Estrogen Receptor Beta Signaling and Transglutaminase 2 in Sex Specific ASD-like Behavior in Mice

Background: Autism Spectrum Disorders (ASD) are a heterogeneous set of disorders affecting 1 in 68 children in America and approximately 1% of the population worldwide. ASD is approximately 5 times more common in males than in females, suggesting the possible protective role of female sex hormone, estrogen in this disorder. Our recently published study, for the first time, found decreased expression of estrogen receptor β (ERβ) in the prefrontal cortex of male ASD subjects (Crider et al., 2014). ERβ plays an important role in neuroprotection and cognitive functions suggesting that deficits ERβ signaling could contribute to the more prevalence of ASD phenotype seen in males. To further investigate the mechanism(s) connecting ERβ signaling and ASD pathophysiology, we investigated the role of transglutaminase 2 (TG2) in mediating ERβ signaling in ASD. TG2 is a calcium-dependent enzyme that plays an important role in the posttranslational modification of proteins. At the cellular level, endoplasmic reticulum (ER) stress, which has been implicated in ASD, is shown to induce TG2 activity. Moreover, TG2 has an estrogen response element (ERE), further implicating its role in estrogen signaling.

Objectives: Our long term goal is to understand the role of TG2 in mediating ERβ signaling in ASD. This study could provide a better understanding of gender differences in and novel treatment options for ASD.

Methods: Human postmortem prefrontal cortex samples from ASD/Autism and control subjects were obtained from NICHD. Animal experiments were performed in C57BL/6 mice overexpressing Transglutaminase 2 and littermate controls. ER stress was induced by tunicamycin treatment in male mice. Protein levels were measured by western blotting. mRNA levels were measured by RT-PCR.Behavioral measures in mice included open field, light/dark test, tail suspension test, forced swim test, social interaction test, grooming, and marble bury test.

Results: We found significant increases in TG2 mRNA and protein levels in the frontal cortex of ASD subjects. In vivo, ER stress by tunicamycin treatment induced ASD-like phenotype in marble bury test, social interaction and open field tests in mice. TG2 overexpression resulted in ASD-like phenotype in male mice. To further examine the role of ERβ in ASD-like behavior, male mice were treated with PHTPP, an ERβ antagonist. Mice treated with PHTPP showed significant changes in social interaction test, marble bury test and grooming behavior (indicating ASD-like phenotype) with no changes in open field, TST, FST orlight/dark test. Additional studies using TG2 inhibitor (Cysteamine) and ERβ agonist (ERB-041) support the role of TG2 in gender-specific changes in ASD-like behavior in mice.

Conclusions: The data from this study provide initial evidence on the mechanism of ERβ in protecting females from ER-stress-induced ASD-like behavior in mice. ERβand TG2 could be potential targets to reverse the ASD-like phenotype in males. In this regard, ERβ agonists are already known to improve brain plasticity and memory in animals (without effects on sexual behavior).

See more of: Animal Models
See more of: Animal Models