Alzheimer’s Disease Phenotype or Inflammatory Insult Does Not Alter Function of L-Type Amino Acid Transporter 1 in Mouse Blood-Brain Barrier and Primary Astrocytes

Abstract

PurposeThe study aim was to evaluate the effect of Alzheimer’s disease (AD) and inflammatory insult on the function of L-type amino acid transporter 1 (Lat1) at the mouse blood-brain barrier (BBB) as well as Lat1 function and expression in mouse primary astrocytes.MethodsThe Lat1 function and expression was determined in wildtype astrocytes with and without lipopolysaccharide (LPS)-induced inflammation and in LPS treated AD APP/PS1 transgenic astrocytes. The function of Lat1 at the BBB was evaluated in wildtype mice with and without LPS-induced neuroinflammation and APP/PS1 transgenic mice by in situ brain perfusion.ResultsThere were 2.1 and 1.6 -fold decreases in Lat1 mRNA and protein expression in LPS-treated wildtype astrocytes compared to vehicle-treated astrocytes. In contrast, Lat1 mRNA and protein expression were increased by 1.7 and 1.2 -fold (not statistically significant) in the transgenic cells. A similar trend was observed in the cell uptake of [14C]-L-leucine. There were no statistically significant differences in [14C]-L-leucine BBB permeation between the groups.ConclusionsThe results showed that neither LPS-induced inflammation or the presence of APP/PS1 mutations alters Lat1 function at the mouse BBB as well as Lat1 protein expression and function in mouse primary astrocytes.

L-Type amino acid transporter 1 as a target for drug delivery

“…In the endothelial cells of the brain microvessels, LAT1 is expressed on both apical and basolateral sides of the cell membranes (30). Additionally, LAT1 expression was detected in brain parenchymal cells such as human and mouse astrocytes, mouse and rat neurons and immortalized microglia cultures (31)(32)(33). LAT1 is also expressed in the inner BRB, ensuring the flux of large neutral amino acids and neurotransmitters (34).…”

“…In addition, the loss of LAT1 due to mutations leads to impairment of amino acid homeostasis in the brain and therefore it has been suggested to be a cause of motor dysfunction and Autism Spectrum Disorder in mice and human (43). Recently, Gynther et al (2018) showed that LAT1 function was not altered at the BBB of lipopolysaccharide (LPS) induced neuroinflammation murine model and in the transgenic Alzheimer's disease model with amyloid precursor protein (APP) and presenilin (PSEN1) gene mutations, (31). In the same study, LAT1 protein expression and function were similar in wild type astrocytes with and without LPS treatment and in APP/PS1 transgenic astrocytes treated with LPS (31).…”

l-Type Amino Acid Transporter 1 (LAT1/Lat1)-Utilizing Prodrugs Can Improve the Delivery of Drugs into Neurons, Astrocytes and Microglia

“…Our group has developed LAT1/Lat1-utilizing prodrugs, which can significantly improve the cellular and brain uptake of several parent drugs, such as anti-inflammatory agent ketoprofen 17–19 , anti-epileptic drug valproic acid 20,21 , anti-parkinsonian prodrug of dopamine 22,23 , investigational immunosuppressive perforin inhibitors 24,25 , and natural phenolic antioxidant ferulic acid 26 . We have also recently reported that neither Alzheimer’s disease (AD) induced alterations of transgenic mice nor lipopolysaccharide (LPS)-induced neuroinflammation changed the expression or function of Lat1 at the BBB or primary astrocytes 27,28 . This signifies that LAT1/Lat1 can be utilized for targeted drug delivery not only into the healthy brain but also brain predisposed to pathological changes of brain diseases.…”

Targeting of Perforin Inhibitor into the Brain Parenchyma Via a Prodrug Approach Can Decrease Oxidative Stress and Neuroinflammation and Improve Cell Survival

“…We have recently characterized mouse primary astrocytes for their LAT1 expression (3.1 ± 0.9 fmol/μg protein) and function ([ 14 C]-L-leucine uptake V max 2.9 ± 0.4 nmol/min/mg protein; K m 66 ± 14 μM) [ 39 ]. Therefore, the ability of LAT1-utilizing prodrug (PFI-PD) to bind to LAT1 was evaluated as half of the maximal inhibition (IC 50 ) of the cellular uptake of [ 14 C]- l -leucine (0.76 μM) and compared to the values of the parent perforin inhibitor (PFI) as well as the reported LAT1 inhibitor (KMH-233) [ 37 ].…”