Increased poly(ADP-ribosyl)ation of nuclear proteins in Alzheimer's disease

Epigenetics of Alzheimer’s Disease: Past, Present and Future

Alzheimer’s disease (AD) exemplifies a looming epidemic lacking effective treatment and manifests with the accumulation of neurofibrillary tangles, amyloid-β plaques, neuroinflammation, behavioral changes, and acute cognitive impairments. It is a complex, multifactorial disorder that arises from the intricate interaction between environment and genetic factors, restrained via epigenetic machinery. Though the research progress has improved the understanding of clinical manifestations and disease advancement, the causal mechanism of detrimental consequences remains undefined. Despite the substantial improvement in recent diagnostic modalities, it is challenging to distinguish AD from other forms of dementia. Accurate diagnosis is a major glitch in AD as it banks on the symptoms and clinical criteria. Several studies are underway in exploring novel and reliable biomarkers for AD. In this direction, epigenetic alterations have transpired as key modulators in AD pathogenesis with the impeding inferences for the management of this neurological disorder. The present chapter aims to discuss the significance of epigenetic modifications reported in the pathophysiology of AD such as DNA methylation, hydroxy-methylation, methylation of mtDNA, histone modifications, and noncoding RNAs. Additionally, the chapter also describes the possible therapeutic avenues that target epigenetic modifications in AD.

Mutant-Huntingtin Molecular Pathways Elucidate New Targets for Drug Repurposing

The spectrum of neurodegenerative diseases known today is quite extensive. The complexities of their research and treatment lie not only in their diversity. Even many years of struggle and narrowly focused research on common pathologies such as Alzheimer's, Parkinson's, and other brain diseases have not brought cures for these illnesses. What can be said about orphan diseases? In particular, Huntington's disease (HD), despite affecting a smaller part of the human population, still attracts many researchers. This disorder is known to result from a mutation in the HTT gene, but having this information still does not simplify the task of drug development and studying the mechanisms of disease progression. Nonetheless, the data accumulated over the years and their analysis provide a good basis for further research. Here, we review studies devoted to understanding the mechanisms of HD. We analyze genes and molecular pathways involved in HD pathogenesis to describe the action of repurposed drugs and try to find new therapeutic targets.

Poly (ADP-ribose) polymerase 1 and neurodegenerative diseases: Past, present, and future

Poly (ADP-ribose) polymerase 1 (PARP1) is a first responder that recognizes DNA damage and facilitates its repair. Neurodegenerative diseases, characterized by progressive neuron loss driven by various risk factors, including DNA damage, have increasingly shed light on the pivotal involvement of PARP1. During the early phases of neurodegenerative diseases, PARP1 experiences controlled activation to swiftly address mild DNA damage, thereby contributing to maintain brain homeostasis. However, in late stages, exacerbated PARP1 activation precipitated by severe DNA damage exacerbates the disease condition. Consequently, inhibition of PARP1 overactivation emerges as a promising therapeutic approach for neurodegenerative diseases. In this review, we comprehensively synthesize and explore the multifaceted role of PARP1 in neurodegenerative diseases, with a particular emphasis on its over-activation in the aggregation of misfolded proteins, dysfunction of the autophagy-lysosome pathway, mitochondrial dysfunction, neuroinflammation, and blood-brain barrier (BBB) injury. Additionally, we encapsulate the therapeutic applications and limitations intrinsic of PARP1 inhibitors, mainly including limited specificity, intricate pathway dynamics, constrained clinical translation, and the heterogeneity of patient cohorts. We also explore and discuss the potential synergistic implementation of these inhibitors alongside other agents targeting DNA damage cascades within neurodegenerative diseases. Simultaneously, we propose several recommendations for the utilization of PARP1 inhibitors within the realm of neurodegenerative disorders, encompassing factors like the disease-specific roles of PARP1, combinatorial therapeutic strategies, and personalized medical interventions. Lastly, the encompassing review presents a forward-looking perspective along with strategic recommendations that could guide future research endeavors in this field.

Protease-independent control of parthanatos by HtrA2/Omi

HtrA2/Omi is a mitochondrial serine protease with ascribed pro-apoptotic as well as pro-necroptotic functions. Here, we establish that HtrA2/Omi also controls parthanatos, a third modality of regulated cell death. Deletion of HtrA2/Omi protects cells from parthanatos while reconstitution with the protease restores the parthanatic death response. The effects of HtrA2/Omi on parthanatos are specific and cannot be recapitulated by manipulating other mitochondrial proteases such as PARL, LONP1 or PMPCA. HtrA2/Omi controls parthanatos in a manner mechanistically distinct from its action in apoptosis or necroptosis, i.e., not by cleaving cytosolic IAP proteins but rather exerting its effects without exiting mitochondria, and downstream of PARP-1, the first component of the parthanatic signaling cascade. Also, previously identified or candidate substrates of HtrA2/Omi such as PDXDC1, VPS4B or moesin are not cleaved and dispensable for parthanatos, whereas DBC-1 and stathmin are cleaved, and thus represent potential parthanatic downstream mediators of HtrA2/Omi. Moreover, mass-spectrometric screening for novel parthanatic substrates of HtrA2/Omi revealed that the induction of parthanatos does not cause a substantial proteolytic cleavage or major alterations in the abundance of mitochondrial proteins. Resolving these findings, reconstitution of HtrA2/Omi-deficient cells with a catalytically inactive HtrA2/Omi mutant restored their sensitivity against parthanatos to the same level as the protease-active HtrA2/Omi protein. Additionally, an inhibitor of HtrA2/Omi's protease activity did not confer protection against parthanatic cell death. Our results demonstrate that HtrA2/Omi controls parthanatos in a protease-independent manner, likely via novel, unanticipated functions as a scaffolding protein and an interaction with so far unknown mitochondrial proteins.

Regulation of Biomolecular Condensates by Poly(ADP-ribose)

Biomolecular condensates are reversible compartments that form through a process called phase separation. Post-translational modifications like ADP-ribosylation can nucleate the formation of these condensates by accelerating the self-association of proteins. Poly(ADP-ribose) (PAR) chains are remarkably transient modifications with turnover rates on the order of minutes, yet they can be required for the formation of granules in response to oxidative stress, DNA damage, and other stimuli. Moreover, accumulation of PAR is linked with adverse phase transitions in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. In this review, we provide a primer on how PAR is synthesized and regulated, the diverse structures and chemistries of ADP-ribosylation modifications, and protein-PAR interactions. We review substantial progress in recent efforts to determine the molecular mechanism of PAR-mediated phase separation, and we further delineate how inhibitors of PAR polymerases may be effective treatments for neurodegenerative pathologies. Finally, we highlight the need for rigorous biochemical interrogation of ADP-ribosylation in vivo and in vitro to clarify the exact pathway from PARylation to condensate formation.

The old second messenger cAMP teams up with novel cell death mechanisms: potential translational therapeutical benefit for Alzheimer's disease and Parkinson's disease

Alzheimer's disease (AD) and Parkinson's disease (PD) represent the most prevalent neurodegenerative disorders severely impacting life expectancy and quality of life of millions of people worldwide. AD and PD exhibit both a very distinct pathophysiological disease pattern. Intriguingly, recent researches, however, implicate that overlapping mechanisms may underlie AD and PD. In AD and PD, novel cell death mechanisms, encompassing parthanatos, netosis, lysosome-dependent cell death, senescence and ferroptosis, apparently rely on the production of reactive oxygen species, and seem to be modulated by the well-known, "old" second messenger cAMP. Signaling of cAMP via PKA and Epac promotes parthanatos and induces lysosomal cell death, while signaling of cAMP via PKA inhibits netosis and cellular senescence. Additionally, PKA protects against ferroptosis, whereas Epac1 promotes ferroptosis. Here we review the most recent insights into the overlapping mechanisms between AD and PD, with a special focus on cAMP signaling and the pharmacology of cAMP signaling pathways.

Redox dysregulation as a driver for DNA damage and its relationship to neurodegenerative diseases

Redox homeostasis refers to the balance between the production of reactive oxygen species (ROS) as well as reactive nitrogen species (RNS), and their elimination by antioxidants. It is linked to all important cellular activities and oxidative stress is a result of imbalance between pro-oxidants and antioxidant species. Oxidative stress perturbs many cellular activities, including processes that maintain the integrity of DNA. Nucleic acids are highly reactive and therefore particularly susceptible to damage. The DNA damage response detects and repairs these DNA lesions. Efficient DNA repair processes are therefore essential for maintaining cellular viability, but they decline considerably during aging. DNA damage and deficiencies in DNA repair are increasingly described in age-related neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and Huntington's disease. Furthermore, oxidative stress has long been associated with these conditions. Moreover, both redox dysregulation and DNA damage increase significantly during aging, which is the biggest risk factor for neurodegenerative diseases. However, the links between redox dysfunction and DNA damage, and their joint contributions to pathophysiology in these conditions, are only just emerging. This review will discuss these associations and address the increasing evidence for redox dysregulation as an important and major source of DNA damage in neurodegenerative disorders. Understanding these connections may facilitate a better understanding of disease mechanisms, and ultimately lead to the design of better therapeutic strategies based on preventing both redox dysregulation and DNA damage.

Extract of Ginkgo biloba leaves attenuates neurotoxic damages in rats and SH-SY5Y cells exposed to a high level of fluoride

BACKGROUND

Potential protection against the neurotoxic damages of high levels of fluoride on rats and SH-SY5Y cells by extract of Ginkgo biloba leaves, as well as underlying mechanisms, were examined.

METHODS

The rats were divided randomly into 4 groups, i.e., control, treatment with the extract (100 mg/kg body weight, gavage once daily), treatment with fluoride (50 ppm F^- in drinking water) and combined treatment with both; SH-SY5Y cells exposed to fluoride and fluoride in combination with the extract or 4-Amino-1,8-naphthalimide (4-ANI), an inhibitor of poly (ADP-ribose) polymerase-1 (PARP-1). Spatial learning and memory in the rats were assessed employing Morris water maze test; the contents of fluoride in brains and urine by fluoride ion-selective electrode; cytotoxicity of fluoride was by CCK-8 kit; the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and the content of malondialdehyde (MDA) by appropriate kits; the level of 8-hydroxydeoxyguanosine (8-OHdG) was by ELISA; the content of ROS and frequency of apoptosis by flow cytometry; the expressions of phospho-histone H2A.X_(Ser139), PARP-1, poly (ADP-ribose) (PAR) and Sirtuin-1 (SIRT1) by Western blotting or immunofluorescence.

RESULTS

The rats with prolong treatment of fluoride exhibited dental fluorosis, the increased contents of fluoride in brains and urine and the declined ability of learning and memory. In the hippocampus of the rats and SH-SY5Y cells exposed to fluoride, the levels of ROS, MDA, apoptosis, 8-OHdG and the protein expressions of histone H2A.X_(Ser139), PARP-1 and PAR were all elevated; the activities of SOD and GSH-Px and the protein expression of SIRT1 reduced. Interestingly, the treatment of Ginkgo biloba extract attenuated these neurotoxic effects on rats and SH-SY5Y cells exposed to fluoride and the treatment of 4-ANI produced a neuroprotective effect against fluoride exposure.

CONCLUSION

Ginkgo biloba extract attenuated neurotoxic damages induced by fluoride exposure to rats and SH-SY5Y cells and the underlying mechanism might involve the inhibition of PARP-1 and the promotion of SIRT1.

Importance of NAD+ Anabolism in Metabolic, Cardiovascular and Neurodegenerative Disorders

The role of nicotinamide adenine dinucleotide (NAD+) in ageing has emerged as a critical factor in understanding links to a wide range of chronic diseases. Depletion of NAD+, a central redox cofactor and substrate of numerous metabolic enzymes, has been detected in many major age-related diseases. However, the mechanisms behind age-associated NAD+ decline remains poorly understood. Despite limited conclusive evidence, supplements aimed at increasing NAD+ levels are becoming increasingly popular. This review provides renewed insights regarding the clinical utility and benefits of NAD+ precursors, namely nicotinamide (NAM), nicotinic acid (NA), nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), in attenuating NAD+ decline and phenotypic characterization of age-related disorders, including metabolic, cardiovascular and neurodegenerative diseases. While it is anticipated that NAD+ precursors can play beneficial protective roles in several conditions, they vary in their ability to promote NAD+ anabolism with differing adverse effects. Careful evaluation of the role of NAD⁺, whether friend or foe in ageing, should be considered.

Current Naturopathy to Combat Alzheimer's Disease

Neurodegeneration is the progressive loss of structure or function of neurons, which may ultimately involve cell death. The most common neurodegenerative disorder in the brain happens with Alzheimer's disease (AD), the most common cause of dementia. It ultimately leads to neuronal death, thereby impairing the normal functionality of the central or peripheral nervous system. The onset and prevalence of AD involve heterogeneous etiology, either in terms of genetic predisposition, neurometabolomic malfunctioning, or lifestyle. The worldwide relevancies are estimated to be over 45 million people. The rapid increase in AD has led to a concomitant increase in the research work directed towards discovering a lucrative cure for AD. The neuropathology of AD comprises the deficiency in the availability of neurotransmitters and important neurotrophic factors in the brain, extracellular betaamyloid plaque depositions, and intracellular neurofibrillary tangles of hyperphosphorylated tau protein. Current pharmaceutical interventions utilizing synthetic drugs have manifested resistance and toxicity problems. This has led to the quest for new pharmacotherapeutic candidates naturally prevalent in phytochemicals. This review aims to provide an elaborative description of promising Phyto component entities having activities against various potential AD targets. Therefore, naturopathy may combine with synthetic chemotherapeutics to longer the survival of the patients.

A Review of the Recent Advances in Alzheimer's Disease Research and the Utilization of Network Biology Approaches for Prioritizing Diagnostics and Therapeutics

Alzheimer's disease (AD) is a polygenic multifactorial neurodegenerative disease that, after decades of research and development, is still without a cure. There are some symptomatic treatments to manage the psychological symptoms but none of these drugs can halt disease progression. Additionally, over the last few years, many anti-AD drugs failed in late stages of clinical trials and many hypotheses surfaced to explain these failures, including the lack of clear understanding of disease pathways and processes. Recently, different epigenetic factors have been implicated in AD pathogenesis; thus, they could serve as promising AD diagnostic biomarkers. Additionally, network biology approaches have been suggested as effective tools to study AD on the systems level and discover multi-target-directed ligands as novel treatments for AD. Herein, we provide a comprehensive review on Alzheimer's disease pathophysiology to provide a better understanding of disease pathogenesis hypotheses and decipher the role of genetic and epigenetic factors in disease development and progression. We also provide an overview of disease biomarkers and drug targets and suggest network biology approaches as new tools for identifying novel biomarkers and drugs. We also posit that the application of machine learning and artificial intelligence to mining Alzheimer's disease multi-omics data will facilitate drug and biomarker discovery efforts and lead to effective individualized anti-Alzheimer treatments.

Does oxidative DNA damage trigger histotoxic hypoxia via PARP1/AMP-driven mitochondrial ADP depletion-induced ATP synthase inhibition in Alzheimer's disease?

The low cerebral metabolic rate of oxygen despite the relatively preserved perfusion in Alzheimer's disease (AD) patients' medial temporal lobes suggest histotoxic hypoxia due to mitochondrial dysfunction that is independent of, but could precede, insulin resistance. Neuropathological, metabolomic, and preclinical evidence are consistent with the notion that this mitochondrial dysfunction may be contributed to by oxidative stress and DNA damage, leading to poly-(ADP-ribose)-polymerase-1 (PARP1) activation and consequent AMP accumulation, clogging of mitochondrial adenine nucleotide transporters (ANTs), matrix ADP deprivation, and ATP synthase inhibition. Complementary mechanisms may include mitochondrial-protein poly-ADP-ribosylation and mitochondrial-biogenesis suppression via PARPs outcompeting Sirtuin-1 (SIRT1) for nicotinamide-adenine-dinucleotide (NAD⁺).

Neuronal cell death mechanisms in Alzheimer's disease: An insight

Regulated cell death (RCD) is an ordered and tightly orchestrated set of changes/signaling events in both gene expression and protein activity and is responsible for normal development as well as maintenance of tissue homeostasis. Aberrant activation of this pathway results in cell death by various mechanisms including apoptosis, necroptosis, pyroptosis, ferroptosis, and autophagy-dependent cell death. Such pathological changes in neurons alone or in combination have been observed in the pathogenesis of various neurodegenerative diseases including Alzheimer's disease (AD). Pathological hallmarks of AD focus primarily on the accumulation of two main protein markers: amyloid β peptides and abnormally phosphorylated tau proteins. These protein aggregates result in the formation of A-β plaques and neuro-fibrillary tangles (NFTs) and induce neuroinflammation and neurodegeneration over years to decades leading to a multitude of cognitive and behavioral deficits. Autopsy findings of AD reveal massive neuronal death manifested in the form of cortical volume shrinkage, reduction in sizes of gyri to up to 50% and an increase in the sizes of sulci. Multiple forms of cell death have been recorded in neurons from different studies conducted so far. However, understanding the mechanism/s of neuronal cell death in AD patients remains a mystery as the trigger that results in aberrant activation of RCD is unknown and because of the limited availability of dying neurons. This review attempts to elucidate the process of Regulated cell death, how it gets unregulated in response to different intra and extracellular stressors, various forms of unregulated cell death, their interplay and their role in pathogenesis of Alzheimer's Disease in both human and experimental models of AD. Further we plan to explore the correlation of both amyloid-beta and Tau with neuronal loss as seen in AD.

How neurons die in Alzheimer's disease: Implications for neuroinflammation

Despite the long-standing observation of vast neuronal loss in Alzheimer's disease (AD) our understanding of how and when neurons are eliminated is incomplete. While previous investigation has focused on apoptosis, several novel forms of cell death (i.e. necroptosis, parthanatos, ferroptosis, cuproptosis) have emerged that require further investigation. This review aims to collect evidence for different modes of neuronal cell death in AD and to also discuss how these different forms of cell death may impact the neuroinflammatory environment that prevails in the AD brain. Improved understanding of how neurons die may help to delineate disease pathogenesis, provide insights toward treatment, and aid in the development of improved animal models of AD.

Activated or Impaired: An Overview of DNA Repair in Neurodegenerative Diseases

As the population ages, age-related neurodegenerative diseases have become a major challenge in health science. Currently, the pathology of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease, is still not fully understood. Remarkably, emerging evidence indicates a role of genomic DNA damage and repair in various neurodegenerative disorders. Here, we summarized the current understanding of the function of DNA damage repair, especially base excision repair and double strand break repair pathways, in a variety of neurodegenerative diseases. We concluded that exacerbation of DNA lesions is found in almost all types of neurodegenerative diseases, whereas the activities of different DNA repair pathways demonstrate distinct trends, depending on disease type and even brain region. Specifically, key enzymes involved in base excision repair are likely impaired in Alzheimer's disease and amyotrophic lateral sclerosis but activated in Parkinson's disease, while nonhomologous end joining is likely downregulated in most types of neurodegenerative diseases. Hence, impairment of nonhomologous end joining is likely a common etiology for most neurodegenerative diseases, while defects in base excision repair are likely involved in the pathology of Alzheimer's disease and amyotrophic lateral sclerosis but are Parkinson's disease, based on current findings. Although there are still discrepancies and further studies are required to completely elucidate the exact roles of DNA repair in neurodegeneration, the current studies summarized here provide crucial insights into the pathology of neurodegenerative diseases and may reveal novel drug targets for corresponding neurodegenerative diseases.

Cis- and trans-resveratrol have opposite effects on histone serine-ADP-ribosylation and tyrosine induced neurodegeneration

Serum tyrosine levels increase during aging, neurocognitive, metabolic, and cardiovascular disorders. However, calorie restriction (CR) and sleep lower serum tyrosine levels. We previously showed that tyrosine inhibits tyrosyl-tRNA synthetase (TyrRS)-mediated activation of poly-ADP-ribose polymerase 1 (PARP1). Here, we show that histone serine-ADP-ribosylation is decreased in Alzheimer's Disease (AD) brains, and increased tyrosine levels deplete TyrRS and cause neuronal DNA damage. However, dopamine and brain-derived neurotrophic factor (BDNF) increase TyrRS and histone serine-ADP-ribosylation. Furthermore, cis-resveratrol (cis-RSV) that binds to TyrRS mimicking a 'tyrosine-free' conformation increases TyrRS, facilitates histone serine-ADP-ribosylation-dependent DNA repair, and provides neuroprotection in a TyrRS-dependent manner. Conversely, trans-RSV that binds to TyrRS mimicking a 'tyrosine-like' conformation decreases TyrRS, inhibits serine-ADP-ribosylation-dependent DNA repair, and induces neurodegeneration in rat cortical neurons. Our findings suggest that age-associated increase in serum tyrosine levels may effect neurocognitive and metabolic disorders and offer a plausible explanation for divergent results obtained in clinical trials using resveratrol.

Neuroprotective Effects of PARP Inhibitors in Drosophila Models of Alzheimer’s Disease

Alzheimer’s disease (AD) is an irreversible age-related neurodegenerative disorder clinically characterized by severe memory impairment, language deficits and cognitive decline. The major neuropathological hallmarks of AD include extracellular deposits of the β-amyloid (Aβ) peptides and cytoplasmic neurofibrillary tangles (NFTs) of hyperphosphorylated tau protein. The accumulation of plaques and tangles in the brain triggers a cascade of molecular events that culminate in neuronal damage and cell death. Despite extensive research, our understanding of the molecular basis of AD pathogenesis remains incomplete and a cure for this devastating disease is still not available. A growing body of evidence in different experimental models suggests that poly(ADP-ribose) polymerase-1 (PARP-1) overactivation might be a crucial component of the molecular network of interactions responsible for AD pathogenesis. In this work, we combined genetic, molecular and biochemical approaches to investigate the effects of two different PARP-1 inhibitors (olaparib and MC2050) in Drosophila models of Alzheimer’s disease by exploring their neuroprotective and therapeutic potential in vivo. We found that both pharmacological inhibition and genetic inactivation of PARP-1 significantly extend lifespan and improve the climbing ability of transgenic AD flies. Consistently, PARP-1 inhibitors lead to a significant decrease of Aβ42 aggregates and partially rescue the epigenetic alterations associated with AD in the brain. Interestingly, olaparib and MC2050 also suppress the AD-associated aberrant activation of transposable elements in neuronal tissues of AD flies.

Ars moriendi: Proteases as sculptors of cellular suicide

The Ars moriendi, which translates to "The Art of Dying," encompasses two Latin texts that gave advice on how to die well and without fear according to the Christian precepts of the late Middle Ages. Given that ten to hundred billion cells die in our bodies every day, it is obvious that the concept of a well and orderly ("regulated") death is also paramount at the cellular level. In apoptosis, as the most well-studied form of regulated cell death, proteases of the caspase family are the central mediators. However, caspases are not the only proteases that act as sculptors of cellular suicide, and therefore, we here provide an overview of the impact of proteases in apoptosis and other forms of regulated cell death.

Arsenic alters nitric oxide signaling similar to autism spectrum disorder and Alzheimer's disease-associated mutations

Epidemiological studies have proven that exposure to Arsenic (AS) leads to the development of many neurological disorders. However, few studies have investigated its molecular mechanisms in the brain. Our previous work has revealed nitric oxide (NO)-mediated apoptosis and SNO reprogramming in the cortex following arsenic treatment, yet the role of NO and S-nitrosylation (SNO) in AS-mediated neurotoxicity has not been investigated. Therefore, we have conducted a multidisciplinary in-vivo study in mice with two different doses of Sodium Arsenite (SA) (0.1 ppm and 1 ppm) in drinking water. We used the novel SNOTRAP-based mass spectrometry method followed by the bioinformatics analysis, Western blot validation, and five different behavioral tests. Bioinformatics analysis of SA-treated mice showed significant SNO-enrichment of processes involved in mitochondrial respiratory function, endogenous antioxidant systems, transcriptional regulation, cytoskeleton maintenance, and regulation of apoptosis. Western blotting showed increased levels of cleaved PARP-1 and cleaved caspase-3 in SA-treated mice consistent with SA-induced apoptosis. Behavioral studies showed significant cognitive dysfunctions similar to those of Autism spectrum disorder (ASD) and Alzheimer's disease (AD). A comparative analysis of the SNO-proteome of SA-treated mice with two transgenic mouse strains, models of ASD and AD, showed molecular convergence of SA environmental neurotoxicity and the genetic mutations causing ASD and AD. This is the first study to show the effects of AS on SNO-signaling in the striatum and hippocampus and its effects on behavioral characteristics. Finally, further investigation of the NO-dependent mechanisms of AS-mediated neurotoxicity may reveal new drug targets for its prevention.

The Complex Mechanisms by Which Neurons Die Following DNA Damage in Neurodegenerative Diseases

Human cells are exposed to numerous exogenous and endogenous insults every day. Unlike other molecules, DNA cannot be replaced by resynthesis, hence damage to DNA can have major consequences for the cell. The DNA damage response contains overlapping signalling networks that repair DNA and hence maintain genomic integrity, and aberrant DNA damage responses are increasingly described in neurodegenerative diseases. Furthermore, DNA repair declines during aging, which is the biggest risk factor for these conditions. If unrepaired, the accumulation of DNA damage results in death to eliminate cells with defective genomes. This is particularly important for postmitotic neurons because they have a limited capacity to proliferate, thus they must be maintained for life. Neuronal death is thus an important process in neurodegenerative disorders. In addition, the inability of neurons to divide renders them susceptible to senescence or re-entry to the cell cycle. The field of cell death has expanded significantly in recent years, and many new mechanisms have been described in various cell types, including neurons. Several of these mechanisms are linked to DNA damage. In this review, we provide an overview of the cell death pathways induced by DNA damage that are relevant to neurons and discuss the possible involvement of these mechanisms in neurodegenerative conditions.

PARkinson's: From cellular mechanisms to potential therapeutics

Our understanding of the progression and mechanisms underlying the onset of Parkinson's disease (PD) has grown enormously in the past few decades. There is growing evidence suggesting that poly (ADP-ribose) polymerase 1 (PARP-1) hyperactivation is involved in various neurodegenerative disorders, including PD, and that poly (ADP-ribose) (PAR)-dependent cell death is responsible for neuronal loss. In this review, we discuss the contribution of PARP-1 and PAR in the pathological process of PD. We describe the potential pathways regulated by the enzyme, review clinically relevant PARP-1 inhibitors as potential disease-modifying therapeutics for PD, and outline important factors that need to be considered for repurposing PARP-1 inhibitors for use in PD.

Recent advances in preventing neurodegenerative diseases

The worldwide health-care burden of neurodegenerative diseases is on the rise-a crisis created through a combination of increased caseload and lack of effective treatments. The limitations of pharmacotherapy in these disorders have led to an urgent shift toward research and clinical trials for the development of novel compounds, interventions, and methods that target shared features across the spectrum of neurodegenerative diseases. Research targets include neuronal cell death, mitochondrial dysfunction, protein aggregation, and neuroinflammation. In the past few years, there has been a growth in understanding of the pathophysiologic mechanisms of neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, and Huntington's disease. This increase in knowledge has led to the discovery of numerous novel neuroprotective therapeutic targets. In this context, we reviewed and summarized recent advancements in neuroprotective strategies in neurodegenerative diseases.

Extra Virgin Olive Oil consumption from Mild Cognitive Impairment patients attenuates oxidative and nitrative stress reflecting on the reduction of the PARP levels and DNA damage

Oxidative/nitrative stress that results from the unbalance of the overproduction/clearance of reactive oxygen/nitrogen species (ROS/NOS), originated from a variety of endo- and/or exo-genous sources, can have detrimental effects on DNA and is involved in Alzheimer's disease (AD) pathology. An excellent marker of oxidative DNA lesions is 8-hydroxy-2'-deoxyguanosine (8-OHdG) while of nitrative stress the enzyme NOS2 (Nitric oxide synthase 2). Under massive oxidative stress, poly(ADP-ribose)polymerase 1 (PARP-1) enzyme activity, responsible for restoration of DNA damage, is augmented, DNA repair enzymes are recruited, and cell survival/or death is ensued through PARP-1 activation, which is correlated positively with neurodegenerative diseases. In this biochemical study the levels of PARP-1, 8-oxo-dG, and NOS2, Aβ1-42, and p-tau in their sera determined using Enzyme-Linked Immunosorbent Assay (ELISA). Patients diagnosed with Mild Cognitive Impairment participated in MICOIL clinical trial, were daily administered with 50 ml Extra Virgin Olive Oil (EVOO) for one year. All MCI patients' biomarkers that had consumed EVOO were tantamount to those of healthy participants, contrary to MCI patients who were not administered. EVOO administration in MCI patients resulted in the restoration of DNA damage and of the well-established "hallmarks" AD biomarkers, thanks probably to its antioxidant properties exhibiting a therapeutic potentiality against AD. Molecular docking simulations of the EVOO constituents on the crystal structure of PARP-1 and NOS-2 target enzymes were also employed, to study in silico the ability of the compounds to bind to these enzymes and explain the observed in vitro activity. In silico analysis has proved the binding of EVOO constituents on PARP-1and NOS-2 enzymes and their interaction with crucial amino acids of the active sites. CLINICAL TRIAL REGISTRATION: https://clinicaltrials.gov/ct2/show/NCT03362996. MICOIL GOV IDENTIFIER: NCT03362996.

Biallelic ADPRHL2 mutations in complex neuropathy affect ADP ribosylation and DNA damage response

ADP ribosylation is a reversible posttranslational modification mediated by poly(ADP-ribose)transferases (e.g., PARP1) and (ADP-ribosyl)hydrolases (e.g., ARH3 and PARG), ensuring synthesis and removal of mono-ADP-ribose or poly-ADP-ribose chains on protein substrates. Dysregulation of ADP ribosylation signaling has been associated with several neurodegenerative diseases, including Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease. Recessive ADPRHL2/ARH3 mutations are described to cause a stress-induced epileptic ataxia syndrome with developmental delay and axonal neuropathy (CONDSIAS). Here, we present two families with a neuropathy predominant disorder and homozygous mutations in ADPRHL2 We characterized a novel C26F mutation, demonstrating protein instability and reduced protein function. Characterization of the recurrent V335G mutant demonstrated mild loss of expression with retained enzymatic activity. Although the V335G mutation retains its mitochondrial localization, it has altered cytosolic/nuclear localization. This minimally affects basal ADP ribosylation but results in elevated nuclear ADP ribosylation during stress, demonstrating the vital role of ADP ribosylation reversal by ARH3 in DNA damage control.

Nuclear dynamics and stress responses in Alzheimer's disease

In response to extracellular and intracellular stressors, the nucleus and nuclear compartments undergo distinct molecular changes to maintain cell homeostasis. In the context of Alzheimer’s disease, misfolded proteins and various cellular stressors lead to profound structural and molecular changes at the nucleus. This review summarizes recent research on nuclear alterations in AD development, from the nuclear envelope changes to chromatin and epigenetic regulation and then to common nuclear stress responses. Finally, we provide our thoughts on the importance of understanding cell-type-specific changes and identifying upstream causal events in AD pathogenesis and highlight novel sequencing and gene perturbation technologies to address those challenges.

Episodic psychosis, ataxia, motor neuropathy with pyramidal signs (PAMP syndrome) caused by a novel mutation in ADPRHL2 (AHR3)

BACKGROUND

The protein "ADP-Ribosylarginine Hydrolase-Like Protein 2" is encoded by ADPRHL2 and reverses ADP-ribosylation. Recently, mutations in ADPRHL2 were found to be associated with a very rare childhood onset severe neurodegeneration syndrome with episodic, stress-induced seizures, ataxia, and axonal neuropathy. In this study, we evaluate a novel mutation in ADPRHL2 leading to an unknown adult onset syndrome "episodic psychosis, ataxia, motor neuropathy with pyramidal signs (PAMP syndrome)."

DESIGN/METHODS

Four patients with episodic psychosis, ataxia, and motor neuropathy with pyramidal signs were included in this study.

RESULTS

An index patient presented ataxia, postural tremor in the hands, and hallucinations at age 20 years, which had started after a viral infection. She improved within 3 months without any treatment. Her neurological exam revealed mild distal weakness, brisk DTRs, bilateral Babinski sign, impaired vibration sensation, position, and ataxia. Pes cavus and hammer toes were also noted. EMG revealed neurogenic changes in distal muscles and normal sensory nerve conduction studies. Cranial MRI was normal. She had three more severe episodes in recent years, and her neurologic findings got progressively worse. Two of her older sisters had much milder phenotypes. The phenotype of the fourth patient from an unrelated family was identical with the index patient. All affected patients had homozygous novel NM_017825.3:c.838G>A (p.Ala280Thr) mutations in a highly conserved region of ADPRHL2. Western blot analyses demonstrated that ADPRHL2 was not expressed in these patients.

CONCLUSIONS

Here, we describe a novel mutation in ADPRHL2, which further expands the phenotypic and genetic spectrum of the patients harboring these mutations.

Apoptotic Pathways and Alzheimer's Disease: Probing Therapeutic Potential

Apoptosis is an intrinsic biochemical, cellular process that regulates cell death and is crucial for cell survival, cellular homeostasis, and maintaining the optimum functional status. Apoptosis in a predetermined and programmed manner regulates several molecular events, including cell turnover, embryonic development, and immune system functions but may be the exclusive contributor to several disorders, including neurodegenerative manifestations, when it functions in an aberrant and disorganized manner. Alzheimer's disease (AD) is a fatal, chronic neurodegenerative disorder where apoptosis has a compelling and divergent role. The well-characterized pathological features of AD, including extracellular plaques of amyloid-beta, intracellular hyperphosphorylated tangles of tau protein (NFTs), inflammation, mitochondrial dysfunction, oxidative stress, and excitotoxic cell death, also instigate an abnormal apoptotic cascade in susceptible brain regions (cerebral cortex, hippocampus). The apoptotic players in these regions affect cellular organelles (mitochondria and endoplasmic reticulum), interact with trophic factors, and several pathways, including PI3K/AKT, JNK, MAPK, mTOR signalling. This dysregulated apoptotic cascade end with an abnormal neuronal loss which is a primary event that may precede the other events of AD progression and correlates well with the degree of dementia. The present review provides insight into the diverse and versatile apoptotic mechanisms that are indispensable for neuronal survival and constitute an integral part of the pathological progression of AD. Identification of potential targets (restoring apoptotic and antiapoptotic balance, caspases, TRADD, RIPK1, FADD, TNFα, etc.) may be valuable and advantageous to decide the fate of neurons and to develop potential therapeutics for treatment of AD.

Risks and rewards of targeting NAD+ homeostasis in the brain

Strategies to correct declining nicotinamide adenine dinucleotide (NAD⁺) levels in neurological disease and biological ageing are promising therapeutic candidates. These strategies include supplementing with NAD⁺ precursors, small molecule activation of NAD⁺ biosynthetic enzymes, and treatment with small molecule inhibitors of NAD⁺ consuming enzymes such as CD38, SARM1 or members of the PARP family. While these strategies have shown efficacy in animal models of neurological disease, each of these has the mechanistic potential for adverse events that could preclude their preclinical use. Here, we discuss the implications of these strategies for treating neurological diseases, including potential off-target effects that may be unique to the brain.

Emerging role of PARP-1 and PARthanatos in ischemic stroke

Cell death is a key feature of neurological diseases, including stroke and neurodegenerative disorders. Studies in a variety of ischemic/hypoxic mouse models demonstrate that poly(ADP-ribose) polymerase 1 (PARP-1)-dependent cell death, also named PARthanatos, plays a pivotal role in ischemic neuronal cell death and disease progress. PARthanatos has its unique triggers, processors, and executors that convey a highly orchestrated and programmed signaling cascade. In addition to its role in gene transcription, DNA damage repair, and energy homeostasis through PARylation of its various targets, PARP-1 activation in neuron and glia attributes to brain damage following ischemia/reperfusion. Pharmacological inhibition or genetic deletion of PARP-1 reduces infarct volume, eliminates inflammation, and improves recovery of neurological functions in stroke. Here, we reviewed the role of PARP-1 and PARthanatos in stroke and their therapeutic potential.

Neuroprotection in Glaucoma: NAD+/NADH Redox State as a Potential Biomarker and Therapeutic Target

Glaucoma is the leading cause of irreversible blindness worldwide. Its prevalence and incidence increase exponentially with age and the level of intraocular pressure (IOP). IOP reduction is currently the only therapeutic modality shown to slow glaucoma progression. However, patients still lose vision despite best treatment, suggesting that other factors confer susceptibility. Several studies indicate that mitochondrial function may underlie both susceptibility and resistance to developing glaucoma. Mitochondria meet high energy demand, in the form of ATP, that is required for the maintenance of optimum retinal ganglion cell (RGC) function. Reduced nicotinamide adenine dinucleotide (NAD⁺) levels have been closely correlated to mitochondrial dysfunction and have been implicated in several neurodegenerative diseases including glaucoma. NAD⁺ is at the centre of various metabolic reactions culminating in ATP production—essential for RGC function. In this review we present various pathways that influence the NAD⁺(H) redox state, affecting mitochondrial function and making RGCs susceptible to degeneration. Such disruptions of the NAD⁺(H) redox state are generalised and not solely induced in RGCs because of high IOP. This places the NAD⁺(H) redox state as a potential systemic biomarker for glaucoma susceptibility and progression; a hypothesis which may be tested in clinical trials and then translated to clinical practice.

PARP-1 activation leads to cytosolic accumulation of TDP-43 in neurons

Oxidative stress in neurodegenerative disease leads to poly(ADP-ribose) polymerase 1 (PARP-1) overactivation and subsequent cell death via excessive generation of Poly(ADP-ribose) polymer (PAR). PAR binds to neurodegenerative disease linked protein TAR DNA binding protein of 43 kDa (TDP-43). However, the consequence of this interaction is not yet fully understood. TDP-43 translocates from the nucleus to the cytoplasm in response to oxidative stress, but the mechanism of stress-induced translocation remains unknown. We used N-methyl-N-nitroso-N'-nitroguanidine (MNNG) and oxygen-glucose deprivation (OGD) in mouse neuronal cultures to activate PARP-1 and observed that pharmacological inhibition of PARP-1 blocked the cytosolic translocation of TDP-43. PARP-1 inhibition is also neuroprotective against both MNNG and OGD, suggesting that PARP inhibitors could play a role in the neuroprotective role in neurodegenerative diseases involving TDP-43. Together, these data present the novel finding that TDP-43 translocation depends on PARP-1 activation and set a ground for future research of how PARP-1 activation or PAR binding to TDP-43 may facilitate its cytosolic accumulation.

Mechanisms of Regulated Cell Death: Current Perspectives

Balancing cell survival and cell death is fundamental to development and homeostasis. Cell death is regulated by multiple interconnected signaling pathways and molecular mechanisms. Regulated cell death (RCD) is implicated in fundamental processes such as organogenesis and tissue remodeling, removal of unnecessary structures or cells, and regulation of cell numbers. RCD can also be triggered by exogenous perturbations of the intracellular or extracellular microenvironment when the adaptive processes that respond to stress fail. During the past few years, many novel forms of non-apoptotic RCD have been identified, and the characterization of RCD mechanisms at a molecular level has deepened our understanding of diseases encountered in human and veterinary medicine. Given the complexity of these processes, it has become clear that the identification of RCD cannot be based simply on morphologic characteristics and that descriptive and diagnostic terms presently used by pathologists-such as individual cell apoptosis or necrosis-appear inadequate and possibly misleading. In this review, the current understanding of the molecular machinery of each type of non-apoptotic RCD mechanisms is outlined. Due to the continuous discovery of new mechanisms or nuances of previously described processes, the limitations of the terms apoptosis and necrosis to indicate microscopic findings are also reported. In addition, the need for a standard panel of biomarkers and functional tests to adequately characterize the underlying RCD and its role as a mechanism of disease is considered.

Evaluation of a Low-Toxicity PARP Inhibitor as a Neuroprotective Agent for Parkinson's Disease

Repurposing PARP-1 inhibitors (PARPi) for non-oncological applications offers an attractive therapeutic strategy for pathological conditions characterized by PARP-1 hyperactivity. In the context of Parkinson's disease (PD), PARP-1 hyperactivity has been linked to neuronal death and disease progression. From a therapy perspective, the evaluation of PARPi as neuroprotective agents may offer a new therapeutic alternative for neurodegenerative disorders. An ideal PARPi needs to inhibit PARP-1 hyperactivity while also limiting downstream DNA damage and cellular toxicity-an effect that is attractive in cancer but far from ideal in neurological disease applications. Consequently, in this study, we set out to evaluate the neuroprotective properties of a previously reported low-toxicity PARPi (10e) using in vitro neuronal models of PD. 10e is a structural analogue of FDA-approved PARPi olaparib, with high PARP-1 affinity and selectivity. Our studies revealed that 10e protects neuronal cells from oxidative stress and DNA damage. In addition, 10e exhibits neuroprotective properties against α-synuclein pre-formed fibrils (αSyn PFF) mediated effects, including reduction in the levels of phosphorylated αSyn and protection against abnormal changes in NAD⁺ levels. Our in vitro studies with 10e provide support for repurposing high-affinity and low-toxicity PARPi for neurological applications and lay the groundwork for long-term therapeutic studies in animal models of PD.

PARP overactivation in neurological disorders

Poly (ADP-ribose) polymerases (PARPs) constitute a family of enzymes associated with divergent cellular processes that are not limited to DNA repair, chromatin organization, genome integrity, and apoptosis but also found to play a crucial role in inflammation. PARPs mediate poly (ADP-ribosylation) of DNA binding proteins that is often responsible for chromatin remodeling thereby ensure effective repairing of DNA stand breaks although during the conditions of severe genotoxic stress PARPs direct the cell fate towards apoptotic events. Recent discoveries have pushed PARPs into the spotlight as targets for treating cancer, metabolic, inflammatory and neurological disorders. Of note, PARP-1 is the most abundant isoform of PARPs (18 member super family) which executes more than 90% of PARPs functions. Since oxidative/nitrosative stress actuated PARP-1 is linked to vigorous DNA damage and wide spread provocative inflammatory response that underlie the aetiopathogenesis of different neurological disorders, possibility of developing PARP-1 inhibitors as plausible neurotherapeutic agents attracts considerable research interest. This review outlines the recent advances in PARP-1 biology and examines the capability of PARP-1 inhibitors as treatment modalities in intense and interminable diseases of neuronal origin.

Computational Analysis Indicates That PARP1 Acts as a Histone Deacetylases Interactor Sharing Common Lysine Residues for Acetylation, Ubiquitination, and SUMOylation in Alzheimer's and Parkinson's Disease

Aim/Hypothesis : Lysine residues are known for the post-translational modifications (PTMs) such as acetylation, ubiquitination, and SUMOylation. In acetylation, histone deacetylase (HDAC) and its interactors cause transcriptional deregulation and cause mitochondrial dysfunction, apoptosis, inflammatory response, and cell-cycle impairment that cause brain homeostasis and neuronal cell death. Other regulatory PTMs involved in the pathogenesis of neurodegenerative diseases (NDDs) are ubiquitination and SUMOylation for the degradation of the misfolded proteins. Thus, we aim to investigate the potential acetylation/ubiquitination/SUMOylation crosstalk sites in the HDAC interactors, which cause NDDs. Furthermore, we aim to identify the influence of PTMs on the structural features of proteins and the impact of putative lysine mutation on disease susceptibility. Last, we aim to examine the impact of the putative mutation on acetylated lysine for ubiquitination and SUMOylation. Results : Herein, we integrate 1455 genes, 3094 genes, and 1940 genes related to HDAC interactors, Alzheimer's disease (AD), and Parkinson's disease (PD), respectively. Furthermore, the protein-protein interaction and PTM integrations from different databases identified 32 proteins that are associated with HDAC, AD, and PD with 1489 potential lysine-modified sites. HDAC interactors poly(ADP-ribose) polymerase 1 (PARP1), nucleophosmin (NPM1), and cyclin-dependent kinase 1 (CDK1) involved in the progression of NDDs and 64 and 75% of PTM sites in PARP1, NPM1, and CDK1 fall into coiled and ordered regions, respectively. Moreover, 15 putative lysine sites have been found in the crosstalk and K148, K249, K528, K637, K700, and K796 of PARP1 are crosstalk hotspots. Conclusion : The loss of acetylated hotspot sites results in the loss of ubiquitination and SUMOylation function on nearby sites, which is relatively higher when compared to the gain of function.

The expanding genetic landscape of hereditary motor neuropathies

Hereditary motor neuropathies are clinically and genetically diverse disorders characterized by length-dependent axonal degeneration of lower motor neurons. Although currently as many as 26 causal genes are known, there is considerable missing heritability compared to other inherited neuropathies such as Charcot-Marie-Tooth disease. Intriguingly, this genetic landscape spans a discrete number of key biological processes within the peripheral nerve. Also, in terms of underlying pathophysiology, hereditary motor neuropathies show striking overlap with several other neuromuscular and neurological disorders. In this review, we provide a current overview of the genetic spectrum of hereditary motor neuropathies highlighting recent reports of novel genes and mutations or recent discoveries in the underlying disease mechanisms. In addition, we link hereditary motor neuropathies with various related disorders by addressing the main affected pathways of disease divided into five major processes: axonal transport, tRNA aminoacylation, RNA metabolism and DNA integrity, ion channels and transporters and endoplasmic reticulum.

Crosstalk between Different DNA Repair Pathways Contributes to Neurodegenerative Diseases

Simple Summary

Constant exposure to endogenous and environmental factors induces oxidative stress and DNA damage. Rare brain disorders caused by defects in DNA repair and DNA damage response (DDR) signaling establish that failure to process DNA damage may lead to neurodegeneration. In this review, we present mechanisms that link DDR with neurodegeneration in these disorders and discuss their relevance for common age-related neurodegenerative diseases (NDDs). Moreover, we highlight recent insight into the crosstalk between the DDR and other cellular processes known to be disturbed during NDDs.

Abstract

Genomic integrity is maintained by DNA repair and the DNA damage response (DDR). Defects in certain DNA repair genes give rise to many rare progressive neurodegenerative diseases (NDDs), such as ocular motor ataxia, Huntington disease (HD), and spinocerebellar ataxias (SCA). Dysregulation or dysfunction of DDR is also proposed to contribute to more common NDDs, such as Parkinson’s disease (PD), Alzheimer’s disease (AD), and Amyotrophic Lateral Sclerosis (ALS). Here, we present mechanisms that link DDR with neurodegeneration in rare NDDs caused by defects in the DDR and discuss the relevance for more common age-related neurodegenerative diseases. Moreover, we highlight recent insight into the crosstalk between the DDR and other cellular processes known to be disturbed during NDDs. We compare the strengths and limitations of established model systems to model human NDDs, ranging from C. elegans and mouse models towards advanced stem cell-based 3D models.

Epigenetics of Alzheimer's Disease

There are currently no validated biomarkers which can be used to accurately diagnose Alzheimer’s disease (AD) or to distinguish it from other dementia-causing neuropathologies. Moreover, to date, only symptomatic treatments exist for this progressive neurodegenerative disorder. In the search for new, more reliable biomarkers and potential therapeutic options, epigenetic modifications have emerged as important players in the pathogenesis of AD. The aim of the article was to provide a brief overview of the current knowledge regarding the role of epigenetics (including mitoepigenetics) in AD, and the possibility of applying these advances for future AD therapy. Extensive research has suggested an important role of DNA methylation and hydroxymethylation, histone posttranslational modifications, and non-coding RNA regulation (with the emphasis on microRNAs) in the course and development of AD. Recent studies also indicated mitochondrial DNA (mtDNA) as an interesting biomarker of AD, since dysfunctions in the mitochondria and lower mtDNA copy number have been associated with AD pathophysiology. The current evidence suggests that epigenetic changes can be successfully detected, not only in the central nervous system, but also in the cerebrospinal fluid and on the periphery, contributing further to their potential as both biomarkers and therapeutic targets in AD.

Poly (ADP-ribose) polymerase 1 and Parkinson's disease: A study in post-mortem human brain

Poly (ADP-ribose) polymerase 1 (PARP1) is crucial in both maintenance of genome integrity and cell death. PARP1 activation has been very recently linked to Parkinson's disease (PD) and its role in inducing the pathologic accumulation of α-Synuclein demonstrated in a PD mouse model. The objective of this study was to investigate the presence and localization of PARP1 in PD brain. PARP1 localization was assessed by immunostaining and confocal microscopy in post-mortem human brains obtained from PD patients (Braak stage VI) compared to controls. PARP1 positive nuclei in substantia nigra, mainly in dopaminergic neurons but also in astrocytes and oligodendrocytes, were decreased in PD. The same alteration was observed in several areas that are affected in PD pathology, namely the dorsal motor nucleus of vagus, frontal and cingulate cortex, whereas no changes in PARP1 staining were detectable in the inferior olivary nucleus that is unaffected in PD. In addition, PARP1 co-localizes with α-Synuclein that is accumulated in the cytoplasm and in Lewy bodies of PD tissue sections. Our data reveal previously unknown changes of PARP1 localization in the brain of PD patients, in both neurons and glia, supporting its widespread involvement in this pathology and its potential use as a therapeutic target.

Protective effects of PARP1-inhibitory compound in dry age-related macular degeneration

Poly (ADP-ribose) polymerase 1 (PARP1)-dependent cell death in the retinal pigment epithelium (RPE) is implicated in dry age-related macular degeneration (AMD). Although PARP1 inhibitors are available for treating dry AMD, their delivery route is not ideal for patients. The aim of this study was to test the efficacy of a novel PARP1-inhibitory compound (PIC) in vitro and in vivo. This study presents PIC, a novel small molecule, with superior efficacy to PARP1 inhibitors in the market. PIC demonstrated a distinctive inhibitory profile against PARP isotypes than the FDA-approved PARP1 inhibitors. PIC inhibited PARP1 activation at an IC50 of 0.41 ± 0.15 nM in an enzyme-based assay in vitro and at IC50 and EC50 in ARPE-19 cells of 0.11 ± 0.02 nM and 0.22 ± 0.02 nM, respectively, upon H2O2 insult. PIC also moderated mitochondrial fission and depolarization and maintained cellular energy levels under oxidative stress in ARPE-19 cells. Furthermore, PIC demonstrated good corneal penetration in a rat model, presenting PIC as a promising candidate for eye drop therapeutics for dry AMD. When PIC was administered as an eye drop formulation, RPE morphology was preserved, maintaining the thickness of the outer nuclear layers under sodium iodate (SI) treatment in rats. In SI-treated rabbits, eye drop administration of PIC also retained the structural and functional integrity when analyzed using funduscopy and electroretinogram. Collectively, our data portray PIC as an attractive treatment measure for dry AMD.

DNA Repair in Huntington's Disease and Spinocerebellar Ataxias: Somatic Instability and Alternative Hypotheses

The use of genome wide association studies (GWAS) in Huntington's disease (HD) research, driven by unbiased human data analysis, has transformed the focus of new targets that could affect age at onset. While there is a significant depth of information on DNA damage repair, with many drugs and drug targets, most of this development has taken place in the context of cancer therapy. DNA damage repair in neurons does not rely on DNA replication correction mechanisms. However, there is a strong connection between DNA repair and neuronal metabolism, mediated by nucleotide salvaging and the poly ADP-ribose (PAR) response, and this connection has been implicated in other age-onset neurodegenerative diseases. Validation of leads including the mismatch repair protein MSH3, and interstrand cross-link repair protein FAN1, suggest the mechanism is driven by somatic CAG instability, which is supported by the protective effect of CAA substitutions in the CAG tract. We currently do not understand: how somatic instability is triggered; the state of DNA damage within expanding alleles in the brain; whether this damage induces mismatch repair and interstrand cross-link pathways; whether instability mediates toxicity, and how this relates to human ageing. We discuss DNA damage pathways uncovered by HD GWAS, known roles of other polyglutamine disease proteins in DNA damage repair, and a panel of hypotheses for pathogenic mechanisms.

A unifying mechanism of ketogenic diet action: The multiple roles of nicotinamide adenine dinucleotide

The ability of a ketogenic diet to treat seizures and render a neuronal network more resistant to strong electrical activity has been observed for a century in clinics and for decades in research laboratories. Alongside ongoing efforts to understand how this therapy works to stop seizures, metabolic health is increasingly appreciated as critical buffer to resisting and recovering from acute and chronic disease. Accordingly, links between metabolism and health, and the broader emerging impact of the ketogenic diet in improving diverse metabolic, immunological and neurological conditions, have served to intensify the search for its key and/or common mechanisms. Here we review diverse evidence for increased levels of NAD⁺, and thus an altered ratio of NAD⁺/NADH, during metabolic therapy with a ketogenic diet. We propose this as a potential unifying mechanism, and highlight some of the evidence linking altered NAD⁺/NADH with reduced seizures and with a range of short and long-term changes associated with the beneficial effects of a ketogenic diet. An increase in NAD⁺/NADH is consistent with multiple lines of evidence and hypotheses, and therefore we suggest that increased NAD⁺ may be a common mechanism underlying beneficial effects of ketogenic diet therapy.

Nicotinamide, a Poly [ADP-Ribose] Polymerase 1 (PARP-1) Inhibitor, as an Adjunctive Therapy for the Treatment of Alzheimer's Disease

Nicotinamide (vitamin B3) is a key component in the cellular production of Nicotinamide Adenine Dinucleotide (NAD) and has long been associated with neuronal development, survival and death. Numerous data suggest that nicotinamide may offer therapeutic benefits in neurodegenerative disorders, including Alzheimer’s Disease (AD). Beyond its effect in NAD⁺ stores, nicotinamide is an inhibitor of Poly [ADP-ribose] polymerase 1 (PARP-1), an enzyme with multiple cellular functions, including regulation of cell death, energy/metabolism and inflammatory response. PARP-1 functions as a DNA repair enzyme but under intense DNA damage depletes the cell of NAD⁺ and ATP and leads to a non-apoptotic type of cell death called Parthanatos, which has been associated with the pathogenesis of neurodegenerative diseases. Moreover, NAD⁺ availability might potentially improve mitochondrial function, which is severely impaired in AD. PARP-1 inhibition may also exert a protective effect against neurodegeneration by its action to diminish neuroinflammation and microglial activation which are also implicated in the pathogenesis of AD. Here we discuss the evidence supporting the use of nicotinamide as adjunctive therapy for the treatment of early stages of AD based on the inhibitory effect of nicotinamide on PARP-1 activity. The data support evaluating nicotinamide as an adjunctive treatment for AD at early stages of the disease not only to increase NAD⁺ stores but as a PARP-1 inhibitor, raising the hypothesis that other PARP-1 inhibitors – drugs that are already approved for breast cancer treatment – might be explored for the treatment of AD.

New Insights for nicotinamide: Metabolic disease, autophagy, and mTOR

Metabolic disorders, such as diabetes mellitus (DM), are increasingly becoming significant risk factors for the health of the global population and consume substantial portions of the gross domestic product of all nations. Although conventional therapies that include early diagnosis, nutritional modification of diet, and pharmacological treatments may limit disease progression, tight serum glucose control cannot prevent the onset of future disease complications. With these concerns, novel strategies for the treatment of metabolic disorders that involve the vitamin nicotinamide, the mechanistic target of rapamycin (mTOR), mTOR Complex 1 (mTORC1), mTOR Complex 2 (mTORC2), AMP activated protein kinase (AMPK), and the cellular pathways of autophagy and apoptosis offer exceptional promise to provide new avenues of treatment. Oversight of these pathways can promote cellular energy homeostasis, maintain mitochondrial function, improve glucose utilization, and preserve pancreatic beta-cell function. Yet, the interplay among mTOR, AMPK, and autophagy pathways can be complex and affect desired clinical outcomes, necessitating further investigations to provide efficacious treatment strategies for metabolic dysfunction and DM.

Nicotinamide Riboside-The Current State of Research and Therapeutic Uses

Nicotinamide riboside (NR) has recently become one of the most studied nicotinamide adenine dinucleotide (NAD+) precursors, due to its numerous potential health benefits mediated via elevated NAD+ content in the body. NAD+ is an essential coenzyme that plays important roles in various metabolic pathways and increasing its overall content has been confirmed as a valuable strategy for treating a wide variety of pathophysiological conditions. Accumulating evidence on NRs' health benefits has validated its efficiency across numerous animal and human studies for the treatment of a number of cardiovascular, neurodegenerative, and metabolic disorders. As the prevalence and morbidity of these conditions increases in modern society, the great necessity has arisen for a rapid translation of NR to therapeutic use and further establishment of its availability as a nutritional supplement. Here, we summarize currently available data on NR effects on metabolism, and several neurodegenerative and cardiovascular disorders, through to its application as a treatment for specific pathophysiological conditions. In addition, we have reviewed newly published research on the application of NR as a potential therapy against infections with several pathogens, including SARS-CoV-2. Additionally, to support rapid NR translation to therapeutics, the challenges related to its bioavailability and safety are addressed, together with the advantages of NR to other NAD+ precursors.

Pharmacological inhibition of poly (ADP-ribose) polymerase by olaparib, prevents acute lung injury associated cognitive deficits potentially through suppression of inflammatory response

Acute lung injury (ALI) has been reported to be associated with high mortality rate. Moreover, ALI survivors, frequently present chronic cognitive deterioration. We have previously shown that 'two hit' (hydrochloric acid + lipopolysaccharide) induced ALI resulted in cognitive dysfunction through the induction of systemic inflammation. The present study was designed to explore the potential anti-inflammatory effects of olaparib (Poly ADP-ribose polymerase-1 inhibitor), on ALI mediated cognitive impairment. Olaparib was administered at dose of 5 mg/kg body weight (i.p.) 30 min before each hit. Data show that olaparib pre-treatment markedly reduced the neutrophil infiltration, alveolar capillary damage, inflammatory cytokines level (TNF-α/IL-1β/IL-6) and oxidative stress in the lungs at 24 h after ALI induction. Also, olaparib pre-treatment ameliorated the ALI associated cognitive impairment as assessed by Morris water maze test on weekly basis for 2 consecutive weeks. Further, restoration of cognitive function was associated with normalization of serum levels of TNF-α/IL-1β and improved the blood brain barrier (BBB) function, as reflected by data on expression of occludin/claudin-5 and extravasation of Evans-blue/FITC dextran in hippocampus at 1 week post injury. Finally, increased mRNA expression of VCAM-1, TNF-α and IL-1β and NF-κB activation in hippocampus indicate induction of neuro-inflammation, which was downregulated upon olaparib administration. Further, olaparib treatment 1 week after ALI induction blunted the systemic inflammation which was associated with improved BBB and cognitive function. Altogether, our results showed that olaparib protects against ALI and associated cognitive deficits in mice, and thus may offer a new treatment avenue in the area.

Oxidative Stress in Cognitive and Epigenetic Aging: A Retrospective Glance

Brain aging is the critical and common factor among several neurodegenerative disorders and dementia. Cellular, biochemical and molecular studies have shown intimate links between oxidative stress and cognitive dysfunction during aging and age-associated neuronal diseases. Brain aging is accompanied by oxidative damage of nuclear as well as mitochondrial DNA, and diminished repair. Recent studies have reported epigenetic alterations during aging of the brain which involves reactive oxygen species (ROS) that regulates various systems through distinct mechanisms. However, there are studies which depict differing roles of reactive oxidant species as a major factor during aging. In this review, we describe the evidence to show how oxidative stress is intricately linked to age-associated cognitive decline. The review will primarily focus on implications of age-associated oxidative damage on learning and memory, and the cellular events, with special emphasis on associated epigenetic machinery. A comprehensive understanding of these mechanisms may provide a perspective on the development of potential therapeutic targets within the oxidative system.