Bernhard Klaus Mueller - Academia.edu (original) (raw)

Papers by Bernhard Klaus Mueller

Liver failure causes blood-brain-barrier (BBB) breakdown leading to central nervous system damage... more Liver failure causes blood-brain-barrier (BBB) breakdown leading to central nervous system damage, however the mechanisms whereby the liver influences BBB-integrity remain elusive. One possibility is that the liver secretes an as-yet to be identified molecule(s) that circulate in the serum to directly promote BBB integrity. We developed light-sheet imaging for three-dimensional study of BBB function. We show that liver- or muscle-specific knockout of Hfe2 induces BBB breakdown, leading to accumulation of toxic-blood-derived fibrinogen in the brain, lower cortical neuron numbers, and behavioral deficits. In healthy animals, soluble Hfe2 competes with its homologue RGMa for binding to Neogenin, thereby blocking RGMa-induced downregulation of PDGF-B and Claudin-5 in endothelial cells and the ensuing BBB disruption. Hfe2 administration in an animal model of multiple sclerosis prevented paralysis and immune cell infiltration by inhibiting RGMa-mediated BBB alteration. This study has impl...

Abstract. Retinal ganglion cell axons grow towards the optic fissure in close contact with the ba... more Abstract. Retinal ganglion cell axons grow towards the optic fissure in close contact with the basal membrane, an excellent growth substratum. One of the ligands of receptor tyrosine phosphatase CRYP � is located on the retinal and tectal basal membranes. To analyze the role of this RPTP and its ligand in intraretinal growth and guidance of ganglion cell axons, we disrupted ligandreceptor interactions on the retinal basal membrane in culture. Antibodies against CRYP � strongly reduced retinal axon growth on the basal membrane, and induced a dramatic change in morphology of retinal growth cones, reducing the size of growth cone lamellipodia. A similar effect was observed by blocking the ligand with a CRYP � ectodomain fusion protein. These effects did not occur, or were much reduced, when axons were grown either on laminin-1, on matrigel or on basal membranes with glial endfeet removed. This indicates that a ligand for CRYP � is located on glial endfeet. These results show for the fi...

Cells, 2021

Symptomatic treatments are available for Parkinson’s disease and Alzheimer’s disease. An unmet ne... more Symptomatic treatments are available for Parkinson’s disease and Alzheimer’s disease. An unmet need is cure or disease modification. This review discusses possible reasons for negative clinical study outcomes on disease modification following promising positive findings from experimental research. It scrutinizes current research paradigms for disease modification with antibodies against pathological protein enrichment, such as α-synuclein, amyloid or tau, based on post mortem findings. Instead a more uniform regenerative and reparative therapeutic approach for chronic neurodegenerative disease entities is proposed with stimulation of an endogenously existing repair system, which acts independent of specific disease mechanisms. The repulsive guidance molecule A pathway is involved in the regulation of peripheral and central neuronal restoration. Therapeutic antagonism of repulsive guidance molecule A reverses neurodegeneration according to experimental outcomes in numerous disease mo...

Journal of Neuroscience, 2004

In the developing dentate gyrus, afferent fiber projections terminate in distinct laminas. This r... more In the developing dentate gyrus, afferent fiber projections terminate in distinct laminas. This relies on an accurately regulated spatiotemporal network of guidance molecules. Here, we have analyzed the functional role of the glycosylphosphatidylinositol (GPI)-anchored repulsive guidance molecule RGMa. In situ hybridization in embryonic and postnatal brain showed expression of RGMa in the cornu ammonis and hilus of the hippocampus. In the dentate gyrus, RGM immunostaining was confined to the inner molecular layer, whereas the outer molecular layers targeted by entorhinal fibers remained free. To test the repulsive capacity of RGMa, different setups were used: the stripe and explant outgrowth assays with recombinant RGMa, and entorhino-hippocampal cocultures incubated either with a neutralizing RGMa antibody (Ab) or with the GPI anchor-digesting drug phosphatidylinositol-specific phospholipase C. Entorhinal axons were clearly repelled by RGMa in the stripe and outgrowth assays. After disrupting the RGMa function, the specific laminar termination pattern in entorhino-hippocampal cocultures was lost, and entorhinal axons entered inappropriate hippocampal areas. Our data indicate an important role of RGMa for the layer-specific termination of the perforant pathway as a repulsive signal that compels entorhinal fibers to stay in their correct target zone.

Cell reports, Jan 17, 2015

Repulsive guidance molecule A (RGMa) is a potent inhibitor of neuronal regeneration and a regulat... more Repulsive guidance molecule A (RGMa) is a potent inhibitor of neuronal regeneration and a regulator of cell death, and it plays a role in multiple sclerosis (MS). In autopsy material from progressive MS patients, RGMa was found in active and chronic lesions, as well as in normal-appearing gray and white matter, and was expressed by cellular meningeal infiltrates. Levels of soluble RGMa in the cerebrospinal fluid were decreased in progressive MS patients successfully treated with intrathecal corticosteroid triamcinolone acetonide (TCA), showing functional improvements. In vitro, RGMa monoclonal antibodies (mAbs) reversed RGMa-mediated neurite outgrowth inhibition and chemorepulsion. In animal models of CNS damage and MS, RGMa antibody stimulated regeneration and remyelination of damaged nerve fibers, accelerated functional recovery, and protected the retinal nerve fiber layer as measured by clinically relevant optic coherence tomography. These data suggest that targeting RGMa is a pr...

Scientific Reports, 2017

Traumatic spinal cord injury (SCI) causes a cascade of degenerative events including cell death, ... more Traumatic spinal cord injury (SCI) causes a cascade of degenerative events including cell death, axonal damage, and the upregulation of inhibitory molecules which prevent regeneration and limit recovery. Repulsive guidance molecule A (RGMa) is a potent neurite growth inhibitor in the central nervous system, exerting its repulsive activity by binding the Neogenin receptor. Here, we show for the first time that inhibitory RGMa is markedly upregulated in multiple cell types after clinically relevant impactcompression SCI in rats, and importantly, also in the injured human spinal cord. To neutralize inhibitory RGMa, clinically relevant human monoclonal antibodies were systemically administered after acute SCI, and were detected in serum, cerebrospinal fluid, and in the injured tissue. Rats treated with RGMa blocking antibodies showed significantly improved recovery of motor function and gait. Furthermore, RGMa blocking antibodies promoted neuronal survival, and enhanced the plasticity of descending serotonergic pathways and corticospinal tract axonal regeneration. RGMa antibody also attenuated neuropathic pain responses, which was associated with fewer activated microglia and reduced CGRP expression in the dorsal horn caudal to the lesion. These results show the therapeutic potential of the first human RGMa antibody for SCI and uncovers a new role for the RGMa/Neogenin pathway on neuropathic pain. Spinal cord injury (SCI) is a devastating condition with great personal and societal costs. Despite advances in clinical care, currently there is no effective treatment to enhance regeneration after major SCI. Following the initial trauma, there is a cascade of molecular and degenerative events including apoptosis, ischemia, excitotoxicity, and the upregulation of inhibitory molecules 1. Neuronal death and inhibition of axonal regeneration limit neurological recovery following injury. CNS axons show a limited capacity to regenerate and often retract away from the injury site or undergo secondary axonal degeneration due to intrinsic mechanisms and the inhibitory environment of the injured spinal cord. Early studies demonstrating that adult CNS axons can regenerate through a peripheral nerve graft 2 suggested that the local environment of the adult CNS is a major cause for the lack of regeneration. Extracellular inhibitory proteins such as Nogo-A, myelin associated glycoprotein, and oligodendrocyte myelin glycoprotein are present in CNS myelin and combined with the accumulation of chondroitin sulfate proteoglycans (CSPG), comprise the inhibitory glial scar that forms after SCI. Neutralization of these inhibitory proteins by antibodies 3, 4 or enzymatic treatment to reduce CSPG-induced inhibition 5-7 have shown

Toxicologic pathology, 2016

Hepcidin was originally detected as a liver peptide with antimicrobial activity and it functions ... more Hepcidin was originally detected as a liver peptide with antimicrobial activity and it functions as a central regulator in the systemic iron metabolism. Consequently suppression of hepcidin leads to iron accumulation in the liver. AbbVie developed a monoclonal antibody ([mAb]; repulsive guidance molecule [RGMa/c] mAb) that downregulates hepcidin expression by influencing the RGMc/bone morphogenetic protein (BMP)/neogenin receptor complex and causes iron deposition in the liver. In a dose range finding study with RGMa/c mAb, rats were treated with different dose levels for a total of 4 weekly doses. The results of this morphometric analysis in the liver showed that iron accumulation is not homogenous between liver lobes and the left lateral lobe was the most responsive lobe in the rat. Quantitative hepcidin messenger RNA analysis showed that the left lateral lobe was the most responsive lobe showing hepcidin downregulation with increasing antibody dose. In addition, the morphometric ...

Haematologica, 2016

for the generation of anti-RGM antibodies. Many thanks also to Andrea Egly, Isabel Trommer and Al... more for the generation of anti-RGM antibodies. Many thanks also to Andrea Egly, Isabel Trommer and Alice Tischer for their outstanding support. We also thank Carlos Lopez-Otin for providing the Tmprss6 mutant mice, and the staff of the laboratory animal resources (LAR) at EMBL for their dedicated work, especially Klaus Schmitt for his outstanding technical support. We also thank V. Devanarayan for his statistical expertise.

Cell death & disease, 2015

The dependence receptor Neogenin and its ligand, the repulsive guidance molecule a (RGMa), regula... more The dependence receptor Neogenin and its ligand, the repulsive guidance molecule a (RGMa), regulate apoptosis and axonal growth in the developing and the adult central nervous system (CNS). Here, we show that this pathway has also a critical role in neuronal death following stroke, and that providing RGMa to neurons blocks Neogenin-induced death. Interestingly, the Neogenin pro-death function following ischemic insult depends on Neogenin association with lipid rafts. Thus, a peptide that prevents Neogenin association with lipid rafts increased neuronal survival in several in vitro stroke models. In rats, a pro-survival effect was also observed in a model of ocular ischemia, as well as after middle cerebral artery occlusion (MCAO). Treatments that prevented Neogenin association with lipid rafts improved neuronal survival and the complexity of the neuronal network following occlusion of the middle artery. Toward the development of a treatment for stroke, we developed a human anti-RGMa...

The AAPS journal, Jan 22, 2015

High levels of hepcidin, the main regulator of systemic iron metabolism, lead to various diseases... more High levels of hepcidin, the main regulator of systemic iron metabolism, lead to various diseases. Targeting hepcidin and lowering its concentration is a possible form of intervention in order to treat these diseases. High turnover rate of hepcidin is a major drawback of therapies directly targeting this peptide. We developed two monoclonal antibodies ABT-207 and h5F9-AM8 which inhibit hemojuvelin/repulsive guidance molecule C (RGMc) and downregulate hepcidin. We conducted single-application and dose response studies to understand the antibodies' mechanism and subchronic toxicology studies to exclude safety-related concerns. Investigation was carried out at different biological levels through qPCR, Affymetrix, liquid chromatography coupled with mass spectrometry (LC-MS/MS), histopathology, serum iron, unsaturated iron binding capacity (UIBC), and drug concentration measurements. After a single application of these antibodies, hepcidin expression in liver and its serum protein le...

Philosophical Transactions of the Royal Society B: Biological Sciences, 2006

During the development of the nervous system, outgrowing axons often have to travel long distance... more During the development of the nervous system, outgrowing axons often have to travel long distances to reach their target neurons. In this process, outgrowing neurites tipped with motile growth cones rely on guidance cues present in their local environment. These cues are detected by specific receptors expressed on growth cones and neurites and influence the trajectory of the growing fibres. Neurite growth, guidance, target innervation and synapse formation and maturation are the processes that occur predominantly but not exclusively during embryonic or early post-natal development in vertebrates. As a result, a functional neural network is established, which is usually remarkably stable. However, the stability of the neural network in higher vertebrates comes at an expensive price, i.e. the loss of any significant ability to regenerate injured or damaged neuronal connections in their central nervous system (CNS). Most importantly, neurite growth inhibitors prevent any regenerative g...

Nature Cell Biology, 2004

Repulsive guidance molecule (RGM) is an axon guidance protein that repels retinal axons upon acti... more Repulsive guidance molecule (RGM) is an axon guidance protein that repels retinal axons upon activation of the neogenin receptor. To understand the functions of RGM-neogenin complexes in vivo, we used gene transfer technology to perturb their expression in the developing neural tube of chick embryos. Surprisingly, neogenin over-expression or RGM down-expression in the neural tube induces apoptosis. Neogenin pro-apoptotic activity in immortalized neuronal cells and in the neural tube is associated with the cleavage of its cytoplasmic domain by caspases. Thus neogenin is a dependence receptor inducing cell death in the absence of RGM, whereas the presence of RGM inhibits this effect.

Current Opinion in Neurobiology, 2007

Cell Death and Differentiation, 2008

The repulsive guidance molecule (RGM) is a membrane-bound protein that has diverse functions in t... more The repulsive guidance molecule (RGM) is a membrane-bound protein that has diverse functions in the developing central nervous system. Identification of neogenin as a receptor for RGM provided evidence of its cell death-inducing activity in the absence of RGM. Here, we show that the serine/threonine kinase death-associated protein kinase (DAPK) is involved in the signal transduction of neogenin. Neogenin interacts with DAPK and reduces DAPK autophosphorylation on Ser308 in vitro. Neogenininduced cell death is abolished in the presence of RGM or by blocking DAPK. Although neogenin overexpression or RGM downregulation in the chick neural tube in vivo induces apoptosis, coexpression of the dominant-negative mutant or smallinterference RNA of DAPK attenuates this proapoptotic activity. Thus, RGM/neogenin regulates cell fate by controlling the DAPK activity.

Retinal ganglion cell axons grow towards the optic fissure in close contact with the basal membra... more Retinal ganglion cell axons grow towards the optic fissure in close contact with the basal membrane, an excellent growth substratum. One of the ligands of receptor tyrosine phosphatase CRYP ␣ is located on the retinal and tectal basal membranes. To analyze the role of this RPTP and its ligand in intraretinal growth and guidance of ganglion cell axons, we disrupted ligandreceptor interactions on the retinal basal membrane in culture. Antibodies against CRYP ␣ strongly reduced retinal axon growth on the basal membrane, and induced a dramatic change in morphology of retinal growth cones, reducing the size of growth cone lamellipodia. A similar effect was observed by blocking the ligand with a CRYP ␣ ectodomain fusion protein. These effects did not occur, or were much reduced, when axons were grown either on laminin-1, on matrigel or on basal membranes with glial endfeet removed. This indicates that a ligand for CRYP ␣ is located on glial endfeet. These results show for the first time in vertebrates that the interaction of a receptor tyrosine phosphatase with its ligand is crucial not only for promotion of retinal axon growth but also for maintenance of retinal growth cone lamellipodia on basal membranes.

Journal of Cell Biology, 2006

Repulsive guidance molecule (RGM) is a protein implicated in both axonal guidance and neural tube... more Repulsive guidance molecule (RGM) is a protein implicated in both axonal guidance and neural tube closure. We report RGMa as a potent inhibitor of axon regeneration in the adult central nervous system (CNS). RGMa inhibits mammalian CNS neurite outgrowth by a mechanism dependent on the activation of the RhoA–Rho kinase pathway. RGMa expression is observed in oligodendrocytes, myelinated fibers, and neurons of the adult rat spinal cord and is induced around the injury site after spinal cord injury. We developed an antibody to RGMa that efficiently blocks the effect of RGMa in vitro. Intrathecal administration of the antibody to rats with thoracic spinal cord hemisection results in significant axonal growth of the corticospinal tract and improves functional recovery. Thus, RGMa plays an important role in limiting axonal regeneration after CNS injury and the RGMa antibody offers a possible therapeutic agent in clinical conditions characterized by a failure of CNS regeneration.

Nature Reviews Drug Discovery, 2005

Rho kinases (ROCKs), the first Rho effectors to be described, are serine/threonine kinases that a... more Rho kinases (ROCKs), the first Rho effectors to be described, are serine/threonine kinases that are important in fundamental processes of cell migration, cell proliferation and cell survival. Abnormal activation of the Rho/ROCK pathway has been observed in various disorders of the central nervous system. Injury to the adult vertebrate brain and spinal cord activates ROCKs, thereby inhibiting neurite growth and sprouting. Inhibition of ROCKs results in accelerated regeneration and enhanced functional recovery after spinal-cord injury in mammals, and inhibition of the Rho/ROCK pathway has also proved to be efficacious in animal models of stroke, inflammatory and demyelinating diseases, Alzheimer's disease and neuropathic pain. ROCK inhibitors therefore have potential for preventing neurodegeneration and stimulating neuroregeneration in various neurological disorders. NEUROPATHIC PAIN A pain state initiated or caused by a primary lesion or dysfunction in the nervous system. AGC KINASES A group of kinases with a high degree of amino-acid sequence conservation in their kinase domains.

The Journal of cell …, 2000

The ephrins, ligands of Eph receptor tyrosine kinases, have been shown to act as repulsive guidan... more The ephrins, ligands of Eph receptor tyrosine kinases, have been shown to act as repulsive guidance molecules and to induce collapse of neuronal growth cones. For the first time, we show that the ephrin-A5 collapse is mediated by activation of the small GTPase Rho and its downstream effector Rho kinase. In ephrin-A5-treated retinal ganglion cell cultures, Rho was activated and Rac was downregulated. Pretreatment of ganglion cell axons with C3-transferase, a specific inhib-itor of the Rho GTPase, or with Y-27632, a specific inhibitor of the Rho kinase, strongly reduced the collapse rate of retinal growth cones. These results suggest that activation of Rho and its downstream effector Rho kinase are important elements of the ephrin-A5 signal transduction pathway.

Molecular and Cellular …, 2003

Axons fail to regenerate in the central nervous system after injury. Chondroitin sulfate proteogl... more Axons fail to regenerate in the central nervous system after injury. Chondroitin sulfate proteoglycans (CSPG) expressed in the scar significantly contribute to the nonpermissive properties of the central nervous system environment. To examine the inhibitory activity of a CSPG mixture on retina ganglion cell (RGC) axon growth, we employed both a stripe assay and a nerve fiber outgrowth assay. We show that the inhibition exerted by CSPGs in vitro can be blocked by application of either C3 transferase, a specific inhibitor of the Rho GTPase, or Y27632, a specific inhibitor of the Rho kinase. These results demonstrate that CSPG-associated inhibition of neurite outgrowth is mediated by the Rho/ROCK signaling pathway. Consistent with these results, we found that retina ganglion cell axon growth on glial scar tissue was enhanced in the presence of C3 transferase and Y27632, respectively. In addition, we show that the recently identified inhibitory CSPG Te38 is upregulated in the lesioned spinal cord.