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OBJECTIVES: Folates are critical for normal neurodevelopment, and folate transport in the brain is primarily mediated by folate receptor alpha (FRα) at the blood-cerebrospinal fluid barrier (BCSFB). However, studies have reported folate transporter/receptor expression in other brain compartments, which may significantly contribute to overall brain folate uptake. The objective of this study is to characterize the localization of the folate transport systems i.e., reduced folate carrier (RFC), proton-coupled folate transporter (PCFT), and FRα in the mouse central nervous system, which will provide insight on novel routes of brain folate transport. In particular, folate transporter/receptor localization is examined at brain barriers [blood-brain barrier (BBB), BCSFB, arachnoid barrier (AB)] and in brain parenchyma (astrocytes, microglia, neurons). METHODS: The localization of RFC, PCFT and FRα was observed in the brains of C57BL6/N wildtype mice by applying immunohistochemistry (IHC). Mouse brains were isolated, and IHC was performed on frozen coronal sections. Transporter/receptor localization was examined at brain barriers (BBB, BCSFB, AB) and in brain parenchyma (astrocytes, neurons, microglia) using specific antibodies. Standard IHC markers were utilized to identify various brain compartments, with confocal microscopy used for imaging. RESULTS: At the mouse BBB and BCSFB, localization of RFC, PCFT and FRα was observed, which is consistent with previous reported data and our own work. At the AB, in astrocytes and neurons localization of RFC and PCFT (but not FRα) was observed. In microglia, no expression of the folate transporters or receptor was detected. CONCLUSIONS: RFC and PCFT localization at the AB may represent a novel route of folate transport into the CSF, with transporter expression in neurons and astrocytes facilitating folate uptake into brain parenchyma cellular targets. Modulating folate transport at these brain compartments may provide a novel strategy in increasing brain folate uptake in disorders associated with defective FRα and impaired brain folate transport at the BCSFB. FUNDING SOURCES: This work is supported by the Natural Sciences and Engineering Research Council of Canada (RB). VS is a recipient of several graduate scholarships. |
