Very low oxygen concentration (0.1%) reveals two FDCP-Mix cell subpopulations that differ by their cell cycling, differentiation and p27KIP1 expression

Oxygen (O2) concentrations in bone marrow vary from 4% in capillaries to <0.1% in subendosteum, in which hematopoietic stem cells reside in specific niches. Culture at low O2 concentrations (3, 1 and 0.1%) influences hematopoietic stem and progenitor cells survival, proliferation and differentiation, depending on their level of differentiation. Culture of human CD34+ cells at low O2 concentrations (O2 ⩽3%) maintains stem cell engraftment potential better than at 20% O2 (NOD/Scid xenograft model). In contrast, progenitors disappear from cultures at/or <1% O2 concentrations. A very low O2 concentration (0.1%) induces CD34+ quiescence in G0. The exploration of molecules and mechanisms involved in hematopoietic stem and progenitor cells' quiescence and differentiation related to low O2 concentrations is unfeasible with primary CD34+ cells. Therefore, we performed it using murine hematopoietic nonleukemic factor-dependent cell Paterson (FDCP)-Mix progenitor cell line. The culture of the FDCP-Mix line at 0.1% O2 induced in parallel G0 quiescence and granulo-monocytic differentiation of most cells, whereas a minority of undifferentiated self-renewing cells remained in active cell cycle. Hypoxia also induced hypophosphorylation of pRb and increased the expression of p27KIP1, the two proteins that have a major role in the control of G0 and G1 to S-phase transition

The emerging role of hypoxia, HIF-1 and HIF-2 in multiple myeloma

Hypoxia is an imbalance between oxygen supply and demand, which deprives cells or tissues of sufficient oxygen. It is well-established that hypoxia triggers adaptive responses, which contribute to short- and long-term pathologies such as inflammation, cardiovascular disease and cancer. Induced by both microenvironmental hypoxia and genetic mutations, the elevated expression of the hypoxia-inducible transcription factor-1 (HIF-1) and HIF-2 is a key feature of many human cancers and has been shown to promote cellular processes, which facilitate tumor progression. In this review, we discuss the emerging role of hypoxia and the HIFs in the pathogenesis of multiple myeloma (MM), an incurable hematological malignancy of BM PCs, which reside within the hypoxic BM microenvironment. The need for current and future therapeutic interventions to target HIF-1 and HIF-2 in myeloma will also be discussed.SK Martin, P Diamond, S Gronthos, DJ Peet and ACW Zannettin