27908
Comparative Expression Analysis of Autism-Associated Cadherin Superfamily Members
The cadherin superfamily is a group of cell adhesion molecules containing more than one hundred proteins, including classical cadherins type I and II, protocadherins, and atypical cadherins. N-cadherin functions throughout development of nervous system including neurite outgrowth, axon guidance, synaptogenesis, spine morphogenesis and plasticity. Although there is only little known about the function of other cadherins they have been strongly implicated in autism. A genome wide association study identified the classical cadherin type II CDH8 and CDH11, the protocadherin PCDH9 and the atypical cadherin FAT1 as candidate risk genes. This suggests that cadherin signaling pathways could be disrupted and may display increased vulnerability in autism.
Objectives:
As a first step toward understanding the central role of cadherins in the etiology of autism, we focused on CDH8, CDH11, PCDH9 and FAT1 and investigated their expression patterns in specific brain areas, cell types and their subcellular localization during development. This comparative expression analysis could provide novel insights into common and distinct functions of these cadherins in neural circuit formation. We further determined the expression of these cadherins in human postmortem brain tissues of control and autism individuals to evaluate whether cadherin levels are commonly altered in autism.
Methods:
Western blot analyses was performed to evaluate the protein expression of CDH8, CDH11, PCDH9 and FAT1 in the developing mouse brain of embryonic day 14, postnatal day 0, P7, P14 and P21 and adult as well as in different brain areas. To analyze the cellular localization, enrichment of cadherins in synaptic plasma membrane and postsynaptic densities was analyzed. Additionally, primary neurons from different brain regions were cultured for 14 days in vitro and co-stained for cadherins and neuronal marker MAP2 or synaptic markers PSD95, Synapsin1 and GAT1.
Results:
Temporal expression analysis in the developing mouse brain revealed increased expression of CDH8, CDH11, PCDH9 and FAT1 at P7 and P14 with an additional peak of FAT1 expression at E14. Analysis of specific brain areas showed that CDH8, CDH11 and PCDH9 were prominently expressed in the cortex, hippocampus and thalamus/striatum whereas FAT1 expression was restricted to the cerebellum. Additionally, CDH8, CDH11 and FAT1 localized to MAP2-positive dendrites and were enriched in synaptic plasma membrane and post-synaptic density. Moreover, CDH8 and CDH11 were associated with excitatory and inhibitory synaptic markers. In addition, CDH8 expression was elevated in CDH11-kockout brains, indicating at least partially redundant functions of those type II classical cadherins. Preliminary results of CDH8, CDH11 and PCDH9 expression in postmortem cingulate cortices of control and autism individuals suggest an altered expression profile of cadherins in autism brains.
Conclusions:
Our results revealed similar overall expression profiles among CDH8, CDH11 and PCDH9, with a distinct expression pattern for FAT1. The temporal expression and the subcellular localization of cadherins were consistent with the proposed functions in synaptogenesis. Taken together, the present study highlights that cadherins of different subfamilies are expressed in a developmental time window and in brain areas implicated as vulnerable in autism, thus strengthening the hypothesis of a central role of cadherins in this neurodevelopmental condition.