Behavioral and transcriptomic profiling of mice null forLphn3, a gene implicated inADHDand addiction

Abstract

BackgroundThe Latrophilin 3 (LPHN3) gene (recently renamed Adhesion G protein‐coupled receptor L3 (ADGRL3)) has been linked to susceptibility to attention deficit/hyperactivity disorder (ADHD) and vulnerability to addiction. However, its role and function are not well understood as there are no known functional variants.MethodsTo characterize the function of this little known gene, we phenotyped Lphn3 null mice. We assessed motivation for food reward and working memory via instrumental responding tasks, motor coordination via rotarod, and depressive‐like behavior via forced swim. We also measured neurite outgrowth of primary hippocampal and cortical neuron cultures. Standard blood chemistries and blood counts were performed. Finally, we also evaluated the transcriptome in several brain regions.ResultsBehaviorally, loss of Lphn3 increases both reward motivation and activity levels. Lphn3 null mice display significantly greater instrumental responding for food than wild‐type mice, particularly under high response ratios, and swim incessantly during a forced swim assay. However, loss of Lphn3 does not interfere with working memory or motor coordination. Primary hippocampal and cortical neuron cultures demonstrate that null neurons display comparatively enhanced neurite outgrowth after 2 and 3 days in vitro. Standard blood chemistry panels reveal that nulls have low serum calcium levels. Finally, analysis of the transcriptome from prefrontal cortical, striatal, and hippocampal tissue at different developmental time points shows that loss of Lphn3 results in genotype‐dependent differential gene expression (DGE), particularly for cell adhesion molecules and calcium signaling proteins. Much of the DGE is attenuated with age, and is consistent with the idea that ADHD is associated with delayed cortical maturation.ConclusionsTranscriptome changes likely affect neuron structure and function, leading to behavioral anomalies consistent with both ADHD and addiction phenotypes. The data should further motivate analyses of Lphn3 function in the developmental timing of altered gene expression and calcium signaling, and their effects on neuronal structure/function during development.

Genetics of ADHD: What Should the Clinician Know?

“…ADGRL3 was confirmed as an ADHD candidate locus in two other independent casecontrol studies, by association of one haplotype in ADGRL3 [21] and single associations of several SNPs [22]. In the zebrafish model, the loss of adgrl3 leads to a reduction of dopaminergic neurons in the ventral diencephalon and a hyperactive/impulsive phenotype [23], whereas in Adgrl3knockout mice, an increase in reward motivation and activity level as well as other ADHD-analogous behaviors was observed-parallel to dysregulation of the dopamine transporter [24,25]. This suggests that the biological validation of an ADHD candidate gene from a GWAS in an animal model can elucidate potential mechanisms of pathogenesis.…”

Recent developments in the genetics of attention‐deficit hyperactivity disorder

“…In zebrafish, the loss of the ortholog lphn3 leads to a reduction of dopamine‐positive neurons in the ventral diencephalon and a hyperactive/impulsive motor phenotype . In mice, the impact on the brain is not as clearly linked to an ADHD‐related behavioral phenotype, but shows an increase of reward motivation and activity levels in loss‐of‐function LPHN3 …”

Pharmacological analysis of zebrafish lphn3.1 morphant larvae suggests that saturated dopaminergic signaling could underlie the ADHD-like locomotor hyperactivity

“…Furthermore, knockout of Lphn3 in mouse induced hyperactivity, increased DA and 5-HT in the striatum, changed DA and 5-HT receptor expression and increased locomotor sensitivity to cocaine ( Wallis et al, 2012 ). Transcriptomic analysis of Lphn3 null mice identified differential expression of genes coding for calcium signaling proteins and cell adhesion molecules consistent with the hyperactivity ( Orsini et al, 2016 ). There was also an overexpression of Slc6a3 ( Dat , coding for the DA transporter) in the striatum.…”