PLG — Plasminogen

PLG — Plasminogen

<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#e8f4f8;">Plasminogen (PLG)</th></tr>
<tr><td><b>Gene Symbol</b></td><td>PLG</td></tr>
<tr><td><b>Full Name</b></td><td>Plasminogen</td></tr>
<tr><td><b>Chromosomal Location</b></td><td>6q26</td></tr>
<tr><td><b>NCBI Gene ID</b></td><td>[5340](https://www.ncbi.nlm.nih.gov/gene/5340)</td></tr>
<tr><td><b>OMIM</b></td><td>[173120](https://www.omim.org/entry/173120)</td></tr>
<tr><td><b>Ensembl ID</b></td><td>ENSG00000122194</td></tr>
<tr><td><b>UniProt ID</b></td><td>[P00747](https://www.uniprot.org/uniprot/P00747)</td></tr>
<tr><td><b>Associated Diseases</b></td><td>[Alzheimer's Disease](/diseases/alzheimers-disease), [ALS](/diseases/amyotrophic-lateral-sclerosis), Stroke, [Parkinson's Disease](/diseases/parkinsons-disease)</td></tr>
</table>
</div>

Overview

PLG — Plasminogen

<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#e8f4f8;">Plasminogen (PLG)</th></tr>
<tr><td><b>Gene Symbol</b></td><td>PLG</td></tr>
<tr><td><b>Full Name</b></td><td>Plasminogen</td></tr>
<tr><td><b>Chromosomal Location</b></td><td>6q26</td></tr>
<tr><td><b>NCBI Gene ID</b></td><td>[5340](https://www.ncbi.nlm.nih.gov/gene/5340)</td></tr>
<tr><td><b>OMIM</b></td><td>[173120](https://www.omim.org/entry/173120)</td></tr>
<tr><td><b>Ensembl ID</b></td><td>ENSG00000122194</td></tr>
<tr><td><b>UniProt ID</b></td><td>[P00747](https://www.uniprot.org/uniprot/P00747)</td></tr>
<tr><td><b>Associated Diseases</b></td><td>[Alzheimer's Disease](/diseases/alzheimers-disease), [ALS](/diseases/amyotrophic-lateral-sclerosis), Stroke, [Parkinson's Disease](/diseases/parkinsons-disease)</td></tr>
</table>
</div>

Overview

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[@plasminogen2001][@melchor2003].

Summary

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[@nicole2003][@jacobsen2008].

Normal Function

Plasminogen Activation

Plasminogen circulates as an inactive zymogen that can be activated by two principal pathways:

The activation generates plasmin, which then degrades:

• Fibrin (fibrinolysis)
• Extracellular matrix proteins (laminin, fibronectin, vitronectin)
• Growth factors and cytokines
• Amyloid-beta peptides

Regulation by Inhibitors

The plasminogen system is tightly regulated by:

• PAI-1 (SERPINE1): Primary inhibitor of tPA and uPA
• PAI-2 (SERPINE2): Alternative inhibitor expressed in brain
• Alpha-2 antiplasmin: Direct inhibitor of plasmin

Role in the Nervous System

Synaptic Plasticity

Plasminogen plays important roles in synaptic plasticity through several mechanisms:

Blood-Brain Barrier

The plasminogen system affects BBB integrity:

• tPA can increase BBB permeability
• Plasmin can directly degrade tight junction proteins
• The system is activated in various CNS injuries affecting BBB

Neuroinflammation

Plasminogen modulates neuroinflammation:

• Activation of microglia and astrocytes
• Regulation of cytokine and chemokine production
• Effects on peripheral immune cell infiltration

Disease Associations

Alzheimer's Disease

Multiple connections between plasminogen and AD pathogenesis:

Amyotrophic Lateral Sclerosis

Plasminogen dysregulation in ALS:

Parkinson's Disease

Emerging evidence for plasminogen involvement in PD:

Stroke

In stroke and cerebrovascular disease:

Expression Pattern

Tissue Distribution

Plasminogen is primarily synthesized in the liver:

• Liver: Major site of synthesis (>90% of circulating plasminogen)
• Brain: Low-level local synthesis in neurons and glia
• Other tissues: Limited extrahepatic expression

Brain Expression

In the central nervous system:

• Neurons: Express both tPA and plasminogen
• Astrocytes: Express uPA and respond to plasmin activity
• Microglia: Express components of the plasminogen system
• Endothelial cells: Express tPA at the BBB

Therapeutic Implications

Therapeutic Strategies

Modulating plasminogen activity has therapeutic potential:

Challenges

Therapeutic targeting faces challenges:

• Narrow therapeutic window between benefit and bleeding risk
• BBB penetration of tPA is limited
• Optimal timing for intervention

Animal Models

Mouse Models

• Plasminogen knockout mice: Viable but show reduced wound healing and impaired behavior[@choi2019]
• tPA knockout mice: Show deficits in synaptic plasticity and memory
• Transgenic models: Overexpression of human PLG in brain

Disease Models

• Cross with APP/PS1 mice to study Aβ-plasmin interactions
• Cross with SOD1 mice to study ALS

Interaction Network

| 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 |

Key Publications

Molecular Mechanisms

Plasminogen Activation Cascade

The plasminogen system involves a carefully regulated enzymatic cascade[@plasminogen2001]:

Plasminogen (zymogen) → Plasmin (active protease)
↑ ↑
tPA/uPA α2-antiplasmin
↑ ↑
PAI-1 PAI-2

The activation requires:

Substrate Specificity

Plasmin degrades numerous substrates:

Fibrin and Clot Components:

• Fibrinogen
• Fibrin
• Cross-linked fibrin degradation products

• Laminin
• Fibronectin
• Vitronectin
• Tenascin
• Proteoglycans

• Amyloid-beta peptides
• Tau protein
• Alpha-synuclein
• Prion protein

Plasmin in Synaptic Function

Plasmin regulates synaptic plasticity through multiple mechanisms[@nicole2003]:

Blood-Brain Barrier Regulation

The plasminogen system modulates BBB function[@shackabear2002]:

• tPA effects: Increases permeability through proteolytic mechanisms
• Tight junction proteins: Plasmin degrades claudin-5, occludin
• Endothelial activation: Promotes inflammatory response
• Transport regulation: Affects receptor-mediated transcytosis

Mechanism Diagram

Genetic Studies

PLG Variants and Disease

Genetic studies have identified PLG variants associated with disease[@twine2011][@newton2015]:

| Variant | Effect | Disease Association |
|---------|--------|-------------------|
| rs4251961 | Tryptophan insertion | Reduced AD risk |
| rs3794019 | Promoter variant | Altered expression |
| rs7831478 | 5' UTR variant | Modified progression |

GWAS Findings

Genome-wide association studies have identified:

• PLG locus associated with modified AD risk
• Interaction with APOE genotype
• Potential for personalized treatment

Alzheimer's Disease - Detailed Mechanisms

Aβ Clearance

Plasmin directly degrades Aβ peptides[@melchor2003][@jacobsen2008]:

In AD:

• Reduced tPA activity in brain
• Elevated PAI-1 levels
• Imbalance toward inhibitor dominance

Synaptic Dysfunction

Plasmin affects synaptic function in AD:

Tau Pathology

Plasmin-tau interactions:

ALS - Detailed Mechanisms

Neuroinflammation Modulation

Plasminogen affects ALS through neuroinflammation[@clement2018]:

Motor Neuron Survival

The balance of plasmin activity influences motor neuron viability:

• Too much plasmin → extracellular matrix degradation, trophic factor loss
• Too little plasmin → impaired clearance of toxic proteins

Parkinson's Disease - Emerging Evidence

Alpha-Synuclein Clearance

Plasmin may contribute to alpha-synuclein clearance:

Neuroinflammation

Links to microglial activation in PD:

• PAI-1 elevated in PD brain
• Reduced fibrinolytic activity
• Contributes to extracellular protein accumulation

Stroke and Cerebrovascular Disease

Thrombolytic Therapy

tPA is the standard of care for acute ischemic stroke[@krans2019]:

Clinical Use:

• Time window: 4.5 hours from symptom onset
• Dose: 0.9 mg/kg (max 90 mg)
• Mechanism: Activates plasminogen to plasmin

• Risk of hemorrhagic transformation
• Narrow therapeutic window
• Cannot be used in hemorrhagic stroke

Reperfusion Injury

Plasmin contributes to post-stroke injury:

Clinical Considerations

Diagnostic Markers

Therapeutic Monitoring

When treating with tPA:

• Monitor fibrinogen levels
• Check for bleeding complications
• Assess neurological status

Research Directions

Biomarker Development

Therapeutic Development

Targeting Approaches:

• Brain-penetrant tPA variants
• PAI-1 inhibitors
• Plasminogen activators with improved profiles
• Gene therapy for local expression

• Bleeding risk
• BBB penetration
• Optimal timing
• Patient selection

Animal Model Insights

Mouse Studies

Plasminogen knockout mice show[@choi2019]:

• Reduced wound healing
• Impaired behavior in some tests
• Accumulation of fibrin deposits
• Enhanced susceptibility to injury

Transgenic Models

• Human PLG expression in mouse brain
• AD model crosses show Aβ clearance effects
• ALS models show inflammation modulation

Comparison with Other Proteases

| Protease | Substrate | Brain Function |
|----------|-----------|----------------|
| tPA/Plasmin | ECM, Aβ | Plasticity, clearance |
| MMPs | ECM, cytokines | remodeling, signaling |
| Calpains | Cytoskeletal | Excitotoxicity |
| Caspases | Proteins | Apoptosis |

Prognostic Value

Disease Progression

Plasminogen system markers may indicate:

• Disease stage
• Rate of progression
• Treatment response

Therapeutic Response

May predict:

• tPA responsiveness in stroke
• Treatment side effects
• Long-term outcomes

Conclusion

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.

Related Conditions

• [Alzheimer's disease](/diseases/alzheimers-disease)
• [Parkinson's disease](/diseases/parkinsons-disease)
• [Amyotrophic lateral sclerosis](/diseases/amyotrophic-lateral-sclerosis)
• [Stroke](/diseases/stroke)
• [Fibrinolysis](/mechanisms/fibrinolysis)
• [Blood-brain barrier](/mechanisms/blood-brain-barrier)
• [Neuroinflammation](/mechanisms/neuroinflammation)

See Also

• [Genes Directory](/genes/)
• [Proteins Directory](/proteins/)
• [Extracellular matrix remodeling](/mechanisms/extracellular-matrix-remodeling)
• [Synaptic plasticity mechanisms](/mechanisms/synaptic-plasticity)

External Links

• [NCBI Gene: PLG](https://www.ncbi.nlm.nih.gov/gene/5340)
• [Ensembl: ENSG00000122194](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000122194)
• [UniProt: P00747](https://www.uniprot.org/uniprot/P00747)
• [OMIM: 173120](https://www.omim.org/entry/173120)

Pathway Diagram

The following diagram shows the key molecular relationships involving PLG — Plasminogen discovered through SciDEX knowledge graph analysis: