Survival activity of troglitazone in rat motoneurones

An overlap-weighted analysis on the association of constipation symptoms with disease progression and survival in amyotrophic lateral sclerosis: a nested case-control study

Background

Amyotrophic lateral sclerosis (ALS) is a rapidly progressing and rare neurodegenerative disease. Therefore, evaluating the risk factors affecting the survival of patients with ALS is crucial. Constipation, a common but overlooked symptom of ALS, can be effectively managed. It is currently unknown whether constipation contributes to the progression and survival of ALS.

Objectives

This study aimed to investigate the association between constipation and ALS development and survival using a novel overlap-weighted (OW) method to enhance the robustness and reliability of results.

Design

This prospective matching nested case-control (NCC) study was conducted within an ongoing ALS cohort at the Second Hospital of Hebei Medical University. Baseline data were collected from patients meeting the inclusion and exclusion criteria, with constipation as the exposure factor. A 9-month follow-up was conducted, with death as the endpoint event.

Methods

We primarily used the OW method in NCC studies to examine the association between constipation and ALS development and survival. Weighted Cox proportional hazards model was used to assess risk factors associated with overall survival. Survival differences between the two groups were analyzed using Kaplan-Meier's plots and log-rank tests. Finally, the bioinformatic analysis explored common pathways between ALS and constipation.

Results

Among the 190 patients included, the prevalence of constipation was 50%. Patients with ALS constipation exhibited faster disease progression (p < 0.001), with a positive correlation between constipation severity and progression rate (r = 0.356, p < 0.001). The constipation group had poorer survival before and after OW (log-rank test, p < 0.0001). In the Cox proportional hazards model of 114 patients, constipation was a risk factor for ALS both before (hazard ratio (HR) = 5.840, 95% confidence interval (CI) = 1.504-22.675, p = 0.011) and after (HR = 5.271, 95% CI = 1.241-22.379, p = 0.024) OW.

Conclusion

Constipation in individuals with ALS is associated with faster disease progression and reduced survival rates, potentially through the peroxisome proliferator-activated receptor pathway.

Development of PPARγ Agonists for the Treatment of Neuroinflammatory and Neurodegenerative Diseases: Leriglitazone as a Promising Candidate

Increasing evidence suggests that the peroxisome proliferator-activated receptor γ (PPARγ), a member of the nuclear receptor superfamily, plays an important role in physiological processes in the central nervous system (CNS) and is involved in cellular metabolism and repair. Cellular damage caused by acute brain injury and long-term neurodegenerative disorders is associated with alterations of these metabolic processes leading to mitochondrial dysfunction, oxidative stress, and neuroinflammation. PPARγ agonists have demonstrated the potential to be effective treatments for CNS diseases in preclinical models, but to date, most drugs have failed to show efficacy in clinical trials of neurodegenerative diseases including amyotrophic lateral sclerosis, Parkinson's disease, and Alzheimer's disease. The most likely explanation for this lack of efficacy is the insufficient brain exposure of these PPARγ agonists. Leriglitazone is a novel, blood-brain barrier (BBB)-penetrant PPARγ agonist that is being developed to treat CNS diseases. Here, we review the main roles of PPARγ in physiology and pathophysiology in the CNS, describe the mechanism of action of PPARγ agonists, and discuss the evidence supporting the use of leriglitazone to treat CNS diseases.

Uncoupling Protein 2 as a Pathogenic Determinant and Therapeutic Target in Cardiovascular and Metabolic Diseases

Uncoupling protein 2 (UCP2) is a mitochondrial protein that acts as an anion carrier. It is involved in the regulation of several processes, including mitochondrial membrane potential, generation of reactive oxygen species within the inner mitochondrial membrane and calcium homeostasis. UCP2 expression can be regulated at different levels: genetic (gene variants), transcriptional [by peroxisome proliferator-activated receptors (PPARs) and microRNAs], and post-translational. Experimental evidence indicates that activation of UCP2 expression through the AMPK/PPAR-α axis exerts a protective effect toward renal damage and stroke occurrence in an animal model of ischemic stroke (IS) associated with hypertension. UCP2 plays a key role in heart diseases (myocardial infarction and cardiac hypertrophy) and metabolic disorders (obesity and diabetes). In humans, UCP2 genetic variants (-866G/A and Ala55Val) associate with an increased risk of type 2 diabetes mellitus and IS development. Over the last few years, many agents that modulate UCP2 expression have been identified. Some of them are natural compounds of plant origin, such as Brassica oleracea, curcumin, berberine and resveratrol. Other molecules, currently used in clinical practice, include anti-diabetic (gliptin) and chemotherapeutic (doxorubicin and taxol) drugs. This evidence highlights the relevant role of UCP2 for the treatment of a wide range of diseases, which affect the national health systems of Western countries. We will review current knowledge on the physiological and pathological implications of UCP2 with particular regard to cardiovascular and metabolic disorders and will focus on the available therapeutic approaches affecting UCP2 level for the treatment of human diseases.

Exploiting the Therapeutic Potential of Endogenous Immunomodulatory Systems in Multiple Sclerosis-Special Focus on the Peroxisome Proliferator-Activated Receptors (PPARs) and the Kynurenines

Multiple sclerosis (MS) is a progressive neurodegenerative disease, characterized by autoimmune central nervous system (CNS) demyelination attributable to a disturbed balance between encephalitic T helper 1 (Th1) and T helper 17 (Th17) and immunomodulatory regulatory T cell (Treg) and T helper 2 (Th2) cells, and an alternatively activated macrophage (M2) excess. Endogenous molecular systems regulating these inflammatory processes have recently been investigated to identify molecules that can potentially influence the course of the disease. These include the peroxisome proliferator-activated receptors (PPARs), PPARγ coactivator-1alpha (PGC-1α), and kynurenine pathway metabolites. Although all PPARs ameliorate experimental autoimmune encephalomyelitis (EAE), recent evidence suggests that PPARα, PPARβ/δ agonists have less pronounced immunomodulatory effects and, along with PGC-1α, are not biomarkers of neuroinflammation in contrast to PPARγ. Small clinical trials with PPARγ agonists have been published with positive results. Proposed as immunomodulatory and neuroprotective, the therapeutic use of PGC-1α activation needs to be assessed in EAE/MS. The activation of indolamine 2,3-dioxygenase (IDO), the rate-limiting step of the kynurenine pathway of tryptophan (Trp) metabolism, plays crucial immunomodulatory roles. Indeed, Trp metabolites have therapeutic relevance in EAE and drugs with structural analogy to kynurenines, such as teriflunomide, are already approved for MS. Further studies are required to gain deeper knowledge of such endogenous immunomodulatory pathways with potential therapeutic implications in MS.

Effects of cannabidiol interactions with Wnt/β-catenin pathway and PPARγ on oxidative stress and neuroinflammation in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease, in which the primary etiology remains unknown. AD presents amyloid beta (Aβ) protein aggregation and neurofibrillary plaque deposits. AD shows oxidative stress and chronic inflammation. In AD, canonical Wingless-Int (Wnt)/β-catenin pathway is downregulated, whereas peroxisome proliferator-activated receptor γ (PPARγ) is increased. Downregulation of Wnt/β-catenin, through activation of glycogen synthase kinase-3β (GSK-3β) by Aβ, and inactivation of phosphatidylinositol 3-kinase/Akt signaling involve oxidative stress in AD. Cannabidiol (CBD) is a non-psychotomimetic phytocannabinoid from Cannabis sativa plant. In PC12 cells, Aβ-induced tau protein hyperphosphorylation is inhibited by CBD. This inhibition is associated with a downregulation of p-GSK-3β, an inhibitor of Wnt pathway. CBD may also increase Wnt/β-catenin by stimulation of PPARγ, inhibition of Aβ and ubiquitination of amyloid precursor protein. CBD attenuates oxidative stress and diminishes mitochondrial dysfunction and reactive oxygen species generation. CBD suppresses, through activation of PPARγ, pro-inflammatory signaling and may be a potential new candidate for AD therapy.

PPARγ as a therapeutic target to rescue mitochondrial function in neurological disease

There is increasing evidence for the involvement of mitochondrial dysfunction and oxidative stress in the pathogenesis of many of the major neurodegenerative and neuroinflammatory diseases, suggesting that mitochondrial and antioxidant pathways may represent potential novel therapeutic targets. Recent years have seen a rapidly growing interest in the use of therapeutic strategies that can limit the defects in, or even to restore, mitochondrial function while reducing free radical generation. The peroxisome proliferation-activated receptor gamma (PPARγ), a ligand-activated transcription factor, has a wide spectrum of biological functions, regulating mitochondrial function, mitochondrial turnover, energy metabolism, antioxidant defence and redox balance, immune responses and fatty acid oxidation. In this review, we explore the evidence for potential beneficial effects of PPARγ agonists in a number of neurological disorders, including Parkinson's disease, Alzheimer's disease, Amyotrophic lateral sclerosis and Huntington's disease, ischaemia, autoimmune encephalomyelitis and neuropathic pain. We discuss the mechanisms underlying those beneficial effects in particular in relation to mitochondrial function, antioxidant defence, cell death and inflammation, and suggest that the PPARγ agonists show significant promise as therapeutic agents in otherwise intractable neurological disease.

Alzheimer Disease: Crosstalk between the Canonical Wnt/Beta-Catenin Pathway and PPARs Alpha and Gamma

The molecular mechanisms underlying the pathophysiology of Alzheimer's disease (AD) are still not fully understood. In AD, Wnt/beta-catenin signaling has been shown to be downregulated while the peroxisome proliferator-activated receptor (PPAR) gamma (mARN and protein) is upregulated. Certain neurodegenerative diseases share the same Wnt/beta-catenin/PPAR gamma profile, such as bipolar disorder and schizophrenia. Conversely, other NDs share an opposite profile, such as amyotrophic lateral sclerosis, Parkinson's disease, Huntington's disease, multiple sclerosis, and Friedreich's ataxia. AD is characterized by the deposition of extracellular Abeta plaques and the formation of intracellular neurofibrillary tangles in the central nervous system (CNS). Activation of Wnt signaling or inhibition of both glycogen synthase kinase-3beta and Dickkopf 1, two key negative regulators of the canonical Wnt pathway, are able to protect against Abeta neurotoxicity and to ameliorate cognitive performance in AD patients. Although PPAR gamma is upregulated in AD patients, and despite the fact that it has been shown that the PPAR gamma and Wnt/beta catenin pathway systems work in an opposite manner, PPAR gamma agonists diminish learning and memory deficits, decrease Abeta activation of microglia, and prevent hippocampal and cortical neurons from dying. These beneficial effects observed in AD transgenic mice and patients might be partially due to the anti-inflammatory properties of PPAR gamma agonists. Moreover, activation of PPAR alpha upregulates transcription of the alpha-secretase gene and represents a new therapeutic treatment for AD. This review focuses largely on the behavior of two opposing pathways in AD, namely Wnt/beta-catenin signaling and PPAR gamma. It is hoped that this approach may help to develop novel AD therapeutic strategies integrating PPAR alpha signaling.

Role of PPAR γ in the Differentiation and Function of Neurons

Neuronal processes (neurites and axons) have an important role in brain cells communication and, generally, they are damaged in neurodegenerative diseases. Recent evidence has showed that the activation of PPARγ pathway promoted neuronal differentiation and axon polarity. In addition, activation of PPARγ using thiazolidinediones (TZDs) prevented neurodegeneration by reducing neuronal death, improving mitochondrial function, and decreasing neuroinflammation in neuropathic pain. In this review, we will discuss important evidence that supports a possible role of PPARγ in neuronal development, improvement of neuronal health, and pain signaling. Therefore, activation of PPARγ is a potential target with therapeutic applications against neurodegenerative disorders, brain injury, and pain regulation.

Cell-autonomous enhancement of glutamate-uptake by female astrocytes

Since gonadal female hormones act on and protect neurons, it is well known that the female brain is less vulnerable to stroke or other brain insults than the male brain. Although glial functions have been shown to affect the vulnerability of the brain, little is known if such a sex difference exists in glia, much less the mechanism that might cause gender-dependent differences in glial functions. In this study, we show that in vitro astrocytes obtained from either female or male pups show a gonadal hormone-independent phenotype that could explain the gender-dependent vulnerability of the brain. Female spinal astrocytes cleared more glutamate by GLAST than male ones. In addition, motoneurons seeded on female spinal astrocytes were less vulnerable to glutamate than those seeded on male ones. It is suggested that female astrocytes uptake more glutamate and reveal a stronger neuroprotective effect against glutamate than male ones. It should be noted that such an effect was independent of gonadal female hormones, suggesting that astrocytes have cell-autonomous regulatory mechanisms by which they transform themselves into appropriate phenotypes.

Trk and cAMP-dependent survival activity of adenosine A(2A) agonist CGS21680 on rat motoneurons in culture

The survival activity of adenosine A(2A) agonist CGS21680 on motoneurons in culture through the transactivation of neurotrophin receptor TrkB has been reported previously; however, since adenosine A(2A) receptor belongs to a Gs-protein-coupled receptor, we investigated the involvement of the cAMP pathway in the survival activity of CGS21680 using purified motoneurons in culture. CGS21680 alone showed only small survival activity, but the activity was significantly enhanced by the addition of a phosphodiesterase inhibitor, IBMX. This survival activity was partially inhibited by a protein kinase A inhibitor H89 or a neurotrophin receptor tyrosine kinase inhibitor K252a, and was completely inhibited by their combination. These results indicate that the survival activity of CGS21680 on motoneurons is exerted by the mixed effect of the adenylate cyclase-cAMP-PKA pathway and transactivation of Trk neurotrophin receptor. Under conditions in which the maximum survival of motoneurons was supported by sufficient concentrations of brain-derived neurotrophic factor (BDNF), a TrkB ligand, the addition of 100μM AMPA for 3 days led to significant cell death. Treatment with CGS21680 and IBMX protected motoneurons from the toxicity of AMPA, further supporting the presence of a TrkB-independent pathway of CGS21680 activity and suggesting a novel therapeutic approach to motoneuron diseases such as amyotrophic lateral sclerosis.

Agonism of Peroxisome Proliferator Receptor-Gamma may have Therapeutic Potential for Neuroinflammation and Parkinson's Disease

Evidence suggests inflammation, mitochondria dysfunction, and oxidative stress play major roles in Parkinson's disease (PD), where the primary pathology is the significant loss of dopaminergic neurons in the substantia nigra (SN). Current methods used to treat PD focus mainly on replacing dopamine in the nigrostriatal system. However, with time these methods fail and worsen the symptoms of the disease. This implies there is more to the treatment of PD than just restoring dopamine or the dopaminergic neurons, and that a broader spectrum of factors must be changed in order to restore environmental homeostasis. Pharmacological agents that can protect against progressive neuronal degeneration, increase the level of dopamine in the nigrostriatal system, or restore the dopaminergic system offer various avenues for the treatment of PD. Drugs that reduce inflammation, restore mitochondrial function, or scavenge free radicals have also been shown to offer neuroprotection in various animal models of PD. The activation of peroxisome proliferator receptor- gamma (PPAR-gamma ) has been associated with altering insulin sensitivity, increasing dopamine, inhibiting inflammation, altering mitochondrial bioenergetics, and reducing oxidative stress - a variety of factors that are altered in PD. Therefore, PPAR-gamma activation may offer a new clinically relevant treatment approach to neuroinflammation and PD related neurodegeneration. This review will summarize the current understanding of the role of PPAR-gamma agonists in neuroinflammation and discuss their potential for the treatment of PD.

Survival-promoting activity of pituitary adenylate cyclase-activating polypeptide in the presence of phosphodiesterase inhibitors on rat motoneurons in culture: cAMP-protein kinase A-mediated survival

Pituitary adenylate cyclase-activating polypeptide (PACAP) has been shown to be neurotrophic or neuroprotective in various neurons in culture. It is expressed in spinal motoneurons in vivo and its expression is increased markedly after axotomy, suggesting a neuroprotective role via an autocrine mechanism. However, neurotrophic activity of PACAP has not been reported for motoneurons. In the present study, we investigated the effects of PACAP on rat motoneurons in culture. In the presence of a phosphodiesterase inhibitor, PACAP showed significant neurotrophic activity at concentrations as low as 0.01 nM. Previously, we found that glutamate was excitotoxic to motoneurons even in the presence of brain-derived neurotrophic factor, which is neurotrophic for motoneurons. PACAP with a phosphodiesterase inhibitor protected motoneurons against this excitotoxicity. The activity of PACAP was inhibited by the protein kinase A inhibitor N-[2-(p-bromocinnamylamino) ethyl]-5-isoquinolinesulfonamide dihydrochloride, as was the case with the activity of forskolin, suggesting downstream involvement of a cAMP-protein kinase A signaling pathway. The present results may suggest a physiological role of PACAP in vivo, and implicate the PACAP-cAMP signaling pathway for the possible therapeutic target of amyotrophic lateral sclerosis as glutamate excitotoxicity was suggested in sporadic amyotrophic lateral sclerosis.

Effects of the PPARgamma activator pioglitazone on p38 MAP kinase and IkappaBalpha in the spinal cord of a transgenic mouse model of amyotrophic lateral sclerosis

Emerging evidence suggests the involvement of programmed cell death and inflammation in amyotrophic lateral sclerosis (ALS). To assess molecular pathological effects of the anti-inflammatory peroxisome proliferator-activated receptor-gamma (PPARgamma) agonist pioglitazone in ALS, we verified changes in the population of neurons, astrocytes, and microglia in the ventral horns of spinal cord lumbar segments from the pioglitazone-treated and non-treated groups of mice carrying a transgene for G93A mutant human superoxide dismutase-1 (SOD1) (ALS mice) and non-transgenic littermates (control mice), performed immunohistochemical and immunoblot analyses of PPARgamma, active form of phosphorylated p38 mitogen-activated protein kinase (p-p38) and inhibitor of nuclear factor-kappaB (NF-kappaB)-alpha (IkappaBalpha) in the spinal cords, and compared the results between the different groups. Image analysis revealed that optical density of NeuN-immunoreactive neurons was significantly lower in the non-treated groups of presymptomatic and advanced ALS mice than in the non-treated groups of age-matched control mice and was recovered with pioglitazone treatment, and that optical densities of GFAP-immunoreactive astrocytes and Iba1-immunoreactive microglia were significantly higher in the non-treated group of advanced ALS mice than in the non-treated group of control mice and were recovered with pioglitazone treatment. Immunohistochemical analysis demonstrated that immunoreactivities for PPARgamma and p-p38 were mainly localized in neurons, and that IkappaBalpha immunoreactivity was mainly localized in astrocytes and microglia. Immunoblot analysis showed that pioglitazone treatment resulted in no significant change in nuclear PPARgamma-immunoreactive density, a significant decrease in cytosolic p-p38-immunoreactive density, and a significant increase in cytosolic IkappaBalpha-immunoreactive density. Our results suggest that pioglitazone protects motor neurons against p38-mediated neuronal death and NF-kappaB-mediated glial inflammation via a PPARgamma-independent mechanism.

Correction of protein kinase C activity and macrophage migration in peripheral nerve by pioglitazone, peroxisome proliferator activated-gamma-ligand, in insulin-deficient diabetic rats

Pioglitazone, one of thiazolidinediones, a peroxisome proliferator-activated receptor (PPAR)-gamma ligand, is known to have beneficial effects on macrovascular complications in diabetes, but the effect on diabetic neuropathy is not well addressed. We demonstrated the expression of PPAR-gamma in Schwann cells and vascular walls in peripheral nerve and then evaluated the effect of pioglitazone treatment for 12 weeks (10 mg/kg/day, orally) on neuropathy in streptozotocin-diabetic rats. At end, pioglitazone treatment improved nerve conduction delay in diabetic rats without affecting the expression of PPAR-gamma. Diabetic rats showed suppressed protein kinase C (PKC) activity of endoneurial membrane fraction with decreased expression of PKC-alpha. These alterations were normalized in the treated group. Enhanced expression of phosphorylated extracellular signal-regulated kinase detected in diabetic rats was inhibited by the treatment. Increased numbers of macrophages positive for ED-1 and 8-hydroxydeoxyguanosine-positive Schwann cells in diabetic rats were also corrected by the treatment. Pioglitazone lowered blood lipid levels of diabetic rats, but blood glucose and nerve sorbitol levels were not affected by the treatment. In conclusion, our study showed that pioglitazone was beneficial for experimental diabetic neuropathy via correction of impaired PKC pathway and proinflammatory process, independent of polyol pathway.

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.

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.

Altered PPARgamma expression and activation after transient focal ischemia in rats

Stroke is a devastating disease with limited treatment options. Recently, we found that the peroxisome proliferator-activated receptor-gamma (PPARgamma) agonists troglitazone and pioglitazone reduce injury and inflammation in a rat model of transient cerebral ischemia. The mechanism of this protection is unclear, as these agents can act through PPAR-gamma activation or through PPAR-gamma-independent mechanisms. Therefore, we examined PPAR-gamma expression, DNA binding and transcriptional activity following stroke. In addition, we used a PPAR-gamma antagonist, T0070907, to determine the role of PPAR-gamma during ischemia. Using immunohistochemical techniques and real-time PCR, we found low levels of PPAR-gamma mRNA and PPAR-gamma immunoreactivity in nonischemic brain; however, PPAR-gamma expression dramatically increased in ischemic neurons, peaking 24 h following middle cerebral artery occlusion. Interestingly, we found that in both vehicle- and agonist-treated brains, DNA binding was reduced in the ischemic hemisphere relative to the contralateral hemisphere. Expression of a PPAR-gamma target gene, lipoprotein lipase, was also reduced in ischemic relative to nonischemic brain. Both DNA binding and lipoprotein lipase expression were increased by the addition of the PPAR-gamma agonist rosiglitazone. Finally, we found that rosiglitazone-mediated protection after stroke was reversed by the PPAR-gamma antagonist T0070907. Interestingly, infarction size was also increased by T0070907 in the absence of PPAR-gamma agonist, suggesting that endogenous PPAR-gamma ligands may mitigate the effects of cerebral ischemia.

The role of insulin and neurotrophic factor signaling in brain aging and Alzheimer’s Disease

Although increased lifespan is associated with reduced insulin signaling, insulin signaling is essential for neuronal development and survival. Insulin resistance is central to Type II diabetes and is also implicated in the pathogenesis of Alzheimer's Disease (AD). This has prompted ongoing clinical trials in AD patients to test the efficacy of improving insulin - like signaling with dietary omega-3 fatty acids or insulin - sensitizing drugs as well as exercise regimens. Here we review the role of insulin signaling in brain aging and AD, concluding that the signaling pathways downstream to neurotrophic and insulin signaling are defective and coincident with aberrant phosphorylation and translocation of key components, notably AKT and GSK3beta, but also rac> PAK signaling. These responses are likely to contribute to defects in synaptic plasticity, learning and memory. Both oligomers of beta-amyloid (which are elevated in the AD brain) and pro-inflammatory cytokines (which are elevated in the aged or AD brain) can be used to mimic the trophic factor/insulin resistance observed in AD, but details on other factors and mechanisms contributing to this resistance remain elusive. A better understanding of the precise mechanisms underlying alterations in the insulin/neurotrophic factor signal transduction pathways should aid the search for better AD therapeutic and prevention strategies.

The emerging functions of UCP2 in health, disease, and therapeutics

The uncoupling proteins (UCPs) are attracting an increased interest as potential therapeutic targets in a number of important diseases. UCP2 is expressed in several tissues, but its physiological functions as well as potential therapeutic applications are still unclear. Unlike UCP1, UCP2 does not seem to be important to thermogenesis or weight control, but appears to have an important role in the regulation of production of reactive oxygen species, inhibition of inflammation, and inhibition of cell death. These are central features in, for example, neurodegenerative and cardiovascular disease, and experimental evidence suggests that an increased expression and activity of UCP2 in models of these diseases has a beneficial effect on disease progression, implicating a potential therapeutic role for UCP2. UCP2 has an important role in the pathogenesis of type 2 diabetes by inhibiting insulin secretion in islet beta cells. At the same time, type 2 diabetes is associated with increased risk of cardiovascular disease and atherosclerosis where an increased expression of UCP2 appears to be beneficial. This illustrates that therapeutic applications involving UCP2 likely will have to regulate expression and activity in a tissue-specific manner.

Peroxisome Proliferator-activated Receptor γ Is a Novel Target of the Nerve Growth Factor Signaling Pathway in PC12 Cells

Peroxisome proliferator-activated receptor gamma (PPARgamma), a member of the nuclear receptor superfamily, is subject to considerable interest because of its role in adipocyte differentiation, metabolic control, and anti-inflammatory action. PPARgamma research in brain cells is presently focused on glial PPARgamma because of its potential as a pharmacological target in the treatment of neurodegenerative diseases with an inflammatory component. In neurons PPARgamma function is far from clear, and PPARgamma agonist-dependent and -independent effects on cell survival or differentiation have been reported. We used PC12 cells, widely used to study neuronal signaling, such as nerve growth factor (NGF)-induced differentiation and survival or epidermal growth factor-dependent cell proliferation to dissect the possible involvement of PPARgamma in these pathways. We show that NGF but not epidermal growth factor increases the transcriptional activity of PPARgamma, and modulates the expression of this transcription factor. Because NGF signals through the tyrosine kinase (TrkA) NGF receptor and/or the p75NTR receptor, we used rescue experiments with a PC12 cell mutant lacking TrkA to show that NGF-induced PPARgamma activation is dependent on TrkA activation. Our results point out PPARgamma as a novel target of the TrkA-mediated neuronal cell survival and differentiating pathway and suggest a potential new inflammatory-independent therapeutic approach for pharmacological intervention in neurological disorders.

Neuroprotective effects of PPARgamma agonists against oxidative insults in HT-22 cells

Peroxisome proliferator-activated receptors (PPARs) are involved in regulating many metabolic and inflammatory processes. The present study explores the role of PPAR ligands in protecting neuronal cultures from toxic insults. For that purpose, we used WY14643 [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio acetic acid] as a PPARalpha agonist, L-165041 and L-783483 as PPARbeta ligands, and 15-deoxy-Delta(12,14)-PGJ2 (15d-PGJ2), troglitazone, and ciglitazone for PPARgamma. Experiments were performed using HT-22, an immortalized mouse hippocampal cell line, and SK-N-SH, a human neuroblastoma cell line. Cell viability against glutamate, hydrogen peroxide (H(2)O(2)), and serum deprivation insults was determined using a calcein acetoxymethyl (AM) assay. Of the compounds tested, only 15d-PGJ2 and troglitazone showed a dose-dependent neuroprotection from glutamate and H(2)O(2) insults in HT-22 cells. None of the PPAR agonists was protective in SK-N-SH cells. A minimum of 4-6 h preincubation with 15d-PGJ2 was required to achieve significant neuroprotection. On the other hand, troglitazone was protective even when administered simultaneously with glutamate, or for up to 8 h postglutamate insult. To investigate whether the neuroprotective effects are mediated through PPARgamma, we first determined through Western blotting that HT-22 and SK-N-SH cells express PPARgamma. However, the neuroprotective effects of those compounds are unlikely to be mediated through the PPARgamma for two reasons: (1) various concentrations of another PPARgamma agonist (ciglitazone) were not neuroprotective; (2) by itself, PPAR exhibits a low affinity for DNA, and high-affinity binding requires heterodimerization with RXR, the 9-cis-retinoic acid receptor; administering 9-cis-retinoic acid in conjunction with 15d-PGJ2 did not alter the neuroprotective effects of the latter. Our results demonstrate neuroprotective effects of 15d-PGJ2 and troglitazone that are likely independent of PPARgamma.

Adenoviral gene transfer of GDNF, BDNF and TGF beta 2, but not CNTF, cardiotrophin-1 or IGF1, protects injured adult motoneurons after facial nerve avulsion

We examined neuroprotective effects of recombinant adenoviral vectors encoding glial cell line-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), cardiotrophin-1 (CT1), insulin-like growth factor-1 (IGF1), and transforming growth factor-beta2 (TGFbeta2) on lesioned adult rat facial motoneurons. The right facial nerves of adult Fischer 344 male rats were avulsed and removed from the stylomastoid foramen, and adenoviral vectors were injected into the facial canal. Animals avulsed and treated with adenovirus encoding GDNF, BDNF, CNTF, CT1, IGF1 and TGFbeta2 showed intense immunolabeling for these factors in lesioned facial motoneurons, respectively, indicating adenoviral induction of the neurotrophic factors in these neurons. The treatment with adenovirus encoding GDNF, BDNF, or TGFbeta2 after avulsion significantly prevented the loss of lesioned facial motoneurons, improved choline acetyltransferase immunoreactivity and prevented the induction of nitric oxide synthase activity in these neurons. The treatment with adenovirus encoding CNTF, CT1 or IGF1, however, failed to protect these neurons after avulsion. These results indicate that the gene transfer of GDNF and BDNF and TGFbeta2 but not CNTF, CT1 or IGF1 may prevent the degeneration of motoneurons in adult humans with motoneuron injury and motor neuron diseases.

Survival-promoting activity of nimodipine and nifedipine in rat motoneurons: implications of an intrinsic calcium toxicity in motoneurons

L-type calcium channel antagonists, nimodipine and nifedipine, were tested for effects on the survival of purified rat motoneurons in culture. They showed significant activity, with maximum survival at 30 microm after 3 days in culture as high as 75%, which was comparable to the maximum effect obtained with brain-derived neurotrophic factor, a potent neurotrophic factor for rat motoneurons. It was also found that depolarizing conditions with a high potassium concentration (30 mm) were toxic to motoneurons. This toxicity was blocked by co-treatment with nimodipine. These results implicate a pre-existing calcium burden through calcium channels in motoneurons; they may offer further insights into understanding the selective death of motoneurons and have therapeutic implications in amyotrophic lateral screlosis.

Troglitazone inhibits both post-glutamate neurotoxicity and low-potassium-induced apoptosis in cerebellar granule neurons

Both excitotoxicity and apoptosis contribute to neuronal loss in various neurodegenerative diseases such as Alzheimer's disease as well as stroke, and a drug inhibiting both types of cell death may lead to practical treatment for these diseases. Post-treatment with troglitazone, a potent and specific activator of peroxisome proliferator-activated receptor (PPAR)-gamma attenuated the cell death of cerebellar granule neurons, triggered by glutamate exposure. The inhibitory effect of troglitazone against glutamate excitotoxicity, in vitro, was observed even when added 2.5 h after the end of glutamate exposure, a time when glutamate antagonists are no longer neuroprotective. However, troglitazone did not block the glutamate-induced elevation of calcium influx, suggesting that troglitazone interfered with downstream consequences of excitotoxic glutamate receptor overactivation. In addition, troglitazone also suppressed low-potassium-induced apoptosis in cerebellar granule neurons in a phosphatidylinositol 3-kinase independent manner. In conclusion, although the mechanisms of troglitazone's neuroprotective effects are unknown, the post-treatment-neuroprotective effect and the dual-inhibitory-activity against both excitotoxicity and apoptosis may provide a novel therapy for various neurodegenerative diseases.