Excessive activation of microglia and subsequent release of proinflammatory cytokines play a crucial role in neuroinflammation and neurodegeneration in Parkinson's disease (PD). Components of the nucleotide‐binding oligomerization domain and leucine‐rich‐repeat‐ and pyrin‐domain‐containing 3 inflammasome complex, leucine‐rich‐repeat‐ and pyrin‐domain‐containing 3, caspase‐1, and apoptosis‐associated speck‐like protein containing a CARD, are highly expressed in activated microglia in PD patient brains. Findings suggest that neurotoxins, aggregation of α‐synuclein, mitochondrial reactive oxygen species, and disrupted mitophagy are the key regulators of microglial leucine‐rich‐repeat‐ and pyrin‐domain‐containing 3 inflammasome activation and release of interleukin‐1β and interleukin‐18 caspase‐1‐mediated pyroptotic cell death in the substantia nigra of the brain. Although this evidence suggests the leucine‐rich‐repeat‐ and pyrin‐domain‐containing 3 inflammasome may be a potential drug target for treatment of PD, the exact mechanism of how the microglia sense these stimuli and initiate leucine‐rich‐repeat‐ and pyrin‐domain‐containing 3 inflammasome signaling is unknown. Here, the molecular mechanism and regulation of microglial leucine‐rich‐repeat‐ and pyrin‐domain‐containing 3 inflammasome activation and its role in the pathogenesis of PD are discussed. Moreover, the potential of both endogenous and synthetic leucine‐rich‐repeat‐ and pyrin‐domain‐containing 3 inflammasome modulators, long noncoding RNA, microRNA to develop novel therapeutics to treat PD is presented. Overall, we recommend that the microglial leucine‐rich‐repeat‐ and pyrin‐domain‐containing 3 inflammasome can be a potential target for PD treatment. © 2019 International Parkinson and Movement Disorder Society

General control non-depressible 5 (GCN5) or lysine acetyltransferase 2A (KAT2A) is one of the most highly studied histone acetyltransferases. It acts as both histone acetyltransferase (HAT) and lysine acetyltransferase (KAT). As an HAT it plays a pivotal role in the epigenetic landscape and chromatin modification. Besides, GCN5 regulates a wide range of biological events such as gene regulation, cellular proliferation, metabolism and inflammation. Imbalance in the GCN5 activity has been reported in many disorders such as cancer, metabolic disorders, autoimmune disorders and neurological disorders. Therefore, unravelling the role of GCN5 in different diseases progression is a prerequisite for both understanding and developing novel therapeutic agents of these diseases. In this review, we have discussed the structural features, the biological function of GCN5 and the mechanical link with the diseases associated with its imbalance. Moreover, the present GCN5 modulators and their limitations will be presented in a medicinal chemistry perspective.

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder associated with impairment of cognition, memory deficits and behavioral abnormalities. Accumulation of amyloid beta (Aβ) is a characteristic hallmark of AD. Microglia express several GPCRs, which, upon activation by modulators, mediate microglial activation and polarization phenotype. This GPCR-mediated microglial activation has both protective and detrimental effects. Microglial GPCRs are involved in amyloid precursor protein (APP) cleavage and Aβ generation. In addition, microglial GPCRs are featured in the regulation of Aβ degradation and clearance through microglial phagocytosis and chemotaxis. Moreover, in response to Aβ binding on microglial Aβ receptors, they can trigger multiple inflammatory pathways. However, there is still a lack of insight into the mechanistic link between GPCR-mediated microglial activation and its pathological consequences in AD. Currently, the available drugs for the treatment of AD are mostly symptomatic and dominated by acetylcholinesterase inhibitors (AchEI). The selection of a specific microglial GPCR that is highly expressed in the AD brain and capable of modulating AD progression through Aβ generation, degradation and clearance will be a potential source of therapeutic intervention. Here, we have highlighted the expression and distribution of various GPCRs connected to microglial activation in the AD brain and their potential to serve as therapeutic targets of AD.

In response to diverse pathogenic and danger signals, the cytosolic activation of the NLRP3 (NOD-, LRR-, and pyrin domain-containing (3)) inflammasome complex is a critical event in the maturation and release of some inflammatory cytokines in the state of an inflammatory response. After activation of the NLRP3 inflammasome, a series of cellular events occurs, including caspase 1-mediated proteolytic cleavage and maturation of the IL-1β and IL-18, followed by pyroptotic cell death. Therefore, the NLRP3 inflammasome has become a prime target for the resolution of many inflammatory disorders. Since NLRP3 inflammasome activation can be triggered by a wide range of stimuli and the activation process occurs in a complex, it is difficult to target the NLRP3 inflammasome. During the activation process, various post-translational modifications (PTM) of the NLRP3 protein are required to form a complex with other components. The regulation of ubiquitination and deubiquitination of NLRP3 has emerged as a potential therapeutic target for NLRP3 inflammasome-associated inflammatory disorders. In this review, we discuss the ubiquitination and deubiquitination system for NLRP3 inflammasome activation and the inhibitors that can be used as potential therapeutic agents to modulate the activation of the NLRP3 inflammasome.

In Parkinson’s disease, mitochondrial oxidative stress-mediated apoptosis is a major cause of dopaminergic neuronal loss in the substantia nigra (SN). G protein-coupled receptor 4 (GPR4), previously recognised as an orphan G protein coupled-receptor (GPCR), has recently been claimed as a member of the group of proton-activated GPCRs. Its activity in neuronal apoptosis, however, remains undefined. In this study, we investigated the role of GPR4 in the 1-methyl-4-phenylpyridinium ion (MPP+) and hydrogen peroxide (H2O2)-treated apoptotic cell death of stably GPR4-overexpressing and stably GPR4-knockout human neuroblastoma SH-SY5Y cells. In GPR4-OE cells, MPP+ and H2O2 were found to significantly increase the expression levels of both mRNA and proteins of the pro-apoptotic Bcl-2-associated X protein (Bax) genes, while they decreased the anti-apoptotic B-cell lymphoma 2 (Bcl-2) genes. In addition, MPP+ treatment activated Caspase-3, leading to the cleavage of poly (ADP-ribose) polymerase (PARP) and decreasing the mitochondrial membrane potential (ΔΨm) in GPR4-OE cells. In contrast, H2O2 treatment significantly increased the intracellular calcium ions (Ca2+) and reactive oxygen species (ROS) in GPR4-OE cells. Further, chemical inhibition by NE52-QQ57, a selective antagonist of GPR4, and knockout of GPR4 by clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 decreased the Bax/Bcl-2 ratio and ROS generation, and stabilised the ΔΨm, thus protecting the SH-SY5Y cells from MPP+- or H2O2-induced apoptotic cell death. Moreover, the knockout of GPR4 decreased the proteolytic degradation of phosphatidylinositol biphosphate (PIP2) and subsequent release of the endoplasmic reticulum (ER)-stored Ca2+ in the cytosol. Our results suggest that the pharmacological inhibition or genetic deletion of GPR4 improves the neurotoxin-induced caspase-dependent mitochondrial apoptotic pathway, possibly through the modulation of PIP2 degradation-mediated calcium signalling. Therefore, GPR4 presents a potential therapeutic target for neurodegenerative disorders such as Parkinson’s disease.

Lewy bodies that contain aggregated α-synuclein in dopamine neurons are the main culprit for neurodegeneration in Parkinson's disease. However, mitochondrial dysfunction has a well-established and prominent role in the pathogenesis of Parkinson's disease. The exact mechanism by which α-synuclein causes dopamine neuronal loss is unclear. Recent evidence suggests that aggregated α-synuclein localises in the mitochondria contributes to oxidative stress-mediated apoptosis in neurons. Therefore, the involvement of aggregated α-synuclein in mitochondrial dysfunction-mediated neuronal loss has made it an emerging drug target for the treatment of Parkinson's disease. However, the exact mechanism by which α-synuclein permeabilises through the mitochondrial membrane and affects the electron transport chain remains under investigation. In the present study, we describe mitochondria-α-synuclein interactions and how α-synuclein aggregation modulates mitochondrial homeostasis in Parkinson's disease pathogenesis. We also discuss recent therapeutic interventions targeting α-synuclein aggregation that may help researchers to design novel therapeutic treatments for Parkinson's disease.

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