Polyamines in the basal ganglia of human brain. Influence of aging and degenerative movement disorders

Spermidine as an epigenetic regulator of autophagy in neurodegenerative disorders

Autophagy is an abnormal protein degradation and recycling process that is impaired in various neurological diseases like Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease. Spermidine is a natural polyamine found in various plant- and meat-based diets that can induce autophagy, and is decreased in various neurodegenerative diseases. It acts on epigenetic enzymes like E1A-binding protein p300, HAT enzymes like Iki3p and Sas3p, and α-tubulin acetyltransferase 1 that modulate autophagy. Histone modifications like acetylation, phosphorylation, and methylation could influence autophagy. Autophagy is epigenetically regulated in various neurodegenerative disorders with many epigenetic enzymes and miRNAs. Polyamine regulation plays an essential role in the disease pathogenesis of AD and PD. Therefore, in this review, we discuss various enzymes and miRNAs involved in the epigenetic regulation of autophagy in neurodegenerative disorders and the role of spermidine as an autophagy enhancer. The alterations in spermidine-mediated regulation of Beclin-1, LC3-II, and p62 genes in AD and other PD-associated enzymes could impact the process of autophagy in these neurodegenerative diseases. With the ever-growing data and such promising effects of spermidine in autophagy, we feel it could be a promising target in this area and worth further detailed studies.

The microbiota-gut-brain axis in Huntington's disease: pathogenic mechanisms and therapeutic targets

Huntington's disease (HD) is a currently incurable neurogenerative disorder and is typically characterized by progressive movement disorder (including chorea), cognitive deficits (culminating in dementia), psychiatric abnormalities (the most common of which is depression), and peripheral symptoms (including gastrointestinal dysfunction). There are currently no approved disease-modifying therapies available for HD, with death usually occurring approximately 10-25 years after onset, but some therapies hold promising potential. HD subjects are often burdened by chronic diarrhea, constipation, esophageal and gastric inflammation, and a susceptibility to diabetes. Our understanding of the microbiota-gut-brain axis in HD is in its infancy and growing evidence from preclinical and clinical studies suggests a role of gut microbial population imbalance (gut dysbiosis) in HD pathophysiology. The gut and the brain can communicate through the enteric nervous system, immune system, vagus nerve, and microbiota-derived-metabolites including short-chain fatty acids, bile acids, and branched-chain amino acids. This review summarizes supporting evidence demonstrating the alterations in bacterial and fungal composition that may be associated with HD. We focus on mechanisms through which gut dysbiosis may compromise brain and gut health, thus triggering neuroinflammatory responses, and further highlight outcomes of attempts to modulate the gut microbiota as promising therapeutic strategies for HD. Ultimately, we discuss the dearth of data and the need for more longitudinal and translational studies in this nascent field. We suggest future directions to improve our understanding of the association between gut microbes and the pathogenesis of HD, and other 'brain and body disorders'.

Anti-inflammatory effect of pepper extract with high polyamine levels; inhibition of ERK/MAPK pathway in mice

Polyamines have been reported to have cell proliferative and anti-inflammatory effects on normal metabolism in the body. This study aimed to investigate polyamine content of AIG01 pepper and the anti-inflammatory effect of AIG01 pepper extract (PAE) in mice. Polyamine content was analyzed by HPLC after acid hydrolysis of peppers with different acidic solvents. AIG01 pepper has the highest total polyamine content at about 1.5 mg/g. In LPS-stimulated RAW264.7, PAE inhibits nitric oxide production in a concentration-dependent manner and decreased the levels of pro-inflammatory cytokines. PAE has been shown to inhibit phosphorylation of MAPK/ERK. In TPA-stimulated Balb/C, PAE treatment showed tissue-level reductions in pro-inflammatory cytokines, reductions in ear thickness, and inhibition of neutrophil invasion. The polyamine content, polyamine extraction efficiency and anti-inflammatory effect of AIG01 obtained in this study suggest that it is useful as a raw material for the treatment of inflammatory diseases.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01333-x.

ATP13A2 (PARK9) and basal ganglia function

ATP13A2 is a lysosomal protein involved in polyamine transport with loss of function mutations associated with multiple neurodegenerative conditions. These include early onset Parkinson's disease, Kufor-Rakeb Syndrome, neuronal ceroid lipofuscinosis, hereditary spastic paraplegia, and amyotrophic lateral sclerosis. While ATP13A2 mutations may result in clinical heterogeneity, the basal ganglia appear to be impacted in the majority of cases. The basal ganglia is particularly vulnerable to environmental exposures such as heavy metals, pesticides, and industrial agents which are also established risk factors for many neurodegenerative conditions. Not surprisingly then, impaired function of ATP13A2 has been linked to heavy metal toxicity including manganese, iron, and zinc. This review discusses the role of ATP13A2 in basal ganglia function and dysfunction, potential common pathological mechanisms in ATP13A2-related disorders, and how gene x environment interactions may contribute to basal ganglia dysfunction.

Targeted metabolomic analysis in Parkinson's disease brain frontal cortex and putamen with relation to cognitive impairment

We performed liquid chromatography tandem mass spectrometry analysis with the targeted metabolomic kit Biocrates MxP Quant 500, in human brain cortex (Brodmann area 9) and putamen, to reveal metabolic changes characteristic of Parkinson's disease (PD) and PD-related cognitive decline. This case-control study involved 101 subjects (33 PD without dementia, 32 PD with dementia (cortex only), 36 controls). We found changes associated with PD, cognitive status, levodopa levels, and disease progression. The affected pathways include neurotransmitters, bile acids, homocysteine metabolism, amino acids, TCA cycle, polyamines, β-alanine metabolism, fatty acids, acylcarnitines, ceramides, phosphatidylcholines, and several microbiome-derived metabolites. Previously reported levodopa-related homocysteine accumulation in cortex still best explains the dementia status in PD, which can be modified by dietary supplementation. Further investigation is needed to reveal the exact mechanisms behind this pathological change.

The Effects of 5-Fluorouracil/Leucovorin Chemotherapy on Cognitive Function in Male Mice

5-Fluorouracil (5-Fu) and leucovorin (LV) are often given in combination to treat colorectal cancer. 5-Fu/LV prevents cell proliferation by inhibiting thymidylate synthase, which catalyzes the conversion of deoxyuridine monophosphate to deoxythymidine monophosphate. While 5-Fu has been shown to cause cognitive impairment, the synergistic effect of 5-Fu with LV has not been fully explored. The present investigation was designed to assess how the combination of 5-Fu and LV affect cognition in a murine model. Six-month-old male mice were used in this study; 15 mice received saline injections and 15 mice received 5-Fu/LV injections. One month after treatment, the elevated plus maze, Y-maze, and Morris water maze behavioral tasks were performed. Brains were then extracted, cryosectioned, and stained for CD68 to assay microglial activation and with tomato lectin to assay the vasculature. All animals were able to locate the visible and hidden platform locations in the water maze. However, a significant impairment in spatial memory retention was observed in the probe trial after the first day of hidden-platform training (first probe trial) in animals that received 5-Fu/LV, but these animals showed spatial memory retention by day 5. There were no significant increases in inflammation as measured by CD68, but 5-Fu/LV treatment did modulate blood vessel morphology. Tandem mass tag proteomics analysis identified 6,049 proteins, 7 of which were differentially expressed with a p-value of <0.05 and a fold change of >1.5. The present data demonstrate that 5-Fu/LV increases anxiety and significantly impairs spatial memory retention.

A Systematic Review of Transcriptional Dysregulation in Huntington's Disease Studied by RNA Sequencing

Huntington's disease (HD) is a chronic neurodegenerative disorder caused by an expansion of polyglutamine repeats in exon 1 of the Huntingtin gene. Transcriptional dysregulation accompanied by epigenetic alterations is an early and central disease mechanism in HD yet, the exact mechanisms and regulators, and their associated gene expression programs remain incompletely understood. This systematic review investigates genome-wide transcriptional studies that were conducted using RNA sequencing (RNA-seq) technology in HD patients and models. The review protocol was registered at the Open Science Framework (OSF). The biomedical literature and gene expression databases, PubMed and NCBI BioProject, Array Express, European Nucleotide Archive (ENA), European Genome-Phenome Archive (EGA), respectively, were searched using the defined terms specified in the protocol following the PRISMA guidelines. We conducted a complete literature and database search to retrieve all RNA-seq-based gene expression studies in HD published until August 2020, retrieving 288 articles and 237 datasets from PubMed and the databases, respectively. A total of 27 studies meeting the eligibility criteria were included in this review. Collectively, comparative analysis of the datasets revealed frequent genes that are consistently dysregulated in HD. In postmortem brains from HD patients, DNAJB1, HSPA1B and HSPB1 genes were commonly upregulated across all brain regions and cell types except for medium spiny neurons (MSNs) at symptomatic disease stage, and HSPH1 and SAT1 genes were altered in expression in all symptomatic brain datasets, indicating early and sustained changes in the expression of genes related to heat shock response as well as response to misfolded proteins. Specifically in indirect pathway medium spiny neurons (iMSNs), mitochondria related genes were among the top uniquely dysregulated genes. Interestingly, blood from HD patients showed commonly differentially expressed genes with a number of brain regions and cells, with the highest number of overlapping genes with MSNs and BA9 region at symptomatic stage. We also found the differential expression and predicted altered activity of a set of transcription factors and epigenetic regulators, including BCL6, EGR1, FOSL2 and CREBBP, HDAC1, KDM4C, respectively, which may underlie the observed transcriptional changes in HD. Altogether, our work provides a complete overview of the transcriptional studies in HD, and by data synthesis, reveals a number of common and unique gene expression and regulatory changes across different cell and tissue types in HD. These changes could elucidate new insights into molecular mechanisms of differential vulnerability in HD. Systematic Review Registration: https://osf.io/pm3wq.

A six-metabolite panel as potential blood-based biomarkers for Parkinson's disease

Characterisation and diagnosis of idiopathic Parkinson's disease (iPD) is a current challenge that hampers both clinical assessment and clinical trial development with the potential inclusion of non-PD cases. Here, we used a targeted mass spectrometry approach to quantify 38 metabolites extracted from the serum of 231 individuals. This cohort is currently one of the largest metabolomic studies including iPD patients, drug-naïve iPD, healthy controls and patients with Alzheimer's disease as a disease-specific control group. We identified six metabolites (3-hydroxykynurenine, aspartate, beta-alanine, homoserine, ornithine (Orn) and tyrosine) that are significantly altered between iPD patients and control participants. A multivariate model to predict iPD from controls had an area under the curve (AUC) of 0.905, with an accuracy of 86.2%. This panel of metabolites may serve as a potential prognostic or diagnostic assay for clinical trial prescreening, or for aiding in diagnosing pathological disease in the clinic.

Flaxseed Increases Animal Lifespan and Reduces Ovarian Cancer Severity by Toxically Augmenting One-Carbon Metabolism

We used an LC-MS/MS metabolomics approach to investigate one-carbon metabolism in the plasma of flaxseed-fed White Leghorn laying hens (aged 3.5 years). In our study, dietary flaxseed (via the activity of a vitamin B6 antagonist known as "1-amino d-proline") induced at least 15-fold elevated plasma cystathionine. Surprisingly, plasma homocysteine (Hcy) was stable in flaxseed-fed hens despite such highly elevated cystathionine. To explain stable Hcy, our data suggest accelerated Hcy remethylation via BHMT and MS-B12. Also supporting accelerated Hcy remethylation, we observed elevated S-adenosylmethionine (SAM), an elevated SAM:SAH ratio, and elevated methylthioadenosine (MTA), in flaxseed-fed hens. These results suggest that flaxseed increases SAM biosynthesis and possibly increases polyamine biosynthesis. The following endpoint phenotypes were observed in hens consuming flaxseed: decreased physiological aging, increased empirical lifespan, 9-14% reduced body mass, and improved liver function. Overall, we suggest that flaxseed can protect women from ovarian tumor metastasis by decreasing omental adiposity. We also propose that flaxseed protects cancer patients from cancer-associated cachexia by enhancing liver function.

The Convergence of Alpha-Synuclein, Mitochondrial, and Lysosomal Pathways in Vulnerability of Midbrain Dopaminergic Neurons in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease, characterized by progressive bradykinesia, rigidity, resting tremor, and gait impairment, as well as a spectrum of non-motor symptoms including autonomic and cognitive dysfunction. The cardinal motor symptoms of PD stem from the loss of substantia nigra (SN) dopaminergic (DAergic) neurons, and it remains unclear why SN DAergic neurons are preferentially lost in PD. However, recent identification of several genetic PD forms suggests that mitochondrial and lysosomal dysfunctions play important roles in the degeneration of midbrain dopamine (DA) neurons. In this review, we discuss the interplay of cell-autonomous mechanisms linked to DAergic neuron vulnerability and alpha-synuclein homeostasis. Emerging studies highlight a deleterious feedback cycle, with oxidative stress, altered DA metabolism, dysfunctional lysosomes, and pathological alpha-synuclein species representing key events in the pathogenesis of PD. We also discuss the interactions of alpha-synuclein with toxic DA metabolites, as well as the biochemical links between intracellular iron, calcium, and alpha-synuclein accumulation. We suggest that targeting multiple pathways, rather than individual processes, will be important for developing disease-modifying therapies. In this context, we focus on current translational efforts specifically targeting lysosomal function, as well as oxidative stress via calcium and iron modulation. These efforts could have therapeutic benefits for the broader population of sporadic PD and related synucleinopathies.

Spermidine, an autophagy inducer, as a therapeutic strategy in neurological disorders

Spermidine is a naturally occurring endogenous polyamine synthesized from diamine putrescine. It is a well-known autophagy inducer that maintains cellular and neuronal homeostasis. Healthy brain development and function are dependent on brain polyamine concentration. Polyamines interact with the opioid system, glutamatergic signaling and neuroinflammation in the neuronal and glial compartments. Among the polyamines, spermidine is found highest in the human brain. Age-linked fluctuations in the spermidine levels may possibly contribute to the impairments in neural network and neurogenesis. Exogenously administered spermidine helps in the treatment of brain diseases. Further, current studies highlight the ability of spermidine to promote longevity by inducing autophagy. Still, the causal neuroprotective mechanism of spermidine in neuronal dysfunction remains unidentified. This review aims to summarize various neuroprotective effects of spermidine related to anti-aging/ anti-inflammatory properties and the prevention of neurotoxicity that helps in achieving beneficial effects in age-related neurological disorder. We also expose the signaling cascades modulated by spermidine which might result in therapeutic action. The present review highlights clinical studies along with in-vivo and in-vitro preclinical studies to provide a new dimension for the therapeutic potential of spermidine in neurological disorders.

Nutritional Aspects of Spermidine

Natural polyamines (spermidine and spermine) are small, positively charged molecules that are ubiquitously found within organisms and cells. They exert numerous (intra)cellular functions and have been implicated to protect against several age-related diseases. Although polyamine levels decline in a complex age-dependent, tissue-, and cell type–specific manner, they are maintained in healthy nonagenarians and centenarians. Increased polyamine levels, including through enhanced dietary intake, have been consistently linked to improved health and reduced overall mortality. In preclinical models, dietary supplementation with spermidine prolongs life span and health span. In this review, we highlight salient aspects of nutritional polyamine intake and summarize the current knowledge of organismal and cellular uptake and distribution of dietary (and gastrointestinal) polyamines and their impact on human health. We further summarize clinical and epidemiological studies of dietary polyamines.

Spermidine intake is associated with cortical thickness and hippocampal volume in older adults

BACKGROUND

The natural polyamine spermidine, known to be important for cellular function, decreases during aging. Previous research has demonstrated beneficial impact of spermidine intake on memory functions in both animal models and humans, suggesting that spermidine may be a preventive approach to delay age-related cognitive decline and possibly even Alzheimer's disease (AD). However, the association of spermidine intake with brain health in humans is still unknown. In this study, we aimed to determine the association between dietary spermidine intake and structural brain measures in older individuals with subjective cognitive decline (SCD) and healthy controls (HC).

METHODS

Dietary spermidine intake and adherence to Mediterranean Diet (MeDi) were assessed by a self-reported food frequency questionnaire in 90 older adults with SCD and 47 HC. Processing of structural MRI data yielded global brain volumes, hippocampal volume, mean and regional cortical thickness, and cortical thickness in a template encompassing AD-vulnerable regions. In exploratory analyses, the association between spermidine intake and structural brain measures was assessed using adjusted and unadjusted linear regression models. Additionally, we tested for differential associations as a function of group. Mediation analyses were performed to examine whether dietary spermidine intake mediates the associations between adherence to MeDi and structural brain measures.

RESULTS

Higher spermidine intake was associated with larger hippocampal volume (standardized β ​= ​0.262, p ​= ​0.002), greater mean cortical thickness (standardized β ​= ​0.187, p ​= ​0.031), and greater cortical thickness in AD-vulnerable brain regions (standardized β ​= ​0.176, p ​= ​0.042), the parietal (standardized β ​= ​0.202, p ​= ​0.020), and temporal lobes (standardized β ​= ​0.217, p ​= ​0.012). No significant differential effect emerged between older adults with SCD and HC. Moreover, a substantial mediating effect of dietary spermidine intake on the associations between adherence to MeDi and structural brain measures was observed.

CONCLUSION

Higher dietary spermidine intake was positively associated with several structural brain measures, irrespective of the presence of SCD, and substantially mediated the relationship of adherence to MeDi and structural brain measures. Our data suggest that higher spermidine intake might be a promising dietary approach to preserve brain health in older adults, a hypothesis currently tested in an interventional trial.

Spermidine and spermine delay brain aging by inducing autophagy in SAMP8 mice

The natural polyamine spermidine and spermine have been reported to ameliorate aging and aging-induced dementia. However, the mechanism is still confused. An aging model, the senescence accelerated mouse-8 (SAMP8), was used in this study. Novel object recognition and the open field test results showed that oral administration of spermidine, spermine and rapamycin increased discrimination index, modified number, inner squares distance and times. Spermidine and spermine increased the activity of SOD, and decreased the level of MDA in the aging brain. Spermidine and spermine phosphorylate AMPK and regulate autophagy proteins (LC3, Beclin 1 and p62). Spermidine and spermine balanced mitochondrial and maintain energy for neuron, with the regulation of MFN1, MFN2, DRP1, COX IV and ATP. In addition, western blot results (Bcl-2, Bax and Caspase-3, NLRP3, IL-18, IL-1β) showed that spermidine and spermine prevented apoptosis and inflammation, and elevate the expression of neurotrophic factors, including NGF, PSD95and PSD93 and BDNF in neurons of SAMP8 mice. These results indicated that the effect of spermidine and spermine on anti-aging is related with improving autophagy and mitochondrial function.

Polyamines and its analogue modulates amyloid fibrillation in lysozyme: A comparative investigation

BACKGROUND

Polyamines can induce protein aggregation that can be related to the physiology of the cellular function. Polyamines have been implicated in protein aggregation which may lead to neuropathic and non neuropathic amyloidosis.

SCOPE OF REVIEW

Change in the level of polyamine concentration has been associated with ageing and neurodegeneration such as Parkinson's disease, Alzheimer's disease. Lysozyme aggregation in the presence of polyamines leads to non neuropathic amyloidosis. Polyamine analogues can suppress or inhibit protein aggregation suggesting their efficacy against amyloidogenic protein aggregates.

MAJOR CONCLUSIONS

In this study we report the comparative interactions of lysozyme with the polyamine analogue, 1-naphthyl acetyl spermine in comparison with the biogenic polyamines through spectroscopy, calorimetry, imaging and docking techniques. The findings revealed that the affinity of binding varied as spermidine > 1-naphthyl acetyl spermine > spermine. The biogenic polyamines accelerated the rate of fibrillation significantly, whereas the analogue inhibited the rate of fibrillation to a considerable extent. The polyamines bind near the catalytic diad residues viz. Glu35 and Asp52, and in close proximity of Trp62 residue. However, the analogue showed dual nature of interaction where its alkyl amine region bind in same way as the biogenic polyamines bind to the catalytic site, while the naphthyl group makes hydrophobic contacts with Trp62 and Trp63, thereby suggesting its direct influence on fibrillation.

GENERAL SIGNIFICANCE

This study, thus, potentiates, the development of a polyamine analogue that can perform as an effective inhibitor targeted towards aggregation of amyloidogenic proteins.

Longevity in response to lowered insulin signaling requires glycine N-methyltransferase-dependent spermidine production

Reduced insulin/IGF signaling (IIS) extends lifespan in multiple organisms. Different processes in different tissues mediate this lifespan extension, with a set of interplays that remain unclear. We here show that, in Drosophila, reduced IIS activity modulates methionine metabolism, through tissue-specific regulation of glycine N-methyltransferase (Gnmt), and that this regulation is required for full IIS-mediated longevity. Furthermore, fat body-specific expression of Gnmt was sufficient to extend lifespan. Targeted metabolomics showed that reducing IIS activity led to a Gnmt-dependent increase in spermidine levels. We also show that both spermidine treatment and reduced IIS activity are sufficient to extend the lifespan of Drosophila, but only in the presence of Gnmt. This extension of lifespan was associated with increased levels of autophagy. Finally, we found that increased expression of Gnmt occurs in the liver of liver-specific IRS1 KO mice and is thus an evolutionarily conserved response to reduced IIS. The discovery of Gnmt and spermidine as tissue-specific modulators of IIS-mediated longevity may aid in developing future therapeutic treatments to ameliorate aging and prevent disease.

Spermidine protects from age-related synaptic alterations at hippocampal mossy fiber-CA3 synapses

Aging is associated with functional alterations of synapses thought to contribute to age-dependent memory impairment (AMI). While therapeutic avenues to protect from AMI are largely elusive, supplementation of spermidine, a polyamine normally declining with age, has been shown to restore defective proteostasis and to protect from AMI in Drosophila. Here we demonstrate that dietary spermidine protects from age-related synaptic alterations at hippocampal mossy fiber (MF)-CA3 synapses and prevents the aging-induced loss of neuronal mitochondria. Dietary spermidine rescued age-dependent decreases in synaptic vesicle density and largely restored defective presynaptic MF-CA3 long-term potentiation (LTP) at MF-CA3 synapses (MF-CA3) in aged animals. In contrast, spermidine failed to protect CA3-CA1 hippocampal synapses characterized by postsynaptic LTP from age-related changes in function and morphology. Our data demonstrate that dietary spermidine attenuates age-associated deterioration of MF-CA3 synaptic transmission and plasticity. These findings provide a physiological and molecular basis for the future therapeutic usage of spermidine.

Electrophysiological evaluation of extracellular spermine and alkaline pH on synaptic human GABAA receptors

Polyamines have fundamental roles in brain homeostasis as key modulators of cellular excitability. Several studies have suggested alterations in polyamine metabolism in stress related disorders, suicide, depression, and neurodegeneration, making the pharmacological modulation of polyamines a highly appealing therapeutic strategy. Polyamines are small aliphatic molecules that can modulate cationic channels involved in neuronal excitability. Previous indirect evidence has suggested that polyamines can modulate anionic GABA_A receptors (GABA_ARs), which mediate inhibitory signaling and provide a direct route to reduce hyperexcitability. Here, we attempted to characterize the effect that spermine, the polyamine with the strongest reported effect on GABA_ARs, has on human postmortem native GABA_ARs. We microtransplanted human synaptic membranes from the dorsolateral prefrontal cortex of four cases with no history of mental or neurological disorders, and directly recorded spermine effects on ionic GABA_ARs responses on microtransplanted oocytes. We show that in human synapses, inhibition of GABA_ARs by spermine was better explained by alkalization of the extracellular solution. Additionally, spermine had no effect on the potentiation of GABA-currents by diazepam, indicating that even if diazepam binding is enhanced by spermine, it does not translate to changes in functional activity. Our results clearly demonstrate that while extracellular spermine does not have direct effects on human native synaptic GABA_ARs, spermine-mediated shifts of pH inhibit GABA_ARs. Potential spermine-mediated increase of pH in synapses in vivo may therefore participate in increased neuronal activity observed during physiological and pathological states, and during metabolic alterations that increase the release of spermine to the extracellular milieu.

A metabolic profile of polyamines in parkinson disease: A promising biomarker

Objective

Aging is the highest risk factor for Parkinson disease (PD). Under physiological conditions, spermidine and spermine experimentally enhance longevity via autophagy induction. Accordingly, we evaluated the ability of each polyamine metabolite to act as an age‐related, diagnostic, and severity‐associated PD biomarker.

Methods

Comprehensive metabolome analysis of plasma was performed in Cohort A (controls, n = 45; PD, n = 145), followed by analysis of 7 polyamine metabolites in Cohort B (controls, n = 49; PD, n = 186; progressive supranuclear palsy, n = 19; Alzheimer disease, n = 23). Furthermore, 20 patients with PD who were successively examined within Cohort B were studied using diffusion tensor imaging (DTI). Association of each polyamine metabolite with disease severity was assessed according to Hoehn and Yahr stage (H&Y) and Unified Parkinson's Disease Rating Scale motor section (UPDRS‐III). Additionally, the autophagy induction ability of each polyamine metabolite was examined in vitro in various cell lines.

Results

In Cohort A, N8‐acetylspermidine and N‐acetylputrescine levels were significantly and mildly elevated in PD, respectively. In Cohort B, spermine levels and spermine/spermidine ratio were significantly reduced in PD, concomitant with hyperacetylation. Furthermore, N1,N8‐diacetylspermidine levels had the highest diagnostic value, and correlated with H&Y, UPDRS‐III, and axonal degeneration quantified by DTI. The spermine/spermidine ratio in controls declined with age, but was consistently suppressed in PD. Among polyamine metabolites, spermine was the strongest autophagy inducer, especially in SH‐SY5Y cells. No significant genetic variations in 5 genes encoding enzymes associated with spermine/spermidine metabolism were detected compared with controls.

Interpretation

Spermine synthesis and N1,N8‐diacetylspermidine may respectively be useful diagnostic and severity‐associated biomarkers for PD. ANN NEUROL 2019;86:251–263

Spermine protects alpha-synuclein expressing dopaminergic neurons from manganese-induced degeneration

Manganese exposure is among the many environmental risk factors linked to the progression of neurodegenerative diseases, such as manganese-induced parkinsonism. In animal models, chronic exposure to manganese causes loss of cell viability, neurodegeneration, and functional deficits. Polyamines, such as spermine, have been shown to rescue animals from age-induced neurodegeneration in an autophagy-dependent manner; nonetheless, it is not understood whether polyamines can prevent manganese-induced toxicity. In this study, we used two model systems, the Caenorhabditis elegans UA44 strain and SK-MEL-28 cells, both expressing the protein alpha-synuclein (α-syn) to determine whether spermine could ameliorate manganese-induced toxicity. Manganese caused a substantial reduction in the viability of SK-MEL-28 cells and hastened neurodegeneration in the UA44 strain. Spermine protected both the SK-MEL-28 cells and the UA44 strain from manganese-induced toxicity. Spermine also reduced the age-associated neurodegeneration observed in the UA44 strain compared with a control strain without α-syn expression and led to improved avoidance behavior in a functional assay. Treatment with berenil, an inhibitor of polyamine catabolism, which leads to increased intracellular polyamine levels, also showed similar cellular protection against manganese toxicity. While both translation blocker cycloheximide and autophagy blocker chloroquine caused a reduction in the cytoprotective effect of spermine, transcription blocker actinomycin D had no effect. This study provides new insights on the effect of spermine in preventing manganese-induced toxicity, which is most likely via translational regulation of several candidate genes, including those of autophagy. Thus, our results indicate that polyamines positively influence neuronal health, even when exposed to high levels of manganese and α-syn, and supplementing polyamines through diet might delay the onset of diseases involving degeneration of dopaminergic neurons.

Uncovering Natural Longevity Alleles from Intercrossed Pools of Aging Fission Yeast Cells

Chronological lifespan of non-dividing yeast cells is a quantitative trait that reflects cellular aging. By monitoring allele frequencies in aging segregant pools, Ellis et al. uncover regulatory variants in the 5'-untranslated regions of two genes...

Quantitative traits often show large variation caused by multiple genetic factors . One such trait is the chronological lifespan of non-dividing yeast cells, serving as a model for cellular aging. Screens for genetic factors involved in aging typically assay mutants of protein-coding genes. To identify natural genetic variants contributing to cellular aging, we exploited two strains of the fission yeast, Schizosaccharomyces pombe, that differ in chronological lifespan. We generated segregant pools from these strains and subjected them to advanced intercrossing over multiple generations to break up linkage groups. We chronologically aged the intercrossed segregant pool, followed by genome sequencing at different times to detect genetic variants that became reproducibly enriched as a function of age. A region on Chromosome II showed strong positive selection during aging. Based on expected functions, two candidate variants from this region in the long-lived strain were most promising to be causal: small insertions and deletions in the 5′-untranslated regions of ppk31 and SPBC409.08. Ppk31 is an ortholog of Rim15, a conserved kinase controlling cell proliferation in response to nutrients, while SPBC409.08 is a predicted spermine transmembrane transporter. Both Rim15 and the spermine-precursor, spermidine, are implicated in aging as they are involved in autophagy-dependent lifespan extension. Single and double allele replacement suggests that both variants, alone or combined, have subtle effects on cellular longevity. Furthermore, deletion mutants of both ppk31 and SPBC409.08 rescued growth defects caused by spermidine. We propose that Ppk31 and SPBC409.08 may function together to modulate lifespan, thus linking Rim15/Ppk31 with spermidine metabolism.

Neuroprotective potential of spermidine against rotenone induced Parkinson's disease in rats

Parkinson's disease is a leading hypokinetic disorder characterized by selective loss of dopaminergic neurons in substantia nigra pars compacta (SNpc) region of mid-brain. Degeneration of dopaminergic neurons is considered to be due to oxidative stress, neuroinflammation, disturbed calcium homeostasis and glutamate excitotoxicity etc. Spermidine is a polyamine which counteracts age associated cell death by scavenging free radical formation, activates authophagic machinery by enhancing formation of autophagosome, and antagonizes NMDA receptor. In the current study we investigated the neuroprotective potential of spermidine against rotenone induced PD in rats. Rats were treated subcutaneously with rotenone 1.5 mg/kg daily for 28 days. Spermidine 5&10 mg/kg was administered orally 1 h prior to rotenone administration from 15 to 28. Rotenone caused significant reduction in motor functioning and elevated levels of oxidative stress markers and proinflammatory cytokines levels (IL-1β, IL6 and TNF-α). The neurochemical analysis revealed a significant decrease in serotonin, norepinephrine, dopamine and their metabolites accompanied by a significant loss of dopaminergic neurons in the SNpc following ROT injection. However, treatment with spermidine rescued DAergic neurons in SNpc and nerve terminals in the striatum following ROT insult. Spermidine treatment also attenuated oxidative stress, neuroinflammation and restored striatal neurochemistry. Results of our study suggest that spermidine has promising neuroprotective effect against degenerative changes in experimental PD, and the protective effects are mediated through its antioxidant and anti-inflammatory properties.

Safety and tolerability of spermidine supplementation in mice and older adults with subjective cognitive decline

Supplementation of spermidine, an autophagy-inducing agent, has been shown to protect against neurodegeneration and cognitive decline in aged animal models. The present translational study aimed to determine safety and tolerability of a wheat germ extract containing enhanced spermidine concentrations. In a preclinical toxicity study, supplementation of spermidine using this extract did not result in morbidities or changes in behavior in BALBc/Rj mice during the 28-days repeated-dose tolerance study. Post mortem examination of the mice organs showed no increase in tumorigenic and fibrotic events. In the human cohort (participants with subjective cognitive decline, n=30, 60 to 80 years of age), a 3-month randomized, placebo-controlled, double-blind Phase II trial was conducted with supplementation of the spermidine-rich plant extract (dosage: 1.2 mg/day). No differences were observed between spermidine and placebo-treated groups in vital signs, weight, clinical chemistry and hematological parameters of safety, as well as in self-reported health status at the end of intervention. Compliance rates above 85% indicated excellent tolerability. The data demonstrate that spermidine supplementation using a spermidine-rich plant extract is safe and well-tolerated in mice and older adults. These findings allow for longer-term intervention studies in humans to investigate the impact of spermidine treatment on cognition and brain integrity.

Better Living through Chemistry: Caloric Restriction (CR) and CR Mimetics Alter Genome Function to Promote Increased Health and Lifespan

Caloric restriction (CR), defined as decreased nutrient intake without causing malnutrition, has been documented to increase both health and lifespan across numerous organisms, including humans. Many drugs and other compounds naturally occurring in our diet (nutraceuticals) have been postulated to act as mimetics of caloric restriction, leading to a wave of research investigating the efficacy of these compounds in preventing age-related diseases and promoting healthier, longer lifespans. Although well studied at the biochemical level, there are still many unanswered questions about how CR and CR mimetics impact genome function and structure. Here we discuss how genome function and structure are influenced by CR and potential CR mimetics, including changes in gene expression profiles and epigenetic modifications and their potential to identify the genetic fountain of youth.

Spermidine protects against α-synuclein neurotoxicity

As our society ages, neurodegenerative disorders like Parkinson`s disease (PD) are increasing in pandemic proportions. While mechanistic understanding of PD is advancing, a treatment with well tolerable drugs is still elusive. Here, we show that administration of the naturally occurring polyamine spermidine, which declines continuously during aging in various species, alleviates a series of PD-related degenerative processes in the fruit fly Drosophila melanogaster and the nematode Caenorhabditis elegans, two established model systems for PD pathology. In the fruit fly, simple feeding with spermidine inhibited loss of climbing activity and early organismal death upon heterologous expression of human α-synuclein, which is thought to be the principal toxic trigger of PD. In this line, administration of spermidine rescued α-synuclein-induced loss of dopaminergic neurons, a hallmark of PD, in nematodes. Alleviation of PD-related neurodegeneration by spermidine was accompanied by induction of autophagy, suggesting that this cytoprotective process may be responsible for the beneficial effects of spermidine administration.

The Chemistry of Neurodegeneration: Kinetic Data and Their Implications

We collected experimental kinetic rate constants for chemical processes responsible for the development and progress of neurodegeneration, focused on the enzymatic and non-enzymatic degradation of amine neurotransmitters and their reactive and neurotoxic metabolites. A gross scheme of neurodegeneration on the molecular level is based on two pathways. Firstly, reactive species oxidise heavy atom ions, which enhances the interaction with alpha-synuclein, thus promoting its folding to the beta form and giving rise to insoluble amyloid plaques. The latter prevents the function of vesicular transport leading to gradual neuronal death. In the second pathway, radical species, OH(·) in particular, react with the methylene groups of the apolar part of the lipid bilayer of either the cell or mitochondrial wall, resulting in membrane leakage followed by dyshomeostasis, loss of resting potential and neuron death. Unlike all other central neural system (CNS)-relevant biogenic amines, dopamine and noradrenaline are capable of a non-enzymatic auto-oxidative reaction, which produces hydrogen peroxide. This reaction is not limited to the mitochondrial membrane where scavenging enzymes, such as catalase, are located. On the other hand, dopamine and its metabolites, such as dopamine-o-quinone, dopaminechrome, 5,6-dihydroxyindole and indo-5,6-quinone, also interact directly with alpha-synuclein and reversibly inhibit plaque formation. We consider the role of the heavy metal ions, selected scavengers and scavenging enzymes, and discuss the relevance of certain foods and food supplements, including curcumin, garlic, N-acetyl cysteine, caffeine and red wine, as well as the long-term administration of non-steroid anti-inflammatory drugs and occasional tobacco smoking, that could all act toward preventing neurodegeneration. The current analysis can be employed in developing strategies for the prevention and treatment of neurodegeneration, and, hopefully, aid in the building of an overall kinetic molecular model of neurodegeneration itself.

Transglutaminse 2 and EGGL, the protein cross-link formed by transglutaminse 2, as therapeutic targets for disabilities of old age

Aging of the extracellular matrix (ECM), the protein matrix that surrounds and penetrates the tissues and binds the body together, contributes significantly to functional aging of tissues. ECM proteins become increasingly cross-linked with age, and this cross-linking is probably important in the decline of the ECM's function. This article reviews the role of ε-(γ-glutamyl)-lysine (EGGL), a cross-link formed by transglutaminase enzymes, and particularly the widely expressed isozyme transglutaminase 2 (TG2), in the aging ECM. There is little direct data on EGGL accumulation with age, and no direct evidence of a role of EGGL in the aging of the ECM with pathology. However, several lines of circumstantial evidence suggest that EGGL accumulates with age, and its association with pathology suggests that this might reflect degradation of ECM function. TG activity increases with age in many circumstances. ECM protein turnover is such that some EGGL made by TG is likely to remain in place for years, if not decades, in healthy tissue, and both EGGL and TG levels are enhanced by age-related diseases. If further research shows EGGL does accumulate with age, removing it could be of therapeutic benefit. Also reviewed is the blockade of TG and active removal of EGGL as therapeutic strategies, with the conclusion that both have promise. EGGL removal may have benefit for acute fibrotic diseases, such as tendinopathy, and for treating generalized decline in ECM function with old age. Extracellular TG2 and EGGL are therefore therapeutic targets both for specific and more generalized diseases of aging.

Restoring polyamines protects from age-induced memory impairment in an autophagy-dependent manner

Age-dependent memory impairment is known to occur in several organisms, including Drosophila, mouse and human. However, the fundamental cellular mechanisms that underlie these impairments are still poorly understood, effectively hampering the development of pharmacological strategies to treat the condition. Polyamines are among the substances found to decrease with age in the human brain. We found that levels of polyamines (spermidine, putrescine) decreased in aging fruit flies, concomitant with declining memory abilities. Simple spermidine feeding not only restored juvenile polyamine levels, but also suppressed age-induced memory impairment. Ornithine decarboxylase-1, the rate-limiting enzyme for de novo polyamine synthesis, also protected olfactory memories in aged flies when expressed specifically in Kenyon cells, which are crucial for olfactory memory formation. Spermidine-fed flies showed enhanced autophagy (a form of cellular self-digestion), and genetic deficits in the autophagic machinery prevented spermidine-mediated rescue of memory impairments. Our findings indicate that autophagy is critical for suppression of memory impairments by spermidine and that polyamines, which are endogenously present, are candidates for pharmacological intervention.

Cellular polyamines promote amyloid-beta (Aβ) peptide fibrillation and modulate the aggregation pathways

The cellular polyamines spermine, spermidine, and their metabolic precursor putrescine, have long been associated with cell-growth, tumor-related gene regulations, and Alzheimer's disease. Here, we show by in vitro spectroscopy and AFM imaging, that these molecules promote aggregation of amyloid-beta (Aβ) peptides into fibrils and modulate the aggregation pathways. NMR measurements showed that the three polyamines share a similar binding mode to monomeric Aβ(1-40) peptide. Kinetic ThT studies showed that already very low polyamine concentrations promote amyloid formation: addition of 10 μM spermine (normal intracellular concentration is ~1 mM) significantly decreased the lag and transition times of the aggregation process. Spermidine and putrescine additions yielded similar but weaker effects. CD measurements demonstrated that the three polyamines induce different aggregation pathways, involving different forms of induced secondary structure. This is supported by AFM images showing that the three polyamines induce Aβ(1-40) aggregates with different morphologies. The results reinforce the notion that designing suitable ligands which modulate the aggregation of Aβ peptides toward minimally toxic pathways may be a possible therapeutic strategy for Alzheimer's disease.

The complex regulation of human glud1 and glud2 glutamate dehydrogenases and its implications in nerve tissue biology

Mammalian glutamate dehydrogenase (GDH) is a housekeeping mitochondrial enzyme (hGDH1 in the human) that catalyses the reversible inter-conversion of glutamate to α-ketoglutarate and ammonia, thus interconnecting amino acid and carbohydrate metabolism. It displays an energy sensing mechanism, which permits enzyme activation under low cellular energy states. As GDH is at the crossroads of important metabolic pathways, a tight control of its activity is essential. Indeed, to fulfill its role in metabolism and cellular energetics, mammalian GDH has evolved into a highly regulated enzyme subject to allosteric modulation by diverse compounds. The recent emergence (<23 million years ago) in apes and humans of a hGDH2 isoenzyme with distinct regulatory properties, as well as, the detection of gain-of-function variants in hGDH1 and hGDH2 that affect the nervous system, have introduced additional complexities. The properties of the two highly homologous human GDHs were studied using purified recombinant hGDH1 and hGDH2 obtained by expression of the corresponding cDNAs in Sf21 cells. Results showed that, in contrast to hGDH1 that maintains substantial basal activity (35-40% of its maximal capacity), hGDH2 displays low basal activity (3-8% of maximal) that is remarkably responsive to activation by rising levels of ADP and/or l-leucine. This is primarily due to the Arg443Ser evolutionary change, which also made hGDH2 markedly sensitive to estrogens and neuroleptic drugs. In contrast to hGDH1, which is subject to potent GTP inhibition, hGDH2 has dissociated its function from this energy switch, being able to metabolize glutamate even when the Krebs cycle generates GTP levels sufficient to inactivate the housekeeping hGDH1. Our data also show that spermidine, a polyamine thought to reduce oxidative stress and to prolong survival, and EGCG, a green tea polyphenol, inhibit hGDH2 at lower concentrations than hGDH1. The implications of these findings in nerve tissue biology are discussed.

Polyamines in aging and disease

Polyamines are polycations that interact with negatively charged molecules such as DNA, RNA and proteins. They play multiple roles in cell growth, survival and proliferation. Changes in polyamine levels have been associated with aging and diseases. Their levels decline continuously with age and polyamine (spermidine or high-polyamine diet) supplementation increases life span in model organisms. Polyamines have also been involved in stress resistance. On the other hand, polyamines are increased in cancer cells and are a target for potential chemotherapeutic agents. In this review, we bring together these various results and draw a picture of the state of our knowledge on the roles of polyamines in aging, stress and diseases.

Spermine binding to Parkinson's protein alpha-synuclein and its disease-related A30P and A53T mutants

Aggregation of alpha-synuclein (alpha-syn), a protein implicated in Parkinson's disease (PD), is believed to progress through formation of a partially folded intermediate. Using nanoelectrospray ionization (nano-ESI) mass spectrometry combined with ion mobility measurements we found evidence for a highly compact partially folded family of structures for alpha-syn and its disease-related A53T mutant with net charges of -6, -7, and -8. For the other early onset PD mutant, A30P, this highly compact population was only evident when the protein had a net charge of -6. When bound to spermine near physiologic pH, all three proteins underwent a charge reduction from the favored solution charge state of -10 to a net charge of -6. This charge reduction is accompanied by a dramatic size reduction of about a factor of 2 (cross section of 2600 A2 (-10 charge state) down to 1430 A2 (-6 charge state)). We conclude that spermine increases the aggregation rate of alpha-syn by inducing a collapsed conformation, which then proceeds to form aggregates.

Increased levels of gamma-glutamylamines in Huntington disease CSF

Transglutaminases (TGases) catalyze several reactions with protein substrates, including formation of gamma-glutamyl-epsilon-lysine cross-links and gamma-glutamylpolyamine residues. The resulting gamma-glutamylamines are excised intact during proteolysis. TGase activity is altered in several diseases, highlighting the importance of in situ enzymatic determinations. Previous work showed that TGase activity (as measured by an in vitro assay) and free gamma-glutamyl-epsilon-lysine levels are elevated in Huntington disease (HD) and that gamma-glutamyl-epsilon-lysine is increased in HD CSF. Although free gamma-glutamyl-epsilon-lysine was used in these studies as an index of in situ TGase activity, gamma-glutamylpolyamines may also be diagnostic. We have devised methods for the simultaneous determination of four gamma-glutamylamines in CSF: gamma-glutamyl-epsilon-lysine, gamma-glutamylspermidine, gamma-glutamylputrescine, and bis-gamma-glutamylputrescine and showed that all are present in normal human CSF at concentrations of approximately 150, 670, 40, and 240 nM, respectively. The high gamma-glutamylspermidine/gamma-glutamylputrescine and gamma-glutamylspermidine/bis-gamma-glutamylputrescine ratios presumably reflect in part the large spermidine to putrescine mole ratio in human brain. We also showed that all four gamma-glutamylamines are elevated in HD CSF. Our findings support the hypotheses that (i) gamma-glutamylpolyamines are reflective of TGase activity in human brain, (ii) polyamination is an important post-translational modification of brain proteins, and (iii) TGase-catalyzed modification of proteins is increased in HD brain.

Age-related changes in polyamines in memory-associated brain structures in rats

Polyamines putrescine, spermidine and spermine are positively charged aliphatic amines and have important roles in maintaining normal cellular function, regulating neurotransmitter receptors and modulating learning and memory. Recent evidence suggests a role of putrescine in hippocampal neurogenesis, that is significantly impaired during aging. The present study measured the polyamine levels in memory-related brain structures in 24- (aged), 12- (middle-aged) and 4- (young) month-old rats using liquid chromatography/mass spectrometry and high performance liquid chromatography. In the hippocampus, the putrescine levels were significantly decreased in the CA1 and dentate gyrus, and increased in the CA2/3 with age. Significant age-related increases in the spermidine levels were found in the CA1 and CA2/3. There was no difference between groups in spermine in any sub-regions examined. In the parahippocampal region, increased putrescine level with age was observed in the entorhinal cortex, and age did not alter the spermidine levels. The spermine level was significantly decreased in the perirhinal cortex and increased in the postrhinal cortex with age. In the prefrontal cortex, there was age-related decrease in putrescine, and the spermidine and spermine levels were significantly increased with age. This study, for the first time, demonstrates age-related region-specific changes in polyamines in memory-associated structures, suggesting that polyamine system dysfunction may potentially contribute to aged-related impairments in hippocampal neurogenesis and learning and memory.

Disrupted spermine homeostasis: a novel mechanism in polyglutamine-mediated aggregation and cell death

Our data suggest a novel mechanism whereby pathological-length polyglutamine (polyQ) proteins promote the spermine synthetic pathway, increasing polyQ-aggregation and cell death. As detected in a cell-free turbidity assay, spermine promotes aggregation of thio-polyQ62 in a dose-dependent manner. Using a stable neuronal cell line expressing pathological-length [polyQ57-yellow fluorescent protein (YFP) (Q57)] or non-pathological-length [polyQ19-YFP (Q19)] polyglutamine protein, we show that multiple steps in the production of polyamines are affected in Q57 cells, suggesting dysfunctional spermine homeostasis. As the building block for spermine synthesis, arginine transport is significantly increased in neuronal cell lines stably expressing Q57. Q57 lines displayed upregulated basal and inducible arginase I activities that were not seen in polyQ19-YFP lines. Normal induction of spermidine/spermine N-acetyltransferase in Q19 lines regulating back-conversion of spermine, thereby reducing spermine levels, however, was not observed in Q57 lines. Pharmacological activation of ornithine decarboxylase (ODC), a key enzyme of the polyamine synthetic pathway, increased cellular aggregates and increased cell death in Q57 cells not observed in Q19 cells. Inhibition of ODC by difluoromethylornithine prevented basal and induced cell death in Q57 cells, demonstrating a central role for polyamines in this process.

Maintained regulation of polyamines in spinal cord from patients with amyotrophic lateral sclerosis

Levels of the polyamines putrescine, spermidine, and spermine were investigated in postmortem spinal cord from seven patients with amyotrophic lateral sclerosis (ALS) and seven control subjects. The method consisted of precolumn derivatization of the polyamines, followed by high-performance liquid chromatography (HPLC) analysis and fluorescence detection. The stability of the polyamines was examined in rat spinal cord during the interval of 0-36 h postmortem. The levels of putrescine, spermidine, and spermine increased by 32%, 15%, and 2%, respectively. Polyamine levels did not differ significantly between the ALS group and the control group, suggesting a maintained regulation of polyamines in the end stage of the disease. However, an effect of gender on the levels of spermidine and spermine was observed. Levels of spermidine and spermine in the ventral horn region of female ALS patients were significantly higher in comparison with the same region of the male ALS group (p<0.05). The female ALS group also presented significantly higher levels of spermidine in comparison with female controls (p<0.05).

Effect of tissue transglutaminase on the solubility of proteins containing expanded polyglutamine repeats

The expansion of a polyglutamine (polyQ) domain in neuronal proteins is the molecular genetic cause of at least eight neurodegenerative diseases. Proteins with a polyQ domain that is greater than 40 Q (Q40) residues form insoluble intranuclear and cytoplasmic inclusions. Expanded polyQ proteins self-associate by non-covalent interactions and become insoluble. They can also be covalently cross-linked by tissue transglutaminase (TTG), a calcium-dependent enzyme present in cells throughout the nervous system. However, it remains unclear whether TTG cross-linking directly contributes to the insolubility of the expanded polyQ proteins. Using an in vitro solubility assay, we found TTG cross-linked Q62 monomers into high molecular weight soluble complexes in a calcium-dependent reaction. Inhibition of TTG cross-linking by primary amine substrates including putrescine and biotinylated pentylamine antagonized TTG's ability to form soluble complexes. In contrast, primary amines (histamine and lysine) that were less effective inhibitors of TTG cross-linking did not inhibit Q62 from becoming insoluble. In summary, TTG can increase the solubility of expanded polyQ proteins by catalyzing intermolecular cross-links. This demonstrates directly that TTG will reduce the ability of expanded polyQ proteins from becoming insoluble. Furthermore, the effectiveness of a primary amine substrate at inhibiting formation of insoluble inclusions may be related to their ability to inhibit intermolecular cross-linking by TTG.

Polyamines in a genetic animal model of paroxysmal dyskinesia

Previous studies suggested that glutamatergic overactivity contributes to the manifestation of dystonia in the dt(sz) mutant hamster, a model of idiopathic paroxysmal dyskinesia in which dystonic episodes occur in response to mild stress. Therefore, the role of polyamines, known as positive modulators of NMDA receptors, was examined in the present study. The levels of polyamines (putrescine, spermidine, spermine) were determined in forebrain, cerebellum and brainstem in dt(sz) hamsters at an age of most marked expression of dystonia (32 days) and in age-matched non-dystonic control hamsters. Spermine was found to be significantly increased in the forebrain (35%) of dystonic animals, while spermidine was unaltered in dystonic brains and only a moderate increase in putrescine (12%) was detected in the cerebellum of dt(sz) mutants. In view of enhanced spermine levels, the effect of the putative polyamine receptor antagonist ifenprodil on the severity of dystonia was examined in dystonic hamsters. Ifenprodil (5-40 mg/kg i.p.) failed to exert a beneficial effect, but even aggravated dystonia in the dt(sz) mutant at higher doses. These data together with previous pharmacological findings in mutant hamsters do not completely exclude a pathophysiological role of enhanced polyamine levels but suggest that overstimulation of NMDA receptors which contain NR2B subunits by enhanced spermine levels is not involved in the dystonic syndrome.

Dicarboxylic amino acids and glycine-betaine regulate chaperone-mediated protein-disaggregation under stress

Active protein-disaggregation by a chaperone network composed of ClpB and DnaK + DnaJ + GrpE is essential for the recovery of stress-induced protein aggregates in vitro and in Escherichia coli cells. K-glutamate and glycine-betaine (betaine) naturally accumulate in salt-stressed cells. In addition to providing thermo-protection to native proteins, we found that these osmolytes can strongly and specifically activate ClpB, resulting in an increased efficiency of chaperone-mediated protein disaggregation. Moreover, factors that inhibited the chaperone network by impairing the stability of the ClpB oligomer, such as natural polyamines, dilution, or high salt, were efficiently counteracted by K-glutamate or betaine. The combined protective, counter-negative and net activatory effects of K-glutamate and betaine, allowed protein disaggregation and refolding under heat-shock temperatures that otherwise cause protein aggregation in vitro and in the cell. Mesophilic organisms may thus benefit from a thermotolerant osmolyte-activated chaperone mechanism that can actively rescue protein aggregates, correctly refold and maintain them in a native state under heat-shock conditions.

Polycation-induced oligomerization and accelerated fibrillation of human alpha-synuclein in vitro

The aggregation and fibrillation of alpha-synuclein has been implicated as a causative factor in Parkinson's disease and several other neurodegenerative disorders known as synucleinopathies. The effect of different factors on the process of fibril formation has been intensively studied in vitro. We show here that alpha-synuclein interacts with different unstructured polycations (spermine, polylysine, polyarginine, and polyethyleneimine) to form specific complexes. In addition, the polycations catalyze alpha-synuclein oligomerization. The formation of alpha-synuclein-polycation complexes was not accompanied by significant structural changes in alpha-synuclein. However, alpha-synuclein fibrillation was dramatically accelerated in the presence of polycations. The magnitude of the accelerating effect depended on the nature of the polymer, its length, and concentration. The results illustrate the potential critical role of electrostatic interactions in protein aggregation, and the potential role of naturally occurring polycations in modulating alpha-synuclein aggregation.

Cellular polyamines promote the aggregation of alpha-synuclein

The cellular polyamines putrescine, spermidine, and spermine accelerate the aggregation and fibrillization of alpha-synuclein, the major protein component of Lewy bodies associated with Parkinson's disease. Circular dichroism and fluorometric thioflavin T kinetic studies showed a transition of alpha-synuclein from unaggregated to highly aggregated states, characterized by lag and transition phases. In the presence of polyamines, both the lag and transition times were significantly shorter. All three polyamines accelerated the aggregation and fibrillization of alpha-synuclein to a degree that increased with the total charge, length, and concentration of the polyamine. Electron and scanning force microscopy of the reaction products after the lag phase revealed the presence of aggregated particles (protofibrils) and small fibrils. At the end of the transition phase, alpha-synuclein formed long fibrils in all cases, although some morphological variations were apparent. In the presence of polyamines, fibrils formed large networks leading ultimately to condensed aggregates. In the absence of polyamines, fibrils were mostly isolated. We conclude that the polyamines at physiological concentrations can modulate the propensity of alpha-synuclein to form fibrils and may hence play a role in the formation of cytosolic alpha-synuclein aggregates.

Increased red blood cell polyamines in ALS and Parkinson's disease

The polyamines spermidine (SPD) and spermine (SPM) are implicated in nerve cell degeneration and regeneration. Over 70% of circulating polyamines are associated with red blood cells (RBC). Against this background we have analysed RBC polyamines in two neurodegenerative disorders, amyotrophic lateral sclerosis (ALS) and Parkinson's disease (PD). Twenty patients with the sporadic form of ALS, 20 patients with PD, and 20 healthy controls were studied. The highest levels of SPD and SPM were found in the PD group where the mean values were 134 and 115%, respectively, above those of the controls. The patients with PD also presented the lowest levels of the SPD precursor, putrescine (PUTR). In the patients suffering from ALS the SPD and SPM mean levels were increased by 46 and 112%, respectively. The RBC SPD/SPM ratio in the patients suffering from PD was significantly elevated in comparison with that of ALS patient group, suggesting a different involvement of the polyamine system in these disorders. It is at present unknown if raised polyamine levels may contribute to induce the degeneration of susceptible neurons or if the increase represents a compensatory protective reaction, or simply an unspecific epiphenomenon.