Distinct signaling programs control human hematopoietic stem cell survival and proliferation

Area of Science:

• Hematology
• Stem Cell Biology
• Molecular Signaling

Background:

• Human hematopoietic stem cell (HSC) expansion ex vivo is crucial for transplantation and research.
• Existing growth factors (GFs) promote HSC expansion, but their precise molecular mechanisms remain unclear.
• Understanding GF-driven signaling is vital for optimizing HSC expansion and function.

Purpose of the Study:

• To elucidate the rapid molecular signaling events induced by multiple GFs in primitive human HSCs.
• To identify key signaling intermediates and transcription factors involved in GF-mediated HSC survival and proliferation.
• To investigate the role of AKT and β-catenin signaling in regulating HSC responses to GFs.

Main Methods:

• Mass cytometry was employed to simultaneously measure surface markers, transcription factors, signaling intermediates, viability, and cell-cycle status in single CD34+ cord blood cells.
• Cells were stimulated with a combination of five GFs (stem cell factor, Fms-like tyrosine kinase 3 ligand, interleukin-3, interleukin-6, and granulocyte colony-stimulating factor).
• Responses were analyzed in CD34+CD38-CD45RA-CD90+CD49f+ (HSCs) and CD90-CD49f- (MPPs) populations, with targeted manipulation of AKT and β-catenin.

Main Results:

• The combination of five GFs rapidly activated STAT1/3/5, ERK1/2, AKT, CREB, S6, and β-catenin in CD49f+ HSCs.
• Distinct signaling profiles were observed in GF-responsive and non-responsive HSC subsets, correlating with transcription factor activity.
• While MPPs showed similar GF response amplitudes, CD49f+ HSCs exhibited higher baseline signaling and direct modulation of survival/proliferation by AKT and β-catenin.

Conclusions:

• Five GFs elicit rapid and distinct signaling events in primitive human HSCs, crucial for their immediate survival and proliferation.
• AKT and β-catenin signaling are direct regulators of CD49f+ HSC survival and proliferation in response to GFs.
• These findings provide critical insights into the molecular basis of HSC expansion and potential therapeutic targets.