Hippocampal neuronal cyclooxygenase-2 downstream signaling imbalance in a rat model of chronic aluminium gluconate administration

Abstract

Background: Acute and chronic brain damages including neurodegenerative diseases are a group of neuroinflammation-associated diseases characterized by cognitive function defect and progressive neuron loss. The pathophysiological procession of brain damages involves the overexpression of cyclooxygenase (COX)-2. Owing to the limited benefit to chronic brain damage and the late adverse effect of COX-2 inhibitors, the COX downstream signaling pathway has become a focus in neurological research. In order to explore the mechanism of aluminum neurotoxicity and the importance of COX2 downstream signaling pathways to chronic brain damage, the present study was designed to simultaneously observe the prostaglandin (PG) contents, and the expressions of PG synthases and PG receptors of hippocampus in a rat model induced by chronic administration of aluminium gluconate.

Methods: A rat model of chronic brain damage was established by chronic intragastric administration of aluminium gluconate (Al3+ 200 mg/kg per day, 5d a week for 20 weeks). PG contents, the expressions of PG synthases, and the expressions of PG receptors in rats were measured by ELISA, RT-PCR and Western blotting, respectively.

Results: Chronic aluminium gluconate administration resulted in hippocampal neuron injury and learning and memory disorders in rats. Aluminium gluconate administration also resulted in increased levels of PGE2, PGD2, TXA2, PGI2, and PGF2α in rat hippocampus. The DP1, EP2, IP, mPGES-1, EP4, PGIS and TXAS mRNA expressions, and the DP1, EP2 and IP protein expressions significantly increased in the Al-treated hippocampus, while the EP3 and FP mRNA and protein expressions and the TP mRNA expression decreased.

Conclusions: The PGS/PGs/PG receptors signaling pathway in chronic aluminium gluconate-overloaded rat hippocampus is disturbed, which may be involved in the mechanism of aluminium neurotoxicity.

Figure 1

Morphological changes of rat hippocampal neuron induced by aluminium gluconate overload. (a) Representative graph of HE-stained CA1 section, 400×. Scale bars = 50 μm. Arrow indicates cell karyopyknosis. Dead nerve cells are characterized by eosinophilic changes; for instance, nerve cells became deep and red with nuclear pyknosis and nucleoli disappearance under light microscopy. (b) Data showing the cell death rate (n = 4). Data are expressed as mean ± SD of four individual experiments. ∗P < 0.05 compared with control group.

Figure 2

Expression of PG synthase mRNA in rat hippocampus (n = 4). The expression of PG synthase mRNA was measured by RT-PCR. The middle band on the PCR images is a marker. The relative mRNA level of PG synthase was standardized to endogenous β-actin mRNA for each sample. Data are expressed as mean ± SD of four individual experiments. Al administration induced a significant increase of TXAS, mPGES-1 and PGIS compared with the control group (∗P < 0.05).

Figure 3

Expression of PG receptors mRNA in rat hippocampus (n = 4). The mRNA expression of PG receptors was measured by RT-PCR. The middle band on the PCR images is a marker. The relative mRNA level of PG receptors was standardized to endogenous β-actin mRNA for each sample. Data are expressed as mean ± SD of four individual experiments. Al administration induced a significant increase of EP2, EP4, DP1 and IP levels and a significant decrease of EP3, FP and TP levels compared with the control group (∗P < 0.05).

Figure 4

Protein expression of PG receptors in rat hippocampus (n = 4). The protein expression of PG receptors was measured by Western blot. The relative protein level of PG receptors was standardized to endogenous β-actin protein for each sample. Data are expressed as mean ± SD of four individual experiments. Al administration induced a significant increase of EP2, DP1 and IP levels and a significant decrease of EP3 and FP levels compared with the control group (∗P < 0.05).