Absence of tissue transglutaminase reduces amyloid-beta pathology in APP23 mice

Pathogenetic Contributions and Therapeutic Implications of Transglutaminase 2 in Neurodegenerative Diseases

Neurodegenerative diseases encompass a heterogeneous group of disorders that afflict millions of people worldwide. Characteristic protein aggregates are histopathological hallmark features of these disorders, including Amyloid β (Aβ)-containing plaques and tau-containing neurofibrillary tangles in Alzheimer's disease, α-Synuclein (α-Syn)-containing Lewy bodies and Lewy neurites in Parkinson's disease and dementia with Lewy bodies, and mutant huntingtin (mHTT) in nuclear inclusions in Huntington's disease. These various aggregates are found in specific brain regions that are impacted by neurodegeneration and associated with clinical manifestations. Transglutaminase (TG2) (also known as tissue transglutaminase) is the most ubiquitously expressed member of the transglutaminase family with protein crosslinking activity. To date, Aβ, tau, α-Syn, and mHTT have been determined to be substrates of TG2, leading to their aggregation and implicating the involvement of TG2 in several pathophysiological events in neurodegenerative disorders. In this review, we summarize the biochemistry and physiologic functions of TG2 and describe recent advances in the pathogenetic role of TG2 in these diseases. We also review TG2 inhibitors tested in clinical trials and discuss recent TG2-targeting approaches, which offer new perspectives for the design of future highly potent and selective drugs with improved brain delivery as a disease-modifying treatment for neurodegenerative disorders.

Tissue transglutaminase: a multifunctional and multisite regulator in health and disease

Tissue transglutaminase (TG2) is a widely distributed multifunctional protein involved in a broad range of cellular and metabolic functions carried out in a variety of cellular compartments. In addition to transamidation, TG2 also functions as a Gα signaling protein, a protein disulfide isomerase (PDI), a protein kinase, and a scaffolding protein. In the nucleus, TG2 modifies histones and transcription factors. The PDI function catalyzes the trimerization and activation of heat shock factor-1 in the nucleus and regulates the oxidation state of several mitochondrial complexes. Cytosolic TG2 modifies proteins by the addition of serotonin or other primary amines and in this way affects cell signaling. Modification of protein-bound glutamines reduces ubiquitin-dependent proteasomal degradation. At the cell membrane, TG2 is associated with G protein-coupled receptors (GPCRs), where it functions in transmembrane signaling. TG2 is also found in the extracellular space, where it functions in protein cross-linking and extracellular matrix stabilization. Of particular importance in transglutaminase research are recent findings concerning the role of TG2 in gene expression, protein homeostasis, cell signaling, autoimmunity, inflammation, and hypoxia. Thus, TG2 performs a multitude of functions in multiple cellular compartments, making it one of the most versatile cellular proteins. Additional evidence links TG2 with multiple human diseases including preeclampsia, hypertension, cardiovascular disease, organ fibrosis, cancer, neurodegenerative diseases, and celiac disease. In conclusion, TG2 provides a multifunctional and multisite response to physiological stress.

Critical thinking of Alzheimer's transgenic mouse model: current research and future perspective

Transgenic models are useful tools for studying the pathogenesis of and drug development for Alzheimer's Disease (AD). AD models are constructed usually using overexpression or knock-in of multiple pathogenic gene mutations from familial AD. Each transgenic model has its unique behavioral and pathological features. This review summarizes the research progress of transgenic mouse models, and their progress in the unique mechanism of amyloid-β oligomers, including the first transgenic mouse model built in China based on a single gene mutation (PSEN1 V97L) found in Chinese familial AD. We further summarized the preclinical findings of drugs using the models, and their future application in exploring the upstream mechanisms and multitarget drug development in AD.

TG2 promotes amyloid beta aggregates: Impact on ER-mitochondria crosstalk, calcium homeostasis and synaptic function in Alzheimer’s disease

Alzheimer's Disease (AD) is a neurodegenerative disorder characterized by cognitive impairment that increasingly affects the elderly. AD's main features have been related to cellular and molecular events, including the aberrant aggregation of the amyloid beta peptide (Aβ), Ca²⁺ dyshomeostasis, and increased mitochondria-associated membranes (MAMs). Transglutaminase type 2 (TG2) is a ubiquitous enzyme whose primary role is the Ca²⁺-dependent proteins transamidation, including the Aβ peptide. TG2 activity has been closely related to cellular damage and death. We detected increased TG2 levels in neuronal cells treated with Aβ oligomers (AβOs) and hippocampal slices from J20 mice using cellular and molecular approaches. In this work, we characterized the capacity of TG2 to interact and promote Aβ toxic aggregates (AβTG2). AβTG2 induced an acute increase in intracellular Ca²⁺, miniature currents, and hiperexcitability, consistent with an increased mitochondrial Ca²⁺ overload, IP3R-VDAC tethering, and mitochondria-endoplasmic reticulum contacts (MERCs). AβTG2 also decreased neuronal viability and excitatory postsynaptic currents, reinforcing the idea of synaptic failure associated with MAMs dysregulation mediated by TG2. Z-DON treatment, TG2 inhibitor, reduced calcium overload, mitochondrial membrane potential loss, and synaptic failure, indicating an involvement of TG2 in a toxic cycle which increases Aβ aggregation, Ca²⁺ overload, and MAMs upregulation. These data provide novel information regarding the role TG2 plays in synaptic function and contribute additional evidence to support the further development of TG2 inhibitors as a disease-modifying strategy for AD.