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Table 5 Differential expression of water channels and peptide transporters at the BCSFB and BBB: Implications for CNS fluid and peptide homeostasis

From: Multiplicity of cerebrospinal fluid functions: New challenges in health and disease

Aquaporin 1 (Blood-CSF Interface) Aquaporin 4 (Blood-Brain Interface)
AQP1 is present at the CSF-facing pole of choroid plexus epithelium [70 – 73, 77, 78], and in the CSF-brain ependymal lining [281]. AQP4 is located in astrocytic foot processes at the BBB. It is associated with fluid transfer across cerebral microvessels.
Reduced expression in choroid plexus is associated with slower rates of CSF secretion and thus decreases ICP [77, 78]. Elevated expression of AQP4 in the BBB occurs in chronic hydrocephalus [281 – 283]; may be associated with fluid reabsorption.
Attenuated expression in aging [57] and in Alzheimer's disease is accompanied by slower fluid turnover rate [79]. Diminished expression at BBB leads to a reduction in brain edema formation in some animal models.
LRP-1 (Low density lipophilic receptor associated protein) RAGE (Receptor for advanced glycation end products)
Expressed in choroidal epithelium and capillary endothelium [229, 257]. Expressed in choroidal epithelium and brain capillary endothelium [257].
Removes Aβ peptide from CSF and brain ISF [229, 243] for excretion via blood. Transports Aβ from blood into brain ISF where the retained peptide may predispose to Aβ plaque formation in the interstitium.
Sustained or increased expression in choroid plexus during aging, NPH and AD. Enhanced expression of RAGE at BBB in aging, NPH [219] and AD [225] may destabilize BBB and precipitate plaque.
Decreased expression of LRP-1 at the BBB in aging, NPH and AD likely interferes with Aβ removal [219, 225, 229]. Expression of RAGE is generally opposite to that of LRP-1 at the barriers and in neurons [225].