Disruption of the non-canonical Wnt gene PRICKLE2 leads to autism-like behaviors with evidence for hippocampal synaptic dysfunction.
Autism spectrum disorders (ASDs) have been suggested to arise from abnormalities in the canonical and non-canonical Wnt signaling pathways.
However, a direct connection between a human variant in a Wnt pathway gene and ASD-relevant brain pathology has not been established.
Prickle2 (Pk2) is a post-synaptic non-canonical Wnt signaling protein shown to interact with post-synaptic density 95 (PSD-95). Here, we show that mice with disruption in Prickle2 display behavioral abnormalities including altered social interaction, learning abnormalities and behavioral inflexibility.
Prickle2 disruption in mouse hippocampal neurons led to reductions in dendrite branching, synapse number and PSD size. Consistent with these findings, Prickle2 null neurons show decreased frequency and size of spontaneous miniature synaptic currents. These behavioral and physiological abnormalities in Prickle2 disrupted mice are consistent with ASD-like phenotypes present in other mouse models of ASDs.
In 384 individuals with autism, we identified two with distinct, heterozygous, rare, non-synonymous PRICKLE2 variants (p.E8Q and p.V153I) that were shared by their affected siblings and inherited paternally.
Unlike wild-type PRICKLE2, the PRICKLE2 variants found in ASD patients exhibit deficits in morphological and electrophysiological assays.
These data suggest that these PRICKLE2 variants cause a critical loss of PRICKLE2 function. The data presented here provide new insight into the biological roles of Prickle2, its behavioral importance, and suggest disruptions in non-canonical Wnt genes such as PRICKLE2 may contribute to synaptic abnormalities underlying ASDs.Molecular Psychiatry advance online publication, 28 May 2013; doi:10.1038/mp.2013.71.
Further Readings of Interest
A review of the evidence for the canonical Wnt pathway in autism spectrum disorders.
Microdeletion and microduplication copy number variations are found in patients with autism spectrum disorder and in a number of cases they include genes that are involved in the canonical Wnt signaling pathway (for example, FZD9, BCL9 or CDH8). Association studies investigating WNT2, DISC1, MET, DOCK4 or AHI1 also provide evidence that the canonical Wnt pathway might be affected in autism.
Prenatal medication with sodium-valproate or antidepressant drugs increases autism risk. In animal studies, it has been found that these medications promote Wnt signaling, including among others an increase in Wnt2 gene expression. Notably, the available genetic information indicates that not only canonical Wnt pathway activation, but also inhibition seems to increase autism risk.
The canonical Wnt pathway plays a role in dendrite growth and suboptimal activity negatively affects the dendritic arbor.
In principle, this provides a logical explanation as to why both hypo- and hyperactivity may generate a similar set of behavioral and cognitive symptoms. However, without a validated biomarker to stratify for deviant canonical Wnt pathway activity, it is probably too dangerous to treat patients with compounds that modify pathway activity.
Systemic effects of Wnt signaling.
Wnt signaling plays a key role in several physiological and pathological aspects. Even if Wnt signal was first described more than 20 years ago, its role in systemic effects, such as angiogenesis and vascular disorders, bone biology, autoimmune diseases, neurological diseases and neoplastic disorders, was only recently emerged through the use of animal and in vitro models. Moreover, Wnt signaling inhibitors, such as DKK-1, may be advantageously considered targets for the treatment of several diseases, including osteoporosis, vascular diseases, inflammatory diseases, neurological diseases and cancer. Nevertheless, further studies are required to provide a complete understanding of this complex signaling pathway, and especially of its role in human diseases, considering the possible advantageous effects of Wnt signaling inhibitors on the progression of disease conditions.
This gene encodes a homolog of Drosophila prickle. The exact function of this gene is not known, however, studies in mice suggest that it may be involved in seizure prevention. Mutations in this gene are associated with progressive myoclonic epilepsy type 5. [provided by RefSeq, Dec 2011]