Retinoic acid affects apoptosis of neurons injured by hypoxic-ischemic brain damage via retinoic acid receptor alpha

Abstract

Objective To explore the effect of the retinoic acid (RA) on the apoptosis of neurons caused by hypoxic ischemic brain damage (HIBD). Methods Seventy-two newborn Sprague-Dawley rats were randomly divided into an RA deficiency (RAD) group, an RA normal (RAN) group and a control group, each of 24. The HIBD model was established in the RAD and RAN groups using Rice′s method. The left common carotid artery was exposed, ligated and cut, inducing hypoxia. In the control group the left common carotid artery was exposed without any other treatment. Three and 7 days after the operation, neuron apoptosis in the brain tissue was evaluated using TUNEL staining. The degree of HIBD was quantified using modified neurological severity scores (mNSS) 7, 14, 21 and 28 days after the operation. Primary neurons were cultured in vitro, and oxygen glucose deprivation (OGD) was induced, then control, OGD and RA+ OGD groups were formed. The gene transcription and the protein activity of retinoic acid receptor alpha (RARα), GDNF (glial cell line-derived neurotrophic factor) and Caspase-8 were examined with polymerase chain reactions (PCR) and Western blotting. The RA+ OGD group was exposed to RA and SiRNA adenovirus, and divided into a silenced group and a negative transfection group according to the infection. Results The average mNSS of the RAD group was significantly higher than that of the RAN group. TUNEL staining showed that the apoptotic cells in the cortex increased from day 3 to 7 after the operation, but significantly more in the RAD group than in the RAN group. The gene transcription and protein activity of RARα and GDNF in the RA+ OGD group were significantly higher than in the OGD group, and those of Caspase-8 were significantly lower. The gene transcription and protein activity of RARα and GDNF in the silenced group were significantly lower than in the negative transfection group, while those of Caspase-8 were just the opposite. Conclusion RA can inhibit the apoptosis of primary neurons after HIBD by up-regulating the expression of GDNF and down-regulating that of Caspase-8 via RARα. Key words: Retinoic acid receptor alpha; Neuron apoptosis; Adenovirus; Glial cell-derived neurotrophic factor; Caspase-8