miR-99 regulates normal and malignant hematopoietic stem cell self-renewal

Area of Science:

• Stem cell biology
• Molecular oncology
• Noncoding RNA research

Background:

• MicroRNA-99 (miR-99) family members are highly expressed in hematopoietic stem cells (HSCs) and acute myeloid leukemia stem cells (LSCs).
• These stem cells possess self-renewal capabilities crucial for maintaining blood homeostasis and driving leukemia progression.
• The precise role of miR-99 in regulating stem cell self-renewal and differentiation remains to be fully elucidated.

Purpose of the Study:

• To investigate the regulatory role of the miR-99 family in the self-renewal of both normal HSCs and LSCs.
• To determine the therapeutic potential of targeting miR-99 in acute myeloid leukemia (AML).
• To identify key downstream mediators of miR-99 function in stem cell maintenance.

Main Methods:

• Utilized a MLL-AF9-driven mouse model of AML to study miR-99 inhibition effects.
• Administered miR-99 inhibitors to mice and primary AML patient cells.
• Performed a forward genetic shRNA library screen to identify miR-99 mediators.
• Assessed stem cell self-renewal, differentiation, and leukemia-initiating activity.

Main Results:

• miR-99 inhibition induced differentiation and depletion of LSCs in an AML mouse model, reducing leukemia-initiating capacity.
• miR-99 inhibition led to improved survival in secondary transplants, indicating a reduction in residual leukemia stem cells.
• miR-99 inhibition promoted differentiation of primary AML patient blasts.
• Hoxa1 was identified as a critical mediator of miR-99 function in HSC maintenance, confirmed in both HSCs and LSCs.

Conclusions:

• The miR-99 family is a critical regulator of self-renewal in both HSCs and LSCs.
• miR-99 inhibition represents a potential therapeutic strategy for AML by targeting leukemia stem cells.
• Noncoding RNAs, like miR-99, play significant roles in regulating stem cell function in both normal and malignant hematopoiesis.