C/EBPβ isoforms sequentially regulate regenerating mouse hematopoietic stem/progenitor cells

Area of Science:

• Hematopoiesis
• Stem Cell Biology
• Molecular Biology

Background:

• CCAAT enhancer-binding protein β (C/EBPβ) is crucial for stress-induced granulopoiesis.
• The specific roles and mechanisms of C/EBPβ in hematopoietic stem/progenitor cells (HSPCs) under stress remain unclear.

Purpose of the Study:

• To investigate the regulation and function of C/EBPβ in HSPCs, particularly during hematopoietic stress.
• To elucidate the distinct roles of C/EBPβ isoforms in HSPC response to stress.

Main Methods:

• Utilized 5-fluorouracil treatment and bone marrow transplantation models in mice.
• Analyzed Cebpb-/- HSPCs for cell-cycle activation and myeloid differentiation.
• Employed intracellular flow cytometry to detect and quantify C/EBPβ isoforms (LIP, LAP/LAP*) in long-term hematopoietic stem cells (LT-HSCs).

Main Results:

• Cebpb deficiency impaired early cell-cycle activation and late myeloid differentiation of HSPCs following stress.
• C/EBPβ expression was upregulated in HSPCs, especially LT-HSCs, during hematopoietic stress.
• The C/EBPβ isoform liver-enriched inhibitory protein (LIP) was upregulated early, promoting LT-HSC cell-cycle entry and HSPC pool expansion via Myc.
• The C/EBPβ isoforms liver-enriched activating protein (LAP)/LAP* were upregulated later, mediating myeloid differentiation of amplified HSPCs.

Conclusions:

• Stress-induced sequential upregulation of C/EBPβ isoforms is essential for regulating HSPC proliferation and differentiation during hematopoietic regeneration.
• Distinct temporal expression of C/EBPβ isoforms (LIP followed by LAP/LAP*) orchestrates the recovery of the hematopoietic system after stress.