Melchers, F. | Search bioRxiv

bioRxiv2023

MicroRNA-221/222-expression in HSC and MPP safeguards their quiescence and multipotency by downregulating stress-independent and dependent expression of IEG and of several myelo/granulopoiesis-enhancing target genes.

The microRNA cluster-221/222 is expressed in hematopoietic stem cells (HSC) and multipotent progenitors (MPP). To study its function in hematopoiesis, we generated mice, in which this cluster is selectively deleted by Vav-cre in HSC and, thus, in all hematopoietic cells. Fluorescence-activated cell sorting analyses of the lineage-negative HSC and MPP compartments in bone marrow at unperturbed, steady state hematopoiesis detect strong activation of HSC to MPP, as well as increased granulocytes in the periphery, induced by miR-221/222-deficiency. Short-term social stress on mice also activates HSC to MPP, but the time of stress is too short to detect further increases in granulocyte numbers. Single cell deep mRNA sequencing identifies Fos as direct, and Jun as well as six other immediate early genes (IEG) as indirect targets of miR-221/222 at unperturbed hematopoiesis. Three of these IEG - Klf6, Nr4a1 and Zfp36 - have previously been found to influence myelo/granulopoiesis. Short stress induces higher levels of the same, and an even larger number of IEGs, now also in MPP, indicating, that stress and miR-221/222 both activate HSC to MPP by IEG upregulation in perturbed hematopoiesis. Furthermore, combined stress and miR-221/222-deficiency rapidly increase numbers of myelo/granulocyte progenitors (MEP, GMP) in bone marrow. Additional indirect miR-221/222-targets become detectable in MPP, of which H3f3b has previously been found to influence myelopoiesis. In serial transplantations, miR-221/222-deficient HSC retain their capacity to home to, and become resident in bone marrow, but they loose their lymphopoietic capacities, thus their multipotency. Our results suggest, that miR-221/222-expression in HSC and MPP safeguards their quiescence and multipotency by downregulating the expression of IEG and of myelo/granulopoiesis-enhancing target genes. Since miR-221/222 is also expressed in human HSC and MPP, its expression should improve clinical settings of human bone marrow transplantations.

immunology↗

bioRxiv2019

Stromal cell-contact dependent PI3K and APRIL induced NF-κB signaling complement each other to prevent mitochondrial- and endoplasmic reticulum stress induced cell death of bone marrow plasma cells

Persistence of long-lived, memory plasma cells in the bone marrow depends on survival factors available in the bone marrow, provided in niches organized by stromal cells. Here we describe that ex vivo we can prevent apoptosis of bone marrow plasma cells by supplying direct cell contact with stromal cells and the soluble cytokine APRIL. Integrin-mediated contact of bone marrow plasma cells with stromal cells activates the PI3K signaling pathway, leading to critical inactivation of FoxO1/3 and preventing the activation of mitochondrial stress-associated effector caspases 3 and 7. Likely, inhibition of PI3K signaling in vivo ablates bone marrow plasma cells. APRIL signaling, via the NF-{kappa}B pathway, blocks activation of the endoplasmic reticulum stress-associated initiator caspase 12. Thus, stromal cell-contact induced PI3K and APRIL-induced NF-{kappa}B signaling provide necessary and complementary signals to maintain bone marrow memory plasma cells.

immunology↗