Peroxisome-proliferator-activated receptor-gamma (PPARgamma) activation protects neurons from NMDA excitotoxicity

Effects of long-term pioglitazone treatment on peripheral and central markers of aging

BACKGROUND

Thiazolidinediones (TZDs) activate peroxisome proliferator-activated receptor gamma (PPARgamma) and are used clinically to help restore peripheral insulin sensitivity in Type 2 diabetes (T2DM). Interestingly, long-term treatment of mouse models of Alzheimer's disease (AD) with TZDs also has been shown to reduce several well-established brain biomarkers of AD including inflammation, oxidative stress and Abeta accumulation. While TZD's actions in AD models help to elucidate the mechanisms underlying their potentially beneficial effects in AD patients, little is known about the functional consequences of TZDs in animal models of normal aging. Because aging is a common risk factor for both AD and T2DM, we investigated whether the TZD, pioglitazone could alter brain aging under non-pathological conditions.

METHODS AND FINDINGS

We used the F344 rat model of aging, and monitored behavioral, electrophysiological, and molecular variables to assess the effects of pioglitazone (PIO-Actos(R) a TZD) on several peripheral (blood and liver) and central (hippocampal) biomarkers of aging. Starting at 3 months or 17 months of age, male rats were treated for 4-5 months with either a control or a PIO-containing diet (final dose approximately 2.3 mg/kg body weight/day). A significant reduction in the Ca(2+)-dependent afterhyperpolarization was seen in the aged animals, with no significant change in long-term potentiation maintenance or learning and memory performance. Blood insulin levels were unchanged with age, but significantly reduced by PIO. Finally, a combination of microarray analyses on hippocampal tissue and serum-based multiplex cytokine assays revealed that age-dependent inflammatory increases were not reversed by PIO.

CONCLUSIONS

While current research efforts continue to identify the underlying processes responsible for the progressive decline in cognitive function seen during normal aging, available medical treatments are still very limited. Because TZDs have been shown to have benefits in age-related conditions such as T2DM and AD, our study was aimed at elucidating PIO's potentially beneficial actions in normal aging. Using a clinically-relevant dose and delivery method, long-term PIO treatment was able to blunt several indices of aging but apparently affected neither age-related cognitive decline nor peripheral/central age-related increases in inflammatory signaling.

Neuroprotective role of haptoglobin after intracerebral hemorrhage

After intracerebral hemorrhage (ICH), the brain parenchyma is exposed to blood containing red blood cells (RBCs) and consequently to its lysis products. Iron-rich hemoglobin (Hb) is the most abundant protein in RBCs. When released into the brain parenchyma during hemolysis, Hb becomes a central mediator of cytotoxicity. Our study indicates that haptoglobin (Hp), an acute-phase response protein primarily synthesized in the liver and known to bind and neutralize Hb in the bloodstream, is also expressed in brain in which it plays an important role in defending neurons from damage induced by hemolytic products after ICH. We demonstrate that the Hb-induced hypohaptoglobinemia aggravates ICH-induced brain damage while pharmacologic intervention with sulforaphane to induce brain Hp is linked to a reduction in brain damage. In agreement with these findings, Hp deficiency worsens whereas Hp overexpression alleviates ICH-mediated brain injury. We also identified that oligodendroglia are the primary source of brain-derived Hp among brain cells and that oligodendroglia-released Hp plays protective roles against Hb-mediated toxicity to neurons and oligodendrocytes. We conclude that Hp, particularly the brain-derived Hp, plays cytoprotective roles and represents a potential therapeutic target for ICH treatment.

Caffeinol at the receptor level: anti-ischemic effect of N-methyl-D-aspartate receptor blockade is potentiated by caffeine

BACKGROUND AND PURPOSE

Although caffeinol (a combination of a low dose of caffeine and ethanol) was shown to robustly reduce stroke damage in experimental models and is now in clinical evaluation for treatment of ischemic stroke, little is known about the potential mechanism of its action.

METHODS

We used an in vivo excitotoxicity model based on intracortical infusion of N-methyl-D-aspartate (NMDA) and a model of reversible focal ischemia to demonstrate NMDA receptor inhibition as a potential mechanism of caffeinol anti-ischemic activity.

RESULTS

Caffeinol reduced the size of excitotoxic lesion, and substitution of ethanol in caffeinol with the NMDA antagonists CNS-1102 and MK-801 but not with MgSO(4) produced treatment with strong synergistic effect that was at least as robust in reducing ischemic damage as caffeinol. This NMDA receptor antagonist and caffeine combination demonstrated a long window of opportunity, activity in spontaneously hypertensive rats, and, unlike caffeinol, was fully effective in animals chronically pretreated with ethanol.

CONCLUSIONS

Our study suggests that antiexcitotoxic properties may underlie some of the anti-ischemic effect of caffeinol. This study provides strong evidence that the anti-ischemic effect of NMDA receptor blockers in general can be dramatically augmented by caffeine, thus opening a possibility for new use of NMDA-based pharmacology in the treatment of stroke.

Insulin and Insulin-Sensitizing Drugs in Neurodegeneration: Mitochondria as Therapeutic Targets

Insulin, besides its glucose lowering effects, is involved in the modulation of lifespan, aging and memory and learning processes. As the population ages, neurodegenerative disorders become epidemic and a connection between insulin signaling dysregulation, cognitive decline and dementia has been established. Mitochondria are intracellular organelles that despite playing a critical role in cellular metabolism are also one of the major sources of reactive oxygen species. Mitochondrial dysfunction, oxidative stress and neuroinflammation, hallmarks of neurodegeneration, can result from impaired insulin signaling. Insulin-sensitizing drugs such as the thiazolidinediones are a new class of synthetic compounds that potentiate insulin action in the target tissues and act as specific agonists of the peroxisome proliferator-activated receptor gamma (PPAR-γ). Recently, several PPAR agonists have been proposed as novel and possible therapeutic agents for neurodegenerative disorders. Indeed, the literature shows that these agents are able to protect against mitochondrial dysfunction, oxidative damage, inflammation and apoptosis. This review discusses the role of mitochondria and insulin signaling in normal brain function and in neurodegeneration. Furthermore, the potential protective role of insulin and insulin sensitizers in Alzheimer´s, Parkinson´s and Huntington´s diseases and amyotrophic lateral sclerosis will be also discussed.

Rescue of neurons from ischemic injury by peroxisome proliferator-activated receptor-gamma requires a novel essential cofactor LMO4

Activation of peroxisome proliferator-activated receptor-gamma (PPARgamma) signaling after stroke may reduce brain injury, but this effect will depend on the levels of receptor and cofactors. Here, we showed that the direct effect of PPARgamma signaling to protect neurons from ischemic injury requires a novel cofactor LMO4, because this effect was lost in LMO4-null cortical neurons. PPARgamma agonist also failed to reduce cerebral infarction after transient focal ischemia in CaMKIIalphaCre/LMO4loxP mice with LMO4 ablated in neurons of the forebrain. Expressing LMO4 in LMO4-null cortical neurons rescued the PPARgamma-protective effect. PPARgamma signaling activates the promoter of the antioxidant gene SOD2 and this process requires LMO4. Addition of a superoxide dismutase mimetic MnTBAP [manganese(III)tetrakis(4-benzoic acid)porphyrin] bypassed the deficiency in PPARgamma signaling and was able to directly rescue LMO4-null cortical neurons from ischemic injury. Like LMO4, PPARgamma and PGC1alpha (PPARgamma coactivator 1alpha) levels in neurons are elevated by hypoxic stress, and absence of LMO4 impairs their upregulation. Coimmunoprecipitation and mammalian two-hybrid assays revealed that LMO4 interacts in a ligand-dependent manner with PPARgamma. LMO4 augments PPARgamma-dependent gene activation, in part, by promoting RXRalpha (retinoid X receptor-alpha) binding to PPARgamma and by increasing PPARgamma binding to its target DNA sequence. Together, our results identify LMO4 as an essential hypoxia-inducible cofactor required for PPARgamma signaling in neurons. Thus, upregulation of LMO4 expression after stroke is likely to be an important determinant of neuron survival.

Neuronal PPARgamma deficiency increases susceptibility to brain damage after cerebral ischemia

Peroxisome proliferator-activated receptor gamma (PPARgamma) plays a role in regulating a myriad of biological processes in virtually all brain cell types, including neurons. We and others have reported recently that drugs which activate PPARgamma are effective in reducing damage to brain in distinct models of brain disease, including ischemia. However, the cell type responsible for PPARgamma-mediated protection has not been established. In response to ischemia, PPARgamma gene is robustly upregulated in neurons, suggesting that neuronal PPARgamma may be a primary target for PPARgamma-agonist-mediated neuroprotection. To understand the contribution of neuronal PPARgamma to ischemic injury, we generated conditional neuron-specific PPARgamma knock-out mice (N-PPARgamma-KO). These mice are viable and appeared to be normal with respect to their gross behavior and brain anatomy. However, neuronal PPARgamma deficiency caused these mice to experience significantly more brain damage and oxidative stress in response to middle cerebral artery occlusion. The primary cortical neurons harvested from N-PPARgamma-KO mice, but not astroglia, exposed to ischemia in vitro demonstrated more damage and a reduced expression of numerous key gene products that could explain increased vulnerability, including SOD1 (superoxide dismutase 1), catalase, glutathione S-transferase, uncoupling protein-1, or transcription factor liver X receptor-alpha. Also, PPARgamma agonist-based neuroprotective effect was lost in neurons from N-PPARgamma neurons. Therefore, we conclude that PPARgamma in neurons play an essential protective function and that PPARgamma agonists may have utility in neuronal self-defense, in addition to their well established anti-inflammatory effect.

Distinct modulation of voltage-gated and ligand-gated Ca2+ currents by PPAR-gamma agonists in cultured hippocampal neurons

Type 2 diabetes mellitus is a metabolic disorder characterized by hyperglycemia and is especially prevalent in the elderly. Because aging is a risk factor for type 2 diabetes mellitus, and insulin resistance may contribute to the pathogenesis of Alzheimer's disease (AD), anti-diabetic agents (thiazolidinediones-TZDs) are being studied for the treatment of cognitive decline associated with AD. These agents normalize insulin sensitivity in the periphery and can improve cognition and verbal memory in AD patients. Based on evidence that Ca(2+) dysregulation is a pathogenic factor of brain aging/AD, we tested the hypothesis that TZDs could impact Ca(2+) signaling/homeostasis in neurons. We assessed the effects of pioglitazone and rosiglitazone (TZDs) on two major sources of Ca(2+) influx in primary hippocampal cultured neurons, voltage-gated Ca(2+) channel (VGCC) and the NMDA receptor (NMDAR). VGCC- and NMDAR-mediated Ca(2+) currents were recorded using patch-clamp techniques, and Ca(2+) intracellular levels were monitored with Ca(2+) imaging techniques. Rosiglitazone, but not pioglitazone reduced VGCC currents. In contrast, NMDAR-mediated currents were significantly reduced by pioglitazone but not rosiglitazone. These results show that TZDs modulate Ca(2+)-dependent pathways in the brain and have different inhibitory profiles on two major Ca(2+) sources, potentially conferring neuroprotection to an area of the brain that is particularly vulnerable to the effects of aging and/or AD.

Synthesis of lipoxin A4 by 5-lipoxygenase mediates PPARgamma-dependent, neuroprotective effects of rosiglitazone in experimental stroke

Peroxisome proliferator-activated receptors gamma (PPARgamma) are nuclear receptors with essential roles as transcriptional regulators of glucose and lipid homeostasis. PPARgamma are also potent anti-inflammatory receptors, a property that contributes to the neuroprotective effects of PPARgamma agonists in experimental stroke. The mechanism of these beneficial actions, however, is not fully elucidated. Therefore, we have explored further the actions of the PPARgamma agonist rosiglitazone in experimental stroke induced by permanent middle cerebral artery occlusion (MCAO) in rodents. Rosiglitazone induced brain 5-lipoxygenase (5-LO) expression in ischemic rat brain, concomitantly with neuroprotection. Rosiglitazone also increased cerebral lipoxin A(4) (LXA(4)) levels and inhibited MCAO-induced production of leukotriene B4 (LTB(4)). Furthermore, pharmacological inhibition and/or genetic deletion of 5-LO inhibited rosiglitazone-induced neuroprotection and downregulation of inflammatory gene expression, LXA(4) synthesis and PPARgamma transcriptional activity in rodents. Finally, LXA(4) caused neuroprotection, which was partly inhibited by the PPARgamma antagonist T0070907, and increased PPARgamma transcriptional activity in isolated nuclei, showing for the first time that LXA(4) has PPARgamma agonistic actions. Altogether, our data illustrate that some effects of rosiglitazone are attributable to de novo synthesis of 5-LO, able to induce a switch from the synthesis of proinflammatory LTB(4) to the synthesis of the proresolving LXA(4). Our study suggests novel lines of study such as the interest of lipoxin-like anti-inflammatory drugs or the use of these molecules as prognostic and/or diagnostic markers for pathologies in which inflammation is involved, such as stroke.

Rosiglitazone acts as a neuroprotectant in retinal cells via up-regulation of sestrin-1 and SOD-2

Rosiglitazone is a member of the thiazolidinedione family of synthetic peroxisome proliferator-activated receptor (PPAR) agonists. It is a selective ligand of the PPARgamma subtype and functions by regulating the transcription of insulin-responsive genes. A screen of FDA-approved compounds identified rosiglitazone as a novel anti-apoptotic agent in retinal cells both in vitro and in vivo, functioning as a neuroprotectant in response to oxidative and calcium stress. We have found that the likely mechanism of action is via increased protein expression of the antioxidant enzymes superoxide dismutase 2 (SOD-2) and sestrin-1, boosting antioxidant defences. Transcription of both genes appears to be mediated by PPARgamma as their up-regulation is reversed by the PPARgamma antagonist GW9662 and proliferator hormone response elements were found in the putative promoter regions of mouse SOD-2 and sestrin-1. However, further investigation revealed that p53 expression was also induced in response to rosiglitazone and chromatin immunoprecipitation assays confirm that it is a bona fide target of PPARgamma. Furthermore, inhibition of p53 partially blocks the observed increase in SOD-2 and sestrin-1 expression indicating that p53 expression is upstream of both antioxidants. We conclude that rosiglitazone may increase cell survival in retinal diseases and potentially other neuronal diseases in which oxidative stress is a key factor.

The neuroprotective properties of calorie restriction, the ketogenic diet, and ketone bodies

Both calorie restriction and the ketogenic diet possess broad therapeutic potential in various clinical settings and in various animal models of neurological disease. Following calorie restriction or consumption of a ketogenic diet, there is notable improvement in mitochondrial function, a decrease in the expression of apoptotic and inflammatory mediators and an increase in the activity of neurotrophic factors. However, despite these intriguing observations, it is not yet clear which of these mechanisms account for the observed neuroprotective effects. Furthermore, limited compliance and concern for adverse effects hamper efforts at broader clinical application. Recent research aimed at identifying compounds that can reproduce, at least partially, the neuroprotective effects of the diets with less demanding changes to food intake suggests that ketone bodies might represent an appropriate candidate. Ketone bodies protect neurons against multiple types of neuronal injury and are associated with mitochondrial effects similar to those described during calorie restriction or ketogenic diet treatment. The present review summarizes the neuroprotective effects of calorie restriction, of the ketogenic diet and of ketone bodies, and compares their putative mechanisms of action.

Stress mediators regulate brain prostaglandin synthesis and peroxisome proliferator-activated receptor-gamma activation after stress in rats

Stress exposure leads to oxidative/nitrosative and neuroinflammatory changes that have been shown to be regulated by antiinflammatory pathways in the brain. In particular, acute restraint stress is followed by cyclooxygenase (COX)-2 up-regulation and subsequent proinflammatory prostaglandin (PG) E2 release in rat brain cortex. Concomitantly, the synthesis of the antiinflammatory prostaglandin 15d-PGJ(2) and the activation of its nuclear target the peroxisome proliferator-activated receptor (PPAR)-gamma are also produced. This study aimed to determine the possible role of the main stress mediators: catecholamines, glucocorticoids, and excitatory amino acids (glutamate) in the above-mentioned stress-related effects. By using specific pharmacological tools, our results show that the main mediators of the stress response are implicated in the regulation of prostaglandin synthesis and PPARgamma activation in rat brain cortex described after acute restraint stress exposure. Pharmacological inhibition (predominantly through beta-adrenergic receptor) of the stress-released catecholamines in the central nervous system regulates 15d-PGJ(2) and PGE(2) synthesis, by reducing COX-2 overexpression, and reduces PPARgamma activation. Stress-produced glucocorticoids carry out their effects on prostaglandin synthesis through their interaction with mineralocorticoid and glucocorticoid receptors to a very similar degree. However, in the case of PPARgamma regulation, only the actions through the glucocorticoid receptor seem to be relevant. Finally, the selective blockade of the N-methyl-d-aspartate type of glutamate receptor after stress also negatively regulates 15d-PGJ(2) and PGE(2) production by COX-2 down-regulation and decrease in PPARgamma transcriptional activity and expression. In conclusion, we show here that the main stress mediators, catecholamines, GCs, and glutamate, concomitantly regulate the activation of proinflammatory and antiinflammatory pathways in a possible coregulatory mechanism of the inflammatory process induced in rat brain cortex by acute restraint stress exposure.

Neuroprotective effect of the new thiadiazolidinone NP00111 against oxygen-glucose deprivation in rat hippocampal slices: implication of ERK1/2 and PPARgamma receptors

Thiadiazolidinones (TDZDs) are small molecules that inhibit glycogen synthase kinase 3-beta (GSK3-beta) activity in a non competitive manner to ATP. NP00111, a new TDZD, besides causing inhibition of GSK-3beta, has also shown to be an agonist of PPARgamma . Since phosphorylation and consequent inhibition of GSK-3beta by PI-3K/Akt and agonism of PPARgamma have shown to afford neuroprotection in several in vitro and in vivo models, we have studied the potential neuroprotective effect of NP00111 in an "in vitro" model of ischemia-reperfusion. NP00111, at the concentration of 10 microM, significantly protected adult rat hippocampal slices subjected to oxygen and glucose deprivation (OGD) for 1 h followed by 3 h re-oxygenation, measured as lactic dehydrogenase (LDH) released to the extracellular media. The protective effects of NP00111 were more pronounced during the re-oxygenation period in comparison to the OGD period. Other GSK-3beta inhibitors like lithium or AR-A014418 did not afford protection in this model. However, the PPARgamma agonist rosiglitazone was protective at 3 microM. Protection afforded by NP00111 and rosiglitazone were prevented by the PPARgamma antagonist GW9662, suggesting that both NP00111 and rosiglitazone were preventing cell death caused by oxygen-glucose deprivation via activation of PPARgamma. NP00111 increased by two fold phosphorylation of ERK1/2 and its protective effects were lost when the hippocampal slices were co-incubated with the mitogen-activated protein kinase (MAPK) inhibitor PD98059. In conclusion, the novel TDZD NP00111 was protective against OGD in rat hippocampal slices by a mechanism related to phosphorylation of ERK1/2 via activation of PPARgamma.

Neuroprotective actions of noradrenaline: effects on glutathione synthesis and activation of peroxisome proliferator activated receptor delta

The endogenous neurotransmitter noradrenaline (NA) can protect neurons from the toxic consequences of various inflammatory stimuli, however the exact mechanisms of neuroprotection are not well known. In the current study, we examined neuroprotective effects of NA in primary cultures of rat cortical neurons. Exposure to oligomeric amyloid beta (Abeta) 1-42 peptide induced neuronal damage revealed by increased staining with fluorojade, and toxicity assessed by LDH release. Abeta-dependent neuronal death did not involve neuronal expression of the inducible nitric oxide synthase 2 (NOS2), since Abeta did not induce nitrite production from neurons, LDH release was not reduced by co-incubation with NOS2 inhibitors, and neurotoxicity was similar in wildtype and NOS2 deficient neurons. Co-incubation with NA partially reduced Abeta-induced neuronal LDH release, and completely abrogated the increase in fluorojade staining. Treatment of neurons with NA increased expression of gamma-glutamylcysteine ligase, reduced levels of GSH peroxidase, and increased neuronal GSH levels. The neuroprotective effects of NA were partially blocked by co-treatment with an antagonist of peroxisome proliferator activated receptors (PPARs), and replicated by incubation with a selective PPARdelta (PPARdelta) agonist. NA also increased expression and activation of PPARdelta. Together these data demonstrate that NA can protect neurons from Abeta-induced damage, and suggest that its actions may involve activation of PPARdelta and increases in GSH production.

Peroxisome proliferator-activated receptor gamma up-regulates the Bcl-2 anti-apoptotic protein in neurons and induces mitochondrial stabilization and protection against oxidative stress and apoptosis

Peroxisome proliferator-activated receptor gamma (PPARgamma) has been proposed as a therapeutic target for neurodegenerative diseases because of its anti-inflammatory action in glial cells. However, PPARgamma agonists preventbeta-amyloid (Abeta)-induced neurodegeneration in hippocampal neurons, and PPARgamma is activated by the nerve growth factor (NGF) survival pathway, suggesting a neuroprotective anti-inflammatory independent action. Here we show that the PPARgamma agonist rosiglitazone (RGZ) protects hippocampal and dorsal root ganglion neurons against Abeta-induced mitochondrial damage and NGF deprivation-induced apoptosis, respectively, and promotes PC12 cell survival. In neurons and in PC12 cells RGZ protective effects are associated with increased expression of the Bcl-2 anti-apoptotic protein. NGF-differentiated PC12 neuronal cells constitutively overexpressing PPARgamma are resistant to Abeta-induced apoptosis and morphological changes and show functionally intact mitochondria and no increase in reactive oxygen species when challenged with up to 50 microM H2O2. Conversely, cells expressing a dominant negative mutant of PPARgamma show increased Abeta-induced apoptosis and disruption of neuronal-like morphology and are highly sensitive to oxidative stress-induced impairment of mitochondrial function. Cells overexpressing PPARgamma present a 4- to 5-fold increase in Bcl-2 protein content, whereas in dominant negative PPARgamma-expressing cells, Bcl-2 is barely detected. Bcl-2 knockdown by small interfering RNA in cells overexpressing PPARgamma results in increased sensitivity to Abeta and oxidative stress, further suggesting that Bcl-2 up-regulation mediates PPARgamma protective effects. PPARgamma prosurvival action is independent of the signal-regulated MAPK or the Akt prosurvival pathways. Altogether, these data suggest that PPARgamma supports survival in neurons in part through a mechanism involving increased expression of Bcl-2.

Water soluble RNA based antagonist of AMPA receptors

Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors are one of the important receptor classes involved in glutamate-mediated excitotoxicity. Although small molecule antagonists of this receptor have been shown to have neuroprotective properties, their low solubilities pose severe side effects in clinical trials. Here we have used the SELEX method to obtain water-soluble nuclease-resistant RNA ligands that bind to the agonist binding site of AMPA receptors. Using whole-cell current recordings, we have characterized the functional consequences of a representative aptamer from this class and show that it is a competitive antagonist of AMPA receptors and in the concentration range where it acts as an inhibitor of the AMPA receptor the RNA has no effect on the GluR6 homomeric kainate receptors. Additionally, using a fluorescence resonance energy transfer (FRET) probe, we show that this RNA ligand stabilizes the open cleft conformation of the ligand binding domain, consistent with the known structures of small antagonist-bound states of the soluble domain of this protein. Finally, using rat primary cortical neurons, we show that this RNA ligand significantly reduces neurotoxicity associated with oxygen glucose deprivation. The water-soluble and antagonistic properties of this aptamer coupled with its neuroprotective properties make it an excellent candidate for potential use in diseases or pathological conditions involving glutamate-mediated excitotoxicity.

Effects of peroxisome proliferator-activated receptor gamma agonists on brain glucose and glutamate transporters after stress in rats

Repeated stress causes an energy-compromised status in the brain, with a decrease in glucose utilization by the brain cells, which might account for excitotoxicity processes seen in this condition. In fact, brain glucose metabolism mechanisms are impaired in some neurodegenerative disorders, including stress-related neuropsychopathologies. More recently, it has been demonstrated that some synthetic peroxisome proliferator-activated receptor gamma (PPARgamma) agonists increase glucose utilization in rat cortical slices and astrocytes, as well as inhibit brain oxidative damage after repeated stress, which add support for considering these drugs as potential neuroprotective agents. To assess if stress causes glucose utilization impairment in the brain and to study the mechanisms by which this effect is achieved, young-adult male Wistar rats (control and immobilized for 6 h during 7 or 14 consecutive days, S7, S14) were i.p. injected with the natural ligand 15-deoxy-Delta-12,14-prostaglandin J2 (PGJ2, 120 microg/kg) or the high-affinity ligand rosiglitazone (RG, 3 mg/kg) at the onset of stress. Repeated immobilization during 1 or 2 weeks produces a decrease in brain cortical synaptosomal glucose uptake, and this effect was prevented by treatment with both natural and synthetic PPARgamma ligands by restoring protein expression of the neuronal glucose transporter, GLUT-3 in membrane fractions. On the other hand, treatment with PPARgamma ligands prevents stress-induced ATP loss in rat brain. Finally, repeated immobilization stress also produces a decrease in brain cortical synaptosomal glutamate uptake, and this effect was prevented by treatment with PPARgamma ligands by restoring synaptosomal protein expression of the glial glutamate transporter, EAAT2. In summary, our results demonstrate that 15d-PGJ2 and the thiazolidinedione rosiglitazone increase neuronal glucose metabolism, restore brain ATP levels and prevent the impairment in glutamate uptake mechanisms induced by exposure to stress, suggesting that this class of drugs may be therapeutically useful in conditions in which brain glucose levels or availability are limited after exposure to stress.

Protective effects of 15-deoxy-Δ12,14-prostaglandin J2against glutamate-induced cell death in primary cortical neuron cultures: induction of adaptive response and enhancement of cell tolerance primarily through up-regulation of cellular glutathione

There is increasing evidence to suggest that reactive oxygen species, including a variety of lipid oxidation products and other physiologically existing oxidative stimuli, can induce an adaptive response and enhance cell tolerance. In the present study, by using cultured cortical neurons, we investigated the effect of electrophilic lipids, such as 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) and 4-hydroxy-2-nonenal (4-HNE) against the cell death induced by H(2)O(2) and glutamate. Pre-treatment with both 15d-PGJ(2) and 4-HNE at sublethal concentrations resulted in a significant protective effect against oxidative stress, and 15d-PGJ(2), in particular, exhibited a complete protective effect against glutamate-induced neuronal cell death. Pre-treatment with 15d-PGJ(2) increased the intracellular glutathione (GSH) as well as the gene expression of glutamate-cysteine ligase (GCL), the rate-limiting enzyme of GSH synthesis. 15d-PGJ(2) protected cells from glutamate-induced GSH depletion, while the inhibition of cellular GSH synthesis by buthionine sulfoximine abolished the adaptive response induced by 15d-PGJ(2). These findings indicate that at low levels, 15d-PGJ(2) acts as a potent survival mediator against glutamate-induced insults via the induction of an adaptive response primarily through the up-regulation of the intracellular GSH synthesis.

Hematoma resolution as a target for intracerebral hemorrhage treatment: Role for peroxisome proliferator-activated receptor γ in microglia/macrophages

OBJECTIVE

Phagocytosis is necessary to eliminate the hematoma after intracerebral hemorrhage (ICH); however, release of proinflammatory mediators and free radicals during phagocyte activation is toxic to neighboring cells, leading to secondary brain injury. Promotion of phagocytosis in a timely and efficient manner may limit the toxic effects of persistent blood products on surrounding tissue and may be important for recovery after ICH.

METHODS

Intrastriatal blood injection in rodents and primary microglia in culture exposed to red blood cells were used to model ICH and to study mechanisms of hematoma resolution and phagocytosis regulation by peroxisome proliferator-activated receptor gamma (PPARgamma) in microglia/macrophages.

RESULTS

Our study demonstrated that the PPARgamma agonist, rosiglitazone, promoted hematoma resolution, decreased neuronal damage, and improved functional recovery in a mouse ICH model. Microglia isolated from murine brains showed more efficient phagocytosis in response to PPARgamma activators. PPARgamma activators significantly increased PPARgamma-regulated gene (catalase and CD36) expression, whereas reducing proinflammatory gene (tumor necrosis factor-alpha, interleukin-1beta, matrix metalloproteinase-9, and inducible nitric oxide synthase) expression, extracellular H(2)O(2) level, and neuronal damage. Phagocytosis by microglia was significantly inhibited by PPARgamma gene knockdown or neutralizing anti-CD36 antibody, whereas it was enhanced by exogenous catalase.

INTERPRETATION

PPARgamma in macrophages acts as an important factor in promoting hematoma absorption and protecting other brain cells from ICH-induced damage.

PPAR-gamma: therapeutic target for ischemic stroke

The peroxisome proliferator activated receptors (PPARs), which belong to the nuclear receptor superfamily, are key regulators of glucose and fat metabolism. The PPAR-gamma isoform is involved in the regulation of cellular glucose uptake, protection against atherosclerosis and control of immune reactions. In addition, the activation of PPAR-gamma effectively attenuates neurodegenerative and inflammatory processes in the brain. Here, we review a novel aspect of beneficial and clinically relevant PPAR-gamma actions: neuroprotection against ischemic injury mediated by intracerebral PPAR-gamma, which is expressed in neurons and microglia. Together with the recent observation that the PPAR-gamma ligand pioglitazone reduces the incidence of stroke in patients with type 2 diabetes, this review supports the concept that activators of PPAR-gamma are effective drugs against ischemic injury.

PPAR: a new pharmacological target for neuroprotection in stroke and neurodegenerative diseases

PPARs (peroxisome-proliferator-activated receptors) are ligand-activated transcriptional factor receptors belonging to the so-called nuclear receptor family. The three isoforms of PPAR (alpha, beta/delta and gamma) are involved in regulation of lipid or glucose metabolism. Beyond metabolic effects, PPARalpha and PPARgamma activation also induces anti-inflammatory and antioxidant effects in different organs. These pleiotropic effects explain why PPARalpha or PPARgamma activation has been tested as a neuroprotective agent in cerebral ischaemia. Fibrates and other non-fibrate PPARalpha activators as well as thiazolidinediones and other non-thiazolidinedione PPARgamma agonists have been demonstrated to induce both preventive and acute neuroprotection. This neuroprotective effect involves both cerebral and vascular mechanisms. PPAR activation induces a decrease in neuronal death by prevention of oxidative or inflammatory mechanisms implicated in cerebral injury. PPARalpha activation induces also a vascular protection as demonstrated by prevention of post-ischaemic endothelial dysfunction. These vascular effects result from a decrease in oxidative stress and prevention of adhesion proteins, such as vascular cell adhesion molecule 1 or intercellular cell-adhesion molecule 1. Moreover, PPAR activation might be able to induce neurorepair and endothelium regeneration. Beyond neuroprotection in cerebral ischaemia, PPARs are also pertinent pharmacological targets to induce neuroprotection in chronic neurodegenerative diseases.

Neuronal expression of peroxisome proliferator-activated receptor-gamma (PPARγ) and 15d-prostaglandin J2—Mediated protection of brain after experimental cerebral ischemia in rat

Existing experimental evidence suggests that PPARgamma may play a beneficial role in neuroprotection from various brain pathologies. Here we found that focal cerebral ischemia induced by middle cerebral/common carotid arteries occlusion (MCA/CCAo) induced up-regulation of PPARgamma messenger RNA in the ischemic hemisphere as early as 6 h after the ischemic event. The increased PPARgamma mRNA expression was primarily associated with neurons in the ischemic penumbra, suggesting an important role for PPARgamma in neurons after ischemia. Intraventricular injection of 15d-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), a proposed endogenous PPARgamma agonist, into the ischemic rat brains significantly increased the PPARgamma-DNA-binding activity and reduced infarction volume at 24 h after reperfusion. We propose that PPARgamma up-regulation in response to ischemia may contribute to PPARgamma activation in the presence of PPARgamma agonists. Activation of PPARgamma in neurons at an early stage after ischemia may represent a pro-survival mechanism against ischemic injury.