A small molecule Toll-like receptor antagonist rescues α-synuclein fibril pathology

Structure based design, synthesis and identification of novel covalent reversible dual TLR2/TLR9 small molecule antagonists

Inflammation is a key driver of the onset and progression of neurodegenerative diseases and cancer and can be caused by aggregated proteins, injured neurons or synapses, dysregulation of inflammatory control mechanisms, and other factors. Tolllike receptors (TLRs) are important mediators of inflammatory pathways, and their activation leads to pro-inflammatory cytokine release by immune cells in the periphery or in the central nervous system (CNS). TLR2 and TLR9 are implicated in the inflammatory pathogenesis of CNS degenerative diseases such as Parkinson's Disease (PD) and amyotrophic lateral sclerosis (ALS). They are also held to be important in the etiology of certain malignancies like inflammatory pancreatic ductal adenocarcinoma and glioblastoma. Inactivation of TLR2/9 in animal models of neurodegeneration has reduced pathological markers and diminished neuronal loss, while in animal models of cancer it has suppressed tumors. Therefore, TLR2 and TLR9 may be potential targets for the treatment of neurodegenerative disorders and cancers. We identified for the first time a key binding locus in TLR2/9 TIR domain which guided reversible covalent drug (RCD) design of a novel, first-in class series of dual TLR2/9 antagonists. Sub-micromolar antagonist concentrations potently inhibited TLR2 and TLR9 signaling induced by TLR2/9 specific agonists. Importantly, this series of antagonists did not discernably activate other TLRs and exhibited favorable in-vitro ADME and safety. The analogs described here may help realize effective TLR2/9 antagonism as a viable therapeutic strategy for inflammation driven CNS diseases and various malignancies with an inflammatory etiology.

Emerging targets of α-synuclein spreading in α-synucleinopathies: a review of mechanistic pathways and interventions

α-Synucleinopathies constitute a spectrum of neurodegenerative disorders, including Parkinson's disease (PD), Lewy body dementia (LBD), Multiple System Atrophy (MSA), and Alzheimer's disease concurrent with LBD (AD-LBD). These disorders are unified by a pathological hallmark: aberrant misfolding and accumulation of α-synuclein (α-syn). This review delves into the pivotal role of α-syn, the key agent in α-synucleinopathy pathophysiology, and provides a survey of potential therapeutics that target cell-to-cell spread of pathologic α-syn. Recognizing the intricate complexity and multifactorial etiology of α-synucleinopathy, the review illuminates the potential of various membrane receptors, proteins, intercellular spreading pathways, and pathological agents for therapeutic interventions. While significant progress has been made in understanding α-synucleinopathy, the pursuit of efficacious treatments remains challenging. Several strategies involving decreasing α-syn production and aggregation, increasing α-syn degradation, lowering extracellular α-syn, and inhibiting cellular uptake of α-syn are presented. The paper underscores the necessity of meticulous and comprehensive investigations to advance our knowledge of α-synucleinopathy pathology and ultimately develop innovative therapeutic strategies for α-synucleinopathies.

Astrocytes contribute to toll-like receptor 2-mediated neurodegeneration and alpha-synuclein pathology in a human midbrain Parkinson's model

BACKGROUND

Parkinson's disease (PD) is characterised by degeneration of ventral midbrain dopaminergic (DA) neurons and abnormal deposition of α-synuclein (α-syn) in neurons. Activation of the innate immune pathogen recognition receptor toll-like receptor 2 (TLR2) is associated with exacerbation of α-syn pathology. TLR2 is increased on neurons in the PD brain, and its activation results in the accumulation and propagation of α-syn through autophagy inhibition in neurons. In addition to the aggregation and propagation of pathological α-syn, dysfunction of astrocytes may contribute to DA neuronal death and subsequent clinical progression of PD. However, the role of astrocytes in TLR2-mediated PD pathology is less explored but important to address, given that TLR2 is a potential therapeutic target for PD.

METHODS

Induced pluripotent stem cells from three controls and three PD patients were differentiated into a midbrain model comprised of neurons (including DA neurons) and astrocytes. Cells were treated with or without the TLR2 agonist Pam3CSK4, and α-syn pathology was seeded using pre-formed fibrils. Confocal imaging was used to assess lysosomal function and α-syn pathology in the different cell types, as well as DA neuron health and astrocyte activation.

RESULTS

TLR2 activation acutely impaired the autophagy lysosomal pathway, and potentiated α-syn pathology seeded by pre-formed fibrils in PD neurons and astrocytes, leading to degeneration and loss of DA neurons. The astrocytes displayed impaired chaperone-mediated autophagy reducing their ability to clear accumulated α-syn, and increases of A1 neurotoxic phenotypic proteins SerpinG1, complement C3, PSMB8 and GBP2. Moreover, the phenotypic changes in astrocytes correlated with a specific loss of DA neurons.

CONCLUSIONS

Taken together, these results support a role for astrocyte dysfunction in α-syn accumulation and DA neuronal loss following TLR2 activation in PD.

TIR domains of TLR family-from the cell culture to the protein sample for structural studies

Toll-like receptors (TLRs) are key players in the innate immune system. Despite the great efforts in TLR structural biology, today we know the spatial structures of only four human TLR intracellular TIR domains. All of them belong to one of five subfamilies of receptors. One of the main bottlenecks is the high-level production of correctly folded proteins in soluble form. Here we used a rational approach to find the optimal parameters to produce TIR domains of all ten human TLR family members in soluble form in E. coli cells. We showed that dozens of milligrams of soluble His-tagged TLR2/3/6/7TIR and MBP-tagged TLR3/5/7/8TIR can be produced. We also developed the purification protocols and demonstrated by CD and NMR spectroscopy that purified TLR2/3/7TIR demonstrate a structural organization inherent to TIR domains. This illustrates the correct folding of produced proteins and their suitability for further structural and functional investigations.

What Can Inflammation Tell Us about Therapeutic Strategies for Parkinson's Disease?

Parkinson's disease (PD) is a common neurodegenerative disorder with a complicated etiology and pathogenesis. α-Synuclein aggregation, dopaminergic (DA) neuron loss, mitochondrial injury, oxidative stress, and inflammation are involved in the process of PD. Neuroinflammation has been recognized as a key element in the initiation and progression of PD. In this review, we summarize the inflammatory response and pathogenic mechanisms of PD. Additionally, we describe the potential anti-inflammatory therapies, including nod-like receptor pyrin domain containing protein 3 (NLRP3) inflammasome inhibition, nuclear factor κB (NF-κB) inhibition, microglia inhibition, astrocyte inhibition, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibition, the peroxisome proliferator-activated receptor γ (PPARγ) agonist, targeting the mitogen-activated protein kinase (MAPK) pathway, targeting the adenosine monophosphate-activated protein kinase (AMPK)-dependent pathway, targeting α-synuclein, targeting miRNA, acupuncture, and exercise. The review focuses on inflammation and will help in designing new prevention strategies for PD.

Alpha-Synuclein Contribution to Neuronal and Glial Damage in Parkinson's Disease

Parkinson's disease (PD) is a complex neurodegenerative disease characterized by the progressive loss of dopaminergic neurons in the substantia nigra and the widespread accumulation of alpha-synuclein (αSyn) protein aggregates. αSyn aggregation disrupts critical cellular processes, including synaptic function, mitochondrial integrity, and proteostasis, which culminate in neuronal cell death. Importantly, αSyn pathology extends beyond neurons-it also encompasses spreading throughout the neuronal environment and internalization by microglia and astrocytes. Once internalized, glia can act as neuroprotective scavengers, which limit the spread of αSyn. However, they can also become reactive, thereby contributing to neuroinflammation and the progression of PD. Recent advances in αSyn research have enabled the molecular diagnosis of PD and accelerated the development of targeted therapies. Nevertheless, despite more than two decades of research, the cellular function, aggregation mechanisms, and induction of cellular damage by αSyn remain incompletely understood. Unraveling the interplay between αSyn, neurons, and glia may provide insights into disease initiation and progression, which may bring us closer to exploring new effective therapeutic strategies. Herein, we provide an overview of recent studies emphasizing the multifaceted nature of αSyn and its impact on both neuron and glial cell damage.

Live cell in situ lysosomal GCase activity correlates to alpha-synuclein levels in human differentiated neurons with LRRK2 and GBA1 mutations

Introduction

Heterozygous mutations in GBA1, which encodes the lysosomal hydrolase glucocerebrosidase (GCase), are a common risk factor for the neurodegenerative movement disorder Parkinson's disease (PD). Consequently, therapeutic options targeting the GCase enzyme are in development. An important aspect of this development is determining the effect of potential modifying compounds on GCase activity, which can be complicated by the different methods and substrate probes that are commonly employed for this purpose.

Methods

In this study, we employed the GCase substrate probe 5-(pentafluorobenzoylamino)fluorescein di-D-glucopyranoside (PFB-FDGlu) in combination with live cell imaging to measure GCase activity in situ in the lysosome.

Results

The live cell assay was validated using the GCase inhibitor conduritol-B-epoxide and with GBA1 knockout neural cells and was then used to assess GCase activity in iPSC differentiated into neural stem cells and neurons that were obtained from idiopathic PD patients and PD patients with the LRRK2 G2019S and GBA N370S mutations, as well as controls (n = 4 per group). Heterogeneity in GCase activity was observed across all groups. However, a significant inverse correlation between GCase activity and levels of alpha-synuclein protein was observed.

Discussion

The live cell imaging assay for GCase activity could be useful for further understanding the role of GCase in PD and screening potential modifying compounds in differentiated human cell models.

An Update on Toll-like Receptor 2, Its Function and Dimerization in Pro- and Anti-Inflammatory Processes

While a certain level of inflammation is critical for humans to survive infection and injury, a prolonged inflammatory response can have fatal consequences. Pattern recognition Toll-like receptors (TLRs) are key players in the initiation of an inflammatory process. TLR2 is one of the most studied pattern recognition receptors (PRRs) and is known to form heterodimers with either TLR1, TLR4, TLR6, and TLR10, allowing it to recognize a wide range of pathogens. Although a large number of studies have been conducted over the past decades, there are still many unanswered questions regarding TLR2 mechanisms in health and disease. In this review, we provide an up-to-date overview of TLR2, including its homo- and heterodimers. Furthermore, we will discuss the pro- and anti-inflammatory properties of TLR2 and recent findings in prominent TLR2-associated infectious and neurodegenerative diseases.

Alpha Synuclein: Neurodegeneration and Inflammation

Alpha-Synuclein (α-Syn) is one of the most important molecules involved in the pathogenesis of Parkinson's disease and related disorders, synucleinopathies, but also in several other neurodegenerative disorders with a more elusive role. This review analyzes the activities of α-Syn, in different conformational states, monomeric, oligomeric and fibrils, in relation to neuronal dysfunction. The neuronal damage induced by α-Syn in various conformers will be analyzed in relation to its capacity to spread the intracellular aggregation seeds with a prion-like mechanism. In view of the prominent role of inflammation in virtually all neurodegenerative disorders, the activity of α-Syn will also be illustrated considering its influence on glial reactivity. We and others have described the interaction between general inflammation and cerebral dysfunctional activity of α-Syn. Differences in microglia and astrocyte activation have also been observed when in vivo the presence of α-Syn oligomers has been combined with a lasting peripheral inflammatory effect. The reactivity of microglia was amplified, while astrocytes were damaged by the double stimulus, opening new perspectives for the control of inflammation in synucleinopathies. Starting from our studies in experimental models, we extended the perspective to find useful pointers to orient future research and potential therapeutic strategies in neurodegenerative disorders.