Netrin-1 is a secreted protein that was first identified 20 years ago as an axon guidance molecule that regulates midline crossing in the CNS. It plays critical roles in various tissues throughout development and is implicated in tumorigenesis and inflammation in adulthood. Despite extensive studies, no inherited human disease has been directly associated with mutations in NTN1, the gene coding for netrin-1. Here, we have identified 3 mutations in exon 7 of NTN1 in 2 unrelated families and 1 sporadic case with isolated congenital mirror movements (CMM), a disorder characterized by involuntary movements of one hand that mirror intentional movements of the opposite hand. Given the diverse roles of netrin-1, the absence of manifestations other than CMM in NTN1 mutation carriers was unexpected. Using multimodal approaches, we discovered that the anatomy of the corticospinal tract (CST) is abnormal in patients with NTN1-mutant CMM. When expressed in HEK293 or stable HeLa cells, the 3 mutated netrin-1 proteins were almost exclusively detected in the intracellular compartment, contrary to WT netrin-1, which is detected in both intracellular and extracellular compartments. Since netrin-1 is a diffusible extracellular cue, the pathophysiology likely involves its loss of function and subsequent disruption of axon guidance, resulting in abnormal decussation of the CST.
Aurélie Méneret, Elizabeth A. Franz, Oriane Trouillard, Thomas C. Oliver, Yvrick Zagar, Stephen P. Robertson, Quentin Welniarz, R.J. MacKinlay Gardner, Cécile Gallea, Myriam Srour, Christel Depienne, Christine L. Jasoni, Caroline Dubacq, Florence Riant, Jean-Charles Lamy, Marie-Pierre Morel, Raphael Guérois, Jessica Andreani, Coralie Fouquet, Mohamed Doulazmi, Marie Vidailhet, Guy A. Rouleau, Alexis Brice, Alain Chédotal, Isabelle Dusart, Emmanuel Roze, David Markie
Neural stem cells (NSCs) differentiate into both neurons and glia, and strategies using human NSCs have the potential to restore function following spinal cord injury (SCI). However, the time period of maturation for human NSCs in adult injured CNS is not well defined, posing fundamental questions about the design and implementation of NSC-based therapies. This work assessed human H9 NSCs that were implanted into sites of SCI in immunodeficient rats over a period of 1.5 years. Notably, grafts showed evidence of continued maturation over the entire assessment period. Markers of neuronal maturity were first expressed 3 months after grafting. However, neurogenesis, neuronal pruning, and neuronal enlargement continued over the next year, while total graft size remained stable over time. Axons emerged early from grafts in very high numbers, and half of these projections persisted by 1.5 years. Mature astrocyte markers first appeared after 6 months, while more mature oligodendrocyte markers were not present until 1 year after grafting. Astrocytes slowly migrated from grafts. Notably, functional recovery began more than 1 year after grafting. Thus, human NSCs retain an intrinsic human rate of maturation, despite implantation into the injured rodent spinal cord, yet they support delayed functional recovery, a finding of great importance in planning human clinical trials.
Paul Lu, Steven Ceto, Yaozhi Wang, Lori Graham, Di Wu, Hiromi Kumamaru, Eileen Staufenberg, Mark H. Tuszynski
Demyelination in the central nervous system (CNS) leads to severe neurological deficits that can be partially reversed by spontaneous remyelination. Because the CNS is isolated from the peripheral milieu by the blood-brain barrier, remyelination is thought to be controlled by the CNS microenvironment. However, in this work we found that factors derived from peripheral tissue leak into the CNS after injury and promote remyelination in a murine model of toxin-induced demyelination. Mechanistically, leakage of circulating fibroblast growth factor 21 (FGF21), which is predominantly expressed by the pancreas, drives proliferation of oligodendrocyte precursor cells (OPCs) through interactions with β-klotho, an essential coreceptor of FGF21. We further confirmed that human OPCs expressed β-klotho and proliferated in response to FGF21 in vitro. Vascular barrier disruption is a common feature of many CNS disorders; thus, our findings reveal a potentially important role for the peripheral milieu in promoting CNS regeneration.
Mariko Kuroda, Rieko Muramatsu, Noriko Maedera, Yoshihisa Koyama, Machika Hamaguchi, Harutoshi Fujimura, Mari Yoshida, Morichika Konishi, Nobuyuki Itoh, Hideki Mochizuki, Toshihide Yamashita
The EGFR belongs to the well-studied ErbB family of receptor tyrosine kinases. EGFR is activated by numerous endogenous ligands that promote cellular growth, proliferation, and tissue regeneration. In the present study, we have demonstrated a role for EGFR and its natural ligand, epiregulin (EREG), in pain processing. We show that inhibition of EGFR with clinically available compounds strongly reduced nocifensive behavior in mouse models of inflammatory and chronic pain. EREG-mediated activation of EGFR enhanced nociception through a mechanism involving the PI3K/AKT/mTOR pathway and matrix metalloproteinase-9. Moreover, EREG application potentiated capsaicin-induced calcium influx in a subset of sensory neurons. Both the EGFR and EREG genes displayed a genetic association with the development of chronic pain in several clinical cohorts of temporomandibular disorder. Thus, EGFR and EREG may be suitable therapeutic targets for persistent pain conditions.
Loren J. Martin, Shad B. Smith, Arkady Khoutorsky, Claire A. Magnussen, Alexander Samoshkin, Robert E. Sorge, Chulmin Cho, Noosha Yosefpour, Sivaani Sivaselvachandran, Sarasa Tohyama, Tiffany Cole, Thang M. Khuong, Ellen Mir, Dustin G. Gibson, Jeffrey S. Wieskopf, Susana G. Sotocinal, Jean Sebastien Austin, Carolina B. Meloto, Joseph H. Gitt, Christos Gkogkas, Nahum Sonenberg, Joel D. Greenspan, Roger B. Fillingim, Richard Ohrbach, Gary D. Slade, Charles Knott, Ronald Dubner, Andrea G. Nackley, Alfredo Ribeiro-da-Silva, G. Gregory Neely, William Maixner, Dmitri V. Zaykin, Jeffrey S. Mogil, Luda Diatchenko
Lesions and neurologic disability in inflammatory CNS diseases such as multiple sclerosis (MS) result from the translocation of leukocytes and humoral factors from the vasculature, first across the endothelial blood-brain barrier (BBB) and then across the astrocytic glia limitans (GL). Factors secreted by reactive astrocytes open the BBB by disrupting endothelial tight junctions (TJs), but the mechanisms that control access across the GL are unknown. Here, we report that in inflammatory lesions, a second barrier composed of reactive astrocyte TJs of claudin 1 (CLDN1), CLDN4, and junctional adhesion molecule A (JAM-A) subunits is induced at the GL. In a human coculture model, CLDN4-deficient astrocytes were unable to control lymphocyte segregation. In models of CNS inflammation and MS, mice with astrocyte-specific Cldn4 deletion displayed exacerbated leukocyte and humoral infiltration, neuropathology, motor disability, and mortality. These findings identify a second inducible barrier to CNS entry at the GL. This barrier may be therapeutically targetable in inflammatory CNS disease.
Sam Horng, Anthony Therattil, Sarah Moyon, Alexandra Gordon, Karla Kim, Azeb Tadesse Argaw, Yuko Hara, John N. Mariani, Setsu Sawai, Per Flodby, Edward D. Crandall, Zea Borok, Michael V. Sofroniew, Candice Chapouly, Gareth R. John
Adipocytes secrete the hormone leptin to signal the sufficiency of energy stores. Reductions in circulating leptin concentrations reflect a negative energy balance, which augments sympathetic nervous system (SNS) activation in response to metabolically demanding emergencies. This process ensures adequate glucose mobilization despite low energy stores. We report that leptin receptor–expressing neurons (LepRb neurons) in the periaqueductal gray (PAG), the largest population of LepRb neurons in the brain stem, mediate this process. Application of noxious stimuli, which often signal the need to mobilize glucose to support an appropriate response, activated PAG LepRb neurons, which project to and activate parabrachial nucleus (PBN) neurons that control SNS activation and glucose mobilization. Furthermore, activating PAG LepRb neurons increased SNS activity and blood glucose concentrations, while ablating LepRb in PAG neurons augmented glucose mobilization in response to noxious stimuli. Thus, decreased leptin action on PAG LepRb neurons augments the autonomic response to noxious stimuli, ensuring sufficient glucose mobilization during periods of acute demand in the face of diminished energy stores.
Jonathan N. Flak, Deanna Arble, Warren Pan, Christa Patterson, Thomas Lanigan, Paulette B. Goforth, Jamie Sacksner, Maja Joosten, Donald A. Morgan, Margaret B. Allison, John Hayes, Eva Feldman, Randy J. Seeley, David P. Olson, Kamal Rahmouni, Martin G. Myers Jr.
After traumatic brain injury (TBI), glial cells have both beneficial and deleterious roles in injury progression and recovery. However, few studies have examined the influence of reactive astrocytes in the tripartite synapse following TBI. Here, we have demonstrated that hippocampal synaptic damage caused by controlled cortical impact (CCI) injury in mice results in a switch from neuronal to astrocytic d-serine release. Under nonpathological conditions, d-serine functions as a neurotransmitter and coagonist for NMDA receptors and is involved in mediating synaptic plasticity. The phasic release of neuronal d-serine is important in maintaining synaptic function, and deficiencies lead to reductions in synaptic function and plasticity. Following CCI injury, hippocampal neurons downregulated d-serine levels, while astrocytes enhanced production and release of d-serine. We further determined that this switch in the cellular source of d-serine, together with the release of basal levels of glutamate, contributes to synaptic damage and dysfunction. Astrocyte-specific elimination of the astrocytic d-serine–synthesizing enzyme serine racemase after CCI injury improved synaptic plasticity, brain oscillations, and learning behavior. We conclude that the enhanced tonic release of d-serine from astrocytes after TBI underlies much of the synaptic damage associated with brain injury.
Enmanuel J. Perez, Stephen A. Tapanes, Zachary B. Loris, Darrick T. Balu, Thomas J. Sick, Joseph T. Coyle, Daniel J. Liebl
Obesity increases sympathetic nerve activity (SNA) via activation of proopiomelanocortin neurons in the arcuate nucleus (ArcN), and this action requires simultaneous withdrawal of tonic neuropeptide Y (NPY) sympathoinhibition. However, the sites and neurocircuitry by which NPY decreases SNA are unclear. Here, using designer receptors exclusively activated by designer drugs (DREADDs) to selectively activate or inhibit ArcN NPY neurons expressing agouti-related peptide (AgRP) in mice, we have demonstrated that this neuronal population tonically suppresses splanchnic SNA (SSNA), arterial pressure, and heart rate via projections to the paraventricular nucleus (PVN) and dorsomedial hypothalamus (DMH). First, we found that ArcN NPY/AgRP fibers closely appose PVN and DMH presympathetic neurons. Second, nanoinjections of NPY or an NPY receptor Y1 (NPY1R) antagonist into PVN or DMH decreased or increased SSNA, respectively. Third, blockade of DMH NPY1R reversed the sympathoinhibition elicited by selective, DREADD-mediated activation of ArcN NPY/AgRP neurons. Finally, stimulation of ArcN NPY/AgRP terminal fields in the PVN and DMH decreased SSNA. Considering that chronic obesity decreases ArcN NPY content, we propose that the ArcN NPY neuropathway to the PVN and DMH is pivotal in obesity-induced elevations in SNA.
Zhigang Shi, Christopher J. Madden, Virginia L. Brooks
Huntington’s disease is a neurodegenerative disorder caused by a polyglutamine repeat in the Huntingtin gene (HTT). Although suppressing the expression of mutant HTT (mHTT) has been explored as a therapeutic strategy to treat Huntington’s disease, considerable efforts have gone into developing allele-specific suppression of mHTT expression, given that loss of Htt in mice can lead to embryonic lethality. It remains unknown whether depletion of HTT in the adult brain, regardless of its allele, could be a safe therapy. Here, we report that permanent suppression of endogenous mHTT expression in the striatum of mHTT-expressing mice (HD140Q-knockin mice) using CRISPR/Cas9-mediated inactivation effectively depleted HTT aggregates and attenuated early neuropathology. The reduction of mHTT expression in striatal neuronal cells in adult HD140Q-knockin mice did not affect viability, but alleviated motor deficits. Our studies suggest that non–allele-specific CRISPR/Cas9-mediated gene editing could be used to efficiently and permanently eliminate polyglutamine expansion–mediated neuronal toxicity in the adult brain.
Su Yang, Renbao Chang, Huiming Yang, Ting Zhao, Yan Hong, Ha Eun Kong, Xiaobo Sun, Zhaohui Qin, Peng Jin, Shihua Li, Xiao-Jiang Li
The progressive death of retinal ganglion cells and resulting visual deficits are hallmarks of glaucoma, but the underlying mechanisms remain unclear. In many neurodegenerative diseases, cell death induced by primary insult is followed by a wave of secondary loss. Gap junctions (GJs), intercellular channels composed of subunit connexins, can play a major role in secondary cell death by forming conduits through which toxic molecules from dying cells pass to and injure coupled neighbors. Here we have shown that pharmacological blockade of GJs or genetic ablation of connexin 36 (Cx36) subunits, which are highly expressed by retinal neurons, markedly reduced loss of neurons and optic nerve axons in a mouse model of glaucoma. Further, functional parameters that are negatively affected in glaucoma, including the electroretinogram, visual evoked potential, visual spatial acuity, and contrast sensitivity, were maintained at control levels when Cx36 was ablated. Neuronal GJs may thus represent potential therapeutic targets to prevent the progressive neurodegeneration and visual impairment associated with glaucoma.
Abram Akopian, Sandeep Kumar, Hariharasubramanian Ramakrishnan, Kaushambi Roy, Suresh Viswanathan, Stewart A. Bloomfield