FASN Protein

FASN Protein

Pathway Diagram

```mermaid
flowchart TD
FAS_gene["FAS<br/>Gene"]
FAS_protein["FAS<br/>Protein"]
FOXO["FOXO<br/>Transcription Factor"]
AMBRA1["AMBRA1<br/>Autophagy Regulator"]

apoptosis["Apoptosis<br/>Cell Death"]
neurodegeneration["Neurodegeneration<br/>Disease Process"]
neuroinflammation["Neuroinflammation<br/>Immune Response"]

alzheimer["Alzheimer's<br/>Disease"]
als["ALS<br/>Disease"]
ms["Multiple<br/>Sclerosis"]

TNF["TNF<br/>Cytokine"]
IL6["IL6<br/>Cytokine"]
APOE["APOE<br/>Lipid Transport"]

inflammation["Chronic<br/>Inflammation"]
aging["Cellular<br/>Aging"]
senescence["Cellular<br/>Senescence"]

FOXO -->|"activates"| FAS_gene
AMBRA1 -->|"regulates"| FAS_protein
FAS_gene -->|"encodes"| FAS_protein

FAS_protein -->|"activates"| apoptosis
FAS_gene -->|"activates"| neurodegeneration
FAS_gene -->|"activates"| neuroinflammation

FAS_gene -->|"activates"| alzheimer
FAS_gene -->|"activates"| als
FAS_gene -->|"activates"| ms

FAS_gene -->|"activates"| TNF
FAS_gene -->|"activates"| IL6
FAS_gene -->|"interacts_with"| APOE

FAS_gene -->|"regulates"| inflammation
FAS_gene -->|"regulates"| aging
FAS_gene -->|"regulates"| senescence

apoptosis -->|"contributes_to"| neurodegeneration
neuroinflammation -->|"promotes"| neurodegeneration

style FAS_gene fill:#006494
style FAS_protein fill:#006494
style AMBRA1 fill:#4a1a6b
style FOXO fill:#4a1a6b
style apoptosis fill:#ef5

FASN Protein

Pathway Diagram

Introduction

Fasn Protein is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

<nav class="infobox .infobox-protein">
| FASN Protein | |
|---|---|
| Full Name | Fatty Acid Synthase |
| Gene | FASN |
| UniProt ID | P49327 |
| Molecular Weight | 273 kDa (homodimer: 546 kDa) |
| Subcellular Localization | Cytoplasm, Cytosolic |
| Protein Family | Fatty Acid Synthase Family |
</nav>

Overview

FASN (Fatty Acid Synthase) is a large multifunctional enzyme complex that catalyzes the de novo synthesis of long-chain fatty acids, primarily palmitate (C16:0). As a homodimer of 270 kDa subunits, FASN represents one of the largest and most complex enzyme systems in mammalian cells[@chirala2003]. Each subunit contains seven catalytic domains arranged in a linear array, enabling sequential processing of substrate through each step of fatty acid synthesis.

In the brain, FASN plays crucial roles in maintaining neuronal lipid homeostasis, which is essential for synaptic function, membrane biosynthesis, myelination, and cell signaling. Dysregulation of FASN is increasingly recognized as a significant factor in the pathogenesis of neurodegenerative diseases, particularly Alzheimer's disease and Parkinson's disease[@pihlajamaki2009].

Structure

FASN is a symmetrical homodimer with a complex domain organization:

Catalytic Domains (each subunit contains 7 domains)

Structural Features

• Dimer Interface: Extensive contact between subunits creates a "head-to-tail" arrangement where each subunit's KS domain interacts with the TE domain of the other subunit
• Flexibility: The ACP domain undergoes large conformational changes to deliver intermediates between catalytic sites
• Regulation: Multiple phosphorylation sites and allosteric regulation points control FASN activity

Normal Function

FASN is the central enzyme for de novo lipogenesis:

Fatty Acid Synthesis

• Acetyl-CoA (2C) + 7 Malonyl-CoA (2C each) + 14 NADPH → Palmitate (16C) + 7 CO₂ + 14 NADP⁺ + 8 CoA

Products

• Palmitate (C16:0): The primary product, serving as a precursor for:
• Longer chain fatty acids (stearate, oleate)
• Triglycerides for energy storage
• Phospholipids for membrane construction
• Cholesterol and steroid hormones
• Wax esters and other lipids

Brain-Specific Functions

• Myelin Synthesis: Oligodendrocytes require massive lipid synthesis for myelin production
• Synaptic Membrane Turnover: High rates of phospholipid synthesis at synapses
• Neuronal Energy Storage: Lipid droplets in [neurons](/entities/neurons) can provide energy during stress
• Lipid Signaling: Production of lipid second messengers (e.g., diacylglycerol, phosphatidic acid)

Role in Neurodegeneration

Alzheimer's Disease

FASN dysregulation is a prominent feature of Alzheimer's disease:

Increased Expression in AD Brain

• FASN expression and activity are significantly increased in AD brain tissue[@kuhajda2000]
• The increase is observed in both neurons and glia
• Elevated FASN correlates with disease severity

Mechanisms

• Amyloid Processing: Altered lipid composition from increased FASN activity affects [APP](/entities/app-protein) processing and [Aβ](/proteins/amyloid-beta) generation
• Lipid Raft Formation: Enhanced fatty acid synthesis promotes lipid raft formation, which concentrates amyloidogenic processing
• Neuronal Energy Crisis: While lipids provide energy, dysregulated FASN may contribute to metabolic dysfunction
• Lipid Droplet Accumulation: FASN-generated fatty acids can accumulate as lipid droplets, which are observed in AD brain
• Neuroinflammation: FASN-derived lipid mediators influence inflammatory responses in [microglia](/entities/microglia)

Therapeutic Implications

• FASN inhibitors may reduce amyloid pathology by decreasing lipid raft abundance
• However, CNS penetration of current FASN inhibitors is limited
• Targeting FASN downstream pathways may be more feasible

Parkinson's Disease

In Parkinson's disease, FASN plays complex roles:

Altered Lipid Metabolism

• Brain lipid profiles are significantly altered in PD
• FASN dysregulation contributes to these changes
• Specific fatty acid species (e.g., polyunsaturated fatty acids) are reduced

Mitochondrial Function

• FASN provides lipids for mitochondrial membranes
• Altered FASN activity affects mitochondrial integrity
• The high lipid content of dopaminergic neurons makes them vulnerable

Alpha-Synuclein Interactions

• Cellular lipid composition influences [α-synuclein](/proteins/alpha-synuclein) aggregation
• FASN-derived membrane lipids may affect α-synuclein membrane binding and toxicity

Amyotrophic Lateral SALS

• Motor neurons have high lipid requirements for axonal maintenance
• FASN is essential for providing membrane lipids
• Dysregulation may contribute to axonal degeneration

Huntington's Disease

• Mutant [huntingtin](/proteins/huntingtin-protein) affects lipid metabolism pathways
• FASN dysregulation contributes to the lipid abnormalities observed in HD
• Altered fatty acid metabolism affects neuronal function

Therapeutic Targeting

FASN is a therapeutic target for several diseases, but CNS applications face challenges:

Small Molecule Inhibitors

| Compound | IC₅₀ | Development Stage | CNS Penetration | Notes |
|----------|------|------------------|-----------------|-------|
| Orlistat | ~1 μM | Approved (obesity) | Poor | Irreversible inhibitor, GI side effects |
| TVB-2640 | ~0.5 μM | Phase II (cancer) | Limited | First-generation clinical FASN inhibitor |
| Fasnall | ~10 μM | Preclinical | Unknown | Cerulenin analog |
| G28U | ~5 μM | Preclinical | Unknown | Multiple analogs available |

Challenges for Neurodegeneration

• [Blood-Brain Barrier](/entities/blood-brain-barrier): Most FASN inhibitors have poor CNS penetration
• Systemic Toxicity: FASN is essential in peripheral tissues
• Therapeutic Window: Balancing lipid synthesis needs with inhibition
• Alternative Pathways: Dietary fatty acids can bypass FASN inhibition

Promising Approaches

• Brain-Penetrant Derivatives: New FASN inhibitors with improved CNS penetration
• Local Delivery: Intranasal or targeted delivery approaches
• Indirect Modulation: Targeting upstream regulators (SREBP1, mTOR)
• Combination with Other Therapies: Synergistic effects with amyloid/tau-targeting approaches

Key Publications

Background

The study of Fasn Protein has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.

References

See Also

• FASN Gene
• SREBF1 Gene
• [SREBP1 Protein](/proteins/srebp1-protein)
• [Lipid Metabolism Pathway](/mechanisms/lipid-metabolism-neurodegeneration)
• Brain Cholesterol Metabolism
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis)
• [Huntington's Disease](/diseases/huntingtons-disease)
• [Mitochondrial Dysfunction Pathway](/mechanisms/mitochondrial-dysfunction)

External Links

• [UniProt: P49327](https://www.uniprot.org/uniprot/P49327)
• [NCBI Protein: FASN](https://www.ncbi.nlm.nih.gov/protein/2194)
• [PDB: FASN Domains](https://www.rcsb.org/structure/2PX2)