Lkb1 regulates quiescence and metabolic homeostasis of haematopoietic stem cells

Abstract

The capacity to fine-tune cellular bioenergetics with the demands of stem-cell maintenance and regeneration is central to normal development and ageing, and to organismal survival during periods of acute stress. How energy metabolism and stem-cell homeostatic processes are coordinated is not well understood. Lkb1 acts as an evolutionarily conserved regulator of cellular energy metabolism in eukaryotic cells and functions as the major upstream kinase to phosphorylate AMP-activated protein kinase (AMPK) and 12 other AMPK-related kinases. Whether Lkb1 regulates stem-cell maintenance remains unknown. Here we show that Lkb1 has an essential role in haematopoietic stem cell (HSC) homeostasis. We demonstrate that ablation of Lkb1 in adult mice results in severe pancytopenia and subsequent lethality. Loss of Lkb1 leads to impaired survival and escape from quiescence of HSCs, resulting in exhaustion of the HSC pool and a marked reduction of HSC repopulating potential in vivo. Lkb1 deletion has an impact on cell proliferation in HSCs, but not on more committed compartments, pointing to context-specific functions for Lkb1 in haematopoiesis. The adverse impact of Lkb1 deletion on haematopoiesis was predominantly cell-autonomous and mTOR complex 1 (mTORC1)-independent, and involves multiple mechanisms converging on mitochondrial apoptosis and possibly downregulation of PGC-1 coactivators and their transcriptional network, which have critical roles in mitochondrial biogenesis and function. Thus, Lkb1 serves as an essential regulator of HSCs and haematopoiesis, and more generally, points to the critical importance of coupling energy metabolism and stem-cell homeostasis.

Figure 1. Lkb1 deletion leads to severe pancytopenia phenotype

a, Kaplan-Meier survival analysis of Lkb1 WT and KO mice. b, c, The percentages of erythroid lineage from bone marrow (b) and Mac-1⁺/Gr-1⁺ cells (c) in Lkb1 WT and KO mice at 5 DPI. d, The numbers of bone marrow B cell lineage at 7 DPI from Lkb1 WT and KO mice. e, The percentages of apoptotic cells in erythroid, myeloid and B cells of Lkb1 WT and KO bone marrow cells at 3 DPI. n > 3 (b–e).

Figure 2. Lkb1 ablation results in reduced HSC reserves and decreased repopulating potential

a, b, The numbers of LSK cells (a) and LT-HSCs (b) at various DPIs in Lkb1 WT and KO bone marrows. c, The relative fold changes (Lkb1 KO/WT) of the percentages of BrdU⁺ cells from various hematopoietic cell lineages in Lkb1 WT and KO bone marrows at 1 DPI. n = or > 3 at each time point (a–c). d, The percentages of donor-derived cells in peripheral blood by CD45 staining in 1:1 competitive transplantation. n = 15. *: P > 0.4; **: P < 0.01.

Figure 3. LKB1 regulation of hematopoiesis is TSC-mTORC1-independent

a, b, c, The percentages of B220⁺ and Ter119⁺ populations in bone marrow and thymic CD4⁺/CD8⁺ cells (a), bone marrow LSK cells (b), and BrdU⁺ bone marrow LSK cells (c) from the mice indicated. n = 3 (a–c).

Figure 4. Lkb1 deletion diminishes mitochondrial biogenesis and energy production in the hematopoietic system

a, b, c, The relative expression levels of PGC-1α/β at 2 DPI (a), the mitochondrial membrane potential at 4 DPI (b), and the relative mitochondria DNA copy numbers at 4 and 10 DPI (c) of Lkb1 WT and KO bone marrow LSKs. d, The relative basal ATP levels in spleen and thymus from Lkb1 WT and KO mice at 4 DPI. n = 3 (a–d).