Activation of the intrinsic cell death pathway, increased apoptosis and modulation of astrocytes in the cerebellum of diabetic rats

Protective effects of treadmill exercise on apoptotic neuronal damage and astrocyte activation in ovariectomized and/or diabetic rat prefrontal cortex: molecular and histological aspects

OBJECTIVE

Both estrogen deprivation and diabetes mellitus are known as risk factors for neuronal damage. Using an animal model of ovariectomized and/or streptozotocin (STZ)-induced diabetes mellitus, we examined expression of apoptosis-related proteins, neuronal damage, and astrocyte activation in prefrontal cortex of rats with/without treadmill exercise.

METHODS

Adult female Wistar rats were divided into control, ovariectomized (Ovx, bilateral ovariectomy), diabetic (Dia, STZ 60 mg/kg; i.p.), and ovariectomized diabetic (Ovx + Dia) groups. Next, animals in each group were randomly subdivided into non-exercise and exercise subgroups. Animals in the exercise groups underwent moderate treadmill running for 4 weeks (5 days/week). Thereafter, expression of Bax, Bcl-2, and caspase-3, as apoptosis-related proteins, number of neurons, and number of glial fibrillary acidic protein (GFAP)-positive cells in prefrontal cortex were measured using immunoblotting, cresyl violet staining, and immunohistochemistry, respectively.

RESULTS

In both Dia and Ovx + Dia groups, Bax and caspase-3 protein levels and number of GFAP-positive cells were higher than those in the control group, while Bcl-2 protein level and number of neurons compared were lower than the control group. Beneficial effects of exercise to prevent apoptosis-mediated neuronal damage and astrocyte activation were also observed in the Dia group.

CONCLUSION

Based on our results, physical exercise could be beneficial to attenuate diabetes-induced neuronal damage in the prefrontal cortex via inhibition of apoptosis.

Feeding High-Fat Diet Accelerates Development of Peripheral and Central Insulin Resistance and Inflammation and Worsens AD-like Pathology in APP/PS1 Mice

Alzheimer's disease (AD) is a progressive brain disorder characterized by extracellular amyloid-β (Aβ) plaques, intracellular neurofibrillary tangles formed by hyperphosphorylated Tau protein and neuroinflammation. Previous research has shown that obesity and type 2 diabetes mellitus, underlined by insulin resistance (IR), are risk factors for neurodegenerative disorders. In this study, obesity-induced peripheral and central IR and inflammation were studied in relation to AD-like pathology in the brains and periphery of APP/PS1 mice, a model of Aβ pathology, fed a high-fat diet (HFD). APP/PS1 mice and their wild-type controls fed either a standard diet or HFD were characterized at the ages of 3, 6 and 10 months by metabolic parameters related to obesity via mass spectroscopy, nuclear magnetic resonance, immunoblotting and immunohistochemistry to quantify how obesity affected AD pathology. The HFD induced substantial peripheral IR leading to central IR. APP/PS1-fed HFD mice had more pronounced IR, glucose intolerance and liver steatosis than their WT controls. The HFD worsened Aβ pathology in the hippocampi of APP/PS1 mice and significantly supported both peripheral and central inflammation. This study reveals a deleterious effect of obesity-related mild peripheral inflammation and prediabetes on the development of Aβ and Tau pathology and neuroinflammation in APP/PS1 mice.

Alteration of Aquaporins 1 and 4 immunohistochemical and gene expression in the cerebellum of diabetic albino rat

Aquaporins (AQPs) are a family of transmembrane channel proteins. AQP1 and AQP4 are expressed in cerebellum amongst others. This study was designed to assess the effect of diabetes on AQP1 and AQP4 expression in cerebellum of rats. Diabetes was induced by a single intraperitoneal injection of Streptozotocin 45 mg/kg in 24 adult male Sprague Dawley rats. Six rats from control and diabetic groups were sacrificed at one, four, and eight weeks post diabetic confirmation. After eight weeks, measurement of malondialdehyde (MDA), reduced glutathione (GSH) concentrations, and cerebellar mRNA expression for AQP1 and AQP4 genes were performed. Immunohistochemical evaluation of AQP1, AQP4, and glial fibrillary acidic protein (GFAP) for cerebellar sections was performed for all groups. Diabetes caused degenerative changes in Purkinje cells with a significant increase in the cerebellar level of MDA and AQP1 immunoreactivity and a significant decrease in GSH level and AQP4 expression levels. However, the alteration in the AQP1 mRNA level was not statistically significant. GFAP immunoreactivity was increased in 8 W diabetic rats following its decrease in 1 W diabetic rats. Diabetes caused some alteration in the AQPs 1 and 4 expression in the cerebellum of diabetic rats which may contribute to diabetes-induced cerebellar complications.

Impaired spatial navigation and age-dependent hippocampal synaptic dysfunction are associated with chronic inflammatory response in db/db mice

Type 2 diabetes mellitus (T2DM) increases the risk of developing Alzheimer's disease (AD), which has been proposed to be driven by an abnormal neuroinflammatory response affecting cognitive function. However, the impact of T2DM on hippocampal function and synaptic integrity during aging has not been investigated. Here, we investigated the effects of aging in T2DM on AD-like pathology using the leptin receptor-deficient db/db mouse model of T2DM. Our results indicate that adult T2DM mice exhibited impaired spatial acquisition in the Morris water maze (MWM). Morphological analysis showed an age-dependent neuronal loss in the dentate gyrus. We found that astrocyte density was significantly decreased in all regions of the hippocampus in T2DM mice. Our analysis showed that microglial activation was increased in the CA3 and the dentate gyrus of the hippocampus in an age-dependent manner in T2DM mice. However, the expression of presynaptic marker protein (synaptophysin) and the postsynaptic marker protein [postsynaptic density protein 95 (PSD95)] was unchanged in the hippocampus of adult T2DM mice. Interestingly, synaptophysin and PSD95 expression significantly decreased in the hippocampus of aged T2DM mice, suggesting an impaired hippocampal synaptic integrity. Cytokine profiling analysis displayed a robust pro-inflammatory cytokine profile in the hippocampus of aged T2DM mice compared with the younger cohort, outlining the role of aging in exacerbating the neuroinflammatory profile in the diabetic state. Our results suggest that T2DM impairs cognitive function by promoting neuronal loss in the dentate gyrus and triggering an age-dependent deterioration in hippocampal synaptic integrity, associated with an aberrant neuroinflammatory response.

Microglia activation and inflammation in hippocampus attenuates memory and mood functions during experimentally induced diabetes in rat

Incidence of cognitive and emotional alterations are reportedly two times more in diabetic patients than in non-diabetic population with hitherto unexplained causation and mechanism. Purview of the hippocampus functional diversity sanctions the accessibility and the necessity to investigate the regional neuro-immunological aspects of neurodegeneration and related functional alterations following diabetes. We examined the possible involvement of microglia activation, macrophage response, oxidative stress and inflammatory stature in both ventral and dorsal hippocampus of rats rendered diabetic by a single injection of streptozotocin (STZ; 45 mg/ kg body weight; intraperitoneal). Cognitive and behavioural alterations were studied using open field test (locomotor activity), elevated plus maze (anxiety), Barnes maze (spatial cognition) and T maze (working memory) at 2nd, 4th, 6th, 8th, 10th and 12th week post diabetic confirmation. Oxidative stress was investigated via measuring the level of lipid peroxidation biochemically. Scenario of microglia activation, macrophage response and inflammation was gauged using qualitative and quantitative analysis. Pronounced macrophage expression and activation directed microglia phenotypic switching was prominent in both ventral and dorsal hippocampus indicating the impact of oxidative stress following diabetes in hippocampus. The resultant inflammatory response was also progressive and persistent in both ventral and dorsal hippocampus parallel to the altered cognitive, locomotor ability and anxiety behaviour in diabetic rats. Conclusively, present data not only comprehends the microglia, macrophage physiology and related immune response in functionally different hippocampal regions associated cognitive and behavioural deficits, but also offers a suggestive region-specific cellular mechanism pathway for developing an imminent therapeutic approach during particular diabetes deficits.

β-HB inhibits the apoptosis of high glucose-treated astrocytes via activation of CREB/BDNF axis

OBJECTIVE

Nerve damage can cause severe limb dysfunction and even leave a lifelong disability. The apoptosis of astrocytes may contribute to the nerve damage. In this research, we sought to investigate the effect of β-HB on nerve damage in vitro.

DESIGN

Astrocytes were treated with high glucose (HG) to mimic in vitro model of nerve damage. RT-qPCR and western blot were used to detect expressions of CREB, BDNF, Ki-67, PCNA, Bax, Bcl-2 and cleaved caspase 3 in astrocytes, respectively. MTT was used to measure the cell viability. In addition, flow cytometry was used to detect the cell apoptosis.

RESULTS

β-HB significantly promoted the proliferation and inhibited apoptosis in HG-treated astrocytes. Results showed that of PCNA and Bcl-2 were upregulated, and Bax and cleaved caspase 3 were downregulated after β-HB stimulated in HG-treated astrocytes. In addition, HG-induced inhibition on BDNF expression in astrocytes was notably reversed by β-HB. Furthermore, β-HB promoted the growth and inhibited apoptosis of high glucose-treated astrocytes via activation of CREB/BDNF axis.

CONCLUSION

β-HB promotes the growth and inhibits the apoptosis of high glucose-treated astrocytes via activation of CREB/BDNF axis, which may serve as a new target for treatment of nerve damage.

Melatonin ameliorates diabetes-induced brain injury in rats

Diabetic brain is a serious complication of diabetes, and it is associated with oxidative stress and neuronal injury. This study investigated the protective effect of melatonin (MLT) on diabetes-induced brain injury. A rat model of type 2 diabetes mellitus was produced by intraperitoneal injection of nicotinamide 100 mg/kg, followed by intraperitoneal injection of streptozotocin 55 mg/kg. The diabetic rats were orally administered MLT 10 mg/kg of body weight for 15 days. MLT remarkably downregulated serum glucose levels. It also improved levels of the lipid peroxidation product 4-hydroxynonenal, improved levels of antioxidants including glutathione, glutathione peroxidase and glutathione reductase in the brains of the diabetic rats, and this is indicative of the antioxidant potential of MLT. MLT also prevented increase in homocysteine, amyloid-β42 and tau levels in diabetic rats, and this suggests that it can reduce the risk of dementia. This is associated with reduction in the levels of the dopamine, serotonin, and glutamate and is indicative of the regulatory effect of MLT on neurotransmitters. Treatment with MLT improved diabetes-induced structural alteration in the hippocampus and cerebral cortex. MLT significantly reduced caspase-3 and Bax as well as significantly increase Bcl-2 protein and GFAP-positive astrocytes indicating its anti-apoptotic effect. MLT showed remarkable ameliorative effect against biochemical and molecular alterations in the brains of diabetic rats most likely through its antioxidant property.

Evaluation of the modulation of nitric oxide synthase expression in the cerebellum of diabetic albino rats and the possible protective effect of ferulic acid

INTRODUCTION

Diabetes mellitus is a multisystem disease. Oxidative stress and nitric oxide isoforms are involved in diabetic pathogenesis. Ferulic acid is a natural substance that is distributed broadly in plants with strong potent properties.

THE AIM OF THE RESEARCH

This research was designed to study the possible protective role of ferulic acid on oxidative stress and different Nitric oxide synthase isoforms (NOS) in the cerebellum of streptozotocin-induced diabetic rats.

MATERIALS AND METHODS

Twenty-four albino male rats were randomly divided into equal four groups: control group, group 2 received ferulic acid orally (10 mg/kg), group 3 diabetic group, group 4 diabetic rats received ferulic acid. After 8 weeks, the left cerebellar hemisphere was taken for tissue homogenate for oxidative markers and real-time PCR for NOS isoforms. Paraffin sections of the right cerebellar hemisphere were stained with cresyl violet, Luxol fast blue and immnunohistochemically stained for neuronal NOS, inducible NOS and endothelial NOS.

RESULTS

Degenerative changes were seen in the cerebella of the diabetic rats with significant elevation of Malondialdehyde, Nitric Oxide, and decrease of Superoxide dismutase levels. nNOS expression decreased and iNOS expression increased significantly. The ferulic acid-treated group showed a reduction of the degenerative changes in the cerebellum with significant improvement in oxidative stress marker, an increase of nNOS expression, and a decrease of iNOS expression.

CONCLUSIONS

Ferulic acid improves cerebellar functional and histopathological changes induced by diabetes which can be attributed mainly to its anti-oxidative effect and its ability to modulate NOS isoforms.

Experimentally induced diabetes causes glial activation, glutamate toxicity and cellular damage leading to changes in motor function

Behavioral impairments are the most empirical consequence of diabetes mellitus documented in both humans and animal models, but the underlying causes are still poorly understood. As the cerebellum plays a major role in coordination and execution of the motor functions, we investigated the possible involvement of glial activation, cellular degeneration and glutamate transportation in the cerebellum of rats, rendered diabetic by a single injection of streptozotocin (STZ; 45 mg/kg body weight; intraperitoneally). Motor function alterations were studied using Rotarod test (motor coordination) and grip strength (muscle activity) at 2nd, 4th, 6th, 8th, 10th, and 12th week post-diabetic confirmation. Scenario of glial (astroglia and microglia) activation, cell death and glutamate transportation was gaged using immunohistochemistry, histological study and image analysis. Cellular degeneration was clearly demarcated in the diabetic cerebellum. Glial cells were showing sequential and marked activation following diabetes in terms of both morphology and cell number. Bergmann glial cells were hypertrophied and distorted. Active caspase-3 positive apoptotic cells were profoundly present in all three cerebellar layers. Reduced co-labeling of GLT-1 and GFAP revealed the altered glutamate transportation in cerebellum following diabetes. These results, exclusively derived from histology, immunohistochemistry and cellular quantification, provide first insight over the associative reciprocity between the glial activation, cellular degeneration and reduced glutamate transportation, which presumably lead to the behavioral alterations following STZ-induced diabetes.

Prediabetes-induced vascular alterations exacerbate central pathology in APPswe/PS1dE9 mice

Age remains the main risk factor for developing Alzheimer's disease (AD) although certain metabolic alterations, including prediabetes and hyperinsulinemia, also increase this risk. We present a mouse model of AD (APPswe/PS1dE9 mouse) with severe hyperinsulinemia induced by long-term high fat diet (HFD) treatment. After 23 weeks on HFD learning and memory processes were compromised. We observed a significant increase in tau hyperphosphorylation and Aβ pathology, including Aβ levels and amyloid burden. Microglia activation was also significantly increased in HFD-treated mice, both in close proximity to and far from senile plaques. Insulin degrading enzyme and neprilysin levels were not affected, suggesting that Aβ degradation pathways were preserved, whereas we detected an increase in spontaneous cortical bleeding that could underlay an impairment of Aβ interstitial fluid drainage, contributing to the increase in Aβ deposition in APP/PS1-HFD mice. Altogether our data suggest that early hyperinsulinemia is enough to exacerbate AD pathology observed in APP/PS1 mice, and supports the role of insulin-resistance therapies to stop or delay central complications associated.

Disturbance of the glutamatergic system in mood disorders

The role of glutamatergic system in the neurobiology of mood disorders draws increasing attention, as disturbance of this system is consistently implicated in mood disorders including major depressive disorder and bipolar disorder. Thus, the glutamate hypothesis of mood disorders is expected to complement and improve the prevailing monoamine hypothesis, and may indicate novel therapeutic targets. Since the contribution of astrocytes is found to be crucial not only in the modulation of the glutamatergic system but also in the maintenance of brain energy metabolism, alterations in the astrocytic function and neuroenergetic environment are suggested as the potential neurobiological underpinnings of mood disorders. In the present review, the evidence of glutamatergic abnormalities in mood disorders based on postmortem and magnetic resonance spectroscopy (MRS) studies is presented, and disrupted energy metabolism involving astrocytic dysfunction is proposed as the underlying mechanism linking altered energy metabolism, perturbations in the glutamatergic system, and pathogenesis of mood disorders.

Advanced glycation end product-induced astrocytic differentiation of cultured neurospheres through inhibition of Notch-Hes1 pathway-mediated neurogenesis

This study aims to investigate the roles of the Notch-Hes1 pathway in the advanced glycation end product (AGE)-mediated differentiation of neural stem cells (NSCs). We prepared pLentiLox3.7 lentiviral vectors that express short hairpin RNA (shRNA) against Notch1 and transfected it into NSCs. Cell differentiation was analyzed under confocal laser-scanning microscopy. The percentage of neurons and astrocytes was quantified by normalizing the total number of TUJ1⁺ (Neuron-specific class III β-tubulin) and GFAP⁺ (Glial fibrillary acidic protein) cells to the total number of Hoechst 33342-labeled cell nuclei. The protein and gene expression of Notch-Hes1 pathway components was examined via western blot analysis and real-time PCR. After 1 week of incubation, we found that AGE-bovine serum albumin (BSA) (400 μg/mL) induced the astrocytic differentiation of cultured neurospheres and inhibited neuronal formation. The expression of Notch-Hes1 pathway components was upregulated in the cells in the AGE-BSA culture medium. Immunoblot analysis indicated that shRNA silencing of Notch1 expression in NSCs significantly increases neurogenesis and suppresses astrocytic differentiation in NSCs incubated with AGE-BSA. AGEs promote the astrocytic differentiation of cultured neurospheres by inhibiting neurogenesis through the Notch-Hes1 pathway, providing a potential therapeutic target for hyperglycemia-related cognitive deficits.

Insulin and insulin-like growth factor prevent brain atrophy and cognitive impairment in diabetic rats

There are an estimated 36 million dementia patients worldwide. The anticipated tripling of this number by year 2050 will negatively impact the capacity to deliver quality health care. The epidemic in diabetes is particularly troubling, because diabetes is a substantial risk factor for dementia independently of cerebrovascular disease. There is an urgent need to elucidate the pathogenesis of progressive brain atrophy, the cause of dementia, to allow rational design of new therapeutic interventions. This review summarizes recent tests of the hypothesis that the concomitant loss of insulin and insulin-like growth factors (IGFs) is the dominant cause for age-dependent, progressive brain atrophy with degeneration and cognitive decline. These tests are the first to show that insulin and IGFs regulate adult brain mass by maintaining brain protein content. Insulin and IGF levels are reduced in diabetes, and replacement of both ligands can prevent loss of total brain protein, widespread cell degeneration, and demyelination. IGF alone prevents retinal degeneration in diabetic rats. It supports synapses and is required for learning and memory. Replacement doses in diabetic rats can cross the blood-brain barrier to prevent hippocampus-dependent memory impairment. Insulin and IGFs are protective despite unabated hyperglycemia in diabetic rats, severely restricting hyperglycemia and its consequences as dominant pathogenic causes of brain atrophy and impaired cognition. These findings have important implications for late-onset alzheimer's disease (LOAD) where diabetes is a major risk factor, and concomitant decline in insulin and IGF activity suggest a similar pathogenesis for brain atrophy and dementia.

Effects of physical exercise on spatial memory and astroglial alterations in the hippocampus of diabetic rats

Type 1 diabetes mellitus (T1DM) is associated with neurocognitive dysfunction and astrogliosis. Physical exercise prevents cognitive impairments and induces important brain modifications. The aim of our study was to investigate the effect of treadmill exercise on spatial memory and astrocytic function in the hippocampus of a T1DM model. Fifty-seven Wistar rats were divided into four groups: trained control (TC) (n = 15), non-trained control (NTC) (n = 13), trained diabetic (TD) (n = 14) and non-trained diabetic (NTD) (n = 15). One month after streptozotocin-induced diabetes, exercise groups were submitted to 5 weeks of physical training, and then, all groups were assessed in the novel object-placement recognition task. Locomotor activity was analyzed in the open field apparatus using Any-maze software. The expression of glial fibrillary acidic protein (GFAP) and S100B in hippocampus and cerebrospinal fluid were measured using ELISA assay, and hippocampal GFAP immunoreactivity was evaluated by means of immunohistochemistry and optical densitometry. The results showed that physical exercise prevents and/or reverts spatial memory impairments observed in NTD animals (P < 0.01). Decreased locomotor activity was observed in both the NTD and TD groups when compared with controls (P < 0.05). ELISA and immunohistochemistry analyzes showed there was a reduction in GFAP levels in the hippocampus of NTD animals, which was not found in TD group. ELISA also showed an increase in S100B levels in the cerebrospinal fluid from the NTD group (P < 0.01) and no such increase was found in the TD group. Our findings indicate that physical exercise prevents and/or reverts the cognitive deficits and astroglial alterations induced by T1DM.

Neuroprotective actions of ghrelin and growth hormone secretagogues

The brain incorporates and coordinates information based on the hormonal environment, receiving information from peripheral tissues through the circulation. Although it was initially thought that hormones only acted on the hypothalamus to perform endocrine functions, it is now known that they in fact exert diverse actions on many different brain regions including the hypothalamus. Ghrelin is a gastric hormone that stimulates growth hormone secretion and food intake to regulate energy homeostasis and body weight by binding to its receptor, growth hormone secretagogues–GH secretagogue-receptor, which is most highly expressed in the pituitary and hypothalamus. In addition, ghrelin has effects on learning and memory, reward and motivation, anxiety, and depression, and could be a potential therapeutic agent in neurodegenerative disorders where excitotoxic neuronal cell death and inflammatory processes are involved.

Davunetide (NAP) as a preventative treatment for central nervous system complications in a diabetes rat model

AIMS

Central nervous system complications including cognitive impairment are an early manifestation of diabetes mellitus, also evident in animal models. NAP (generic name, davunetide), a neuroprotective peptide was tested here for its ability to prevent diabetes-related brain pathologies in the streptozotocin injected diabetes rat model.

METHODS

Diabetes was induced by an intraperitoneal streptozotocin injection (55 mg/kg). Intranasal NAP or vehicle was administered daily starting on the day following streptozotocin injection. Cognitive assessment was performed 12 weeks after diabetes induction, using the Morris water maze paradigm. Brain structural integrity was assessed on the 15th week of diabetes by magnetic resonance T2 scan. Characterization of cellular populations, apoptosis and synaptic density was performed 16 weeks after diabetes induction, using immunohistochemical markers and quantified in the prefrontal cortex, the cerebral cortex and the hippocampus of both hemispheres.

RESULTS

Impaired spatial memory of the diabetic rats was observed in the water maze by attenuated learning curve and worsened performance in the probe memory test. NAP treatment significantly improved both measurements. T2 magnetic resonance imaging revealed atrophy in the prefrontal cortex of the diabetes rat group, which was prevented by NAP treatment. Immunohistochemical analysis showed that NAP treatment protected against major loss of the synaptic marker synaptophysin and astrocytic apoptosis, resulting from streptozotocin treatment.

CONCLUSIONS

Our results show for the first time protective effects for NAP (davuentide) in a diabetes rat model at the behavioral and structural levels against one of the most severe complications of diabetes.

Insulin and growth hormone-releasing peptide-6 (GHRP-6) have differential beneficial effects on cell turnover in the pituitary, hypothalamus and cerebellum of streptozotocin (STZ)-induced diabetic rats

Poorly controlled type1 diabetes is associated with hormonal imbalances and increased cell death in different tissues, including the pituitary, hypothalamus and cerebellum. In the pituitary, lactotrophs are the cell population with the greatest increase in cell death, whereas in the hypothalamus and cerebellum astrocytes are most highly affected. Insulin treatment can delay, but does not prevent, diabetic complications. As ghrelin and growth hormone (GH) secretagogues are reported to prevent apoptosis in different tissues, and to modulate glucose homeostasis, a combined hormonal treatment may be beneficial. Hence, we analyzed the effect of insulin and GH-releasing peptide 6 (GHRP-6) on diabetes-induced apoptosis in the pituitary, hypothalamus and cerebellum of diabetic rats. Adult male Wistar rats were made diabetic by streptozotocin injection (65 mg/kg ip) and divided into four groups from diabetes onset: those receiving a daily sc injection of saline (1 ml/kg/day), GHRP-6 (150 μg/kg/day), insulin (1-8U/day) or insulin plus GHRP-6 for 8 weeks. Control non-diabetic rats received saline (1 ml/kg/day). Diabetes increased cell death in the pituitary, hypothalamus and cerebellum (P<0.05). In the pituitary, insulin treatment prevented diabetes-induced apoptosis (P<0.01), as well as the decline in prolactin and GH mRNA levels (P<0.05). In the hypothalamus, neither insulin nor GHRP-6 decreased diabetes-induced cell death. However, the combined treatment of insulin+GHRP-6 prevented the diabetes induced-decrease in glial fibrillary acidic protein (GFAP) levels (P<0.05). In the cerebellum, although insulin treatment increased GFAP levels (P<0.01), only the combined treatment of insulin+ GHRP-6 decreased diabetes-induced apoptosis (P<0.05). In conclusion, insulin and GHRP-6 exert tissue specific effects in STZ-diabetic rats and act synergistically on some processes. Indeed, insulin treatment does not seem to be effective on preventing some of the diabetes-induced alterations in the central nervous system.

Effects of diabetes on expression of glial fibrillary acidic protein and neurotrophins in rat colon

Diabetes can result in loss of enteric neurons and subsequent gastrointestinal complications, but the influence of diabetes on the expression of glial fibrillary acidic protein (GFAP) and neurotrophins in gut remains unknown. The aim of this study was to determine the changes of GFAP and neurotrophins in the colon of diabetic rats. The distribution of the glial marker-GFAP was explored by immunofluorescence histochemistry and western blot in colons of streptozotocin (STZ)-diabetic and age-matched control rats. And the expression of glia cell-derived neurotrophic factor (GDNF), neurotrophin 3 (NT-3) and nerve growth factor (NGF) was analyzed by real-time PCR and western blot. Studies were carried out at 4 and 12weeks of diabetes duration. Immunostaining and western blot showed diabetes induced a decrease in the intensity of staining of GFAP positive enteric glial cells (EGCs) and GFAP protein levels at 4weeks and attenuated GFAP expression was more evident at 12weeks. Moreover, mRNA and protein analysis indicated that the levels of GDNF, NT-3 and NGF were down-regulated in diabetic rats. These findings suggest that the induction of diabetes is associated with a reduction in GFAP and neurotrophins expression in the colon, which may affect the role of EGCs and neurotrophins in the enteric plexus. This in turn may partly contribute to the physiopathologic changes associated with diabetic state in the gastrointestinal tract.

Insulin and IGF-I prevent brain atrophy and DNA loss in diabetes

The aim of this study was to identify factors that regulate the bulk of adult brain mass, and test the hypothesis that concomitantly reduced insulin and insulin-like growth factor (IGF) levels are pathogenic for brain atrophy associated with impaired learning and memory in diabetes. Doses of insulin, or insulin plus IGF-I that were too small to prevent hyperglycemia were infused for 12 weeks into the brain lateral ventricles of streptozotocin-diabetic adult rats. Brain wet, water and dry weights were significantly decreased in diabetic rats; insulin prevented these decreases. The decrease in brain DNA and protein contents in diabetic rats was prevented by the combination treatment, but not by insulin alone. Levels of several glia- and neuron-associated proteins were reduced in diabetes; these reductions were also prevented by the combination treatment. Although hyperglycemia was not prevented in plasma or cerebrospinal fluid, insulin prevented brain atrophy but not bulk DNA loss in diabetes, whereas the combination prevented both. Insulin actively prevented the loss of brain water content as well. Brain atrophy is associated with concomitantly reduced levels of insulin and IGF in other disorders such as Alzheimer's disease.

Death of hypothalamic astrocytes in poorly controlled diabetic rats is associated with nuclear translocation of apoptosis inducing factor

Astrocytes in the hypothalamus of poorly controlled diabetic rats are reduced in number, due to increased apoptosis and decreased proliferation, and undergo morphological changes, including a decrease in projections. These changes are associated with modifications in synaptic proteins and most likely affect neuroendocrine signalling and function. The present study aimed to determine the intracellular mechanisms underlying this increase in hypothalamic cell death. Adult male Wistar rats were injected with streptozotocin (70 mg/kg, i.p) and controls received vehicle. Rats were killed at 1, 4, 6 and 8 weeks after diabetes onset (glycaemia > 300 mg/dl). Cell death, as detected by enzyme-linked immunosorbent assay, increased at 4 weeks of diabetes. Immunohistochemistry and terminal dUTP nick-end labelling (TUNEL) assays indicated that these cells corresponded to glial fibrillary acidic protein (GFAP) positive cells. No significant change in fragmentation of caspases 2, 3, 6, 7, 8, 9, or 12 was observed with western blot analysis. However, enzymatic assays indicated that caspase 3 activity increased significantly after 1 week of diabetes and decreased below control levels thereafter. In the hypothalamus, cell bodies lining the third ventricle, fibres radiating from the third ventricle and GFAP positive cells expressed fragmented caspase 3, with this labelling increasing at 1 week of diabetes. However, because no nuclear labelling was observed and this increase in activity did not correlate temporally with the increased cell death, this caspase may not be involved in astrocyte death. By contrast, nuclear translocation of apoptosis inducing factor (AIF) increased significantly in astrocytes in parallel with the increase in death and AIF was found in TUNEL positive cells. Thus, nuclear translocation of AIF could underlie the increased death, whereas fragmentation of caspase 3 could be associated with the morphological changes found in hypothalamic astrocytes of diabetic rats.

S100B content and secretion decrease in astrocytes cultured in high-glucose medium

S100B is an astrocyte calcium-binding protein that plays a regulatory role in the cytoskeleton and cell cycle. Moreover, extracellular S100B, a marker of glial activation in several conditions of brain injury, has a trophic or apoptotic effect on neurons, depending on its concentration. Hyperglycemic rats show changes in glial parameters, including S100B expression. Here, we investigated cell density, morphological and biochemical alterations in primary cortical astrocytes from rats and C6 glioma cells cultured in high-glucose medium. Astrocytes and C6 glioma cells have a reduced content of S100B and glial fibrillary acidic protein when cultured in a high-glucose environment, as well as a reduced content of glutathione and cell proliferation rate. Although these cells have been used indistinctly to study S100B secretion, we observed a contrasting profile of S100B secretion in a high-glucose medium: a decrease in primary astrocytes and an increase in C6 glioma cells. Based on the in vitro neurotrophic effects of the S100B protein, our data suggest that chronic elevated glucose levels affect astrocyte activity, reducing extracellular secretion of S100B and that this, in turn, could affect neuronal activity and survival. Such astrocyte alterations could contribute to cognitive deficit and other impairments observed in diabetic patients.

Reduction in the number of astrocytes and their projections is associated with increased synaptic protein density in the hypothalamus of poorly controlled diabetic rats

Processes under hypothalamic control, such as thermogenesis, feeding behavior, and pituitary hormone secretion, are disrupted in poorly controlled diabetes, but the underlying mechanisms are poorly understood. Because glial cells regulate neurosecretory neurons through modulation of synaptic inputs and function, we investigated the changes in hypothalamic glia in rats with streptozotocin-induced diabetes mellitus. Hypothalamic glial fibrillary acidic protein (GFAP) levels decreased significantly 6 wk after diabetes onset. This was coincident with decreased GFAP immunoreactive surface area, astrocyte number, and the extension of GFAP immunoreactive processes/astrocyte in the arcuate nucleus. Cell death, analyzed by terminal deoxyuridine 5-triphosphate nick-end labeling and ELISA, increased significantly at 4 wk of diabetes. Proliferation, measured by Western blot for proliferating cell nuclear antigen and immunostaining for phosphorylated histone H-3, decreased in the hypothalamus of diabetic rats throughout the study, becoming significantly reduced by 8 wk. Both proliferation and death affected astroctyes because both phosphorylated histone H-3- and terminal deoxyuridine 5-triphosphate nick-end labeling-labeled cells were GFAP positive. Western blot analysis revealed that postsynaptic density protein 95 and the presynaptic proteins synapsin I and synaptotagmin increased significantly at 8 wk of diabetes, suggesting increased hypothalamic synaptic density. Thus, in poorly controlled diabetic rats, there is a decrease in the number of hypothalamic astrocytes that is correlated with modifications in synaptic proteins and possibly synaptic inputs. These morphological changes in the arcuate nucleus could be involved in neurosecretory and metabolic changes seen in diabetic animals.