Only a small percentage of the autism spectrum disorders appear to have a clear genetic etiology (~25%), leaving a majority of cases with unclear origins. Alterations in environmentally sensitive epigenetic marks (e.g., DNA methylation) have been implicated in mental illness, including autism. A novel epigenetic mark, 5- hydroxymethylcytosine (5hmC), is enriched in neurons and is associated with active transcription of neuronal genes. While numerous studies have profiled 5hmC and found links to neurological disorders, less effort has been invested in determining the functional role of 5hmC, as it pertains to gene expression. As a result, the full functional potential of 5hmC modifications has yet to be realized in outcomes related to behavior. A recent genome-wide profile of striatal 5hmC in an autism mouse model (i.e., a Cntnap2-/- homozygote) that exhibits core autism features, including deficits in striatal GABAergic signaling, revealed a genome-wide disruption of 5hmC in the orthologs of a remarkable number of genes implicated in human autism (N=68/233). Thus, these data suggest a role for 5hmC-mediated epigenetic modulation in the pathogenesis of autism and represent a critical step toward understanding the genome-wide molecular consequences of a homozygous mutation that results in an autism-like phenotype. Notably, Cntnap2+/- heterozygous mutant mice lack autistic-like features. Since 5hmC levels are environmentally sensitive, these findings led to the hypothesis that Cntnap2+/- heterozygous mice subjected to an early environmental stress would have disruptions in 5hmC and may exhibit autistic-like behaviors similar to the Cntnap2-/- homozygous mutant. To test this hypothesis, beginning at embryonic day 12, Cntnap2+/- heterozygous mice were subjected to seven days of prenatal stress and subsequently examined for adult behaviors. Unlike wild-type littermates, prenatally stressed female Cntnap2+/- heterozygous mice exhibited social deficits. In addition, genomic profiling revealed disruptions in 5hmC throughout the striatal genome, which were similar to those seen in Cntnap2-/- homozygous mice. Finally, integration of the above data with striatal gene expression data revealed that differential hydroxymethylation correlated with altered transcript levels of genes shown to contribute to the deficits in GABAergic signaling and social behavior of the Cntnap2-/- homozygous mutant mouse (e.g., GABA receptors and Oxytocin). Thus, these data demonstrate that gene by environment interactions lead to deficits in social interactions and suggest that 5hmC levels likely contribute to this outcome. Here, the proposed studies will: 1) identify the functional role of 5hmC in social deficits resulting from prenatal stress; and 2) identify the contribution of oxytocin in social deficits exhibited following prenatal stress. These findings will identify stress-related molecular targets in the brain that are influenced by environmentally sensitive epigenetic mechanisms and may be involved in the etiology of developmental brain disorders. Importantly, the plan builds on the applicant's training in genomic studies, combining genomics will in-depth training in molecular and behavioral approaches.
/PUBLIC HEALTH RELEVANCE Psychiatric disorders such as autism, depression, and schizophrenia, are prevalent mental illnesses that have few effective treatments available. Defining the molecular functions and mechanisms of environmentally sensitive contributors to mental health can lead to new, more objective, strategies for diagnosis of mental illness and aid in finding new methods of treatment in the eradication of psychiatric disorders.
| Madrid, Andy; Chopra, Pankaj; Alisch, Reid S (2018) Species-Specific 5 mC and 5 hmC Genomic Landscapes Indicate Epigenetic Contribution to Human Brain Evolution. Front Mol Neurosci 11:39 |
