pH regulates hematopoietic stem cell potential via polyamines

Abstract

Upon ex vivo culture, hematopoietic stem cells (HSCs) quickly lose potential and differentiate into progenitors. The identification of culture conditions that maintain the potential of HSCs ex vivo is therefore of high clinical interest. Here, we demonstrate that the potential of murine and human HSCs is maintained when cultivated for 2 days ex vivo at a pH of 6.9, in contrast to cultivation at the commonly used pH of 7.4. When cultivated at a pH of 6.9, HSCs remain smaller, less metabolically active, less proliferative and show enhanced reconstitution ability upon transplantation compared to HSC cultivated at pH 7.4. HSCs kept at pH 6.9 show an attenuated polyamine pathway. Pharmacological inhibition of the polyamine pathway in HSCs cultivated at pH 7.4 with DFMO mimics phenotypes and potential of HSCs cultivated at pH 6.9. Ex vivo exposure to a pH of 6.9 is therefore a positive regulator of HSC function by reducing polyamines. These findings might improve HSC short‐term cultivation protocols for transplantation and gene therapy interventions. image Culture conditions that maintain HSC potential ex vivo are of high clinical interest. This study shows that the potential of murine or human HSCs is maintained for 2 days by reducing polyamines when cultivated at a pH of 6.9. The pH in the bone marrow can be lower than the serum pH of 7.4 and can be as low as pH 6.4 in pH pockets. Two‐day cultivation of HSCs at a pH of 6.9 results in the maintenance of murine or human HSC functions. A change in pH from 7.4 to 6.9 alters the metabolism of HSCs, including attenuation of the polyamine pathway. Blocking polyamine synthesis in HSCs by DMFO recapitulates maintenance of murine or human HSCs at pH 7.4.