| Full Name | ATP Binding Cassette Subfamily B Member 1 |
| Gene Symbol | ABCB1 (MDR1, PGP) |
| Chromosomal Location | 7q21.12 |
| NCBI Gene ID | [5243](https://www.ncbi.nlm.nih.gov/gene/5243) |
| OMIM | [171050](https://omim.org/entry/171050) |
| Ensembl | [ENSG00000085563](https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000085563) |
| UniProt (Protein) | [P08183 (P-glycoprotein)](https://www.uniprot.org/uniprot/P08183) |
| Associated Diseases | [Alzheimer's Disease](/diseases/alzheimers-disease), [Parkinson's Disease](/diseases/parkinsons-disease), [ALS](/diseases/amyotrophic-lateral-sclerosis) |
ABCB1 (ATP Binding Cassette Subfamily B Member 1), also known as MDR1 (multidrug resistance protein 1) or P-glycoprotein (P-gp), encodes a 170 kDa ATP-dependent efflux transporter that is a critical component of the blood-brain barrier. P-glycoprotein is the most extensively studied drug efflux transporter at the BBB and plays a central role in limiting brain penetration of xenobiotics, toxins, and therapeutic agents. Its dysfunction has been implicated in multiple neurodegenerative diseases, where impaired efflux contributes to both toxic accumulation and therapeutic failure.
ABCB1 spans approximately 209 kb on chromosome 7q21.12 and contains 29 exons encoding a 1,280 amino acid protein. The gene produces two major transcript variants through alternative splicing. ABCB1 expression is regulated by multiple transcription factors including PXR, CAR, and NF-κB, with promoter methylation serving as an additional regulatory mechanism.
In the brain, ABCB1 is predominantly expressed at the luminal (blood-facing) membrane of brain capillary endothelial cells, where it functions as the primary efflux pump of the blood-brain barrier. Lower levels of expression are detected in astrocyte end-feet, microglia, and neurons. Expression is highest in the cortex and hippocampus, with moderate levels in the cerebellum and brainstem. The Allen Brain Atlas confirms enriched endothelial expression across all brain regions.
P-glycoprotein is a member of the ABC transporter superfamily and functions as an ATP-dependent efflux pump with remarkably broad substrate specificity. The protein contains two transmembrane domains (TMDs), each with six transmembrane helices forming a drug-binding cavity, and two nucleotide-binding domains (NBDs) that hydrolyze ATP to power substrate translocation.
The transport cycle follows an alternating access model:
P-glycoprotein recognizes an extraordinarily diverse range of substrates, typically hydrophobic or amphipathic compounds with molecular weights of 300–4,000 Da. This includes many CNS drugs (antiepileptics, antidepressants, antipsychotics, opioids), chemotherapeutics, and endogenous substrates including amyloid-beta peptides.
A critical function in neurodegeneration is the transport of amyloid-beta (Aβ) across the BBB. P-glycoprotein mediates the efflux of both Aβ40 and Aβ42 from the brain parenchyma into the bloodstream. This clearance pathway operates in concert with LRP1-mediated transcytosis and represents a major route for Aβ elimination. Impaired P-gp function leads to reduced Aβ clearance and accelerated amyloid deposition, directly linking ABCB1 dysfunction to Alzheimer's disease pathogenesis.
Multiple lines of evidence connect ABCB1 to Alzheimer's disease:
P-glycoprotein dysfunction at the BBB may contribute to Parkinson's disease by:
P-gp overexpression in epileptic brain tissue contributes to antiepileptic drug resistance by limiting drug penetration to seizure foci. This "transporter hypothesis" of pharmacoresistance extends to treatment-resistant depression and other CNS disorders.
| Variant | rsID | Consequence | Clinical Significance |
|---|---|---|---|
| C3435T | rs1045642 | Synonymous (Ile1145Ile) | Altered mRNA stability, reduced P-gp expression; associated with AD/PD risk |
| G2677T/A | rs2032582 | Ala893Ser/Thr | Altered substrate specificity and transport kinetics |
| C1236T | rs1128503 | Synonymous (Gly412Gly) | Haplotype effects on protein folding and function |
| T-129C | rs3213619 | Promoter variant | Altered transcription; associated with drug response variability |
The C3435T–G2677T–C1236T haplotype is the most extensively studied, with the TTT haplotype associated with reduced P-gp expression and function.
P-glycoprotein shows the following expression pattern relevant to neurodegeneration:
Expression decreases with age (approximately 50% reduction from age 40 to 80), with accelerated decline in Alzheimer's disease and cerebral amyloid angiopathy.