were higher in the bone marrow (BM) after LPS than after 5-FU administration. Furthermore, exogenous in vivo administration of IL-1β could induce cell cycle entry of DKO HSCs. Our findings have clinical implications for the use of PI3K inhibitors in combination with chemotherapy.

Authors

Shayda Hemmati, Taneisha Sinclair, Meng Tong, Boris Bartholdy, Rachel O. Okabe, Kristina Ames, Leanne Ostrodka, Tamanna Haque, Imit Kaur, Taylor S. Mills, Anupriya Agarwal, Eric M. Pietras, Jean J. Zhao, Thomas M. Roberts, Kira Gritsman

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Figure 5

DKO HSCs have an impaired cycling response to 5-fluorouracil injection.

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DKO HSCs have an impaired cycling response to 5-fluorouracil injection. ...
(A) Cell cycle analysis of HSCs (Lin–c-Kit+Sca-1+CD150+CD48– cells) from DKO (n = 4), δ–/– (n = 3), or WT;Cre (n = 3) BM at 3 weeks after 2 pIpC injections. Representative Hoechst/Ki-67 HSC plots are shown from one of 3 independent experiments, with quantification of the frequency of HSCs found in G0, G1, or S-G2-M phase of the cell cycle on the right. (B) Experimental schematic for 5-fluorouracil (5-FU) experiments. (C) Kaplan-Meier survival curve of mice injected with pIpC once, followed by a single injection of 200 mg/kg 5-FU (WT;Cre, n = 6; p110δ–/–, n = 5; DKO, n = 8). Log-rank analysis was used to compare the groups. (D) Serial WBC counts of the mice shown in C. Representative data from one of 3 experiments is shown. (E) Representative cell cycle analysis of HSCs in the BM of mice that were sacrificed at 7 days after 5-FU injection (WT;Cre, n = 3; δ–/–, n = 3; DKO, n = 3). Representative flow cytometry plots from one of 3 experiments are shown. Quantification of the frequency of HSCs found in G0, G1, or S-G2-M phase of the cell cycle is shown on the right. For the experiments in A and E, ANOVA with Tukey’s multiple-comparisons test was used. *P < 0.05, **P < 0.01. Data represent mean ± SEM.