P3-192: acidic ph activates autophagy pathway in human hippocampal neural precursor cells and induces the neuronal phenotype

The pH balance is essential for cell survival, slight pH variations had a great impact on the fate of undifferentiated cells (Ying et.al., 1999). Autophagy is the major intracellular degradation system by which cytoplasmic materials are delivered to and degraded in the lysosome and plays a pivotal role in maintaining homeostasis and defending the cells against adverse microenvironments. There are different stimuli that can trigger autophagy, nutrient deprivation is the most common one. We have previously reported that the absence of bFGF is enough to cause autophagy in neural precursor cells (Cardenas-Aguayo et.al., 2003). It is known that in neurodegenerative diseases, such as Alzheimer disease, there is acidification in the brain, ischemia, oxidative stress and hypoxia. In this study we found that acidic pH induces autophagy in human embryonic hippocampal cells, and that this induction of autophagy is further enhanced by the absence of growth factors. We cultured human embryonic neural precursor cells (PhoenixSongs Biologicals HIPP009), in chemical defined medium, in the presence of bFGF, EGF and LIF, over a substrate of laminin, on different pH conditions (from pH 4 to 7) during 25 min at 37o C, and then washed and further cultured for 2 to 7 days, in the presence or absence of growth factors. We performed Western blotting, qRT-PCR and immunofluorescence with confocal microscopy, to evaluate the expression of pULK1 (555), LC3, CatD, Lamp2, p70S6K. We also evaluate the expression of neuronal markers and tau protein. We performed viability LDH viability assays, Autophagy colorimetric assay (CYTO-ID). And a caspase 3 assay. Autophagy was induced in human embryonic hippocampal cells treated with acidic pH and cultured in the absence of bFGF. Apoptosis was not induced in cells treated with acidic pH. Tau protein was overexpressed in acidic pH cultured conditions. ROS production was also increased in cultures exposed to acidic pH. Neural precursor cells exposed to acidic pH differentiate into the neuronal phenotype. The pH balance is crucial for cell survival, and maturation of stem cells. Acidic pH environment induced autophagy in human embryonic Hippocampal neural precursor cells and induced neuronal phenotype.