EXTRACELLULAR ACIDOSIS PROMOTES HEMATOPOIETIC STEM CELL APOTOSIS.

D’ATRI, LINA P.; MALAVER, ELISA; PACIENZA, NATALIA; POZNER, ROBERTO G.; NEGROTTO, SOLEDAD; GOMEZ, RICARDO M.; SCHATTNER, MIRTA

Estambul, Turquia.

Congreso; 77th Congress of the European Atherosclerosis Society,; 2008

European Atherosclerosis Society

It has been suggested that hematopoietic stem cells (HSCs, CD34+) can restore tissue vascularization after ischemic events. Extracellular acidosis, a critical feature of not only inflammatory but also isquemic tissues, is a key regulator of activation and survival responses of different cell types. In this study we evaluated the effect of acidic millieu on HSCs survival. Human umbilical cord blood CD34+ cells were obtained by positive immunomagnetic selection. Apoptosis analysis by fluorescence microscopy showed that CD34+ cells cultured for 48 hs in acidic medium (pH6.5) significantly increased apoptosis (pH7.4: 18±4, pH6.5: 53±6% n=9). Apoptosis induction was confirmed by an increase of annexin V-positive cells (pH7.4: 28, pH6.5: 75%, n=2) and by detection of hypodiploid nuclei (pH7.4: 8, pH6.5: 45%, n=2). TPO, SCF and IL-3 as well as a cAMP analog prevented the acidic-induced apoptosis (C: 53±6, TPO: 30±4, SCF: 30±6, IL-3: 10±4, BIMPs: 37±6 %, p<0.05 vs C, n=6). However, in all cases, cell survival never reached control values. Interestingly, other distinctive cytokines released during isquemia such as VEGF or SDF-1 were not able to prevent apoptosis induced by acidic medium. Acidic exposure triggered a marked reduction in Bcl-xL expression (pH7.4: 90; pH6.5: 63% n=2) and an increase of positive cells for the active caspase-3 (pH7.4: 17; pH6.5: 68% n=2). In addition, loss of mitochondrial membrane potential which was prevented by SCF treatment (pH7.4: 13; pH6.5: 35; pH6.5+SCF: 8% n=2) was also found in CD34+ at pH 6.5. These findings reveal that extracellular acidosis induces programmed cellular death of HSC.