Abstract
The Kearns-Sayre syndrome is a mitochondrial disorder (generally due to mitochondrial DNA deletions) that causes ophthalmoplegia, retinopathy, ataxia and brain abnormalities such as leukoencephalopathy. In this syndrome, the choroid plexus epithelial cells, unlike brain cells, are greatly enlarged and granular, consistent with their inability to adequately transport folate from blood into cerebrospinal fluid (CSF), and homovanillic acid (a dopamine metabolite) from CSF into blood. This inability to transport folates from blood into CSF (and brain) adequately, causes cerebral folate deficiency that can be partially reversed by very high doses of reduced folates. The Kearns-Sayre syndrome is a disease that interferes with key choroid plexus functions and is a cause of generalized choroid plexus failure.
Highlights
Besides secreting most of the cerebrospinal fluid (CSF), the choroid plexus (CP) epithelial cells, a locus of the blood-CSF barrier, like renal tubule cells, have myriad other functions
The vectorial transport of methyltetrahydrofolic acid (MeTHF) from blood into CSF via the CP is due to a three-part active transport system in series: first, the folate receptor alpha (FRa) transfers MeTHF from blood into CP endosomes; MeTHF is released from the endosomes into the CP cytoplasm by the proton-coupled folate transporter (PCFT); and MeTHF is released from the cytoplasm into CSF by facilitated diffusion via the reduced folate carrier (RFC) [1]
Kearns-Sayre syndrome (KSS) is an example of a systemic mitochondrial disorder that affects the CP anatomically and physiologically
Summary
Besides secreting most of the cerebrospinal fluid (CSF), the choroid plexus (CP) epithelial cells, a locus of the blood-CSF barrier, like renal tubule cells, have myriad other functions. These include the active transport of essential micronutrients into CSF from blood, e.g., methyltetrahydrofolic acid (MeTHF) and ascorbic acid (AA) [1]. The vectorial transport of MeTHF (the principal folate in plasma and CSF) from blood into CSF via the CP is due to a three-part active transport system in series: first, the folate receptor alpha (FRa) transfers MeTHF from blood into CP endosomes; MeTHF is released from the endosomes into the CP cytoplasm by the proton-coupled folate transporter (PCFT); and MeTHF is released from the cytoplasm into CSF by facilitated diffusion via the reduced folate carrier (RFC) [1]. Another example is AA that is transported into CP from blood by the active sodium-
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