Caspase-8 is required for cell death induced by expanded polyglutamine repeats

Microglia-mediated neuron death requires TNF and is exacerbated by mutant Huntingtin

Microglia, the resident immune cells of the brain, regulate the balance of inflammation in the central nervous system under healthy and pathogenic conditions. Huntington's disease (HD) is a chronic neurodegenerative disease characterized by activated microglia and elevated concentrations of pro-inflammatory cytokines within the brain. Chronic hyperactivation of microglia is associated with brain pathology and eventual neuron death. However, it is unclear which specific cytokines are required for neuron death and whether HD neurons may be hypersensitive to neuroinflammation. We assessed the profile of microglia-secreted proteins in response to LPS and IFNγ, and a conditioned media paradigm was used to examine the effects of these secreted proteins on cultured neuronal cells. STHdhQ7/Q7 and STHdhQ111/Q111 neuronal cells were used to model wild-type and HD neurons, respectively. We determined that STHdhQ111/Q111 cells were hypersensitive to pro-inflammatory factors secreted by microglia, and that TNF was required to induce neuronal death. Microglia-mediated neuronal death could be effectively halted through the use of JAK-STAT or TNF inhibitors which supported the requirement for TNF as well as IFNγ in the process of secondary neurotoxicity. Further data derived from human HD patients as well as HD mice were suggestive of enhanced receptor density for TNF (TNFR1) and IFNγ (IFNGR) which could sensitize the HD brain to these cytokines. This highlights several potential mechanisms by which microglia may induce neuronal death and suggests that these mechanisms may be upregulated in the brain of HD patients.

Significance of Programmed Cell Death Pathways in Neurodegenerative Diseases

Programmed cell death (PCD) is a form of cell death distinct from accidental cell death (ACD) and is also referred to as regulated cell death (RCD). Typically, PCD signaling events are precisely regulated by various biomolecules in both spatial and temporal contexts to promote neuronal development, establish neural architecture, and shape the central nervous system (CNS), although the role of PCD extends beyond the CNS. Abnormalities in PCD signaling cascades contribute to the irreversible loss of neuronal cells and function, leading to the onset and progression of neurodegenerative diseases. In this review, we summarize the molecular processes and features of different modalities of PCD, including apoptosis, necroptosis, pyroptosis, ferroptosis, cuproptosis, and other novel forms of PCD, and their effects on the pathogenesis of neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), multiple sclerosis (MS), traumatic brain injury (TBI), and stroke. Additionally, we examine the key factors involved in these PCD signaling pathways and discuss the potential for their development as therapeutic targets and strategies. Therefore, therapeutic strategies targeting the inhibition or facilitation of PCD signaling pathways offer a promising approach for clinical applications in treating neurodegenerative diseases.

A clinical study and future prospects for bioactive compounds and semi-synthetic molecules in the therapies for Huntington's disease

A neurodegenerative disorder (ND) refers to Huntington's disease (HD) which affects memory loss, weight loss, and movement dysfunctions such as chorea and dystonia. In the striatum and brain, HD most typically impacts medium-spiny neurons. Molecular genetics, excitotoxicity, oxidative stress (OS), mitochondrial, and metabolic dysfunction are a few of the theories advanced to explicit the pathophysiology of neuronal damage and cell death. Numerous in-depth studies of the literature have supported the therapeutic advantages of natural products in HD experimental models and other treatment approaches. This article briefly discusses the neuroprotective impacts of natural compounds against HD models. The ability of the discovered natural compounds to suppress HD was tested using either in vitro or in vivo models. Many bioactive compounds considerably lessened the memory loss and motor coordination brought on by 3-nitropropionic acid (3-NP). Reduced lipid peroxidation, increased endogenous enzymatic antioxidants, reduced acetylcholinesterase activity, and enhanced mitochondrial energy generation have profoundly decreased the biochemical change. It is significant since histology showed that therapy with particular natural compounds lessened damage to the striatum caused by 3-NP. Moreover, natural products displayed varying degrees of neuroprotection in preclinical HD studies because of their antioxidant and anti-inflammatory properties, maintenance of mitochondrial function, activation of autophagy, and inhibition of apoptosis. This study highlighted about the importance of bioactive compounds and their semi-synthetic molecules in the treatment and prevention of HD.

Depletion of muscularis macrophages ameliorates inflammation-driven dysmotility in murine colitis model

Previously, the presence of a blood-myenteric plexus barrier and its disruption was reported in experimentally induced colitis via a macrophage-dependent process. The aim of this study is to reveal how myenteric barrier disruption and subsequent neuronal injury affects gut motility in vivo in a murine colitis model. We induced colitis with dextran sulfate sodium (DSS), with the co-administration of liposome-encapsulated clodronate (L-clodronate) to simultaneously deplete blood monocytes contributing to macrophage infiltration in the inflamed muscularis of experimental mice. DSS-treated animals receiving concurrent L-clodronate injection showed significantly decreased blood monocyte numbers and colon muscularis macrophage (MM) density compared to DSS-treated control (DSS-vehicle). DSS-clodronate-treated mice exhibited significantly slower whole gut transit time than DSS-vehicle-treated animals and comparable to that of controls. Experiments with oral gavage-fed Evans-blue dye showed similar whole gut transit times in DSS-clodronate-treated mice as in control animals. Furthermore, qPCR-analysis and immunofluorescence on colon muscularis samples revealed that factors associated with neuroinflammation and neurodegeneration, including Bax1, Hdac4, IL-18, Casp8 and Hif1a are overexpressed after DSS-treatment, but not in the case of concurrent L-clodronate administration. Our findings highlight that MM-infiltration in the muscularis layer is responsible for colitis-associated dysmotility and enteric neuronal dysfunction along with the release of mediators associated with neurodegeneration in a murine experimental model.

Total recall: the role of PIDDosome components in neurodegeneration

The PIDDosome is a multiprotein complex that includes p53-induced protein with a death domain 1 (PIDD1), receptor-interacting protein-associated ICH-1/CED-3 homologous protein with a death domain (RAIDD), and caspase-2, the activation of which is driven by PIDDosome assembly. In addition to the key role of the PIDDosome in the regulation of cell differentiation, tissue homeostasis, and organogenesis and regeneration, caspase-2, RAIDD and PIDD1 engagement in neuronal development was shown. Here, we focus on the involvement of PIDDosome components in neurodegenerative disorders, including retinal neuropathies, different types of brain damage, and Alzheimer's disease (AD), Huntington's disease (HD), and Lewy body disease. We also discuss pathogenic variants of PIDD1, RAIDD, and caspase-2 that are associated with intellectual, behavioral, and psychological abnormalities, together with prospective PIDDosome inhibition strategies and their potential clinical application.

Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

Proteochemometrics modeling for prediction of the interactions between caspase isoforms and their inhibitors

Caspases (cysteine-aspartic proteases) play critical roles in inflammation and the programming of cell death in the form of necroptosis, apoptosis, and pyroptosis. The name of these enzymes has been chosen in accordance with their cysteine protease activity. They act as cysteines in nucleophilically active sites to attack and cleave target proteins in the aspartic acid and amino acid C-terminal. Based on the substrate's structure and the specificity, the physiological activity of caspases is divided. However, in apoptosis, the division of caspases into initiating caspases (caspase 2, 8, 9, and 10) and executive caspases (caspase 3, 6, and 7) is essential. The present study aimed to perform Proteochemometrics Modeling to generalize the data on caspases, which could predict ligand and protein interactions. In this study, we employed protein and ligand descriptors. Moreover, protein descriptors were computed using the Protr R package, while PADEL-Descriptor was employed for the computation of ligand descriptors. In addition, NCA (Neighborhood Component Analyses) was used for descriptor selection, and SVR, decision tree, and ensemble methods were utilized for the proteochemometrics modeling. This study shows that the ensemble model demonstrates superior performance compared with other models in terms of R², Q², and RMSE criteria.

Emerging Role of NLRP3 Inflammasome/Pyroptosis in Huntington's Disease

Huntington's disease (HD) is a neurodegenerative disease characterized by several symptoms encompassing movement, cognition, and behavior. The mutation of the IT15 gene encoding for the huntingtin protein is the cause of HD. Mutant huntingtin interacts with and impairs the function of several transcription factors involved in neuronal survival. Although many mechanisms determining neuronal death have been described over the years, the significant role of inflammation has gained momentum in the last decade. Drugs targeting the elements that orchestrate inflammation have been considered powerful tools to treat HD. In this review, we will describe the data supporting inflammasome and NLRP3 as a target of therapeutics to fight HD, deepening the possible mechanisms of action underlying these effects.

Involvement of molecular chaperone in protein-misfolding brain diseases

Protein misfolding causes aggregation and build-up in a variety of brain diseases. There are numeral molecules that are linked with the protein homeostasis mechanism. Molecular chaperones are one of such molecules that are responsible for protection against protein misfolded and aggregation-induced neurotoxicity. Many studies have explored the participation of molecular chaperones in Parkinson's disease, Alzheimer's disease, Amyotrophic lateral sclerosis, and Huntington's diseases. In this review, we highlighted the constructive role of molecular chaperones in neurological diseases characterized by protein misfolding and aggregation and their capability to control aberrant protein interactions at an early stage thus successfully suppressing pathogenic cascades. A comprehensive understanding of the protein misfolding associated with brain diseases and the molecular basis of involvement of chaperone against aggregation-induced cellular stress might lead to the progress of new therapeutic intrusion-related to protein misfolding and aggregation.

Apoptosis in health and diseases of the eye and brain

Apoptosis is a form of programmed cell death (PCD) and enables the immunologically silent disposal of senescent or unwanted cells, causing minimal damage to the surrounding environment. Apoptosis can occur via intrinsic or extrinsic pathways that initiate a series of intracellular and extracellular signaling events. This ultimately leads to the clearance of the cell by phagocytes. This normal physiological mechanism may be accelerated in several diseases including those involving the eyes and brain, leading to loss of structure and function. This review presents the role of PCD in the health of the eyes and brain, and the evidence presented for its aberrant role in disease.

Early deficits in olfaction are associated with structural and molecular alterations in the olfactory system of a Huntington disease mouse model

Olfactory dysfunction and altered neurogenesis are observed in several neurodegenerative disorders including Huntington disease (HD). These deficits occur early and correlate with a decline in global cognitive performance, depression and structural abnormalities of the olfactory system including the olfactory epithelium, bulb and cortices. However, the role of olfactory system dysfunction in the pathogenesis of HD remains poorly understood and the mechanisms underlying this dysfunction are unknown. We show that deficits in odour identification, discrimination and memory occur in HD individuals. Assessment of the olfactory system in an HD murine model demonstrates structural abnormalities in the olfactory bulb (OB) and piriform cortex, the primary cortical recipient of OB projections. Furthermore, a decrease in piriform neuronal counts and altered expression levels of neuronal nuclei and tyrosine hydroxylase in the OB are observed in the YAC128 HD model. Similar to the human HD condition, olfactory dysfunction is an early phenotype in the YAC128 mice and concurrent with caspase activation in the murine HD OB. These data provide a link between the structural olfactory brain region atrophy and olfactory dysfunction in HD and suggest that cell proliferation and cell death pathways are compromised and may contribute to the olfactory deficits in HD.

Multiple roles of caspase-8 in cell death, inflammation, and innate immunity

Caspase-8 is an apical caspase involved in the programmed form of cell death called apoptosis that is critically important for mammalian development and immunity. Apoptosis was historically described as immunologically silent in contrast to other types of programmed cell death such as necroptosis or pyroptosis. Recent reports suggest considerable crosstalk between these different forms of cell death. It is becoming increasingly clear that caspase-8 has many non-apoptotic roles, participating in multiple processes including regulation of necroptosis (mediated by receptor-interacting serine/threonine kinases, RIPK1-RIPK3), inflammatory cytokine expression, inflammasome activation, and cleavage of IL-1β and gasdermin D, and protection against shock and microbial infection. In this review, we discuss the involvement of caspase-8 in cell death and inflammation and highlight its role in innate immune responses and in the relationship between different forms of cell death. Caspase-8 is one of the central components in this type of crosstalk.

Caenorhabditis elegans as a model system for studying aging-associated neurodegenerative diseases

Neurodegenerative diseases (NDs) are a heterogeneous group of aging-associated disorders characterized by the disruption of cellular proteostasis machinery and the misfolding of distinct protein species to form toxic aggregates in neurons. The increasing prevalence of NDs represents a growing healthcare burden worldwide, a concern compounded by the fact that few, if any, treatments exist to target the underlying cause of these diseases. Consequently, the application of a high-throughput, physiologically relevant model system to studies dissecting the molecular mechanisms governing ND pathology is crucial for identifying novel avenues for the development of targeted therapeutics. The nematode Caenorhabditis elegans (C. elegans) has emerged as a powerful tool for the study of disease mechanisms due to its ease of genetic manipulation and swift cultivation, while providing a whole-animal system amendable to numerous molecular and biochemical techniques. To date, numerous C. elegans models have been generated for a variety of NDs, allowing for the large-scale in vivo study of protein-conformation disorders. Furthermore, the comparatively low barriers to entry in the development of transgenic worm models have facilitated the modeling of rare or "orphan" NDs, thereby providing unparalleled insight into the shared mechanisms underlying these pathologies. In this review, we summarize findings from a comprehensive collection of C. elegans neurodegenerative disease models of varying prevalence to emphasize shared mechanisms of proteotoxicity, and highlight the utility of these models in elucidating the molecular basis of ND pathologies.

An elongated tract of polyQ in the carboxyl‑terminus of human α1A calcium channel induces cell apoptosis by nuclear translocation

An aberrant elongated tract of glutamine residues (polyQ) in proteins induces multiple diseases treated in the clinic. In our previous study of progressive myoclonic epilepsy (PME), using whole-exome sequencing, a mutant Cav2.1 protein with an aberrant elongated polyQ tract was identified in PME patients. To investigate the molecular mechanism and cell biology of this aberrant elongated polyQ tract, wild-type Cav2.1 with 13 polyQ repeats (Cav2.1 wt-Q13) and mutant-type Cav2.1 with 26 polyQ repeats (Cav2.1 mt-Q26) were prepared and introduced into human SH-SY5Y neuroblastoma cells. Using a WST-1 assay, it was revealed that Cav2.1 mt-Q26 markedly suppressed the proliferation of the SH-SY5Y cells, a result not observed for the Cav2.1 wt-Q13-transfected cells. It was also revealed that Cav2.1 mt and its truncated molecules suppressed cell proliferation by inducing apoptosis rather than arresting the cell cycle. Further investigations indicated a nuclear translocation phenomenon associated with the Cav2.1 mt molecules. Mechanistically, it was revealed that the Cav2.1 mt molecules activated the Bcl-2/Bax, caspase-3 and poly ADP-ribose polymerase (PARP) apoptotic pathways. The present study may provide new insights for interpreting the pathogenesis of PME and the relationship among polyQ, CACNA1A gene mutations and PME.

Protein droplets in systems of disordered homopeptides and the amyloid glass phase

We study phase diagrams and liquid droplet formation for systems of polyglutamine and polyalanine chains in a coarse-grained model.

New Therapeutic Approaches for the Treatment of Huntington’s Disease

The use of transplantation (TR) of fetal neural tissue as a therapeutic method started much later in patients suffering from Huntington’s disease (HD) than in those with Parkinson’s disease. The clinical trial, following a wide range of animal experiments (neurotoxic models and newly also transgenic mice), includes about 30 HD patients until now. Because of limited use of the human fetal tissue by ethical and technical concerns, there is necessity to search for the alternative sources for neural grafting. The first attempt with xenotransplantation (in 12 HD patients) and with TR of encapsulated genetically modified cells (in 6 HD patients) was performed, but no appreciable improvement of status in any of those patients was noted. Since no effective pharmacological treatment of HD is available, the TR of fetal neural tissue is now the only therapeutic approach which provides a reduction of symptoms in most of grafted patients. The possibilities are enormous offered by neural stem cells, optionally by embryonic stem cells, which could be expanded in cultures, cloned or genetically modified and then grafted into the patient’s brain. On the other hand, the neural progenitor and stem cells, normally present within the subependymal layer of the lateral brain ventricles also in adulthood, might be induced to become an endogenous source of glia and neurons participating in the brain’s repair.

Targeting Caspase 8: Using Structural and Ligand-Based Approaches to Identify Potential Leads for the Treatment of Multi-Neurodegenerative Diseases

Caspase 8 is a central player in the apoptotic cell death pathway and is also essential for cytokine processing. The critical role of this protease in cell death pathways has generated research interest because its activation has also been linked with neural cell death. Thus, blocking the activity of caspase 8 is considered a potential therapy for neurodegenerative diseases. To extend the repertoire of caspase 8 inhibitors, we employed several computational approaches to identify potential caspase 8 inhibitors. Based on the structural information of reported inhibitors, we designed several individual and consensus pharmacophore models and then screened the ZINC database, which contains 105,480 compounds. Screening generated 5332 candidates, but after applying stringent criteria only two candidate compounds, ZINC19370490 and ZINC04534268, were evaluated by molecular dynamics simulations and subjected to Molecular Mechanics/Poisson Boltzmann Surface Area (MM-PBSA) analysis. These compounds were stable throughout simulations and interacted with targeted protein by forming hydrogen and van der Waal bonds. MM-PBSA analysis showed that these compounds were comparable or better than reported caspase 8 inhibitors. Furthermore, their physical properties were found to be acceptable, and they are non-toxic according to the ADMET online server. We suggest that the inhibitory efficacies of ZINC19370490 and ZINC04534268 be subjected to experimental validation.

Cellular Models: HD Patient-Derived Pluripotent Stem Cells

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by expanded polyglutamine (polyQ)-encoding repeats in the Huntingtin (HTT) gene. Traditionally, HD cellular models consisted of either patient cells not affected by disease or rodent neurons expressing expanded polyQ repeats in HTT. As these models can be limited in their disease manifestation or proper genetic context, respectively, human HD pluripotent stem cells (PSCs) are currently under investigation as a way to model disease in patient-derived neurons and other neural cell types. This chapter reviews embryonic stem cell (ESC) and induced pluripotent stem cell (iPSC) models of disease, including published differentiation paradigms for neurons and their associated phenotypes, as well as current challenges to the field such as validation of the PSCs and PSC-derived cells. Highlighted are potential future technical advances to HD PSC modeling, including transdifferentiation, complex in vitro multiorgan/system reconstruction, and personalized medicine. Using a human HD patient model of the central nervous system, hopefully one day researchers can tease out the consequences of mutant HTT (mHTT) expression on specific cell types within the brain in order to identify and test novel therapies for disease.

SOX2 participates in spermatogenesis of Zhikong scallop Chlamys farreri

As an important transcription factor, SOX2 involves in embryogenesis, maintenance of stem cells and proliferation of primordial germ cell (PGC). However, little was known about its function in mature gonads. Herein, we investigated the SOX2 gene profiles in testis of scallop, Chlamys farreri. The level of C. farreri SOX2 (Cf-SOX2) mRNA increased gradually along with gonadal development and reached the peak at mature stage, and was located in all germ cells, including spermatogonia, spermatocytes, spermatids and spermatozoa. Knockdown of Cf-SOX2 using RNAi leaded to a mass of germ cells lost, and only a few spermatogonia retained in the nearly empty testicular acini after 21 days. TUNEL assay showed that apoptosis occurred in spermatocytes. Furthermore, transcriptome profiles of the testes were compared between Cf-SOX2 knockdown and normal scallops, 131,340 unigenes were obtained and 2,067 differential expression genes (DEGs) were identified. GO and KEGG analysis showed that most DEGs were related to cell apoptosis (casp2, casp3, casp8), cell proliferation (samd9, crebzf, iqsec1) and spermatogenesis (htt, tusc3, zmynd10, nipbl, mfge8), and enriched in p53, TNF and apoptosis pathways. Our study revealed Cf-SOX2 is essential in spermatogenesis and testis development of C. farreri and provided important clues for better understanding of SOX2 regulatory mechanisms in bivalve testis.

Molecular Pathogenesis in Huntington's Disease

Huntington's disease (HD) is a severe autosomal dominant neurodegenerative disorder characterized by a combination of motor, cognitive, and psychiatric symptoms, atrophy of the basal ganglia and the cerebral cortex, and inevitably progressive course resulting in death 5-20 years after manifestation of its symptoms. HD is caused by expansion of CAG repeats in the HTT gene, which leads to pathological elongation of the polyglutamine tract within the respective protein - huntingtin. In this review, we present a modern view on molecular biology of HD as a representative of the group of polyglutamine diseases, with an emphasis on conformational changes of mutant huntingtin, disturbances in its cellular processing, and proteolytic stress in degenerating neurons. Main pathogenetic mechanisms of neurodegeneration in HD are discussed in detail, such as systemic failure of transcription, mitochondrial dysfunction and suppression of energy metabolism, abnormalities of cytoskeleton and axonal transport, microglial inflammation, decrease in synthesis of brain-derived neurotrophic factor, etc.

Planar cell polarity gene Fuz triggers apoptosis in neurodegenerative disease models

Planar cell polarity (PCP) describes a cell-cell communication process through which individual cells coordinate and align within the plane of a tissue. In this study, we show that overexpression of Fuz, a PCP gene, triggers neuronal apoptosis via the dishevelled/Rac1 GTPase/MEKK1/JNK/caspase signalling axis. Consistent with this finding, endogenous Fuz expression is upregulated in models of polyglutamine (polyQ) diseases and in fibroblasts from spinocerebellar ataxia type 3 (SCA3) patients. The disruption of this upregulation mitigates polyQ-induced neurodegeneration in Drosophila We show that the transcriptional regulator Yin Yang 1 (YY1) associates with the Fuz promoter. Overexpression of YY1 promotes the hypermethylation of Fuz promoter, causing transcriptional repression of Fuz Remarkably, YY1 protein is recruited to ATXN3-Q84 aggregates, which reduces the level of functional, soluble YY1, resulting in Fuz transcriptional derepression and induction of neuronal apoptosis. Furthermore, Fuz transcript level is elevated in amyloid beta-peptide, Tau and α-synuclein models, implicating its potential involvement in other neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases. Taken together, this study unveils a generic Fuz-mediated apoptotic cell death pathway in neurodegenerative disorders.

4-Hydroxynonenal (HNE) modified proteins in metabolic diseases

4-Hydroxynonenal (HNE) is one of the quantitatively most important products of lipid peroxidation. Due to its high toxicity it is quickly metabolized, however, a small share of HNE avoids enzymatic detoxification and reacts with biomolecules including proteins. The formation of HNE-protein-adducts is one of the accompanying processes in oxidative stress or redox disbalance. The modification of proteins might occur at several amino acids side chains, leading to a variety of products and having effects on the protein function and fate. This review summarizes current knowledge on the formation of HNE-modified proteins, their fate in mammalian cells and their potential role as a damaging agents during oxidative stress. Furthermore, the potential of HNE-modified proteins as biomarkers for several diseases are highlighted.

Methylmalonate Induces Inflammatory and Apoptotic Potential: A Link to Glial Activation and Neurological Dysfunction

Methylmalonic acid (MMA) accumulates in tissues in methylmalonic acidemia, a heterogeneous group of inherited childhood diseases characterized by neurological dysfunction, oxidative stress and neuroinflammation; it is associated with degeneration of striatal neurons and cerebral cortical atrophy. It is presently unknown, however, whether transient exposure to MMA in the neonatal period is sufficient to trigger inflammatory and apoptotic processes that lead to brain structural damage. Here, newborn mice were given a single intracerebroventricular dose of MMA at 12 hours after birth. Maze testing of 21- and 40-day-old mice showed that MMA-injected animals exhibited deficit in the working memory test but not in the reference test. MMA-injected mice showed increased levels of the reactive oxygen species marker 2',7'-dichlorofluorescein diacetate, tumor necrosis factor, interleukin-1β, caspases 1, 3, and 8, and increased acetylcholinesterase activity in the cortex, hippocampus and striatum. This was associated with increased astrocyte and microglial immunoreactivity in all brain regions. These findings suggest that transient exposure to MMA may alter the redox state and cause neuroinflammatory/apoptotic processes and glial activation during critical periods of brain development. Similar processes may underlie brain dysfunction and cognitive impairment in patients with methylmalonic acidemia.

Huntington's Disease: Pathological Mechanisms and Therapeutic Strategies

Huntington's disease (HD) is a devastating neurodegenerative disorder that occurs in patients with a mutation in the huntingtin or IT15 gene. Patients are plagued by early cognitive signs, motor deficits, and psychiatric disturbances. Symptoms are attributed to cell death in the striatum and disruption of cortical–striatal circuitry. Mechanisms of cell death are unclear, but processes involving mitochondrial abnormalities, excitotoxicity, and abnormal protein degradation have been implicated. Many factors likely contribute to neuron death and dysfunction, and this has made it difficult to systematically address the pathology in HD. Pharmaceutical therapies are commonly used in patients to treat disease symptoms. These have limited benefit and do not address the inexorable disease progression. Several neuroprotective therapies are being evaluated in animal models of HD as well as in clinical trials. Similarly, cell replacement strategies such as fetal transplantation have been used in the clinic with minimal success, making future cell replacement strategies such as stem cell therapy uncertain. This review describes the disease pathology in HD and addresses many of the past and emerging therapeutic strategies.

Post-translational Modifications and Protein Quality Control in Motor Neuron and Polyglutamine Diseases

Neurodegenerative diseases, including motor neuron and polyglutamine (polyQ) diseases, are a broad class of neurological disorders. These diseases are characterized by neuronal dysfunction and death, and by the accumulation of toxic aggregation-prone proteins in the forms of inclusions and micro-aggregates. Protein quality control is a cellular mechanism to reduce the burden of accumulation of misfolded proteins, a function that results from the coordinated actions of chaperones and degradation systems, such as the ubiquitin-proteasome system (UPS) and autophagy-lysosomal degradation system. The rate of turnover, aggregation and degradation of the disease-causing proteins is modulated by post-translational modifications (PTMs), such as phosphorylation, arginine methylation, palmitoylation, acetylation, SUMOylation, ubiquitination, and proteolytic cleavage. Here, we describe how PTMs of proteins linked to motor neuron and polyQ diseases can either enhance or suppress protein quality control check and protein aggregation and degradation. The identification of molecular strategies targeting these modifications may offer novel avenues for the treatment of these yet incurable diseases.

Rare Neurodegenerative Diseases: Clinical and Genetic Update

More than 600 human disorders afflict the nervous system. Of these, neurodegenerative diseases are usually characterised by onset in late adulthood, progressive clinical course, and neuronal loss with regional specificity in the central nervous system. They include Alzheimer's disease and other less frequent dementias, brain cancer, degenerative nerve diseases, encephalitis, epilepsy, genetic brain disorders, head and brain malformations, hydrocephalus, stroke, Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis (ALS or Lou Gehrig's Disease), Huntington's disease, and Prion diseases, among others. Neurodegeneration usually affects, but is not limited to, the cerebral cortex, intracranial white matter, basal ganglia, thalamus, hypothalamus, brain stem, and cerebellum. Although the majority of neurodegenerative diseases are sporadic, Mendelian inheritance is well documented. Intriguingly, the clinical presentations and neuropathological findings in inherited neurodegenerative forms are often indistinguishable from those of sporadic cases, suggesting that converging genomic signatures and pathophysiologic mechanisms underlie both hereditary and sporadic neurodegenerative diseases. Unfortunately, effective therapies for these diseases are scarce to non-existent. In this chapter, we highlight the clinical and genetic features associated with the rare inherited forms of neurodegenerative diseases, including ataxias, multiple system atrophy, spastic paraplegias, Parkinson's disease, dementias, motor neuron diseases, and rare metabolic disorders.

Differential proteomic and genomic profiling of mouse striatal cell model of Huntington's disease and control; probable implications to the disease biology

Huntington's disease (HD) is an autosomal dominant disorder of central nervous system caused by expansion of CAG repeats in exon1 of the huntingtin gene (Htt). Among various dysfunctions originated from the mutation in Htt gene, transcriptional deregulation has been considered to be one of the most important abnormalities. Large numbers of investigations identified altered expressions of genes in brains of HD patients and many models of HD. In this study we employed 2D SDS-PAGE/MALDI-MS coupled with 2D-DIGE and real-time PCR experiments of an array of genes focused to HD pathway to determine altered protein and gene expressions in STHdh(Q111)/Hdh(Q111) cells, a cell model of HD and compared with STHdh(Q7)/Hdh(Q7) cells, its wild type counterpart. We annotated 76 proteins from these cells and observed differential expressions of 31 proteins (by 2D-DIGE) involved in processes like unfolded protein binding, negative regulation of neuron apoptosis, response to superoxides etc. Our PCR array experiments identified altered expressions of 47 genes. Altogether significant alteration of 77 genes/proteins could be identified in this HD cell line with potential relevance to HD biology.

BIOLOGICAL SIGNIFICANCE

In this study we intended to find out differential proteomic and genomic profiles in HD condition. We used the STHdh cells, a cellular model for HD and control. These are mouse striatal neuronal cell lines harboring 7 and 111 knock-in CAG repeats in their two alleles. The 111Q containing cell line (STHdh(Q111)/Hdh(Q111)) mimics diseased condition, whereas the 7Q containing ones (STHdh(Q7)/Hdh(Q7)), serves as the proper control cell line. Proteomic experiments were performed earlier to obtain differential expressions of proteins in R6/2 mice models, Hdh(Q) knock-in mice and in plasma and CSF from HD patients. However, no earlier report on proteomic alterations in these two HD cell lines and control was available in literature. It was, therefore, an important objective to find out differential expressions of proteins in these two cell lines. In this study, we annotated 76 proteins from STHdh(Q7)/Hdh(Q7) and STHdh(Q111)/Hdh(Q111) cells using 2D-gel/mass spectrometry. Next, by performing 2D-DIGE, we observed differential expressions of 31 proteins (16 upregulated and 15 downregulated) between these two cell lines. We also performed customized qRT-PCR array focused to HD pathway and found differential expressions of 47 genes (8 gene expressions increased and 39 genes were decreased significantly). A total of 77 genes/proteins (Htt downregulated in both the studies) were found to be significantly altered from both the experimental paradigms. We validated the differential expressions of Vim, Hypk, Ran, Dstn, Hspa5 and Sod2 either by qRT-PCR or Western blot analysis or both. Out of these 77, similar trends in alteration of 19 out of 31 and 38 out of 47 proteins/genes were reported in earlier studies. Thus our study confirmed earlier observations on differential gene/protein expressions in HD and are really useful. Additionally, we observed differential expression of some novel genes/proteins. One of this was Hypk, a Htt-interacting chaperone protein with the ability to solubilize mHtt aggregated structures in cell lines. We propose that downregulation of Hypk in STHdh(Q111)/Hdh(Q111) has a causal effect towards HD pathogenesis. Thus the novel findings from our study need further research and might be helpful to understand the molecular mechanism behind HD pathogenesis.

Lost after translation: insights from pulmonary surfactant for understanding the role of alveolar epithelial dysfunction and cellular quality control in fibrotic lung disease

Dating back nearly 35 years ago to the Witschi hypothesis, epithelial cell dysfunction and abnormal wound healing have reemerged as central concepts in the pathophysiology of idiopathic pulmonary fibrosis (IPF) in adults and in interstitial lung disease in children. Alveolar type 2 (AT2) cells represent a metabolically active compartment in the distal air spaces responsible for pulmonary surfactant biosynthesis and function as a progenitor population required for maintenance of alveolar integrity. Rare mutations in surfactant system components have provided new clues to understanding broader questions regarding the role of AT2 cell dysfunction in the pathophysiology of fibrotic lung diseases. Drawing on data generated from a variety of model systems expressing disease-related surfactant component mutations [surfactant proteins A and C (SP-A and SP-C); the lipid transporter ABCA3], this review will examine the concept of epithelial dysfunction in fibrotic lung disease, provide an update on AT2 cell and surfactant biology, summarize cellular responses to mutant surfactant components [including endoplasmic reticulum (ER) stress, mitochondrial dysfunction, and intrinsic apoptosis], and examine quality control pathways (unfolded protein response, the ubiquitin-proteasome system, macroautophagy) that can be utilized to restore AT2 homeostasis. This integrated response and its derangement will be placed in the context of cell stress and quality control signatures found in patients with familial or sporadic IPF as well as non-surfactant-related AT2 cell dysfunction syndromes associated with a fibrotic lung phenotype. Finally, the need for targeted therapeutic strategies for pulmonary fibrosis that address epithelial ER stress, its downstream signaling, and cell quality control are discussed.

HSP70 mediates survival in apoptotic cells-Boolean network prediction and experimental validation

Neuronal stress or injury results in the activation of proteins, which regulate the balance between survival and apoptosis. However, the complex mechanism of cell signaling involving cell death and survival, activated in response to cellular stress is not yet completely understood. To bring more clarity about these mechanisms, a Boolean network was constructed that represented the apoptotic pathway in neuronal cells. FasL and neurotrophic growth factor (NGF) were considered as inputs in the absence and presence of heat shock proteins known to shift the balance toward survival by rescuing pro-apoptotic cells. The probabilities of survival, DNA repair and apoptosis as cellular fates, in the presence of either the growth factor or FasL, revealed a survival bias encoded in the network. Boolean predictions tested by measuring the mRNA level of caspase-3, caspase-8, and BAX in neuronal Neuro2a (N2a) cell line with NGF and FasL as external input, showed positive correlation with the observed experimental results for survival and apoptotic states. It was observed that HSP70 contributed more toward rescuing cells from apoptosis in comparison to HSP27, HSP40, and HSP90. Overexpression of HSP70 in N2a transfected cells showed reversal of cellular fate from FasL-induced apoptosis to survival. Further, the pro-survival role of the proteins BCL2, IAP, cFLIP, and NFκB determined by vertex perturbation analysis was experimentally validated through protein inhibition experiments using EM20-25, Embelin and Wedelolactone, which resulted in 1.27-, 1.26-, and 1.46-fold increase in apoptosis of N2a cells. The existence of a one-to-one correspondence between cellular fates and attractor states shows that Boolean networks may be employed with confidence in qualitative analytical studies of biological networks.

Coenzyme Q10 and spinocerebellar ataxias

The aim of this study was to investigate the association between drug exposure and disease severity in SCA types 1, 2, 3 and 6. The Clinical Research Consortium for Spinocerebellar Ataxias (CRC-SCA) enrolled 319 participants with SCA1, 2, 3, and 6 from 12 medical centers in the United States and repeatedly measured clinical severity by the Scale for Assessment and Rating of Ataxia (SARA), the Unified Huntington's Disease Rating Scale part IV (UHDRS-IV), and the 9-item Patient Health Questionnaire during July 2009 to May 2012. We employed generalized estimating equations in regression models to study the longitudinal effects of coenzyme Q10 (CoQ10), statin, and vitamin E on clinical severity of ataxia after adjusting for age, sex, and pathological CAG repeat number. Cross-sectionally, exposure to CoQ10 was associated with lower SARA and higher UHDRS-IV scores in SCA1 and 3. No association was found between statins, vitamin E, and clinical outcome. Longitudinally, CoQ10, statins, and vitamin E did not change the rates of clinical deterioration indexed by SARA and UHDRS-IV scores within 2 years. CoQ10 is associated with better clinical outcome in SCA1 and 3. These drug exposures did not appear to influence clinical progression within 2 years. Further studies are warranted to confirm the association.

Ataxin-3 protein and RNA toxicity in spinocerebellar ataxia type 3: current insights and emerging therapeutic strategies

Ataxin-3 is a ubiquitously expressed deubiqutinating enzyme with important functions in the proteasomal protein degradation pathway and regulation of transcription. The C-terminus of the ataxin-3 protein contains a polyglutamine (PolyQ) region that, when mutationally expanded to over 52 glutamines, causes the neurodegenerative disease spinocerebellar ataxia 3 (SCA3). In spite of extensive research, the molecular mechanisms underlying the cellular toxicity resulting from mutant ataxin-3 remain elusive and no preventive treatment is currently available. It has become clear over the last decade that the hallmark intracellular ataxin-3 aggregates are likely not the main toxic entity in SCA3. Instead, the soluble PolyQ containing fragments arising from proteolytic cleavage of ataxin-3 by caspases and calpains are now regarded to be of greater influence in pathogenesis. In addition, recent evidence suggests potential involvement of a RNA toxicity component in SCA3 and other PolyQ expansion disorders, increasing the pathogenic complexity. Herein, we review the functioning of ataxin-3 and the involvement of known protein and RNA toxicity mechanisms of mutant ataxin-3 that have been discovered, as well as future opportunities for therapeutic intervention.

Structure based molecular inhibition of Caspase-8 for treatment of multi-neurodegenerative diseases using known natural compounds

Neurodegenerative disorders are often associated with excessive neuronal apoptosis. It is well known that apoptosis is regulated by some intracellular proteases, such as, Caspases (cysteine-dependent, aspartate-specific proteases). In fact, Caspase-8 which is an initiator caspase, has been identified as a key mediator of neuronal apoptosis. In addition, Caspase-8 is found to be coupled with the regulation of various neurodegenerative disorders including Alzheimer׳s disease (AD), Parkinson׳s disease (PD), Huntington׳s Diseases (HD) and Dentatorubral Pallidoluysian Atrophy (DRPLA). Caspase-8 inhibition may provide an effective means of treatment for multiple neurodegenerative disorders. Therefore, the present study describes the molecular interaction of some selected natural compounds with known anti neurodegenerative properties with Caspase-8. Docking between Caspase-8 and each of these compounds (separately) was performed using 'Autodock4.2'. Out of all the selected compounds, rosmarinic acid and curcumin proved to be the most potent inhibitors of Caspase-8 with binding energy (ΔG) of -7.10 Kcal/mol and -7.08 Kcal/mol, respectively. However, further in vitro and in vivo studies are needed to validate the anti-neurodegenerative potential of these compounds.

Therapeutic Approaches for Inhibition of Protein Aggregation in Huntington's Disease

Huntington's disease (HD) is a late-onset and progressive neurodegenerative disorder that is caused by aggregation of mutant huntingtin protein which contains expanded-polyglutamine. The molecular chaperones modulate the aggregation in early stage and known for the most potent protector of neurodegeneration in animal models of HD. Over the past decades, a number of studies have demonstrated molecular chaperones alleviate the pathogenic symptoms by polyQ-mediated toxicity. Moreover, chaperone-inducible drugs and anti-aggregation drugs have beneficial effects on symptoms of disease. Here, we focus on the function of molecular chaperone in animal models of HD, and review the recent therapeutic approaches to modulate expression and turn-over of molecular chaperone and to develop anti-aggregation drugs.

Polyglutamine expansion disturbs the endoplasmic reticulum formation, leading to caspase-7 activation through Bax

The endoplasmic reticulum (ER) plays a pivotal role in cellular functions such as the ER stress response. However, the effect of the ER membrane on caspase activation remains unclear. This study reveals that polyglutamine oligomers augmented at ER induce insertion of Bax into the ER membrane, thereby activating caspase-7. In line with the role of ER in cell death induced by polyglutamine expansion, the ER membrane was found to be disrupted and dilated in the brain of a murine model of Huntington's disease. We can conclude that polyglutamine expansion may drive caspase-7 activation by disrupting the ER membrane.

mRNA expression and hypermethylation of tumor suppressor genes apoptosis protease activating factor-1 and death-associated protein kinase in oral squamous cell carcinoma

Apoptosis protease activating factor-1 (Apaf-1) and death-associated protein kinase (DAPK) are p53 pathway-related genes that play significant roles in the activation of caspases, which are involved in mitochondrial-mediated apoptosis. The present study aimed to confirm the role of hyper-methylation of the Apaf-1 and DAPK gene promoter regions in oral squamous cell carcinoma (OSCC) and the effect of the demethylation drug, 5-aza-2'-deoxycytidine (DAC). mRNA from 53 OSCC samples, 23 normal oral mucosa samples and Tca8113 human tongue carcinoma cell lines was detected using semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). The DNA from each sample was analyzed using methylation-specific PCR (MSP). The Tca8113 cells were demethylated using DAC and the demethylation and re-expression of Apaf-1 and DAPK were analyzed. The Apaf-1 and DAPK mRNA expression index was decreased in 51 (96.23%) and 50 (94.34%) cases, respectively, in the tumor tissues. Hypermethylation of the Apaf-1 and DAPK promoter regions was detected in 46 (86.79%) and 38 (71.69%) cases, respectively. Promoter hypermethylation of the two genes correlated with a decreased mRNA expression in the tumor tissues. Subsequent to being treated with DAC, Apaf-1 and DAPK were demethylated and re-expressed in the Tca8113 cells. Apaf-1 and DAPK promoter hypermethylation may be associated with low gene expression in OSCC. Furthermore, a loss of Apaf-1 and DAPK expression may recover following demethylation. The data provide evidence that methylation exists in OSCC and may play a role in the development of this disease.

Defining the role of the Bcl-2 family proteins in Huntington's disease

B-cell lymphoma 2 (Bcl-2) family proteins regulate survival, mitochondria morphology dynamics and metabolism in many cell types including neurons. Huntington's disease (HD) is a neurodegenerative disorder caused by an expanded CAG repeat tract in the IT15 gene that encodes for the protein huntingtin (htt). In vitro and in vivo models of HD and HD patients' tissues show abnormal mitochondrial function and increased cell death rates associated with alterations in Bcl-2 family protein expression and localization. This review aims to draw together the information related to Bcl-2 family protein alterations in HD to decipher their potential role in mutated htt-related cell death and mitochondrial dysfunction.

Protein truncation as a common denominator of human neurodegenerative foldopathies

Neurodegenerative foldopathies are characterized by aberrant folding of diseased modified proteins, which are major constituents of the intracellular and extracellular lesions. These lesions correlate with the cognitive and/or motor impairment seen in these diseases. The majority of the disease modified proteins in neurodegenerative foldopathies belongs to the group of proteins termed as intrinsically disordered proteins (IDPs). Several independent studies have showed that abnormal protein processing constitutes the key pathological feature of these disorders. The current review focuses on protein truncation as a common denominator of neurodegenerative foldopathies, which is considered to be the major driving force behind the pathological metamorphosis of brain IDPs. The aim of the review is to emphasize the key role of the protein truncation in the pathogenic pathways of neurodegenerative diseases. A deeper understanding of the complex downstream processing of the IDPs, resulting in the generation of pathologically modified proteins might be a prerequisite for the successful therapeutic strategies of several fatal neurodegenerative diseases.

Hyperactivation of the mammalian degenerin MDEG promotes caspase-8 activation and apoptosis

Intracellular calcium overload plays a critical role in numerous pathological syndromes such as heart failure, brain ischemia, and stroke. Hyperactivation of the acid-sensing ion channels including degenerin/epithelial amiloride-sensitive sodium (DEG/ENaC) channels has been shown to elevate intracellular calcium and cause subsequent neuronal cell death that is independent of the canonical Egl-1/Ced-9/Ced-4/Ced-3 apoptotic pathway in Caenorhabditis elegans. In mammalian cells, hyperactivation of the DEG/ENaC channels can also lead to cell death, although the underlying mechanism remains largely unknown. Here, we use a tetracycline-inducible system to express the hyperactivation mutant of a mammalian DEG/ENaC channel protein, MDEG G430F, in murine kidney epithelial cells deficient in the key mitochondrial apoptotic proteins Bax and Bak. Remarkably, expression of MDEG G430F induces increased intracellular calcium, reactive oxygen species (ROS) production, and cell death. The MDEG G430F-induced cell death is blocked by the intracellular calcium chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (acetoxymethyl ester), ROS scavengers, and the caspase inhibitor z-VAD-fmk (where z and fmk are benzyloxycarbonyl and fluoromethyl ketone). Mechanistically, the intracellular calcium overload and ROS increase lead to the inhibition of proteasomal and autophagic protein degradation, which promotes the accumulation of protein aggregates containing caspase-8 and subsequent caspase-8 activation. As protein aggregation upon the inhibition of proteasomal and autophagic degradation pathways is mediated by the ubiquitin-binding protein SQSTM1/p62 and the autophagy-related protein LC3, silencing of p62 and LC3 protects cells from MDEG G430F-induced cell death. Our results uncover a new mechanism of caspase-8-mediated apoptosis induced by intracellular calcium overload that is dependent on the autophagy-related proteins LC3 and p62 upon hyperactivation of DEG/ENaC channels.

Spinocerebellar ataxia type 35 (SCA35)-associated transglutaminase 6 mutants sensitize cells to apoptosis

Spinocerebellar ataxia type 35 (SCA35) is an autosomal dominant neurodegenerative disorder. In our previous study, using exome sequencing and linkage analysis, two missense mutations of the transglutaminase 6 (TGM6) gene were identified as causative for SCA35. TGM6 encodes transglutaminase 6 (TG6), a member of the transglutaminase family of enzymes that catalyze the formation of a covalent bond between a free amine group and the γ-carboxamide group of protein- or peptide-bound glutamine. However, the precise role of TG6 in contributing to SCA35 remains unclear. In this study, we analyzed the subcellular distribution, expression and in vitro activity of two missense mutations of TG6 (D327G, L517W) and found that both mutants exhibited decreased transglutaminase activity and stability. Furthermore, overexpressing the TG6 mutants sensitized cells to staurosporine-induced apoptosis by increasing the activity of caspases. We propose that the pro-apoptotic role of these mutants might underlie the pathogenesis of SCA35.

Therapeutic approaches to preventing cell death in Huntington disease

Neurodegenerative diseases affect the lives of millions of patients and their families. Due to the complexity of these diseases and our limited understanding of their pathogenesis, the design of therapeutic agents that can effectively treat these diseases has been challenging. Huntington disease (HD) is one of several neurological disorders with few therapeutic options. HD, like numerous other neurodegenerative diseases, involves extensive neuronal cell loss. One potential strategy to combat HD and other neurodegenerative disorders is to intervene in the execution of neuronal cell death. Inhibiting neuronal cell death pathways may slow the development of neurodegeneration. However, discovering small molecule inhibitors of neuronal cell death remains a significant challenge. Here, we review candidate therapeutic targets controlling cell death mechanisms that have been the focus of research in HD, as well as an emerging strategy that has been applied to developing small molecule inhibitors-fragment-based drug discovery (FBDD). FBDD has been successfully used in both industry and academia to identify selective and potent small molecule inhibitors, with a focus on challenging proteins that are not amenable to traditional high-throughput screening approaches. FBDD has been used to generate potent leads, pre-clinical candidates, and has led to the development of an FDA approved drug. This approach can be valuable for identifying modulators of cell-death-regulating proteins; such compounds may prove to be the key to halting the progression of HD and other neurodegenerative disorders.

Apoptosis in health and disease and modulation of apoptosis for therapy: An overview

Apoptosis a physiological mechanism that eliminates excessive, damaged or unwanted cells, is a highly regulated pathway important for maintaining homeostasis in multicellular organisms. It can be initiated through various signals via the extrinsic pathway which involves death receptors, or via the intrinsic pathway which is initiated by intracellular damage and involves the mitochondria and release of cytochrome c from it to further activate caspases. The Bcl-2 family of proteins is situated upstream to the irreversible damage of cellular constituents and is an important checkpoint in the fate of a cell. The pro-apoptotic members, BH3 only members include BID, BAD and BIM. They directly or indirectly activate multidomain BAX/BAK that constitute the requisite gateway to the intrinsic pathway which operates at the mitochondrial surface and endoplasmic reticulum. In contrast, antiapoptotic members such as Bcl-2, Bcl-XL bind and sequester activation. Downstream of mitochondria, the apoptosome involvement is seen to generate caspase activity. Post mitochondria regulation involves IAPs, and their inhibitors. The pathogenesis of several diseases such as cancer, neurodegenerative disorders, autoimmune disorders, heart disease, infectious diseases including AIDS is closely related to aberrant apoptosis. Consequently interest has emerged in employing various the rapeutic approaches such as gene therapy, antisense therapy, recombinant biologicals, organic and combinatorial chemistry, to specifically target apoptosis signaling pathways such as death receptors FAS/TRAIL, Bcl-2, p53, IAPs, SMAC and caspases, etc. and are now advancing from preclinical to clinical phase.

Protein damage, repair and proteolysis

Proteins are continuously affected by various intrinsic and extrinsic factors. Damaged proteins influence several intracellular pathways and result in different disorders and diseases. Aggregation of damaged proteins depends on the balance between their generation and their reversal or elimination by protein repair systems and degradation, respectively. With regard to protein repair, only few repair mechanisms have been evidenced including the reduction of methionine sulfoxide residues by the methionine sulfoxide reductases, the conversion of isoaspartyl residues to L-aspartate by L-isoaspartate methyl transferase and deglycation by phosphorylation of protein-bound fructosamine by fructosamine-3-kinase. Protein degradation is orchestrated by two major proteolytic systems, namely the lysosome and the proteasome. Alteration of the function for both systems has been involved in all aspects of cellular metabolic networks linked to either normal or pathological processes. Given the importance of protein repair and degradation, great effort has recently been made regarding the modulation of these systems in various physiological conditions such as aging, as well as in diseases. Genetic modulation has produced promising results in the area of protein repair enzymes but there are not yet any identified potent inhibitors, and, to our knowledge, only one activating compound has been reported so far. In contrast, different drugs as well as natural compounds that interfere with proteolysis have been identified and/or developed resulting in homeostatic maintenance and/or the delay of disease progression.