PDGF B-chain in neurons of the central nervous system, posterior pituitary, and in a transgenic model

Exome Sequencing has a high diagnostic rate in sporadic congenital hypopituitarism and reveals novel candidate genes

CONTEXT

The pituitary gland is key for childhood growth, puberty, and metabolism. Pituitary dysfunction is associated with a spectrum of phenotypes, from mild to severe. Congenital Hypopituitarism (CH) is the most commonly reported pediatric endocrine dysfunction with an incidence of 1:4000, yet low rates of genetic diagnosis have been reported.

OBJECTIVE

We aimed to unveil the genetic etiology of CH in a large cohort of patients from Argentina.

METHODS

We performed whole exome sequencing of 137 unrelated cases of CH, the largest cohort examined with this method to date.

RESULTS

Of the 137 cases, 19.1% and 16% carried pathogenic or likely pathogenic variants in known and new genes, respectively, while 28.2% carried variants of uncertain significance. This high yield was achieved through the integration of broad gene panels (genes described in animal models and/or other disorders), an unbiased candidate gene screen with a new bioinformatics pipeline (including genes high loss of function intolerance), and analysis of copy number variants. Three novel findings emerged. First, the most prevalent affected gene encodes the cell adhesion factor ROBO1. Affected children had a spectrum of phenotypes, consistent with a role beyond pituitary stalk interruption syndrome. Second, we found that CHD7 mutations also produce a phenotypic spectrum, not always associated with full CHARGE syndrome. Third, we add new evidence of pathogenicity in the genes PIBF1 and TBC1D32, and report 13 novel candidate genes associated with CH (e.g. PTPN6, ARID5B).

CONCLUSION

Overall, these results provide an unprecedented insight into the diverse genetic etiology of hypopituitarism.

Transcriptomics and translatomics identify a robust inflammatory gene signature in brain endothelial cells after ischemic stroke

Vascular endothelial function is challenged during cerebral ischemia and reperfusion. The endothelial responses are involved in inflammatory leukocyte attraction, adhesion and infiltration, blood-brain barrier leakage, and angiogenesis. This study investigated gene expression changes in brain endothelial cells after acute ischemic stroke using transcriptomics and translatomics. We isolated brain endothelial mRNA by: (i) translating ribosome affinity purification, enabling immunoprecipitation of brain endothelial ribosome-attached mRNA for translatome sequencing and (ii) isolating CD31+ endothelial cells by fluorescence-activating cell sorting for classical transcriptomic analysis. Both techniques revealed similar pathways regulated by ischemia but they showed specific differences in some transcripts derived from non-endothelial cells. We defined a gene set characterizing the endothelial response to acute stroke (24h) by selecting the differentially expressed genes common to both techniques, thus corresponding with the translatome and minimizing non-endothelial mRNA contamination. Enriched pathways were related to inflammation and immunoregulation, angiogenesis, extracellular matrix, oxidative stress, and lipid trafficking and storage. We validated, by flow cytometry and immunofluorescence, the protein expression of several genes encoding cell surface proteins. The inflammatory response was associated with the endothelial upregulation of genes related to lipid storage functions and we identified lipid droplet biogenesis in the endothelial cells after ischemia. The study reports a robust translatomic signature of brain endothelial cells after acute stroke and identifies enrichment in novel pathways involved in membrane signaling and lipid storage. Altogether these results highlight the endothelial contribution to the inflammatory response, and identify novel molecules that could be targets to improve vascular function after ischemic stroke.

Chronic Morphine Modulates PDGFR-β and PDGF-B Expression and Distribution in Dorsal Root Ganglia and Spinal Cord in Male Rats

The analgesic effect of opioids decreases over time due to the development of analgesic tolerance. We have shown that inhibition of the platelet-derived growth factor beta (PDGFR-β) signaling eliminates morphine analgesic tolerance in rats. Although the PDGFR-β and its ligand, the platelet-derived growth factor type B (PDGF-B), are expressed in the substantia gelatinosa of the spinal cord (SG) and in the dorsal root ganglia (DRG), their precise distribution within different cell types of these structures is unknown. Additionally, the impact of a tolerance-mediating chronic morphine treatment, on the expression and distribution of PDGF-B and PDGFR-β has not yet been studied. Using immunohistochemistry (IHC), we found that in the spinal cord, PDGFR-β and PDGF-B were expressed in neurons and oligodendrocytes and co-localized with the mu-opioid receptor (MOPr) in opioid naïve rats. PDGF-B was also found in microglia and astrocytes. Both PDGFR-β and PDGF-B were detected in DRG neurons but not in spinal primary afferent terminals. Chronic morphine exposure did not change the cellular distribution of PDGFR-β or PDGF-B. However, PDGFR-β expression was downregulated in the SG and upregulated in the DRG. Consistent with our previous finding that morphine caused tolerance by inducing PDGF-B release, PDGF-B was upregulated in the spinal cord. We also found that chronic morphine exposure caused a spinal proliferation of oligodendrocytes. The changes in PDGFR-β and PDGF-B expression induced by chronic morphine treatment suggest potential mechanistic substrates underlying opioid tolerance.

Mu-opioid receptor and receptor tyrosine kinase crosstalk: Implications in mechanisms of opioid tolerance, reduced analgesia to neuropathic pain, dependence, and reward

Despite the prevalence of opioid misuse, opioids remain the frontline treatment regimen for severe pain. However, opioid safety is hampered by side-effects such as analgesic tolerance, reduced analgesia to neuropathic pain, physical dependence, or reward. These side effects promote development of opioid use disorders and ultimately cause overdose deaths due to opioid-induced respiratory depression. The intertwined nature of signaling via μ-opioid receptors (MOR), the primary target of prescription opioids, with signaling pathways responsible for opioid side-effects presents important challenges. Therefore, a critical objective is to uncouple cellular and molecular mechanisms that selectively modulate analgesia from those that mediate side-effects. One such mechanism could be the transactivation of receptor tyrosine kinases (RTKs) via MOR. Notably, MOR-mediated side-effects can be uncoupled from analgesia signaling via targeting RTK family receptors, highlighting physiological relevance of MOR-RTKs crosstalk. This review focuses on the current state of knowledge surrounding the basic pharmacology of RTKs and bidirectional regulation of MOR signaling, as well as how MOR-RTK signaling may modulate undesirable effects of chronic opioid use, including opioid analgesic tolerance, reduced analgesia to neuropathic pain, physical dependence, and reward. Further research is needed to better understand RTK-MOR transactivation signaling pathways, and to determine if RTKs are a plausible therapeutic target for mitigating opioid side effects.

Platelet derived growth factor and its receptor in intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a common and highly disabling or fatal neurological disorder in adults. Recent studies have suggested that the platelet derived growth factor (PDGF) signaling pathway plays an important role in the development of ICH. PDGF is involved in vascular remodeling and can be used as a biomarker of cerebral amyloid angiopathy which is one of the major causes of ICH. PDGF and its receptors are involved in the mechanism of the secondary injury after ICH by affecting the integrity of the blood-brain barrier and inflammatory response. PDGF and its receptors may also participate in the mechanism of repair after ICH by promoting angiogenesis. This article reviews the latest research progress on the involvement of PDGF signaling pathway in the pathophysiology of intracerebral hemorrhage, and introduces the relevant antagonists using PDGFR as the therapeutic target, to provide information for the development of therapeutic options for intracerebral hemorrhage.

Cathepsin B Gene Knockout Improves Behavioral Deficits and Reduces Pathology in Models of Neurologic Disorders

Cathepsin B (CTSB) is a powerful lysosomal protease. This review evaluated CTSB gene knockout (KO) outcomes for amelioration of brain dysfunctions in neurologic diseases and aging animal models. Deletion of the CTSB gene resulted in significant improvements in behavioral deficits, neuropathology, and/or biomarkers in traumatic brain injury, ischemia, inflammatory pain, opiate tolerance, epilepsy, aging, transgenic Alzheimer's disease (AD), and periodontitis AD models as shown in 12 studies. One study found beneficial effects for double CTSB and cathepsin S KO mice in a multiple sclerosis model. Transgenic AD models using amyloid precursor protein (APP) mimicking common sporadic AD in three studies showed that CTSB KO improved memory, neuropathology, and biomarkers; two studies used APP representing rare familial AD and found no CTSB KO effect, and two studies used highly engineered APP constructs and reported slight increases in a biomarker. In clinical studies, all reports found that CTSB enzyme was upregulated in diverse neurologic disorders, including AD in which elevated CTSB was positively correlated with cognitive dysfunction. In a wide range of neurologic animal models, CTSB was also upregulated and not downregulated. Further, human genetic mutation data provided precedence for CTSB upregulation causing disease. Thus, the consilience of data is that CTSB gene KO results in improved brain dysfunction and reduced pathology through blockade of CTSB enzyme upregulation that causes human neurologic disease phenotypes. The overall findings provide strong support for CTSB as a rational drug target and for CTSB inhibitors as therapeutic candidates for a wide range of neurologic disorders. SIGNIFICANCE STATEMENT: This review provides a comprehensive compilation of the extensive data on the effects of deleting the cathepsin B (CTSB) gene in neurological and aging mouse models of brain disorders. Mice lacking the CTSB gene display improved neurobehavioral deficits, reduced neuropathology, and amelioration of neuronal cell death and inflammatory biomarkers. The significance of the compelling CTSB evidence is that the data consilience validates CTSB as a drug target for discovery of CTSB inhibitors as potential therapeutics for treating numerous neurological diseases.

Insights Into the Role of Platelet-Derived Growth Factors: Implications for Parkinson’s Disease Pathogenesis and Treatment

Parkinson’s disease (PD), the second most common neurodegenerative disease after Alzheimer’s disease, commonly occurs in the elderly population, causing a significant medical and economic burden to the aging society worldwide. At present, there are few effective methods that achieve satisfactory clinical results in the treatment of PD. Platelet-derived growth factors (PDGFs) and platelet-derived growth factor receptors (PDGFRs) are important neurotrophic factors that are expressed in various cell types. Their unique structures allow for specific binding that can effectively regulate vital functions in the nervous system. In this review, we summarized the possible mechanisms by which PDGFs/PDGFRs regulate the occurrence and development of PD by affecting oxidative stress, mitochondrial function, protein folding and aggregation, Ca2+ homeostasis, and cell neuroinflammation. These modes of action mainly depend on the type and distribution of PDGFs in different nerve cells. We also summarized the possible clinical applications and prospects for PDGF in the treatment of PD, especially in genetic treatment. Recent advances have shown that PDGFs have contradictory roles within the central nervous system (CNS). Although they exert neuroprotective effects through multiple pathways, they are also associated with the disruption of the blood–brain barrier (BBB). Our recommendations based on our findings include further investigation of the contradictory neurotrophic and neurotoxic effects of the PDGFs acting on the CNS.

A Historical Review of Brain Drug Delivery

The history of brain drug delivery is reviewed beginning with the first demonstration, in 1914, that a drug for syphilis, salvarsan, did not enter the brain, due to the presence of a blood-brain barrier (BBB). Owing to restricted transport across the BBB, FDA-approved drugs for the CNS have been generally limited to lipid-soluble small molecules. Drugs that do not cross the BBB can be re-engineered for transport on endogenous BBB carrier-mediated transport and receptor-mediated transport systems, which were identified during the 1970s-1980s. By the 1990s, a multitude of brain drug delivery technologies emerged, including trans-cranial delivery, CSF delivery, BBB disruption, lipid carriers, prodrugs, stem cells, exosomes, nanoparticles, gene therapy, and biologics. The advantages and limitations of each of these brain drug delivery technologies are critically reviewed.

Blood-brain barrier leakage in Alzheimer's disease: From discovery to clinical relevance

Alzheimer's disease (AD) is the most common form of dementia. AD brain pathology starts decades before the onset of clinical symptoms. One early pathological hallmark is blood-brain barrier dysfunction characterized by barrier leakage and associated with cognitive decline. In this review, we summarize the existing literature on the extent and clinical relevance of barrier leakage in AD. First, we focus on AD animal models and their susceptibility to barrier leakage based on age and genetic background. Second, we re-examine barrier dysfunction in clinical and postmortem studies, summarize changes that lead to barrier leakage in patients and highlight the clinical relevance of barrier leakage in AD. Third, we summarize signaling mechanisms that link barrier leakage to neurodegeneration and cognitive decline in AD. Finally, we discuss clinical relevance and potential therapeutic strategies and provide future perspectives on investigating barrier leakage in AD. Identifying mechanistic steps underlying barrier leakage has the potential to unravel new targets that can be used to develop novel therapeutic strategies to repair barrier leakage and slow cognitive decline in AD and AD-related dementias.

Therapeutic potential of Nlrp1 inflammasome, Caspase-1, or Caspase-6 against Alzheimer disease cognitive impairment

The sequential activation of Nucleotide-binding oligomerization domain, Leucine rich Repeat and Pyrin domain containing protein 1 (Nlrp1) inflammasome, Caspase-1 (Casp1), and Caspase-6 (Casp6) is implicated in primary human neuron cultures and Alzheimer Disease (AD) neurodegeneration. To validate the Nlrp1-Casp1-Casp6 pathway in vivo, the APP^{Swedish/Indiana} J20 AD transgenic mouse model was generated on either a Nlrp1, Casp1 or Casp6 null genetic background and mice were studied at 4-5 months of age. Episodic memory deficits assessed with novel object recognition were normalized by genetic ablation of Nlrp1, Casp1, or Casp6 in J20 mice. Spatial learning deficits, assessed with the Barnes Maze, were normalized in genetically ablated J20, whereas memory recall was normalized in J20/Casp1^-/- and J20/Casp6^-/-, and improved in J20/Nlrp1^-/- mice. Hippocampal CA1 dendritic spine density of the mushroom subtype was reduced in J20, and normalized in genetically ablated J20 mice. Reduced J20 hippocampal dentate gyrus and CA3 synaptophysin levels were normalized in genetically ablated J20. Increased Iba1⁺-microglia in the hippocampus and cortex of J20 brains were normalized by Casp1 and Casp6 ablation and reduced by Nlrp1 ablation. Increased pro-inflammatory cytokines, TNF-α and CXCL1, in the J20 hippocampus were normalized by Nlrp1 or Casp1 genetic ablation. CXCL1 was also normalized by Casp6 genetic ablation. IFN-γ was increased and total amyloid β peptide was decreased in genetically ablated Nlrp1, Casp1 or Casp6 J20 hippocampi. We conclude that Nlrp1, Casp1, or Casp6 are implicated in AD-related cognitive impairment, inflammation, and amyloidogenesis. These results indicate that Nlrp1, Casp1, and Casp6 represent rational therapeutic targets against cognitive impairment and inflammation in AD.

A Review of the Current Mammalian Models of Alzheimer's Disease and Challenges That Need to Be Overcome

Alzheimer's disease (AD) is one of the looming health crises of the near future. Increasing lifespans and better medical treatment for other conditions mean that the prevalence of this disease is expected to triple by 2050. The impact of AD includes both the large toll on individuals and their families as well as a large financial cost to society. So far, we have no way to prevent, slow, or cure the disease. Current medications can only alleviate some of the symptoms temporarily. Many animal models of AD have been created, with the first transgenic mouse model in 1995. Mouse models have been beset by challenges, and no mouse model fully captures the symptomatology of AD without multiple genetic mutations and/or transgenes, some of which have never been implicated in human AD. Over 25 years later, many mouse models have been given an AD-like disease and then 'cured' in the lab, only for the treatments to fail in clinical trials. This review argues that small animal models are insufficient for modelling complex disorders such as AD. In order to find effective treatments for AD, we need to create large animal models with brains and lifespan that are closer to humans, and underlying genetics that already predispose them to AD-like phenotypes.

Many roles for oligodendrocyte precursor cells in physiology and pathology

Oligodendrocyte precursor cells (OPCs) are a fourth resident glial cell population in the mammalian central nervous system. They are evenly distributed throughout the gray and white matter and continue to proliferate and generate new oligodendrocytes (OLs) throughout life. They were understudied until a few decades ago when immunolabeling for NG2 and platelet-derived growth factor receptor alpha revealed cells that are distinct from mature OLs, astrocytes, neurons, and microglia. In this review, we provide a summary of the known properties of OPCs with some historical background, followed by highlights from recent studies that suggest new roles for OPCs in certain pathological conditions.

Life-long oligodendrocyte development and plasticity

Oligodendrocyte precursor cells (OPCs) originate in localized germinal zones in the embryonic neural tube, then migrate and proliferate to populate the entire central nervous system, both white and gray matter. They divide and generate myelinating oligodendrocytes (OLs) throughout postnatal and adult life. OPCs express NG2 and platelet-derived growth factor receptor alpha subunit (PDGFRα), two functionally important cell surface proteins, which are also widely used as markers for OPCs. The proliferation of OPCs, their terminal differentiation into OLs, survival of new OLs, and myelin synthesis are orchestrated by signals in the local microenvironment. We discuss advances in our mechanistic understanding of paracrine effects, including those mediated through PDGFRα and neuronal activity-dependent signals such as those mediated through AMPA receptors in OL survival and myelination. Finally, we review recent studies supporting the role of new OL production and “adaptive myelination” in specific behaviours and cognitive processes contributing to learning and long-term memory formation. Our article is not intended to be comprehensive but reflects the authors’ past and present interests.

Vascular PDGFR-alpha protects against BBB dysfunction after stroke in mice

Blood-brain barrier (BBB) dysfunction underlies the pathogenesis of many neurological diseases. Platelet-derived growth factor receptor-alpha (PDGFRα) induces hemorrhagic transformation (HT) downstream of tissue plasminogen activator in thrombolytic therapy of acute stroke. Thus, PDGFs are attractive therapeutic targets for BBB dysfunction. In the present study, we examined the role of PDGF signaling in the process of tissue remodeling after middle cerebral arterial occlusion (MCAO) in mice. Firstly, we found that imatinib increased lesion size after permanent MCAO in wild-type mice. Moreover, imatinib-induced HT only when administrated in the subacute phase of MCAO, but not in the acute phase. Secondly, we generated genetically mutated mice (C-KO mice) that showed decreased expression of perivascular PDGFRα. Additionally, transient MCAO experiments were performed in these mice. We found that the ischemic lesion size was not affected; however, the recruitment of PDGFRα/type I collagen-expressing perivascular cells was significantly downregulated, and HT and IgG leakage was augmented only in the subacute phase of stroke in C-KO mice. In both experiments, we found that the expression of tight junction proteins and PDGFRβ-expressing pericyte coverage was not significantly affected in imatinib-treated mice and in C-KO mice. The specific implication of PDGFRα signaling was suggestive of protective effects against BBB dysfunction during the subacute phase of stroke. Vascular TGF-β1 expression was downregulated in both imatinib-treated and C-KO mice, along with sustained levels of MMP9. Therefore, PDGFRα effects may be mediated by TGF-β1 which exerts potent protective effects in the BBB.

Establishment of a Cre-rat resource for creating conditional and physiological relevant models of human diseases

The goal of this study is to establish a Cre/loxP rat resource for conditional and physiologically predictive rat models of human diseases. The laboratory rat (R. norvegicus) is a central experimental animal in several fields of biomedical research, such as cardiovascular diseases, aging, infectious diseases, autoimmunity, cancer models, transplantation biology, inflammation, cancer risk assessment, industrial toxicology, pharmacology, behavioral and addiction studies, and neurobiology. Up till recently, the ability of creating genetically modified rats has been limited compared to that in the mouse mainly due to lack of genetic manipulation tools and technologies in the rat. Recent advances in nucleases, such as CRISPR/Cas9 (clustered regularly-interspaced short palindromic repeats/CRISPR associated protein 9), as well as TARGATT™ integrase system enables fast, efficient and site-specific introduction of exogenous genetic elements into the rat genome. Here, we report the generation of a collection of tissue-specific, inducible transgenic Cre rats as tool models using TARGATT™, CRISPR/Cas9 and random transgenic approach. More specifically, we generated Cre driver rat models that allow controlled gene expression or knockout (conditional models) both temporally and spatially through the Cre-ERT2/loxP system. A total of 10 Cre rat lines and one Cre reporter/test line were generated, including eight (8) Cre lines for neural specific and two (2) lines for cardiovascular specific Cre expression. All of these lines have been deposited with the Rat Resource and Research Center and provide a much-needed resource for the bio-medical community who employ rat models for their studies of human diseases.

Cholinergic neurodegeneration in Alzheimer disease mouse models

Cholinergic signaling is critical for cognitive function. The basal forebrain is the major cholinergic output of the central nervous system. Degeneration of basal forebrain cholinergic neurons is a hallmark of Alzheimer's disease (AD). Mouse models are invaluable tools in disease research and have been used to study AD for over 25 years. However, animal models of AD vary greatly with respect to the degree of cholinergic degeneration observed. The following review will outline the most influential animal models of AD with an emphasis on the basal forebrain cholinergic system.

Brain Delivery of Nanomedicines: Trojan Horse Liposomes for Plasmid DNA Gene Therapy of the Brain

Non-viral gene therapy of the brain is enabled by the development of plasmid DNA brain delivery technology, which requires the engineering and manufacturing of nanomedicines that cross the blood-brain barrier (BBB). The development of such nanomedicines is a multi-faceted problem that requires progress at multiple levels. First, the type of nanocontainer, e.g., nanoparticle or liposome, which encapsulates the plasmid DNA, must be developed. Second, the type of molecular Trojan horse, e.g., peptide or receptor-specific monoclonal antibody (MAb), must be selected for incorporation on the surface of the nanomedicine, as this Trojan horse engages specific receptors expressed on the BBB, and the brain cell membrane, to trigger transport of the nanomedicine from blood into brain cells beyond the BBB. Third, the plasmid DNA must be engineered without bacterial elements, such as antibiotic resistance genes, to enable administration to humans; the plasmid DNA must also be engineered with tissue-specific gene promoters upstream of the therapeutic gene, to insure gene expression in the target organ with minimal off-target expression. Fourth, upstream manufacturing of the nanomedicine must be developed and scalable so as to meet market demand for the target disease, e.g., annual long-term treatment of 1,000 patients with an orphan disease, short term treatment of 10,000 patients with malignant glioma, or 100,000 patients with new onset Parkinson's disease. Fifth, downstream manufacturing problems, such as nanomedicine lyophilization, must be solved to ensure the nanomedicine has a commercially viable shelf-life for treatment of CNS disease in humans.

Protective Functions of Reactive Astrocytes Following Central Nervous System Insult

Astrocytes play important roles in numerous central nervous system disorders including autoimmune inflammatory, hypoxic, and degenerative diseases such as Multiple Sclerosis, ischemic stroke, and Alzheimer’s disease. Depending on the spatial and temporal context, activated astrocytes may contribute to the pathogenesis, progression, and recovery of disease. Recent progress in the dissection of transcriptional responses to varying forms of central nervous system insult has shed light on the mechanisms that govern the complexity of reactive astrocyte functions. While a large body of research focuses on the pathogenic effects of reactive astrocytes, little is known about how they limit inflammation and contribute to tissue regeneration. However, these protective astrocyte pathways might be of relevance for the understanding of the underlying pathology in disease and may lead to novel targeted approaches to treat autoimmune inflammatory and degenerative disorders of the central nervous system. In this review article, we have revisited the emerging concept of protective astrocyte functions and discuss their role in the recovery from inflammatory and ischemic disease as well as their role in degenerative disorders. Focusing on soluble astrocyte derived mediators, we aggregate the existing knowledge on astrocyte functions in the maintenance of homeostasis as well as their reparative and tissue-protective function after acute lesions and in neurodegenerative disorders. Finally, we give an outlook of how these mediators may guide future therapeutic strategies to tackle yet untreatable disorders of the central nervous system.

Overexpression of GSK-3β in Adult Tet-OFF GSK-3β Transgenic Mice, and Not During Embryonic or Postnatal Development, Induces Tau Phosphorylation, Neurodegeneration and Learning Deficits

GSK-3β or tau-kinase I is particularly abundant in the central nervous system (CNS), playing a key role in the pathogenesis of Alzheimer’s disease (AD). Accordingly, transgenic mouse models overexpressing this kinase recapitulate some aspects of this disease, such as tau hyperphosphorylation, neuronal death, and microgliosis. These alterations have been studied in mouse models showing GSK-3β overexpression from birth. In this case, some of these alterations may be due to adaptations that occur during development. Here we explored the potential of the Tet-OFF conditional system in the murine CamKIIα-tTA/GSK-3β model to increase the activity of GSK-3β only during adulthood. To this end, the overexpression of GSK-3β remained OFF during embryonic and postnatal development by administration of doxycycline in drinking water for 6 months, while it was turned ON in adult animals by removal of the treatment for 6 months. In these conditions, the CamKIIα-tTA/GSK-3β mouse is characterized by an increase in phosphorylated tau, cell death, and microgliosis. Furthermore, the increase in GSK-3β expression in the adult animals triggered a cognitive deficit, as determined through the hippocampus-dependent object recognition test (OR). These results demonstrate that the GSK-3β plays a key role in AD and that previously published data with other transgenic models are neither caused by or a consequence of adaptations to high levels of the enzyme during development.

Plasmid DNA gene therapy of the Niemann-Pick C1 mouse with transferrin receptor-targeted Trojan horse liposomes

Niemann-Pick C1 (NPC1) is a lysosomal cholesterol storage disorder, that severely affects the brain, and is caused by mutations in the NPC1 gene, which encodes an intracellular membrane transporter of non-esterified cholesterol. Therapeutic options for NPC1 are few, and classical enzyme replacement therapy with the recombinant protein is not possible as the NPC1 gene product is an insoluble membrane protein, which increases the need for development of gene therapy for NPC1. While viral based gene therapy is under development, it is important to investigate alternative approaches to brain gene therapy without viral vectors. The present work develops a plasmid DNA approach to gene therapy of NPC1 using Trojan horse liposomes (THLs), wherein the plasmid DNA is encapsulated in 100 nm pegylated liposomes, which are targeted to organs with a monoclonal antibody against the mouse transferrin receptor. THLs were encapsulated with a 8.0 kb plasmid DNA encoding the 3.9 kb human NPC1 open reading frame, under the influence of a 1.5 kb platelet derived growth factor B (PDGFB) promoter. THLs were administered weekly beginning at 6–7 weeks in the NPC1^−/− null mouse, and delivery of the plasmid DNA, and NPC1 mRNA expression in brain, spleen, and liver were confirmed by quantitative PCR. THL treatment reduced tissue inclusion bodies in brain, and peripheral organs, but did not prolong lifespan in these mice. The work suggests that early treatment after birth may be required to reverse this disease model with NPC1 gene replacement therapy.

Platelet-derived growth factor activates nociceptive neurons by inhibiting M-current and contributes to inflammatory pain

Supplemental Digital Content is Available in the Text.

Our work reveals that the platelet-derived growth factor-BB, by inhibiting nociceptive M-type potassium channels, acts as a pain-inducing proinflammatory factor that significantly contributes to inflammatory pain.

Endogenous inflammatory mediators contribute to the pathogenesis of pain by acting on nociceptors, specialized sensory neurons that detect noxious stimuli. Here, we describe a new factor mediating inflammatory pain. We show that platelet-derived growth factor (PDGF)-BB applied in vitro causes repetitive firing of dissociated nociceptor-like rat dorsal root ganglion neurons and decreased their threshold for action potential generation. Injection of PDGF-BB into the paw produced nocifensive behavior in rats and led to thermal and mechanical pain hypersensitivity. We further detailed the biophysical mechanisms of these PDGF-BB effects and show that PDGF receptor–induced inhibition of nociceptive M-current underlies PDGF-BB–mediated nociceptive hyperexcitability. Moreover, in vivo sequestration of PDGF or inhibition of the PDGF receptor attenuates acute formalin-induced inflammatory pain. Our discovery of a new pain-facilitating proinflammatory mediator, which by inhibiting M-current activates nociceptive neurons and thus contributes to inflammatory pain, improves our understanding of inflammatory pain pathophysiology and may have important clinical implications for pain treatment.

Chronic Presence of Oligomeric Aβ Differentially Modulates Spine Parameters in the Hippocampus and Cortex of Mice With Low APP Transgene Expression

Alzheimer’s disease is regarded as a synaptopathy with a long presymptomatic phase. Soluble, oligomeric amyloid-β (Aβ) is thought to play a causative role in this disease, which eventually leads to cognitive decline. However, most animal studies have employed mice expressing high levels of the Aβ precursor protein (APP) transgene to drive pathology. Here, to understand how the principal neurons in different brain regions cope with moderate, chronically present levels of Aβ, we employed transgenic mice expressing equal levels of mouse and human APP carrying a combination of three familial AD (FAD)-linked mutations (Swedish, Dutch, and London), that develop plaques only in old age. We analyzed dendritic spine parameters in hippocampal and cortical brain regions after targeted expression of EGFP to allow high-resolution imaging, followed by algorithm-based evaluation of mice of both sexes from adolescence to old age. We report that Aβ species gradually accumulated throughout the life of APP_SDL mice, but not the oligomeric forms, and that the amount of membrane-associated oligomers decreased at the onset of plaque formation. We observed an age-dependent loss of thin spines under most conditions as an indicator of a loss of synaptic plasticity in older mice. We further found that hippocampal pyramidal neurons respond to increased Aβ levels by lowering spine density and shifting spine morphology, which reached significance in the CA1 subfield. In contrast, the spine density in cortical pyramidal neurons of APP_SDL mice was unchanged. We also observed an increase in the protein levels of PSD-95 and Arc in the hippocampus and cortex, respectively. Our data demonstrated that increased concentrations of Aβ have diverse effects on dendritic spines in the brain and suggest that hippocampal and cortical neurons have different adaptive and compensatory capacity during their lifetime. Our data also indicated that spine morphology differs between sexes in a region-specific manner.

EGFR Signaling Causes Morphine Tolerance and Mechanical Sensitization in Rats

The safety and efficacy of opioids are compromised as analgesic tolerance develops. Opioids are also ineffective against neuropathic pain. Recent reports have suggested that inhibitors of the epidermal growth factor receptor (EGFR), a receptor tyrosine kinase (RTK), may have analgesic effects in cancer patients suffering from neuropathic pain. It has been shown that the platelet-derived growth factor receptor-β (PDGFR-β), an RTK that has been shown to interact with the EGFR, mediates opioid tolerance but does not induce analgesia. Therefore, we sought to determine whether EGFR signaling was involved in opioid tolerance and whether EGFR and PDGFR signaling could induce pain in rats. We found that gefitinib, an EGFR antagonist, eliminated morphine tolerance. In addition, repeated EGF administration rendered animals unresponsive to subsequent analgesic doses of morphine, a phenomenon we call "pre-tolerance." Using a nerve injury model, we found that gefitinib alone was not analgesic. Rather, it reversed insensitivity to morphine analgesia (pre-tolerance) caused by the release of EGF by injured nerves. We also showed that repeated, but not acute EGF or PDGF-BB administration induced mechanical hypersensitivity in rats. EGFR and PDGFR-β signaling interacted to produce this sensitization. EGFR was widely expressed in primary sensory afferent cell bodies, demonstrating a neuroanatomical substrate for our findings. Taken together, our results suggest a direct mechanistic link between opioid tolerance and mechanical sensitization. EGFR antagonism could eventually play an important clinical role in the treatment of opioid tolerance and neuropathic pain that is refractory to opioid treatment.

Suppression of PDGF induces neuronal apoptosis after neonatal cerebral hypoxia and ischemia by inhibiting P-PI3K and P-AKT signaling pathways

Neonatal hypoxic-ischemic encephalopathy (HIE) always results in severe neurologic dysfunction, nevertheless effective treatments are limited and the underlying mechanism also remains unclear. In this study, we firstly established the neonatal HIE model in the postnatal day 7 SD rats, Zea-Longa score and TTC staining were employed to assess the neurological behavior and infarct volume of the brain after cerebral hypoxia-ischemia (HI). Afterwards, protein chip was adopted to detect the differential proteins in the right cortex, hippocampus and lung, ultimately, PDGF was noticed. Then, immunohistochemistry, immunofluorescence double staining of NeuN/PDGF, and western blot were used to validate the expression level of PDGF in the cortex and hippocampus at 6 hours (h), 12 h and 24 h after HI. To determine the role of PDGF, the primary cortical neurons were prepared and performed PDGF shRNA administration. The results showed that HIE induced a severe behavioral dysfunction and brain infarction in neonatal rats, and the expression of PDGF in right cortex and hippocampus was remarkably increased after HI. Whereas, suppressing PDGF resulted in a significant loss of neurons and inhibition of neurite growth. Moreover, the protein level of P-PI3K and P-AKT signaling pathways were largely decreased following PDGF-shRNA application in the cortical neurons. In conclusion, PDGF suppression aggravated neuronal dysfunction, and the underlying mechanism is associated with inhibiting the phosphorylation of P-PI3K and P-AKT. Together, PDGF regulating PI3K and AKT may be an important panel in HIE events and therefore may provide possible strategy for the treatment of HIE in future clinic trail.

Angioneurins - Key regulators of blood-brain barrier integrity during hypoxic and ischemic brain injury

The loss of blood-brain barrier (BBB) integrity leading to vasogenic edema and brain swelling is a common feature of hypoxic/ischemic brain diseases such as stroke, but is also central to the etiology of other CNS disorders. In the past decades, numerous proteins, belonging to the family of angioneurins, have gained increasing attention as potential therapeutic targets for ischemic stroke, but also other CNS diseases attributed to BBB dysfunction. Angioneurins encompass mediators that affect both neuronal and vascular function. Recently, increasing evidence has been accumulated that certain angioneurins critically determine disease progression and outcome in stroke among others through multifaceted effects on the compromised BBB. Here, we will give a concise overview about the family of angioneurins. We further describe the most important cellular and molecular components that contribute to structural integrity and low permeability of the BBB under steady-state conditions. We then discuss BBB alterations in ischemic stroke, and highlight underlying cellular and molecular mechanisms. For the most prominent angioneurin family members including vascular endothelial growth factors, angiopoietins, platelet-derived growth factors and erythropoietin, we will summarize current scientific literature from experimental studies in animal models, and if available from clinical trials, on the following points: (i) spatiotemporal expression of these factors in the healthy and hypoxic/ischemic CNS, (ii) impact of loss- or gain-of-function during cerebral hypoxia/ischemia for BBB integrity and beyond, and (iii) potential underlying molecular mechanisms. Moreover, we will highlight novel therapeutic strategies based on the activation of endogenous angioneurins that might improve BBB dysfuntion during ischemic stroke.

Emergence of synaptic and cognitive impairment in a mature-onset APP mouse model of Alzheimer's disease

The synaptic changes underlying the onset of cognitive impairment in Alzheimer’s disease (AD) are poorly understood. In contrast to the well documented inhibition of long-term potentiation (LTP) in CA3-CA1 synapses by acute Aβ application in adult neurons from rodents, young amyloid precursor protein (APP) transgenic mouse models often, surprisingly, show normal LTP. This suggests that there may be important differences between mature-onset and developmental-onset APP expression/ Aβ accumulation and the ensuing synaptic and behavioural phenotype. Here, in agreement with previous studies, we observed that developmental expression of APP_Sw,Ind (3–4 month old mice from line 102, PLoS Med 2:e355, 2005), resulted in reduced basal synaptic transmission in CA3-CA1 synapses, normal LTP, impaired spatial working memory, but normal spatial reference memory. To analyse early Aβ-mediated synaptic dysfunction and cognitive impairment in a more mature brain, we used controllable mature-onset APP_Sw,Ind expression in line 102 mice. Within 3 weeks of mature-onset APP_Sw,Ind expression and Aβ accumulation, we detected the first synaptic dysfunction: an impairment of LTP in hippocampal CA3-CA1 synapses. Cognitively, at this time point, we observed a deficit in short-term memory. A reduction in basal synaptic strength and deficit in long-term associative spatial memory were only evident following 12 weeks of APP_Sw,Ind expression. Importantly, the plasticity impairment observed after 3 weeks of mature-onset APP expression is reversible. Together, these findings demonstrate important differences between developmental and mature-onset APP expression. Further research targeted at this early stage of synaptic dysfunction could help identify mechanisms to treat cognitive impairment in mild cognitive impairment (MCI) and early AD.

Optogenetic control of iPS cell-derived neurons in 2D and 3D culture systems using channelrhodopsin-2 expression driven by the synapsin-1 and calcium-calmodulin kinase II promoters

Development of an optogenetically controllable human neural network model in three-dimensional (3D) cultures can provide an investigative system that is more physiologically relevant and better able to mimic aspects of human brain function. Light-sensitive neurons were generated by transducing channelrhodopsin-2 (ChR2) into human induced pluripotent stem cell (hiPSC) derived neural progenitor cells (Axol) using lentiviruses and cell-type specific promoters. A mixed population of human iPSC-derived cortical neurons, astrocytes and progenitor cells were obtained (Axol-ChR2) upon neural differentiation. Pan-neuronal promoter synapsin-1 (SYN1) and excitatory neuron-specific promoter calcium-calmodulin kinase II (CaMKII) were used to drive reporter gene expression in order to assess the differentiation status of the targeted cells. Expression of ChR2 and characterisation of subpopulations in differentiated Axol-ChR2 cells were evaluated using flow cytometry and immunofluorescent staining. These cells were transferred from 2D culture to 3D alginate hydrogel functionalised with arginine-glycine-aspartate (RGD) and small molecules (Y-27632). Improved RGD-alginate hydrogel was physically characterised and assessed for cell viability to serve as a generic 3D culture system for human pluripotent stem cells (hPSCs) and neuronal cells. Prior to cell encapsulation, neural network activities of Axol-ChR2 cells and primary neurons were investigated using calcium imaging. Results demonstrate that functional activities were successfully achieved through expression of ChR2- by both the CaMKII and SYN1 promoters. The RGD-alginate hydrogel system supports the growth of differentiated Axol-ChR2 cells whilst allowing detection of ChR2 expression upon light stimulation. This allows precise and non-invasive control of human neural networks in 3D.

Distinct cytokine profiles in human brains resilient to Alzheimer's pathology

Our group has previously studied the brains of some unique individuals who are able to tolerate robust amounts of Alzheimer's pathological lesions (amyloid plaques and neurofibrillary tangles) without experiencing dementia while alive. These rare resilient cases do not demonstrate the patterns of neuronal/synaptic loss that are normally found in the brains of typical demented Alzheimer's patients. Moreover, they exhibit decreased astrocyte and microglial activation markers GFAP and CD68, suggesting that a suppressed neuroinflammatory response may be implicated in human brain resilience to Alzheimer's pathology. In the present work, we used a multiplexed immunoassay to profile a panel of 27 cytokines in the brains of controls, typical demented Alzheimer's cases, and two groups of resilient cases, which possessed pathology consistent with either high probability (HP, Braak stage V-VI and CERAD 2-3) or intermediate probability (IP, Braak state III-IV and CERAD 1-3) of Alzheimer's disease in the absence of dementia. We used a multivariate partial least squares regression approach to study differences in cytokine expression between resilient cases and both Alzheimer's and control cases. Our analysis identified distinct profiles of cytokines in the entorhinal cortex (one of the earliest and most severely affected brain regions in Alzheimer's disease) that are up-regulated in both HP and IP resilient cases relative to Alzheimer's and control cases. These cytokines, including IL-1β, IL-6, IL-13, and IL-4 in HP resilient cases and IL-6, IL-10, and IP-10 in IP resilient cases, delineate differential inflammatory activity in brains resilient to Alzheimer's pathology compared to Alzheimer's cases. Of note, these cytokines all have been associated with pathogen clearance and/or the resolution of inflammation. Moreover, our analysis in the superior temporal sulcus (a multimodal association cortex that consistently accumulates Alzheimer's pathology at later stages of the disease along with overt symptoms of dementia) revealed increased expression of neurotrophic factors, such as PDGF-bb and basic FGF in resilient compared to AD cases. The same region also had reduced expression of chemokines associated with microglial recruitment, including MCP-1 in HP resilient cases and MIP-1α in IP resilient cases compared to AD. Altogether, our data suggest that different patterns of cytokine expression exist in the brains of resilient and Alzheimer's cases, link these differences to reduced glial activation, increased neuronal survival and preserved cognition in resilient cases, and reveal specific cytokine targets that may prove relevant to the identification of novel mechanisms of brain resiliency to Alzheimer's pathology.

The integration site of the APP transgene in the J20 mouse model of Alzheimer's disease

Background: Transgenic animal models are a widely used and powerful tool to investigate human disease and develop therapeutic interventions. Making a transgenic mouse involves random integration of exogenous DNA into the host genome that can have the effect of disrupting endogenous gene expression. The J20 mouse model of Alzheimer's disease (AD) is a transgenic overexpresser of human APP with familial AD mutations and has been extensively utilised in preclinical studies and our aim was to determine the genomic location of the J20 transgene insertion. Methods: We used a combination of breeding strategy and Targeted Locus Amplification with deep sequencing to identify the insertion site of the J20 transgene array. To assess RNA and protein expression of Zbtb20, we used qRT-PCR and Western Blotting. Results: We demonstrate that the J20 transgene construct has inserted within the genetic locus of endogenous mouse gene Zbtb20 on chromosome 16 in an array , disrupting expression of mRNA from this gene in adult hippocampal tissue, while expression of Zbtb20 protein remains unchanged. We note that the endogenous mouse App gene also lies on chromosome 16, although 42 Mb from the Zbtb20 locus. Conclusions: These data will be useful for future studies utilising this popular model of AD, particularly those investigating gene interactions between the J20 APP transgene and other genes present on Mmu16 in the mouse.

The integration site of the APP transgene in the J20 mouse model of Alzheimer's disease

Background: Transgenic animal models are a widely used and powerful tool to investigate human disease and develop therapeutic interventions. Making a transgenic mouse involves random integration of exogenous DNA into the host genome that can have the effect of disrupting endogenous gene expression. The J20 mouse model of Alzheimer's disease (AD) is a transgenic overexpresser of human APP with familial AD mutations and has been extensively utilised in preclinical studies and our aim was to determine the genomic location of the J20 transgene insertion. Methods: We used a combination of breeding strategy and Targeted Locus Amplification with deep sequencing to identify the insertion site of the J20 transgene array. To assess RNA and protein expression of Zbtb20, we used qRT-PCR and Western Blotting. Results: We demonstrate that the J20 transgene construct has inserted within the genetic locus of endogenous mouse gene Zbtb20 on chromosome 16 in an array , disrupting expression of mRNA from this gene in adult hippocampal tissue. Preliminary data suggests that ZBTB20 protein levels remain unchanged in this tissue, however further study is necessary. We note that the endogenous mouse App gene also lies on chromosome 16, although 42 Mb from the Zbtb20 locus. Conclusions: These data will be useful for future studies utilising this popular model of AD, particularly those investigating gene interactions between the J20 APP transgene and other genes present on Mmu16 in the mouse.

The rise of soluble platelet-derived growth factor receptor β in CSF early after subarachnoid hemorrhage correlates with cerebral vasospasm

Platelet-derived growth factor β (PDGFβ) has been proposed to contribute to the development of cerebral vasospasm (CVS) after subarachnoid hemorrhage (SAH), and soluble PDGFRβ (sPDGFRβ) is considered to be an inhibitor of PDGF signaling. We aimed at determining the sPDGFRβ concentrations in the cerebrospinal fluid (CSF) of patients with aneurysmal SAH (aSAH) and analyzing the relationship between sPDGFRβ level and CVS. CSF was sampled from 32 patients who suffered aSAH and five normal controls. Enzyme-linked immunosorbent assay was performed to determine the sPDGFRβ concentrations in the CSF. Functional outcome was assessed using modified Rankin scale (mRS) at 6 months after aSAH. CVS was identified using transcranial Doppler or angio-CT or DSA. The cutoff of sPDGFRβ for CVS was defined on the ROC curve. The concentrations of sPDGFRβ following aSAH were both higher than those of normal controls on days 1-3 and 4-6, and peaked on days 7-9 post-SAH. The cutoff value of sPDGFRβ level on days 1-3 for CVS was defined as 975.38 pg/ml according to the ROC curve (AUC = 0.680, p = 0.082). In addition, CSF sPDGFRβ concentrations correlated with CVS (r = 0.416, p = 0.018), and multivariate analysis indicated that sPDGFRβ level higher than 975.38 pg/ml on days 1-3 was an independent predictor of CVS (p = 0.001, OR = 19.22, 95% CI: 3.27-113.03), but not for unfavorable outcome after aSAH in the current study. CSF sPDGFRβ level increases after aSAH and is higher in patients who developed CVS, and sPDGFRβ level higher than 975.38 pg/ml on days 1-3 is a potential predictor for CVS after SAH.

Practical considerations for choosing a mouse model of Alzheimer's disease

Alzheimer’s disease (AD) is behaviorally identified by progressive memory impairment and pathologically characterized by the triad of β-amyloid plaques, neurofibrillary tangles, and neurodegeneration. Genetic mutations and risk factors have been identified that are either causal or modify the disease progression. These genetic and pathological features serve as basis for the creation and validation of mouse models of AD. Efforts made in the past quarter-century have produced over 100 genetically engineered mouse lines that recapitulate some aspects of AD clinicopathology. These models have been valuable resources for understanding genetic interactions that contribute to disease and cellular reactions that are engaged in response. Here we focus on mouse models that have been widely used stalwarts of the field or that are recently developed bellwethers of the future. Rather than providing a summary of each model, we endeavor to compare and contrast the genetic approaches employed and to discuss their respective advantages and limitations. We offer a critical account of the variables which may contribute to inconsistent findings and the factors that should be considered when choosing a model and interpreting the results. We hope to present an insightful review of current AD mouse models and to provide a practical guide for selecting models best matched to the experimental question at hand.

Oligomer-prone E57K-mutant alpha-synuclein exacerbates integration deficit of adult hippocampal newborn neurons in transgenic mice

In the adult mammalian hippocampus, new neurons are constantly added to the dentate gyrus. Adult neurogenesis is impaired in several neurodegenerative mouse models including α-synuclein (a-syn) transgenic mice. Among different a-syn species, a-syn oligomers were reported to be the most toxic species for neurons. Here, we studied the impact of wild-type vs. oligomer-prone a-syn on neurogenesis. We compared the wild-type a-syn transgenic mouse model (Thy1-WTS) to its equivalent transgenic for oligomer-prone E57K-mutant a-syn (Thy1-E57K). Transgenic a-syn was highly expressed within the hippocampus of both models, but was not present within adult neural stem cells and neuroblasts. Proliferation and survival of newly generated neurons were unchanged in both transgenic models. Thy1-WTS showed a minor integration deficit regarding mushroom spine density of newborn neurons, whereas Thy1-E57K exhibited a severe reduction of all spines. We conclude that cell-extrinsic a-syn impairs mushroom spine formation of adult newborn neurons and that oligomer-prone a-syn exacerbates this integration deficit. Moreover, our data suggest that a-syn reduces the survival of newborn neurons by a cell-intrinsic mechanism during the early neuroblast development. The finding of increased spine pathology in Thy1-E57K is a new pathogenic function of oligomeric a-syn and precedes overt neurodegeneration. Thus, it may constitute a readout for therapeutic approaches.

Effects of ischemic preconditioning on PDGF-BB expression in the gerbil hippocampal CA1 region following transient cerebral ischemia

Ischemic preconditioning (IPC) is induced by exposure to brief durations of transient ischemia, which results in ischemic tolerance to a subsequent longer or lethal period of ischemia. In the present study, the effects of IPC (2 min of transient cerebral ischemia) were examined on immunoreactivity of platelet‑derived growth factor (PDGF)‑BB and on neuroprotection in the gerbil hippocampal CA1 region following lethal transient cerebral ischemia (LTCI; 5 min of transient cerebral ischemia). IPC was subjected to a 2‑min sublethal ischemia and a LTCI was given 5‑min transient ischemia. The animals in all of the groups were given recovery times of 1, 2 and 5 days and change in PDGF‑BB immunoreactivity was examined as was the neuronal damage/death in the hippocampus induced by LTCI. LTCI induced a significant loss of pyramidal neurons in the hippocampal CA1 region 5 days after LTCI, and significantly decreased PDGF‑BB immunoreactivity in the CA1 pyramidal neurons from day 1 after LTCI. Conversely, IPC effectively protected the CA1 pyramidal neurons from LTCI and increased PDGF‑BB immunoreactivity in the CA1 pyramidal neurons post‑LTCI. In conclusion, the results demonstrated that LTCI significantly altered PDGF‑BB immunoreactivity in pyramidal neurons in the hippocampal CA1 region, whereas IPC increased the immunoreactivity. These findings indicated that PDGF‑BB may be associated with IPC‑mediated neuroprotection.

Neuroprotection and Blood-Brain Barrier Restoration by Salubrinal After a Cortical Stab Injury

Following a central nervous system (CNS) injury, restoration of the blood-brain barrier (BBB) integrity is essential for recovering homeostasis. When this process is delayed or impeded, blood substances and cells enter the CNS parenchyma, initiating an additional inflammatory process that extends the initial injury and causes so-called secondary neuronal loss. Astrocytes and profibrotic mesenchymal cells react to the injury and migrate to the lesion site, creating a new glia limitans that restores the BBB. This process is beneficial for the resolution of the inflammation, neuronal survival, and the initiation of the healing process. Salubrinal is a small molecule with neuroprotective properties in different animal models of stroke and trauma to the CNS. Here, we show that salubrinal increased neuronal survival in the neighbourhood of a cerebral cortex stab injury. Moreover, salubrinal reduced cortical blood leakage into the parenchyma of injured animals compared with injured controls. Adjacent to the site of injury, salubrinal induced immunoreactivity for platelet-derived growth factor subunit B (PDGF-B), a specific mitogenic factor for mesenchymal cells. This effect might be responsible for the increased immunoreactivity for fibronectin and the decreased activation of microglia and macrophages in injured mice treated with salubrinal, compared with injured controls. The immunoreactivity for PDGF-B colocalized with neuronal nuclei (NeuN), suggesting that cortical neurons in the proximity of the injury were the main source of PDGF-B. Our results suggest that after an injury, neurons play an important role in both, the healing process and the restoration of the BBB integrity. J. Cell. Physiol. 232: 1501-1510, 2017. © 2016 Wiley Periodicals, Inc.

Autophagy modulates SNCA/α-synuclein release, thereby generating a hostile microenvironment

SNCA/α-synuclein aggregation plays a crucial role in synucleinopathies such as Parkinson disease and dementia with Lewy bodies. Aggregating and nonaggregating SNCA species are degraded by the autophagy-lysosomal pathway (ALP). Previously, we have shown that the ALP is not only responsible for SNCA degradation but is also involved in the intracellular aggregation process of SNCA. An additional role of extracellular SNCA in the pathology of synucleinopathies substantiating a prion-like propagation hypothesis has been suggested since released SNCA species and spreading of SNCA pathology throughout neural cells have been observed. However, the molecular interplay between intracellular pathways, SNCA aggregation, release, and response of the local microenvironment remains unknown. Here, we attributed SNCA-induced toxicity mainly to secreted species in a cell culture model of SNCA aggregation and in SNCA transgenic mice: We showed that ALP inhibition by bafilomycinA1 reduced intracellular SNCA aggregation but increased secretion of smaller oligomers that exacerbated microenvironmental response including uptake, inflammation, and cellular damage. Low-aggregated SNCA was predominantly released by exosomes and RAB11A-associated pathways whereas high-aggregated SNCA was secreted by membrane shedding. In summary, our study revealed a novel role of the ALP by linking protein degradation to nonclassical secretion for toxic SNCA species. Thus, impaired ALP in the diseased brain not only limits intracellular degradation of misfolded proteins, but also leads to a detrimental microenvironmental response due to enhanced SNCA secretion. These findings suggest that the major toxic role of SNCA is related to its extracellular species and further supports a protective role of intracellular SNCA aggregation.

PDGFR-β Plays a Key Role in the Ectopic Migration of Neuroblasts in Cerebral Stroke

The neuroprotective agents and induction of endogenous neurogenesis remain to be the urgent issues to be established for the care of cerebral stroke. Platelet-derived growth factor receptor beta (PDGFR-β) is mainly expressed in neural stem/progenitor cells (NSPCs), neurons and vascular pericytes of the brain; however, the role in pathological neurogenesis remains elusive. To this end, we examined the role of PDGFR-β in the migration and proliferation of NSPCs after stroke. A transient middle cerebral-arterial occlusion (MCAO) was introduced into the mice with conditional Pdgfrb-gene inactivation, including N-PRβ-KO mice where the Pdgfrb-gene was mostly inactivated in the brain except that in vascular pericytes, and E-PRβ-KO mice with tamoxifen-induced systemic Pdgfrb-gene inactivation. The migration of the DCX(+) neuroblasts from the subventricular zone toward the ischemic core was highly increased in N-PRβ-KO, but not in E-PRβ-KO as compared to Pdgfrb-gene preserving control mice. We showed that CXCL12, a potent chemoattractant for CXCR4-expressing NSPCs, was upregulated in the ischemic lesion of N-PRβ-KO mice. Furthermore, integrin α3 intrinsically expressed in NSPCs that critically mediates extracellular matrix-dependent migration, was upregulated in N-PRβ-KO after MCAO. NSPCs isolated from N-PRβ-KO rapidly migrated on the surface coated with collagen type IV or fibronectin that are abundant in vascular niche and ischemic core. PDGFR-β was suggested to be critically involved in pathological neurogenesis through the regulation of lesion-derived chemoattractant as well as intrinsic signal of NSPCs, and we believe that a coordinated regulation of these molecular events may be able to improve neurogenesis in injured brain for further functional recovery.

Neural Plasticity in Multiple Sclerosis: The Functional and Molecular Background

Multiple sclerosis is an autoimmune neurodegenerative disorder resulting in motor dysfunction and cognitive decline. The inflammatory and neurodegenerative changes seen in the brains of MS patients lead to progressive disability and increasing brain atrophy. The most common type of MS is characterized by episodes of clinical exacerbations and remissions. This suggests the presence of compensating mechanisms for accumulating damage. Apart from the widely known repair mechanisms like remyelination, another important phenomenon is neuronal plasticity. Initially, neuroplasticity was connected with the developmental stages of life; however, there is now growing evidence confirming that structural and functional reorganization occurs throughout our lifetime. Several functional studies, utilizing such techniques as fMRI, TBS, or MRS, have provided valuable data about the presence of neuronal plasticity in MS patients. CNS ability to compensate for neuronal damage is most evident in RR-MS; however it has been shown that brain plasticity is also preserved in patients with substantial brain damage. Regardless of the numerous studies, the molecular background of neuronal plasticity in MS is still not well understood. Several factors, like IL-1β, BDNF, PDGF, or CB1Rs, have been implicated in functional recovery from the acute phase of MS and are thus considered as potential therapeutic targets.

The temporal expression pattern of alpha-synuclein modulates olfactory neurogenesis in transgenic mice

Background

Adult neurogenesis mirrors the brain´s endogenous capacity to generate new neurons throughout life. In the subventricular zone/ olfactory bulb system adult neurogenesis is linked to physiological olfactory function and has been shown to be impaired in murine models of neuronal alpha-Synuclein overexpression. We analyzed the degree and temporo-spatial dynamics of adult olfactory bulb neurogenesis in transgenic mice expressing human wild-type alpha-Synuclein (WTS) under the murine Thy1 (mThy1) promoter, a model known to have a particularly high tg expression associated with impaired olfaction.

Results

Survival of newly generated neurons (NeuN-positive) in the olfactory bulb was unchanged in mThy1 transgenic animals. Due to decreased dopaminergic differentiation a reduction in new dopaminergic neurons within the olfactory bulb glomerular layer was present. This is in contrast to our previously published data on transgenic animals that express WTS under the control of the human platelet-derived growth factor β (PDGF) promoter, that display a widespread decrease in survival of newly generated neurons in regions of adult neurogenesis, resulting in a much more pronounced neurogenesis deficit. Temporal and quantitative expression analysis using immunofluorescence co-localization analysis and Western blots revealed that in comparison to PDGF transgenic animals, in mThy1 transgenic animals WTS is expressed from later stages of neuronal maturation only but at significantly higher levels both in the olfactory bulb and cortex.

Conclusions

The dissociation between higher absolute expression levels of alpha-Synuclein but less severe impact on adult olfactory neurogenesis in mThy1 transgenic mice highlights the importance of temporal expression characteristics of alpha-Synuclein on the maturation of newborn neurons.

The wish to cure and the curiosity to investigate - or how I used my life to become a physician-scientist

The author describes how he became a physician-scientist: difficulties he had to overcome coming from outside of the US (visa, funding, resident training), and his way back to Germany, while experiencing the thrill of actively participating in moving science. Setbacks, scientific success, adaptation to new developments, and the encounter of kindred spirits characterize this lifelong effort.

Compartmental organization of synaptic inputs to parvalbumin-expressing GABAergic neurons in mouse primary somatosensory cortex

Parvalbumin (PV)-positive fast-spiking cells in the neocortex are known to generate gamma oscillations by mutual chemical and electrical connections. Recent findings suggest that this rhythm might be responsible for higher-order brain functions, and related to psychiatric disorders. To elucidate the precise structural rules of the connections of PV neurons, we first produced genetic tools. Using a lentiviral expression system, we developed neuron-specific promoters and a new reporter protein that labels the somatodendritic membrane of neurons. We applied the reporter protein to the generation of transgenic mice, and succeeded in visualizing the dendrites and cell bodies of PV neurons efficiently. Then we analyzed excitatory and inhibitory inputs to PV neurons in the primary somatosensory cortex using the mice. Corticocortical glutamatergic inputs were more frequently found on the distal dendrites than on the soma, whereas thalamocortical inputs did not differ between the proximal and distal portions. Corticocortical inhibitory inputs were more densely distributed on the soma than on the dendrites. We further investigated which types of neocortical GABAergic neurons preferred the PV soma over their dendrites. We revealed that the somatic and dendritic compartments principally received GABAergic inputs from vasoactive intestinal polypeptide (VIP)-positive and PV neurons, respectively. This compartmental organization suggests that PV neurons communicate with each other mainly via the dendrites, and that their activity is effectively controlled by the somatic inputs of VIP neurons. These findings provide new insights into the neuronal circuits involving PV neurons, and contribute to a better understanding of brain functions and mental disorders.

Platelet-derived growth factor receptor-β antagonism restores morphine analgesic potency against neuropathic pain

Background

Chronic, intractable pain is a problem of pandemic proportions. Pain caused by nerve injuries (neuropathic pain) is extremely difficult to treat. For centuries, opiates such as morphine have been the first-line treatment for severe chronic pain. However, opiates are often ineffective against neuropathic pain, leaving few options for suffering patients. We previously demonstrated that platelet-derived growth factor- β (PDGFR-β) inhibition completely eliminated morphine tolerance. In these studies, we determined whether PDGFR-β inhibition could improve the effectiveness of morphine for neuropathic pain treatment.

Results and Findings

Spinal nerve ligation was performed in male Sprague-Dawley rats. The clinically used PDGFR antagonist imatinib did not relieve mechanical pain in a nerve injury model as determined by Von Frey assay. Surprisingly, combining imatinib with a previously ineffective dose of morphine led to complete pain relief. Scavenging released PDGF-B also markedly augmented the analgesic effect of morphine.

Conclusions

These findings suggest the novel hypothesis that PDGF-B released by injured nerves renders animals resistant to morphine, implying that PDGFR-β inhibition could potentially eliminate the tremendous suffering caused by neuropathic pain.

Growth factors and synaptic plasticity in relapsing-remitting multiple sclerosis

During multiple sclerosis (MS) inflammatory attacks, and in subsequent clinical recovery phases, immune cells contribute to neuronal and oligodendroglial cell survival and tissue repair by secreting growth factors. Animal studies showed that growth factors also play a substantial role in regulating synaptic plasticity, and namely in long-term potentiation (LTP). LTP could drive clinical recovery in relapsing patients by restoring the excitability of denervated neurons. We recently reported that maintenance of synaptic plasticity reserve is crucial to contrast clinical deterioration in MS and that the platelet-derived growth factor (PDGF) may play a key role in its regulation. We also reported that a Hebbian form of LTP-like cortical plasticity, explored by paired associative stimulation (PAS), correlates with clinical recovery from a relapse in MS. Here, we explored the role of PDGF in clinical recovery and in adaptive neuroplasticity in relapsing-remitting MS (RR-MS) patients. We found a correlation between the cerebrospinal fluid (CSF) PDGF concentrations and the extent of clinical recovery after a relapse, as full recovery was more likely observed in patients with high PDGF concentrations and poor recovery in subjects with low PDGF levels. Consistently with the idea that PDGF-driven synaptic plasticity contributes to attenuate the clinical consequences of tissue damage in RR-MS, we also found a striking correlation between CSF levels of PDGF and the amplitude of LTP-like cortical plasticity explored by PAS. CSF levels of fibroblast growth factor, granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor did not correlate with clinical recovery nor with measures of synaptic transmission and plasticity.

Synaptic plasticity and PDGF signaling defects underlie clinical progression in multiple sclerosis

Neuroplasticity is essential to prevent clinical worsening despite continuing neuronal loss in several brain diseases, including multiple sclerosis (MS). The precise nature of the adaptation mechanisms taking place in MS brains, ensuring protection from disability appearance and accumulation, is however unknown. Here, we explored the hypothesis that long-term synaptic potentiation (LTP), potentially able to minimize the effects of neuronal loss by providing extra excitation of denervated neurons, is the most relevant form of adaptive plasticity in stable MS patients, and it is disrupted in progressing MS patients. We found that LTP, explored by means of transcranial magnetic theta burst stimulation over the primary motor cortex, was still possible, and even favored, in stable relapsing-remitting (RR-MS) patients, whereas it was absent in individuals with primary progressive MS (PP-MS). We also provided evidence that platelet-derived growth factor (PDGF) plays a substantial role in favoring both LTP and brain reserve in MS patients, as this molecule: (1) was reduced in the CSF of PP-MS patients, (2) enhanced LTP emergence in hippocampal mouse brain slices, (3) was associated with more pronounced LTP in RR-MS patients, and (4) was associated with the clinical compensation of new brain lesion formation in RR-MS. Our results show that brain plasticity reserve, in the form of LTP, is crucial to contrast clinical deterioration in MS. Enhancing PDGF signaling might represent a valuable treatment option to maintain brain reserve and to attenuate the clinical consequences of neuronal damage in the progressive phases of MS and in other neurodegenerative disorders.