Activation of microglia/macrophages expressing phosphorylated S6 ribosomal protein in a case of hemimegalencephaly with progressive calcification and atrophy

Deficiency of Microglial Autophagy Increases the Density of Oligodendrocytes and Susceptibility to Severe Forms of Seizures

Excessive activation of mTOR in microglia impairs CNS homeostasis and causes severe epilepsy. Autophagy constitutes an important part of mTOR signaling. The contribution of microglial autophagy to CNS homeostasis and epilepsy remains to be determined. Here, we report that ATG7KO mice deficient for autophagy in microglia display a marked increase of myelination markers, a higher density of mature oligodendrocytes (ODCs), and altered lengths of the nodes of Ranvier. Moreover, we found that deficiency of microglial autophagy (ATG7KO) leads to increased seizure susceptibility in three seizure models (pilocarpine, kainic acid, and amygdala kindling). We demonstrated that ATG7KO mice develop severe generalized seizures and display nearly 100% mortality to convulsions induced by pilocarpine and kainic acid. In the amygdala kindling model, we observed significant facilitation of contralateral propagation of seizures, a process underlying the development of generalized seizures. Taken together, our results reveal impaired microglial autophagy as a novel mechanism underlying altered homeostasis of ODCs and increased susceptibility to severe and fatal generalized seizures.

Microglial mTOR is Neuronal Protective and Antiepileptogenic in the Pilocarpine Model of Temporal Lobe Epilepsy

Excessive activation of mammalian target of rapamycin (mTOR) signaling is epileptogenic in genetic epilepsy. However, the exact role of microglial mTOR in acquired epilepsy remains to be clarified. In the present study, we found that mTOR is strongly activated in microglia following excitatory injury elicited by status epilepticus. To determine the role of microglial mTOR signaling in excitatory injury and epileptogenesis, we generated mice with restrictive deletion of mTOR in microglia. Both male and female mice were used in the present study. We found that mTOR-deficient microglia lost their typical proliferative and inflammatory responses to excitatory injury, whereas the proliferation of astrocytes was preserved. In addition, mTOR-deficient microglia did not effectively engulf injured/dying neurons. More importantly, microglial mTOR-deficient mice displayed increased neuronal loss and developed more severe spontaneous seizures. These findings suggest that microglial mTOR plays a protective role in mitigating neuronal loss and attenuating epileptogenesis in the excitatory injury model of epilepsy.SIGNIFICANCE STATEMENT The mammalian target of rapamycin (mTOR) pathway is strongly implicated in epilepsy. However, the effect of mTOR inhibitors in preclinical models of acquired epilepsy is inconsistent. The broad presence of mTOR signaling in various brain cells could prevent mTOR inhibitors from achieving a net therapeutic effect. This conundrum has spurred further investigation of the cell type-specific effects of mTOR signaling in the CNS. We found that activation of microglial mTOR is antiepileptogenic. Thus, microglial mTOR activation represents a novel antiepileptogenic route that appears to parallel the proepileptogenic route of neuronal mTOR activation. This may explain why the net effect of mTOR inhibitors is paradoxical in the acquired models of epilepsy. Our findings could better guide the use of mTOR inhibitors in preventing acquired epilepsy.

miR32-5p promoted vascular smooth muscle cell calcification by upregulating TNFα in the microenvironment

BACKGROUND

Vascular calcification is often associated with chronic inflammation and is a risk factor for brain arterial stiffness. Our previous results showed that miR32-5p was positively correlated with vascular smooth muscle cells (VSMC) calcification, but it is unclear whether miR32-5p promoted VSMC calcification by regulating inflammatory factor production.

RESULTS

In this study, bioinformatics analysis was used to select tumour necrosis factor α (TNFα) as a candidate inflammatory factor associated with calcification. Moreover, alizarin red staining and qRT-PCR analysis revealed that TNFα produced by BV2 cells was the key promoting factor of VSMC calcification. Interestingly, the expression of TNFα was significantly increased at the mRNA and protein levels after miR32-5p mimic treatment but significantly decreased after miR32-5p antagomir treatment. To explore the mechanism of the regulation of TNFα expression by miR32-5p, bioinformatics analysis indicated that PIKfyve was a candidate target gene of miR32-5p, and luciferase assays verified that the expression of PIKfyve was significantly repressed by miR32-5p mimics. Importantly, rescue experiments showed that the expression of TNFα in BV2 cells treated with miR32-5p antagomir and the PIKfyve inhibitor YM201636 was significantly increased.

CONCLUSIONS

The production of TNFα in microglia could be affected by miR32-5p targeting PIKfyve, and these results will be beneficial to reveal the mechanism of brain arterial calcification.

[Correlation of phosphorylated S6 protein expression in blood and brain tissue in mice and rats with kainic acid-induced seizure]

OBJECTIVE

To determine the correlation of phosphorylated ribosomal S6 protein (P-S6) content in blood and brain tissue in mice and rats with seizure.

METHODS

Seizure models were induced by intraperitoric injection of kainic acid (KA) in C57BL/mice and SD rats. Flow cytometry was used to detect the content of P-S6 in blood; Western blot was used to detect the expression of P-S6 in brain tissues. The correlation between P-S6 expression in blood and in brain tissue was examine by Pearson analysis, and the correlation between P-S6 expression in blood and the severity of seizure was also observed.

RESULTS

Western blotting analysis showed that the expression of P-S6 was significantly increased in peripheral blood and brain tissue in mice 1 h after KA-induced seizure,and the expression levels increased to (1.49±0.45) times (P<0.05) and (2.55±0.66) times (P <0.01) of the control group, respectively. Flow cytometry showed that the positive percentage and average fluorescence intensity of P-S6 in the blood of mice increased significantly 1 h after KA-induced seizures (P<0.01), which was consistent with the expression of P-S6 in brain tissue (r=0.8474, P<0.01). Flow cytometry showed that the average fluorescence intensity of P-S6 in blood increased from 14.89±9.75 to 52.35±21.72 (P<0.01) in rats with seizure, which was consistent with the change of P-S6 in brain tissue (r=0.9385, P<0.01). Rats with higher levels of seizure were of higher levels of P-S6 in peripheral blood.

CONCLUSIONS

Consistent correlation of P-S6 expression is demonstrated in peripheral blood and in brain tissue after KA-induced seizure, suggesting that the expression of P-S6 in blood can accurately reflect the changes of mTOR signaling pathway in brain tissue.

Exercise increases mTOR signaling in brain regions involved in cognition and emotional behavior

Exercise can enhance learning and memory and produce resistance against stress-related psychiatric disorders such as depression and anxiety. In rats, these beneficial effects of exercise occur regardless of exercise controllability: both voluntary and forced wheel running produce stress-protective effects. The mechanisms underlying these beneficial effects of exercise remain unknown. The mammalian target of rapamycin (mTOR) is a translation regulator important for cell growth, proliferation, and survival. mTOR has been implicated in enhancing learning and memory as well as antidepressant effects. Moreover, mTOR is sensitive to exercise signals such as metabolic factors. The effects of exercise on mTOR signaling, however, remain unknown. The goal of the present study was to test the hypothesis that exercise, regardless of controllability, increases levels of phosphorylated mTOR (p-mTOR) in brain regions important for learning and emotional behavior. Rats were exposed to 6 weeks of either sedentary (locked wheel), voluntary, or forced wheel running conditions. At 6 weeks, rats were sacrificed during peak running and levels of p-mTOR were measured using immunohistochemistry. Overall, both voluntary and forced exercise increased p-mTOR-positive neurons in the medial prefrontal cortex, striatum, hippocampus, hypothalamus, and amygdala compared to locked wheel controls. Exercise, regardless of controllability, also increased numbers of p-mTOR-positive glia in the striatum, hippocampus, and amygdala. For both neurons and glia, the largest increase in p-mTOR positive cells was observed after voluntary running, with forced exercise causing a more modest increase. Interestingly, voluntary exercise preferentially increased p-mTOR in astrocytes (GFAP+), while forced running increased p-mTOR in microglia (CD11+) in the inferior dentate gyrus. Results suggest that mTOR signaling is sensitive to exercise, but subtle differences exist depending on exercise controllability. Increases in mTOR signaling could contribute to the beneficial effects of exercise on cognitive function and mental health.

Brain Inflammation in an Infant With Hemimegalencephaly, Escalating Seizures, and Epileptic Encephalopathy

Hemimegalencephaly, a congenital brain malformation typically characterized by enlargement of one hemisphere, is frequently associated with intractable epilepsy. The authors report a case of a 12-month-old girl with hemimegalencephaly who underwent semiurgent hemispherectomy because of rapidly escalating seizures, arrested development, and associated encephalopathy. The brain tissue was examined and evaluated for neuroinflammation. Immunohistochemical analysis of the brain tissue revealed the presence of abundant activated CD68-positive microglia and reactive astrogliosis. Detection of active inflammatory changes in the brain of a patient with hemimegalencephaly complicated by intractable epilepsy suggests a potential role of ongoing brain inflammation in seizure exacerbation and epileptic encephalopathy.

Increased Ki-67 immunoreactivity in the white matter in hemimegalencephaly

Hemimegalencephaly (HMG) is a developmental brain disorder characterized by an enlarged unilateral hemisphere with cortical malformation comprising abnormal hypertrophic cells. To address the proliferative status of HMG, Ki-67 immunoreactivity was investigated in HMG specimens obtained during epilepsy surgery. Nine HMG tissues were stained with a Ki-67 antibody and Ki-67 labeling index in the malformed cortex, and the underlying white matter was measured separately and compared with tissues from focal cortical dysplasias and normal brains from autopsy. In HMG tissues, Ki-67-positive cells were scattered in both the gray and white matter, with a significantly higher Ki-67 labeling index in the white matter compared with gray matter. No dysmorphic neuron or balloon cell was stained for Ki-67. As Ki-67 immunoreactivity overlapped with that of ionized calcium-binding adaptor protein-1, Ki-67-positive cells were identified as microglia. In HMG, microglia were activated and entered into a proliferative status with higher distribution in the white matter, implying an ongoing neuroinflammatory process involving the white matter.

Hypoalbuminemia in early onset dentatorubral-pallidoluysian atrophy due to leakage of albumin in multiple organs

We delineate a complication of hypoalbuminemia in dentatorubral-pallidoluysian atrophy (DRPLA), which we have found to be common in this disorder. In addition, we explored the pathogenesis of this phenomenon through clinical and histological examinations. Clinical course and laboratory findings of nine patients with childhood-onset DRPLA (aged 6-49 years; CAG repeat length 62-93) were retrospectively reviewed. Autopsied specimens from three patients were examined by histopathological and immunohistochemical analyses. Eight DRPLA patients showed hypoalbuminemia <3.5 g/dl in the initial stages of the disease (age, 2-32 years), which correlated with the CAG repeat length in each patient. Disease worsened in six patients, often triggered by febrile infections and accompanied by increased urinary protein excretion. One patient showed increased fecal α1-antitripsin while another showed accumulation of radioactive albumin in the urinary and gastrointestinal tracts after intravenous infusion. Immunohistochemistry revealed albumin-containing monocytes and astrocytes in the perivascular areas of the cerebral white matter. Fluid collection in the glomerular capillaries was noted. Immunolabeling using antibodies against the expanded polyglutamine (polyQ) polypeptide was positive in cerebral cortical neurons, hepatocytes, renal collecting ducts, and glomerular podocytes, which act as filtration barrier against serum proteins. Serum albumin appears to easily leak from blood vessels in certain visceral organs in DRPLA during later stages of the illness, particularly in the kidneys of patients with largely expanded CAG repeats. We hypothesize that the accumulation of the DRPLA gene product with expanded polyQ sequences in the podocytes results in the dysfunction of the glomerular filtration barrier.

ATP-dependent potassium channel blockade strengthens microglial neuroprotection after hypoxia-ischemia in rats

Stroke causes CNS injury associated with strong fast microglial activation as part of the inflammatory response. In rat models of stroke, sulphonylurea receptor blockade with glibenclamide reduced cerebral edema and infarct volume. We postulated that glibenclamide administered during the early stages of stroke might foster neuroprotective microglial activity through ATP-sensitive potassium (K(ATP)) channel blockade. We found in vitro that BV2 cell line showed upregulated expression of K(ATP) channel subunits in response to pro-inflammatory signals and that glibenclamide increases the reactive morphology of microglia, phagocytic capacity and TNFα release. Moreover, glibenclamide administered to rats 6, 12 and 24h after transient Middle Cerebral Artery occlusion improved neurological outcome and preserved neurons in the lesioned core three days after reperfusion. Immunohistochemistry with specific markers to neuron, astroglia, microglia and lymphocytes showed that resident amoeboid microglia are the main cell population in that necrotic zone. These reactive microglial cells express SUR1, SUR2B and Kir6.2 proteins that assemble in functional K(ATP) channels. These findings provide that evidence for the key role of K(ATP) channels in the control of microglial reactivity are consistent with a microglial effect of glibenclamide into the ischemic brain and suggest a neuroprotective role of microglia in the early stages of stroke.