Chemical induction of Hsp70 reduces α-synuclein aggregation in neuroglioma cells

Identification of HSP70 genes in Diaphorina citri Kuwayama Reveals Their Involvement in Immunity and Development

Huanglongbing (HLB), a global citrus threat, is transmitted by Diaphorina citri Kuwayama, a widespread insect pest. The disease's rapid spread and incurability necessitate efficient, sustainable control strategies. This study investigates heat shock protein 70 (HSP70) genes in D. citri, known to play a pivotal role in insect survival and stress response. The genome-wide identification, gene structure analysis, and conserved protein domain analysis of 22 HSP70 genes in D. citri were performed. Furthermore, the expression of these genes during HLB infection or developmental processes was gauged. Phylogenetic analysis revealed the functional categorization of the identified genes, while gene structure and conserved motifs offered insights into gene function. The expression analysis unveiled dynamic profiles in response to infection and across development stages, potentially aiding future targeted pest control strategies. These findings offer promising leads for the design of novel inhibitors or RNAi strategies targeting D. citri and HLB.

Linking Heat Shock Protein 70 and Parkin in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disease that affects millions of elderly people worldwide and is characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The precise mechanisms underlying the pathogenesis of PD are still not fully understood, but it is well accepted that the misfolding, aggregation, and abnormal degradation of proteins are the key causative factors of PD. Heat shock protein 70 (Hsp70) is a molecular chaperone that participates in the degradation of misfolded and aggregated proteins in living cells and organisms. Parkin, an E3 ubiquitin ligase, participates in the degradation of proteins via the proteasome pathway. Recent studies have indicated that both Hsp70 and Parkin play pivotal roles in PD pathogenesis. In this review, we focus on discussing how dysregulation of Hsp70 and Parkin leads to PD pathogenesis, the interaction between Hsp70 and Parkin in the context of PD and their therapeutic applications in PD.

Uncovering the Role of Natural and Synthetic Small Molecules in Counteracting the Burden of α-Synuclein Aggregates and Related Toxicity in Different Models of Parkinson's Disease

A proteostasis network represents a sophisticated cellular system that controls the whole process which leads to properly folded functional proteins. The imbalance of proteostasis determines a quantitative increase in misfolded proteins prone to aggregation and elicits the onset of different diseases. Among these, Parkinson's Disease (PD) is a progressive brain disorder characterized by motor and non-motor signs. In PD pathogenesis, alpha-Synuclein (α-Syn) loses its native structure, triggering a polymerization cascade that leads to the formation of toxic inclusions, the PD hallmark. Because molecular chaperones represent a "cellular arsenal" to counteract protein misfolding and aggregation, the modulation of their expression represents a compelling PD therapeutic strategy. This review will discuss evidence concerning the effects of natural and synthetic small molecules in counteracting α-Syn aggregation process and related toxicity, in different in vitro and in vivo PD models. Firstly, the role of small molecules that modulate the function(s) of chaperones will be highlighted. Then, attention will be paid to small molecules that interfere with different steps of the protein-aggregation process. This overview would stimulate in-depth research on already-known small molecules or the development of new ones, with the aim of developing drugs that are able to modify the progression of the disease.

Transcriptional repressor AGL79 positively regulates flowering time in Arabidopsis

The MADS-box gene family is widely distributed in higher plants and the members of the angiosperm-specific APETALA1/FRUITFULL (AP1/FUL) subfamily plays important roles in the regulation of plant reproductive development. Recent studies revealed that the AP1/FUL subfamily member Dt2, VEGETATIVE1/PsFRUITFULc (VEG1/PsFULc) and MtFRUITFULc (MtFULc) are essential for the stem growth, branching and inflorescence development in legume species soybean (Glycine max), pea (Pisum sativum) and Medicago truncatula. However, the biological function of their homologue in Arabidopsis thaliana, AGAMOUS-LIKE 79 (AGL79), has not been well elucidated. In this study, we investigated the developmental roles of Arabidopsis AGL79 by CRISPR/Cas9-mutagenesis and molecular and physiological analyses. We found that AGL79 mainly acts as a transcriptional repressor and positively regulates Arabidopsis flowering time. We further revealed that AGL79 interacts with SUPPRESSOR OF OVEREXPRESSION OF CO1 (SOC1) and represses the expression of TERMINAL FLOWER 1 (TFL1). Our results demonstrated the AGL79-mediated flowering regulation in Arabidopsis and added an additional layer of complexity to the understanding of flowering time regulation in dicot plants.

Mechanistic insights into monomer level prevention of amyloid aggregation of lysozyme by glycyrrhizic acid

As the primary bioactive compound of glycyrrhiza rhizome, the triterpene glycoside conjugate Glycyrrhizic acid (GA) has demonstrated neuroprotective effects in vivo. This study evaluates the effectiveness of GA as an inhibitor of GuHCl-induced amyloid aggregation of hen egg white lysozyme (HEWL). Fibril formation as measured by Thioflavin-T fluorescence, 90⁰ light scattering, and 8-Anilinonaphthalene-1-sulfonic acid (ANS) fluorescence illustrated ∼90 % prevention of fibrils at [GA]/[HEWL] ≥2:1. Images of Transmission electron microscopy evidence for the absence of any fibril or amorphous aggregation products. The spectral characteristics of soluble HEWL were in close resemblance to unfolded monomer. Computational and fluorescence investigations performed to analyse GA-HEWL interactions demonstrated slightly higher affinity of GA to unfolded HEWL and aggregation-prone regions. The likely mechanism of monomer level aggregation prevention by GA as dermined by computational, stability, and ANS experiments illustrated that GA modulated the compactness, solvent-accessible surface, and solvent-exposed hydrophobic surfaces of aggregation-prone state of HEWL. Our findings corroborate GA as an effective inhibitor of HEWL amyloid formation. To our knowledge, GA interaction-induced inhibition of aggregation-prone states has not been previously discussed. GA's modulation of aggregation-prone states of disease-related proteins will successfully develop GA as an amyloid inhibitor for clinical trials of amyloidosis and neurodegenerative illnesses.

Chemical Chaperones to Inhibit Endoplasmic Reticulum Stress: Implications in Diseases

The endoplasmic reticulum (ER) is responsible for structural transformation or folding of de novo proteins for transport to the Golgi. When the folding capacity of the ER is exceeded or excessive accumulation of misfolded proteins occurs, the ER enters a stressed condition (ER stress) and unfolded protein responses (UPR) are triggered in order to rescue cells from the stress. Recovery of ER proceeds toward either survival or cell apoptosis. ER stress is implicated in many pathologies, such as diabetes, cardiovascular diseases, inflammatory diseases, neurodegeneration, and lysosomal storage diseases. As a survival or adaptation mechanism, chaperone molecules are upregulated to manage ER stress. Chemical versions of chaperone have been developed in search of drug candidates for ER stress-related diseases. In this review, synthetic or semi-synthetic chemical chaperones are categorized according to potential therapeutic area and listed along with their chemical structure and activity. Although only a few chemical chaperones have been approved as pharmaceutical drugs, a dramatic increase in literatures over the recent decades indicates enormous amount of efforts paid by many researchers. The efforts warrant clearer understanding of ER stress and the related diseases and consequently will offer a promising drug discovery platform with chaperone activity.

Praja1 RING-finger E3 ubiquitin ligase is a common suppressor of neurodegenerative disease-associated protein aggregation

The formation of misfolded protein aggregates is one of the pathological hallmarks of neurodegenerative diseases. We have previously demonstrated the cytoplasmic aggregate formation of adenovirally expressed transactivation response DNA-binding protein of 43 kDa (TDP-43), the main constituent of neuronal cytoplasmic aggregates in cases of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD), in cultured neuronal cells under the condition of proteasome inhibition. The TDP-43 aggregate formation was markedly suppressed by co-infection of adenoviruses expressing heat shock transcription factor 1 (HSF1), a master regulator of heat shock response, and Praja1 RING-finger E3 ubiquitin ligase (PJA1) located downstream of the HSF1 pathway. In the present study, we examined other reportedly known E3 ubiquitin ligases for TDP-43, i.e. Parkin, RNF112 and RNF220, but failed to find their suppressive effects on neuronal cytoplasmic TDP-43 aggregate formation, although they all bind to TDP-43 as verified by co-immunoprecipitation. In contrast, PJA1 also binds to adenovirally expressed wild-type and mutated fused in sarcoma, superoxide dismutase 1, α-synuclein and ataxin-3, and huntingtin polyglutamine proteins in neuronal cultures and suppressed the aggregate formation of these proteins. These results suggest that PJA1 is a common sensing factor for aggregate-prone proteins to counteract their aggregation propensity, and could be a potential therapeutic target for neurodegenerative diseases that include ALS, FTLD, Parkinson's disease and polyglutamine diseases.

FLOWERING LOCUS M isoforms differentially affect the subcellular localization and stability of SHORT VEGETATIVE PHASE to regulate temperature-responsive flowering in Arabidopsis

Temperature is an important environmental cue that affects flowering time in plants. The MADS-box transcription factor FLOWERING LOCUS M (FLM) forms a heterodimeric complex with SHORT VEGETATIVE PHASE (SVP) and controls ambient temperature-responsive flowering in Arabidopsis. FLM-β and FLM-δ, two major splice variants produced from the FLM locus, exert opposite effects on flowering, but the molecular mechanism by which the interaction between FLM isoforms and SVP affects temperature-responsive flowering remains poorly understood. Here, we show that FLM-β and FLM-δ play important roles in modulating the temperature-dependent behavior, conformation, and stability of SVP. Nuclear localization of SVP decreases as temperature increases. FLM-β is required for SVP nuclear translocation at low temperature, whereas SVP interacts with FLM-δ mainly in the cytoplasm at high temperature. SVP preferentially binds to FLM-β at low temperature in tobacco leaf cells. SVP shows high binding affinity to FLM-β at low temperature and to FLM-δ at high temperature. SVP undergoes similar structural changes in the interactions with FLM-β and FLM-δ; however, FLM-δ likely causes more pronounced conformational changes in the SVP structure. FLM-δ causes rapid degradation of SVP at high temperature, compared with FLM-β, possibly via ubiquitination. Mutation of lysine 53 or lysine 165 in SVP causes increased abundance of SVP due to reduced ubiquitination of SVP and thus delays flowering at high temperature. Our findings suggest that temperature-dependent differential interactions between SVP and FLM isoforms modulate the temperature-responsive induction of flowering in Arabidopsis.

Implications of intracellular protein degradation pathways in Parkinson's disease and therapeutics

Parkinson's disease (PD) pathology is the most common motor neurodegenerative disease that occurs due to the progressive degeneration of dopaminergic neurons of the nigrostriatal pathway of the brain. The histopathological hallmark of the disease is fibrillary aggregate called Lewy bodies which majorly contain α-synuclein, suggesting the critical implication of diminished protein degradation mechanisms in disease pathogenesis. This α-synuclein-containing Lewy bodies are evident in both experimental models as well as in postmortem PD brain and are speculated to be pathogenic but still, the lineal association between these aggregates and the complexity of disease pathology is not yet well established and needs further attention. However, it has been reported that α-synuclein aggregates have consorted with the declined proteasome and lysosome activities. Therefore, in this review, we reappraise intracellular protein degradation mechanisms during PD pathology. This article focused on the findings of the last two decades suggesting the implications of protein degradation mechanisms in disease pathogenesis and based on shreds of evidence, some of the approaches are also suggested which may be adopted to find out the novel therapeutic targets for the management of PD patients.

Heat Shock Protein 70 as a Sex-Skewed Regulator of α-Synucleinopathy

The role of molecular chaperones, such as heat shock protein 70 (Hsp70), is not typically studied as a function of biological sex, but by addressing this gap we might improve our understanding of proteinopathic disorders that predominate in one sex. Therefore, we exposed male or female primary hippocampal cultures to preformed α-synuclein fibrils in a model of early-stage Lewy pathology. We first discovered that two mechanistically distinct inhibitors of Hsp70 function increased phospho-α-synuclein+ inclusions more robustly in male-derived neurons. Because Hsp70 is released into extracellular compartments and may restrict cell-to-cell transmission/amplification of α-synucleinopathy, we then tested the effects of low-endotoxin, exogenous Hsp70 (eHsp70) in primary hippocampal cultures. eHsp70 was taken up by and reduced α-synuclein+ inclusions in cells of both sexes, but pharmacological suppression of Hsp70 function attenuated the inhibitory effect of eHsp70 on perinuclear inclusions only in male neurons. In 20-month-old male mice infused with α-synuclein fibrils in the olfactory bulb, daily intranasal eHsp70 delivery also reduced inclusion numbers and the time to locate buried food. eHsp70 penetrated the limbic system and spinal cord of male mice within 3 h but was cleared within 72 h. Unexpectedly, no evidence of eHsp70 uptake from nose into brain was observed in females. A trend towards higher expression of inducible Hsp70-but not constitutive Hsp70 or Hsp40-was observed in amygdala tissues from male subjects with Lewy body disorders compared to unaffected male controls, supporting the importance of this chaperone in human disease. Women expressed higher amygdalar Hsp70 levels compared to men, regardless of disease status. Together, these data provide a new link between biological sex and a key chaperone that orchestrates proteostasis.

Recent advances in understanding the role of proteostasis

Maintenance of a functional proteome is achieved through the mechanism of proteostasis that involves precise coordination between molecular machineries assisting a protein from its conception to demise. Although each organelle within a cell has its own set of proteostasis machinery, inter-organellar communication and cell non-autonomous signaling bring forth the multidimensional nature of the proteostasis network. Exposure to extrinsic and intrinsic stressors can challenge the proteostasis network, leading to the accumulation of aberrant proteins or a decline in the proteostasis components, as seen during aging and in several diseases. Here, we summarize recent advances in understanding the role of proteostasis and its regulation in aging and disease, including monogenetic and infectious diseases. We highlight some of the emerging as well as unresolved questions in proteostasis that need to be addressed to overcome pathologies associated with damaged proteins and to promote healthy aging.

The Role of Protein S-Nitrosylation in Protein Misfolding-Associated Diseases

Abnormal and excessive nitrosative stress contributes to neurodegenerative disease associated with the production of pathological levels of misfolded proteins. The accumulated findings strongly suggest that excessive NO production can induce and deepen these pathological processes, particularly by the S-nitrosylation of target proteins. Therefore, the relationship between S-nitrosylated proteins and the accumulation of misfolded proteins was reviewed. We particularly focused on the S-nitrosylation of E3-ubiquitin-protein ligase, parkin, and endoplasmic reticulum chaperone, PDI, which contribute to the accumulation of misfolded proteins. In addition to the target proteins being S-nitrosylated, NOS, which produces NO, and GSNOR, which inhibits S-nitrosylation, were also suggested as potential therapeutic targets for protein misfolding-associated diseases.

Sodium sulfite causes gastric mucosal cell death by inducing oxidative stress

Sulfites are commonly used as a preservative and antioxidant additives in the food industry. Sulfites are absorbed by the gastrointestinal tract and distributed essentially to all body tissues. Although sulfites have been believed to be safe food additives, some studies have shown that they exhibit adverse effects in various tissues. In this study, we examined the cytotoxic effect of sodium sulfite (Na₂SO₃) against rat gastric mucosal cells (RGM1) and further investigated its underlying molecular mechanism. We demonstrated that exposure to Na₂SO₃ exerts significant cytotoxicity in RGM1 cells through induction of oxidative stress. Exposure of RGM1 cells to Na₂SO₃ caused a significant formation of protein carbonyls and 8-hydroxy-2'-deoxyguanosine, major oxidative stress markers, with a concomitant accumulation of carbonylated protein-related aggregates. Furthermore, we found that incubation of lysozyme with Na₂SO₃ evokes protein carbonylation and aggregation via the metal ion-catalyzed free radical formation derived from Na₂SO₃. Our results suggest that Na₂SO₃ might lead to gastric tissue injury via induction of oxidative stress by the formation of Na₂SO₃-related free radicals.

Synthesis and Selective Functionalization of Thiadiazine 1,1-Dioxides with Efficacy in a Model of Huntington's Disease

The scope of the acid-mediated 3-component synthesis of thiadiazines was investigated. A selective functionalization of the six-membered heterocyclic core structure was accomplished by sequential alkylations, saponifications, and coupling reactions. Several new analogs of a dihydropyrimidinone Hsp70 chaperone agonist, MAL1-271, showed promising activity in a cell based model of Huntington's disease.

Hsp70 and the Unfolded Protein Response as a Challenging Drug Target and an Inspiration for Probe Molecule Development

The unfolded protein response (UPR) is a cellular stress response mechanism that is critical for cell survival. Pharmacological modulation of the ATPase activity of the chaperone Hsp70 can trigger UPR-mediated cell death, thus removing pathogenic cells in human malignancies, or, alternatively, stimulate survival, thereby preventing apoptosis in neuronal cells and slowing the progress of inflammation, neurodegeneration, and aging. This Viewpoint highlights the complexity of the protein homeostasis network and discusses different approaches for modulating Hsp70 activity, including the use of a chemical reaction development-inspired library of Hsp70 agonists and antagonists.

Targeting α-synuclein for PD Therapeutics: A Pursuit on All Fronts

Parkinson's Disease (PD) is characterized both by the loss of dopaminergic neurons in the substantia nigra and the presence of cytoplasmic inclusions called Lewy Bodies. These Lewy Bodies contain the aggregated α-synuclein (α-syn) protein, which has been shown to be able to propagate from cell to cell and throughout different regions in the brain. Due to its central role in the pathology and the lack of a curative treatment for PD, an increasing number of studies have aimed at targeting this protein for therapeutics. Here, we reviewed and discussed the many different approaches that have been studied to inhibit α-syn accumulation via direct and indirect targeting. These analyses have led to the generation of multiple clinical trials that are either completed or currently active. These clinical trials and the current preclinical studies must still face obstacles ahead, but give hope of finding a therapy for PD with time.

Biologically Active Echinulin-Related Indolediketopiperazines from the Marine Sediment-Derived Fungus Aspergillus niveoglaucus

Seven known echinulin-related indolediketopiperazine alkaloids (1–7) were isolated from the Vietnamese sediment-derived fungus Aspergillus niveoglaucus. Using chiral HPLC, the enantiomers of cryptoechinuline B (1) were isolated as individual compounds for the first time. (+)-Cryptoechinuline B (1a) exhibited neuroprotective activity in 6-OHDA-, paraquat-, and rotenone-induced in vitro models of Parkinson’s disease. (−)-Cryptoechinuline B (1b) and neoechinulin C (5) protected the neuronal cells against paraquat-induced damage in a Parkinson’s disease model. Neoechinulin B (4) exhibited cytoprotective activity in a rotenone-induced model, and neoechinulin (7) showed activity in the 6-OHDA-induced model.

Lycopodium Attenuates Loss of Dopaminergic Neurons by Suppressing Oxidative Stress and Neuroinflammation in a Rat Model of Parkinson's Disease

Parkinson's disease, a chronic, age related neurodegenerative disorder, is characterized by a progressive loss of nigrostriatal dopaminergic neurons. Several studies have proven that the activation of glial cells, presence of alpha-synuclein aggregates, and oxidative stress, fuels neurodegeneration, and currently there is no definitive treatment for PD. In this study, a rotenone-induced rat model of PD was used to understand the neuroprotective potential of Lycopodium (Lyc), a commonly-used potent herbal medicine. Immunohistochemcial data showed that rotenone injections significantly increased the loss of dopaminergic neurons in the substantia nigra, and decreased the striatal expression of tyrosine hydroxylase. Further, rotenone administration activated microglia and astroglia, which in turn upregulated the expression of α-synuclein, pro-inflammatory, and oxidative stress factors, resulting in PD pathology. However, rotenone-injected rats that were orally treated with lycopodium (50 mg/kg) were protected against dopaminergic neuronal loss by diminishing the expression of matrix metalloproteinase-3 (MMP-3) and MMP-9, as well as reduced activation of microglia and astrocytes. This neuroprotective mechanism not only involves reduction in pro-inflammatory response and α-synuclein expression, but also synergistically enhanced antioxidant defense system by virtue of the drug's multimodal action. These findings suggest that Lyc has the potential to be further developed as a therapeutic candidate for PD.

In vitro models of synucleinopathies: informing on molecular mechanisms and protective strategies

Alpha-synuclein (α-Syn) is a central player in Parkinson's disease (PD) and in a spectrum of neurodegenerative diseases collectively known as synucleinopathies. The protein was first associated with PD just over 20 years ago, when it was found to (i) be a major component of Lewy bodies and (ii) to be also associated with familial forms of PD. The characterization of α-Syn pathology has been achieved through postmortem studies of human brains. However, the identification of toxic mechanisms associated with α-Syn was only achieved through the use of experimental models. In vitro models are highly accessible, enable relatively rapid studies, and have been extensively employed to address α-Syn-associated neurodegeneration. Given the diversity of models used and the outcomes of the studies, a cumulative and comprehensive perspective emerges as indispensable to pave the way for further investigations. Here, we subdivided in vitro models of α-Syn pathology into three major types: (i) models simulating α-Syn fibrillization and the formation of different aggregated structures in vitro, (ii) models based on the intracellular expression of α-Syn, reporting on pathogenic conditions and cellular dysfunctions induced, and (iii) models using extracellular treatment with α-Syn aggregated species, reporting on sites of interaction and their downstream consequences. In summary, we review the underlying molecular mechanisms discovered and categorize protective strategies, in order to pave the way for future studies and the identification of effective therapeutic strategies. This article is part of the Special Issue "Synuclein".

Radicicol rescues yeast cell death triggered by expression of human α-synuclein and its A53T mutant, but not by human βA4 peptide and proapoptotic protein bax

Aggregation/misfolding of α-synuclein and βA4 proteins cause neuronal cell death (NCD) associated with Parkinson's and Alzheimer's disease. It has been suggested that a heat shock protein-90 (Hsp90) inhibitor can prevent NCD by activating the heat shock transcription factor-1 which, in turn, upregulates molecular chaperones such as Hsp70 that targets aggregated/misfolded proteins for refolding/degradation. We have isolated radicicol, an Hsp90 inhibitor, from a fungus occurring in the crevices of marble rocks of Central India. Radicicol, which was found to be a strong antioxidant, was tested for its ability to rescue yeast cells from death induced by expression of wild-type α-synuclein, its more toxic A53T mutant, and βA4. It effectively overcomes wild-type/mutant α-synuclein mediated yeast cell death, concomitantly diminishes ROS levels, reverses mitochondrial dysfunction and prevents nuclear DNA-fragmentation, a hallmark of apoptosis. Surprisingly however, radicicol is unable to rescue yeast cells from death triggered by expression of secreted βA4. Moreover, although radicicol acts as an antioxidant it fails to prevent yeast cell death inflicted by the proapoptotic protein, Bax. Our results indicate that radicicol specifically targets aggregated/misfolded α-synuclein's toxicity and opens up the possibility of using multiple yeast assays to screen natural product libraries for compounds that would unambiguously target α-synuclein aggregation/misfolding.

Carbenoxolone-mediated cytotoxicity inhibits Vaccinia virus replication in a human keratinocyte cell line

The re-emergence of poxviral zoonotic infections and the threat of bioterrorism emphasise the demand for effective antipoxvirus therapies. Here, we show that carbenoxolone, a pharmacological inhibitor of gap junction function and a compound widely used in cell culture, is capable of hindering the replication of Vaccinia virus, the prototypical poxvirus, in a gap junction-independent manner in a human keratinocyte cell line. Viral protein synthesis occurs in the presence of carbenoxolone but infectious virion formation is minimal, indicating that carbenoxolone blocks viral morphogenesis. Initial viability tests suggested that carbenoxolone was not toxic to cells. However, electron microscopic analysis of carbenoxolone treated cells revealed that it alters the cellular endomembrane system. This widespread ultrastructural damage prevents Vaccinia virus virion assembly. These results strengthen the need for thorough characterisation of the effects of antiviral compounds on the cellular ultrastructure.

Synthesis and evaluation of esterified Hsp70 agonists in cellular models of protein aggregation and folding

Over-expression of the Hsp70 molecular chaperone prevents protein aggregation and ameliorates neurodegenerative disease phenotypes in model systems. We identified an Hsp70 activator, MAL1-271, that reduces α-synuclein aggregation in a Parkinson's Disease model. We now report that MAL1-271 directly increases the ATPase activity of a eukaryotic Hsp70. Next, twelve MAL1-271 derivatives were synthesized and examined in a refined α-synuclein aggregation model as well as in an assay that monitors maturation of a disease-causing Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) mutant, which is also linked to Hsp70 function. Compared to the control, MAL1-271 significantly increased the number of cells lacking α-synuclein inclusions and increased the steady-state levels of the CFTR mutant. We also found that a nitrile-containing MAL1-271 analog exhibited similar effects in both assays. None of the derivatives exhibited cellular toxicity at concentrations up to 100 μm, nor were cellular stress response pathways induced. These data serve as a gateway for the continued development of a new class of Hsp70 agonists with efficacy in these and potentially other disease models.

Autophagic response to cellular exposure to titanium dioxide nanoparticles

Titanium dioxide is "generally regarded as safe" and titanium dioxide nanoparticles (TiO₂ NPs) are used in a wide variety of consumer products. Cellular exposure to TiO₂ NPs results in complex effects on cell physiology including induction of oxidative stress and impairment of lysosomal function, raising concerns about the impact of TiO₂ NPs on biological systems. We investigated the effects of TiO₂ NPs (15, 50, and 100 nm in diameter) on the lysosome-autophagy system, the main cellular catabolic pathway that mediates degradation of nanomaterials. Specifically, we monitored a comprehensive set of markers of the lysosome-autophagy system upon cell exposure to TiO₂ NPs, ranging from transcriptional activation of genes required for the formation of autophagic vesicles to clearance of autophagic substrates. This study reveals that uptake of TiO₂ NPs induces a response of the lysosome-autophagy system mediated by the transcription factor EB and consequent upregulation of the autophagic flux. Prolonged exposure to TiO₂ NPs, however, was found to induce lysosomal dysfunction and membrane permeabilization, leading to a blockage in autophagic flux. Results from this study will inform the design of TiO₂ NP based devices with specific autophagy-modulating properties.

Amyloid assembly and disassembly

Amyloid fibrils are protein homopolymers that adopt diverse cross-β conformations. Some amyloid fibrils are associated with the pathogenesis of devastating neurodegenerative disorders, including Alzheimer's disease and Parkinson's disease. Conversely, functional amyloids play beneficial roles in melanosome biogenesis, long-term memory formation and release of peptide hormones. Here, we showcase advances in our understanding of amyloid assembly and structure, and how distinct amyloid strains formed by the same protein can cause distinct neurodegenerative diseases. We discuss how mutant steric zippers promote deleterious amyloidogenesis and aberrant liquid-to-gel phase transitions. We also highlight effective strategies to combat amyloidogenesis and related toxicity, including: (1) small-molecule drugs (e.g. tafamidis) to inhibit amyloid formation or (2) stimulate amyloid degradation by the proteasome and autophagy, and (3) protein disaggregases that disassemble toxic amyloid and soluble oligomers. We anticipate that these advances will inspire therapeutics for several fatal neurodegenerative diseases.

Summary: This Review showcases important advances in our understanding of amyloid structure, assembly and disassembly, which are inspiring novel therapeutic strategies for amyloid disorders.

Quantitatively Predictable Control of Cellular Protein Levels through Proteasomal Degradation

Protein function is typically studied and engineered by modulating protein levels within the complex cellular environment. To achieve fast, targeted, and predictable control of cellular protein levels without genetic manipulation of the target, we developed a technology for post-translational depletion based on a bifunctional molecule (NanoDeg) consisting of the antigen-binding fragment from the Camelidae species heavy-chain antibody (nanobody) fused to a degron signal that mediates degradation through the proteasome. We provide proof-of-principle demonstration of targeted degradation using a nanobody against the green fluorescent protein (GFP). Guided by predictive modeling, we show that customizing the NanoDeg rate of synthesis, rate of degradation, and mode of degradation enables quantitative and predictable control over the target's levels. Integrating the GFP-specific NanoDeg within a genetic circuit based on stimulus-dependent GFP output results in enhanced dynamic range and resolution of the output signal. By providing predictable control over cellular proteins' levels, the NanoDeg system could be readily used for a variety of systems-level analyses of cellular protein function.

Emerging preclinical pharmacological targets for Parkinson's disease

Parkinson's disease (PD) is a progressive neurological condition caused by the degeneration of dopaminergic neurons in the basal ganglia. It is the most prevalent form of Parkinsonism, categorized by cardinal features such as bradykinesia, rigidity, tremors, and postural instability. Due to the multicentric pathology of PD involving inflammation, oxidative stress, excitotoxicity, apoptosis, and protein aggregation, it has become difficult to pin-point a single therapeutic target and evaluate its potential application. Currently available drugs for treating PD provide only symptomatic relief and do not decrease or avert disease progression resulting in poor patient satisfaction and compliance. Significant amount of understanding concerning the pathophysiology of PD has offered a range of potential targets for PD. Several emerging targets including AAV-hAADC gene therapy, phosphodiesterase-4, potassium channels, myeloperoxidase, acetylcholinesterase, MAO-B, dopamine, A2A, mGlu5, and 5-HT-1A/1B receptors are in different stages of clinical development. Additionally, alternative interventions such as deep brain stimulation, thalamotomy, transcranial magnetic stimulation, and gamma knife surgery, are also being developed for patients with advanced PD. As much as these therapeutic targets hold potential to delay the onset and reverse the disease, more targets and alternative interventions need to be examined in different stages of PD. In this review, we discuss various emerging preclinical pharmacological targets that may serve as a new promising neuroprotective strategy that could actually help alleviate PD and its symptoms.

Engineering therapeutic protein disaggregases

Therapeutic agents are urgently required to cure several common and fatal neurodegenerative disorders caused by protein misfolding and aggregation, including amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), and Alzheimer's disease (AD). Protein disaggregases that reverse protein misfolding and restore proteins to native structure, function, and localization could mitigate neurodegeneration by simultaneously reversing 1) any toxic gain of function of the misfolded form and 2) any loss of function due to misfolding. Potentiated variants of Hsp104, a hexameric AAA+ ATPase and protein disaggregase from yeast, have been engineered to robustly disaggregate misfolded proteins connected with ALS (e.g., TDP-43 and FUS) and PD (e.g., α-synuclein). However, Hsp104 has no metazoan homologue. Metazoa possess protein disaggregase systems distinct from Hsp104, including Hsp110, Hsp70, and Hsp40, as well as HtrA1, which might be harnessed to reverse deleterious protein misfolding. Nevertheless, vicissitudes of aging, environment, or genetics conspire to negate these disaggregase systems in neurodegenerative disease. Thus, engineering potentiated human protein disaggregases or isolating small-molecule enhancers of their activity could yield transformative therapeutics for ALS, PD, and AD.

N-Acetyl-l-Cysteine Protects Astrocytes against Proteotoxicity without Recourse to Glutathione

N-acetyl-l-cysteine (NAC) exhibits protective properties in brain injury models and has undergone a number of clinical trials. Most studies of NAC have focused on neurons. However, neuroprotection may be complemented by the protection of astrocytes because healthier astrocytes can better support the viability of neurons. Here, we show that NAC can protect astrocytes against protein misfolding stress (proteotoxicity), the hallmark of neurodegenerative disorders. Although NAC is thought to be a glutathione precursor, NAC protected primary astrocytes from the toxicity of the proteasome inhibitor MG132 without eliciting any increase in glutathione. Furthermore, glutathione depletion failed to attenuate the protective effects of NAC. MG132 elicited a robust increase in the folding chaperone heat shock protein 70 (Hsp70), and NAC mitigated this effect. Nevertheless, three independent inhibitors of Hsp70 function ablated the protective effects of NAC, suggesting that NAC may help preserve Hsp70 chaperone activity and improve protein quality control without need for Hsp70 induction. Consistent with this view, NAC abolished an increase in ubiquitinated proteins in MG132-treated astrocytes. However, NAC did not affect the loss of proteasome activity in response to MG132, demonstrating that it boosted protein homeostasis and cell viability without directly interfering with the efficacy of this proteasome inhibitor. The thiol-containing molecules l-cysteine and d-cysteine both mimicked the protective effects of NAC, whereas the thiol-lacking molecule N-acetyl-S-methyl-l-cysteine failed to exert protection or blunt the rise in ubiquitinated proteins. Collectively, these findings suggest that the thiol group in NAC is required for its effects on glial viability and protein quality control.

Chaperone-Based Therapies for Disease Modification in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder and is characterized by the presence of pathological intracellular aggregates primarily composed of misfolded α-synuclein. This pathology implicates the molecular machinery responsible for maintaining protein homeostasis (proteostasis), including molecular chaperones, in the pathobiology of the disease. There is mounting evidence from preclinical and clinical studies that various molecular chaperones are downregulated, sequestered, depleted, or dysfunctional in PD. Current therapeutic interventions for PD are inadequate as they fail to modify disease progression by ameliorating the underlying pathology. Modulating the activity of molecular chaperones, cochaperones, and their associated pathways offers a new approach for disease modifying intervention. This review will summarize the potential of chaperone-based therapies that aim to enhance the neuroprotective activity of molecular chaperones or utilize small molecule chaperones to promote proteostasis.

TFEB-mediated activation of the lysosome-autophagy system affects the transduction efficiency of adeno-associated virus 2

Adeno-associated virus (AAV)-mediated gene transfer is an appealing therapeutic option due to AAV's safety profile. Effective delivery of AAV's genetic cargo to the nucleus, however, requires evasion of host cell barriers, including cellular clearance mechanisms mediated by the lysosome-autophagy system. We used AAV serotype 2 to monitor the autophagic response to cellular internalization of AAV and to characterize the effect of AAV-induced activation of autophagy on transgene expression. We found AAV2 internalization to induce activation of transcription factor EB, a master regulator of autophagy and lysosomal biogenesis, and upregulation of the lysosome-autophagy system. We showed that AAV2-induced activation of autophagy parallels a reduction in transgene expression, but also an increase in autophagic clearance of protein aggregates. These results can inform the design of AAV vectors with autophagy-modulating properties for applications ranging from the design of efficient gene delivery vectors to the treatment of diseases characterized by accumulation of autophagic cargo.

Using bicistronic constructs to evaluate the chaperone activities of heat shock proteins in cells

Heat shock proteins (Hsps) are molecular chaperones that prevent the aggregation of client proteins by facilitating their refolding, or trafficking them for degradation. The chaperone activities of Hsps are dependent on dynamic protein-protein interactions, including their oligomerisation into large multi-subunit complexes. Thus, tagging Hsps with fluorescent proteins can interfere with their chaperone activity. To overcome this limitation, we have exploited bicistronic constructs for the concurrent expression of a non-tagged Hsp and fluorescent reporter from a single mRNA in cells. We used the Hsp-encoding bicistronic constructs in a cell-based model of protein aggregation, using a destabilised (mutant) form of firefly luciferase (mFluc) that forms inclusion bodies in cells. Expression of Hsp40, Hsp70, or Hsp40 and Hsp70 in cells expressing mFluc decreased the formation of inclusion bodies by 25–46% compared to controls. Moreover, there was a concentration-dependent decrease in the proportion of cells with inclusions when Hsp70, or Hsp40 and Hsp70 were co-expressed with mFluc in cells. The Hsp-encoding bicistronic constructs enable transfection efficiencies and concentration-dependent effects of Hsp expression to be determined using fluorescence based techniques, without the need to tag the Hsp with a fluorescent protein.

Targeting chaperones, heat shock factor-1, and unfolded protein response: Promising therapeutic approaches for neurodegenerative disorders

Protein misfolding, which is known to cause several serious diseases, is an emerging field that addresses multiple therapeutic areas. Misfolding of a disease-specific protein in the central nervous system ultimately results in the formation of toxic aggregates that may accumulate in the brain, leading to neuronal cell death and dysfunction, and associated clinical manifestations. A large number of neurodegenerative diseases in humans, including Alzheimer's, Parkinson's, Huntington's, and prion diseases, are primarily caused by protein misfolding and aggregation. Notably, the cellular system is equipped with a protein quality control system encompassing chaperones, ubiquitin proteasome system, and autophagy, as a defense mechanism that monitors protein folding and eliminates inappropriately folded proteins. As the intrinsic molecular mechanisms of protein misfolding become more clearly understood, the novel therapeutic approaches in this arena are gaining considerable interest. The present review will describe the chaperones network and different approaches as the therapeutic targets for neurodegenerative diseases. Current and emerging therapeutic approaches to combat neurodegenerative diseases, addressing the roles of molecular, chemical, and pharmacological chaperones, as well as heat shock factor-1 and the unfolded protein response, are also discussed in detail.

Designer protein disaggregases to counter neurodegenerative disease

Protein misfolding and aggregation unify several devastating neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. There are no effective therapeutics for these disorders and none that target the reversal of the aberrant protein misfolding and aggregation that cause disease. Here, I showcase important advances to define, engineer, and apply protein disaggregases to mitigate deleterious protein misfolding and counter neurodegeneration. I focus on two exogenous protein disaggregases, Hsp104 from yeast and gene 3 protein from bacteriophages, as well as endogenous human protein disaggregases, including: (a) Hsp110, Hsp70, Hsp40, and small heat-shock proteins; (b) HtrA1; and (c) NMNAT2 and Hsp90. I suggest that protein-disaggregase modalities can be channeled to treat numerous fatal and presently incurable neurodegenerative diseases.

Expanding role of molecular chaperones in regulating α-synuclein misfolding; implications in Parkinson's disease

Protein misfolding under stressful environmental conditions cause several cellular problems owing to the disturbed cellular protein homeostasis, which may further lead to neurological disorders like Parkinson's disease (PD), Alzheimer's disease (AD), Amyloid lateral sclerosis and Huntington disease (HD). The presence of cellular defense mechanisms like molecular chaperones and proteasomal degradation systems prevent protein misfolding and aggregation. Molecular chaperones plays primary role in preventing protein misfolding by mediating proper native folding, unfolding and refolding of the polypeptides along with vast number of cellular functions. In past few years, the understanding of molecular chaperone mechanisms has been expanded enormously although implementation to prevent protein aggregation diseases is still deficient. We in this review evaluated major classes of molecular chaperones and their mechanisms relevant for preventing protein aggregation, specific case of α-synuclein aggregation. We also evaluate the molecular chaperone function as a novel therapeutic approach and the chaperone inhibitors or activators as small molecular drug targets.

Lanosterol Suppresses the Aggregation and Cytotoxicity of Misfolded Proteins Linked with Neurodegenerative Diseases

Accumulation of misfolded or aberrant proteins in neuronal cells is linked with neurodegeneration and other pathologies. Which molecular mechanisms fail and cause inappropriate folding of proteins and what is their relationship to cellular toxicity is not well known. How does it happen and what are the probable therapeutic or molecular approaches to counter them are also not clear. Here, we demonstrate that treatment of lanosterol diminishes aberrant proteotoxic aggregation and mitigates their cytotoxicity via induced expression of co-chaperone CHIP and elevated autophagy. The addition of lanosterol not only reduces aggregation of mutant bonafide misfolded proteins but also effectively prevents accumulation of various mutant disease-prone proteotoxic proteins. Finally, we observed that lanosterol mitigates cytotoxicity in cells, mediated by different stress-inducing agents. Taken together, our present results suggest that upregulation of cellular molecular chaperones, primarily using small molecules, can probably offer an efficient therapeutic approach in the future against misfolding of different disease-causing proteins and neurodegenerative disorders. Graphical Abstract ᅟ.

Characterization of aggregate/aggresome structures formed by polyhedrin of Bombyx mori nucleopolyhedrovirus

Virus infections often lead to formation of aggregates and aggresomes in host cells. In this study, production of aggregates and aggresomes by the highly expressed protein polyhedrin of Bombyx mori nucleopolyhedrovirus (BmNPV) at 24 h postinfection (p.i.) was detected with a fluorescent molecular dye, and verified by colocalization of polyhedrin with aggresomal markers, GFP-250 and γ-tubulin. Polyhedrin aggregates showed hallmark characteristics of aggresomes: formation was microtubule-dependent; they colocalized with heat shock cognates/proteins of the 70-kDa family (HSC/HSP70s), ubiquitinated proteins and recruited the mitochondria. Aggregated polyhedrin protein gradually gained its active conformation accompanying progress of BmNPV infection. At 48 h p.i. recovered polyhedrin bound directly to Bombyx mori microtubule-associated protein 1-light chain 3 (BmLC3), an autophagosome marker, and was colocalized with BmLC3 to the isolation membrane of autophagosome, implying the involvement of polyhedrin in cellular autophagy. Inhibition of autophagy by 3-methyladenine (3-MA) dramatically resulted in decrease of polyhedrin expression and polyhedra particle production. These observations suggested that highly expressed polyhedrin forms aggregate to get involved in cellular autophagy then play an important role in polyhedra production.

A Novel Hsp90 Inhibitor Activates Compensatory Heat Shock Protein Responses and Autophagy and Alleviates Mutant A53T α-Synuclein Toxicity

A potential cause of neurodegenerative diseases, including Parkinson's disease (PD), is protein misfolding and aggregation that in turn leads to neurotoxicity. Targeting Hsp90 is an attractive strategy to halt neurodegenerative diseases, and benzoquinone ansamycin (BQA) Hsp90 inhibitors such as geldanamycin (GA) and 17-(allylamino)-17-demethoxygeldanamycin have been shown to be beneficial in mutant A53T α-synuclein PD models. However, current BQA inhibitors result in off-target toxicities via redox cycling and/or arylation of nucleophiles at the C19 position. We developed novel 19-substituted BQA (19BQA) as a means to prevent arylation. In this study, our data demonstrated that 19-phenyl-GA, a lead 19BQA in the GA series, was redox stable and exhibited little toxicity relative to its parent quinone GA in human dopaminergic SH-SY5Y cells as examined by oxygen consumption, trypan blue, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT), and apoptosis assays. Meanwhile, 19-phenyl-GA retained the ability to induce autophagy and potentially protective heat shock proteins (HSPs) such as Hsp70 and Hsp27. We found that transduction of A53T, but not wild type (WT) α-synuclein, induced toxicity in SH-SY5Y cells. 19-Phenyl-GA decreased oligomer formation and toxicity of A53T α-synuclein in transduced cells. Mechanistic studies indicated that mammalian target of rapamycin (mTOR)/p70 ribosomal S6 kinase signaling was activated by A53T but not WT α-synuclein, and 19-phenyl-GA decreased mTOR activation that may be associated with A53T α-synuclein toxicity. In summary, our results indicate that 19BQAs such as 19-phenyl-GA may provide a means to modulate protein-handling systems including HSPs and autophagy, thereby reducing the aggregation and toxicity of proteins such as mutant A53T α-synuclein.

Icariin reduces α-synuclein over-expression by promoting α-synuclein degradation

The objectives of this study are to investigate the effects of icariin (a main component extracted from Epimedium) on over-expression of α-synuclein and to explore the underlying mechanisms. APPV717I transgenic (Tg) mice and A53T α-synuclein-transfected PC12 cells were used in this study. The content of α-synuclein mRNA was determined by reverse-transcription PCR (RT-PCR). Western blotting and immunohistochemistry were used to detect the protein expression of α-synuclein, parkin, ubiquitin carboxy-terminal hydrolase L1 (UCH-L1), and heat shock protein 70 (HSP70). In 10-month-old APP Tg mice, α-synuclein expression was increased, and the expression of Parkin, UCH-L1, and HSP70 was decreased in the hippocampus. Intragastrical administration of icariin (30 and 100 μmol/kg) for 6 months (from 4 to 10 months old) decreased α-synuclein expression and increased the expression of Parkin, UCH-L1, and HSP70 in the hippocampus of APP Tg mice. Incubation of icariin (40 and 80 μM) with A53T α-synuclein-transfected PC12 cells for 24 h showed no difference in the expressions of α-synuclein mRNA among model group and icariin-treated groups, but decreased α-synuclein protein expression in both monomer and tetramer. Along with the downregulation of α-synuclein, icariin (40 and 80 μM) elevated the expression of Parkin, UCH-L1, and HSP70 in A53T α-synuclein-transfected cells. Icariin inhibited the over-expression of α-synuclein both in vivo and in vitro. The mechanism of icariin may be related to upregulate Parkin and UCH-L1 expression in ubiquitin-proteasome system and HSP70 in molecular chaperone, thus enhancing the degradation of α-synuclein. It is suggested that icariin may have the potential to treat Alzheimer's disease (AD) and other synucleinopathies.

Fibril growth and seeding capacity play key roles in α-synuclein-mediated apoptotic cell death

The role of extracellular α-synuclein (α-syn) in the initiation and the spreading of neurodegeneration in Parkinson's disease (PD) has been studied extensively over the past 10 years. However, the nature of the α-syn toxic species and the molecular mechanisms by which they may contribute to neuronal cell loss remain controversial. In this study, we show that fully characterized recombinant monomeric, fibrillar or stabilized forms of oligomeric α-syn do not trigger significant cell death when added individually to neuroblastoma cell lines. However, a mixture of preformed fibrils (PFFs) with monomeric α-syn becomes toxic under conditions that promote their growth and amyloid formation. In hippocampal primary neurons and ex vivo hippocampal slice cultures, α-syn PFFs are capable of inducing a moderate toxicity over time that is greatly exacerbated upon promoting fibril growth by addition of monomeric α-syn. The causal relationship between α-syn aggregation and cellular toxicity was further investigated by assessing the effect of inhibiting fibrillization on α-syn-induced cell death. Remarkably, our data show that blocking fibril growth by treatment with known pharmacological inhibitor of α-syn fibrillization (Tolcapone) or replacing monomeric α-syn by monomeric β-synuclein in α-syn mixture composition prevent α-syn-induced toxicity in both neuroblastoma cell lines and hippocampal primary neurons. We demonstrate that exogenously added α-syn fibrils bind to the plasma membrane and serve as nucleation sites for the formation of α-syn fibrils and promote the accumulation and internalization of these aggregates that in turn activate both the extrinsic and intrinsic apoptotic cell death pathways in our cellular models. Our results support the hypothesis that ongoing aggregation and fibrillization of extracellular α-syn play central roles in α-syn extracellular toxicity, and suggest that inhibiting fibril growth and seeding capacity constitute a viable strategy for protecting against α-syn-induced toxicity and slowing the progression of neurodegeneration in PD and other synucleinopathies.

Genetic and chemical activation of TFEB mediates clearance of aggregated α-synuclein

Aggregation of α-synuclein (α-syn) is associated with the development of a number of neurodegenerative diseases, including Parkinson’s disease (PD). The formation of α-syn aggregates results from aberrant accumulation of misfolded α-syn and insufficient or impaired activity of the two main intracellular protein degradation systems, namely the ubiquitin-proteasome system and the autophagy-lysosomal pathway. In this study, we investigated the role of transcription factor EB (TFEB), a master regulator of the autophagy-lysosomal pathway, in preventing the accumulation of α-syn aggregates in human neuroglioma cells. We found that TFEB overexpression reduces the accumulation of aggregated α-syn by inducing autophagic clearance of α-syn. Furthermore, we showed that pharmacological activation of TFEB using 2-hydroxypropyl-β-cyclodextrin promotes autophagic clearance of aggregated α-syn. In summary, our findings demonstrate that TFEB modulates autophagic clearance of α-syn and suggest that pharmacological activation of TFEB is a promising strategy to enhance the degradation of α-syn aggregates.

Heat shock protein responses to aging and proteotoxicity in the olfactory bulb

The olfactory bulb is one of the most vulnerable brain regions in age-related proteinopathies. Proteinopathic stress is mitigated by the heat shock protein (Hsp) family of chaperones. Here, we describe age-related decreases in Hsc70 in the olfactory bulb of the female rat and higher levels of Hsp70 and Hsp25 in middle and old age than at 2-4 months. To model proteotoxic and oxidative stress in the olfactory bulb, primary olfactory bulb cultures were treated with the proteasome inhibitors lactacystin and MG132 or the pro-oxidant paraquat. Toxin-induced increases were observed in Hsp70, Hsp25, and Hsp32. To determine the functional consequences of the increase in Hsp70, we attenuated Hsp70 activity with two mechanistically distinct inhibitors. The Hsp70 inhibitors greatly potentiated the toxicity of sublethal lactacystin or MG132 but not of paraquat. Although ubiquitinated protein levels were unchanged with aging in vivo or with sublethal MG132 in vitro, there was a large, synergistic increase in ubiquitinated proteins when proteasome and Hsp70 functions were simultaneously inhibited. Our study suggests that olfactory bulb cells rely heavily on Hsp70 chaperones to maintain homeostasis during mild proteotoxic, but not oxidative insults, and that Hsp70 prevents the accrual of ubiquitinated proteins in these cells. The olfactory bulb is affected in the early phases of many age-related neurodegenerative disorders. Here, we described the impact of aging on multiple heat shock proteins (Hsps), such as Hsp70, in the female rat olfactory bulb in vivo. Using multiple proteasome and Hsp70 inhibitors (see schematic), we found that proteotoxicity elicited a compensatory increase in Hsp70 in primary olfactory bulb cells in vitro. Hsp70 then reduced the proteotoxic buildup of ubiquitinated proteins and robustly protected against cell death according to three independent viability assays. Thus, olfactory bulb neurons can mount impressive natural adaptations to proteotoxic injury, perhaps explaining why neurodegenerative disorders are so delayed in onset and so slow to progress.

Heat shock protein defenses in the neocortex and allocortex of the telencephalon

The telencephalic allocortex develops protein inclusions before the neocortex in many age-related proteinopathies. One major defense mechanism against proteinopathic stress is the heat shock protein (Hsp) network. We therefore contrasted Hsp defenses in stressed primary neocortical and allocortical cells. Neocortical neurons were more resistant to the proteasome inhibitor MG132 than neurons from 3 allocortical subregions: entorhinal cortex, piriform cortex, and hippocampus. However, allocortical neurons exhibited higher MG132-induced increases in Hsp70 and heat shock cognate 70 (Hsc70). MG132-treated allocortical neurons also exhibited greater levels of protein ubiquitination. Inhibition of Hsp70/Hsc70 activity synergistically exacerbated MG132 toxicity in allocortical neurons more than neocortical neurons, suggesting that the allocortex is more reliant on these Hsp defenses. In contrast, astrocytes harvested from the neocortex or allocortex did not differ in their response to Hsp70/Hsc70 inhibition. Consistent with the idea that chaperones are maximally engaged in allocortical neurons, an increase in Hsp70/Hsc70 activity was protective only in neocortical neurons. Finally, the levels of select Hsps were altered in the neocortex and allocortex in vivo with aging.

Inhibition of neuroinflammation and mitochondrial dysfunctions by carbenoxolone in the rotenone model of Parkinson's disease

α-Synuclein aggregation contributes to the Parkinson's disease (PD) pathology in multiple ways-the two most important being the activation of neuroinflammation and mitochondrial dysfunction. Our recent studies have shown the beneficial effects of a heat shock protein (HSP) inducer, carbenoxolone (Cbx), in reducing the aggregation of α-synuclein in a rotenone-based rat model of PD. The present study was designed to explore its ability to attenuate the α-synuclein-mediated alterations in neuroinflammation and mitochondrial functions. The PD model was generated by the rotenone administration (2 mg/kg b.wt.) to the male SD rats for a period of 5 weeks. Cbx (20 mg/kg b.wt.) co-administration was seen to reduce the activation of astrocytes incited by rotenone. Subsequently, the release of pro-inflammatory cytokines TNF-α, IL-6, and IL-1β was inhibited. Further, the expression level of various inflammatory mediators such as COX-2, iNOS, and NF-κB was also reduced following Cbx co-treatment. Cbx was also shown to reduce the rotenone-induced decline in activity of mitochondrial complexes-I, -II, and -IV. Protection of mitochondrial functions and reduction in neuroinflammation lead to the lesser production of ROS and subsequently reduced oxidative stress. This was reflected by the increase in both the cytosolic and mitochondrial GSH levels as well as SOD activity during Cbx co-treatment. Thus, Cbx reduces the inflammatory response and improves the mitochondrial dysfunctions by reducing α-synuclein aggregation. In addition, it also reduces the associated oxidative stress. Due to its ability to target the multiple pathways implicated in the PD, Cbx can serve as a highly beneficial prophylactic agent.

Molecular chaperones and protein folding as therapeutic targets in Parkinson's disease and other synucleinopathies

Changes in protein metabolism are key to disease onset and progression in many neurodegenerative diseases. As a prime example, in Parkinson's disease, folding, post-translational modification and recycling of the synaptic protein α-synuclein are clearly altered, leading to a progressive accumulation of pathogenic protein species and the formation of intracellular inclusion bodies. Altered protein folding is one of the first steps of an increasingly understood cascade in which α-synuclein forms complex oligomers and finally distinct protein aggregates, termed Lewy bodies and Lewy neurites. In neurons, an elaborated network of chaperone and co-chaperone proteins is instrumental in mediating protein folding and re-folding. In addition to their direct influence on client proteins, chaperones interact with protein degradation pathways such as the ubiquitin-proteasome-system or autophagy in order to ensure the effective removal of irreversibly misfolded and potentially pathogenic proteins. Because of the vital role of proper protein folding for protein homeostasis, a growing number of studies have evaluated the contribution of chaperone proteins to neurodegeneration. We herein review our current understanding of the involvement of chaperones, co-chaperones and chaperone-mediated autophagy in synucleinopathies with a focus on the Hsp90 and Hsp70 chaperone system. We discuss genetic and pathological studies in Parkinson's disease as well as experimental studies in models of synucleinopathies that explore molecular chaperones and protein degradation pathways as a novel therapeutic target. To this end, we examine the capacity of chaperones to prevent or modulate neurodegeneration and summarize the current progress in models of Parkinson's disease and related neurodegenerative disorders.