Complicated Role of Post-translational Modification and Protease-Cleaved Fragments of Tau in Alzheimer's Disease and Other Tauopathies

Methylglyoxal-induced neuronal dysfunction: Linking diabetes to Alzheimer's disease through cytoskeletal disruption

This study investigates how methylglyoxal affects Alzheimer's disease, which is common in patients with diabetes mellitus. Using SH-SY5Y cells as a model of AD, we investigated the effects of MGO on cell viability, morphology, inflammation, and stress responses. Exposure to MGO induces cytotoxicity, inflammation and oxidative stress that contribute to AD in diabetic patients. We analyzed how MGO (150-900 μM) affects SH-SY5Y cells and its effects on cell survival, gene expression, cytoskeletal integrity, stress indicators, and Aβ42 accumulation (dose- and time-dependent). MGO dramatically affected cell viability depending on the dose and exposure time. Cell death occurred via intrinsic (BAX, CASP9) and extrinsic (FAS, FASLG) apoptotic pathways. Markers related to insulin signaling such as INSR, IRS1, IRS2, SLC2A4, etc. were downregulated, whereas markers of inflammation such as TNF-α, IL-6 and oxidative markers such as HMOX1, G6PD, etc. were upregulated with MGO (P < 0.001). Changes in MAP2 and TUBB3 expression were associated with cytoskeletal damage (P < 0.01). High levels of Aβ42 and low SOD activity confirmed that oxidative stress was induced. LPS treatment exacerbated these effects (P < 0.01). The results highlight the possible role of MGO in cognitive decline associated with diabetes and suggest the need for novel treatment against MGO-related neurotoxicity.

Synaptic sabotage: How Tau and α-Synuclein undermine synaptic health

Synaptic dysfunction is one of the earliest cellular defects observed in Alzheimer's disease (AD) and Parkinson's disease (PD), occurring before widespread protein aggregation, neuronal loss, and cognitive decline. While the field has focused on the aggregation of Tau and α-Synuclein (α-Syn), emerging evidence suggests that these proteins may drive presynaptic pathology even before their aggregation. Therefore, understanding the mechanisms by which Tau and α-Syn affect presynaptic terminals offers an opportunity for developing innovative therapeutics aimed at preserving synapses and potentially halting neurodegeneration. This review focuses on the molecular defects that converge on presynaptic dysfunction caused by Tau and α-Syn. Both proteins have physiological roles in synapses. However, during disease, they acquire abnormal functions due to aberrant interactions and mislocalization. We provide an overview of current research on different essential presynaptic pathways influenced by Tau and α-Syn. Finally, we highlight promising therapeutic targets aimed at maintaining synaptic function in both tauopathies and synucleinopathies.

Targeting Protein Misfolding and Aggregation as a Therapeutic Perspective in Neurodegenerative Disorders

The abnormal deposition and intercellular propagation of disease-specific protein play a central role in the pathogenesis of many neurodegenerative disorders. Recent studies share the common observation that the formation of protein oligomers and subsequent pathological filaments is an essential step for the disease. Synucleinopathies such as Parkinson's disease (PD), dementia with Lewy bodies (DLB) or multiple system atrophy (MSA) are neurodegenerative diseases characterized by the aggregation of the α-synucleinprotein in neurons and/or in oligodendrocytes (glial cytoplasmic inclusions), neuronal loss, and astrogliosis. A similar mechanism of protein Tau-dependent neurodegeneration is a major feature of tauopathies, represented by Alzheimer's disease (AD), corticobasal degeneration (CBD), progressive supranuclear palsy (PSP), and Pick's disease (PD). The specific inhibition of the protein misfolding and their interneuronal spreading represents a promising therapeutic strategy against both disease pathology and progression. The most recent research focuses on finding potential applications targeting the pathological forms of proteins responsible for neurodegeneration. This review highlights the mechanisms relevant to protein-dependent neurodegeneration based on the most common disorders and describes current therapeutic approaches targeting protein misfolding and aggregation.

New Insights into the Development of Donepezil-Based Hybrid and Natural Molecules as Multi-Target Drug Agents for Alzheimer's Disease Treatment

Alzheimer's disease (AD) involves a complex pathophysiology with multiple interconnected subpathologies, including protein aggregation, impaired neurotransmission, oxidative stress, and microglia-mediated neuroinflammation. Current treatments, which generally target a single subpathology, have failed to modify the disease's progression, providing only temporary symptom relief. Multi-target drugs (MTDs) address several subpathologies, including impaired aggregation of pathological proteins. In this review, we cover hybrid molecules published between 2014 and 2024. We offer an overview of the strategies employed in drug design and approaches that have led to notable improvements and reduced hepatotoxicity. Our aim is to offer insights into the potential development of new Alzheimer's disease drugs. This overview highlights the potential of multi-target drugs featuring heterocycles with N-benzylpiperidine fragments and natural compounds in improving Alzheimer's disease treatment.

Antineoplastics for treating Alzheimer's disease and dementia: Evidence from preclinical and observational studies

As the world population ages, there will be an increasing need for effective therapies for aging-associated neurodegenerative disorders, which remain untreatable. Dementia due to Alzheimer's disease (AD) is one of the leading neurological diseases in the aging population. Current therapeutic approaches to treat this disorder are solely symptomatic, making the need for new molecular entities acting on the causes of the disease extremely urgent. One of the potential solutions is to use compounds that are already in the market. The structures have known pharmacokinetics, pharmacodynamics, toxicity profiles, and patient data available in several countries. Several drugs have been used successfully to treat diseases different from their original purposes, such as autoimmunity and peripheral inflammation. Herein, we divulge the repurposing of drugs in the area of neurodegenerative diseases, focusing on the therapeutic potential of antineoplastics to treat dementia due to AD and dementia. We briefly touch upon the shared pathological mechanism between AD and cancer and drug repurposing strategies, with a focus on artificial intelligence. Next, we bring out the current status of research on the development of drugs, provide supporting evidence from retrospective, clinical, and preclinical studies on antineoplastic use, and bring in new areas, such as repurposing drugs for the prion-like spreading of pathologies in treating AD.

Protein modification in neurodegenerative diseases

Posttranslational modifications play a crucial role in governing cellular functions and protein behavior. Researchers have implicated dysregulated posttranslational modifications in protein misfolding, which results in cytotoxicity, particularly in neurodegenerative diseases such as Alzheimer disease, Parkinson disease, and Huntington disease. These aberrant posttranslational modifications cause proteins to gather in certain parts of the brain that are linked to the development of the diseases. This leads to neuronal dysfunction and the start of neurodegenerative disease symptoms. Cognitive decline and neurological impairments commonly manifest in neurodegenerative disease patients, underscoring the urgency of comprehending the posttranslational modifications' impact on protein function for targeted therapeutic interventions. This review elucidates the critical link between neurodegenerative diseases and specific posttranslational modifications, focusing on Tau, APP, α-synuclein, Huntingtin protein, Parkin, DJ-1, and Drp1. By delineating the prominent aberrant posttranslational modifications within Alzheimer disease, Parkinson disease, and Huntington disease, the review underscores the significance of understanding the interplay among these modifications. Emphasizing 10 key abnormal posttranslational modifications, this study aims to provide a comprehensive framework for investigating neurodegenerative diseases holistically. The insights presented herein shed light on potential therapeutic avenues aimed at modulating posttranslational modifications to mitigate protein aggregation and retard neurodegenerative disease progression.

PTMs of PD-1/PD-L1 and PROTACs application for improving cancer immunotherapy

Immunotherapy has been developed, which harnesses and enhances the innate powers of the immune system to fight disease, particularly cancer. PD-1 (programmed death-1) and PD-L1 (programmed death ligand-1) are key components in the regulation of the immune system, particularly in the context of cancer immunotherapy. PD-1 and PD-L1 are regulated by PTMs, including phosphorylation, ubiquitination, deubiquitination, acetylation, palmitoylation and glycosylation. PROTACs (Proteolysis Targeting Chimeras) are a type of new drug design technology. They are specifically engineered molecules that target specific proteins within a cell for degradation. PROTACs have been designed and demonstrated their inhibitory activity against the PD-1/PD-L1 pathway, and showed their ability to degrade PD-1/PD-L1 proteins. In this review, we describe how PROTACs target PD-1 and PD-L1 proteins to improve the efficacy of immunotherapy. PROTACs could be a novel strategy to combine with radiotherapy, chemotherapy and immunotherapy for cancer patients.

Exploring the significance of caspase-cleaved tau in tauopathies and as a complementary pathology to phospho-tau in Alzheimer's disease: implications for biomarker development and therapeutic targeting

Tauopathies are neurodegenerative diseases that typically require postmortem examination for a definitive diagnosis. Detecting neurotoxic tau fragments in cerebrospinal fluid (CSF) and serum provides an opportunity for in vivo diagnosis and disease monitoring. Current assays primarily focus on total tau or phospho-tau, overlooking other post-translational modifications (PTMs). Caspase-cleaved tau is a significant component of AD neuropathological lesions, and experimental studies confirm the high neurotoxicity of these tau species. Recent evidence indicates that certain caspase-cleaved tau species, such as D13 and D402, are abundant in AD brain neurons and only show a modest degree of co-occurrence with phospho-tau, meaning caspase-truncated tau pathology is partially distinct and complementary to phospho-tau pathology. Furthermore, these caspase-cleaved tau species are nearly absent in 4-repeat tauopathies. In this review, we will discuss the significance of caspase-cleaved tau in the development of tauopathies, specifically emphasizing its role in AD. In addition, we will explore the potential of caspase-cleaved tau as a biomarker and the advantages for drug development targeting caspase-6. Developing specific and sensitive assays for caspase-cleaved tau in biofluids holds promise for improving the diagnosis and monitoring of tauopathies, providing valuable insights into disease progression and treatment efficacy.