Prosaposin Overexpression following Kainic Acid-Induced Neurotoxicity

Abstract

Because excessive glutamate release is believed to play a pivotal role in numerous neuropathological disorders, such as ischemia or seizure, we aimed to investigate whether intrinsic prosaposin (PS), a neuroprotective factor when supplied exogenously in vivo or in vitro, is up-regulated after the excitotoxicity induced by kainic acid (KA), a glutamate analog. In the present study, PS immunoreactivity and its mRNA expression in the hippocampal and cortical neurons showed significant increases on day 3 after KA injection, and high PS levels were maintained even after 3 weeks. The increase in PS, but not saposins, detected by immunoblot analysis suggests that the increase in PS-like immunoreactivity after KA injection was not due to an increase in saposins as lysosomal enzymes after neuronal damage, but rather to an increase in PS as a neurotrophic factor to improve neuronal survival. Furthermore, several neurons with slender nuclei inside/outside of the pyramidal layer showed more intense PS mRNA expression than other pyramidal neurons. Based on the results from double immunostaining using anti-PS and anti-GABA antibodies, these neurons were shown to be GABAergic interneurons in the extra- and intra-pyramidal layers. In the cerebral cortex, several large neurons in the V layer showed very intense PS mRNA expression 3 days after KA injection. The choroid plexus showed intense PS mRNA expression even in the normal rat, and the intensity increased significantly after KA injection. The present study indicates that inhibitory interneurons as well as stimulated hippocampal pyramidal and cortical neurons synthesize PS for neuronal survival, and the choroid plexus is highly activated to synthesize PS, which may prevent neurons from excitotoxic neuronal damage. To the best of our knowledge, this is the first study that demonstrates axonal transport and increased production of neurotrophic factor PS after KA injection.

A Prosaposin-Derived Peptide Alleviates Kainic Acid-Induced Brain Injury

“…Furthermore, the hippocampus, particularly the DG, is the region where c-Fos expression (i.e., neuronal activation) is moderately observed under normal conditions, and is strongly observed following acute and chronic social stress [ 43 ]. The degree of KA-induced neuronal injury is influenced by temperature, anesthesia, or anticonvulsant drugs [ 15 ]. These delicate and complex mechanisms may be responsible for the variation in KA neurotoxicity in the CA3.…”

“…After 10 minutes, rats were anesthetized again with diethyl ether, and 12 mg/kg of KA, dissolved in phosphate-buffered saline (PBS), was subcutaneously injected [ 32 ]. After KA injection, the animals were housed at a constant temperature (22°C), as KA effects are at least partly dependent on body temperature [ 15 ]. The dose of KA was chosen based on the results of previous studies [ 15 ], and clonazepam did not result in any obvious convulsion during the experimental time, and all 24 rats were survived until the fixation.…”

“…In addition, unprocessed PS is found in various secretory fluids, such as seminal plasma, bile, pancreatic juice, human breast milk, and cerebrospinal fluid [ 12 , 13 ]. PS mRNA and PS are strongly expressed in the choroid plexus [ 14 , 15 ].…”

“…We showed that PS and its mRNA increase in the facial nerve nucleus after nerve transection [ 36 , 37 ] and decrease in the brain of mdx (X chromosome-linked muscular dystrophy) mice [ 38 ]. In a previous study, we showed an increase in PS and PS mRNA in brain neurons and in the choroid plexus after a systemic KA injection [ 15 ].…”

Effects of Excitotoxic Lesion with Inhaled Anesthetics on Nervous System Cells of Rodents

“…The nature of neuronal degeneration caused by systemic KA injection resembles some forms of ischemia [79]. The degree of KA-induced neuronal injury is influenced by temperature, anesthesia, and anticonvulsant drugs [80,81].…”