Dopamine- and cAMP-regulated phosphoprotein of molecular weight 32 kDa (DARPP-32), encoded by PPP1R1B, is a pivotal integrator of information in dopaminoceptive neurons, regulating the response to neuroleptics, psychotomimetics, and drugs of abuse, and affecting striatal function and plasticity. Despite extensive preclinical work, there are almost no data on DARPP-32 function in humans. Here, we identify, through resequencing in 298 chromosomes, a frequent PPP1R1B haplotype predicting mRNA expression of PPP1R1B isoforms in postmortem human brain. This haplotype was associated with enhanced performance on several cognitive tests that depend on frontostriatal function. Multimodal imaging of healthy subjects revealed an impact of the haplotype on neostriatal volume, activation, and the functional connectivity of the prefrontal cortex. The haplotype was associated with the risk for schizophrenia in 1 family-based association analysis. Our convergent results identify a prefrontal-neostriatal system affected by variation in PPP1R1B and suggest that DARPP-32 plays a pivotal role in cognitive function and possibly in the pathogenesis of schizophrenia.
Andreas Meyer-Lindenberg, Richard E. Straub, Barbara K. Lipska, Beth A. Verchinski, Terry Goldberg, Joseph H. Callicott, Michael F. Egan, Stephen S. Huffaker, Venkata S. Mattay, Bhaskar Kolachana, Joel E. Kleinman, Daniel R. Weinberger
Markers of oxidative damage have been detected in brain tissue from patients with Alzheimer disease (AD) and other neurodegenerative disorders. These findings implicate oxidative injury in the neurodegenerative process, but whether oxidative stress is a cause or a consequence of neurotoxicity remains unclear. We used a Drosophila model of human tauopathies to investigate the role of oxidative stress in neurodegeneration. Genetic and pharmacological manipulation of antioxidant defense mechanisms significantly modified neurodegeneration in our model, suggesting that oxidative stress plays a causal role in neurotoxicity. We demonstrate that the JNK signaling pathway is activated in our model, which is in agreement with previous findings in AD tissue. Furthermore, we show that the extent of JNK activation correlates with the degree of tau-induced neurodegeneration. Finally, our findings suggest that oxidative stress acts not to promote tau phosphorylation, but to enhance tau-induced cell cycle activation. In summary, our study identifies oxidative stress as a causal factor in tau-induced neurodegeneration in Drosophila.
Dora Dias-Santagata, Tudor A. Fulga, Atanu Duttaroy, Mel B. Feany
Prion diseases are fatal neurodegenerative diseases characterized by the accumulation of PrPSc, the infectious and protease-resistant form of the cellular prion protein (PrPC). We generated lentivectors expressing PrPC-specific short hairpin RNAs (shRNAs) that efficiently silenced expression of the prion protein gene (Prnp) in primary neuronal cells. Treatment of scrapie-infected neuronal cells with these lentivectors resulted in an efficient and stable suppression of PrPSc accumulation. After intracranial injection, lentiviral shRNA reduced PrPC expression in transgenic mice carrying multiple copies of Prnp. To test the therapeutic potential of lentiviral shRNA, we used what we believe to be a novel approach in which the clinical situation was mimicked. We generated chimeric mice derived from lentivector-transduced embryonic stem cells. Depending on the degree of chimerism, these animals carried the lentiviral shRNAs in a certain percentage of brain cells and expressed reduced levels of PrPC. Importantly, in highly chimeric mice, survival after scrapie infection was significantly extended. Taken together, these data suggest that lentivector-mediated RNA interference could be an approach for the treatment of prion disease.
Alexander Pfeifer, Sabina Eigenbrod, Saba Al-Khadra, Andreas Hofmann, Gerda Mitteregger, Markus Moser, Uwe Bertsch, Hans Kretzschmar
Alzheimer’s disease (AD) is characterized by progressive neurodegeneration and cerebral accumulation of the β-amyloid peptide (Aβ), but it is unknown what makes neurons susceptible to degeneration. We report that the TGF-β type II receptor (TβRII) is mainly expressed by neurons, and that TβRII levels are reduced in human AD brain and correlate with pathological hallmarks of the disease. Reducing neuronal TGF-β signaling in mice resulted in age-dependent neurodegeneration and promoted Aβ accumulation and dendritic loss in a mouse model of AD. In cultured cells, reduced TGF-β signaling caused neuronal degeneration and resulted in increased levels of secreted Aβ and β-secretase–cleaved soluble amyloid precursor protein. These results show that reduced neuronal TGF-β signaling increases age-dependent neurodegeneration and AD-like disease in vivo. Increasing neuronal TGF-β signaling may thus reduce neurodegeneration and be beneficial in AD.
Ina Tesseur, Kun Zou, Luke Esposito, Frederique Bard, Elisabeth Berber, Judith Van Can, Amy H. Lin, Leslie Crews, Patrick Tremblay, Paul Mathews, Lennart Mucke, Eliezer Masliah, Tony Wyss-Coray
Caveolin-3, the muscle-specific isoform of caveolins, plays important roles in signal transduction. Dominant-negative mutations of the caveolin-3 gene cause autosomal dominant limb-girdle muscular dystrophy 1C (LGMD1C) with loss of caveolin-3. However, identification of the precise molecular mechanism leading to muscular atrophy in caveolin-3–deficient muscle has remained elusive. Myostatin, a member of the muscle-specific TGF-β superfamily, negatively regulates skeletal muscle volume. Here we report that caveolin-3 inhibited myostatin signaling by suppressing activation of its type I receptor; this was followed by hypophosphorylation of an intracellular effector, Mad homolog 2 (Smad2), and decreased downstream transcriptional activity. Loss of caveolin-3 in P104L mutant caveolin-3 transgenic mice caused muscular atrophy with increase in phosphorylated Smad2 (p-Smad2) as well as p21 (also known as Cdkn1a), a myostatin target gene. Introduction of the myostatin prodomain, an inhibitor of myostatin, by genetic crossing or intraperitoneal administration of the soluble type II myostatin receptor, another inhibitor, ameliorated muscular atrophy of the mutant caveolin-3 transgenic mice with suppression of p-Smad2 and p21 levels. These findings suggest that caveolin-3 normally suppresses the myostatin-mediated signal, thereby preventing muscular atrophy, and that hyperactivation of myostatin signaling participates in the pathogenesis of muscular atrophy in a mouse model of LGMD1C. Myostatin inhibition may be a promising therapy for LGMD1C patients.
Yutaka Ohsawa, Hiroki Hagiwara, Masashi Nakatani, Akihiro Yasue, Keiji Moriyama, Tatsufumi Murakami, Kunihiro Tsuchida, Sumihare Noji, Yoshihide Sunada
Luigi Puglielli, Avi L. Friedlich, Kenneth D.R. Setchell, Seiichi Nagano, Carlos Opazo, Robert A. Cherny, Kevin J. Barnham, John D. Wade, Simon Melov, Dora M. Kovacs, Ashley I. Bush
Kennedy disease, a degenerative disorder characterized by androgen-dependent neuromuscular weakness, is caused by a CAG/glutamine tract expansion in the androgen receptor (Ar) gene. We developed a mouse model of Kennedy disease, using gene targeting to convert mouse androgen receptor (AR) to human sequence while introducing 113 glutamines. AR113Q mice developed hormone and glutamine length–dependent neuromuscular weakness characterized by the early occurrence of myopathic and neurogenic skeletal muscle pathology and by the late development of neuronal intranuclear inclusions in spinal neurons. AR113Q males unexpectedly died at 2–4 months. We show that this androgen-dependent death reflects decreased expression of skeletal muscle chloride channel 1 (CLCN1) and the skeletal muscle sodium channel α-subunit, resulting in myotonic discharges in skeletal muscle of the lower urinary tract. AR113Q limb muscles show similar myopathic features and express decreased levels of mRNAs encoding neurotrophin-4 and glial cell line–derived neurotrophic factor. These data define an important myopathic contribution to the Kennedy disease phenotype and suggest a role for muscle in non–cell autonomous toxicity of lower motor neurons.
Zhigang Yu, Nahid Dadgar, Megan Albertelli, Kirsten Gruis, Cynthia Jordan, Diane M. Robins, Andrew P. Lieberman
Neurotoxicity from accumulation of misfolded/mutant proteins is thought to drive pathogenesis in neurodegenerative diseases. Since decreasing levels of proteins responsible for such accumulations is likely to ameliorate disease, a therapeutic strategy has been developed to downregulate almost any gene in the CNS. Modified antisense oligonucleotides, continuously infused intraventricularly, have been demonstrated to distribute widely throughout the CNS of rodents and primates, including the regions affected in the major neurodegenerative diseases. Using this route of administration, we found that antisense oligonucleotides to superoxide dismutase 1 (SOD1), one of the most abundant brain proteins, reduced both SOD1 protein and mRNA levels throughout the brain and spinal cord. Treatment initiated near onset significantly slowed disease progression in a model of amyotrophic lateral sclerosis (ALS) caused by a mutation in SOD1. This suggests that direct delivery of antisense oligonucleotides could be an effective, dosage-regulatable means of treating neurodegenerative diseases, including ALS, where appropriate target proteins are known.
Richard A. Smith, Timothy M. Miller, Koji Yamanaka, Brett P. Monia, Thomas P. Condon, Gene Hung, Christian S. Lobsiger, Chris M. Ward, Melissa McAlonis-Downes, Hongbing Wei, Ed V. Wancewicz, C. Frank Bennett, Don W. Cleveland
We used diffusion tensor imaging (DTI) to study 2 patients with traumatic brain injury. The first patient recovered reliable expressive language after 19 years in a minimally conscious state (MCS); the second had remained in MCS for 6 years. Comparison of white matter integrity in the patients and 20 normal subjects using histograms of apparent diffusion constants and diffusion anisotropy identified widespread altered diffusivity and decreased anisotropy in the damaged white matter. These findings remained unchanged over an 18-month interval between 2 studies in the first patient. In addition, in this patient, we identified large, bilateral regions of posterior white matter with significantly increased anisotropy that reduced over 18 months. In contrast, notable increases in anisotropy within the midline cerebellar white matter in the second study correlated with marked clinical improvements in motor functions. This finding was further correlated with an increase in resting metabolism measured by PET in this subregion. Aberrant white matter structures were evident in the second patient’s DTI images but were not clinically correlated. We propose that axonal regrowth may underlie these findings and provide a biological mechanism for late recovery. Our results are discussed in the context of recent experimental studies that support this inference.
Henning U. Voss, Aziz M. Uluç, Jonathan P. Dyke, Richard Watts, Erik J. Kobylarz, Bruce D. McCandliss, Linda A. Heier, Bradley J. Beattie, Klaus A. Hamacher, Shankar Vallabhajosula, Stanley J. Goldsmith, Douglas Ballon, Joseph T. Giacino, Nicholas D. Schiff
Leptin and insulin have been identified as fuel sensors acting in part through their hypothalamic receptors to inhibit food intake and stimulate energy expenditure. As their intracellular signaling converges at the PI3K pathway, we directly addressed the role of phosphatidylinositol3,4,5-trisphosphate–mediated (PIP3-mediated) signals in hypothalamic proopiomelanocortin (POMC) neurons by inactivating the gene for the PIP3 phosphatase Pten specifically in this cell type. Here we show that POMC-specific disruption of Pten resulted in hyperphagia and sexually dimorphic diet-sensitive obesity. Although leptin potently stimulated Stat3 phosphorylation in POMC neurons of POMC cell–restricted Pten knockout (PPKO) mice, it failed to significantly inhibit food intake in vivo. POMC neurons of PPKO mice showed a marked hyperpolarization and a reduction in basal firing rate due to increased ATP-sensitive potassium (KATP) channel activity. Leptin was not able to elicit electrical activity in PPKO POMC neurons, but application of the PI3K inhibitor LY294002 and the KATP blocker tolbutamide restored electrical activity and leptin-evoked firing of POMC neurons in these mice. Moreover, icv administration of tolbutamide abolished hyperphagia in PPKO mice. These data indicate that PIP3-mediated signals are critical regulators of the melanocortin system via modulation of KATP channels.
Leona Plum, Xiaosong Ma, Brigitte Hampel, Nina Balthasar, Roberto Coppari, Heike Münzberg, Marya Shanabrough, Denis Burdakov, Eva Rother, Ruth Janoschek, Jens Alber, Bengt F. Belgardt, Linda Koch, Jost Seibler, Frieder Schwenk, Csaba Fekete, Akira Suzuki, Tak W. Mak, Wilhelm Krone, Tamas L. Horvath, Frances M. Ashcroft, Jens C. Brüning