Effect of hyperglycemia on microglial polarization after cerebral ischemia-reperfusion injury in rats.

Hyperglycemia has been shown to aggravate ischemic brain damage, in which the inflammatory reaction induced by hyperglycemia is involved in the worsening of cerebral ischemia-reperfusion injury. However, the role of microglial polarization in hyperglycemia-aggravating cerebral ischemia-reperfusion injury remains unknown. The present study investigated whether diabetic hyperglycemia inhibited or activated microglia, as well as microglial subtypes 1 and 2. Rats were used to establish the diabetic hyperglycemia and middle cerebral artery occlusion (MCAO) model. The markers CD11b, CD16, CD32, CD86, CD206, and Arg1 were used to show M1 or M2 microglia. The results revealed increased neurological deficits, infarct volume, and neural apoptosis in rats with hyperglycemia subjected to MCAO for 30 min and reperfused at 1, 3, and 7 days compared with the normoglycemic rats. Microglia and astrocyte activation and proliferation were inhibited in hyperglycemic rats. Furthermore, M1 microglia polarization was promoted, while that of M2 microglia was inhibited in hyperglycemic rats. These findings suggested that the polarization of M1 and M2 microglia is activated and inhibited, respectively, in hyperglycemic rats and may be involved in the aggravated brain damage caused by ischemia-reperfusion in diabetic hyperglycemia.

Region-specific changes in aquaporin 4 induced by hyperglycemia underlie the differences in cell swelling in the cortex and striatum after cerebral ischemia-reperfusion.

Brain edema is a major cause of death in patients who suffer an ischemic stroke. Diabetes has been shown to aggravate brain edema after cerebral ischemia-reperfusion, but few studies have focused on the heterogeneity of this response across different brain regions. Aquaporin 4 plays an important role in the formation and regression of brain edema. Here, we report that hyperglycemia mainly affects the continuity of aquaporin 4 distribution around blood vessels in the cortical penumbra after ischemia-reperfusion; however, in the striatal penumbra, in addition to affecting the continuity of distribution, it also substantially affects the fluorescence intensity and the polarity distribution in astrocytes. Accordingly, hyperglycemia induces a more significant increase in the number of swelling cells in the striatal penumbra than in the cortical penumbra. These results can improve our understanding of the mechanism underlying the effects of diabetes in cerebral ischemic injury and provide a theoretical foundation for identification of appropriate therapeutic modalities.

Hyperhomocysteinemia-induced autophagy and apoptosis with downregulation of hairy enhancer of split 1/5 in cortical neurons in mice.

It has been reported that hyperhomocysteinemia (HHcy) is associated with neurodegenerative and cardiovascular diseases. However, little is known about brain histomorphology, neuronal organelles, and hairy enhancer of split ( hes) expression under HHcy. In this study, non-HHcy and HHcy induced by high-methionine diet in apolipoprotein E-deficient (Apo E-/-) mice were comparatively investigated. The histomorphology, ultrastructure, autophagosomes, apoptosis, and expression of proteins, HES1, HES5 and P62, were designed to assess the effects of HHcy on brain. The results showed that compared to the non-HHcy mice, the HHcy group had an increase in autophagosomes, vacuolization in mitochondria, and neuron apoptosis; treatment with folate and vitamin B12 reduced the extent of these lesions. However, the elementary histomorphology, the numbers of cortical neurons, and Nissl bodies had no significant difference between the HHcy and the non-HHcy groups or the group treated with folate and vitamin B12. Immunohistochemistry and immunofluorescence demonstrated a decrease in HES1- or HES5-positive neurons in the HHcy group when compared to the non-HHcy groups, wild-type, and Apo E-/- controls, or the HHcy mice with folate and vitamin B12 supplement. Western blots showed that HHcy induced a decreased expression of HES1 and HES5, or P62, in which the expression of HES1 and P62 was elevated by treating with folate and vitamin B12 supplement. These results suggest that HHcy-enhanced brain damage is associated with increased autophagy and neuronal apoptosis in Apo E-/- mice, in which downregulation of hes1 and hes5 is involved.

Coenzyme Q10 ameliorates cerebral ischemia reperfusion injury in hyperglycemic rats.

The purpose of this study is to investigate the effect of coenzyme Q10 (CoQ10) on focal cerebral ischemia/reperfusion (I/R) injury in hyperglycemic rats and the possible involved mechanisms. In this study, we established the transient middle cerebral artery occlusion (MCAO) for 30min in the rats with diabetic hyperglycemia. The neurological deficit score, 2,3,5-triphenyltetrazolium chloride (TTC) staining and pathohistology are applied to detect the extent of the damage. The expression of Fis1, Mfn2 and Lc3 in the brain is investigated by immunohistochemical and Western blotting techniques. The results showed that the streptozotocin-induced diabetic hyperglycemia and MCAO-induced focal cerebral ischemia were successfully prepared in rats. In the hyperglycemic group, the neurological deficit scores, infarct volumes, and number of pyknotic cells were higher than that in the normalglycemic group at 24h and/or 72h reperfusion. Pretreated with CoQ10 (10mg/kg) for four weeks could significantly reduce the neurological scores, infarct volume, and pyknotic cells at 24h and/or 72h reperfusion of the hyperglycemic rats compared with non-CoQ10 pretreated hyperglycemic animals. Immunohistochemistry and Western blotting showed that pretreatment with CoQ10 or insulin could significantly reduce the expression of Fis1 protein in the brain at 24h and 72h reperfusion. Inversely, a significantly increased expression of Mfn2 was observed in the rats CoQ10 or insulin pretreated at 24h and/or 72h reperfusion when compared with matched hyperglycemic rats. These results demonstrated that hyperglycemia could aggravate ischemic brain injury. Pretreatment with CoQ10 might ameliorate the diabetic hyperglycemia aggravated I/R brain damage in the MCAO rats by maintain the balance between mitochondrial fission and fusion.

Overexpression of selenoprotein H prevents mitochondrial dynamic imbalance induced by glutamate exposure.

Selenium and selenoproteins play important roles in neuroprotection against glutamate­induced cell damage, in which mitochondrial dysfunction is considered a major pathogenic feature. Recent studies have revealed that mitochondrial fission could activates mitochondrial initiated cell death pathway. The objectives of the study are to determine whether glutamate induced cell death is mediated through mitochondrial initiated cell death pathway and activation of autophagy, and whether overexpression of selenoprotein H can protect cells from glutamate toxicity by preserving mitochondrial morphology and suppressing autophagy. Vector- or human selenoprotein H (SelH)-transfected HT22 cells (V-HT22 and SelH-HT22, respectively) were exposed to glutamate. The results showed that glutamate-induced cytotoxicity was associated with increased ROS production and imbalance in mitochondrial dynamics and autophagy. These alterations were reversed and cellular integrity restored by overexpression of SelH in HT22 cells.