Deletion of Slc7a5 from the endothelial cells of the blood-brain barrier in mice resulted in an atypical amino acid profile in the brain, abnormal mRNA translation, reduced mIPSC frequency in pyramidal neurons of the somatosensory cortex and cerebellar Purkinje cells, decreased exploratory behavior and locomotion, and abnormalities in social interaction (Tarlungeanu et al., 2016). In the same report, homozygous loss-of-function missense variants in the SLC7A5 gene were identified in two consanguineous families with affected individuals displaying ASD, delays in gross motor, fine motor, and social milestones, delayed or absent language development, and microcephaly or seizures.
Molecular Function
The SLC7A5 gene encodes for a sodium-independent, high-affinity transport of large neutral amino acids such as phenylalanine, tyrosine, leucine, arginine and tryptophan.
External Links
References
Type
Title
Type of Disorder
Associated Disorders
Author, Year
Primary
Impaired Amino Acid Transport at the Blood Brain Barrier Is a Cause of Autism Spectrum Disorder.
Slc7a5 endothelial cell specific conditional knockout mice exhibit abnormal brain amino acid profile, abnormal mRNA translation, hunched posture, hind limb clasping, poor motor coordination, and abnormal gait. The mice also display deficits in social related behaviors, such as rearing behavior, social approach, and reciprocal social interaction. Decreased frequency of mIPSCs and increased amplitude of mEPSCs are observed in the pyramidal neurons in somatosensory cortex or cerebellar Purkinje cells. Intracerebroventricular administration of BCAA partially rescues the motor phenotypes.
References
Type
Title
Author, Year
Primary
Impaired Amino Acid Transport at the Blood Brain Barrier Is a Cause of Autism Spectrum Disorder.
Model Type:
Genetic
Model Genotype:
Homozygous
Mutation:
Conditional deletion of exon 1 of the Slc7a5 gene using Tie2-Cre, in endothelial cells (including those in the brain)
Allele Type: Conditional loss-of-function
Strain of Origin: Not specified
Genetic Background: C57BL/6J
ES Cell Line: Mutant ES Cell Line: Not specified
Model Source: Not specified
Model Type:
Genetic
Model Genotype:
Homozygous
Mutation:
The Slc7a5-flox;Emx1-Cre conditional line was generated by crossing Slc7a5-flox mouse line (MGI:5618433) with animals expressing the Cre recombinase under the Emx1 promoter (MGI:2684610). In the Slc7a5-flox mouse line, exon 1, including the initiation codon, is flanked by two loxP sites.
Allele Type: Conditional knockout
Strain of Origin: Genetic Background: C57BL/6J
ES Cell Line: Mutant ES Cell Line: Model Source:
Description: Slc7a5 conditional nulls exhibit decreased locomotor activity (decreased total distance moved and decreased mean velocity) with similar habituation time course relative to heterozygous controls
Exp Paradigm: Open field test: total distance moved and mean velocity
Description: Slc7a5 conditional nulls have decreased performance in walking beam test relative to heterozygous controls
Exp Paradigm: Balance beam test
Miniature post synaptic current amplitude: excitatory1
Increased
Description: Slc7a5 conditional nulls exhibit an increase in the amplitude of mepscs
Exp Paradigm: Whole-cell patch clamp: pyramidal neurons in layer 2/3 of the somatosensory cortex
Description: The presynaptic vesicle number in the inhibitory neurons is decreased in slc7a5 conditional null somatosensory cortices when compared with heterozygous controls
Exp Paradigm: Immunostaining: vesicular gaba transporter (vgat); electron microscopy
Miniature post synaptic current frequency: inhibitory1
Decreased
Description: Slc7a5 conditional nulls exhibit a decrease in the frequency of mepscs
Exp Paradigm: Whole-cell patch clamp: pyramidal neurons in layer 2/3 of the somatosensory cortex
Description: Slc7a5 conditional nulls tend to stay farther apart from their cagemates and display a decreased number of nose-to-nose contacts relative to wildtype controls
Exp Paradigm: Reciprocal social interaction test
Description: Slc7a5 conditional nulls display no preference to unfamiliar mouse over an object as wildtype controls do
Exp Paradigm: Three-chamber social approach test
Description: Slc7a5 conditional nulls exhibit enhanced expression of two amino acid transporters, cat1 and cat2 (encoded by slc7a1 or slc7a2, respectively)
Exp Paradigm: Rna sequencing
Description: Slc7a5 conditional nulls display complete deletion of slc7a5 protein in the endothelial cells of the brain blood barrier
Exp Paradigm: Immunostaining
Description: Brain amino acid levels of histidine, phenylalanine, proline, glycine, threonine, or serine are high in slc7a5 conditional nulls relative to controls (slc7a5fl/fl)
Exp Paradigm: High-performance liquid chromatography (hplc)
Description: Compared with their littermate controls, adult animals have a significantly lower number of inhibitory neurons, particularly in the upper cortical layers.
Description: Histological analysis revealed a reduction in the thickness of the cerebral cortex of P40 Slc7a5 mutant animals, with layers II and III being the drivers of this difference.
Description: Mutant mice are born with normal brain size. However, by P40, the brain of mutant mice is significantly smaller than that of their control littermates. By monitoring the brain weight over time, we found that the difference in brain size between control and Slc7a5 mutant animals appears during the first postnatal week and remains stable from P10 onward.
Action potential property: rate of depolarization1
Decreased
Description: Action potential rise time is decreased at P6-7 in mutant mice compared to control mice.
Exp Paradigm: layers II and III pyramidal neurons from the somatosensory cortex
Description: Amino acids transported by Slc7a5, grouped into the term â??â??aminoacyl-tRNA biosynthesisâ??â??, are the major class of affected metabolites in conditional knockout animals. However, the deletion of Slc7a5 alters the levels of these amino acids in cortical tissue only at P2, but not E14.5 or P40. The level of these amino acids is higher, not lower, in mutants compared with controls, suggesting that in the absence of Slc7a5, the amino acids accumulate in the extracellular space and are not consumed by neural cells. At P2, intracellular levels of amino acids that are the primary Slc7a5 substrates are indeed significantly reduced in mutant cells.
Description: Recordings from mutant mice show decreased firing rate at P6-7 but not P25-26, compared to control mice.
Exp Paradigm: layers II and III pyramidal neurons from the somatosensory cortex
Description: Amino acids transported by Slc7a5, grouped into the term "aminoacyl-tRNA biosynthesis", are the major class of affected metabolites in conditional knockout animals. However, the deletion of Slc7a5 alters the levels of these amino acids in cortical tissue only at P2, but not E14.5 or P40. The level of these amino acids is higher, not lower, in mutants compared with controls, suggesting that in the absence of Slc7a5, the amino acids accumulate in the extracellular space and are not consumed by neural cells. At P2, intracellular levels of amino acids that are the primary Slc7a5 substrates are indeed significantly reduced in mutant cells.
Description: Recordings from mutant mice show altered firing pattern when action potential is plotted as dV/dt vs voltage (phase-plane plot).
Exp Paradigm: layers II and III pyramidal neurons from the somatosensory cortex
Description: Action potential threshold is decreased at P6-7 in mutant mice compared to control mice.
Exp Paradigm: layers II and III pyramidal neurons from the somatosensory cortex
Description: Recordings from mutant mice show action potential amplitude is increased compared to control mice.
Exp Paradigm: layers II and III pyramidal neurons from the somatosensory cortex
Description: In the three-chamber sociability test, mutant mice show no preference for the social stimulus chamber, whereas control mice explore the chamber with a stranger mouse significantly more than the chamber with an inanimate object.
Description: In the three-chamber sociability test, mutant mice show no preference for the chamber with a stranger mouse, whereas control mice explore the chamber with a stranger mouse significantly more than the chamber with a familiar mouse.
Description: However, we found that loss of Slc7a5 in neurons affects the levels of metabolites related to glycerophospholipids (GPLs). Specifically, an analysis of all the detected lipid-related metabolites disclosed that while at E14.5 and P40 mutant and control samples cluster together, P2 samples separate by genotype. A comparative untargeted lipidomic analysis of P2 mutant and control cortical tissue and dissociated cells reveals a specific reduction of GPLs in mutant cortical cells. Members of the GPLs are the main components of the phospholipid bilayer of biological membranes.
Description: The comparative untargeted lipidomic analysis of P2 mutant and control cortical tissue and dissociated cells that reveals a specific reduction of GPLs in mutant cortical cells, also shows an increase of triacylglycerols (TGs) in Slc7a5 deficient cortical tissue. TGs account for the majority of dietary fats and represent a way to store energy.
Description: Conditional knockout mice show reduced expression of Slc7a5 protein in the brain, including the excitatory neurons of the neocortex and hippocampus as well as in the glial cells of the pallium, but not in the endothelial cells of the BBB.
Description: In a proteomic study of perinatal control and mutant cerebral cortices, 1,202 proteins were identified to be deregulated in mutant samples, comprising 954 upregulated and 248 downregulated proteins in the conditional knockout cortex. Gene ontology (GO) enrichment analysis returned proteins involved in lipid metabolism as being the most significant and numerous among the upregulated proteins, while among the downregulated GO terms, an enrichment for neuron projection and membrane-associated proteins was found.
Description: Three palmitoyltransferases are deregulated in Slc7a5 mutants. These include a reduction in Zdhhc17, which specifically modifies proteins involved in neuronal functions.
Description: Protein level of cleaved caspase-3, a pro-apoptotic marker, was increased in cortical samples obtained from mutant mice compared to control mice. A significant increase in cleaved caspase-3 was specifically seen at P2 and P5.
