This web page was produced as an assignment for Genetics 564, an undergraduate course at UW-Madison.
Impulsivity is a trait that is found as a symptom in various psychiatric disorders and neurodegenerative diseases and is associated with addictive behavior such as substance abuse [1,2]. The dopamine receptor D2 (DRD2), a G protein-coupled receptor, is hypothesized to be linked to impulse control. Studies in animal models have shown that DRD2 levels are inversely related to impulsive behavior [3]. In humans, various association studies have described correlations between different DRD2 alleles and impulsivity-related behavior like drug addiction [4] and smoking [5]. However, there are also association studies that report no significant correlations between DRD2 and impulsivity-related behavior. Conflicting results may possibly be due to complex regulatory mechanisms of DRD2. As an example, various polymorphisms in the DRD2 gene have been suggested to influence the severity of impulsivity-related behavior and antipsychotic treatment effectiveness [5,6]. Also, there are two major DRD2 isoforms, with a third isoform having been more recently identified in individuals who died with psychosis. This third isoform may possibly be due to abnormal splicing [7].
Because the molecular mechanisms related to the onset of impulsive behavior have not been extensively characterized, the primary goal is to elucidate how regulation of DRD2 at the transcript and protein level may lead to impulsive behavior. It is hypothesized that DRD2 regulation influences impulse control and responsiveness to certain compounds. The long-term goal is to be able to characterize the role of DRD2 in the context of psychiatric illnesses and neurodegeneration, which can help in the development of therapies to offset impulse control dysregulation that is characteristic of those illnesses.
Specific Aim 1: To study the prevalence of the third DRD2 variant.
Approach: Obtain mRNA from post-mortem brain tissue of individuals placed into three groups: One control group, one group of subjects with history of substance abuse, and one group of subjects with psychiatric illnesses. Then, perform RNA-Seq to quantify the abundance of the third DRD2 mRNA variant. The DRD2 isoforms can also be quantified by quantitative mass spectrometry.
Hypothesis: The third DRD2 variant is more prevalent in subjects with impulsivity-related behaviors and psychiatric illnesses compared to the control group.
Specific Aim 2: To identify protein interactions with different DRD2 isoforms.
Approach: Perform affinity purification mass spectrometry (AP-MS) on DRD2 protein isoform samples. The interacting proteins identified in different isoforms can be compared to STRING—a protein interaction database—to uncover novel interacting proteins or to find out if there are proteins that do not interact in one isoform relative to another.
Hypothesis: There may be different proteins that interact in different DRD2 isoforms. In the short isoform, there may possibly be fewer interacting proteins due to its truncated sequence.
Specific Aim 3: To study the relationship between gene polymorphisms and DRD2 protein affinity to specific compounds.
Approach: Perform genotyping on individuals with different DRD2 gene polymorphisms. Then, create human cell lines expressing the different polymorphisms by editing their genomes with the CRISPR-Cas9 system based on the sequences obtained from the individuals. Isolate the DRD2 proteins expressed by the cell lines, and test their affinity for compounds known to interact with DRD2.
Hypothesis: Different DRD2 gene polymorphisms result in DRD2 proteins that have varying levels of affinity to a compound.
Dopaminergic pathways are very complex, which makes it difficult to study multifactorial traits like impulsivity. This project aims to elucidate some aspects of DRD2 regulatory mechanisms, which include its different isoforms and interactions with other proteins and compounds. Although DRD2 is only a small part of the larger dopaminergic network, studying it will give insight to impulse-related behavior and ultimately, psychiatric disorders and neurodegenerative diseases that are associated with the trait.
References
(1) Antonelli, F., Ray, N., & Strafella, A. P. (2011). Impulsivity and Parkinson's disease: More than just disinhibition. Journal of the neurological sciences,310(1), 202-207.
(2) Prado-Lima, P. A. S. D. (2009). Pharmacological treatment of impulsivity and aggressive behavior. Revista Brasileira de Psiquiatria, 31, S58-S65.
(3) Dalley, J. W. et al. (2007). Nucleus accumbens D2/3 receptors predict trait impulsivity and cocaine reinforcement. science, 315(5816), 1267-1270.
(4) Najafabadi, M. S. et al. (2005). Association between the DRD2 A1 allele and opium addiction in the Iranian population. American Journal of Medical Genetics Part B: Neuropsychiatric Genetics, 134(1), 39-41.
(5) Comings, D. E. et al. (1996). The dopamine D2 receptor (DRD2) gene: a genetic risk factor in smoking. Pharmacogenetics and Genomics, 6(1), 73-79.
(6) Zahari, Z., Teh, L. K., Ismail, R., & Razali, S. M. (2011). Influence of DRD2 polymorphisms on the clinical outcomes of patients with schizophrenia. Psychiatric genetics, 21(4), 183-189.
(7) Seeman, P., Nam, D., Ulpian, C., Liu, I. S., & Tallerico, T. (2000). New dopamine receptor, D2 Longer, with unique TG splice site, in human brain. Molecular brain research, 76(1), 132-141.
Because the molecular mechanisms related to the onset of impulsive behavior have not been extensively characterized, the primary goal is to elucidate how regulation of DRD2 at the transcript and protein level may lead to impulsive behavior. It is hypothesized that DRD2 regulation influences impulse control and responsiveness to certain compounds. The long-term goal is to be able to characterize the role of DRD2 in the context of psychiatric illnesses and neurodegeneration, which can help in the development of therapies to offset impulse control dysregulation that is characteristic of those illnesses.
Specific Aim 1: To study the prevalence of the third DRD2 variant.
Approach: Obtain mRNA from post-mortem brain tissue of individuals placed into three groups: One control group, one group of subjects with history of substance abuse, and one group of subjects with psychiatric illnesses. Then, perform RNA-Seq to quantify the abundance of the third DRD2 mRNA variant. The DRD2 isoforms can also be quantified by quantitative mass spectrometry.
Hypothesis: The third DRD2 variant is more prevalent in subjects with impulsivity-related behaviors and psychiatric illnesses compared to the control group.
Specific Aim 2: To identify protein interactions with different DRD2 isoforms.
Approach: Perform affinity purification mass spectrometry (AP-MS) on DRD2 protein isoform samples. The interacting proteins identified in different isoforms can be compared to STRING—a protein interaction database—to uncover novel interacting proteins or to find out if there are proteins that do not interact in one isoform relative to another.
Hypothesis: There may be different proteins that interact in different DRD2 isoforms. In the short isoform, there may possibly be fewer interacting proteins due to its truncated sequence.
Specific Aim 3: To study the relationship between gene polymorphisms and DRD2 protein affinity to specific compounds.
Approach: Perform genotyping on individuals with different DRD2 gene polymorphisms. Then, create human cell lines expressing the different polymorphisms by editing their genomes with the CRISPR-Cas9 system based on the sequences obtained from the individuals. Isolate the DRD2 proteins expressed by the cell lines, and test their affinity for compounds known to interact with DRD2.
Hypothesis: Different DRD2 gene polymorphisms result in DRD2 proteins that have varying levels of affinity to a compound.
Dopaminergic pathways are very complex, which makes it difficult to study multifactorial traits like impulsivity. This project aims to elucidate some aspects of DRD2 regulatory mechanisms, which include its different isoforms and interactions with other proteins and compounds. Although DRD2 is only a small part of the larger dopaminergic network, studying it will give insight to impulse-related behavior and ultimately, psychiatric disorders and neurodegenerative diseases that are associated with the trait.
References
(1) Antonelli, F., Ray, N., & Strafella, A. P. (2011). Impulsivity and Parkinson's disease: More than just disinhibition. Journal of the neurological sciences,310(1), 202-207.
(2) Prado-Lima, P. A. S. D. (2009). Pharmacological treatment of impulsivity and aggressive behavior. Revista Brasileira de Psiquiatria, 31, S58-S65.
(3) Dalley, J. W. et al. (2007). Nucleus accumbens D2/3 receptors predict trait impulsivity and cocaine reinforcement. science, 315(5816), 1267-1270.
(4) Najafabadi, M. S. et al. (2005). Association between the DRD2 A1 allele and opium addiction in the Iranian population. American Journal of Medical Genetics Part B: Neuropsychiatric Genetics, 134(1), 39-41.
(5) Comings, D. E. et al. (1996). The dopamine D2 receptor (DRD2) gene: a genetic risk factor in smoking. Pharmacogenetics and Genomics, 6(1), 73-79.
(6) Zahari, Z., Teh, L. K., Ismail, R., & Razali, S. M. (2011). Influence of DRD2 polymorphisms on the clinical outcomes of patients with schizophrenia. Psychiatric genetics, 21(4), 183-189.
(7) Seeman, P., Nam, D., Ulpian, C., Liu, I. S., & Tallerico, T. (2000). New dopamine receptor, D2 Longer, with unique TG splice site, in human brain. Molecular brain research, 76(1), 132-141.
lyefinaldraftsaims4-14-15.docx | |
File Size: | 169 kb |
File Type: | docx |