Redox proteomics in selected neurodegenerative disorders: from its infancy to future applications

Abstract Several studies demonstrated that oxidative damage is a characteristic feature of many neurodegenerative diseases. The accumulation of oxidatively modified proteins may disrupt cellular functions by affecting protein expression, protein turnover, cell signaling, and induction of apoptosis and necrosis, suggesting that protein oxidation could have both physiological and pathological significance. For nearly two decades, our laboratory focused particular attention on studying oxidative damage of proteins and how their chemical modifications induced by reactive oxygen species/reactive nitrogen species correlate with pathology, biochemical alterations, and clinical presentations of Alzheimer's disease. This comprehensive article outlines basic knowledge of oxidative modification of proteins and lipids, followed by the principles of redox proteomics analysis, which also involve recent advances of mass spectrometry technology, and its application to selected age-related neurodegenerative diseases. Redox proteomics results obtained in different diseases and animal models thereof may provide new insights into the main mechanisms involved in the pathogenesis and progression of oxidative-stress-related neurodegenerative disorders. Redox proteomics can be considered a multifaceted approach that has the potential to provide insights into the molecular mechanisms of a disease, to find disease markers, as well as to identify potential targets for drug therapy. Considering the importance of a better understanding of the cause/effect of protein dysfunction in the pathogenesis and progression of neurodegenerative disorders, this article provides an overview of the intrinsic power of the redox proteomics approach together with the most significant results obtained by our laboratory and others during almost 10 years of research on neurodegenerative disorders since we initiated the field of redox proteomics. Antioxid. Redox Signal. 17, 1610-1655.     

Redox proteomics in study of kidney-associated hypertension: new insights to old diseases

Abstract Significance: The kidney helps to maintain low blood pressure in the human body, and impaired kidney function is a common attribute of aging that is often associated with high blood pressure (hypertension). Kidney-related pathologies are important contributors (either directly or indirectly) to overall human mortality. In comparison with other organs, kidney has an unusually wide range of oxidative status, ranging from the well-perfused cortex to near-anoxic medulla. Recent Advances: Oxidative stress has been implicated in many kidney pathologies, especially chronic kidney disease, and there is considerable research interest in oxidative stress biomarkers for earlier prediction of disease onset. Proteomics approaches have been taken to study of human kidney tissue, serum/plasma, urine, and animal models of hypertension. Critical Issues: Redox proteomics, in which oxidative post-translational modifications can be identified in protein targets of oxidative or nitrosative stress, has not been very extensively pursued in this set of pathologies. Future Directions: Proteomics studies of kidney and related tissues have relevance to chronic kidney disease, and redox proteomics, in particular, represents an under-exploited toolkit for identification of novel biomarkers in this commonly occurring pathology. Antioxid. Redox Signal. 17, 1560-1570.     

Redox proteomics and the dynamic molecular landscape of the aging brain

It is well established that the risk to develop neurodegenerative disorders increases with chronological aging. Accumulating studies contributed to characterize the age-dependent changes either at gene and protein expression level which, taken together, show that aging of the human brain results from the combination of the normal decline of multiple biological functions with environmental factors that contribute to defining disease risk of late-life brain disorders. Finding the “way out” of the labyrinth of such complex molecular interactions may help to fill the gap between “normal” brain aging and development of age-dependent diseases. To this purpose, proteomics studies are a powerful tool to better understand where to set the boundary line of healthy aging and age-related disease by analyzing the variation of protein expression levels and the major post translational modifications that determine “protein” physio/pathological fate. Increasing attention has been focused on oxidative modifications due to the crucial role of oxidative stress in aging, in addition to the fact that this type of modification is irreversible and may alter protein function. Redox proteomics studies contributed to decipher the complexity of brain aging by identifying the proteins that were increasingly oxidized and eventually dysfunctional as a function of age.The purpose of this review is to summarize the most important findings obtained by applying proteomics approaches to murine models of aging with also a brief overview of some human studies, in particular those related to dementia.     

Redox albuminomics: oxidized albumin in human diseases

Abstract Significance: Albumin is the major contributor to colloid oncotic pressure and also serves as an important carrier protein of many endogenous and exogenous molecules throughout the body. In blood and extravascular fluids, albumin is susceptible to different oxidative modifications, especially thiol oxidation and carbonylation. Because of its metal-binding properties and the redox properties of its Cys34 thiol, albumin displays an important antioxidant activity. As albumin is the predominant protein in most body fluids, its Cys34 represents the largest fraction of free thiols within body fluids. Recent Advances: Evidence that albumin oxidation takes place in vivo has been reported only recently. Different redox proteomic, mass spectrometric, and chromatographic techniques have shown albumin redox modifications in various human pathophysiological conditions. As a whole, most data here presented demonstrate that massive albumin oxidation occurs in vivo in different biological fluids and, to some extent, that this process is correlated to organ dysfunction. Critical Issues: Recent reports suggest that the albumin redox state may serve as a global biomarker for the redox state in the body in various human diseases. However, further study is required to elucidate the exact relationship between albumin oxidation and pathology. In addition, it is unknown if some albumin oxidized forms may also have diagnostic uses. Future Directions: Application of specific redox proteomics techniques for the characterization of oxidized albumin forms in screening studies is required. A further challenge will be to analyze how these oxidative albumin modifications are related to real impact to the body. Antioxid. Redox Signal. 17, 1515-1527.     

4-hydroxy-2-nonenal, a reactive product of lipid peroxidation, and neurodegenerative diseases: a toxic combination illuminated by redox proteomics studies

Abstract Significance: Among different forms of oxidative stress, lipid peroxidation comprises the interaction of free radicals with polyunsaturated fatty acids, which in turn leads to the formation of highly reactive electrophilic aldehydes. Among these, the most abundant aldehydes are 4-hydroxy-2-nonenal (HNE) and malondialdehyde, while acrolein is the most reactive. HNE is considered a robust marker of oxidative stress and a toxic compound for several cell types. Proteins are particularly susceptible to modification caused by HNE, and adduct formation plays a critical role in multiple cellular processes. Recent Advances: With the outstanding progress of proteomics, the identification of putative biomarkers for neurodegenerative disorders has been the main focus of several studies and will continue to be a difficult task. Critical Issues: The present review focuses on the role of lipid peroxidation, particularly of HNE-induced protein modification, in neurodegenerative diseases. By comparing results obtained in different neurodegenerative diseases, it may be possible to identify both similarities and specific differences in addition to better characterize selective neurodegenerative phenomena associated with protein dysfunction. Results obtained in our laboratory and others support the common deregulation of energy metabolism and mitochondrial function in neurodegeneration. Future Directions: Research towards a better understanding of the molecular mechanisms involved in neurodegeneration together with identification of specific targets of oxidative damage is urgently required. Redox proteomics will contribute to broaden the knowledge in regard to potential biomarkers for disease diagnosis and may also provide insight into damaged metabolic networks and potential targets for modulation of disease progression. Antioxid. Redox Signal. 17, 1590-1609.     

S-glutathionylation: from molecular mechanisms to health outcomes

Redox homeostasis governs a number of critical cellular processes. In turn, imbalances in pathways that control oxidative and reductive conditions have been linked to a number of human disease pathologies, particularly those associated with aging. Reduced glutathione is the most prevalent biological thiol and plays a crucial role in maintaining a reduced intracellular environment. Exposure to reactive oxygen or nitrogen species is causatively linked to the disease pathologies associated with redox imbalance. In particular, reactive oxygen species can differentially oxidize certain cysteine residues in target proteins and the reversible process of S-glutathionylation may mitigate or mediate the damage. This post-translational modification adds a tripeptide and a net negative charge that can lead to distinct structural and functional changes in the target protein. Because it is reversible, S-glutathionylation has the potential to act as a biological switch and to be integral in a number of critical oxidative signaling events. The present review provides a comprehensive account of how the S-glutathionylation cycle influences protein structure/function and cellular regulatory events, and how these may impact on human diseases. By understanding the components of this cycle, there should be opportunities to intervene in stress- and aging-related pathologies, perhaps through prevention and diagnostic and therapeutic platforms.     

The disulfide proteome and other reactive cysteine proteomes: analysis and functional significance

Ten years ago, proteomics techniques designed for large-scale investigations of redox-sensitive proteins started to emerge. The proteomes, defined as sets of proteins containing reactive cysteines that undergo oxidative post-translational modifications, have had a particular impact on research concerning the redox regulation of cellular processes. These proteomes, which are hereafter termed "disulfide proteomes," have been studied in nearly all kingdoms of life, including animals, plants, fungi, and bacteria. Disulfide proteomics has been applied to the identification of proteins modified by reactive oxygen and nitrogen species under stress conditions. Other studies involving disulfide proteomics have addressed the functions of thioredoxins and glutaredoxins. Hence, there is a steadily growing number of proteins containing reactive cysteines, which are probable targets for redox regulation. The disulfide proteomes have provided evidence that entire pathways, such as glycolysis, the tricarboxylic acid cycle, and the Calvin-Benson cycle, are controlled by mechanisms involving changes in the cysteine redox state of each enzyme implicated. Synthesis and degradation of proteins are processes highly represented in disulfide proteomes and additional biochemical data have established some mechanisms for their redox regulation. Thus, combined with biochemistry and genetics, disulfide proteomics has a significant potential to contribute to new discoveries on redox regulation and signaling.     

Tyrosine modifications in aging

Abstract Significance: The understanding of physiological and pathological processes involving protein oxidation, particularly under conditions of aging and oxidative stress, can be aided by proteomic identification of proteins that accumulate oxidative post-translational modifications only if these detected modifications are connected to functional consequences. The modification of tyrosine (Tyr) residues can elicit significant changes in protein structure and function, which, in some cases, may contribute to biological aging and age-related pathologies, such as atherosclerosis, neurodegeneration, and cataracts. Recent Advances: Studies characterizing proteins in which Tyr has been modified to 3-nitrotyrosine, 3,4-dihydroxyphenylalanine, 3,3'-dityrosine and other cross-links, or 3-chlorotyrosine are reviewed, with an emphasis on structural and functional consequences. Critical Issues: Distinguishing between inconsequential modifications and functionally significant ones requires careful biochemical and biophysical analysis of target proteins, as well as innovative methods for isolating the effects of the multiple modifications that often occur under oxidizing conditions. Future Directions: The labor-intensive task of isolating and characterizing individual modified proteins must continue, especially given the expanding list of known modifications. Emerging approaches, such as genetic and metabolic incorporation of unnatural amino acids, hold promise for additional focused studies of this kind. Antioxid. Redox Signal. 17, 1571-1579.     

Thioredoxin 1-mediated post-translational modifications: reduction, transnitrosylation, denitrosylation, and related proteomics methodologies

Despite the significance of redox post-translational modifications (PTMs) in regulating diverse signal transduction pathways, the enzymatic systems that catalyze reversible and specific oxidative or reductive modifications have yet to be firmly established. Thioredoxin 1 (Trx1) is a conserved antioxidant protein that is well known for its disulfide reductase activity. Interestingly, Trx1 is also able to transnitrosylate or denitrosylate (defined as processes to transfer or remove a nitric oxide entity to/from substrates) specific proteins. An intricate redox regulatory mechanism has recently been uncovered that accounts for the ability of Trx1 to catalyze these different redox PTMs. In this review, we will summarize the available evidence in support of Trx1 as a specific disulfide reductase, and denitrosylation and transnitrosylation agent, as well as the biological significance of the diverse array of Trx1-regulated pathways and processes under different physiological contexts. The dramatic progress in redox proteomics techniques has enabled the identification of an increasing number of proteins, including peroxiredoxin 1, whose disulfide bond formation and nitrosylation status are regulated by Trx1. This review will also summarize the advancements of redox proteomics techniques for the identification of the protein targets of Trx1-mediated PTMs. Collectively, these studies have shed light on the mechanisms that regulate Trx1-mediated reduction, transnitrosylation, and denitrosylation of specific target proteins, solidifying the role of Trx1 as a master regulator of redox signal transduction.     

Thiol-disulfide balance: from the concept of oxidative stress to that of redox regulation

Originally, small thiols, including glutathione, were viewed as protective antioxidants, acting as free radical scavengers in the context of oxidative damage. Recently, there is a growing literature showing that protein glutathionylation (formation of protein-glutathione mixed disulfides) and other forms of cysteine oxidation may be a means of redox regulation under physiological conditions. This review discusses the importance of protein oxidation in redox regulation in view of the recent data originating from the application of redox proteomics to identify redox-sensitive targets.     

Redox proteomics identification of oxidized proteins in Alzheimer's disease hippocampus and cerebellum: an approach to understand pathological and biochemical alterations in AD

Alzheimer's disease (AD) is characterized by the presence of neurofibrillary tangles, senile plaques and loss of synapses. There is accumulating evidence that oxidative stress plays an important role in AD pathophysiology. Previous redox proteomics studies from our laboratory on AD inferior parietal lobule led to the identification of oxidatively modified proteins that were consistent with biochemical or pathological alterations in AD. The present study was focused on the identification of specific targets of protein oxidation in AD and control hippocampus and cerebellum using a redox proteomics approach. In AD hippocampus, peptidyl prolyl cis-trans isomerase, phosphoglycerate mutase 1, ubiquitin carboxyl terminal hydrolase 1, dihydropyrimidinase related protein-2 (DRP-2), carbonic anhydrase II, triose phosphate isomerase, alpha-enolase, and gamma-SNAP were identified as significantly oxidized protein with reduced enzyme activities relative to control hippocampus. In addition, no significant excessively oxidized protein spots were identified in cerebellum compared to control, consistent with the lack of pathology in this brain region in AD. The identification of oxidatively modified proteins in AD hippocampus was verified by immunochemical means. The identification of common oxidized proteins in different brain regions of AD brain suggests a potential role for these oxidized proteins and thereby oxidative stress in the pathogenesis of Alzheimer's disease.     

Redox reactions of hemoglobin

Redox reactions of hemoglobin have gained importance because of the general interest of the role of oxidative stress in diseases and the possible role of red blood cells in oxidative stress. Although electron paramagnetic resonance (EPR) is extremely valuable in studying hemoglobin redox reactions it has not been adequately used. We have focused in this review on the important contributions of EPR to our understanding of hemoglobin redox reactions. We have limited our discussion to the redox reactions thought to occur under physiological conditions. This includes autoxidation as well as the reactions of hydrogen peroxide generated by superoxide dismutation. We have also discussed redox reactions associated with nitric oxide produced in the circulation. We have pinpointed the value of using EPR to detect and study the paramagnetic species and free radicals formed during these reactions. We have shown how EPR not only identifies the paramagnetic species formed but can also be used to provide insights into the mechanism involved in the redox reactions.     

Redox Proteomics Analyses of the Influence of Co-Expression of Wild-Type or Mutated LRRK2 and Tau on C. elegans Protein Expression and Oxidative Modification: Relevance to Parkinson Disease

Abstract Aims: The human LRRK2 gene has been identified as the most common causative gene of autosomal-dominantly inherited and idiopathic Parkinson disease (PD). The G2019S substitution is the most common mutation in LRRK2. The R1441C mutation also occurs in cases of familial PD, but is not as prevalent. Some cases of LRRK2-based PD exhibit Tau pathology, which suggests that alterations on LRRK2 activity affect the pathophysiology of Tau. To investigate how LRRK2 might affect Tau and the pathophysiology of PD, we generated lines of C. elegans expressing human LRRK2 [wild-type (WT) or mutated (G2019S or R1441C)] with and without V337M Tau. Expression and redox proteomics were used to identify the effects of LRRK2 (WT and mutant) on protein expression and oxidative modifications. Results: Co-expression of WT LRRK2 and Tau led to increased expression of numerous proteins, including several 60S ribosomal proteins, mitochondrial proteins, and the V-type proton ATPase, which is associated with autophagy. C. elegans expressing mutant LRRK2 showed similar changes, but also showed increased protein oxidation and lipid peroxidation, the latter indexed as increased protein-bound 4-hydroxy-2-nonenal (HNE). Innovation: Our study brings new knowledge about the possible alterations induced by LRRK2 (WT and mutated) and Tau interactions, suggesting the involvement of G2019S and R1441C in Tau-dependent neurodegenerative processes. Conclusion: These results suggest that changes in LRRK2 expression or activity lead to corresponding changes in mitochondrial function, autophagy, and protein translation. These findings are discussed with reference to the pathophysiology of PD. Antioxid. Redox Signal. 17, 1490-1506.     

Epigenetic modifications in spinal ligament aging

Spinal stenosis is a common degenerative spine disorder in the aged population and the spinal ligament aging is a main contributor to this chronic disease. However, the underlying mechanisms of spinal ligament aging remain unclear. Epigenetics is the study of heritable and reversible changes in the function of a gene or genome that occur without any alteration in the primary DNA sequence. Epigenetic alterations have been demonstrated to play crucial roles in age-related diseases and conditions, and they are recently studied as biomarkers and therapeutic targets in the field of cancer research. The main epigenetic modifications, including DNA methylation alteration, histone modifications as well as dysregulated noncoding RNA modulation, have all been implicated in spinal ligament aging diseases. DNA methylation modulates the expression of critical genes including WNT5A, GDNF, ACSM5, miR-497 and miR-195 during spinal ligament degeneration. Histone modifications widely affect gene expression and obvious histone modification abnormalities have been found in spinal ligament aging. MicroRNAs (miRNAs), long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs) exert crucial regulating effects on spinal ligament aging conditions via targeting various osteogenic or fibrogenic differentiation related genes. To our knowledge, there is no systematic review yet to summarize the involvement of epigenetic mechanisms of spinal ligament aging in degenerative spinal diseases. In this study, we systematically discussed the different epigenetic modifications and their potential functions in spinal ligament aging process.     

Proteomics of Blood-Based Therapeutics

Blood-based therapeutics are cellular or plasma components derived from human blood. Their production requires appropriate selection and treatment of the donor and processing of cells or plasma proteins. In contrast to clearly defined, chemically synthesized drugs, blood-derived therapeutics are highly complex mixtures of plasma proteins or even more complex cells. Pathogen transmission by the product as well as changes in the integrity of blood constituents resulting in loss of function or immune modulation are currently important issues in transfusion medicine. Protein modifications can occur during various steps of the production process, such as acquisition, enrichment of separate components (e.g. coagulation factors, cell populations), virus inactivation, conservation, and storage. Contemporary proteomic strategies allow a comprehensive assessment of protein modifications with high coverage, offer capabilities for qualitative and even quantitative analysis, and for high-throughput protein identification. Traditionally, proteomics approaches predominantly relied on two-dimensional gel electrophoresis (2-DE). Even if 2-DE is still state of the art, it has inherent limitations that are mainly based on the physicochemical properties of the proteins analyzed; for example, proteins with extremes in molecular mass and hydrophobicity (most membrane proteins) are difficult to assess by 2-DE. These limitations have fostered the development of mass spectrometry centered on non-gel-based separation approaches, which have proven to be highly successful and are thus complementing and even partially replacing 2-DE-based approaches. Although blood constituents have been extensively analyzed by proteomics, this technology has not been widely applied to assess or even improve blood-derived therapeutics, or to monitor the production processes. As proteomic technologies have the capacity to provide comprehensive information about changes occurring during processing and storage of blood products, proteomics can potentially guide improvement of pathogen inactivation procedures and engineering of stem cells, and may also allow a better understanding of factors influencing the immunogenicity of blood-derived therapeutics. An important development in proteomics is the reduction of inter-assay variability. This now allows the screening of samples taken from the same product over time or before and after processing. Optimized preparation procedures and storage conditions will reduce the risk of protein alterations, which in turn may contribute to better recovery, reduced exposure to allogeneic proteins, and increased transfusion safety.     

Protein Targets of Oxidative Damage in Human Neurodegenerative Diseases with Abnormal Protein Aggregates

Human neurodegenerative diseases with abnormal protein aggregates are associated with aberrant post-translational modifications, solubility, aggregation and fibril formation of selected proteins which cannot be degraded by cytosolic proteases, ubiquitin–protesome system and autophagy, and, therefore, accumulate in cells and extracellular compartments as residual debris. In addition to the accumulation of “primary” proteins, several other mechanisms are involved in the degenerative process and probably may explain crucial aspects such as the timing, selective cellular vulnerability and progression of the disease in particular individuals. One of these mechanisms is oxidative stress, which occurs in the vast majority of, if not all, degenerative diseases of the nervous system. The present review covers most of the protein targets that have been recognized as modified proteins mainly using bidimensional gel electrophoresis, Western blotting with oxidative and nitrosative markers, and identified by mass spectrometry in Alzheimer disease; certain tauopathies such as progressive supranuclear palsy, Pick disease, argyrophilic grain disease and frontotemporal lobar degeneration linked to mutations in tau protein, for example, FTLD-tau, Parkinson disease and related α-synucleinopathies; Huntington disease; and amyotrophic lateral sclerosis, together with related animal and cellular models. Vulnerable proteins can be mostly grouped in defined metabolic pathways covering glycolysis and energy metabolism, cytoskeletal, chaperoning, cellular stress responses, and members of the ubiquitin–proteasome system. Available information points to the fact that vital metabolic pathways are hampered by protein oxidative damage in several human degenerative diseases and that oxidative damage occurs at very early stages of the disease. Yet parallel functional studies are limited and further work is needed to document whether protein oxidation results in loss of activity and impaired performance. A better understanding of proteins susceptible to oxidation and nitration may serve to define damaged metabolic networks at early stages of disease and to advance therapeutic interventions to attenuate disease progression.     

Proteomic identification of brain proteins in the canine model of human aging following a long-term treatment with antioxidants and a program of behavioral enrichment: relevance to Alzheimer's disease

Aging and age-related disorders such as Alzheimer's disease (AD) are usually accompanied by oxidative stress as one of the main mechanisms contributing to neurodegeneration and cognitive decline. Aging canines develop cognitive dysfunction and neuropathology similar to those seen in humans, and the use of antioxidants results in reductions in oxidative damage and in improvement in cognitive function in this canine model of human aging. In the present study, the effect of a long-term treatment with an antioxidant-fortified diet and a program of behavioral enrichment on oxidative damage was studied in aged canines. To identify the neurobiological mechanisms underlying these treatment effects, the parietal cortex from 23 beagle dogs (8.1-12.4 years) were treated for 2.8 years in one of four treatment groups: i.e., control food-control behavioral enrichment (CC); control food-behavioral enrichment (CE); antioxidant food-control behavioral enrichment (CA); enriched environment-antioxidant-fortified food (EA). We analyzed the levels of the oxidative stress biomarkers, i.e., protein carbonyls, 3-nitrotyrosine (3-NT), and the lipid peroxidation product, 4-hydroxynonenal (HNE), and observed a decrease in their levels on all treatments when compared to control, with the most significant effects found in the combined treatment, EA. Since EA treatment was most effective, we also carried out a comparative proteomics study to identify specific brain proteins that were differentially expressed and used a parallel redox proteomics approach to identify specific brain proteins that were less oxidized following EA. The specific protein carbonyl levels of glutamate dehydrogenase [NAD (P)], glyceraldehyde-3-phosphate dehydrogenase (GAPDH), alpha-enolase, neurofilament triplet L protein, glutathione-S-transferase (GST) and fascin actin bundling protein were significantly reduced in brain of EA-treated dogs compared to control. We also observed significant increases in expression of Cu/Zn superoxide dismutase, fructose-bisphosphate aldolase C, creatine kinase, glutamate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase. The increased expression of these proteins and in particular Cu/Zn SOD correlated with improved cognitive function. In addition, there was a significant increase in the enzymatic activities of glutathione-S-transferase (GST) and total superoxide dismutase (SOD), and significant increase in the protein levels of heme oxygenase (HO-1) in EA treated dogs compared to control. These findings suggest that the combined treatment reduces the levels of oxidative damage and improves the antioxidant reserve systems in the aging canine brain, and may contribute to improvements in learning and memory. These observations provide insights into a possible neurobiological mechanism underlying the effects of the combined treatment. These results support the combination treatments as a possible therapeutic approach that could be translated to the aging human population who are at risk for age-related neurodegenerative disorders, including Alzheimer's disease.     

Chronic inflammation – inflammaging – in the ageing cochlea: A novel target for future presbycusis therapy

Chronic, low-grade inflammation, or inflammaging, is a crucial contributor to various age-related pathologies and natural processes in aging tissue, including the nervous system. Over the past two decades, much effort has been done to understand the mechanisms of inflammaging in disease models such as type II diabetes, cardiovascular disease, Alzheimer’s disease, Parkinson’s disease, and others. However, despite being the most prevalent neurodegenerative disorder, the number one communication disorder, and one of the top three chronic medical conditions of our aged population; little research has been conducted on the potential role of inflammation in age-related hearing loss (ARHL). Recently, it has been suggested that there is an inflammatory presence in the cochlea, perhaps involving diffusion processes of the blood-brain barrier as it relates to the inner ear. Recent research has found correlations between hearing loss and markers such as C-reactive protein, IL-6, and TNF-α indicating inflammatory status in human case-cohort studies. However, there have been very few reports of in vivo research investigating the role of chronic inflammation’s in hearing loss in the aging cochlea. Future research directed at better understanding the mechanisms of inflammation in the cochlea as well as the natural changes acquired with aging may provide a better understanding of how this process can accelerate presbycusis. Animal model experimentation and pre-clinical studies designed to recognize and characterize cochlear inflammatory mechanisms may suggest novel treatment strategies for preventing or treating ARHL. In this review, we seek to summarize key research in chronic inflammation, discuss its implications for possible roles in ARHL, and finally suggest directions for future investigations.     

Proteomics in heart failure: top-down or bottom-up?

The pathophysiology of heart failure (HF) is diverse, owing to multiple etiologies and aberrations in a number of cellular processes. Therefore, it is essential to understand how defects in the molecular pathways that mediate cellular responses to internal and external stressors function as a system to drive the HF phenotype. Mass spectrometry (MS)-based proteomics strategies have great potential for advancing our understanding of disease mechanisms at the systems level because proteins are the effector molecules for all cell functions and, thus, are directly responsible for determining cell phenotype. Two MS-based proteomics strategies exist: peptide-based bottom-up and protein-based top-down proteomics—each with its own unique strengths and weaknesses for interrogating the proteome. In this review, we will discuss the advantages and disadvantages of bottom-up and top-down MS for protein identification, quantification, and analysis of post-translational modifications, as well as highlight how both of these strategies have contributed to our understanding of the molecular and cellular mechanisms underlying HF. Additionally, the challenges associated with both proteomics approaches will be discussed and insights will be offered regarding the future of MS-based proteomics in HF research.