{{.infobox .infobox-gene}}
| Symbol | SLC12A5 |
| Full Name | Solute Carrier Family 12 Member 5 (K⁺/Cl⁻ Cotransporter 2, KCC2) |
| Chromosome | 20q13.12 |
| NCBI Gene ID | 57468 |
| OMIM | 607707 |
| Ensembl ID | ENSG00000124140 |
| UniProt ID | Q9NPJ9 |
| Associated Diseases | Epilepsy, Hyperekplexia, Autism Spectrum Disorder, Schizophrenia, Alzheimer's Disease |
The SLC12A5 gene encodes the potassium-chloride cotransporter 2 (KCC2), a neuron-specific ion transporter essential for maintaining chloride homeostasis in the mature brain. KCC2 is a critical determinant of the polarity of GABAergic signaling, as it establishes the low intracellular chloride concentration required for hyperpolarizing GABA-A receptor responses.
KCC2 is expressed almost exclusively in neurons, particularly in hippocampal pyramidal neurons, cortical pyramidal cells, cerebellar Purkinje cells, and spinal cord motor neurons. Its expression is developmentally regulated, with a dramatic increase during the first two weeks of postnatal development in rodents (corresponding to early childhood in humans) that parallels the maturation of inhibitory circuits.
KCC2 is a member of the cation-chloride cotransporter (CCC) family, which includes:
The protein contains 12 transmembrane domains with intracellular N- and C-termini. It forms homomeric complexes that function as active transporters.
KCC2 operates as an electroneutral symporter:
This establishes the chloride gradient where [Cl⁻]ᵢ ≈ 10-20 mM vs [Cl⁻]₀ ≈ 130 mM in mature neurons.
The primary function of KCC2 is to maintain chloride homeostasis for proper GABAergic inhibition:
In the mature brain, GABA binding opens GABA-A receptor channels, allowing chloride to flow IN, hyperpolarizing the neuron and inhibiting firing. In the developing brain or in disease states with impaired KCC2, the chloride gradient is reduced or reversed, making GABA excitatory.
During neuronal development, there is a transition from NKCC1-dominant to KCC2-dominant chloride extrusion:
| Developmental Stage | Primary Transporter | GABA Effect |
|---|---|---|
| Embryonic/Early Postnatal | NKCC1 | Depolarizing (excitatory) |
| Postnatal Day 14+ | KCC2 | Hyperpolarizing (inhibitory) |
This "developmental switch" is critical for proper circuit maturation [1].
KCC2 contributes to network stability through:
KCC2 dysfunction has been implicated in Alzheimer's disease pathogenesis:
KCC2 dysfunction is both cause and consequence of epileptic activity:
KCC2 represents a promising therapeutic target for multiple neurological conditions:
| Compound | Mechanism | Status |
|---|---|---|
| CLP257/CLP290 | KCC2 activator | Preclinical |
| Daphnetin | KCC2 restoration | Preclinical |
| VU0463271 | KCC2 positive allosteric modulator | Research |
Restoring KCC2 function can:
Rivera C, Voipio J, Payne JA, et al. The K⁺/Cl⁻ cotransporter KCC2 renders GABA hyperpolarizing during neuronal maturation. 1999. ↩︎
Umerani M, et al. The KCC2 chloride transporter is a drug target for refractory neurological disorders. 2024. ↩︎