kyu ri hahn

Vacuolar H+-ATPase is a highly conserved enzyme that plays an important role in maintaining an acidic environment for lysosomal function and accumulating neurotransmitters in synaptic vesicles. In the present study, we investigated the time-dependent changes in the expression of vacuolar H+-ATPase V1B2 (ATP6V1B2), a major neuronal subtype of vacuolar H+-ATPase located in the hippocampus, after 5 min of transient forebrain ischemia in gerbils. We also examined the pH and lactate levels in the hippocampus after ischemia to elucidate the correlation between ATP6V1B2 expression and acidosis.

Transient forebrain ischemia was induced by occlusion of both common carotid arteries for 5 min and animals were sacrificed at various time points after ischemia for immunohistochemical staining of ATP6V1B2 and measurements of pH and lactate levels in the hippocampus.

ATP6V1B2 immunoreactivity was found to be transiently increased in the hippocampal CA1 region and dentate gyrus 12–24 hr after ischemia when the pH and lactate levels were decreased. In addition, ATP6V1B2 immunoreactivity significantly increased in the hippocampal CA3 and dentate gyrus, regions relatively resistant to ischemic damage, 4 days after ischemia, when the NeuN-positive, mature neuron numbers were significantly decreased in the hippocampal CA1 region. 

These results suggest that ATP6V1B2 expression is transiently increased in the hippocampus following ischemia, which may be intended to compensate for ischemia-related dysfunction of ATP6V1B2 in the hippocampus.

Prostaglandin E2 E-prostanoid 2 receptor (PGE2 EP2), downstream of cyclooxygenase-2 (COX-2), plays an important role in inflammatory responses, but there are some reports about synaptic functions of COX-2 and PGE2 EP2 in the hippocampus. C57BL/6J mice were sacrificed at postnatal days (P) 1, 7, 14, 28, and 56 for immunohistochemical staining for EP2 and doublecortin as well as western blot for EP2. In addition, COX-2 knockout and its wild-type mice were euthanized for immunohistochemical staining for EP2. EP2 immunoreactivity was observed in the majority of the cells in the dentate gyrus at P1 and P7, while at P14, it was detected in the outer granule cell layer and was confined to its subgranular zone at P28 and P56. EP2 protein levels in the hippocampal homogenates were also highest at P7 and lowest at P56. EP2 immunoreactivity was partially colocalized, with doublecortin (DCX)-immunoreactive neuroblasts appearing in the mid-zone of the granule cell layer at P14 and in the subgranular zone of the dentate gyrus at P28. Co-localization of EP2 and DCX was significantly decreased in the dentate gyrus in the P28 group compared with that in the P14 group. In COX-2 knockout mice, EP2 immunoreactivity was significantly decreased in the hippocampal CA1 region (P=0.000165) and dentate gyrus (P=0.00898). EP2 decreases with age, which is expressed in DCX-immunoreactive neuroblasts in the dentate gyrus. This suggests that EP2 is closely linked to structural lamination and adult neurogenesis in the dentate gyrus.