HIF-1 alpha is an essential effector for purine nucleoside-mediated neuroprotection against hypoxia in PC12 cells and primary cerebellar granule neurons

Hypoxia-inducible factor-1 alpha (HIF-1 alpha) and purine nucleosides adenosine and inosine are critical mediators of physiological responses to acute and chronic hypoxia. The specific aim of this paper was to evaluate the potential role of HIF-1 alpha in purine-mediated neuroprotection. We show that adenosine and inosine efficiently rescued clonal rat pheochromocytoma (PC12) cells (up to 43.6%) as well as primary cerebellar granule neurons (up to 25.1%) from hypoxic insult, and furthermore, that HIF-1 alpha is critical for purine-mediated neuroprotection. Next, we studied hypoxia or purine nucleoside increased nuclear accumulation of HIF-1 alpha PC12 cells. As a possible result of increased protein stabilization or synthesis an up to 2.5-fold induction of HIF-1 alpha accumulation was detected. In cerebellar granule neurons, purine nucleosides induced an up to 3.1-fold HIF-1 alpha accumulation in cell lysates. Concomitant with these results, small interfering RNA-mediated reduction of HIF-1 alpha completely abolished adenosine- and inosine-mediated protection in PC12 cells and severely hampered purine nucleoside-mediated protection in primary neurons (up to 94.2%). Data presented in this paper thus clearly demonstrate that HIF-1 alpha is a key regulator of purine nucleoside-mediated rescue of hypoxic neuronal cells.