Neuroprotective effect of PACAP on translational control alteration and cognitive decline in MPTP parkinsonian mice

Examining the Influence of Zinc Oxide Nanoparticles and Bulk Zinc Oxide on Rat Brain Functions: a Comprehensive Neurobehavioral, Antioxidant, Gene Expression, and Histopathological Investigation

The study aimed to assess the impact of zinc oxide nanoparticles (ZnONPs) on rats' neurobehavior compared to bulk zinc oxide (BZnO). Thirty male Sprague-Dawley rats were randomly assigned to five groups. The control group received Tween 80 (10%), while the ZnONP groups were given ZnONPs at 5 and 10 mg/kg body weight dosages, and the bulk zinc oxide (BZnO) groups received BZnO at the same dosages. Behavioral observations, neurobehavioral examinations, and assessments of brain tissue oxidative markers, neurotransmitter levels, and histopathological changes were performed. The results indicated that ZnONP at a dosage of 5 mg/kg improved general behavior, locomotor activity, memory, and recognition and reduced fearfulness in rats. Conversely, the higher dosage of 10 mg/kg and the bulk form had adverse effects on general behavior, locomotor activity, and learning ability, with the bulk form demonstrating the most severe impact-znONP-5 treatment increased antioxidant enzyme levels and decreased inflammatory markers. BZnO-5 exhibited lower oxidative stress markers, although still higher than BZnO-10. Furthermore, ZnONP-5 and BZnO-5 increased neurotransmitter levels compared to higher dosages. ZnONP-5 upregulated the expression of brain-derived neurotrophic factor (BDNF) mRNA, while BZnO-5 showed increased BDNF mRNA expression and decreased expression of genes related to apoptosis and inflammation. In summary, ZnONPs at 5 mg/kg demonstrated positive effects on rat brain function and behavior, while higher dosages and the bulk form had detrimental effects. In conclusion, the studies emphasized the importance of further assessing various doses and forms of zinc oxide on brain health, highlighting the significance of dosage considerations when using nanomaterials.

Recent Uses of Lipid Nanoparticles, Cell-Penetrating and Bioactive Peptides for the Development of Brain-Targeted Nanomedicines against Neurodegenerative Disorders

The lack of effective treatments for neurodegenerative diseases (NDs) is an important current concern. Lipid nanoparticles can deliver innovative combinations of active molecules to target the various mechanisms of neurodegeneration. A significant challenge in delivering drugs to the brain for ND treatment is associated with the blood-brain barrier, which limits the effectiveness of conventional drug administration. Current strategies utilizing lipid nanoparticles and cell-penetrating peptides, characterized by various uptake mechanisms, have the potential to extend the residence time and bioavailability of encapsulated drugs. Additionally, bioactive molecules with neurotropic or neuroprotective properties can be delivered to potentially mediate the ND targeting pathways, e.g., neurotrophin deficiency, impaired lipid metabolism, mitochondrial dysfunction, endoplasmic reticulum stress, accumulation of misfolded proteins or peptide fragments, toxic protein aggregates, oxidative stress damage, and neuroinflammation. This review discusses recent advancements in lipid nanoparticles and CPPs in view of the integration of these two approaches into nanomedicine development and dual-targeted nanoparticulate systems for brain delivery in neurodegenerative disorders.

Downregulation of PACAP and the PAC1 Receptor in the Basal Ganglia, Substantia Nigra and Centrally Projecting Edinger-Westphal Nucleus in the Rotenone model of Parkinson's Disease

Numerous in vitro and in vivo models of Parkinson's disease (PD) demonstrate that pituitary adenylate cyclase-activating polypeptide (PACAP) conveys its strong neuroprotective actions mainly via its specific PAC1 receptor (PAC1R) in models of PD. We recently described the decrease in PAC1R protein content in the basal ganglia of macaques in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD that was partially reversed by levodopa therapy. In this work, we tested whether these observations occur also in the rotenone model of PD in the rat. The rotarod test revealed motor skill deterioration upon rotenone administration, which was reversed by benserazide/levodopa (B/L) treatment. The sucrose preference test suggested increased depression level while the open field test showed increased anxiety in rats rendered parkinsonian, regardless of the received B/L therapy. Reduced dopaminergic cell count in the substantia nigra pars compacta (SNpc) diminished the dopaminergic fiber density in the caudate-putamen (CPu) and decreased the peptidergic cell count in the centrally projecting Edinger-Westphal nucleus (EWcp), supporting the efficacy of rotenone treatment. RNAscope in situ hybridization revealed decreased PACAP mRNA (Adcyap1) and PAC1R mRNA (Adcyap1r1) expression in the CPu, globus pallidus, dopaminergic SNpc and peptidergic EWcp of rotenone-treated rats, but no remarkable downregulation occurred in the insular cortex. In the entopeduncular nucleus, only the Adcyap1r1 mRNA was downregulated in parkinsonian animals. B/L therapy attenuated the downregulation of Adcyap1 in the CPu only. Our current results further support the evolutionarily conserved role of the PACAP/PAC1R system in neuroprotection and its recruitment in the development/progression of neurodegenerative states such as PD.

gH625-liposomes deliver PACAP through a dynamic in vitro model of the blood–brain barrier

The blood–brain barrier (BBB) selectively protects the central nervous system (CNS) from external insults, but its function can represent a limit for the passage of therapeutic molecules. Numerous in vitro models of the BBB have been realized in order to study the passage of drugs for neurodegenerative diseases, but these in vitro models are not very representative of the physiological conditions because of a limited supply of oxygen and nutrients due to static conditions. To avoid this phenomenon, we used a millifluidic bioreactor model that ensures a circulation of the medium and, therefore, of the nutrients, thanks to the continuous laminar flow. This dynamic model consists of a double-culture chamber separated by a membrane on which brain endothelial cells are cultured in order to evaluate the passage of the drug. Furthermore, in the lower chamber, SH-SY5Y were seeded as 3D spheroids to evaluate the drug passage through these cells. As nanodelivery system, we used liposomes functionalized with viral fusion peptide to evaluate the passage of a neuroprotective agent, pituitary adenylate cyclase-activating polypeptide (PACAP), through the dynamic in vitro model of the BBB. We showed that our nanodelivery system, made of functionalized liposomes and loaded with specific molecules, efficiently crosses the in vitro fluid-dynamic model of the BBB. Our findings represent an important step for further experimental investigations on PACAP administration as a therapeutic agent by an enhanced drug delivery system. Our results can improve the diffusion of good practice in neuroscience laboratories, helping to spread the 3R rules.

The effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on the cognitive and motor functions in rodents: A systematic review and meta-analysis

Memory and motor deficits are commonly identified in Parkinson's disease (PD). 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is transformed to MPP+ via monoamine oxidase B (MAOB), which causes oxidative stress and destroys dopaminergic (DA) neurons in substantia nigra pars compacta (SNc) and is widely used to create animal models of PD. However, to-date, a comprehensive analysis of the MPTP effects on various aspects of PD does not exist. Here, we provide a systematic review and meta-analysis on the MPTP effects on memory and motor functions by analyzing 51 studies on more than one thousand animals mainly including rats and mice. The results showed that in addition to motor functions such as coordination, balance and locomotor activity, MPTP significantly affects various mnemonic processes including spatial memory, working memory, recognition memory, and associative memory compared with the control group with some differences between systemic and intra-nigral injections on spatial memory, familiar object recognition, and anxiety-like behaviors. Nevertheless, our analysis failed to find systematic relationship between MPTP injection protocol parameters reported and the extent of the induced PD symptoms that can be a cause of concern for replicability of MPTP studies.

Demystifying the Neuroprotective Role of Neuropeptides in Parkinson's Disease: A Newfangled and Eloquent Therapeutic Perspective

Parkinson's disease (PD) refers to one of the eminently grievous, preponderant, tortuous nerve-cell-devastating ailments that markedly impacts the dopaminergic (DArgic) nerve cells of the midbrain region, namely the substantia nigra pars compacta (SN-PC). Even though the exact etiopathology of the ailment is yet indefinite, the existing corroborations have suggested that aging, genetic predisposition, and environmental toxins tremendously influence the PD advancement. Additionally, pathophysiological mechanisms entailed in PD advancement encompass the clumping of α-synuclein inside the lewy bodies (LBs) and lewy neurites, oxidative stress, apoptosis, neuronal-inflammation, and abnormalities in the operation of mitochondria, autophagy lysosomal pathway (ALP), and ubiquitin-proteasome system (UPS). The ongoing therapeutic approaches can merely mitigate the PD-associated manifestations, but until now, no therapeutic candidate has been depicted to fully arrest the disease advancement. Neuropeptides (NPs) are little, protein-comprehending additional messenger substances that are typically produced and liberated by nerve cells within the entire nervous system. Numerous NPs, for instance, substance P (SP), ghrelin, neuropeptide Y (NPY), neurotensin, pituitary adenylate cyclase-activating polypeptide (PACAP), nesfatin-1, and somatostatin, have been displayed to exhibit consequential neuroprotection in both in vivo and in vitro PD models via suppressing apoptosis, cytotoxicity, oxidative stress, inflammation, autophagy, neuronal toxicity, microglia stimulation, attenuating disease-associated manifestations, and stimulating chondriosomal bioenergetics. The current scrutiny is an effort to illuminate the neuroprotective action of NPs in various PD-experiencing models. The authors carried out a methodical inspection of the published work procured through reputable online portals like PubMed, MEDLINE, EMBASE, and Frontier, by employing specific keywords in the subject of our article. Additionally, the manuscript concentrates on representing the pathways concerned in bringing neuroprotective action of NPs in PD. In sum, NPs exert substantial neuroprotection through regulating paramount pathways indulged in PD advancement, and consequently, might be a newfangled and eloquent perspective in PD therapy.

Examination of pituitary adenylate cyclase-activating polypeptide in Parkinson’s disease focusing on correlations with motor symptoms

The neuroprotective effects of pituitary adenylate cyclase-activating polypeptide (PACAP) have been shown in numerous in vitro and in vivo models of Parkinson’s disease (PD) supporting the theory that PACAP could have an important role in the pathomechanism of the disorder affecting mostly older patients. Earlier studies found changes in PACAP levels in neurological disorders; therefore, the aim of our study was to examine PACAP in plasma samples of PD patients. Peptide levels were measured with ELISA and correlated with clinical parameters, age, stage of the disorder based on the Hoehn and Yahr (HY) scale, subtype of the disease, treatment, and specific scores measuring motor and non-motor symptoms, such as movement disorder society-unified Parkinson’s disease rating scale (MDS-UPDRS), Epworth sleepiness scale (ESS), Parkinson’s disease sleep scale (PDSS-2), and Beck depression inventory (BDI). Our results showed significantly decreased PACAP levels in PD patients without deep brain stimulation (DBS) therapy and in akinetic-rigid subtype; additionally we also observed a further decrease in the HY stage 3 and 4. Elevated PACAP levels were found in patients with DBS. There were no significant correlations between PACAP level with MDS-UPDRS, type of pharmacological treatment, PDSS-2 sleepiness, or depression (BDI) scales, but we found increased PACAP level in patients with more severe sleepiness problems based on the ESS scale. Based on these results, we suggest that following the alterations of PACAP with other frequently used clinical biomarkers in PD patients might improve strategic planning of further therapeutic interventions and help to provide a clearer prognosis regarding the future perspective of the disease.

MPTP-Treated Zebrafish Recapitulate 'Late-Stage' Parkinson's-like Cognitive Decline

The zebrafish is a promising model species in biomedical research, including neurotoxicology and neuroactive drug screening. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) evokes degeneration of dopaminergic neurons and is commonly used to model Parkinson's disease (PD) in laboratory animals, including zebrafish. However, cognitive phenotypes in MPTP-evoked experimental PD models remain poorly understood. Here, we established an LD50 (292 mg/kg) for intraperitoneal MPTP administration in adult zebrafish, and report impaired spatial working memory (poorer spontaneous alternation in the Y-maze) in a PD model utilizing fish treated with 200 µg of this agent. In addition to conventional behavioral analyses, we also employed artificial intelligence (AI)-based approaches to independently and without bias characterize MPTP effects on zebrafish behavior during the Y-maze test. These analyses yielded a distinct cluster for 200-μg MPTP (vs. other) groups, suggesting that high-dose MPTP produced distinct, computationally detectable patterns of zebrafish swimming. Collectively, these findings support MPTP treatment in adult zebrafish as a late-stage experimental PD model with overt cognitive phenotypes.

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Protects Striatal Cells and Improves Motor Function in Huntington’s Disease Models: Role of PAC1 Receptor

Huntington’s disease (HD) is a hereditary neurodegenerative disorder caused by the expression of mutant huntingtin (mHtt). One of the main features of HD is the degeneration of the striatum that leads to motor discoordination. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that acts through three receptors named PAC1R, VPAC1R, and VPAC2R. In the present study, we first investigated the effect of PACAP on STHdhQ7/Q7 and STHdhQ111/Q111 cells that express wild-type Htt with 7 and mHtt with 111 glutamines, respectively. Then we explored the capacity of PACAP to rescue motor symptoms in the R6/1, a murine model of HD. We found that PACAP treatment (10^–7 M) for 24 h protects STHdhQ111/Q111 cells from mHtt-induced apoptosis. This effect is associated with an increase in PAC1R transcription, phosphorylation of ERK and Akt, and an increase of intracellular c-fos, egr1, CBP, and BDNF protein content. Moreover, the use of pharmacological inhibitors revealed that activation of ERK and Akt mediates these antiapoptotic and neurotrophic effects of PACAP. To find out PAC1R implication, we treated STHdh cells with vasoactive intestinal peptide (VIP), which exhibits equal affinity for VPAC1R and VPAC2R, but lower affinity for PAC1R, in contrast to PACAP which has same affinity for the three receptors. VIP reduced cleaved caspase-3 protein level, without promoting the expression of c-fos, egr1, CBP, and the neurotrophin BDNF. We next measured the protein level of PACAP receptors in the striatum and cortex of R6/1 mice. We observed a specific reduction of PAC1R at the onset of motor symptoms. Importantly, the intranasal administration of PACAP to R6/1 animals restored the motor function and increased the striatal levels of PAC1R, CBP, and BDNF. In conclusion, PACAP exerts antiapoptotic and neurotrophic effects in striatal neurons mainly through PAC1R. This effect in HD striatum allows the recovery of motor function and point out PAC1R as a therapeutic target for treatment of HD.

Resistance Exercise Improves Spatial Learning Ability Through Phosphorylation of 5'-Adenosine Monophosphate-Activated Protein Kinase in Parkinson Disease Mice

Purpose

Exercise is a representative noninvasive treatment that can be applied to various diseases. We studied the effect of resistance exercise on motor function and spatial learning ability in Parkinson disease (PD) mice.

Methods

The rotarod test and beam walking test were conducted to evaluate the effect of resistance exercise on motor function, and the Morris water maze test was conducted to examine the effect of resistance exercise on spatial learning ability. The effect of resistance exercise on brain-derived neurotrophic factor (BDNF) and tropomyosin receptor kinase B (TrkB) expression and 5’-adenosine monophosphate-activated protein kinase (AMPK) phosphorylation was investigated by Western blot analysis. New cell generation was confirmed by immunohistochemistry for 5-bromo-2’-deoxyuridine.

Results

Resistance exercise improved coordination, balance, and spatial learning ability in PD mice. Resistance exercise enhanced new cell production, BDNF and TrkB expression, and AMPK phosphorylation in PD mice. The effect of such resistance exercise was similar to that of levodopa application.

Conclusions

In PD-induced mice, resistance exercise enhanced AMPK phosphorylation to increase BDNF expression and new neuron generation, thereby improving spatial learning ability. Resistance exercise is believed to help improve symptoms of PD.

Correlation of Decreased Serum Pituitary Adenylate Cyclase-Activating Polypeptide and Vasoactive Intestinal Peptide Levels With Non-motor Symptoms in Patients With Parkinson's Disease

Objective: Pituitary adenylate-cyclase activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are two neuropeptides that exhibit anti-inflammatory and neuroprotective properties, modulating the production of cytokines and chemokines, and the behavior of immune cells. However, the relationship between PACAP and VIP levels and Parkinson’s disease (PD) are not clear. The aim of the current study was to evaluate serum PACAP and VIP levels in PD patients and to analysis the correlation between neuropeptide levels and non-motor symptoms.

Methods: In this cross-sectional study, we enrolled 72 patients with idiopathic PD and 71 healthy volunteers. Serum PACAP and VIP levels were measured using an enzyme-linked immunosorbent assay (ELISA) kit. Non-motor symptoms were assessed with the Non-Motor Symptoms Scale (NMSS) for PD, including total and single-item scores.

Results: The serum PACAP levels of PD patients were significantly lower than those of healthy controls [(76.02 ± 43.78) pg/ml vs. (154.96 ± 76.54) pg/ml, P < 0.001]; and the serum VIP levels of PD patients were also significantly lower than those of healthy controls [(109.56 ± 15.39) pg/ml vs. (136.46 ± 24.16) pg/ml, P < 0.001]. PACAP levels were inversely correlated only with the score on NMSS item five, assessing Attention/memory (r = −0.276, P < 0.05) and lower serum PACAP levels were detected in the cognitive dysfunction subgroup than in the cognitively intact subgroup [(61.87 ± 32.66) pg/ml vs. (84.51 ± 47.59) pg/ml, P < 0.05]; meanwhile, VIP levels were inversely correlated with the NMSS total score (r = −0.285, P < 0.05) and the single-item scores for item one, assessing Cardiovascular (r = −0.257, P < 0.05) and item three, assessing Mood/cognition (r = −0.373, P < 0.05), and lower serum VIP levels were detected in the anxiety subgroup and depression subgroup than in the non-anxiety subgroup and non-depression subgroup, respectively [(107.45 ± 15.40) pg/ml vs. (116.41 ± 13.67) pg/ml, P < 0.05]; [(104.45 ± 15.26) pg/ml vs. (113.43 ± 14.52) pg/ml, P < 0.05].

Conclusion: The serum PACAP and VIP levels of PD patients were significantly lower than those of healthy controls. The non-motor symptoms significantly negatively correlated with serum PACAP level was cognitive dysfunction, while mood disorder was significantly correlated with serum VIP level.

A Novel Synthetic Precursor of Styryl Sulfone Neuroprotective Agents Inhibits Neuroinflammatory Responses and Oxidative Stress Damage through the P38 Signaling Pathway in the Cell and Animal Model of Parkinson's Disease

A novel class of styryl sulfones were designed and synthesized as CAPE derivatives by our work team, which showed a multi-target neuroprotective effect, including antioxidative and anti-neuroinflammatory properties. However, the underlying mechanisms remain unclear. In the present study, the anti-Parkinson’s disease (PD) activity of 10 novel styryl sulfone compounds was screened by the cell viability test and the NO inhibition test in vitro. It was found that 4d exhibited the highest activity against PD among them. In a MPTP-induced mouse model of PD, the biological activity of 4d was validated through suppressing dopamine neurotoxicity, microglial activation, and astrocytes activation. With compound 4d, we conducted the mechanistic studies about anti-inflammatory responses through inhibition of p38 phosphorylation to protect dopaminergic neurons, and antioxidant effects through promoting nuclear factor erythroid 2-related factor 2 (Nrf2). The results revealed that 4d could significantly inhibit 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/1-methyl-4-phenylpyridinium (MPTP/MPP⁺)-induced p38 mitogen-activated protein kinase (MAPK) activation in both in vitro and in vivo PD models, thus inhibiting the NF-κB-mediated neuroinflammation-related apoptosis pathway. Simultaneously, it could promote Nrf2 nuclear transfer, and upregulate the expression of antioxidant phase II detoxification enzymes HO-1 and GCLC, and then reduce oxidative damage.

The Potential Role of Protein Kinase R as a Regulator of Age-Related Neurodegeneration

There is a growing evidence describing a decline in adaptive homeostasis in aging-related diseases affecting the central nervous system (CNS), many of which are characterized by the appearance of non-native protein aggregates. One signaling pathway that allows cell adaptation is the integrated stress response (ISR), which senses stress stimuli through four kinases. ISR activation promotes translational arrest through the phosphorylation of the eukaryotic translation initiation factor 2 alpha (eIF2α) and the induction of a gene expression program to restore cellular homeostasis. However, depending on the stimulus, ISR can also induce cell death. One of the ISR sensors is the double-stranded RNA-dependent protein kinase [protein kinase R (PKR)], initially described as a viral infection sensor, and now a growing evidence supports a role for PKR on CNS physiology. PKR has been largely involved in the Alzheimer’s disease (AD) pathological process. Here, we reviewed the antecedents supporting the role of PKR on the efficiency of synaptic transmission and cognition. Then, we review PKR’s contribution to AD and discuss the possible participation of PKR as a player in the neurodegenerative process involved in aging-related pathologies affecting the CNS.

A New Tool to Study Parkinsonism in the Context of Aging: MPTP Intoxication in a Natural Model of Multimorbidity

The diurnal rodent Octodon degus (O. degus) is considered an attractive natural model for Alzheimer's disease and other human age-related features. However, it has not been explored so far if the O. degus could be used as a model to study Parkinson's disease. To test this idea, 10 adult male O. degus were divided into control group and MPTP-intoxicated animals. Motor condition and cognition were examined. Dopaminergic degeneration was studied in the ventral mesencephalon and in the striatum. Neuroinflammation was also evaluated in the ventral mesencephalon, in the striatum and in the dorsal hippocampus. MPTP animals showed significant alterations in motor activity and in visuospatial memory. Postmortem analysis revealed a significant decrease in the number of dopaminergic neurons in the ventral mesencephalon of MPTP animals, although no differences were found in their striatal terminals. We observed a significant increase in neuroinflammatory responses in the mesencephalon, in the striatum and in the hippocampus of MPTP-intoxicated animals. Additionally, changes in the subcellular expression of the calcium-binding protein S100β were found in the astrocytes in the nigrostriatal pathway. These findings prove for the first time that O. degus are sensitive to MPTP intoxication and, therefore, is a suitable model for experimental Parkinsonism in the context of aging.

The Emerging Role of Neuropeptides in Parkinson's Disease

Parkinson’s disease (PD), the second most common age-related neurodegenerative disease, results from the loss of dopamine neurons in the substantia nigra. This disease is characterized by cardinal non-motor and motor symptoms. Several studies have demonstrated that neuropeptides, such as ghrelin, neuropeptide Y, pituitary adenylate cyclase-activating polypeptide, substance P, and neurotensin, are related to the onset of PD. This review mainly describes the changes in these neuropeptides and their receptors in the substantia nigra-striatum system as well as the other PD-related brain regions. Based on several in vitro and in vivo studies, most neuropeptides play a significant neuroprotective role in PD by preventing caspase-3 activation, decreasing mitochondrial-related oxidative stress, increasing mitochondrial biogenesis, inhibiting microglial activation, and anti-autophagic activity. Thus, neuropeptides may provide a new strategy for PD therapy.

Protective Effects of Pituitary Adenylate Cyclase-Activating Polypeptide and Vasoactive Intestinal Peptide Against Cognitive Decline in Neurodegenerative Diseases

Cognitive impairment is one of the major symptoms in most neurodegenerative disorders such as Alzheimer’s (AD), Parkinson (PD), and Huntington diseases (HD), affecting millions of people worldwide. Unfortunately, there is no treatment to cure or prevent the progression of those diseases. Cognitive impairment has been related to neuronal cell death and/or synaptic plasticity alteration in important brain regions, such as the cerebral cortex, substantia nigra, striatum, and hippocampus. Therefore, compounds that can act to protect the neuronal loss and/or to reestablish the synaptic activity are needed to prevent cognitive decline in neurodegenerative diseases. Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are two highly related multifunctional neuropeptides widely distributed in the central nervous system (CNS). PACAP and VIP exert their action through two common receptors, VPAC1 and VPAC2, while PACAP has an additional specific receptor, PAC1. In this review article, we first presented evidence showing the therapeutic potential of PACAP and VIP to fight the cognitive decline observed in models of AD, PD, and HD. We also reviewed the main transduction pathways activated by PACAP and VIP receptors to reduce cognitive dysfunction. Furthermore, we identified the therapeutic targets of PACAP and VIP, and finally, we evaluated different novel synthetic PACAP and VIP analogs as promising pharmacological tools.

Regulation of Protein Synthesis and Apoptosis in Lymphocytes of Parkinson Patients: The Effect of Dopaminergic Treatment

BACKGROUND

Parkinson disease (PD) is a neurodegenerative disorder characterized by progressive degeneration of the dopaminergic neurons in the substantia nigra, presumably due to increased apoptosis. In previous studies, we showed altered expression of proteins involved in mammalian target of rapamycin (mTOR) antiapoptotic and double-stranded RNA-dependent protein kinase (PKR) apoptotic pathways of translational control in experimental cellular and animal models of PD.

RESULTS

In this work, our results showed clear modifications in the expression of kinases involved in mTOR and PKR apoptosis pathways, in lymphocytes of PD patients treated or not with anti-PD treatment (levodopa), which confirmed the role played by apoptosis in the pathogenesis of this disease and the positive effect of treatment with medication on this parameter. Others proteins involved in apo-ptosis were also evaluated in lymphocytes of patients as the expression of the peripheral benzodiazepine receptor and caspase-3.

CONCLUSION

Translational control is altered in PD and hence its evaluation in peripheral blood mononuclear cells may serve as an early marker of apoptosis and indicate the efficacy of the dopaminergic treatment.

Toxicity and effects of copper oxide nanoparticles on cognitive performances in rats

There is increasing scientific evidences that the physical and chemical properties of manufactured nanoparticles lead to an increase in their bioavailability and toxicity. Among them Copper oxide nanoparticles (CuO-NPs) are widely used in different fields. However their potential adverse effects namely on brain functions are still discussed. Thus, the present study aimed to investigate the subacute oral toxicity and effects of CuO-NPs on cognitive performances in rats. Rats were randomly divided into three groups of 8 animals each, a control group received a dose 9‰ sodium chloride and the other groups received a suspension of CuO-NPs at doses of 250 and 500 mg/kg through oral gavage for 14 consecutive days. Multiple behavioral tests showed that CuO-NPs caused little changes in memory and learning performances as well as the locomotors activity, while the anxiety index increased. Copper NPs exposure increased also the liver and stomach relative weights and altered some blood biochemical parameters.

Pituitary Adenylate Cyclase-Activating Polypeptide Modulates Hippocampal Synaptic Transmission and Plasticity: New Therapeutic Suggestions for Fragile X Syndrome

Pituitary adenylate cyclase-activating polypeptide (PACAP) modulates glutamatergic synaptic transmission and plasticity in the hippocampus, a brain area with a key role in learning and memory. In agreement, several studies have demonstrated that PACAP modulates learning in physiological conditions. Recent publications show reduced PACAP levels and/or alterations in PACAP receptor expression in different conditions associated with cognitive disability. It is noteworthy that PACAP administration rescued impaired synaptic plasticity and learning in animal models of aging, Alzheimer's disease, Parkinson's disease, and Huntington's chorea. In this context, results from our laboratory demonstrate that PACAP rescued metabotropic glutamate receptor-mediated synaptic plasticity in the hippocampus of a mouse model of fragile X syndrome (FXS), a genetic form of intellectual disability. PACAP is actively transported through the blood-brain barrier and reaches the brain following intranasal or intravenous administration. Besides, new studies have identified synthetic PACAP analog peptides with improved selectivity and pharmacokinetic properties with respect to the native peptide. Our review supports the shared idea that pharmacological activation of PACAP receptors might be beneficial for brain pathologies with cognitive disability. In addition, we suggest that the effects of PACAP treatment might be further studied as a possible therapy in FXS.

Transcranial Magneto-Acoustic Stimulation Improves Neuroplasticity in Hippocampus of Parkinson's Disease Model Mice

In this study, we have, for the first time, demonstrated the beneficial effects of transcranial magneto-acoustic stimulation (TMAS), a technique based on focused ultrasound stimulation within static magnetic field, on the learning and memory abilities and neuroplasticity of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease (PD). Our results showed that chronic TMAS treatment (2 weeks) improved the outcome of Morris water maze, long-term potentiation (LTP), and dendritic spine densities in the dentate gyrus (DG) region of the hippocampus of PD model mice. To further investigate into the underlying mechanisms of these beneficial effects by TMAS, we quantified the proteins in the hippocampus that regulated neuroplasticity. Results showed that the level of postsynaptic density protein 95 was elevated in the brain of TMAS-treated PD model mice while the level of synaptophysin (SYP) did not show any change. We further quantified proteins that mediated neuroplasticity mechanisms, such as brain-derived neurotrophic factor (BDNF) and other important proteins that mediated neuroplasticity. Results showed that TMAS treatment elevated the levels of BDNF, cAMP response element-binding protein (CREB), and protein kinase B (p-Akt) in the PD model mouse hippocampus, but not in the non-PD mouse hippocampus. These results suggest that the beneficial effects on the neuroplasticity of PD model mice treated with TMAS could possibly be conducted through postsynaptic regulations and mediated by BDNF.

Design and biological assessment of membrane-tethering neuroprotective peptides derived from the pituitary adenylate cyclase-activating polypeptide type 1 receptor

BACKGROUND

The pituitary adenylate cyclase-activating polypeptide (PACAP) type 1 receptor (PAC1), a class B G protein-coupled receptor (GPCR), has emerged as a promising target for treating neurodegenerative conditions. Unfortunately, despite years of research, no PAC1-specific agonist has been discovered, as activity on two other GPCRs, VPAC1 and VPAC2, is retained with current analogs. Cell signaling is related to structural modifications in the intracellular loops (ICLs) of GPCRs. Thus, we hypothesized that peptides derived from the ICLs (called pepducins) of PAC1 might initiate, as allosteric ligands, signaling cascades after recognition of the parent receptor and modulation of its conformational landscape.

METHODS

Three pepducins were synthesized and evaluated for their ability to 1) promote cell survival; 2) stimulate various signaling pathways associated with PAC1 activation; 3) modulate selectively PAC1, VPAC1 or VPAC2 activation; and 4) sustain mobility and prevent death of dopaminergic neurons in a zebrafish model of neurodegeneration.

RESULTS

Assays demonstrated that these molecules promote SH-SY5Y cell survival, a human neuroblastoma cell line expressing PAC1, and activate signaling via Gα_s and Gα_q, with distinct potencies and efficacies. Also, PAC1-Pep1 and PAC1-Pep2 activated selectively PAC1-mediated Gα_s stimulation. Finally, experiments, using a zebrafish neurodegeneration model, showed a neuroprotective action with all three pepducins and in particular, revealed the ability of PAC1-Pep1 and PAC1-Pep3 to preserve fish mobility and tyrosine hydroxylase expression in the brain.

CONCLUSION

We have developed the first neuroprotective pepducins derived from PAC1, a class B GPCR.

GENERAL SIGNIFICANCE

PAC1-derived pepducins represent attractive templates for the development of innovative neuroprotecting molecules.

The toxin MPTP generates similar cognitive and locomotor deficits in hTau and tau knock-out mice

Parkinson's disease (PD) is characterized by motor deficits, although cognitive disturbances are frequent and have been noted early in the disease. The main pathological characteristics of PD are the loss of dopaminergic neurons and the presence of aggregated α-synuclein in Lewy bodies of surviving cells. Studies have also documented the presence of other proteins within Lewy bodies, particularly tau, a microtubule-associated protein implicated in a wide range of neurodegenerative diseases, including Alzheimer's disease (AD). In AD, tau pathology correlates with cognitive dysfunction, and tau mutations have been reported to lead to dementia associated with parkinsonism. However, the role of tau in PD pathogenesis remains unclear. To address this question, we induced parkinsonism by injecting the toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in hTau mice, a mouse model of tauopathy expressing human tau, and a mouse model knock-out for tau (TKO). We found that although MPTP impaired locomotion (gait analysis) and cognition (Barnes maze), there were no discernable differences between hTau and TKO mice. MPTP also induced a slight but significant increase in tau phosphorylation (Thr205) in the hippocampus of hTau mice, as well as a significant decrease in the soluble and insoluble tau fractions that correlated with the loss of dopaminergic neurons in the brainstem. Overall, our findings suggest that, although MPTP can induce an increase in tau phosphorylation at specific epitopes, tau does not seem to causally contribute to cognitive and locomotor deficits induced by this toxin.

Sub-acute intravenous exposure to Fe2O3 nanoparticles does not alter cognitive performances and catecholamine levels, but slightly disrupts plasma iron level and brain iron content in rats

Engineered nanomaterials are used in various applications due to their particular properties. Among them, Iron Oxide Nanoparticles (Fe₂O₃-NPs) are used in Biomedicine as theranostic agents i.e. contrast agents in Magnetic Resonance Imaging and cancer treatment. With the increasing production and use of these Fe₂O₃-NPs, there is an evident raise of Fe₂O₃-NPs exposure and subsequently a higher risk of adverse outcomes for the environment and Human. In the present paper, we investigated the effects of an intravenous daily Fe₂O₃-NPs exposure on Wistar rat for one week. As results, we showed that several hematological parameters and transaminase (ALT and AST) levels as well as organ histology remained unchanged in treated rats. Neither the catecholamine levels nor the emotional behavior and learning / memory capacities of rats were impacted by the sub-acute intravenous exposure to Fe₂O₃-NPs. However, iron level in plasma and iron content homeostasis in brain were disrupted after this exposure. Thus, our results demonstrated that Fe₂O₃-NPs could have transient effects on rat but the intravenous route is still safer that others which is encouraging for their use in medical and/or biological applications.

Effect of nano-sized SiO2 particles on the cognitive function and biochemical response

Several in vitro studies have convincingly demonstrated that SiO₂NPs mediated cytotoxicity, which was dose-, time- and size-dependent. The data on in vivo toxicity of SiO₂NPs are even more contradictory. In the present study, we investigated the effects of sub-acute exposure to SiO₂-NPs on spatial learning and memory, the biochemical parameters and the histology of organs. Rats were injected intravenously with a single dose of SiO₂-NPs (20 mg/kg) during five consecutive days. The analysis of spatial memory in the Morris water maze showed that SiO₂-NPs disrupt the cognitive abilities of rats. Moreover, SiO₂-NPs could changes the blood counts. However, biochemical markers remained unchanged. Histological examination showed that SiO₂-NPs induced pathological changes in rat organs. In this finding NPs were shown to cause granuloma formation and inflammatory cells infiltration in the liver.

Trx-1 ameliorates learning and memory deficits in MPTP-induced Parkinson's disease model in mice

Parkinson's disease (PD) is characterized by a progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc), characteristic motor symptoms and cognitive impairment. Thioredoxin-1 (Trx-1) is a redox protein and protects neurons from various injuries. Our previous study has shown that Trx-1 overexpression attenuates movement disorder in PD. However, whether Trx-1 ameliorates cognitive deficits in PD is still unknown. In the present study, we investigated the effects of Trx-1 on learning and memory in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD model in mice. We demonstrated that deficits in learning and memory were induced by MPTP in mice through the elevated plus-maze test. We found that the retention transfer latency time was shorten, escape latency was decreased and the number of platform crossings was increased in the Morris water maze (MWM) in Trx-1 transgenic (TG) mice when compared with wild type mice. The expressions of tyrosine hydroxylase (TH) and dopamine D1 receptor (D1R) were decreased by MPTP, which were restored in Trx-1 TG mice. The expression of N-methyl-D-aspartate receptor 2B subunit (NR2B), the levels of phosphorylation of extracellular signal-regulated kinase (ERK1/2) and cAMP-response element binding protein (CREB) in the hippocampus were decreased by MPTP, which were reversed in Trx-1 TG mice. These results suggest that Trx-1 ameliorates learning and memory deficits in MPTP-induced PD model in mice via modulating the D1R and the NMDAR-ERK1/2-CREB pathway. Trx-1 may be a therapy target for learning and memory deficits in PD.

Intranasal instillation of iron oxide nanoparticles induces inflammation and perturbation of trace elements and neurotransmitters, but not behavioral impairment in rats

Over the last decades, engineered nanomaterials have been widely used in various applications due to their interesting properties. Among them, iron oxide nanoparticles (IONPs) are used as theranostic agents for cancer, and also as contrast agents in magnetic resonance imaging. With the increasing production and use of these IONPs, there is an evident raise of IONP exposure and subsequently a higher risk of adverse outcome for humans and the environment. In this work, we aimed to investigate the effects of sub-acute IONP exposure on Wistar rat, particularly (i) on the emotional and learning/memory behavior, (ii) on the hematological and biochemical parameters, (iii) on the neurotransmitter content, and (vi) on the trace element homeostasis. Rats were treated during seven consecutive days by intranasal instillations at a dose of 10 mg/kg body weight. The mean body weight increased significantly in IONP-exposed rats. Moreover, several hematological parameters were normal in treated rats except the platelet count which was increased. The biochemical study revealed that phosphatase alkaline level decreased in IONP-exposed rats, but no changes were observed for the other hepatic enzymes (ALT and AST) levels. The trace element homeostasis was slightly modulated by IONP exposure. Sub-acute intranasal exposure to IONPs increased dopamine and norepinephrine levels in rat brain; however, it did not affect the emotional behavior, the anxiety index, and the learning/memory capacities of rats.

Indomethacin promotes survival of new neurons in the adult murine hippocampus accompanied by anti-inflammatory effects following MPTP-induced dopamine depletion

BACKGROUND

Parkinson's disease (PD) is characterized by dopaminergic cell loss and inflammation in the substantia nigra (SN) leading to motor deficits but also to hippocampus-associated non-motor symptoms such as spatial learning and memory deficits. The cognitive decline is correlated with impaired adult hippocampal neurogenesis resulting from dopamine deficit and inflammation, represented in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP) mouse model of PD. In the inflammatory tissue, cyclooxygenase (COX) is upregulated leading to an ongoing inflammatory process such as prostaglandin-mediated increased cytokine levels. Therefore, inhibition of COX by indomethacin may prevent the inflammatory response and the impairment of adult hippocampal neurogenesis.

METHODS

Wildtype C57Bl/6 and transgenic Nestin-GFP mice were treated with MPTP followed by short-term or long-term indomethacin treatment. Then, aspects of inflammation and neurogenesis were evaluated by cell counts using immunofluorescence and immunohistochemical stainings in the SN and dentate gyrus (DG). Furthermore, hippocampal mRNA expression of neurogenesis-related genes of the Notch, Wnt, and sonic hedgehog signaling pathways and neurogenic factors were assessed, and protein levels of serum cytokines were measured.

RESULTS

Indomethacin restored the reduction of the survival rate of new mature neurons and reduced the amount of amoeboid CD68+ cells in the DG after MPTP treatment. Indomethacin downregulated genes of the Wnt and Notch signaling pathways and increased neuroD6 expression. In the SN, indomethacin reduced the pro-inflammatory cellular response without reversing dopaminergic cell loss.

CONCLUSION

Indomethacin has a pro-neurogenic and thereby restorative effect and an anti-inflammatory effect on the cellular level in the DG following MPTP treatment. Therefore, COX inhibitors such as indomethacin may represent a therapeutic option to restore adult neurogenesis in PD.

Inflammation kinase PKR phosphorylates α-synuclein and causes α-synuclein-dependent cell death

Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy comprise a group of neurodegenerative diseases termed synucleinopathies. Synucleinopathie are, characterized by presence of inclusion bodies in degenerating brain cells which contain aggregated α-synuclein phosphorylated on Ser129. Although the inflammation-associated serine-threonine kinase, PKR (EIF2AK2), promotes cellular protection against infection, we demonstrate a pro-degenerative role of activated PKR in an α-synuclein-dependent cell model of multiple system atrophy, where inhibition and silencing of PKR decrease cellular degeneration. In vitro phosphorylation demonstrates that PKR can directly bind and phosphorylate monomeric and filamenteous α-synuclein on Ser129. Inhibition and knockdown of PKR reduce Ser129 phosphorylation in different models (SH-SY5Y ASYN cells, OLN-AS7 cells, primary mouse hippocampal neurons, and acute brain slices), while overexpression of constitutively active PKR increases Ser129 α-syn phosphorylation. Treatment with pre-formed α-synuclein fibrils, proteostatic stress-promoting MG-132 and known PKR activators, herpes simplex virus-1-∆ICP34.5 and LPS, as well as PKR inducer, IFN-β-1b, lead to increased levels of phosphorylated Ser129 α-synuclein that is completely blocked by simultaneous PKR inhibition. These results reveal a direct link between PKR and the phosphorylation and toxicity of α-synuclein, and they support that neuroinflammatory processes play a role in modulating the pathogenicity of α-synuclein.

Aluminium oxide nanoparticles compromise spatial learning and memory performance in rats

Recently, the biosafety and potential influences of nanoparticles on central nervous system have received more attention. In the present study, we assessed the effect of aluminium oxide nanoparticles (Al2O3-NPs) on spatial cognition. Male Wistar rats were intravenously administered Al2O3-NP suspension (20 mg/kg body weight/day) for four consecutive days, after which they were assessed. The results indicated that Al2O3-NPs impaired spatial learning and memory ability. An increment in malondialdehyde levels with a concomitant decrease in superoxide dismutase activity confirmed the induction of oxidative stress in the hippocampus. Additionally, our findings showed that exposure to Al2O3-NPs resulted in decreased acetylcholinesterase activity in the hippocampus. Furthermore, Al2O3-NPs enhanced aluminium (Al) accumulation and disrupted mineral element homoeostasis in the hippocampus. However, they did not change the morphology of the hippocampus. Our results show a connection among oxidative stress, disruption of mineral element homoeostasis, and Al accumulation in the hippocampus, which leads to spatial memory deficit in rats treated with Al2O3-NPs.

Alteration of the PAC1 Receptor Expression in the Basal Ganglia of MPTP-Induced Parkinsonian Macaque Monkeys

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a well-known neuropeptide with strong neurotrophic and neuroprotective effects. PACAP exerts its protective actions via three G protein-coupled receptors: the specific Pac1 receptor (Pac1R) and the Vpac1/Vpac2 receptors, the neuroprotective effects being mainly mediated by the Pac1R. The protective role of PACAP in models of Parkinson's disease and other neurodegenerative diseases is now well-established in both in vitro and in vivo studies. PACAP and its receptors occur in the mammalian brain, including regions associated with Parkinson's disease. PACAP receptor upregulation or downregulation has been reported in several injury models or human diseases, but no data are available on alterations of receptor expression in Parkinson's disease. The model closest to the human disease is the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced macaque model. Therefore, our present aim was to evaluate changes in Pac1R expression in basal ganglia related to Parkinson's disease in a macaque model. Monkeys were rendered parkinsonian with MPTP, and striatum, pallidum, and cortex were evaluated for Pac1R immunostaining. We found that Pac1R immunosignal was markedly reduced in the caudate nucleus, putamen, and internal and external parts of the globus pallidus, while the immunoreactivity remained unchanged in the cortex of MPTP-treated parkinsonian monkey brains. This decrease was attenuated in some brain areas in monkeys treated with L-DOPA. The strong, specific decrease of the PACAP receptor immunosignal in the basal ganglia of parkinsonian macaque monkey brains suggests that the PACAP/Pac1R system may play an important role in the development/progression of the disease.

Nonmotor Symptoms in Experimental Models of Parkinson's Disease

Nonmotor symptoms of Parkinson's disease (PD) range from neuropsychiatric, cognitive to sleep and sensory disorders and can arise from the disease process as well as from drug treatment. The clinical heterogeneity of nonmotor symptoms of PD is underpinned by a wide range of neuropathological and molecular pathology, affecting almost the entire range of neurotransmitters present in brain and the periphery. Understanding the neurobiology and pathology of nonmotor symptoms is crucial to the effective treatment of PD and currently a key unmet need. This bench-to-bedside translational concept can only be successful if robust animal models of PD charting the genesis and natural history of nonmotor symptoms can be devised. Toxin-based and transgenic rodent and primate models of PD have given us important clues to the underlying basis of motor symptomatology and in addition, can provide a snapshot of some nonmotor aspects of PD, although the data are far from complete. In this chapter, we discuss some of the nonmotor aspects of the available experimental models of PD and how the development of robust animal models to understand and treat nonmotor symptoms needs to become a research priority.

Characterizations of a synthetic pituitary adenylate cyclase-activating polypeptide analog displaying potent neuroprotective activity and reduced in vivo cardiovascular side effects in a Parkinson's disease model

Parkinson's disease (PD) is characterized by a steady loss of dopamine neurons through apoptotic, inflammatory and oxidative stress processes. In that line of view, the pituitary adenylate cyclase-activating polypeptide (PACAP), with its ability to cross the blood-brain barrier and its anti-apoptotic, anti-inflammatory and anti-oxidative properties, has proven to offer potent neuroprotection in various PD models. Nonetheless, its peripheral actions, paired with low metabolic stability, hampered its clinical use. We have developed Ac-[Phe(pI)(6), Nle(17)]PACAP(1-27) as an improved PACAP-derived neuroprotective compound. In vitro, this analog stimulated cAMP production, maintained mitochondrial potential and protected SH-SY5Y neuroblastoma cells from 1-methyl-4-phenylpyridinium (MPP(+)) toxicity, as potently as PACAP. Furthermore, contrasting with PACAP, it is stable in human plasma and against dipeptidyl peptidase IV activity. When injected intravenously to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice, PACAP and Ac-[Phe(pI)(6), Nle(17)]PACAP(1-27) restored tyrosine hydoxylase expression into the substantia nigra and modulated the inflammatory response. Albeit falls of mean arterial pressure (MAP) were observed with both PACAP- and Ac-[Phe(pI)(6), Nle(17)]PACAP(1-27)-treated mice, the intensity of the decrease as well as its duration were significantly less marked after iv injections of the analog than after those of the native polypeptide. Moreover, no significant changes in heart rate were measured with the animals for both compounds. Thus, Ac-[Phe(pI)(6), Nle(17)]PACAP(1-27) appears as a promising lead molecule for the development of PACAP-derived drugs potentially useful for the treatment of PD or other neurodegenerative diseases.

Physical exercise counteracts MPTP-induced changes in neural precursor cell proliferation in the hippocampus and restores spatial learning but not memory performance in the water maze

Parkinson's disease (PD) is characterized by a continuous loss of dopaminergic neurons in the substantia nigra, which not only leads to characteristic motor symptoms but also to cognitive impairments. Physical exercise has been shown to improve hippocampus-dependent cognitive functions in PD patients. Animal studies have demonstrated the involvement of adult hippocampal neurogenesis in exercise-induced improvements of visuo-spatial learning and memory. Here, we investigated the direct impact of voluntary wheel running on hippocampal neurogenesis and spatial learning and memory in the Morris water maze (MWM) using the1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. We also analyzed striatal and hippocampal dopamine transmission and mRNA expression levels of dopamine receptors. We show that MPTP-induced spatial learning deficits were alleviated by short-term physical exercise but not MPTP-induced spatial memory impairments in either exercise intervention group. Neural precursor proliferation was transiently altered in MPTP-treated mice, while the cell survival was increased by exercise. Dopamine was progressively depleted by MPTP and its turnover altered by exercise. In addition, gene expression of dopamine receptor D1/D5 was transiently upregulated following MPTP treatment but not affected by physical exercise. Our findings suggest that physical exercise benefits spatial learning but not memory performance in the MWM after MPTP-induced dopamine depletion by restoring precursor cell proliferation in the hippocampus and influencing dopamine transmission. This adds to the understanding of cognitive decline and mechanisms for potential improvements by physical exercise in PD patients.

Effect of the pituitary adenylate cyclase-activating polypeptide on the autophagic activation observed in in vitro and in vivo models of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder that leads to destruction of the midbrain dopaminergic (DA) neurons. This phenomenon is related to apoptosis and its activation can be blocked by the pituitary adenylate cyclase-activating polypeptide (PACAP). Growing evidence indicates that autophagy, a self-degradation activity that cleans up the cell, is induced during the course of neurodegenerative diseases. However, the role of autophagy in the pathogenesis of neuronal disorders is yet poorly understood and the potential ability of PACAP to modulate the related autophagic activation has never been significantly investigated. Hence, we explored the putative autophagy-modulating properties of PACAP in in vitro and in vivo models of PD, using the neurotoxic agents 1-methyl-4-phenylpyridinium (MPP(+)) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), respectively, to trigger alterations of DA neurons. In both models, following the toxin exposure, PACAP reduced the autophagic activity as evaluated by the production of LC3 II, the modulation of the p62 protein levels, and the formation of autophagic vacuoles. The ability of PACAP to inhibit autophagy was also observed in an in vitro cell assay by the blocking of the p62-sequestration activity produced with the autophagy inducer rapamycin. Thus, the results demonstrated that autophagy is induced in PD experimental models and that PACAP exhibits not only anti-apoptotic but also anti-autophagic properties.

PACAP as a neuroprotective factor in ischemic neuronal injuries

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 27- or 38-amino acid neuropeptide, which belongs to the vasoactive intestinal polypeptide/glucagon/secretin family. PACAP and its three receptor subtypes are expressed in neural tissues, with PACAP known to exert pleiotropic effects on the nervous system. This review provides an overview of current knowledge regarding the neuroprotective effects, mechanisms of action, and therapeutic potential of PACAP in response to ischemic brain injuries.

A mouse model of L-2-hydroxyglutaric aciduria, a disorder of metabolite repair

The purpose of the present work was to progress in our understanding of the pathophysiology of L-2-hydroxyglutaric aciduria, due to a defect in L-2-hydroxyglutarate dehydrogenase, by creating and studying a mouse model of this disease. L-2-hydroxyglutarate dehydrogenase-deficient mice (l2hgdh-/-) accumulated L-2-hydroxyglutarate in tissues, most particularly in brain and testis, where the concentration reached ≈ 3.5 μmol/g. Male mice showed a 30% higher excretion of L-2-hydroxyglutarate compared to female mice, supporting that this dicarboxylic acid is partially made in males by lactate dehydrogenase C, a poorly specific form of this enzyme exclusively expressed in testes. Involvement of mitochondrial malate dehydrogenase in the formation of L-2-hydroxyglutarate was supported by the commensurate decrease in the formation of this dicarboxylic acid when down-regulating this enzyme in mouse l2hgdh-/- embryonic fibroblasts. The concentration of lysine and arginine was markedly increased in the brain of l2hgdh-/- adult mice. Saccharopine was depleted and glutamine was decreased by ≈ 40%. Lysine-α-ketoglutarate reductase, which converts lysine to saccharopine, was inhibited by L-2-hydroxyglutarate with a Ki of ≈ 0.8 mM. As low but significant activities of the bifunctional enzyme lysine-α-ketoglutarate reductase/saccharopine dehydrogenase were found in brain, these findings suggest that the classical lysine degradation pathway also operates in brain and is inhibited by the high concentrations of L-2-hydroxyglutarate found in l2hgdh-/- mice. Pathological analysis of the brain showed significant spongiosis. The vacuolar lesions mostly affected oligodendrocytes and myelin sheats, as in other dicarboxylic acidurias, suggesting that the pathophysiology of this model of leukodystrophy may involve irreversible pumping of a dicarboxylate in oligodendrocytes. Neurobehavioral testing indicated that the mice mostly suffered from a deficit in learning capacity. In conclusion, the findings support the concept that L-2-hydroxyglutaric aciduria is a disorder of metabolite repair. The accumulation of L-2-hydroxyglutarate exerts toxic effects through various means including enzyme inhibition and glial cell swelling.

Neuroprotective roles of pituitary adenylate cyclase-activating polypeptide in neurodegenerative diseases

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic bioactive peptide that was first isolated from an ovine hypothalamus in 1989. PACAP belongs to the secretin/glucagon/vasoactive intestinal polypeptide (VIP) superfamily. PACAP is widely distributed in the central and peripheral nervous systems and acts as a neurotransmitter, neuromodulator, and neurotrophic factor via three major receptors (PAC1, VPAC1, and VPAC2). Recent studies have shown a neuroprotective role of PACAP using in vitro and in vivo models. In this review, we briefly summarize the current findings on the neurotrophic and neuroprotective effects of PACAP in different brain injury models, such as cerebral ischemia, Parkinson’s disease (PD), and Alzheimer’s disease (AD). This review will provide information for the future development of therapeutic strategies in treatment of these neurodegenerative diseases. [BMB Reports 2014; 47(7): 369-375]

The cyclic AMP effects and neuroprotective activities of PACAP and VIP in cultured astrocytes and neurons exposed to oxygen-glucose deprivation

BACKGROUND

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are endogenous peptides, widely expressed in the central and peripheral nervous system. The adenylyl cyclase (AC)/cyclic AMP (cAMP) is their main intracellular signal transduction pathway. Numerous data suggest that PACAP and VIP have considerable neuroprotective potential, indicating the possibility for their use as new therapeutic strategies in stroke treatment. The aim of this study was to evaluate the effect of oxygen-glucose deprivation (OGD) - an established in vitro model for ischemic cell stress - on PACAP and VIP-evoked receptor-mediated cAMP generation in glial and neuronal cells, and to determine whether PACAP and VIP have neuroprotective activity under these conditions.

METHODS

The formation of [(3)H]cAMP by PACAP, VIP and forskolin (a direct activator of AC) was measured in [(3)H]adenine prelabeled primary rat glial and neuronal cells under normoxia and OGD conditions. The effects of PACAP and VIP on cell viability were measured using the MTT conversion method, and were compared to tacrolimus (FK506), a well known neuroprotective agent.

RESULTS

The OGD model inhibited the PACAP and VIP-induced cAMP formation in rat astrocytes and neurons. Incubation of neuronal cells with PACAP prevented OGD-induced cell death, more efficiently than VIP and FK506.

CONCLUSION

The obtained results showed that hypoxia/ischemia may trigger down-regulation of the brain AC-coupled PACAP/VIP receptors, with a consequent decrease of PACAP- and/or VIP-ergic-dependent cAMP-driven signaling. Moreover, our findings indicate that PACAP and VIP can prevent the deleterious effect of OGD on rat neuronal cells.

PACAP27 prevents Parkinson-like neuronal loss and motor deficits but not microglia activation induced by prostaglandin J2

Neuroinflammation is a major risk factor in Parkinson's disease (PD). Alternative approaches are needed to treat inflammation, as anti-inflammatory drugs such as NSAIDs that inhibit cyclooxygenase-2 (COX-2) can produce devastating side effects, including heart attack and stroke. New therapeutic strategies that target factors downstream of COX-2, such as prostaglandin J2 (PGJ2), hold tremendous promise because they will not alter the homeostatic balance offered by COX-2 derived prostanoids. In the current studies, we report that repeated microinfusion of PGJ2 into the substantia nigra of non-transgenic mice, induces three stages of pathology that mimic the slow-onset cellular and behavioral pathology of PD: mild (one injection) when only motor deficits are detectable, intermediate (two injections) when neuronal and motor deficits as well as microglia activation are detectable, and severe (four injections) when dopaminergic neuronal loss is massive accompanied by microglia activation and motor deficits. Microglia activation was evaluated in vivo by positron emission tomography (PET) with [(11)C](R)PK11195 to provide a regional estimation of brain inflammation. PACAP27 reduced dopaminergic neuronal loss and motor deficits induced by PGJ2, without preventing microglia activation. The latter could be problematic in that persistent microglia activation can exert long-term deleterious effects on neurons and behavior. In conclusion, this PGJ2-induced mouse model that mimics in part chronic inflammation, exhibits slow-onset PD-like pathology and is optimal for testing diagnostic tools such as PET, as well as therapies designed to target the integrated signaling across neurons and microglia, to fully benefit patients with PD.

Pituitary adenylate cyclase activating polypeptide modulates catecholamine storage and exocytosis in PC12 cells

A number of efforts have been made to understand how pituitary adenylate cyclase activating polypeptide (PACAP) functions as a neurotrophic and neuroprotective factor in Parkinson's disease (PD). Recently its effects on neurotransmission and underlying mechanisms have generated interest. In the present study, we investigate the effects of PACAP on catecholamine storage and secretion in PC12 cells with amperometry and transmission electron microscopy (TEM). PACAP increases quantal release induced by high K+ without significantly regulating the frequency of vesicle fusion events. TEM data indicate that the increased volume of the vesicle is mainly the result of enlargement of the fluidic space around the dense core. Moreover, the number of docked vesicles isn't modulated by PACAP. When cells are acutely treated with L-DOPA, the vesicular volume and quantal release both increase dramatically. It is likely that the characteristics of amperometric spikes from L-DOPA treated cells are associated with increased volume of individual vesicles rather than a direct effect on the mechanics of exocytosis. Treatment with PACAP versus L-DOPA results in different profiles of the dynamics of exocytosis. Release via the fusion pore prior to full exocytosis was observed with the same frequency following treatment with PACAP and L-DOPA. However, release events have a shorter duration and higher average current after PACAP treatment compared to L-DOPA. Furthermore, PACAP reduced the proportion of spikes having rapid decay time and shortened the decay time of both fast and slow spikes. In contrast, the distributions of the amperometric spike decay for both fast and slow spikes were shifted to longer time following L-DOPA treatment. Compared to L-DOPA, PACAP may produce multiple favorable effects on dopaminergic neurons, including protecting dopaminergic neurons against neurodegeneration and potentially regulating dopamine storage and release, making it a promising therapeutic agent for the treatment of PD.

Cognitive dysfunction and depression in Parkinson's disease: what can be learned from rodent models?

Parkinson's disease (PD) has for decades been considered a pure motor disorder and its cardinal motor symptoms have been attributed to the loss of dopaminergic (DAergic) neurons in the substantia nigra pars compacta and to nigral Lewy body pathology. However, there has more recently been a shift in the conceptualization of the disease, and its pathological features have now been recognized as involving several other areas of the brain and indeed even outside the central nervous system. There are a corresponding variety of intrinsic non-motor symptoms such as autonomic dysfunction, cognitive impairment, sleep disturbances and neuropsychiatric problems, which cannot be explained exclusively by nigral pathology. In this review, we will focus on cognitive impairment and affective symptoms in PD, and we will consider whether, and how, these deficits can best be modelled in rodent models of the disorder. As only a few of the non-motor symptoms respond to standard DA replacement therapies, the quest for a broader therapeutic approach remains a major research effort, and success in this area in particular will be strongly dependent on appropriate rodent models. In addition, better understanding of the different models, as well as the advantages and disadvantages of the available behavioural tasks, will result in better tools for evaluating new treatment strategies for PD patients suffering from these neuropsychological symptoms.

Closing the gap between clinic and cage: sensori-motor and cognitive behavioural testing regimens in neurotoxin-induced animal models of Parkinson's disease

Animal models that make use of chemical toxins to adversely affect the nigrostriatal dopaminergic pathway of rodents and primates have contributed significantly towards the development of symptomatic therapies for Parkinson's disease (PD) patients. Although their use in developing neuro-therapeutic and -regenerative compounds remains to be ascertained, toxin-based mammalian and a range of non-mammalian models of PD are important tools in the identification and validation of candidate biomarkers for earlier diagnosis, as well as in the development of novel treatments that are currently working their way into the clinic. Toxin models of PD have and continue to be important models to use for understanding the consequences of nigrostriatal dopamine cell loss. Functional assessment of these models is also a critical component for eventual translational success. Sensitive behavioural testing regimens for assessing the extent of dysfunction exhibited in the toxin models, the degree of protection or improvement afforded by potential treatment modalities, and the correlation of these findings with what is observed clinically in PD patients, ultimately determines whether a potential treatment moves to clinical trials. Here, we review existing published work that describes the use of such behavioural outcome measures associated with toxin models of parkinsonism. In particular, we focus on tests assessing sensorimotor and cognitive function, both of which are significantly and progressively impaired in PD.

Cognitive deficits in animal models of basal ganglia disorders

The two most common neurological disorders of the basal ganglia are Parkinson's disease (PD) and Huntington's disease (HD). The most overt symptoms of these diseases are motoric, reflecting the loss of the striatal medium spiny neurons in HD and ascending substantia nigra dopaminergic cells in PD. However, both disease processes induce insidious psychiatric and cognitive syndromes that can manifest well in advance of the onset of motor deficits. These early deficits provide an opportunity for prophylactic therapeutic intervention in order to retard disease progression from the earliest possible point. In order to exploit this opportunity, animal models of HD and PD are being probed for the specific cognitive deficits represented in the disease states. At the neuronal level, these deficits are typically, but not exclusively, mediated by disruption of parallel corticostriatal loops that integrate motor information with sensory and higher order, "executive" cognitive functions. Dysfunction in these systems can be probed with sensitive behavioural tests that selectively probe these cognitive functions in mouse models with focal lesions of striatal or cortical regions, or of specific neurotransmitter systems. Typically these tests were designed and validated in rats. With the advent of genetically modified mouse models of disease, validated tests provide an opportunity to screen mouse models of disease for early onset cognitive deficits. This review seeks to draw together the literature on cognitive deficits in HD and PD, to determine the extent to which these deficits are represented in the current animal models of disease, and to evaluate the viability of selecting cognitive deficits as potential therapeutic targets. This article is part of a Special Issue entitled 'Animal Models'.

Impairment of the septal cholinergic neurons in MPTP-treated A30P α-synuclein mice

Dementia in Parkinson's disease (PDD) and dementia with Lewy bodies (DLB) are characterized by loss of acetylcholine (ACh) from cortical areas. Clinical studies report positive effects of acetylcholine esterase (AChE) inhibitors in PDD and dementia with Lewy bodies. We here report that the number of neurons expressing a cholinergic marker in the medial septum-diagonal band of Broca complex decreases in A30P α-synuclein-expressing mice during aging, paralleled by a lower AChE fiber density in the dentate gyrus and in the hippocampal CA1 field. After inducing dopamine depletion by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP), no acute but a delayed loss of cholinergic neurons and AChE-positive fibers was observed, which was attenuated by L-3,4-dihydroxyphenylalanine (DOPA) treatment. Expression of nerve growth factor (NGF) and tyrosine receptor kinase A (TrkA) genes was upregulated in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride-treated wild type mice, but not in A30P α-synuclein expressing animals. In contrast, upregulation of sortilin and p75(NTR) genes was found in the A30P α-synuclein-expressing mice. These results suggest that dopamine deficiency may contribute to the impairment of the septohippocampal system in patients with PDD and that L-3,4-dihydroxyphenylalanine may not only result in symptomatic treatment of the akinetic-rigid syndrome but may also alleviate the degeneration of basal forebrain cholinergic system and the cognitive decline.