Limits...
Pathogenic disruption of DISC1-serine racemase binding elicits schizophrenia-like behavior via D-serine depletion.

Ma TM, Abazyan S, Abazyan B, Nomura J, Yang C, Seshadri S, Sawa A, Snyder SH, Pletnikov MV - Mol. Psychiatry (2012)

Bottom Line: Expression of mutant DISC1 downregulates endogenous DISC1 and decreases protein but not mRNA levels of SR, resulting in diminished production of D-serine.In contrast, mutant DISC1 does not alter levels of ALDH1L1, connexins, GLT-1 or binding partners of DISC1 and SR, LIS1 or PICK1.These findings support a model wherein mutant DISC1 leads to SR degradation via dominant negative effects, resulting in D-serine deficiency that diminishes NMDA neurotransmission thus linking DISC1 and NMDA pathophysiological mechanisms in mental illness.

View Article: PubMed Central - PubMed

Affiliation: The Solomon H. Snyder Department of Neuroscience, Baltimore, MD, USA.

ABSTRACT
Perturbation of Disrupted-In-Schizophrenia-1 (DISC1) and D-serine/NMDA receptor hypofunction have both been implicated in the pathophysiology of schizophrenia and other psychiatric disorders. In the present study, we demonstrate that these two pathways intersect with behavioral consequences. DISC1 binds to and stabilizes serine racemase (SR), the enzyme that generates D-serine, an endogenous co-agonist of the NMDA receptor. Mutant DISC1 fails to bind to SR, facilitating ubiquitination and degradation of SR and a decrease in D-serine production. To elucidate DISC1-SR interactions in vivo, we generated a mouse model of selective and inducible expression of mutant DISC1 in astrocytes, the main source of D-serine in the brain. Expression of mutant DISC1 downregulates endogenous DISC1 and decreases protein but not mRNA levels of SR, resulting in diminished production of D-serine. In contrast, mutant DISC1 does not alter levels of ALDH1L1, connexins, GLT-1 or binding partners of DISC1 and SR, LIS1 or PICK1. Adult male and female mice with lifelong expression of mutant DISC1 exhibit behavioral abnormalities consistent with hypofunction of NMDA neurotransmission. Specifically, mutant mice display greater responses to an NMDA antagonist, MK-801, in open field and pre-pulse inhibition of the acoustic startle tests and are significantly more sensitive to the ameliorative effects of D-serine. These findings support a model wherein mutant DISC1 leads to SR degradation via dominant negative effects, resulting in D-serine deficiency that diminishes NMDA neurotransmission thus linking DISC1 and NMDA pathophysiological mechanisms in mental illness.

Show MeSH

Related in: MedlinePlus

Mutant DISC1 depletes SR[a] SR protein is depleted when co-expressed with mutant DISC1 in HEK-293, HT-22 and N2A cell lines compared to full-length DISC1.Quantification of mouse [b] and human SR protein [c] when co-expressed with different forms of DISC1 in HEK-293 cells. mSR, mouse SR; hSR, human SR. Data are representative of 4 independent experiments, *p<0.05, ***p<0.0005.[d] Mutant DISC1 decreases D-serine production. L-serine (10 mM) was added to the cell culture media of HEK-293 cells transfected with different constructs and 24 h later, D-serine in the media was measured by the spectrophotometric assay. *p<0.05, **p<0.005.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3475769&req=5

Figure 2: Mutant DISC1 depletes SR[a] SR protein is depleted when co-expressed with mutant DISC1 in HEK-293, HT-22 and N2A cell lines compared to full-length DISC1.Quantification of mouse [b] and human SR protein [c] when co-expressed with different forms of DISC1 in HEK-293 cells. mSR, mouse SR; hSR, human SR. Data are representative of 4 independent experiments, *p<0.05, ***p<0.0005.[d] Mutant DISC1 decreases D-serine production. L-serine (10 mM) was added to the cell culture media of HEK-293 cells transfected with different constructs and 24 h later, D-serine in the media was measured by the spectrophotometric assay. *p<0.05, **p<0.005.

Mentions: DISC1 is thought to function primarily as a scaffold, regulating the disposition of other proteins29, 55. If DISC1 serves as a scaffold for SR, then expression of mutant DISC1, which binds to SR with much lower affinity, might affect SR. In three cell lines, i.e., HEK-293 cells, HT-22 cells and N2A cells, a mouse neuroblastoma cell line, we monitored the effects of mutant DISC1 on levels of SR (Figure 2a). In comparison to wild-type DISC1, mutant DISC1 substantially lowers levels of SR protein in all three cell lines (Figure 2a, b and c). Mutant DISC1, even when co-expressed with wild-type DISC1, also depletes SR in a dose-dependent manner, consistent with a dominant-negative action (Supplementary Figure 4).


Pathogenic disruption of DISC1-serine racemase binding elicits schizophrenia-like behavior via D-serine depletion.

Ma TM, Abazyan S, Abazyan B, Nomura J, Yang C, Seshadri S, Sawa A, Snyder SH, Pletnikov MV - Mol. Psychiatry (2012)

Mutant DISC1 depletes SR[a] SR protein is depleted when co-expressed with mutant DISC1 in HEK-293, HT-22 and N2A cell lines compared to full-length DISC1.Quantification of mouse [b] and human SR protein [c] when co-expressed with different forms of DISC1 in HEK-293 cells. mSR, mouse SR; hSR, human SR. Data are representative of 4 independent experiments, *p<0.05, ***p<0.0005.[d] Mutant DISC1 decreases D-serine production. L-serine (10 mM) was added to the cell culture media of HEK-293 cells transfected with different constructs and 24 h later, D-serine in the media was measured by the spectrophotometric assay. *p<0.05, **p<0.005.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3475769&req=5

Figure 2: Mutant DISC1 depletes SR[a] SR protein is depleted when co-expressed with mutant DISC1 in HEK-293, HT-22 and N2A cell lines compared to full-length DISC1.Quantification of mouse [b] and human SR protein [c] when co-expressed with different forms of DISC1 in HEK-293 cells. mSR, mouse SR; hSR, human SR. Data are representative of 4 independent experiments, *p<0.05, ***p<0.0005.[d] Mutant DISC1 decreases D-serine production. L-serine (10 mM) was added to the cell culture media of HEK-293 cells transfected with different constructs and 24 h later, D-serine in the media was measured by the spectrophotometric assay. *p<0.05, **p<0.005.
Mentions: DISC1 is thought to function primarily as a scaffold, regulating the disposition of other proteins29, 55. If DISC1 serves as a scaffold for SR, then expression of mutant DISC1, which binds to SR with much lower affinity, might affect SR. In three cell lines, i.e., HEK-293 cells, HT-22 cells and N2A cells, a mouse neuroblastoma cell line, we monitored the effects of mutant DISC1 on levels of SR (Figure 2a). In comparison to wild-type DISC1, mutant DISC1 substantially lowers levels of SR protein in all three cell lines (Figure 2a, b and c). Mutant DISC1, even when co-expressed with wild-type DISC1, also depletes SR in a dose-dependent manner, consistent with a dominant-negative action (Supplementary Figure 4).

Bottom Line: Expression of mutant DISC1 downregulates endogenous DISC1 and decreases protein but not mRNA levels of SR, resulting in diminished production of D-serine.In contrast, mutant DISC1 does not alter levels of ALDH1L1, connexins, GLT-1 or binding partners of DISC1 and SR, LIS1 or PICK1.These findings support a model wherein mutant DISC1 leads to SR degradation via dominant negative effects, resulting in D-serine deficiency that diminishes NMDA neurotransmission thus linking DISC1 and NMDA pathophysiological mechanisms in mental illness.

View Article: PubMed Central - PubMed

Affiliation: The Solomon H. Snyder Department of Neuroscience, Baltimore, MD, USA.

ABSTRACT
Perturbation of Disrupted-In-Schizophrenia-1 (DISC1) and D-serine/NMDA receptor hypofunction have both been implicated in the pathophysiology of schizophrenia and other psychiatric disorders. In the present study, we demonstrate that these two pathways intersect with behavioral consequences. DISC1 binds to and stabilizes serine racemase (SR), the enzyme that generates D-serine, an endogenous co-agonist of the NMDA receptor. Mutant DISC1 fails to bind to SR, facilitating ubiquitination and degradation of SR and a decrease in D-serine production. To elucidate DISC1-SR interactions in vivo, we generated a mouse model of selective and inducible expression of mutant DISC1 in astrocytes, the main source of D-serine in the brain. Expression of mutant DISC1 downregulates endogenous DISC1 and decreases protein but not mRNA levels of SR, resulting in diminished production of D-serine. In contrast, mutant DISC1 does not alter levels of ALDH1L1, connexins, GLT-1 or binding partners of DISC1 and SR, LIS1 or PICK1. Adult male and female mice with lifelong expression of mutant DISC1 exhibit behavioral abnormalities consistent with hypofunction of NMDA neurotransmission. Specifically, mutant mice display greater responses to an NMDA antagonist, MK-801, in open field and pre-pulse inhibition of the acoustic startle tests and are significantly more sensitive to the ameliorative effects of D-serine. These findings support a model wherein mutant DISC1 leads to SR degradation via dominant negative effects, resulting in D-serine deficiency that diminishes NMDA neurotransmission thus linking DISC1 and NMDA pathophysiological mechanisms in mental illness.

Show MeSH
Related in: MedlinePlus