The glymphatic system is a recently defined brain-wide paravascular pathway for cerebrospinal fluid (CSF) and interstitial fluid (ISF) exchange that facilitates efficient clearance of solutes and waste from the brain. CSF enters the brain along para-arterial channels to exchange with ISF, which is in turn cleared from the brain along para-venous pathways. Because soluble amyloid β clearance depends on glymphatic pathway function, we proposed that failure of this clearance system contributes to amyloid plaque deposition and Alzheimer’s disease progression. Here we provide proof of concept that glymphatic pathway function can be measured using a clinically relevant imaging technique. Dynamic contrast-enhanced MRI was used to visualize CSF-ISF exchange across the rat brain following intrathecal paramagnetic contrast agent administration. Key features of glymphatic pathway function were confirmed, including visualization of para-arterial CSF influx and molecular size-dependent CSF-ISF exchange. Whole-brain imaging allowed the identification of two key influx nodes at the pituitary and pineal gland recesses, while dynamic MRI permitted the definition of simple kinetic parameters to characterize glymphatic CSF-ISF exchange and solute clearance from the brain. We propose that this MRI approach may provide the basis for a wholly new strategy to evaluate Alzheimer’s disease susceptibility and progression in the live human brain.
Jeffrey J. Iliff, Hedok Lee, Mei Yu, Tian Feng, Jean Logan, Maiken Nedergaard, Helene Benveniste
Oligodendrocyte precursor cells (OPCs) are thought to maintain homeostasis and contribute to long-term repair in adult white matter; however, their roles in the acute phase after brain injury remain unclear. Mice that were subjected to prolonged cerebral hypoperfusion stress developed white matter demyelination over time. Prior to demyelination, we detected increased MMP9 expression, blood-brain barrier (BBB) leakage, and neutrophil infiltration in damaged white matter. Notably, at this early stage, OPCs made up the majority of MMP9-expressing cells. The standard MMP inhibitor GM6001 reduced the early BBB leakage and neutrophil infiltration, indicating that OPC-derived MMP9 induced early BBB disruption after white matter injury. Cell-culture experiments confirmed that OPCs secreted MMP9 under pathological conditions, and conditioned medium prepared from the stressed OPCs weakened endothelial barrier tightness in vitro. Our study reveals that OPCs can rapidly respond to white matter injury and produce MMP9 that disrupts the BBB, indicating that OPCs may mediate injury in white matter under disease conditions.
Ji Hae Seo, Nobukazu Miyamoto, Kazuhide Hayakawa, Loc-Duyen D. Pham, Takakuni Maki, Cenk Ayata, Kyu-Won Kim, Eng H. Lo, Ken Arai
A cell-based therapy for the replacement of dopaminergic neurons has been a long-term goal in Parkinson’s disease research. Here, we show that autologous engraftment of A9 dopaminergic neuron-like cells induced from mesenchymal stem cells (MSCs) leads to long-term survival of the cells and restoration of motor function in hemiparkinsonian macaques. Differentiated MSCs expressed markers of A9 dopaminergic neurons and released dopamine after depolarization in vitro. The differentiated autologous cells were engrafted in the affected portion of the striatum. Animals that received transplants showed modest and gradual improvements in motor behaviors. Positron emission tomography (PET) using [11C]-CFT, a ligand for the dopamine transporter (DAT), revealed a dramatic increase in DAT expression, with a subsequent exponential decline over a period of 7 months. Kinetic analysis of the PET findings revealed that DAT expression remained above baseline levels for over 7 months. Immunohistochemical evaluations at 9 months consistently demonstrated the existence of cells positive for DAT and other A9 dopaminergic neuron markers in the engrafted striatum. These data suggest that transplantation of differentiated autologous MSCs may represent a safe and effective cell therapy for Parkinson’s disease.
Takuya Hayashi, Shohei Wakao, Masaaki Kitada, Takayuki Ose, Hiroshi Watabe, Yasumasa Kuroda, Kanae Mitsunaga, Dai Matsuse, Taeko Shigemoto, Akihito Ito, Hironobu Ikeda, Hidenao Fukuyama, Hirotaka Onoe, Yasuhiko Tabata, Mari Dezawa
Deposition of amyloid β protein (Aβ) to form neuritic plaques in the brain is the pathological hallmark of Alzheimer’s disease (AD). Aβ is generated from sequential cleavages of the β-amyloid precursor protein (APP) by the β- and γ-secretases, and β-site APP-cleaving enzyme 1 (BACE1) is the β-secretase essential for Aβ generation. Previous studies have indicated that glycogen synthase kinase 3 (GSK3) may play a role in APP processing by modulating γ-secretase activity, thereby facilitating Aβ production. There are two highly conserved isoforms of GSK3: GSK3α and GSK3β. We now report that specific inhibition of GSK3β, but not GSK3α, reduced BACE1-mediated cleavage of APP and Aβ production by decreasing BACE1 gene transcription and expression. The regulation of BACE1 gene expression by GSK3β was dependent on NF-κB signaling. Inhibition of GSK3 signaling markedly reduced Aβ deposition and neuritic plaque formation, and rescued memory deficits in the double transgenic AD model mice. These data provide evidence for regulation of BACE1 expression and AD pathogenesis by GSK3β and that inhibition of GSK3 signaling can reduce Aβ neuropathology and alleviate memory deficits in AD model mice. Our study suggests that interventions that specifically target the β-isoform of GSK3 may be a safe and effective approach for treating AD.
Philip T.T. Ly, Yili Wu, Haiyan Zou, Ruitao Wang, Weihui Zhou, Ayae Kinoshita, Mingming Zhang, Yi Yang, Fang Cai, James Woodgett, Weihong Song
Down syndrome (DS) patients exhibit abnormalities of hippocampal-dependent explicit memory, a feature that is replicated in relevant mouse models of the disease. Adult hippocampal neurogenesis, which is impaired in DS and other neuropsychiatric diseases, plays a key role in hippocampal circuit plasticity and has been implicated in learning and memory. However, it remains unknown whether increasing adult neurogenesis improves hippocampal plasticity and behavioral performance in the multifactorial context of DS. We report that, in the Ts65Dn mouse model of DS, chronic administration of lithium, a clinically used mood stabilizer, promoted the proliferation of neuronal precursor cells through the pharmacological activation of the Wnt/β-catenin pathway and restored adult neurogenesis in the hippocampal dentate gyrus (DG) to physiological levels. The restoration of adult neurogenesis completely rescued the synaptic plasticity of newborn neurons in the DG and led to the full recovery of behavioral performance in fear conditioning, object location, and novel object recognition tests. These findings indicate that reestablishing a functional population of hippocampal newborn neurons in adult DS mice rescues hippocampal plasticity and memory and implicate adult neurogenesis as a promising therapeutic target to alleviate cognitive deficits in DS patients.
Andrea Contestabile, Barbara Greco, Diego Ghezzi, Valter Tucci, Fabio Benfenati, Laura Gasparini
Antifibrinolytic drugs are widely used to reduce blood loss during surgery. One serious adverse effect of these drugs is convulsive seizures; however, the mechanisms underlying such seizures remain poorly understood. The antifibrinolytic drugs tranexamic acid (TXA) and ε-aminocaproic acid (EACA) are structurally similar to the inhibitory neurotransmitter glycine. Since reduced function of glycine receptors causes seizures, we hypothesized that TXA and EACA inhibit the activity of glycine receptors. Here we demonstrate that TXA and EACA are competitive antagonists of glycine receptors in mice. We also showed that the general anesthetic isoflurane, and to a lesser extent propofol, reverses TXA inhibition of glycine receptor–mediated current, suggesting that these drugs could potentially be used to treat TXA-induced seizures. Finally, we measured the concentration of TXA in the cerebrospinal fluid (CSF) of patients undergoing major cardiovascular surgery. Surprisingly, peak TXA concentration in the CSF occurred after termination of drug infusion and in one patient coincided with the onset of seizures. Collectively, these results show that concentrations of TXA equivalent to those measured in the CSF of patients inhibited glycine receptors. Furthermore, isoflurane or propofol may prevent or reverse TXA-induced seizures.
Irene Lecker, Dian-Shi Wang, Alexander D. Romaschin, Mark Peterson, C. David Mazer, Beverley A. Orser
In multiple sclerosis (MS) pathogenic B cells likely act on both sides of the blood-brain barrier (BBB). However, it is unclear whether antigen-experienced B cells are shared between the CNS and the peripheral blood (PB) compartments. We applied deep repertoire sequencing of IgG heavy chain variable region genes (IgG-VH) in paired cerebrospinal fluid and PB samples from patients with MS and other neurological diseases to identify related B cells that are common to both compartments. For the first time to our knowledge, we found that a restricted pool of clonally related B cells participated in robust bidirectional exchange across the BBB. Some clusters of related IgG-VH appeared to have undergone active diversification primarily in the CNS, while others have undergone active diversification in the periphery or in both compartments in parallel. B cells are strong candidates for autoimmune effector cells in MS, and these findings suggest that CNS-directed autoimmunity may be triggered and supported on both sides of the BBB. These data also provide a powerful approach to identify and monitor B cells in the PB that correspond to clonally amplified populations in the CNS in MS and other inflammatory states.
H.-Christian von Büdingen, Tracy C. Kuo, Marina Sirota, Christopher J. van Belle, Leonard Apeltsin, Jacob Glanville, Bruce A. Cree, Pierre-Antoine Gourraud, Amy Schwartzburg, Gabriella Huerta, Dilduz Telman, Purnima D. Sundar, Tyler Casey, David R. Cox, Stephen L. Hauser
In Huntington disease (HD), immune cells are activated before symptoms arise; however, it is unclear how the expression of mutant huntingtin (htt) compromises the normal functions of immune cells. Here we report that primary microglia from early postnatal HD mice were profoundly impaired in their migration to chemotactic stimuli, and expression of a mutant htt fragment in microglial cell lines was sufficient to reproduce these deficits. Microglia expressing mutant htt had a retarded response to a laser-induced brain injury in vivo. Leukocyte recruitment was defective upon induction of peritonitis in HD mice at early disease stages and was normalized upon genetic deletion of mutant htt in immune cells. Migration was also strongly impaired in peripheral immune cells from pre-manifest human HD patients. Defective actin remodeling in immune cells expressing mutant htt likely contributed to their migration deficit. Our results suggest that these functional changes may contribute to immune dysfunction and neurodegeneration in HD, and may have implications for other polyglutamine expansion diseases in which mutant proteins are ubiquitously expressed.
Wanda Kwan, Ulrike Träger, Dimitrios Davalos, Austin Chou, Jill Bouchard, Ralph Andre, Aaron Miller, Andreas Weiss, Flaviano Giorgini, Christine Cheah, Thomas Möller, Nephi Stella, Katerina Akassoglou, Sarah J. Tabrizi, Paul J. Muchowski
Angelman syndrome (AS) is a neurodevelopmental disorder caused by maternal deletions or mutations of the ubiquitin ligase E3A (UBE3A) allele and characterized by minimal verbal communication, seizures, and disorders of voluntary movement. Previous studies have suggested that abnormal dopamine neurotransmission may underlie some of these deficits, but no effective treatment currently exists for the core features of AS. A clinical trial of levodopa (l-DOPA) in AS is ongoing, although the underlying rationale for this treatment strategy has not yet been thoroughly examined in preclinical models. We found that AS model mice lacking maternal Ube3a (Ube3am–/p+ mice) exhibit behavioral deficits that correlated with abnormal dopamine signaling. These deficits were not due to loss of dopaminergic neurons or impaired dopamine synthesis. Unexpectedly, Ube3am–/p+ mice exhibited increased dopamine release in the mesolimbic pathway while also exhibiting a decrease in dopamine release in the nigrostriatal pathway, as measured with fast-scan cyclic voltammetry. These findings demonstrate the complex effects of UBE3A loss on dopamine signaling in subcortical motor pathways that may inform ongoing clinical trials of l-DOPA therapy in patients with AS.
Thorfinn T. Riday, Elyse C. Dankoski, Michael C. Krouse, Eric W. Fish, Paul L. Walsh, Ji Eun Han, Clyde W. Hodge, R. Mark Wightman, Benjamin D. Philpot, C.J. Malanga
8-Oxoguanine (8-oxoG), a common DNA lesion caused by reactive oxygen species, is associated with carcinogenesis and neurodegeneration. Although the mechanism by which 8-oxoG causes carcinogenesis is well understood, the mechanism by which it causes neurodegeneration is unknown. Here, we report that neurodegeneration is triggered by MUTYH-mediated excision repair of 8-oxoG–paired adenine. Mutant mice lacking 8-oxo–2′-deoxyguanosine triphosphatase–depleting (8-oxo–dGTP–depleting) MTH1 and/or 8-oxoG–excising OGG1 exhibited severe striatal neurodegeneration, whereas mutant mice lacking MUTYH or OGG1/MUTYH were resistant to neurodegeneration under conditions of oxidative stress. These results indicate that OGG1 and MTH1 are protective, while MUTYH promotes neurodegeneration. We observed that 8-oxoG accumulated in the mitochondrial DNA of neurons and caused calpain-dependent neuronal loss, while delayed nuclear accumulation of 8-oxoG in microglia resulted in PARP-dependent activation of apoptosis-inducing factor and exacerbated microgliosis. These results revealed that neurodegeneration is a complex process caused by 8-oxoG accumulation in the genomes of neurons and microglia. Different signaling pathways were triggered by the accumulation of single-strand breaks in each type of DNA generated during base excision repair initiated by MUTYH, suggesting that suppression of MUTYH may protect the brain under conditions of oxidative stress.
Zijing Sheng, Sugako Oka, Daisuke Tsuchimoto, Nona Abolhassani, Hiroko Nomaru, Kunihiko Sakumi, Hidetaka Yamada, Yusaku Nakabeppu