Does transmembrane communication through gap junctions enable stem cells to overcome stromal inhibition?

Area of Science:

• Hematology
• Stem Cell Biology
• Cellular Communication

Background:

• Long-term bone marrow cultures (LTC) are crucial for studying hematopoietic stem cells (HSCs).
• Amphotericin B (AB) is known to inhibit HSC growth in LTC.
• The mechanism of AB-induced HSC growth inhibition requires clarification.

Purpose of the Study:

• To elucidate the mechanism by which Amphotericin B inhibits hematopoietic stem cell proliferation in long-term bone marrow cultures.
• To investigate the role of cell-to-cell communication between HSCs and bone marrow stromal cells in this process.

Main Methods:

• Utilized long-term bone marrow cultures (LTC) with and without Amphotericin B (AB).
• Employed Transwell inserts to separate HSCs from stromal cells.
• Assessed colony-forming unit-culture (CFU-c) and cobblestone-area forming cell (CAFC) formation.
• Investigated gap junction intercellular communication (GJIC) using micro-injection of lucifer yellow.
• Analyzed cytokine and chemokine transcript levels in stromal cells.

Main Results:

• AB-induced inhibition of HSC growth was reversible upon drug removal, indicating a non-toxic effect.
• HSC growth inhibition by AB occurred only when HSCs were in direct contact with stromal cells, not when separated by Transwell inserts.
• Blocking gap junction intercellular communication (GJIC) mimicked the inhibitory effect of AB on HSC growth.
• Extensive GJIC in stromal cell lines correlated with their ability to support primitive HSC clones (CAFCs).

Conclusions:

• Amphotericin B likely inhibits HSC proliferation by interfering with transmembrane communication between HSCs and stromal cells, rather than direct toxicity.
• Gap junctions are implicated as a key mechanism in this stromal-dependent regulation of HSC proliferation.
• These findings highlight the importance of cell-cell communication in maintaining hematopoietic stem cell function.