CD44 - Cell Surface Glycoprotein

CD44 - Cell Surface Glycoprotein

Introduction

Pathway Diagram

```mermaid
flowchart TD
CD4["CD4<br/>T-helper cell receptor"]

CD4 -->|"regulates"| Neurodegeneration["Neurodegeneration<br/>Process"]
CD4 -->|"activates"| MS["Multiple Sclerosis<br/>Autoimmune demyelination"]
CD4 -->|"inhibits"| ALS["Amyotrophic Lateral Sclerosis<br/>Motor neuron disease"]
CD4 -->|"regulates"| PD["Parkinson's Disease<br/>Dopaminergic degeneration"]
CD4 -->|"regulates"| Dementia["Dementia<br/>Cognitive decline"]

CD4 -->|"regulates"| Inflammation["Neuroinflammation<br/>Immune activation"]
CD4 -->|"regulates"| Autoimmune["Autoimmune Response<br/>Self-reactive immunity"]

Inflammation -->|"promotes"| Neurodegeneration
Inflammation -->|"contributes_to"| MS
Inflammation -->|"damages"| PD

Autoimmune -->|"drives"| MS
Autoimmune -->|"influences"| Neurodegeneration

CD4 -->|"activates"| Aging["Cellular Aging<br/>Senescence processes"]
Aging -->|"accelerates"| Neurodegeneration
Aging -->|"increases_risk"| Dementia

CD4 -->|"therapeutic_target"| MS_Treatment["MS Therapeutics<br/>Immunomodulation"]
CD4 -->|"therapeutic_target"| Neuro_Treatment["Neurodegeneration<br/>Therapeutics"]
CD4 -->|"biomarker_for"| ALS_Diagnosis["ALS Biomarker<br/>Disease monitoring"]

style CD4 fill:#006494
style MS_Treatment fill:#1b5e20
style Neuro_Treatment fill:#1b5e20
style ALS_Diagnosis fill:#1b5e20
style MS fill:#ef5350
style ALS fill:#ef5350
style Neurodegeneration fill:#ef5350
s

CD44 - Cell Surface Glycoprotein

Introduction

Pathway Diagram

Cd44 Cell Surface Glycoprotein is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

<div class="infobox infobox-gene"> [@bickel1993]
<table> [@moretto2006]
<tr><th>Gene Symbol</th><td>CD44</td></tr> [@pietras2018]
<tr><th>Full Name</th><td>Cell Surface Glycoprotein CD44</td></tr> [@nagano2004]
<tr><th>Chromosomal Location</th><td>11p13</td></tr> [@toole2000]
<tr><th>NCBI Gene ID</th><td>960</td></tr> [@pure2005]
<tr><th>OMIM</th><td>604470</td></tr>
<tr><th>Ensembl</th><td>ENSG00000026508</td></tr>
<tr><th>UniProt</th><td>P16070</td></tr>
<tr><th>Protein</th><td>[CD44 Protein](/proteins/cd44-protein)</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/alzheimer" style="color:#ef9a9a">ALZHEIMER</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">ALZHEIMER'S DISEASE</a>, <a href="/wiki/aging" style="color:#ef9a9a">Aging</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">Alzheimer</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">446 edges</a></td>
</tr>
</table>
</div>

Overview

CD44 encodes a cell-surface glycoprotein involved in cell-cell interactions, cell adhesion, and migration PMID:2115452. It plays important roles in immune cell trafficking, synaptic plasticity, and neuroinflammation in neurodegenerative diseases PMID:15905565. CD44 is a major receptor for hyaluronic acid (HA) and mediates numerous cell-matrix interactions critical for tissue homeostasis and disease progression PMID:7642315.

The CD44 gene undergoes extensive alternative splicing, producing multiple isoforms with distinct functions. The standard isoform (CD44s) is widely expressed, while variant isoforms (CD44v) exhibit tissue-specific expression and are often upregulated in disease states PMID:7642315.

Gene Structure and Regulation

Genomic Organization

• Standard Exons: Constitutively spliced, encode CD44s
• Variant Exons: Alternatively spliced, inserted between exons 5 and 6
• Promoter: Contains [NF-κB](/entities/nf-kb), AP-1, and STAT response elements

Transcriptional Regulation

• Growth Factors: EGF, TGF-β upregulate expression PMID:7642315
• Cytokines: TNF-α, IL-1β induce CD44 PMID:15905565
• Hypoxia: HIF-1α enhances CD44 transcription
• Cellular Activation: T-cell activation increases CD44 expression

Protein Structure

CD44 is a type I transmembrane glycoprotein with remarkable diversity:

• N-terminal Extracellular Domain: Contains the hyaluronic acid binding site (≈170 aa)
• Variable Region: Product of alternative splicing (v1-v19 exons)
• Transmembrane Domain: Single pass α-helix (23 aa)
• Cytoplasmic Tail: Interacts with cytoskeleton via ankyrin and ERM proteins (72 aa)

Structural Features

Molecular Function

CD44 binds multiple ligands and mediates diverse functions PMID: 2115452:

Primary Ligands

• Hyaluronic Acid (HA): Primary ligand, mediates cell adhesion and migration PMID:2115452
• Collagen: Types I, II, III, V, VI - extracellular matrix interaction PMID:7642315
• Fibronectin: Cell matrix adhesion and spreading
• MMPs: Interaction with matrix metalloproteinases (MMP-2, MMP-9)

Secondary Ligands

• Osteopontin: Cytokine-like functions
• SDF-1/CXCL12: Chemokine binding
• MHC Class II: Immune cell interactions

Isoforms and Their Functions

| Isoform | Expression | Function |
|---------|-----------|----------|
| CD44s | Most cells | Standard isoform, ubiquitous functions |
| CD44v3 | Activated T cells, neurons | Cytokine binding, synaptic plasticity |
| CD44v6 | Carcinoma, activated immune cells | Metastasis, immune cell trafficking |
| CD44v9 | [Neurons](/entities/neurons), cancer stem cells | Stress response, therapy resistance |
| CD44v10 | Brain, immune cells | Tissue-specific functions |

Normal Biological Functions

Immune System

• Leukocyte Trafficking: CD44 mediates lymphocyte homing to secondary lymphoid organs PMID:7642315
• Immune Cell Activation: T-cell activation requires CD44-HA interactions
• Hematopoiesis: CD44 regulates hematopoietic stem cell niche interactions

Nervous System

• Synaptic Plasticity: CD44v9 expressed in neurons, involved in memory formation PMID:15905565
• Neuronal Migration: HA-CD44 interactions guide neuronal positioning
• Glial Function: Astrocyte and [microglia](/cell-types/microglia-neuroinflammation) express CD44 in response to injury

Tissue Homeostasis

• Cell Adhesion: Anchor cells to extracellular matrix
• Cell Migration: Facilitate directed cell movement
• Wound Healing: Critical for tissue repair

Disease Associations

Alzheimer's Disease (AD)

CD44 is significantly elevated in AD brain and contributes to disease pathogenesis PMID: 15905565:

• [Aβ](/proteins/amyloid-beta) Binding and Clearance: CD44 mediates Aβ binding to microglia and astrocytes, affecting clearance PMID:15905565
• Neuroinflammation: CD44+ microglia surround amyloid plaques, mediating inflammatory responses
• Synaptic Dysfunction: Altered CD44 expression affects synaptic plasticity
• [Tau](/proteins/tau) Pathology: CD44-HA interactions may influence [tau](/proteins/tau) aggregation
• Therapeutic Target: Anti-CD44 antibodies being investigated for AD PMID:15905565

Parkinson's Disease (PD)

• Elevated Expression: CD44 increased in substantia nigra of PD patients PMID:15905565
• [α-Synuclein](/proteins/alpha-synuclein) Interactions: CD44 may mediate α-synuclein uptake and propagation
• Microglial Activation: CD44 regulates microglial response to neuronal injury
• BBB Permeability: CD44 contributes to blood-brain barrier dysfunction

Amyotrophic Lateral Sclerosis (ALS)

• Motor Neuron Expression: Upregulated in ALS motor neurons PMID:15905565
• Inflammatory Responses: Mediates inflammatory cell infiltration
• Disease Progression: Correlates with disease severity
• Therapeutic Potential: CD44 targeting may modulate neuroinflammation

Multiple Sclerosis (MS)

• Immune Cell Trafficking: Critical for T cell entry into CNS PMID:7642315
• Demyelination: CD44-mediated inflammation contributes to myelin damage
• Remyelination: HA-CD44 interactions important for oligodendrocyte progenitor recruitment
• Therapeutic Target: Anti-CD44 therapies in development

Stroke and Cerebral Ischemia

• Post-Ischemic Inflammation: CD44 mediates leukocyte infiltration PMID:15905565
• [Blood-Brain Barrier](/entities/blood-brain-barrier) Breakdown: Contributes to BBB dysfunction
• Edema Formation: HA-CD44 interactions promote vascular leakage
• Recovery Phase: Important for tissue repair and angiogenesis

Cancer (Comorbidity with Neurodegeneration)

• Cancer Stem Cells: CD44 is a cancer stem cell marker
• Metastasis: CD44v6 isoform promotes invasion
• Chemotherapy Resistance: CD44+ cells show enhanced survival

Expression Pattern

Brain Expression

• Neurons: Low baseline, upregulated in disease
• [Astrocytes](/entities/astrocytes): Constitutive expression, increases with activation
• [Microglia](/entities/microglia): Induced by inflammatory stimuli
• Oligodendrocytes: Variable expression

Immune Expression

• T Cells: Activation-induced upregulation
• B Cells: Constitutive expression
• Macrophages: High expression, further induced
• Dendritic Cells: Critical for antigen presentation

Therapeutic Targeting

| Strategy | Approach | Status | Notes |
|----------|----------|--------|-------|
| Blocking Antibodies | Anti-CD44 mAb | Research | Preclinical |
| Hyaluronic Acid Therapy | HA fragments | Research | CD44 engagement |
| Small Molecule | CD44 antagonists | Discovery | Not yet specific |
| RNA Interference | siRNA/shRNA | Research | Gene silencing |
| CAR-T Cells | CD44-targeted | Clinical | Cancer applications |

Clinical Significance

• Diagnostic Marker: CD44 isoforms as disease biomarkers
• Prognostic Marker: CD44v6 in cancer metastasis
• Therapeutic Target: Inflammatory and autoimmune conditions
• Immune Marker: Leukocyte activation and trafficking

Key Publications

See Also

• [CD44 Protein](/proteins/cd44-protein)
• [Hyaluronic Acid](/mechanisms/extracellular-matrix)
• [Microglia](/cell-types/microglia)
• [Neuroinflammation Pathway](/mechanisms/neuroinflammation-pathway)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Multiple Sclerosis](/diseases/multiple-sclerosis)
• [Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis)
• [Extracellular Matrix](/mechanisms/extracellular-matrix)

External Links

• [NCBI Gene: 960](https://www.ncbi.nlm.nih.gov/gene/960)
• [UniProt: P16070](https://www.uniprot.org/uniprot/P16070)
• [OMIM: 604470](https://omim.org/entry/604470)
• [Ensembl: ENSG00000026508](https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000026508)
• [GeneCards: CD44](https://www.genecards.org/cgi-bin/carddisp.pl?gene=CD44)

Background

The study of Cd44 Cell Surface Glycoprotein 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

Pathway Diagram

The following diagram shows the key molecular relationships involving CD44 - Cell Surface Glycoprotein discovered through SciDEX knowledge graph analysis: