Annexin 7-immunoreactive microglia in the hippocampus of control and adrenalectomized rats

Annexin A7 induction of neuronal apoptosis via effect on glutamate release in a rat model of subarachnoid hemorrhage

OBJECTIVE

Glutamate excitotoxicity and neuronal apoptosis are suggested to contribute to early brain injury after subarachnoid hemorrhage (SAH). Annexin A7 (ANXA7) has been shown to regulate glutamate release. However, the role of ANXA7 in early brain injury after SAH has not been illustrated. In this study, we aimed to investigate the effect of ANXA7 knockdown in reducing the severity of early brain injury after SAH, and determine the underlying mechanisms.

METHODS

Endovascular perforation was performed to induce SAH in male Sprague-Dawley rats. ANXA7-siRNA was administered via intraventricular injection 5 days before SAH induction. Neurological test, evaluation of SAH grade, assessment of blood-brain barrier (BBB) permeability, measurement of brain water content, Western blot, double immunofluorescence staining, TUNEL staining, and enzyme-linked immunosorbent assay (ELISA) were performed at 24 hours of SAH induction.

RESULTS

ANXA7 protein expression increased significantly after SAH induction and was seen mainly in neurons. High expression of ANXA7 was associated with poor neurological status. ANXA7 knockdown dramatically ameliorated early brain injury through alleviating BBB disruption and brain edema. Further investigation of the mechanism showed that inhibiting ANXA7 expression can rescue neuronal apoptosis. In addition, ANXA7 knockdown also significantly reduced glutamate release, which was consistent with a significant increase of Bcl-2 expression and decreases of Bax and cleaved caspase-3 expression.

CONCLUSIONS

ANXA7 can induce neuronal apoptosis by affecting glutamate release in rats with SAH. Downregulating the expression of ANXA7 can significantly attenuate early brain injury after SAH. Future therapy targeting ANXA7 may be a promising new choice.

Annexin A7 Levels Increase in Rats With Traumatic Brain Injury and Promote Secondary Brain Injury

The incidence of traumatic brain injury (TBI) has been increasing annually. Annexin A7 is a calcium-dependent phospholipid binding protein. It can promote melting of the cell membrane. Recent studies have shown that it plays an important role in atherosclerosis, other cardiovascular diseases, and a variety of tumors. However, few studies of ANXA7 in TBI have been performed. We here observed how ANXA7 changes after TBI and discuss whether brain injury is associated with the use of ANXA7 antagonist intervention. Experimental Results: 1. After TBI, ANXA7 levels were higher than in the sham group, peaking 24 h after TBI. 2. The use of siA7 was found to reduce the expression of A7 in the injured brain tissue, and also brain edema, BBB damage, cell death, and apoptosis relative to the sham group. Conclusion: ANXA7 promotes the development of secondary brain injury (SBI) after TBI.

Expression profiles of hippocampal regenerative sprouting-related genes and their regulation by E-64d in a developmental rat model of penicillin-induced recurrent epilepticus

E-64d (a calpain and autophagy inhibitor) has previously been shown safe for the treatment of Alzheimer's disease in humans. In the present study, the potential protective mechanism of E-64d on hippocampal aberrant mossy fiber sprouting was examined in a developmental rat model of penicillin-induced recurrent epilepticus. A seizure was induced by penicillin every other day in Sprague-Dawley rats from postnatal day 21 (P21). The rats were randomly assigned into the control group (CONT1), the control plus E-64d (CONT2), the seizure group (EXP1) and the seizure plus E-64d (EXP2). On P51, mossy fiber sprouting and related gene expression in hippocampus were assessed by Timm staining and real-time RT-PCR methods, respectively. To validate the RT-PCR results, western blot analysis was performed on selected genes. E-64d obviously suppressed the aberrant mossy fiber sprouting in the supragranular region of dentate gyrus and CA3 subfield of hippocampus. Among the total twelve genes, six genes were strongly up- (MT-3, ACAT1, clusterin and ApoE) or down- (ZnT-1 and PRG-3) regulated by developmental seizures (EXP1) compared with that in the CONT1. Up-regulation of ApoE and Clusterin was blocked by pretreatment with E-64d both in mRNA and protein levels. Further, E-64d-pretreated seizure rats (EXP2) showed a significant downregulation of mRNA expression of PRG-1, PRG-3 and PRG-5, cathepsin B and ApoE, as well as up-regulated nSMase and ANX7 in hippocampus when compared with EXP1 rats. The results of the present study suggest that E-64d, an elective inhibitor of calpain and autophagy, is potentially useful in the treatment of developmental seizure-induced brain damage both by regulating abnormal zinc signal transduction and through the modulation of altered lipid metabolism via ApoE/clusterin pathway in hippocampus.

Microglia-associated granule cell death in the normal adult dentate gyrus

Microglial cells are constantly monitoring the central nervous system for sick or dying cells and pathogens. Previous studies showed that the microglial cells in the dentate gyrus have a heterogeneous morphology with multipolar cells in the hilus and fusiform cells apposed to the granule cell layer both at the hilar and at the molecular layer borders. Although previous studies showed that the microglia in the dentate gyrus were not activated, the data in the present study show dying granule cells apposed by Iba1-immunolabeled microglial cell bodies and their processes both at hilar and at molecular layer borders of the granule cell layer. Initially, these Iba1-labeled microglial cells surround individual, intact granule cell bodies. When small openings in the plasma membrane of granule cells are observed, microglial cells are apposed to these openings. When larger openings in the plasma membrane occur at this site of apposition, the granule cells display watery perikaryal cytoplasm, watery nucleoplasm and damaged organelles. Such morphological features are characteristic of neuronal edema. The data also show that following this localized disintegration of the granule cell’s plasma membrane, the Iba1-labeled microglial cell body is found within the electron-lucent perikaryal cytoplasm of the granule cell, where it is adjacent to the granule cell’s nucleus which is deformed. We propose that granule cells are dying by a novel microglia-associated mechanism that involves lysis of their plasma membranes followed by neuronal edema and nuclear phagocytosis. Based on the morphological evidence, this type of cell death differs from either apoptosis or necrosis.

Morphological and ultrastructural features of Iba1-immunolabeled microglial cells in the hippocampal dentate gyrus

Microglia are found throughout the central nervous system, respond rapidly to pathology and are involved in several components of the neuroinflammatory response. Iba1 is a marker for microglial cells and previous immunocytochemical studies have utilized this and other microglial-specific antibodies to demonstrate the morphological features of microglial cells at the light microscopic level. However, there is a paucity of studies that have used microglial-specific antibodies to describe the ultrastructural features of microglial cells and their processes. The goal of the present study is to use Iba1 immuno-electron microscopy to elucidate the fine structural features of microglial cells and their processes in the hilar region of the dentate gyrus of adult Sprague-Dawley rats. Iba1-labeled cell bodies were observed adjacent to neurons and capillaries, as well as dispersed in the neuropil. The nuclei of these cells had dense heterochromatin next to the nuclear envelope and lighter chromatin in their center. Iba1-immunolabeling was found within the thin shell of perikaryal cytoplasm that contained the usual organelles, including mitochondria, cisternae of endoplasmic reticulum and Golgi complexes. Iba1-labeled cell bodies also commonly displayed an inclusion body. Iba1-labeled cell bodies gave rise to processes that often had a small side branch arise within 5 mum of the microglial cell body. These data showing "resting" Iba-1 labeled microglial cells in the normal adult rat dentate gyrus provide a basis for comparison with the morphology of microglial cells in disease and injury models where they are activated or phagocytotic.

Cerebral hypoxia-ischemia and middle cerebral artery occlusion induce expression of the cannabinoid CB2 receptor in the brain

Until recently the cannabinoid CB2 receptor was believed to be absent from the central nervous system. In this study we have identified CB2 expressing cells that appear in the rat brain following stroke and hypoxic-ischemia. At 3 days following surgery CB2-positive macrophages, deriving from resident microglia and/or invading monocytes appear on the lesioned side of the brain. By day 7, a mixed population of CB2-positive cells is present. Microglia-derived macrophages are the key cells in the first stages of brain inflammation, and a pivotal step in the neurodegeneration that follows the acute stage of injury. Thus, CB2 may be important in the brain during injury, and in inflammatory neurodegenerative disorders. The presence of CB2-positive cells in the brain following stroke may provide a novel strategy for cannabinoid-mediated intervention into stroke induced neurodegeneration without the psychoactive effects of CB1 receptor stimulation.