Uncoupling of neurodegeneration and gliosis in a murine model of juvenile cortical lesion

Introducing the brain erythropoietin circle to explain adaptive brain hardware upgrade and improved performance

Executive functions, learning, attention, and processing speed are imperative facets of cognitive performance, affected in neuropsychiatric disorders. In clinical studies on different patient groups, recombinant human (rh) erythropoietin (EPO) lastingly improved higher cognition and reduced brain matter loss. Correspondingly, rhEPO treatment of young rodents or EPO receptor (EPOR) overexpression in pyramidal neurons caused remarkable and enduring cognitive improvement, together with enhanced hippocampal long-term potentiation. The 'brain hardware upgrade', underlying these observations, includes an EPO induced ~20% increase in pyramidal neurons and oligodendrocytes in cornu ammonis hippocampi in the absence of elevated DNA synthesis. In parallel, EPO reduces microglia numbers and dampens their activity and metabolism as prerequisites for undisturbed EPO-driven differentiation of pre-existing local neuronal precursors. These processes depend on neuronal and microglial EPOR. This novel mechanism of powerful postnatal neurogenesis, outside the classical neurogenic niches, and on-demand delivery of new cells, paralleled by dendritic spine increase, let us hypothesize a physiological procognitive role of hypoxia-induced endogenous EPO in brain, which we imitate by rhEPO treatment. Here we delineate the brain EPO circle as working model explaining adaptive 'brain hardware upgrade' and improved performance. In this fundamental regulatory circle, neuronal networks, challenged by motor-cognitive tasks, drift into transient 'functional hypoxia', thereby triggering neuronal EPO/EPOR expression.

Brain erythropoietin fine-tunes a counterbalance between neurodifferentiation and microglia in the adult hippocampus

In adult cornu ammonis hippocampi, erythropoietin (EPO) expression drives the differentiation of new neurons, independent of DNA synthesis, and increases dendritic spine density. This substantial brain hardware upgrade is part of a regulatory circle: during motor-cognitive challenge, neurons experience "functional" hypoxia, triggering neuronal EPO production, which in turn promotes improved performance. Here, we show an unexpected involvement of resident microglia. During EPO upregulation and stimulated neurodifferentiation, either by functional or inspiratory hypoxia, microglia numbers decrease. Treating mice with recombinant human (rh)EPO or exposure to hypoxia recapitulates these changes and reveals the involvement of neuronally expressed IL-34 and microglial CSF1R. Surprisingly, EPO affects microglia in phases, initially by inducing apoptosis, later by reducing proliferation, and overall dampens microglia activity and metabolism, as verified by selective genetic targeting of either the microglial or pyramidal neuronal EPO receptor. We suggest that during accelerating neuronal differentiation, EPO acts as regulator of the CSF1R-dependent microglia.

Revisiting adult neurogenesis and the role of erythropoietin for neuronal and oligodendroglial differentiation in the hippocampus

Recombinant human erythropoietin (EPO) improves cognitive performance in neuropsychiatric diseases ranging from schizophrenia and multiple sclerosis to major depression and bipolar disease. This consistent EPO effect on cognition is independent of its role in hematopoiesis. The cellular mechanisms of action in brain, however, have remained unclear. Here we studied healthy young mice and observed that 3-week EPO administration was associated with an increased number of pyramidal neurons and oligodendrocytes in the hippocampus of ~20%. Under constant cognitive challenge, neuron numbers remained elevated until >6 months of age. Surprisingly, this increase occurred in absence of altered cell proliferation or apoptosis. After feeding a ¹⁵N-leucine diet, we used nanoscopic secondary ion mass spectrometry, and found that in EPO-treated mice, an equivalent number of neurons was defined by elevated ¹⁵N-leucine incorporation. In EPO-treated NG2-Cre-ERT2 mice, we confirmed enhanced differentiation of preexisting oligodendrocyte precursors in the absence of elevated DNA synthesis. A corresponding analysis of the neuronal lineage awaits the identification of suitable neuronal markers. In cultured neurospheres, EPO reduced Sox9 and stimulated miR124, associated with advanced neuronal differentiation. We are discussing a resulting working model in which EPO drives the differentiation of non-dividing precursors in both (NG2+) oligodendroglial and neuronal lineages. As endogenous EPO expression is induced by brain injury, such a mechanism of adult neurogenesis may be relevant for central nervous system regeneration.

Microglial activation and progressive brain changes in schizophrenia

Schizophrenia is a debilitating disorder that typically begins in adolescence and is characterized by perceptual abnormalities, delusions, cognitive and behavioural disturbances and functional impairments. While current treatments can be effective, they are often insufficient to alleviate the full range of symptoms. Schizophrenia is associated with structural brain abnormalities including grey and white matter volume loss and impaired connectivity. Recent findings suggest these abnormalities follow a neuroprogressive course in the earliest stages of the illness, which may be associated with episodes of acute relapse. Neuroinflammation has been proposed as a potential mechanism underlying these brain changes, with evidence of increased density and activation of microglia, immune cells resident in the brain, at various stages of the illness. We review evidence for microglial dysfunction in schizophrenia from both neuroimaging and neuropathological data, with a specific focus on studies examining microglial activation in relation to the pathology of grey and white matter. The studies available indicate that the link between microglial dysfunction and brain change in schizophrenia remains an intriguing hypothesis worthy of further examination. Future studies in schizophrenia should: (i) use multimodal imaging to clarify this association by mapping brain changes longitudinally across illness stages in relation to microglial activation; (ii) clarify the nature of microglial dysfunction with markers specific to activation states and phenotypes; (iii) examine the role of microglia and neurons with reference to their overlapping roles in neuroinflammatory pathways; and (iv) examine the impact of novel immunomodulatory treatments on brain structure in schizophrenia.

Erythropoietin dampens injury-induced microglial motility

Traumatic brain injury causes progressive brain atrophy and cognitive decline. Surprisingly, an early treatment with erythropoietin (EPO) prevents these consequences of secondary neurodegeneration, but the mechanisms have remained obscure. Here we show by advanced imaging and innovative analytical tools that recombinant human EPO, a clinically established and neuroprotective growth factor, dampens microglial activity, as visualized also in vivo by a strongly attenuated injury-induced cellular motility.

Erythropoietin improved cognitive function and decreased hippocampal caspase activity in rat pups after traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of acquired neurologic disability in children. Erythropoietin (EPO), an anti-apoptotic cytokine, improved cognitive outcome in adult rats after TBI. To our knowledge, EPO has not been studied in a developmental TBI model.

HYPOTHESIS

We hypothesized that EPO would improve cognitive outcome and increase neuron fraction in the hippocampus in 17-day-old (P17) rat pups after controlled cortical impact (CCI).

METHODS

EPO or vehicle was given at 1, 24, and 48 h after CCI and at post injury day (PID) 7. Cognitive outcome at PID14 was assessed using Novel Object Recognition (NOR). Hippocampal EPO levels, caspase activity, and mRNA levels of the apoptosis factors Bcl2, Bax, Bcl-xL, and Bad were measured during the first 14 days after injury. Neuron fraction and caspase activation in CA1, CA3, and DG were studied at PID2.

RESULTS

EPO normalized recognition memory after CCI. EPO blunted the increased hippocampal caspase activity induced by CCI at PID1, but not at PID2. EPO increased neuron fraction in CA3 at PID2. Brain levels of exogenous EPO appeared low relative to endogenous. Timing of EPO administration was associated with temporal changes in hippocampal mRNA levels of EPO and pro-apoptotic factors. Conclusion/Speculation: EPO improved recognition memory, increased regional hippocampal neuron fraction, and decreased caspase activity in P17 rats after CCI. We speculate that EPO improved cognitive outcome in rat pups after CCI as a result of improved neuronal survival via inhibition of caspase-dependent apoptosis early after injury.

A longitudinal VBM study monitoring treatment with erythropoietin in patients with Friedreich ataxia

Background

Recombinant human erythropoietin (rhuEPO) has received considerable attention because of its neuroprotective properties. It has recently been reported that rhuEPO increases frataxin levels in combination with clinical improvement in rhuEPO treated patients with Friedreich ataxia (FRDA).

Purpose

To determine possible therapy dependent intracranial volume changes after treatment with rhuEPO using voxel-based morphometry (VBM).

Material and Methods

Nine FRDA patients were scanned on the same 1.5-Tesla MRI scanner before and after treatment with rhuEPO. FRDA patients received 5000 IU rhuEPO thrice weekly subcutaneously for a time period of 8 weeks followed by 2000 IU thrice weekly over 6 months. To test for re-test reliability a control group of 12 healthy volunteers were scanned twice on the same scanner without rhuEPO treatment. Neurological state was defined by the Friedreich Ataxia Rating Scale (FARS) and the Scale for the Assessment and Rating of Ataxia (SARA). Statistical parametric mapping software was used for image processing and statistical analysis.

Results

When comparing follow-up scans after rhuEPO treatment with baseline scans (P <0.001 uncorrected) an increase of gray matter volume was observed bilaterally in the Pulvinar and the posterior parietal cortex. Moreover, clinical improvement detected using specific Ataxia scores correlated with VBM results in the pulvinar.

Conclusion

Given the limitation of a small sample size, our study confirms previous findings that MRI may serve as reliable biomarker in neurodegenerative diseases as well as in monitoring of microstructural changes representing disease progression and/or therapy effects.

Effects of erythropoietin in murine-induced pluripotent cell-derived panneural progenitor cells

Induced cell fate changes by reprogramming of somatic cells offers an efficient strategy to generate autologous pluripotent stem (iPS) cells from any adult cell type. The potential of iPS cells to differentiate into various cell types is well established, however the efficiency to produce functional neurons from iPS cells remains modest. Here, we generated panneural progenitor cells (pNPCs) from mouse iPS cells and investigated the effect of the neurotrophic growth factor erythropoietin (EPO) on their survival, proliferation and neurodifferentiation. Under neural differentiation conditions, iPS-derived pNPCs gave rise to microtubule-associated protein-2 positive neuronlike cells (34% to 43%) and platelet-derived growth factor receptor positive oligodendrocytelike cells (21% to 25%) while less than 1% of the cells expressed the astrocytic marker glial fibrillary acidic protein. Neuronlike cells generated action potentials and developed active presynaptic terminals. The pNPCs expressed EPO receptor (EPOR) mRNA and displayed functional EPOR signaling. In proliferating cultures, EPO (0.1-3 U/mL) slightly improved pNPC survival but reduced cell proliferation and neurosphere formation in a concentration-dependent manner. In differentiating cultures EPO facilitated neurodifferentiation as assessed by the increased number of β-III-tubulin positive neurons. Our results show that EPO inhibits iPS pNPC self-renewal and promotes neurogenesis.

Intraperitoneal treatment with S100B enhances hippocampal neurogenesis in juvenile mice and after experimental brain injury

BACKGROUND

Neurogenesis is documented in adult mammals including humans, is promoted by neurotrophic factors, and constitutes an innate repair mechanism following brain injury. The glial neurotrophic protein S100B is released following various types of brain injuries, enhances hippocampal neurogenesis and improves cognitive function following brain injury in rats when applied intrathecally. The present study was designed to elucidate whether the beneficial effect of S100B on injury-induced neurogenesis can be confirmed in mice when applied intraperitoneally (i.p.), and whether this effect is dose-dependent.

METHODS

Male juvenile mice were subjected to a unilateral parietal cryolesion or sham injury, and treated with S100B at 20nM, 200nM or vehicle i.p. once daily. Hippocampal progenitor cell proliferation was quantified following labelling with bromo-deoxyuridine (BrdU, 50 mg/KG i.p.) in the germinative area of the dentate gyrus, the subgranular zone (SGZ), on day 4 as well as on cell survival and migration to the granular cell layer (GCL) on day 28. Progenitor cell differentiation was assessed following colabelling with the glial marker GFAP and the neuronal marker NeuN.

RESULTS

S100B enhanced significantly the early progenitor cell proliferation in the SGZ as well as cell survival and migration to the GCL, and promoted neuronal differentiation. While these effects were predominately dose-dependent, 200nM S100B failed to enhance the proliferation in the SGZ on day 4 post-injury.

CONCLUSION

We conclude that S100B participates in hippocampal neurogenesis after injury at lower nanomolar concentrations. Therefore S100B may serve as a potential adjunct treatment to promote neuroregeneration following brain damage.

Microglial dysregulation in psychiatric disease

Microglia, the brain's resident immune cells, are phagocytes of the macrophage lineage that have a key role in responding to inflammation and immune challenge in the brain. More recently, they have been shown to have a number of important roles beyond immune surveillance and response, including synaptic pruning during development and the support of adult neurogenesis. Microglial abnormalities have been found in several neuropsychiatric conditions, though in most cases it remains unclear whether these are causative or are a reaction to some other underlying pathophysiology. Here we summarize postmortem, animal, neuroimaging, and other evidence for microglial pathology in major depression, schizophrenia, autism, obsessive-compulsive disorder, and Tourette syndrome. We identify gaps in the existing literature and important areas for future research. If microglial pathology proves to be an important causative factor in these or other neuropsychiatric diseases, modulators of microglial function may represent a novel therapeutic strategy.

Neuroinflammation in white matter tracts of Cnp1 mutant mice amplified by a minor brain injury

Oligodendrocytes make myelin for rapid impulse propagation and contribute to the long-term survival of myelinated axons. The mechanisms by which oligodendroglial dysfunction(s) contribute to slowly progressive neurodegeneration are not well understood. Here, we demonstrate in Cnp1 mutant mice that secondary axonal degeneration in the subcortical white matter is associated with an age-dependent activation of both, innate and adaptive immune responses, including an expansion of infiltrating CD8+ T cells. While the detrimental role of lymphocytes in inherited myelin diseases is known, the role of activated microglia for the hypothetical cycle of inflammation/degeneration is unclear. We used a mild standardized cryolesion of the right parietal cortex to activate microglia at the vulnerable age of mouse puberty (postnatal day (P) 28). When applied to Cnp1 mutant mice, analyzed more than 3 months later, minor brain injury had acted as a "second hit" and significantly enhanced astrogliosis, microgliosis and axon degeneration, but not T cell infiltration. Interestingly, exacerbated neuropathological changes were also reflected by specific deterioration of working memory on top of an essentially normal basic behavior. We propose a model in which oligodendroglial dysfunctions can trigger a vicious cycle of neurodegeneration and low-grade inflammation that is amplified by nonspecific activators of the innate immune system. This interaction of genetic and environmental factors may be relevant for neuropsychiatric diseases associated with secondary neuroinflammation.

Blocking of bradykinin receptor B1 protects from focal closed head injury in mice by reducing axonal damage and astroglia activation

The two bradykinin receptors B1R and B2R are central components of the kallikrein-kinin system with different expression kinetics and binding characteristics. Activation of these receptors by kinins triggers inflammatory responses in the target organ and in most situations enhances tissue damage. We could recently show that blocking of B1R, but not B2R, protects from cortical cryolesion by reducing inflammation and edema formation. In the present study, we investigated the role of B1R and B2R in a closed head model of focal traumatic brain injury (TBI; weight drop). Increased expression of B1R in the injured hemispheres of wild-type mice was restricted to the later stages after brain trauma, i.e. day 7 (P<0.05), whereas no significant induction could be observed for the B2R (P>0.05). Mice lacking the B1R, but not the B2R, showed less functional deficits on day 3 (P<0.001) and day 7 (P<0.001) compared with controls. Pharmacological blocking of B1R in wild-type mice had similar effects. Reduced axonal injury and astroglia activation could be identified as underlying mechanisms, while inhibition of B1R had only little influence on the local inflammatory response in this model. Inhibition of B1R may become a novel strategy to counteract trauma-induced neurodegeneration.

Endogenous erythropoietin from astrocyte protects the oligodendrocyte precursor cell against hypoxic and reoxygenation injury

The hypoxia-responsive cytokine erythropoietin (EPO) provides neuroprotective effects in the damaged brain during ischemic events and neurodegenerative diseases. The purpose of the present study is to evaluate the EPO/EPO receptor (EPOR) endogenous system between astrocyte and oligodendrocyte precursor cell (OPC) under hypoxia. We report here elevated EPO mRNA levels and protein release in cultured astrocytes following hypoxic stimulation by quantitative RT-PCR and ELISA. Furthermore, the EPOR gene expressions were detected in cultured OPCs as in astrocytes and microglias by quantitative RT-PCR. Cell staining revealed the EPOR expression in OPC. To evaluate the protective effect of endogenous EPO from astrocyte to OPCs, EPO/EPOR signaling was blocked by EPO siRNA or EPOR siRNA gene silencing in in vitro study. The suppression of endogenous EPO production in astrocytes by EPO siRNA decreased the protection to OPCs against hypoxic stress. Furthermore, OPC with EPOR siRNA had less cell survival after hypoxic/reoxygenation injury. This suggested that EPO/EPOR signaling from astrocyte to OPC could prevent OPC damage under hypoxic/reoxygenation condition. Our present finding of an interaction between astrocytes and OPCs may lead to a new therapeutic approach to OPCs for use against cellular stress and injury.

Erythropoietin attenuates neurological and histological consequences of toxic demyelination in mice

Erythropoietin (EPO) reduces symptoms of experimental autoimmune encephalomyelitis in rodents and shows neuroregenerative effects in chronic progressive multiple sclerosis. The mechanisms of action of EPO in these conditions with shared immunological etiology are still unclear. Therefore, we used a model of toxic demyelination allowing exclusion of T cell-mediated inflammation. In a double-blind (for food/injections), placebo-controlled, longitudinal four-arm design, 8-wk-old C57BL/6 mice (n = 26/group) were assigned to cuprizone-containing (0.2%) or regular food (ground chow) for 6 wks. After 3 wks, mice were injected every other day with placebo or EPO (5,000 IU/kg intraperitoneally) until the end of cuprizone feeding. Half of the mice were exposed to behavioral testing, magnetic resonance imaging (MRI) and histology immediately after treatment cessation, whereas the other half were allowed a 3-wk treatment-free recovery. Immediately after termination of cuprizone feeding, all toxin-exposed mice were compromised regarding vestibulomotor function/coordination, with EPO-treated animals performing better than placebo. Likewise, ventricular enlargement after cuprizone, as documented by MRI, was less pronounced upon EPO. After a 3-wk recovery, remarkable spontaneous improvement was observed in all mice with no measurable further benefit in the EPO group ("ceiling effect"). Histological analysis of the corpus callosum revealed attenuation by EPO of the cuprizone-induced increase in microglial numbers and amyloid precursor protein accumulations as a readout of inflammation and axonal degeneration. To conclude, EPO ameliorates neurological symptoms in the cuprizone model of demyelination, possibly by reduction of inflammation-associated axonal degeneration in white matter tracts. These findings underscore the value of future therapeutic strategies for multiple sclerosis based on EPO or EPO variants.

Focal brain trauma in the cryogenic lesion model in mice

The method to induce unilateral cryogenic lesions was first described in 1958 by Klatzo. We describe here an adaptation of this model that allows reliable measurement of lesion volume and vasogenic edema by 2, 3, 5-triphenyltetrazolium chloride-staining and Evans blue extravasation in mice. A copper or aluminium cylinder with a tip diameter of 2.5 mm is cooled with liquid nitrogen and placed on the exposed skull bone over the parietal cortex (coordinates from bregma: 1.5 mm posterior, 1.5 mm lateral). The tip diameter and the contact time between the tip and the parietal skull determine the extent of cryolesion. Due to an early damage of the blood brain barrier, the cryogenic cortical injury is characterized by vasogenic edema, marked brain swelling, and inflammation. The lesion grows during the first 24 hours, a process involving complex interactions between endothelial cells, immune cells, cerebral blood flow, and the intracranial pressure. These contribute substantially to the damage from the initial injury. The major advantage of the cryogenic lesion model is the circumscribed and highly reproducible lesion size and location.

Erythropoietin: a candidate treatment for mood symptoms and memory dysfunction in depression

OBJECTIVE

Current pharmacological treatments for depression have a significant treatment-onset-response delay, an insufficient efficacy for many patients and fail to reverse cognitive dysfunction. Erythropoietin (EPO) has neuroprotective and neurotrophic actions and improves cognitive function in animal models of acute and chronic neurodegenerative conditions and in patients with cognitive decline.

METHODS

We systematically reviewed the published findings from animal and human studies exploring the potential of EPO to treat depression-related cognitive dysfunction and depression.

RESULTS

We identified five animal studies (two in male rats, two in male mice and one in male rats and mice) and seven human proof-of-concept studies (five in healthy volunteers and two in depressed patients) that investigated the above. All of the reviewed animal studies but one and all human studies demonstrated beneficial effects of EPO on hippocampus-dependent memory and antidepressant-like effects. These effects appear to be mediated through direct neurobiological actions of EPO rather than upregulation of red cell mass.

CONCLUSIONS

The reviewed studies demonstrate beneficial effects of EPO on hippocampus-dependent memory function and on depression-relevant behavior, thus highlighting EPO as a candidate agent for future management of cognitive dysfunction and mood symptoms in depression. Larger-scale clinical trials of EPO as a treatment for mood and neurocognitive symptoms in patients with mood disorder are therefore warranted.

Recombinant human erythropoietin delays loss of gray matter in chronic schizophrenia

Neurodevelopmental abnormalities together with neurodegenerative processes contribute to schizophrenia, an etiologically heterogeneous, complex disease phenotype that has been difficult to model in animals. The neurodegenerative component of schizophrenia is best documented by magnetic resonance imaging (MRI), demonstrating progressive cortical gray matter loss over time. No treatment exists to counteract this slowly proceeding atrophy. The hematopoietic growth factor erythropoietin (EPO) is neuroprotective in animals. Here, we show by voxel-based morphometry in 32 human subjects in a placebo-controlled study that weekly high-dose EPO for as little as 3 months halts the progressive atrophy in brain areas typically affected in schizophrenia, including hippocampus, amygdala, nucleus accumbens, and several neocortical areas. Specifically, gray matter protection is highly associated with improvement in attention and memory functions. These findings suggest that a neuroprotective strategy is effective against common pathophysiological features of schizophrenic patients, and strongly encourage follow-up studies to optimize EPO treatment dose and duration.

Erythropoietin as neuroprotective and neuroregenerative treatment strategy: comprehensive overview of 12 years of preclinical and clinical research

Erythropoietin (EPO), originally discovered as hematopoietic growth factor, has direct effects on cells of the nervous system that make it a highly attractive candidate drug for neuroprotection/neuroregeneration. Hardly any other compound has led to so much preclinical work in the field of translational neuroscience than EPO. Almost all of the >180 preclinical studies performed by many independent research groups from all over the world in the last 12 years have yielded positive results on EPO as a neuroprotective drug. The fact that EPO was approved for the treatment of anemia >20 years ago and found to be well tolerated and safe, facilitated the first steps of translation from preclinical findings to the clinic. On the other hand, the same fact, naturally associated with loss of patent protection, hindered to develop EPO as a highly promising therapeutic strategy for application in human brain disease. Therefore, only few clinical neuroprotection studies have been concluded, all with essentially positive and stimulating results, but no further development towards the clinic has occurred thus far. This article reviews the preclinical and clinical work on EPO for the indications neuroprotection/neuroregeneration and cognition, and hopefully will stimulate new endeavours promoting development of EPO for the treatment of human brain diseases.

Acute white matter differences in the fornix following mild traumatic brain injury using diffusion tensor imaging

The integrity of the fornix using diffusion tensor imaging (DTI) in adolescent participants with acute mild traumatic brain injury (mTBI) compared to a demographically matched control group was examined. Fractional anisotropy (FA) in the fornix was elevated in the mild traumatic brain injured group. Performance on the Automated Neuropsychological Assessment Metrics (ANAM) was lower in the group with mTBI. A relation was found between lower performance on cognitive tasks and higher FA. The potential role of fornix injury as a basis of memory and processing speed deficits in mTBI is discussed.

Erythropoietin amplifies stroke-induced oligodendrogenesis in the rat

BACKGROUND

Erythropoietin (EPO), a hematopoietic cytokine, enhances neurogenesis and angiogenesis during stroke recovery. In the present study, we examined the effect of EPO on oligodendrogenesis in a rat model of embolic focal cerebral ischemia.

METHODOLOGY AND PRINCIPAL FINDINGS

Recombinant human EPO (rhEPO) at a dose of 5,000 U/kg (n = 18) or saline (n = 18) was intraperitoneally administered daily for 7 days starting 24 h after stroke onset. Treatment with rhEPO augmented actively proliferating oligodendrocyte progenitor cells (OPCs) measured by NG2 immunoreactive cells within the peri-infarct white matter and the subventricular zone (SVZ), but did not protect against loss of myelinating oligodendrocytes measured by cyclic nucleotide phosphodiesterase (CNPase) positive cells 7 days after stroke. However, 28 and 42 days after stroke, treatment with rhEPO significantly increased myelinating oligodendrocytes and myelinated axons within the peri-infarct white matter. Using lentivirus to label subventricular zone (SVZ) neural progenitor cells, we found that in addition to the OPCs generated in the peri-infarct white matter, SVZ neural progenitor cells contributed to rhEPO-increased OPCs in the peri-infarct area. Using bromodeoxyuridine (BrdU) for birth-dating cells, we demonstrated that myelinating oligodendrocytes observed 28 days after stroke were derived from OPCs. Furthermore, rhEPO significantly improved neurological outcome 6 weeks after stroke. In vitro, rhEPO increased differentiation of adult SVZ neural progenitor cells into oligodendrocytes and enhanced immature oligodendrocyte cell proliferation.

CONCLUSIONS

Our in vivo and in vitro data indicate that EPO amplifies stroke-induced oligodendrogenesis that could facilitate axonal re-myelination and lead to functional recovery after stroke.

Evaluating the relationship between memory functioning and cingulum bundles in acute mild traumatic brain injury using diffusion tensor imaging

Compromised memory functioning is one of the commonly reported cognitive sequelae seen following mild traumatic brain injury (mTBI). Diffusion tensor imaging (DTI) has been shown to be sufficiently sensitive at detecting early microstructural pathological alterations after mTBI. Given its location and shape, the cingulate, which is comprised of the cingulate gyrus (gray matter) and cingulum bundles (white matter), is selectively vulnerable to mTBI. In this study we examined the integrity of cingulum bundles using DTI, and the relationship between cingulum bundles and memory functioning. Twelve adolescents with mTBI and 11 demographically-matched healthy controls were studied. All participants with mTBI had a Glasgow Coma Scale score of 15, and were without intracranial findings on CT scan. Brain scans were performed on average 2.92 days post-injury, and all participants were administered the Verbal Selective Reminding Test (VSRT), an episodic verbal learning and memory task. Participants with mTBI had a significantly lower apparent diffusion coefficient (ADC) bilaterally than controls (p < 0.001). Despite the marginal significance of the group difference in fractional anisotropy (FA), the effect size between groups was moderate (d = 0.66). Cognitively, healthy controls performed better than the TBI group on immediate and delayed recall; however, the difference did not reach statistical significance. In the mTBI group, FA of the left cingulum bundle was significantly correlated with 30-min delayed recall (r = -0.56, p = 0.05). A marginally significant correlation was found between ADC of the left cingulum bundle and the total words of immediate recall (r = 0.59, p = 0.07). No significant correlation was found between DTI metrics and memory functioning for the control group. These preliminary findings indicate that cingulate injury likely contributes to the cognitive sequelae seen during the early phase post-mTBI.

Complexin2 null mutation requires a 'second hit' for induction of phenotypic changes relevant to schizophrenia

Schizophrenia is a devastating disease that affects approximately 1% of the population across cultures. Its neurobiological underpinnings are still unknown. Accordingly, animal models of schizophrenia often lack construct validity. As concordance rate in monozygotic twins amounts to only 50%, environmental risk factors (e.g. neurotrauma, drug abuse, psychotrauma) likely act as necessary 'second hit' to trigger/drive the disease process in a genetically predisposed individual. Valid animal models would have to consider this genetic-environmental interaction. Based on this concept, we designed an experimental approach for modeling a schizophrenia-like phenotype in mice. As dysfunction in synaptic transmission plays a key role in schizophrenia, and complexin2 (CPLX2) gene expression is reduced in hippocampus of schizophrenic patients, we developed a mouse model with Cplx2 null mutation as genetic risk factor and a mild parietal neurotrauma, applied during puberty, as environmental 'second hit'. Several months after lesion, Cplx2 null mutants showed reduced pre-pulse inhibition, deficit of spatial learning and loss of inhibition after MK-801 challenge. These abnormalities were largely absent in lesioned wild-type mice and non-lesioned Cplx2 null mutants. Forced alternation in T-maze, object recognition, social interaction and elevated plus maze tests were unaltered in all groups. The previously reported mild motor phenotype of Cplx2 null mutants was accentuated upon lesion. MRI volumetrical analysis showed a decrease of hippocampal volume exclusively in lesioned Cplx2 null mutants. These findings provide suggestive evidence for the 'second hit' hypothesis of schizophrenia and may offer new tools for the development of advanced treatment strategies.