Gene: NOS2
UniProt: P35228
Molecular Weight: ~131 kDa
Subcellular Localization: Cytosol, plasma membrane (neuronal), peroxisomes
Protein Family: Nitric oxide synthase family (NOS)
NOS2 (Inducible Nitric Oxide Synthase) produces nitric oxide in response to inflammatory stimuli. It plays a complex role in neuroinflammation and has been implicated in the pathogenesis of various neurodegenerative diseases including Alzheimer's and Parkinson's.
NOS2 is a homodimeric enzyme, with each monomer comprising multiple functional domains:
- N-terminal oxygenase domain (1-498 aa): Contains the catalytic site with binding sites for heme, tetrahydrobiopterin (BH4), L-arginine, and the substrate
- Calmodulin-binding domain (500-532 aa): Binds calcium-calmodulin for enzyme activation
- C-terminal reductase domain (533-1153 aa): Contains FAD and FMN, transfers electrons from NADPH to the oxygenase domain
The enzyme requires multiple cofactors:
- Heme (protoporphyrin IX)
- Tetrahydrobiopterin (BH4)
- FAD and FMN
- Calmodulin (calcium-dependent binding)
Nitric oxide (NO) produced by NOS2 serves as a signaling molecule in the nervous system:
- Neurotransmission: NO acts as a retrograde neurotransmitter, modulating synaptic plasticity, learning, and memory
- Blood flow regulation: NO produced by endothelial NOS (NOS3) and NOS2 regulates cerebral blood flow
- Neuroprotection: Low levels of NO have neuroprotective effects through antioxidant gene activation
- Developmental roles: NO guides axonal pathfinding and participates in synaptic formation
- Immune surveillance: In glial cells, NOS2 produces NO as part of the innate immune response
NOS2 plays a complex, context-dependent role in AD:
- Chronic neuroinflammation: Aβ plaques and tangles activate microglia and astrocytes, inducing NOS2 expression
- Nitrosative stress: Excessive NO production leads to protein nitration, lipid peroxidation, and DNA damage
- NO signaling impairment: Reduced NO bioavailability impairs cerebral blood flow and synaptic plasticity
- Tau nitration: NO contributes to tau pathology through nitrosylation reactions
- Therapeutic targeting: NOS2 inhibitors have shown promise in preclinical AD models
- Dopaminergic neuron vulnerability: NOS2 expression in microglia contributes to dopaminergic neuron death
- Neuroinflammation: MPTP and α-synuclein aggregation activate NOS2 in glial cells
- Mitochondrial dysfunction: NO inhibits mitochondrial respiration and promotes mitochondrial permeability transition
- Motor neuron injury: Activated microglia and astrocytes produce NO through NOS2
- Oxidative stress: Peroxynitrite (ONOO⁻) formed from NO and superoxide causes protein nitration
- Disease progression: NOS2 expression correlates with disease severity in ALS models
- Demyelination: NO produced by NOS2 in immune cells contributes to oligodendrocyte death
- Axonal injury: Nitrosative stress damages axons in MS lesions
- Blood-brain barrier disruption: NO increases vascular permeability
¶ Stroke and Ischemia
- Ischemic injury: NOS2 is upregulated after stroke, contributing to excitotoxic damage
- Therapeutic window: Early NOS2 inhibition may be neuroprotective; late inhibition may be detrimental
| Approach |
Compound |
Mechanism |
Status |
| Selective NOS2 inhibitors |
1400W, L-NIL |
Block NO production |
Preclinical |
| Tetrahydrobiopterin supplementation |
BH4 |
Restore cofactor levels |
Clinical trials |
| Antioxidants |
Tempol, EUK-134 |
Scavenge peroxynitrite |
Research |
| Anti-inflammatory agents |
Minocycline |
Inhibit microglial activation |
Clinical trials |
-
Heneka et al., NOS2 in neurodegenerative disease (2015)
-
Steinert et al., Nitric oxide and neurodegeneration (2022)
-
Lawson et al., Microglial NOS2 in AD and PD (2020)
-
Guix et al., NO signaling in synaptic plasticity (2021)
-
Brown, Targeting NOS2 for neuroprotection (2019)
-
Chabrashvili et al., NOS2 in ALS (2021)
This page was created as part of the NeuroWiki protein page initiative for neurodegeneration research.
NOS2/iNOS plays a complex role in neurodegeneration:
- Neuroinflammation: Activated microglia and astrocytes express NOS2 in response to inflammatory stimuli, producing high levels of NO that can be neurotoxic
- Oxidative stress: NO reacts with superoxide to form peroxynitrite (ONOO-), a potent oxidant that damages proteins, lipids, and DNA
- Alzheimer's disease: Elevated NOS2 expression is observed in AD brains, contributing to amyloid-beta toxicity and tau pathology
- Parkinson's disease: NOS2 is upregulated in PD models and may contribute to dopaminergic neuron death
- ALS: Increased NOS2 expression in motor neurons and microglia
Targeting NOS2 for neuroprotection:
- Selective iNOS inhibitors: Being developed for inflammatory and neurodegenerative conditions
- NO scavengers: Trap excess NO to prevent nitrosative stress
- Antioxidant approaches: Combat peroxynitrite formation
- Anti-inflammatory therapies: Reduce microglial activation and subsequent NO production