SLC34A3 (Solute Carrier Family 34 Member 3), also known as NaPi-IIb or Sodium-Phosphate Transporter 3, is a membrane transport protein that plays a critical role in phosphate homeostasis. While primarily studied in the context of renal and intestinal phosphate absorption, emerging research suggests important functions in the brain and potential connections to neurodegenerative diseases[1].
| SLC34A3 Gene | |
|---|---|
| Gene Symbol | SLC34A3 |
| Protein Name | Sodium-Phosphate Transporter 3 (NaPi-IIb) |
| Chromosomal Location | 9q34.3 |
| NCBI Gene ID | [64759](https://www.ncbi.nlm.nih.gov/gene/64759) |
| Ensembl ID | ENSG00000139433 |
| UniProt ID | [Q8NCC9](https://www.uniprot.org/uniprot/Q8NCC9) |
| OMIM | 609226 |
| Protein Topology | 8 transmembrane domains |
SLC34A3 (NaPi-IIb) is a secondary active transporter that couples phosphate influx to the sodium gradient:
| Feature | Description |
|---|---|
| Transmembrane domains | 8 α-helical segments |
| N-glycosylation sites | Extracellular loops |
| Phosphorylation sites | Intracellular regulatory domains |
| Transport stoichiometry | 2-3 Na+: 1 Pi |
| Transporter | Gene | Tissue Distribution | Stoichiometry |
|---|---|---|---|
| NaPi-IIa | SLC34A1 | Kidney | 3 Na+: 1 Pi |
| NaPi-IIb | SLC34A3 | Intestine, lung, brain | 2-3 Na+: 1 Pi |
| NaPi-IIc | SLC34A2 | Kidney, testis | 2 Na+: 1 Pi |
SLC34A3 is essential for phosphate balance:
| Regulator | Mechanism | Effect |
|---|---|---|
| PTH | Internalization | Decreased activity |
| FGF23 | Internalization | Decreased activity |
| Dietary phosphate | Transcriptional | Adaptive regulation |
| 1,25(OH)2D3 | Transcriptional | Increased expression |
SLC34A3 is expressed in various brain regions[2]:
The bone-secreted hormone FGF23 affects brain function through:
While not directly linked to neurodegeneration, phosphate dysregulation affects:
The transport mechanism involves:
The FGF23-klotho pathway regulates SLC34A3:
Phosphate dysregulation contributes to AD:
| Mechanism | Effect | Evidence |
|---|---|---|
| Tau hyperphosphorylation | Neurofibrillary tangles | Elevated phosphate in AD brain |
| Amyloid processing | Aβ generation | Pi/AD connection studied |
| Calcium dyshomeostasis | Synaptic dysfunction | NaPi dysregulation |
| Mitochondrial dysfunction | Energy deficit | Phosphate transport altered |
| Agent | Mechanism | Clinical Use |
|---|---|---|
| Sevelamer | Phosphate binding | CKD |
| Lanthanum carbonate | Phosphate binding | Hyperphosphatemia |
| Sucroferric oxyhydroxide | Phosphate binding | Phase III trials |
SLC34A3 contributes to:
| Mutation | Type | Phenotype |
|---|---|---|
| R510C | Missense | HHRR |
| G519R | Missense | Tumor calcinosis |
| splice site | Splicing | Variable |
| Tissue | Expression Level | Primary Function |
|---|---|---|
| Small intestine | Highest | Dietary phosphate absorption |
| Kidney | Moderate | Phosphate reabsorption |
| Lung | Moderate | Surfactant production |
| Testis | Low | Unknown |
| Breast | Low | Lactation |
| Interactor | Type | Relationship |
|---|---|---|
| SLC34A1 | Transporter | Functional homolog |
| SLC34A2 | Transporter | Isoform |
| Na+/K+ ATPase | Pump | Provides sodium gradient |
| PTH | Hormone | Regulatory |
| FGF23 | Hormone | Regulatory |
Murer L, et al. Sodium-phosphate transporters: structure, function, and regulatory mechanisms. Physiological Reviews. 2004. ↩︎
Bielohuby M, et al. FGF23 and phosphate metabolism in the brain. Kidney International. 2017. ↩︎
Janahi M, et al. Phosphate transporters in neurological disorders. Journal of Neurochemistry. 2020. ↩︎
Mojiminiyi O, et al. Phosphate dysregulation in Alzheimer's disease. Alzheimer's & Dementia. 2022. ↩︎
Chai Z, et al. SLC34A3 variants and Parkinson's disease. Movement Disorders. 2021. ↩︎ ↩︎
Segawa H, et al. Sodium-phosphate transporters and bone-brain connection. Bone. 2020. ↩︎
Farthing CA, et al. FGF23-klotho axis in neurodegeneration. Brain Research. 2023. ↩︎
Lin MY, et al. Targeting phosphate metabolism in neurodegenerative disease. Theranostics. 2022. ↩︎
Yang L, et al. Phosphate binder therapy in neurodegenerative disease. Journal of Clinical Medicine. 2021. ↩︎
Habibi D, et al. NaPi-IIb in synaptic plasticity. Neurobiology of Learning and Memory. 2021. ↩︎
Chen W, et al. SLC34A3 expression in blood-brain barrier. Fluids and Barriers of the CNS. 2023. ↩︎