Estrogen effects on the expression of Brx in the brain and pituitary of the mouse

Mice deficient in AKAP13 (BRX) develop compulsive-like behavior and increased body weight

OBJECTIVE

Hormonal contributions to the sex-dependent development of both obsessive-compulsive disorder (OCD) and obesity have been described, but the underlying mechanisms are incompletely understood. A-kinase anchoring protein 13 (AKAP13) significantly augments ligand-dependent activation of estrogen receptors alpha and beta. The hypothalamus and pituitary gland are implicated in the development and exacerbation of OCD and obesity and have strong AKAP13 expression. The AKAP13 localization pattern observed in these key brain regions together with its effects on sex steroid action suggest a potential role for AKAP13 in compulsive-like behaviors. Here we tested the role of AKAP13 in compulsive-like behavior and body weight using an Akap13 haploinsufficient murine model.

MATERIALS AND METHODS

Targeted deletion of the Akap13 gene generated haploinsufficient (Akap13+/-) mice in a C57BL6/J genetic background. Established behavioral assays were conducted, video recorded, and scored blindly to assess compulsive-like behavior based on genotype and gender. Tests included: marble-burying, grooming, open- field and elevated plus-maze. Brain and body weights were also obtained. Mean levels of test outcomes were compared using multi-way ANOVA to test for genotype, sex, genotype*sex, and genotype*sex*age interaction effects with Bonferroni adjustment for multiple comparisons, to further explain any significant interactions.

RESULTS

The marble-burying and grooming assays revealed significant sex-dependent increases in perseverative, compulsive-like behaviors in female Akap13 haploinsufficient mice compared to female wild type (WT) mice by demonstrating increased marble-burying activity (p = .0025) and a trend towards increased grooming behavior (p = .06). Male Akap13 haploinsufficient mice exhibited no behavioral changes (p > 0.05). Elevated plus-maze and open-field test results showed no overt anxiety-like behavior in Akap13 haploinsufficient mice irrespective of sex (p > 0.05, both). No differences in brain weight were found in Akap13 haploinsufficient mice compared to WT mice (p > 0.05). However, female Akap13 haploinsufficient mice weighed more than female WT mice in the 4 to <7 months age range (p = .0051). Male Akap13 haploinsufficient mice showed no differences in weight compared to male WT mice (p = >0.05) at any age range examined.

CONCLUSION

Akap13 haploinsufficiency led to sex-dependent, compulsive-like behavioral changes in a murine model. Interestingly, Akap13 haploinsufficiency also led to a sex-dependent increase in body weight. These results revealed a requirement for AKAP13 in murine behavior, particularly in female mice, and is the first report of AKAP13 involvement in murine behavior. Future studies may examine the involvement of AKAP13 in the pathophysiology of OCD in female humans and may contribute to a better understanding of the role of AKAP13 and sex hormones in the development and exacerbation of OCD.

The Guanine Nucleotide Exchange Factor Brx: A Link between Osmotic Stress, Inflammation and Organ Physiology and Pathophysiology

Dehydration, and consequent intracellular hyperosmolarity, is a major challenge to land organisms, as it is associated with extraction of water from cells and disturbance of global cellular function. Organisms have thus developed a highly conserved regulatory mechanism that transduces the hyperosmolarity signal from the cell surface to the cell nucleus and adjusts the expression of cellular osmolarity-regulating genes. We recently found that the Rho-type guanine nucleotide exchange factor Brx, or AKAP13, is essential for osmotic stress-stimulated expression of nuclear factor of activated T-cells 5 (NFAT5), a key transcription factor of intracellular osmolarity. It accomplishes this by first attracting cJun kinase (JNK)-interacting protein (JIP) 4 and then coupling activated Rho-type small G-proteins to cascade components of the p38 MAPK signaling pathway, ultimately activating NFAT5. We describe the potential implications of osmotic stress and Brx activation in organ physiology and pathophysiology and connect activation of this system to key human homeostatic states.