Serotonin 5‐HT 1A receptor activation inhibits HIF‐1α expression in a rat embryonic serotonergic cell line

The 5‐HT 1A receptor (5‐HT 1A R) agonist, 8‐OH‐DPAT, reduces oxidative stress in cerebral ischemia. Hypoxia‐inducible factor 1α (HIF‐1α) is a short‐lived transcription factor that is stabilized by hypoxia and certain ligand‐receptor interactions, and promotes cell survival. Here, we determined if 8‐OH‐DPAT affects HIF‐1α levels in RN46A cells, a neuronal cell line derived from rat embryonic raphe neurons that endogenously express 5‐HT 1A Rs. Differentiation of RN46A cells at 37°C stabilized HIF‐1α levels. Treatment of differentiated RN46A cells with 8‐OH‐DPAT (1μM) transiently decreased HIF‐1α levels (‐60% at 10 min, P<0.05).To determine if this effect was due to 5‐HT 1A R activation, cells were treated with 8‐OH‐DPAT 7 days after transfection with a shRNA sequence targeting the rat 5‐HT 1A R(1ARshRNA) or a scrambled version of the same sequence (scrmshRNA). Transfection with 1ARshRNA decreased 5‐HT 1A R protein expression by approximately 70% compared to untransfected controls (P<0.05) while scrmshRNA did not significantly reduce receptor expression. Treatment with 8‐OH‐DPAT decreased HIF‐1α levels in cells transfected with scrmshRNA by 28% (P>0.05), but increased levels in cells transfected with 1ARshRNA by 95% (P<0.05). The data indicate that 8‐OH‐DPAT reduces HIF‐1α expression through activation of the 5‐HT 1A R, but increases its expression through other mechanisms. Supported by NHLBI 072354