Figure 7.

Impact of LPS on Multilineage Reconstitution and on of PU.1 and CEBP/α

(A and B) 2,500 LSK cells sorted from PBS- or LPS-challenged WT, MYD88^−/−, and TRIF^−/− mice (CD45.2⁺) were transplanted into recipient BoyJ (CD45.1⁺). Recipients were monitored for up to 24 weeks.

(A) Percentage of donor-derived CD45.2⁺ BM CMP (left), GMP (middle), and GR1⁺ (right) in recipient mice at week 24 (n = 7–9).

(B) Line graphs show mean percentage of donor CD45.2⁺ cells in in myeloid cells (GR1⁺), B cells (B220⁺), and T cells (CD4⁺ or CD8⁺) in peripheral blood of recipient mice after transplantation (n = 7–16).

(C) Relative mRNA expression level of Spi1 and CebpA in LSK cells sorted from WT (n = 5–9 samples), MYD88^−/− (n = 4–5 samples), and TRIF^−/− (n = 3 samples) mice challenged with PBS or LPS for 24 hr; each sample derived from cells pooled from 2–3 mice; minimum of three independent experiments.

(D) WT, MYD88^−/−, and TRIF^−/− LSK cells were sorted at 24 weeks after transplantation. Fold change of expression level of Spi1 and CebpA (n = 3–4 samples derived from cells pooled from 2–3 mice).

(E) Working model. TRIF and MYD88 uncouple the effects of TLR4-mediated injury on hematopoietic stem cells and myeloid progenitors during severe sepsis. The role of TLR4 in regulating hematopoiesis in homeostatic conditions is still unclear. It is possible that the gut microbiota maintains a systemic basal state of TLR4 activation. In the state of severe sepsis, maximal activation of TLR4 by bacterial LPS activates: (1) TRIF, leading to injury of LT-HSC (Figure 6) and dysfunctional expansion of MPPs by cell-cycle activation, shift of progenitors re-expressing SCA-1, and impaired egress (Figures 1E, 1F, 2, 7A, and 7B); and (2) MYD88, resulting in damage of myeloid progenitors by increased apoptosis and impaired differentiation (Figures 3 and 5). Cell-autonomous and non-cell-autonomous mechanisms contribute to these effects in both pathways (Figure 4).

Data represent mean ± SEM. LPS versus PBS: ^∗p < 0.05, ^∗∗p < 0.01; WT versus MYD88^−/− or TRIF^−/−: ˆp < 0.05, ˆˆp < 0.01.