idh2
Overview
IDH2 (isocitrate dehydrogenase 2) is a mitochondrial enzyme encoded by the IDH2 gene located on chromosome 15q26.1 in humans. This gene encodes a critical metabolic enzyme belonging to the isocitrate dehydrogenase family, which catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate (α-KG) in the citric acid cycle (Krebs cycle). IDH2 functions as a homodimer and is primarily localized to the mitochondrial matrix, where it plays essential roles in both energy production and cellular redox homeostasis. The enzyme exists as part of a larger family including IDH1 (cytoplasmic/peroxisomal) and IDH3 (mitochondrial complex I component), each with distinct cellular compartmentalization and functions.
Function/Biology
IDH2 catalyzes a reversible reaction in which isocitrate is oxidized to α-ketoglutarate while simultaneously reducing NAD+ to NADH. This reaction serves dual purposes: it generates reducing equivalents (NADH) that fuel ATP production through oxidative phosphorylation, and it produces α-ketoglutarate, a key citric acid cycle intermediate and allosteric regulator of multiple metabolic pathways. Beyond its classical role in energy metabolism, IDH2 functions as a crucial antioxidant enzyme in the mitochondria by maintaining the cellular NADPH/NADP+ ratio through its participation in the reductive carboxylation pathway. This NADPH production is essential for maintaining reduced glutathione (GSH) and thioredoxin systems, which are the primary defenses against reactive oxygen species (ROS).
...idh2
Overview
IDH2 (isocitrate dehydrogenase 2) is a mitochondrial enzyme encoded by the IDH2 gene located on chromosome 15q26.1 in humans. This gene encodes a critical metabolic enzyme belonging to the isocitrate dehydrogenase family, which catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate (α-KG) in the citric acid cycle (Krebs cycle). IDH2 functions as a homodimer and is primarily localized to the mitochondrial matrix, where it plays essential roles in both energy production and cellular redox homeostasis. The enzyme exists as part of a larger family including IDH1 (cytoplasmic/peroxisomal) and IDH3 (mitochondrial complex I component), each with distinct cellular compartmentalization and functions.
Function/Biology
IDH2 catalyzes a reversible reaction in which isocitrate is oxidized to α-ketoglutarate while simultaneously reducing NAD+ to NADH. This reaction serves dual purposes: it generates reducing equivalents (NADH) that fuel ATP production through oxidative phosphorylation, and it produces α-ketoglutarate, a key citric acid cycle intermediate and allosteric regulator of multiple metabolic pathways. Beyond its classical role in energy metabolism, IDH2 functions as a crucial antioxidant enzyme in the mitochondria by maintaining the cellular NADPH/NADP+ ratio through its participation in the reductive carboxylation pathway. This NADPH production is essential for maintaining reduced glutathione (GSH) and thioredoxin systems, which are the primary defenses against reactive oxygen species (ROS).
The enzyme demonstrates substrate specificity for isocitrate and cofactor requirement for NAD+. IDH2 expression is regulated at both transcriptional and post-translational levels, with its activity modulated by allosteric effectors including citrate (inhibitor), ADP (activator), and NADH (inhibitor). Post-translational modifications, including phosphorylation, acetylation, and S-nitrosylation, fine-tune IDH2 activity in response to cellular metabolic demands and stress conditions.
Role in Neurodegeneration
IDH2 dysfunction has emerged as a significant contributor to neurodegeneration through multiple interconnected mechanisms. Neurons exhibit exceptional metabolic demands and heightened susceptibility to oxidative stress due to their high oxygen consumption rates and relatively limited antioxidant defense capacity. Impaired IDH2 function compromises the mitochondrial antioxidant defense system, leading to accumulation of ROS including superoxide and hydrogen peroxide. Excessive ROS generation drives oxidative damage to cellular macromolecules—proteins, lipids, and DNA—a hallmark feature of Alzheimer's disease, Parkinson's disease, and other neurodegenerative conditions.
In Alzheimer's disease, mitochondrial dysfunction and bioenergetic failure are early pathological events, and IDH2 dysregulation has been documented in affected tissues. Similarly, in Parkinson's disease, defects in the cytochrome c oxidase complex and NADH production create conditions where IDH2-derived NADH becomes critically important for maintaining cellular energy status. IDH2 activity also influences the production of α-ketoglutarate, which serves as a cofactor for prolyl hydroxylase domain-containing proteins (PHD) and histone demethylases, thus regulating cellular responses to hypoxia and epigenetic modifications relevant to neuroinflammation in neurodegeneration.
Molecular Mechanisms
IDH2 dysfunction in neurodegeneration operates through multiple molecular pathways. Loss of NADH production impairs Complex I function and reduces ATP synthesis capacity, compromising the energy reserves necessary for maintaining ion gradients, synaptic transmission, and protein quality control. Simultaneously, reduced NADPH generation weakens antioxidant defenses, allowing ROS accumulation that activates pro-apoptotic pathways through p53 activation and caspase cascade engagement. IDH2 dysfunction also promotes defective mitophagy and impaired mitochondrial quality control, leading to accumulation of dysfunctional mitochondria producing excessive ROS in a self-perpetuating cycle.
The enzyme participates in metabolic remodeling associated with neuroinflammation, as reduced IDH2 activity shifts metabolism toward less efficient pathways, exacerbating bioenergetic stress during activated microglial and astrocytic states.
Clinical/Research Significance
IDH2 represents an emerging therapeutic target for neurodegenerative diseases. Enhancement of IDH2 activity through pharmacological approaches or genetic overexpression shows promise in pre-clinical models of neurodegeneration by restoring mitochondrial antioxidant defense and bioenergetic capacity. Conversely, IDH2 polymorphisms may contribute to individual susceptibility to neurodegenerative disease, and IDH2 expression levels serve as potential biomarkers for disease progression and mitochondrial dysfunction severity.
IDH1 — cytoplasmic isocitrate dehydrogenase with overlapping metabolic functions; IDH3 — mitochondrial complex I-associated isocit