טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentEyal Asor
SubjectModeling gene environment interaction hypothesis in rats;
Possible implication for complex behaviors and
mental disorders
DepartmentDepartment of Medicine
Supervisors Full Professor Ben-Shachar Dorit
Professor Emeritus Klein Ehud
Full Thesis textFull thesis text - English Version


Abstract

It is assumed that behavior results from a combination of sensitivity traits and environmental influence. The present study suggests a novel approach to study the complexity of gene environment interaction by a transient early-in-life interference with the expression of multiple genes, blocking Sp1with the chemotherapeutic agent mithramycin, followed by later-in-life exposure to stress. Sp1 is a ubiquitous transcription factor, which plays a role in the regulation of many genes in response to internal and environmental signals and is suggested to have implication in complex behaviors and neuropsychiatric disorders. Exposure of mithramycin treated rats to sub-chronic stress led to anxious unhedonic and indifferent behaviors. However, exposure to chronic stress resulted in "daring", novelty seeking behaviors. Two disparate phenotypes of genetic manipulated rats, upon their exposure to the same stressogenic environment, yet for a dissimilar duration. Next we searched for molecular changes that contribute to the “daring” and novelty seeking behavior in rats exposed to chronic stress. We applied a non-hypothesis driven strategy using whole genome cDNA array analysis, which directed us towards metabolic pathways. Genome Scale Metabolic modeling analysis of the cDNA array data pointed at the branched chain amino acids (BCAA) pathway. In the prefrontal cortex of MTR?? rats, only tryptophan, whose brain levels depend on serum BCAA levels, showed a significant decrease. No change was observed in serotonin or kynurenine levels. However, a significant reduction in mRNA and protein levels of the large neutral amino acid transporter (LAT1), which transports BCAA and tryptophan into the brain, as well as in serum levels of tryptophan/BCAA ratio were observed. The latter could be attributed to the failure to increase serum insulin, following stress, in rats pre-exposed to mithramycin. We showed that specific behavioral patterns are linked to modulations in both peripheral and central physiological processes, which converge and reciprocally interact. We assessed the applicability of the animal experiment findings in healthy human male students by examining the relation between the same serum biochemical factors and psychometric parameters. Significant positive correlation was observed between impulsivity and serum tryptophan/BCAA ratio.  Additionally, a significant quadric correlations between Insulin and Anxiety score was observed, this preliminary results warrant further studies in psychiatric patients. Finally, we followed the long-term effects of early in life MTR treatment on the normal course of alterations in brain gene expression. Interestingly, the immediate effect of MTR, was expressed in a limited number of altered genes from different unconnected trajectories that were simultaneously distorted by the drug. In contrast, three months later we observed a change in expression of more than 1000 genes, which are part of specific cellular processes.  A group of genes demonstrated a significantly different pattern of change in their expression along time in MTR treated rats as compared to controls, suggesting that the difference in gene expression trajectory between two time-points in MTR treated rats, is of relevance to the behavioral abnormalities following treatment. Taking together all the results our study provides a glance  at the complexity of the processes involved in shaping behavior, emphasizing the interwoven relationship between nature and nurture brain and periphery.