Caffeine inhibits hypoxia-induced nuclear accumulation in HIF-1α and promotes neonatal neuronal survival

Apnea of prematurity (AOP) defined as cessation of breathing for 15-20 s, is commonly seen in preterm infants. Caffeine is widely used to treat AOP due to its safety and effectiveness. Caffeine releases respiratory arrest by competing with adenosine for binding to adenosine A(1) and A(2A) receptors (A(1)R and A(2A)R). Long before its use in treating AOP, caffeine has been used as a psychostimulant in adult brains. However, the effect of caffeine on developing brains remains unclear. We found that A(1)R proteins for caffeine binding were expressed in the brains of neonatal rodents and preterm infants (26-27 weeks). Neonatal A(1)R proteins colocalized with PSD-95, suggesting its synaptic localization. In contrast, our finding on A(2)R expression in neonatal neurons was restricted to the mRNA level as detected by single cell RT/PCR due to the lack of specific A(2A)R antibody. Furthermore, caffeine (200 mu M) at a dose twice higher than the clinically relevant dose (36-130 mu M) had minor or no effects on several basic neuronal functions, such as neurite outgrowth, synapse formation, expression of A(1)R and transcription of CREB-1 and c-Fos, further supporting the safety of caffeine for clinical use. We found that treatment with CoCl2 (125 mu M), a hypoxia mimetic agent, for 24 h triggered neuronal death and nuclear accumulation of HIF-1 alpha in primary neuronal cultures. Subsequent treatment with caffeine at a concentration of 100 mu M alleviated CoCl2-induced cell death and prevented nuclear accumulation of HIF-1 alpha. Consistently, caffeine treatment in early postnatal life of neonatal mice (P4-P7) also prevented subsequent hypoxia-induced nuclear increase of HIF-1 alpha. Together, our data support the utility of caffeine in alleviating hypoxia-induced damages in developing neurons.