| Plasminogen (PLG) | |
|---|---|
| Gene Symbol | PLG |
| Full Name | Plasminogen |
| Chromosomal Location | 6q26 |
| NCBI Gene ID | [5340](https://www.ncbi.nlm.nih.gov/gene/5340) |
| OMIM | [173120](https://www.omim.org/entry/173120) |
| Ensembl ID | ENSG00000122194 |
| UniProt ID | [P00747](https://www.uniprot.org/uniprot/P00747) |
| Associated Diseases | [Alzheimer's Disease](/diseases/alzheimers-disease), [ALS](/diseases/amyotrophic-lateral-sclerosis), Stroke, [Parkinson's Disease](/diseases/parkinsons-disease) |
Plasminogen (PLG) is a 810-amino acid zymogen that circulates in plasma at concentrations of 1.5-2.0 mg/mL. Upon activation, plasminogen is converted to plasmin, a serine protease with broad substrate specificity that degrades fibrin clots, extracellular matrix proteins, and various other substrates. Beyond its well-established role in fibrinolysis, plasminogen has emerged as an important regulator of neuronal plasticity, neuroinflammation, and blood-brain barrier (BBB) function. The plasminogen activation system, comprising plasminogen, tissue plasminogen activator (tPA, encoded by PLAT), urokinase plasminogen activator (uPA, encoded by PLAU), and their inhibitors (PAI-1, encoded by SERPINE1), plays complex roles in neurodegeneration. Altered plasminogen activation has been implicated in Alzheimer's disease pathogenesis, where it affects amyloid-beta (Aβ) degradation and synaptic remodeling, and in amyotrophic lateral sclerosis (ALS), where it modulates neuroinflammatory responses and motor neuron survival[1][2].
PLG encodes plasminogen, a zymogen that is converted to the serine protease plasmin by tPA or uPA. The plasminogen activation system has dual roles in the nervous system: it mediates fibrinolysis and extracellular matrix remodeling during injury and plasticity, while also contributing to pathological processes in neurodegenerative diseases. In Alzheimer's disease, reduced fibrinolytic activity may contribute to Aβ accumulation, while in ALS, altered neuroinflammation affects motor neuron survival. Therapeutic modulation of the plasminogen system represents a potential approach for neurodegeneration, though careful balancing of beneficial and detrimental effects is required[3][4].
Plasminogen circulates as an inactive zymogen that can be activated by two principal pathways:
tPA-mediated activation: Tissue plasminogen activator (tPA) activates plasminogen preferentially in the presence of fibrin, making it important for clot-specific fibrinolysis. tPA is expressed in neurons and can be released in response to neuronal activity.
uPA-mediated activation: Urokinase plasminogen activator (uPA) activates plasminogen and is important for pericellular proteolysis. uPA is expressed in microglia and astrocytes.
The activation generates plasmin, which then degrades:
The plasminogen system is tightly regulated by:
The balance between activators and inhibitors determines net plasmin activity[5].
Plasminogen plays important roles in synaptic plasticity through several mechanisms:
Extracellular matrix remodeling: Plasmin degrades ECM components to allow synaptic remodeling during learning and memory formation.
Growth factor activation: Plasmin can activate latent growth factors including BDNF, facilitating synaptic plasticity.
Synaptic protein cleavage: Direct effects on synaptic proteins that modulate neurotransmission.
The plasminogen system affects BBB integrity:
Plasminogen modulates neuroinflammation:
Multiple connections between plasminogen and AD pathogenesis:
Aβ degradation: Plasmin can directly degrade Aβ peptides. Reduced plasmin activity in AD brain may contribute to Aβ accumulation.
Tau pathology: Plasmin can degrade tau protein; altered plasmin may affect tau clearance.
Synaptic plasticity: Impaired plasmin activity may contribute to synaptic dysfunction in AD.
Genetic associations: Certain PLG variants have been associated with modified AD risk[6][7].
Plasminogen dysregulation in ALS:
Neuroinflammation: Altered plasminogen activation affects microglial responses in ALS.
Motor neuron survival: The balance of plasmin activity influences motor neuron viability.
Extracellular matrix: Aberrant ECM remodeling in ALS may involve plasminogen system[8].
Emerging evidence for plasminogen involvement in PD:
Alpha-synuclein degradation: Plasmin may contribute to clearance of alpha-synuclein.
Neuroinflammation: Modulation of microglial responses.
BBB permeability: Effects on blood-brain barrier in PD.
In stroke and cerebrovascular disease:
Thrombolysis: tPA is used clinically for ischemic stroke treatment.
Hemorrhagic risk: Plasminogen activation can increase bleeding risk.
Reperfusion injury: Plasmin may contribute to post-stroke neuroinflammation[9].
Plasminogen is primarily synthesized in the liver:
In the central nervous system:
Modulating plasminogen activity has therapeutic potential:
tPA-based therapies: Recombinant tPA (alteplase) for acute stroke treatment
Plasminogen activators: Development of brain-penetrant variants
Inhibitor modulation: PAI-1 inhibitors to enhance endogenous fibrinolysis
Gene therapy: Approaches to enhance plasminogen expression in brain
Therapeutic targeting faces challenges:
| Protein | Relationship | Function |
|---|---|---|
| tPA (PLAT) | Activator | Converts plasminogen to plasmin |
| uPA (PLAU) | Activator | Pericellular plasminogen activation |
| PAI-1 (SERPINE1) | Inhibitor | Blocks tPA/uPA activity |
| PAI-2 (SERPINE2) | Inhibitor | Alternative inhibitor |
| Alpha-2 antiplasmin | Inhibitor | Direct plasmin inhibitor |
| Aβ peptides | Substrate | Degraded by plasmin |
| Fibrin | Substrate | Primary physiological substrate |
The plasminogen system involves a carefully regulated enzymatic cascade[1:2]:
Plasminogen (zymogen) → Plasmin (active protease)
↑ ↑
tPA/uPA α2-antiplasmin
↑ ↑
PAI-1 PAI-2
The activation requires:
Plasmin degrades numerous substrates:
Fibrin and Clot Components:
Extracellular Matrix:
Pathological Proteins:
Plasmin regulates synaptic plasticity through multiple mechanisms[3:2]:
The plasminogen system modulates BBB function[@shackabear2002]:
Genetic studies have identified PLG variants associated with disease[6:2][7:2]:
| Variant | Effect | Disease Association |
|---|---|---|
| rs4251961 | Tryptophan insertion | Reduced AD risk |
| rs3794019 | Promoter variant | Altered expression |
| rs7831478 | 5' UTR variant | Modified progression |
Genome-wide association studies have identified:
Plasmin directly degrades Aβ peptides[2:2][4:2]:
In AD:
Plasmin affects synaptic function in AD:
Plasmin-tau interactions:
Plasminogen affects ALS through neuroinflammation[8:2]:
The balance of plasmin activity influences motor neuron viability:
Plasmin may contribute to alpha-synuclein clearance:
Links to microglial activation in PD:
tPA is the standard of care for acute ischemic stroke[9:1]:
Clinical Use:
Limitations:
Plasmin contributes to post-stroke injury:
When treating with tPA:
Targeting Approaches:
Challenges:
Plasminogen knockout mice show[10:1]:
| Protease | Substrate | Brain Function |
|---|---|---|
| tPA/Plasmin | ECM, Aβ | Plasticity, clearance |
| MMPs | ECM, cytokines | remodeling, signaling |
| Calpains | Cytoskeletal | Excitotoxicity |
| Caspases | Proteins | Apoptosis |
Plasminogen system markers may indicate:
May predict:
Plasminogen plays complex roles in neurodegeneration through its effects on extracellular matrix remodeling, protein clearance, and neuroinflammation. The dual nature of this system—both protective and pathological—presents challenges for therapeutic targeting. Understanding the specific context and disease stage is essential for developing effective interventions.
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Melchor JP, et al. The tissue plasminogen activator-plasminogen system in Alzheimer's disease. Journal of Neurochemistry. 2003. ↩︎ ↩︎ ↩︎
Nicole O, et al. Proteolytic remodeling of the synaptic extracellular matrix in plasticity. Neuroscientist. 2003. ↩︎ ↩︎ ↩︎
Jacobsen JS, et al. Enhanced clearance of A-beta in brain by peripheral expression of bacterial tPA. Journal of Molecular Neuroscience. 2008. ↩︎ ↩︎ ↩︎
Berger JS, et al. Plasminogen activator inhibitor-1 and the risk of vascular disease. JAMA. 2007. ↩︎
Twine NA, et al. Association of genetic variants in the plasminogen gene with Alzheimer's disease. Neurology. 2011. ↩︎ ↩︎ ↩︎
Newton DF, et al. Plasminogen system in Alzheimer's disease progression. Journal of Alzheimer's Disease. 2015. ↩︎ ↩︎ ↩︎
Clement C, et al. Plasminogen and ALS: role in neuroinflammation and motor neuron survival. Brain. 2018. ↩︎ ↩︎ ↩︎
Krans B, et al. Plasminogen as a therapeutic target in stroke. Stroke. 2019. ↩︎ ↩︎
Choi SH, et al. Plasminogen deficiency exacerbates cerebral hemorrhage after traumatic brain injury. Journal of Neurotrauma. 2019. ↩︎ ↩︎
Koh HS, et al. Plasminogen in the brain: Beyond thrombolysis. Progress in Neurobiology. 2019. ↩︎