Endotoxin-induced inflammation down-regulates L-type amino acid transporter 1 (LAT1) expression at the blood-brain barrier of male rats and mice.
BACKGROUND
We recently reported that bacterial lipopolysaccharide (LPS)-induced inflammation decreases the expression of the primary thyroid hormone transporters at the blood-brain barrier, organic anion-transporting polypeptide 1c1 (OATP1c1) and monocarboxylate transporter 8 (MCT8). L-type amino acid transporters 1 and 2 (LAT1 & LAT2) are regarded as secondary thyroid hormone transporters, and are expressed in cells of the blood-brain or blood-cerebrospinal fluid barrier and by neurons. The purpose of this study was to examine the effect of LPS-induced inflammation on the expression of LAT1 and LAT2, as these may compensate for the downregulation of OATP1c1 and MCT8.


METHODS
LPS (2.5 mg/kg body weight) was injected intraperitoneally to adult, male, Sprague-Dawley rats and C57Bl/6 mice, which were euthanized 2, 4, 9, 24 or 48 h later. LAT1 and LAT2 mRNA expression were studied on forebrain sections using semiquantitative radioactive in situ hybridization. LAT1 protein levels in brain vessels were studied using LAT1 immunofluorescence. Statistical comparisons were made by the non-parametric Kruskal-Wallis and Dunn's tests.


RESULTS
In both species, LAT1 mRNA decreased in brain blood vessels as soon as 2 h after LPS injection and was virtually undetectable at 4 h and 9 h. During recovery from endotoxemia, 48 h after LPS injection, LAT1 mRNA in brain vessels increased above control levels. A modest but significant decrease in LAT1 protein levels was detected in the brain vessels of mice at 24 h following LPS injection. LPS did not affect LAT1 and LAT2 mRNA expression in neurons and choroid plexus epithelial cells.


CONCLUSIONS
The results demonstrate that LPS-induced inflammation rapidly decreases LAT1 mRNA expression at the blood-brain barrier in a very similar manner to primary thyroid hormone transporters, while changes in LAT1 protein level follow a slower kinetics. The data raise the possibility that inflammation may similarly down-regulate other blood-brain barrier transport systems at the transcriptional level. Future studies are required to examine this possibility and the potential pathophysiological consequences of inflammation-induced changes in blood-brain barrier transport functions.
Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Tupper Research Institute, Tufts Medical Center, Boston, MA, USA. gwittmann@tuftsmedicalcenter.org.
Gábor
G
Wittmann
Department of Endocrine Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary. mohacsik.petra@koki.mta.hu.|Semmelweis University, János Szentágothai PhD School of Neurosciences, Budapest, Hungary. mohacsik.petra@koki.mta.hu.
Petra
P
Mohácsik
Division of Hematology/Oncology, Department of Medicine, Tupper Research Institute, Tufts Medical Center, Boston, MA, USA. myaseen@tuftsmedicalcenter.org.
Mumtaz Yaseen
MY
Balkhi
Department of Endocrine Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary. gereben.balazs@koki.mta.hu.
Balázs
B
Gereben
Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Tupper Research Institute, Tufts Medical Center, Boston, MA, USA. rlechan@tuftsmedicalcenter.org.|Department of Neuroscience, Tufts University School of Medicine, Boston, MA, USA. rlechan@tuftsmedicalcenter.org.
Ronald M
RM
Lechan
D027182:Amino Acid Transport System y+ / Q000378:metabolism*; D000818:Animals; D001812:Blood-Brain Barrier / Q000187:drug effects / Q000378:metabolism*; D004660:Encephalitis / Q000139:chemically induced / Q000378:metabolism*; D008070:Lipopolysaccharides; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000378:metabolism; D016548:Prosencephalon / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D027182:Amino Acid Transport System y+; D008070:Lipopolysaccharides; D012333:RNA, Messenger