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Role of genetic interaction between COMT and Dysbindin in cognitive and schizophrenia-related abnormalities

Final Report Summary - SCHIZOGENES (Role of genetic interaction between COMT and Dysbindin in cognitive and schizophrenia-related abnormalities)

The overall objective of this project was to provide genetic-relevant mechanistic insights for cognitive abnormalities and schizophrenia-related phenotypes.
Thanks to the Marie Curie International Reintegration Grant support, this research line initiated in the USA was continued and was expanded at the Italian Institute of Technology (IIT) in Genova, Italy. In particular, this European project allowed to establish a novel and internationally competitive group in Italy leaded by Dr. Papaleo Francesco. The main scientific goal of this research group is to investigate the genetics, behavioral, molecular and neurophysiological mechanisms of cognitive and schizophrenia-related abnormalities.
Schizophrenia is a chronic debilitating disorder with major burden for the affected subjects and their families. In particular, cognitive abnormalities are core enduring symptoms in schizophrenia, dramatically contribute to poor functional outcomes in patients and currently are still incurable. The genetic component has been suggested to play a major role in the development of schizophrenia and its related cognitive deficits. However, while several potential schizophrenia-susceptibility genes have been identified, their clinical association effects are still not clear, likely because of the complexity of human polymorphisms, genetic and clinical heterogeneity and the uncontrollable impact of gene-gene and gene-environment interactions in clinical studies. In this context, this European-funded project have been using mutant mice bearing selective mutations of schizophrenia-susceptibility genes as these constitute a unique tool to elucidate the genetic/neurobiological basis of this devastating disorder and its cognitive alterations. To reach our goal we have been also supported by the collaboration with a multidisciplinary research team including Dr. D.R. Weinberger’s laboratories at the NIMH and Lieber Institute (MD, USA), the clinical research centers Santa Lucia and Bambino Gesu’ in Roma and especially the fruitful research environment of the host institution, the IIT, which includes a number of investigators with diverse scientific backgrounds. Notably, the institute provides an incredible amount of state of the art equipments, facilities and resources dedicated to complementary brain-based studies.

Major results and achievements:
1. Development of innovative tasks with translational validity to human studies
We first optimized a discrete paired-trial variable delay T-maze task for studying prefrontal cortex (PFC)-dependent working memory in mice, to probe the effects of memory load and environmental changes. We then developed an implementation of a 5-choice serial reaction time task able to automatically dissect different aspects of attentional control in mice. We demonstrated how different environmental manipulations and/or the sex of the subject can selectively alter performance in specific aspects of the task while leaving others unaltered. More recently, we developed a novel automated system to dissect different executive functions and cognitive abilities in mice, with high translational validity to human studies. Our new operant-based apparatus for mice was modeled after the human- and non-human primates’ Wisconsin Card Sorting Test and CANTAB Intra-/Extra-dimensional set-shifting tasks. These tasks are commonly used to assess prefrontal function in primates and to identify cognitive abnormalities in several psychiatric diseases. Finally, we have created a machine-learning-based system for automatic visual tracking and analysis of complex social behavior between multiple mice that are free to interact. This system allows to finely analyze social cognition and social behaviors, which are key altered features in human patients affected by schizophrenia.
We emphasize that these new tasks for mice are important as they made possible to exactly indicate what to look for in human studies. Conceptually, screening for genetic effects first in mice can be faster and more reliable than in human populations. Moreover, we can quickly make experimental refinements in mice, to more precisely zero in on what to look for in humans.

2. Dissect genetic-driven cognitive abnormalities relevant to schizophrenia
- We demonstrated how a clinically-relevant genetic modification in the Catechol-O-methyltransferase (COMT) gene can differently modulate attention, impulsivity, stress reactivity, compulsivity, flexibility, and motivation depending on variables such as the sex of the subject and different environmental factors.
- We found detrimental effects of life-long increased BDNF genetic expression in female mice in functions such as working memory, anxiety-like states, sensorimotor gating and susceptibility to seizures.
- We discovered that genetic reduction of COMT produced a selective improvement in switching of attention between different perceptual dimensions but produced apparent impairments of serial reversal learning.
- We established the dysbindin-1 gene as a potential bridge between the alterations found in the dopaminergic and glutamatergic systems in schizophrenia.
- We have found a consistent nonlinear interaction between COMT and dysbindin-1 genes. In mice, we found that a single genetic mutation reducing expression of either COMT or dysbindin-1 alone produces working memory advantages, while genetic reduction of both in the same mouse produces working memory deficits. These results illustrate that epistasis can be functionally multi-directional and nonlinear, and that a putatively beneficial allele in one epistastic context could be a deleterious one in another context.
Overall these findings inform human studies evaluating the role of these functional genetic variations on cognitive abilities and vulnerability to psychiatric disorders.

3. Predicting genetic-driven behavioral phenotypes in humans
Based on our mouse studies, we did predict behavioral phenotypes in humans - both healthy individuals and those with (or at risk to develop) schizophrenia - by analyzing specific functional genetic mutations that we have modeled in the mice. We have been examining psychopathological-neurocognitive profiles and structural-functional brain measures in human subjects, as a direct translational outcome of our mouse studies. In particular, as found in our mouse models, genetically driven reduction in COMT enzyme activity was associated with a selective increase in cortical thickening in the PFC and postero-parieto-temporal cortex of male but not female healthy humans. Moreover, the potential relevance of these sex-specific morphological changes was observed in pertinent cognitive functions such as working memory which also showed that genotype effects varied with sex.
Finally, we found that the same nonlinear COMT-dysbindin genetic interaction found in mice also affect PFC-related function/behaviors in humans. In healthy volunteers studied with fMRI during a working memory paradigm, individuals homozygotic for the COMT rs4680 Met allele (which reduces COMT enzyme activity) showed more efficient PFC engagement, but the same genotype was less efficient on the background of a dysbindin haplotype associated with decreased dysbindin expression.
By identifying human subpopulations with specific genetic background profiles, more focused and effective therapeutic strategies could be applied or developed.