DISC1 regulates N-methyl-D-aspartate receptor dynamics:abnormalities induced by a Disc1 mutation modelling a translocation linked to major mental illness

Abstract The neuromodulatory gene DISC1 is disrupted by a t(1;11) translocation that is highly penetrant for schizophrenia and affective disorders, but how this translocation affects DISC1 function is incompletely understood. N-methyl-D-aspartate receptors (NMDAR) play a central role in synaptic plasticity and cognition, and are implicated in the pathophysiology of schizophrenia through genetic and functional studies. We show that the NMDAR subunit GluN2B complexes with DISC1-associated trafficking factor TRAK1, while DISC1 interacts with the GluN1 subunit and regulates dendritic NMDAR motility in cultured mouse neurons. Moreover, in the first mutant mouse that models DISC1 disruption by the translocation, the pool of NMDAR transport vesicles and surface/synaptic NMDAR expression are increased. Since NMDAR cell surface/synaptic expression is tightly regulated to ensure correct function, these changes in the mutant mouse are likely to affect NMDAR signalling and synaptic plasticity. Consistent with these observations, RNASeq analysis of the translocation carrier-derived human neurons indicates abnormalities of excitatory synapses and vesicle dynamics. RNASeq analysis of the human neurons also identifies many differentially expressed genes previously highlighted as putative schizophrenia and/or depression risk factors through large-scale genome-wide association and copy number variant studies, indicating that the translocation triggers common disease pathways that are shared with unrelated psychiatric patients. Altogether, our findings suggest that translocation-induced disease mechanisms are likely to be relevant to mental illness in general, and that such disease mechanisms include altered NMDAR dynamics and excitatory synapse function. This could contribute to the cognitive disorders displayed by translocation carriers

Familial t(1;11) translocation is associated with disruption of white matter structural integrity and oligodendrocyte–myelin dysfunction

Although the underlying neurobiology of major mental illness (MMI) remains unknown, emerging evidence implicates a role for oligodendrocyte–myelin abnormalities. Here, we took advantage of a large family carrying a balanced t(1;11) translocation, which substantially increases risk of MMI, to undertake both diffusion tensor imaging and cellular studies to evaluate the consequences of the t(1;11) translocation on white matter structural integrity and oligodendrocyte–myelin biology. This translocation disrupts among others the DISC1 gene which plays a crucial role in brain development. We show that translocation-carrying patients display significant disruption of white matter integrity compared with familial controls. At a cellular level, we observe dysregulation of key pathways controlling oligodendrocyte development and morphogenesis in induced pluripotent stem cell (iPSC) derived case oligodendrocytes. This is associated with reduced proliferation and a stunted morphology in vitro. Further, myelin internodes in a humanized mouse model that recapitulates the human translocation as well as after transplantation of t(1;11) oligodendrocyte progenitors were significantly reduced when compared with controls. Thus we provide evidence that the t(1;11) translocation has biological effects at both the systems and cellular level that together suggest oligodendrocyte–myelin dysfunction

PhD

dissertationVertebrate Hox genes encode a family of homeobox transcription factors that regulate developmental programs and determine the embryonic body plan. These functions have largely been determined by the generation of loss-of-function mutations in vertebrate Hox genes through gene targeting technology in mice. Hoxb13 is the last Hox gene to be identified. It is located 5' of Hoxb9 within the HoxB cluster and is expressed in the posterior regions of the developing embryo, including the tail bud and genital tubercule. Loss-of-function mutations of Hoxb13 have not been reported, and the function of this gene was unknown prior to the work outlined herein. This dissertation describes the generation of Hoxb13 null mice and the analyses of mutants that lack Hoxb13 function. Hoxb13 homozygous mutants have an aberrant developmental program in the structures that are derived from the process of secondary neurulation which include the caudal vertebrae within the tail, the caudal spinal ganglia, and the secondary neural tube. The phenotype is novel for Hox gene mutant phenotypes in that all of the aforementioned structures display an overgrowth phenotype, and further analyses in the secondary neural tube reveals that the phenotypes are caused by both over-proliferation of cells and failure of the normal apoptotic pathway that removes the secondary neural tube. This dissertation also addresses the function of Hoxb13 in adults. In contrast to its role in limiting growth during development, Hoxb13 also determines a pathway that is specific to the prostatic luminal epithelium ventral lobe. Hoxb13 homozygous mutants do not secrete the ventral prostate specific secretory proteins including p12, a serine protease inhibitor, and p25, a spermine binding protein. Additionally, homozygote mutant ventral prostates secrete polymeric immunoglobulin receptor (pIgR) and androgen binding protein (ABP), which are not normally secreted by the prostate, indicating that the homozygous mutant prostate luminal cells have lost identity. In addition to losing identity, homozygous mutant ventral prostate luminal cells lose polarity, as indicated by the expression of basal cell markers on the apical surface of luminal cells. This dissertation provides analyses of both the developmental and adult functions of Hoxb13 and underscores how a Hox gene that has a very specific function in embryonic patterning can be later recruited for very different functions in adult tissues

Hoxb13 mutations cause overgrowth of caudal spinal cord and tail vertebrae

Journal ArticleTo address the expression and function of Hoxb13, the 5' most Hox gene in the HoxB cluster, we have generated mice with loss-of-function and beta-galactosidase reporter insertion alleles of this gene. Mice homozygous for Hoxb13 loss-of-function mutations show overgrowth in all major structures derived from the tail bud, including the developing secondary neural tube (SNT), the caudal spinal ganglia, and the caudal vertebrae. Using the beta-galactosidase reporter allele of Hoxb13, also a loss-of-function allele, we found that the expression patterns of Hoxb13 in the developing spinal cord and caudal mesoderm are closely associated with overgrowth phenotypes in the tails of homozygous mutant animals. These phenotypes can be explained by the observed increased cell proliferation and decreased levels of apoptosis within the tail of homozygous mutant mice. This analysis of Hoxb13 function suggests that this 5' Hox gene may act as an inhibitor of neuronal cell proliferation, an activator of apoptotic pathways in the SNT, and as a general repressor of growth in the caudal vertebrae. Copyright 2003 Elsevier Science (USA

Hoxb13 mutations cause overgrowth of caudal spinal cordand tail vertebrae

AbstractTo address the expression and function of Hoxb13, the 5′ most Hox gene in the HoxB cluster, we have generated mice with loss-of-function and β-galactosidase reporter insertion alleles of this gene. Mice homozygous for Hoxb13 loss-of-function mutations show overgrowth in all major structures derived from the tail bud, including the developing secondary neural tube (SNT), the caudal spinal ganglia, and the caudal vertebrae. Using the β-galactosidase reporter allele of Hoxb13, also a loss-of-function allele, we found that the expression patterns of Hoxb13 in the developing spinal cord and caudal mesoderm are closely associated with overgrowth phenotypes in the tails of homozygous mutant animals. These phenotypes can be explained by the observed increased cell proliferation and decreased levels of apoptosis within the tail of homozygous mutant mice. This analysis of Hoxb13 function suggests that this 5′ Hox gene may act as an inhibitor of neuronal cell proliferation, an activator of apoptotic pathways in the SNT, and as a general repressor of growth in the caudal vertebrae

Reduction of liver fibrosis by rationally designed macromolecular telmisartan prodrugs

At present there are no drugs for the treatment of chronic liver fibrosis that have been approved by the Food and Drug Administration of the United States. Telmisartan, a small-molecule antihypertensive drug, displays antifibrotic activity, but its clinical use is limited because it causes systemic hypotension. Here, we report the scalable and convergent synthesis of macromolecular telmisartan prodrugs optimized for preferential release in diseased liver tissue. We have optimized the release of active telmisartan in fibrotic liver to be depot-like (that is, a constant therapeutic concentration) through the molecular design of telmisartan brush-arm star polymers, and show that these lead to improved efficacy and to the avoidance of dose-limiting hypotension in both metabolically and chemically induced mouse models of hepatic fibrosis, as determined by histopathology, enzyme levels in the liver, intact-tissue protein markers, hepatocyte necrosis protection and gene-expression analyses. In rats and dogs, the prodrugs are retained long term in liver tissue, and have a well-tolerated safety profile. Our findings support the further development of telmisartan prodrugs that enable infrequent dosing in the treatment of liver fibrosis.National Institutes of Health (U.S.) (Grant 1R01CA220468-01)National Institutes of Health (U.S.) (Fellowship 1F32EB023101