Aaron M. Swomley

Amyloid β-Peptide (1–42)-Induced Oxidative Stress in Alzheimer Disease: Importance in Disease Pathogenesis and Progression

SIGNIFICANCE Alzheimer disease (AD) is an age-related neurodegenerative disease. AD is characterized by progressive cognitive impairment. One of the main histopathological hallmarks of AD brain is the presence of senile plaques (SPs) and another is elevated oxidative stress. The main component of SPs is amyloid beta-peptide (Aβ) that is derived from the proteolytic cleavage of amyloid precursor protein. RECENT ADVANCES Recent studies are consistent with the notion that methionine present at 35 position of Aβ is critical to Aβ-induced oxidative stress and neurotoxicity. Further, we also discuss the signatures of oxidatively modified brain proteins, identified using redox proteomics approaches, during the progression of AD. CRITICAL ISSUES The exact relationships of the specifically oxidatively modified proteins in AD pathogenesis require additional investigation. FUTURE DIRECTIONS Further studies are needed to address whether the therapies directed toward brain oxidative stress and oxidatively modified key brain proteins might help delay or prevent the progression of AD.

Abeta, oxidative stress in Alzheimer disease: evidence based on proteomics studies.

The initiation and progression of Alzheimer disease (AD) is a complex process not yet fully understood. While many hypotheses have been provided as to the cause of the disease, the exact mechanisms remain elusive and difficult to verify. Proteomic applications in disease models of AD have provided valuable insights into the molecular basis of this disorder, demonstrating that on a protein level, disease progression impacts numerous cellular processes such as energy production, cellular structure, signal transduction, synaptic function, mitochondrial function, cell cycle progression, and proteasome function. Each of these cellular functions contributes to the overall health of the cell, and the dysregulation of one or more could contribute to the pathology and clinical presentation in AD. In this review, foci reside primarily on the amyloid β-peptide (Aβ) induced oxidative stress hypothesis and the proteomic studies that have been conducted by our laboratory and others that contribute to the overall understanding of this devastating neurodegenerative disease.

Oxidative stress in Alzheimer disease and mild cognitive impairment: evidence from human data provided by redox proteomics.

Alzheimer disease (AD) is a neurodegenerative disease with many known pathological features, yet there is still much debate into the exact cause and mechanisms for progression of this degenerative disorder. The amyloid-beta (Aβ)-induced oxidative stress hypothesis postulates that it is the oligomeric Aβ that inserts into membrane systems to initiate much of the oxidative stress observed in brain during the progression of the disease. In order to study the effects of oxidative stress on tissue from patients with AD and amnestic mild cognitive impairment (MCI), we have developed a method called redox proteomics that identifies specific brain proteins found to be selectively oxidized. Here, we discuss experimental findings of oxidatively modified proteins involved in three key cellular processes implicated in the pathogenesis of AD progression: energy metabolism, cell signaling and neurotransmission, as well as the proteasomal degradation pathways and antioxidant response systems. These proteomics studies conducted by our laboratory and others in the field shed light on the molecular changes imposed on the cells of AD and MCI brain, through the deregulated increase in oxidative/nitrosative stress inflicted by Aβ and mitochondrial dysfunction.

Apolipoprotein A-I: Insights from Redox Proteomics for its Role in Neurodegeneration

Proteomics has a wide range of applications, including determination of differences in the proteome in terms of expression and post‐translational protein modifications. Redox proteomics allows the identification of specific targets of protein oxidation in a biological sample. Using proteomic techniques, apolipoprotein A‐I (ApoA‐I) has been found at decreased levels in subjects with a variety of neurodegenerative disorders including in the serum and cerebrospinal fluid (CSF) of Alzheimer disease (AD), Parkinson disease (PD), and Down syndrome (DS) with gout subjects. ApoA‐I plays roles in cholesterol transport and regulation of inflammation. Redox proteomics further showed ApoA‐I to be highly oxidatively modified and particularly susceptible to modification by 4‐hydroxy‐2‐trans‐nonenal (HNE), a lipid peroxidation product. In the current review, we discuss the consequences of oxidation of ApoA‐I in terms of neurodegeneration. ROS‐associated chemotherapy related ApoA‐I oxidation leads to elevation of peripheral levels of tumor necrosis factor‐α (TNF‐α) that can cross the blood‐brain barrier (BBB) causing a signaling cascade that can contribute to neuronal death, likely a contributor to what patients refer to as “chemobrain.” Current evidence suggests ApoA‐I to be a promising diagnostic marker as well as a potential target for therapeutic strategies in these neurodegenerative disorders.

Cell Cycle Proteins in Brain in Mild Cognitive Impairment: Insights into Progression to Alzheimer Disease

Recent studies have demonstrated the re-emergence of cell cycle proteins in brain as patients progress from the early stages of mild cognitive impairment (MCI) into Alzheimer’s disease (AD). Oxidative stress markers present in AD have also been shown to be present in MCI brain suggesting that these events occur in early stages of the disease. The levels of key cell cycle proteins, such as CDK2, CDK5, cyclin G1, and BRAC1 have all been found to be elevated in MCI brain compared to age-matched control. Further, peptidyl prolyl cis–trans isomerase (Pin1), a protein that plays an important role in regulating the activity of key proteins, such as CDK5, GSK3-β, and PP2A that are involved in both the phosphorylation state of Tau and in the cell cycle, has been found to be oxidatively modified and downregulated in both AD and MCI brain. Hyperphosphorylation of Tau then results in synapse loss and the characteristic Tau aggregation as neurofibrillary tangles, an AD hallmark. In this review, we summarized the role of cell cycle dysregulation in the progression of disease from MCI to AD. Based on the current literature, it is tempting to speculate that a combination of oxidative stress and cell cycle dysfunction conceivably leads to neurodegeneration.

Pin1 cysteine-113 oxidation inhibits its catalytic activity and cellular function in Alzheimer's disease.

The unique proline isomerase Pin1 is pivotal for protecting against age-dependent neurodegeneration in Alzheimers disease (AD), with its inhibition providing a molecular link between tangle and plaque pathologies. Pin1 is oxidatively modified in human AD brains, but little is known about its regulatory mechanisms and pathological significance of such Pin1 modification. In this paper, our determination of crystal structures of oxidized Pin1 reveals a series of Pin1 oxidative modifications on Cys113 in a sequential fashion. Cys113 oxidization is further confirmed by generating antibodies specifically recognizing oxidized Cys113 of Pin1. Furthermore, Pin1 oxidation on Cys113 inactivates its catalytic activity in vitro, and Ala point substitution of Cys113 inactivates the ability of Pin1 to isomerize tau as well as to promote protein turnover of tau and APP. Moreover, redox regulation affects Pin1 subcellular localization and Pin1-mediated neuronal survival in response to hypoxia treatment. Importantly, Cys113-oxidized Pin1 is significantly increased in human AD brain comparing to age-matched controls. These results not only identify a novel Pin1 oxidation site to be the critical catalytic residue Cys113, but also provide a novel oxidative regulation mechanism for inhibiting Pin1 activity in AD. These results suggest that preventing Pin1 oxidization might help to reduce the risk of AD.

Age-related Changes in the Proteostasis Network in the Brain of the Naked Mole-Rat: Implications Promoting Healthy Longevity

The naked mole-rat (NMR) is the longest-lived rodent and possesses several exceptional traits: marked cancer resistance, negligible senescence, prolonged genomic integrity, pronounced proteostasis, and a sustained health span. The underlying molecular mechanisms that contribute to these extraordinary attributes are currently under investigation to gain insights that may conceivably promote and extend human health span and lifespan. The ubiquitin-proteasome and autophagy-lysosomal systems play a vital role in eliminating cellular detritus to maintain proteostasis and have been previously shown to be more robust in NMRs when compared with shorter-lived rodents. Using a 2-D PAGE proteomics approach, differential expression and phosphorylation levels of proteins involved in proteostasis networks were evaluated in the brains of NMRs in an age-dependent manner. We identified 9 proteins with significantly altered levels and/or phosphorylation states that have key roles involved in proteostasis networks. To further investigate the possible role that autophagy may play in maintaining cellular proteostasis, we examined aspects of the PI3K/Akt/mammalian target of rapamycin (mTOR) axis as well as levels of Beclin-1, LC3-I, and LC3-II in the brain of the NMR as a function of age. Together, these results show that NMRs maintain high levels of autophagy throughout the majority of their lifespan and may contribute to the extraordinary health span of these rodents. The potential of augmenting human health span via activating the proteostasis network will require further studies.

Metabolic clues to salubrious longevity in the brain of the longest-lived rodent: The naked mole-rat

Naked mole‐rats (NMRs) are the oldest‐living rodent species. Living underground in a thermally stable ecological niche, NMRs have evolved certain exceptional traits, resulting in sustained health spans, negligible cognitive decline, and a pronounced resistance to age‐related disease. Uncovering insights into mechanisms underlying these extraordinary traits involved in successful aging may conceivably provide crucial clues to extend the human life span and health span. One of the most fundamental processes inside the cell is the production of ATP, which is an essential fuel in driving all other energy‐requiring cellular activities. Not surprisingly, a prominent hallmark in age‐related diseases, such as neurodegeneration and cancer, is the impairment and dysregulation of metabolic pathways. Using a two‐dimensional polyacrylamide gel electrophoresis proteomics approach, alterations in expression and phosphorylation levels of metabolic proteins in the brains of NMRs, aged 2–24 years, were evaluated in an age‐dependent manner. We identified 13 proteins with altered levels and/or phosphorylation states that play key roles in various metabolic pathways including glycolysis, β‐oxidation, the malate‐aspartate shuttle, the Tricarboxylic Acid Cycle (TCA) cycle, the electron transport chain, NADPH production, as well as the production of glutamate. New insights into potential pathways involved in metabolic aspects of successful aging have been obtained by the identification of key proteins through which the NMR brain responds and adapts to the aging process and how the NMR brain adapted to resist age‐related degeneration.

Comparative proteomic analyses of the parietal lobe from rhesus monkeys fed a high-fat/sugar diet with and without resveratrol supplementation, relative to a healthy diet: Insights into the roles of unhealthy diets and resveratrol on function

A diet consisting of a high intake of saturated fat and refined sugars is characteristic of a Western-diet and has been shown to have a substantial negative effect on human health. Expression proteomics were used to investigate changes to the parietal lobe proteome of rhesus monkeys consuming either a high fat and sugar (HFS) diet, a HFS diet supplemented with resveratrol (HFS+RSV), or a healthy control diet for 2 years. Here we discuss the modifications in the levels of 12 specific proteins involved in various cellular systems including metabolism, neurotransmission, structural integrity, and general cellular signaling following a nutritional intervention. Our results contribute to a better understanding of the mechanisms by which resveratrol functions through the up- or down-regulation of proteins in different cellular sub-systems to affect the overall health of the brain.

Brain Oxidative Stress in the Pathogenesis and Progression of Alzheimer’s Disease

Alzheimer’s disease is an age-related neurodegenerative disease and is characterized by the presence of senile plaques (SP), neurofibrillary tangles, and synapse loss. Amyloid-beta, one of the main components of SP, has been known to induce oxidative stress and is highly toxic. Using redox proteomics approaches a number of oxidatively modified proteins were identified in AD and mild cognitive impairment (MCI) brain that are consistent with the clinical presentation, pathology, and biochemistry. The identification of key proteins that are highly susceptible to amyloid-beta-mediated oxidation might serve as biomarkers for use in diagnosing and also in the identification of therapeutic targets to prevent or delay this devastating disorder.