endfeettejä

Endfeettejä, in English often referred to as astrocyte endfeet, are the specialized terminal processes of astrocytes that envelop blood vessels in the brain and spinal cord. They form a key part of the gliovascular interface, wrapping perivascularly around capillaries and contributing to the glial limiting membrane and the blood–brain barrier.

Anatomy and molecular features

Endfeet coat the exterior of cerebral microvessels, contacting the endothelial basement membrane and the surrounding glial limitans. They express high levels of aquaporin-4 (AQP4) water channels and potassium channels such as Kir4.1, which support water movement and potassium buffering. Endfeet also participate in neurotransmitter uptake through astrocytic transporters and interact with perivascular cells to regulate the extracellular environment.

Functions

Endfeet regulate brain water homeostasis and ion balance, crucial for maintaining the neuronal environment. By coordinating water flux via AQP4 and potassium buffering via Kir4.1, they aid in neurovascular coupling, linking neural activity to blood flow. They contribute to the integrity of the blood–brain barrier and are involved in clearing waste products through the glymphatic system, in which polarized AQP4 channels facilitate CSF–interstitial fluid exchange.

Clinical relevance

Dysfunction or mislocalization of endfoot components can contribute to brain edema and impaired waste clearance. In neuromyelitis optica, autoantibodies target AQP4 on endfeet, highlighting their clinical significance. Changes in endfoot coverage or astrocyte reactivity after injury or disease can affect neuronal homeostasis and recovery.

See also

Astrocytes, blood–brain barrier, glymphatic system, neurovascular coupling, neuromyelitis optica.