TAT-Bcl-x(L) improves survival of neuronal precursor cells in the lesioned striatum after focal cerebral ischemia

Oxidative stress and mitochondrial dysfunction following traumatic brain injury: From mechanistic view to targeted therapeutic opportunities

Traumatic brain injury (TBI) is one of the most prevalent causes of permanent physical and cognitive disabilities. TBI pathology results from primary insults and a multi-mechanistic biochemical process, termed as secondary brain injury. Currently, there are no pharmacological agents for definitive treatment of patients with TBI. This article is presented with the purpose of reviewing molecular mechanisms of TBI pathology, as well as potential strategies and agents against pathological pathways. In this review article, materials were obtained by searching PubMed, Scopus, Elsevier, Web of Science, and Google Scholar. This search was considered without time limitation. Evidence indicates that oxidative stress and mitochondrial dysfunction are two key mediators of the secondary injury cascade in TBI pathology. TBI-induced oxidative damage results in the structural and functional impairments of cellular and subcellular components, such as mitochondria. Impairments of mitochondrial electron transfer chain and mitochondrial membrane potential result in a vicious cycle of free radical formation and cell apoptosis. The results of some preclinical and clinical studies, evaluating mitochondria-targeted therapies, such as mitochondria-targeted antioxidants and compounds with pleiotropic effects after TBI, are promising. As a proposed strategy in recent years, mitochondria-targeted multipotential therapy is a new hope, waiting to be confirmed. Moreover, based on the available findings, biologics, such as stem cell-based therapy and transplantation of mitochondria are novel potential strategies for the treatment of TBI; however, more studies are needed to clearly confirm the safety and efficacy of these strategies.

Propane-2-sulfonic acid octadec-9-enyl-amide, a novel peroxisome proliferator-activated receptors α and γ dual agonist, enhances hippocampal neurogenesis and neuroplasticity in rats with cerebral ischaemia

Our previous studies showed that propane-2-sulfonic acid octadec-9-enyl-amide (N15), a novel peroxisome proliferator-activated receptors α and γ (PPARα/γ) dual agonist, protected against ischaemia-induced acute brain damage in mice and improved cognitive ability in the chronic phase of ischaemic stroke. It is well known that hippocampal neurogenesis is closely related to cognitive function. In the present study, we investigated the effect of N15 on hippocampal neurogenesis and neuroplasticity in a middle cerebral artery occlusion (MCAO) rat model. The middle cerebral artery of rats was blocked for 2 hours. Oral administration of 100 mg/kg N15 or vehicle was given once daily for days 2-13 after MCAO. The newly mature neurons were detected by staining. The expressions of synapse-related proteins were observed by qRT-PCR or western blotting. We found that N15-treated rats showed improved survival post-MCAO. In addition, N15 treatment markedly increased the newly mature neurons and enhanced the expression levels of growth-associated protein-43, synaptophysin, brain-derived neurotrophic factor and neurotrophin-3 in the hippocampus. Moreover, N15 promoted the activation of PPARα and PPARγ on day 7 and 14 after cerebral ischaemia. These results reveal that N15 may promote neurogenesis and neuroplasticity in MCAO rats through the activation of the PPARα/γ dual signal pathway.

From Tumor Metastasis towards Cerebral Ischemia-Extracellular Vesicles as a General Concept of Intercellular Communication Processes

Extracellular vesicles (EVs) have been tremendous carriers in both experimental and translational science. These vesicles—formerly regarded as artifacts of in vitro research—have a heterogeneous population of vesicles derived from virtually all eukaryotic cells. EVs consist of a bilayer lipid structure with a diameter of about 30 to 1000 nm and have a characteristic protein and non-coding RNA content that make up different forms of EVs such as exosomes, microvesicles, and others. Despite recent progress in the EV field, which is known to serve as potential biomarkers and therapeutic tools under various pathological conditions, fundamental questions are yet to be answered. This short review focuses on recently reported data regarding EVs under pathological conditions with a particular emphasis on the role of EVs under such different conditions like tumor formation and cerebral ischemia. The review strives to point out general concepts of EV intercellular communication processes that might be vital to both diagnostic and therapeutic strategies in the long run.

TAT-Ngn2 Enhances Cognitive Function Recovery and Regulates Caspase-Dependent and Mitochondrial Apoptotic Pathways After Experimental Stroke

Neurogenin-2 (Ngn2) is a basic helix-loop-helix (bHLH) transcription factor that contributes to the identification and specification of neuronal fate during neurogenesis. In our previous study, we found that Ngn2 plays an important role in alleviating neuronal apoptosis, which may be viewed as an attractive candidate target for the treatment of cerebral ischemia. However, novel strategies require an understanding of the function and mechanism of Ngn2 in mature hippocampal neurons after global cerebral ischemic injury. Here, we found that the expression of Ngn2 decreased in the hippocampus after global cerebral ischemic injury in mice and in primary hippocampal neurons after oxygen glucose deprivation (OGD) injury. Then, transactivator of transcription (TAT)-Ngn2, which was constructed by fusing a TAT domain to Ngn2, was effectively transported and incorporated into hippocampal neurons after intraperitoneal (i.p.) injection and enhanced cognitive functional recovery in the acute stage after reperfusion. Furthermore, TAT-Ngn2 alleviated hippocampal neuronal damage and apoptosis, and inhibited the cytochrome C (CytC) leak from the mitochondria to the cytoplasm through regulating the expression levels of brain-derived neurotrophic factor (BDNF), phosphorylation tropomyosin-related kinase B (pTrkB), Bcl-2, Bax and cleaved caspase-3 after reperfusion injury in vivo and in vitro. These findings suggest that the downregulation of Ngn2 expression may have an important role in triggering brain injury after ischemic stroke and that the neuroprotection of TAT-Ngn2 against stroke might involve the modulation of BDNF-TrkB signaling that regulates caspase-dependent and mitochondrial apoptotic pathways, which may be an attractive therapeutic strategy for cerebral ischemic injury.

Immunological and non-immunological effects of stem cell-derived extracellular vesicles on the ischaemic brain

Following the implementation of thrombolysis and endovascular recanalization strategies, stroke therapy has profoundly changed in recent years. In spite of these advancements, a considerable proportion of stroke patients still exhibit functional impairment in the long run, increasing the need for adjuvant therapies that promote neurological recovery. Stem cell therapies have initially attracted great interest in the stroke field, since there were hopes that transplanted cells may allow for the replacement of lost cells. After the recognition that transplanted cells integrate poorly into existing neural networks and that they induce brain remodelling in a paracrine way by secreting a heterogeneous group of nanovesicles, these extracellular vesicles (EVs) have been identified as key players that mediate restorative effects of stem and progenitor cells in ischaemic brain tissue. We herein review restorative effects of EVs in stroke models and discuss immunological and non-immunological mechanisms that may underlie recovery of function.

Concise Review: Extracellular Vesicles Overcoming Limitations of Cell Therapies in Ischemic Stroke

Despite recent advances in stroke therapy, current therapeutic concepts are still limited. Thus, additional therapeutic strategies are in order. In this sense, the transplantation of stem cells has appeared to be an attractive adjuvant tool to help boost the endogenous regenerative capacities of the brain. Although transplantation of stem cells is known to induce beneficial outcome in (preclinical) stroke research, grafted cells do not replace lost tissue directly. Rather, these transplanted cells like neural progenitor cells or mesenchymal stem cells act in an indirect manner, among which the secretion of extracellular vesicles (EVs) appears to be one key factor. Indeed, the application of EVs in preclinical stroke studies suggests a therapeutic role, which appears to be noninferior in comparison to the transplantation of stem cells themselves. In this short review, we highlight some of the recent advances in the field of EVs as a therapeutic means to counter stroke. Stem Cells Translational Medicine2017;6:2044–2052

Interaction of ARC and Daxx: A Novel Endogenous Target to Preserve Motor Function and Cell Loss after Focal Brain Ischemia in Mice

The aim of this study was to explore the signaling and neuroprotective effect of transactivator of transcription (TAT) protein transduction of the apoptosis repressor with CARD (ARC) in in vitro and in vivo models of cerebral ischemia in mice. In mice, transient focal cerebral ischemia reduced endogenous ARC protein in neurons in the ischemic striatum at early reperfusion time points, and in primary neuronal cultures, RNA interference resulted in greater neuronal susceptibility to oxygen glucose deprivation (OGD). TAT.ARC protein delivery led to a dose-dependent better survival after OGD. Infarct sizes 72 h after 60 min middle cerebral artery occlusion (MCAo) were on average 30 ± 8% (mean ± SD; p = 0.005; T2-weighted MRI) smaller in TAT.ARC-treated mice (1 μg intraventricularly during MCAo) compared with controls. TAT.ARC-treated mice showed better performance in the pole test compared with TAT.β-Gal-treated controls. Importantly, post-stroke treatment (3 h after MCAo) was still effective in affording reduced lesion volume by 20 ± 7% (mean ± SD; p < 0.05) and better functional outcome compared with controls. Delayed treatment in mice subjected to 30 min MCAo led to sustained neuroprotection and functional behavior benefits for at least 28 d. Functionally, TAT.ARC treatment inhibited DAXX-ASK1-JNK signaling in the ischemic brain. ARC interacts with DAXX in a CARD-dependent manner to block DAXX trafficking and ASK1-JNK activation. Our work identifies for the first time ARC-DAXX binding to block ASK1-JNK activation as an ARC-specific endogenous mechanism that interferes with neuronal cell death and ischemic brain injury. Delayed delivery of TAT.ARC may present a promising target for stroke therapy.

SIGNIFICANCE STATEMENT

Up to now, the only successful pharmacological target of human ischemic stroke is thrombolysis. Neuroprotective pharmacological strategies are needed to accompany therapies aiming to achieve reperfusion. We describe that apoptosis repressor with CARD (ARC) interacts and inhibits DAXX and proximal signals of cell death. In a murine stroke model mimicking human malignant infarction in the territory of the middle cerebral artery, TAT.ARC salvages brain tissue when given during occlusion or 3 h delayed with sustained functional benefits (28 d). This is a promising novel therapeutic approach because it appears to be effective in a model producing severe injury by interfering with an array of proximal signals and effectors of the ischemic cascade, upstream of JNK, caspases, and BIM and BAX activation.

NSI-189, a small molecule with neurogenic properties, exerts behavioral, and neurostructural benefits in stroke rats

Enhancing neurogenesis may be a powerful stroke therapy. Here, we tested in a rat model of ischemic stroke the beneficial effects of NSI-189, an orally active, new molecular entity (mol. wt. 366) with enhanced neurogenic activity, and indicated as an anti-depressant drug in a clinical trial (Fava et al., , Molecular Psychiatry, DOI: 10.1038/mp.2015.178) and being tested in a Phase 2 efficacy trial (ClinicalTrials.gov, , ClinicalTrials.gov Identifier: NCT02695472) for treatment of major depression. Oral administration of NSI-189 in adult Sprague-Dawley rats starting at 6 hr after middle cerebral artery occlusion, and daily thereafter over the next 12 weeks resulted in significant amelioration of stroke-induced motor and neurological deficits, which was maintained up to 24 weeks post-stroke. Histopathological assessment of stroke brains from NSI-189-treated animals revealed significant increments in neurite outgrowth as evidenced by MAP2 immunoreactivity that was prominently detected in the hippocampus and partially in the cortex. These results suggest NSI-189 actively stimulated remodeling of the stroke brain. Parallel in vitro studies further probed this remodeling process and demonstrated that oxygen glucose deprivation and reperfusion (OGD/R) initiated typical cell death processes, which were reversed by NSI-189 treatment characterized by significant attenuation of OGD/R-mediated hippocampal cell death and increased Ki67 and MAP2 expression, coupled with upregulation of neurogenic factors such as BDNF and SCF. These findings support the use of oral NSI-189 as a therapeutic agent well beyond the initial 6-hr time window to accelerate and enhance the overall functional improvement in the initial 6 months post stroke.

SIRT3 in Neural Stem Cells Attenuates Microglia Activation-Induced Oxidative Stress Injury Through Mitochondrial Pathway

Sirtuin 3 (SIRT3), a mitochondrial protein, is involved in energy metabolism, cell apoptosis and mitochondrial function. However, the role of SIRT3 in neural stem cells (NSCs) remains unknown. In previous studies, we found that microglia activation-induced cytotoxicity negatively regulated survival of NSCs, along with mitochondrial dysfunction. The aim of this study was to investigate the potential neuroprotective effects of SIRT3 on the microglia activation-induced oxidative stress injury in NSCs and its possible mechanisms. In the present study, microglia-NSCs co-culture system was used to demonstrate the crosstalk between both cell types. The cytotoxicity of microglia activation by Amyloid-β (Aβ) resulted in the accumulation of reactive oxygen species (ROS) and down-regulation of SIRT3, manganese superoxide dismutase (MnSOD) gene expression in NSCs, concomitant to cell cycle arrest at G₀/G₁ phase, increased cell apoptosis rate and opening of the mitochondrial permeability transition pore (mPTP) and enhanced mitochondrial membrane potential (ΔΨm) depolarization. Furthermore, SIRT3 knockdown in NSCs via small interfering RNA (siRNA) accelerated cell injury, whereas SIRT3 overexpression provided resistance to microglia activation-induced oxidative stress cellular damage. The mechanisms of SIRT3 attenuated activated microglia-induced NSC dysfunction included the decreased mPTP opening and cyclophilin D (CypD) protein expression, inhibition of mitochondrial cytochrome C (Cyt C) release to cytoplasm, declined Bax/B-cell lymphoma 2 (Bcl-2) ratio and reduced caspase-3/9 activity. Taken together, these data imply that SIRT3 ameliorates microglia activation-induced oxidative stress injury through mitochondrial apoptosis pathway in NSCs, these results may provide a novel intervention target for NSC survival.

Method parameters' impact on mortality and variability in mouse stroke experiments: a meta-analysis

Although hundreds of promising substances have been tested in clinical trials, thrombolysis currently remains the only specific pharmacological treatment for ischemic stroke. Poor quality, e.g. low statistical power, in the preclinical studies has been suggested to play an important role in these failures. Therefore, it would be attractive to use animal models optimized to minimize unnecessary mortality and outcome variability, or at least to be able to power studies more exactly by predicting variability and mortality given a certain experimental setup. The possible combinations of methodological parameters are innumerous, and an experimental comparison of them all is therefore not feasible. As an alternative approach, we extracted data from 334 experimental mouse stroke articles and, using a hypothesis-driven meta-analysis, investigated the method parameters’ impact on infarct size variability and mortality. The use of Swiss and C57BL6 mice as well as permanent occlusion of the middle cerebral artery rendered the lowest variability of the infarct size while the emboli methods increased variability. The use of Swiss mice increased mortality. Our study offers guidance for researchers striving to optimize mouse stroke models.

Cellular prion protein promotes post-ischemic neuronal survival, angioneurogenesis and enhances neural progenitor cell homing via proteasome inhibition

Although cellular prion protein (PrP^c) has been suggested to have physiological roles in neurogenesis and angiogenesis, the pathophysiological relevance of both processes remain unknown. To elucidate the role of PrP^c in post-ischemic brain remodeling, we herein exposed PrP^c wild type (WT), PrP^c knockout (PrP−/−) and PrP^c overexpressing (PrP+/+) mice to focal cerebral ischemia followed by up to 28 days reperfusion. Improved neurological recovery and sustained neuroprotection lasting over the observation period of 4 weeks were observed in ischemic PrP+/+ mice compared with WT mice. This observation was associated with increased neurogenesis and angiogenesis, whereas increased neurological deficits and brain injury were noted in ischemic PrP−/− mice. Proteasome activity and oxidative stress were increased in ischemic brain tissue of PrP−/− mice. Pharmacological proteasome inhibition reversed the exacerbation of brain injury induced by PrP−/−, indicating that proteasome inhibition mediates the neuroprotective effects of PrP^c. Notably, reduced proteasome activity and oxidative stress in ischemic brain tissue of PrP+/+ mice were associated with an increased abundance of hypoxia-inducible factor 1α and PACAP-38, which are known stimulants of neural progenitor cell (NPC) migration and trafficking. To elucidate effects of PrP^c on intracerebral NPC homing, we intravenously infused GFP⁺ NPCs in ischemic WT, PrP−/− and PrP+/+ mice, showing that brain accumulation of GFP⁺ NPCs was greatly reduced in PrP−/− mice, but increased in PrP+/+ animals. Our results suggest that PrP^c induces post-ischemic long-term neuroprotection, neurogenesis and angiogenesis in the ischemic brain by inhibiting proteasome activity.

L-3-n-butylphthalide Promotes Neurogenesis and Neuroplasticity in Cerebral Ischemic Rats

AIMS

This study investigated whether anticerebral ischemia new drug, l-3-n-butylphthalide (l-NBP), improved behavioral recovery and enhanced hippocampal neurogenesis after cerebral ischemia in rats.

METHODS AND RESULTS

The middle cerebral artery of rats was blocked for 2 h. The daily oral administrations of 30 mg/kg l-NBP or vehicle were begun from the second day until the rats were sacrificed. L-NBP treatment markedly increased 5-bromo-2'-deoxyuridine (BrdU)-positive cells in the hippocampal dentate gyrus (DG) of injured hemisphere on day 28 after ischemia. The amount of newborn cells and newly mature neurons was also increased. The expressions of growth-associated protein-43 and synaptophysin were significantly elevated in l-NBP-treated rats. However, l-NBP markedly reduced the percentage of BrdU(+) /GFAP(+) cells. Additionally, the levels of catalytical subunit of protein kinase A (PKA), protein kinase B (Akt), and cAMP response element-binding protein (CREB) were significantly increased, and the activation of the signal transducer and activation of transcription 3 (STAT3) and the expressions of cleaved caspase-3 and Bax were obviously inhibited by l-NBP. Consequently, l-NBP attenuated the behavioral dysfunction.

CONCLUSIONS

It first demonstrates that l-NBP may improve the behavioral outcome of cerebral ischemia by promoting neurogenesis and neuroplasticity. Activation of CREB and Akt and inhibition of STAT3 signaling might be involved in.

Stem cell-based treatments against stroke: observations from human proof-of-concept studies and considerations regarding clinical applicability

Ischemic stroke remains a heavy burden for industrialized countries. The only causal therapy is the recanalization of occluded vessels via thrombolysis, which due to a narrow time window still can be offered only to a minority of patients. Since the majority of patients continues to exhibit neurological deficits even following successful thrombolysis, restorative therapies are urgently needed that promote brain remodeling and repair once stroke injury has occurred. Due to their unique properties of action, stem cell-based strategies gained increasing interest during recent years. Using various stroke models in both rodents and primates, the transplantation of stem cells, namely of bone marrow derived mesenchymal stem cells (MSCs) or neural progenitor cells (NPCs), has been shown to promote neurological recovery most likely via indirect bystander actions. In view of promising observations, clinical proof-of-concept studies are currently under way, in which effects of stem and precursor cells are evaluated in human stroke patients. In this review we summarize already published studies, which due to the broad experience in other medical contexts mostly employed bone marrow-derived MSCs by means of intravenous transplantation. With the overall number of clinical trials limited in number, only a fraction of these studies used non-treated control groups, and only single studies were adequately blinded. Despite these limitations, first promising results justify the need for more elaborate clinical trials in order to make stem cell transplantation a success for stroke treatment in the future.

Effects of neural progenitor cells on post-stroke neurological impairment-a detailed and comprehensive analysis of behavioral tests

Systemic transplantation of neural progenitor cells (NPCs) in rodents reduces functional impairment after cerebral ischemia. In light of upcoming stroke trials regarding safety and feasibility of NPC transplantation, experimental studies have to successfully analyze the extent of NPC-induced neurorestoration on the functional level. However, appropriate behavioral tests for analysis of post-stroke motor coordination deficits and cognitive impairment after NPC grafting are not fully established. We therefore exposed male C57BL6 mice to either 45 min (mild) or 90 min (severe) of cerebral ischemia, using the thread occlusion model followed by intravenous injection of PBS or NPCs 6 h post-stroke with an observation period of three months. Post-stroke motor coordination was assessed by means of the rota rod, tight rope, corner turn, inclined plane, grip strength, foot fault, adhesive removal, pole test and balance beam test, whereas cognitive impairment was analyzed using the water maze, the open field and the passive avoidance test. Significant motor coordination differences after both mild and severe cerebral ischemia in favor of NPC-treated mice were observed for each motor coordination test except for the inclined plane and the grip strength test, which only showed significant differences after severe cerebral ischemia. Cognitive impairment after mild cerebral ischemia was successfully assessed using the water maze test, the open field and the passive avoidance test. On the contrary, the water maze test was not suitable in the severe cerebral ischemia paradigm, as it too much depends on motor coordination capabilities of test mice. In terms of both reliability and cost-effectiveness considerations, we thus recommend the corner turn, foot fault, balance beam, and open field test, which do not depend on durations of cerebral ischemia.

Phosphorylation of p38 MAPK mediates hypoxic preconditioning-induced neuroprotection against cerebral ischemic injury via mitochondria translocation of Bcl-xL in mice

Hypoxic preconditioning (HPC) initiates intracellular signaling pathway to provide protection, but the role of p38 mitogen-activated protein kinase (p38 MAPK) in HPC-induced neuroprotection against cerebral ischemic injuries is a matter of debate. In this study, we found that HPC could reduce 6h middle cerebral artery occlusion (MCAO)-induced infarct volume, edema ratio and cell apoptosis, as well as enhancing the up-regulated p38 MAPK phosphorylation (P-p38 MAPK) levels in the peri-infarct region of mice after 6h MCAO. However, intracerebroventricular injection of p38 MAPK inhibitor SB203580 abolished this HPC-induced neuroprotection. HPC significantly increased the translocation of anti-apoptotic Bcl-2-related protein Bcl-xL from the cytosol to the mitochondria in the peri-infarct region of MCAO mice. Interestingly, the results of reciprocal immunoprecipitation showed that Bcl-xL and P-p38 MAPK were coimmunoprecipitated reciprocally only in the peri-infarct region of HPC and MCAO treated mice, while Bcl-xL and total p38 (T-p38 MAPK), not P-p38 MAPK, could be coimmunoprecipited by each other in the brain of normal control mice. In addition, we found SB203580 significantly decreased P-p38 MAPK levels, and inhibited HPC-induced mitochondria translocation of Bcl-xL in the brain of HPC and MCAO treated mice. Taken together, our findings suggested that P-p38 MAPK mediates HPC-induced neuroprotection against cerebral ischemic injury via mitochondria translocation of Bcl-xL, which might be a key anti-cell apoptotic mechanism of HPC.

Mcl-1 regulates the survival of adult neural precursor cells

Since the discovery of neural precursor cells (NPCs) in the adult mammalian brain, there has been a lot of excitement surrounding the potential for regeneration in the adult brain. For instance, many studies have shown that a significant number of NPCs will migrate to a site of injury and differentiate into all of the neural lineages. However, one of the main challenges affecting endogenous neural regeneration is that many of the NPCs that migrate to the injury site ultimately undergo apoptosis. Therefore, we sought to determine whether myeloid cell leukemia-1 (Mcl-1), an anti-apoptotic Bcl-2 protein, would promote the survival of adult NPCs by impeding apoptosis. To do this, we first confirmed that Mcl-1 is endogenously expressed within the adult NPC population using BrdU labeling assays. Next, we conditionally deleted Mcl-1 in adult NPCs using cre/lox technology and expressed Cre from the NPC-specific promoter Nestin. In vitro, cells that had Mcl-1 conditionally deleted had a 2-fold increase in apoptosis when compared to controls. In vivo, we used electroporation to conditionally delete Mcl-1 in adult NPCs and assessed apoptosis at 72h. after electroporation. As in our in vitro results, there was a 2-fold increase in apoptosis when Mcl-1 was conditionally deleted. Finally, we found that Mcl-1 over-expression reduced the endogenous rate of adult NPC apoptosis 2-fold in vitro. Collectively, these results demonstrate that Mcl-1 is crucial for the survival of adult NPCs and may be a promising target for future neural regeneration therapies.

Inflammation, mitochondria, and the inhibition of adult neurogenesis

The process of neurogenesis continues throughout life, with thousands of new neurons generated every day in the mammalian brain. Impairment of hippocampal neurogenesis has been suggested to be involved in neurodegenerative conditions, including the cognitive decline associated with aging, Alzheimer's disease, Parkinson's disease, and ionizing radiation. These neurodegenerative conditions are all characterized by proinflammatory changes and increased numbers of activated microglia. Activated microglia produce a variety of proinflammatory factors, including interleukin-6, tumor necrosis factor-α, reactive oxygen species, and nitric oxide, all of which are antineurogenic. These same factors have also been shown to suppress mitochondrial function, but the role of mitochondria in neurogenesis remains barely investigated. This brief review summarizes the findings of several studies that support a role for mitochondrial impairment as part of the mechanism of the reduction of neurogenesis associated with inflammation.

Gain of survival signaling by down-regulation of three key miRNAs in brain of calorie-restricted mice

The decline in cognitive robustness with aging can be attributed to complex genetic pathways involving many cellular dysfunctions, cumulative over time, precipitating in frailty and loss of wellness in the elderly brain. The size and health of the neuronal cell population determines cognitive robustness in mammals. A transgenic mouse model over-expressing Bcl-2 has been shown to rescue neurons from naturally occurring cell death (NOCD). Here we show that in the brain of calorie-restricted (CR) mice, there is an age-dependent decreased expression of microRNAs mmu-miR-181a-1*, mmu-miR-30e and mmu-miR-34a, with a corresponding gain in Bcl-2 expression, and decreases in pro-apoptosis genes such as Bax and cleavage of Caspases. Functional characterization shows that these miRNAs repress Bcl-2 expression by the 3'UTR reporter assays, accompanied by loss of this gene's endogenous expression, and a gain in pro-apoptosome-specific proteins. Over-expression of these miRNAs increases the rate of apoptosis, accompanied by a decline in Bcl-2 expression in miRNA-transfected mouse and human cell lines. We report here that down-regulation of miR-34a, -30e, and -181a permits their shared target gene expression (Bcl-2) to remain at a high level without post-transcriptional repression, accompanied by concomitant low levels of Bax expression and Caspase cleaving; this chain event may be a part of the underlying mechanism contributing to the gain in neuronal survival in long-lived CR-fed mice.

Neural stem cell-based therapy for ischemic stroke

Stem cell-based approaches for the treatment of stroke have been the subject of intensive research over the past decade. Based on accumulated experimental evidence, stem cell-based therapy is a very promising prospect for the development of a novel treatment to restore stroke-damaged brain and impaired neurological function. Studies performed on experimental animal models of stroke employed a variety of stem cell types from diverse sources and have demonstrated their ability to replace lost neurons and functionally integrate into the brain, modulate inflammation, and stimulate angiogenesis and neurogenesis from an endogenous stem cell pool, most likely through trophic actions. A few clinical trials in stroke patients using stem cell transplantation have been completed or are on-going but the results have not yet proven the effectiveness of the stem cell-based approaches. A joint effort of stroke researchers and clinicians is needed to further optimize treatment protocols using safe and reproducible stem cell sources tested in relevant animal models of stroke and showing substantial neurological recovery of stroke-impaired function.

Protection by neuroglobin and cell-penetrating peptide-mediated delivery in vivo: a decade of research. Comment on Cai et al: TAT-mediated delivery of neuroglobin protects against focal cerebral ischemia in mice. Exp Neurol. 2011; 227(1): 224-31

Over the last decade, numerous studies have suggested that neuroglobin is able to protect against the effects of ischemia. However, such results have mostly been based on models using transgenic overexpression or viral delivery. As a therapy, new technology would need to be applied to enable delivery of high concentrations of neuroglobin shortly after the patient suffers the stroke. An approach to deliver proteins in ischemia in vivo in a timely manner is the use of cell-penetrating peptides (CPP). CPP have been used in animal models for brain diseases for about a decade as well. In a recent issue of Experimental Neurology, Cai and colleagues test the effect of CPP-coupled neuroglobin in an in vivo stroke model. They find that the fusion protein protects the brain against the effect of ischemia when applied before stroke onset. Here, a concise review of neuroglobin research and the application of CPP peptides in hypoxia and ischemia is provided.

Acute hepatocyte growth factor treatment induces long-term neuroprotection and stroke recovery via mechanisms involving neural precursor cell proliferation and differentiation

Hepatocyte growth factor (HGF) is an interesting candidate for acute stroke treatment as shown by continuous infusion or gene delivery protocols. However, little is known about HGF-mediated long-term effects. The present study therefore analyzed long-term effects of an acute intrastriatal HGF treatment (5 μg) after a 45-minute stroke, with regard to brain injury and neurologic recovery. Hepatocyte growth factor induced long-term neuroprotection as assessed by infarct volume and neuronal cell death analysis for as long as 4 weeks after stroke, which was associated with sustained neurologic recovery as evidenced by corner-turn and tight-rope tests. Analyzing underlying mechanisms of HGF-induced sustained neuroprotection, enhanced cell proliferation followed by increased neuronal differentiation of neural precursor cells (NPCs) was observed in the ischemic striatum of HGF-treated mice, which persisted for up to 4 weeks. In line with this, HGF promoted neurosphere formation as well as proliferation of NPC and decreased caspase-3-dependent hypoxic injury in vitro. Preservation of blood-brain barrier integrity 24  hours after stroke was furthermore noticed in animals receiving HGF, which was associated with the inhibition of matrix metalloproteases (MMP)-2 and MMP-9 at 4 and 24  hours, respectively. We suggest that sustained recruitment of proliferating cells together with improved neurovascular remodeling provides an explanation for HGF-induced long-term neuroprotection.

Transcription factor-based modulation of neural stem cell differentiation using direct protein transduction

In contrast to conventional gene transfer strategies, the direct introduction of recombinant proteins into cells bypasses the risk of insertional mutagenesis and offers an alternative to genetic intervention. Here, we explore whether protein transduction of the gliogenic transcription factor Nkx2.2 can be used to promote oligodendroglial differentiation of mouse embryonic stem cell (ESC)-derived neural stem cells (NSC). To that end, a recombinant cell-permeant form of Nkx2.2 protein was generated. Exposure of ESC-derived NSC to the recombinant protein and initiation of differentiation resulted in a two-fold increase in the number of oligodendrocytes. Furthermore, Nkx2.2-transduced cells exhibited a more mature oligodendroglial phenotype. Comparative viral gene transfer studies showed that the biological effect of Nkx2.2 protein transduction is comparable to that obtained by lentiviral transduction. The results of this proof-of-concept study depict direct intracellular delivery of transcription factors as alternative modality to control lineage differentiation in NSC cultures without genetic modification.

Transplantation of TAT-Bcl-xL-transduced neural precursor cells: long-term neuroprotection after stroke

Neural precursor cells (NPC) are an interesting tool in experimental stroke research, but their therapeutic potential is limited due to poor long-term survival. We therefore in vitro transduced subventricular zone-(SVZ)-derived NPC with the anti-apoptotic fusion protein TAT-Bcl-x(L) and analyzed NPC survival, differentiation, and post-stroke functional deficits after experimental ischemia in mice. Survival of TAT-Bcl-x(L)-transduced NPC, which were injected at day 7 post-stroke into the ischemic striatum, was significantly increased at 4 weeks after stroke. Increased survival of NPC was associated with reduced infarct injury and decreased post-stroke functional deficits. Animals grafted with TAT-Bcl-x(L)-transduced NPC showed an increased number of immature cells expressing the neuronal marker doublecortin. Since mature neuronal differentiation of NPC was not observed, reduced post-stroke injury cannot be attributed to enhanced neuronal regeneration, but rather to indirect by-stander effects of grafted NPC. In line with this, NPC-mediated neuroprotection of cortical neurons in vitro was associated with increased secretion of growth factors. Thus, in vitro transduction of cultivated NPC with TAT-Bcl-x(L) results in enhanced resistance of transplanted NPC followed by long-term neuroprotection and ameliorated functional deficits after transient focal cerebral ischemia in mice.

Protection of hippocampal neurogenesis by TAT-Bcl-x(L) after cerebral ischemia in mice

Endogenous neurogenesis persists in the subgranular zone (SGZ) of the adult rodent brain. Cerebral ischemia stimulates endogenous neurogenesis involving proliferation, migration and differentiation of SGZ-derived neural precursor cells (NPC). However, the biological meaning of this phenomenon is limited by poor survival of NPC. In order to study the effects of an acute neuroprotective treatment on hippocampal endogenous neurogenesis after transient cerebral ischemia in mice, we applied a fusion protein consisting of the TAT domain of the HI virus with the anti-apoptotic Bcl-x(L). Intravenous injection of TAT-Bcl-x(L) resulted in reduced hippocampal cell injury for up to 4weeks after stroke as assessed by TUNEL and NeuN staining. This was in line with a TAT-Bcl-x(L)-mediated reduced postischemic microglia activation. Analysis of endogenous hippocampal cell proliferation revealed an increased number of BrdU(+) cells in the TAT-Bcl-x(L) group 4weeks after stroke compared to animals treated with saline and TAT-HA (negative control). Cell proliferation in non-ischemic sham operated animals was not affected by TAT-Bcl-x(L). Twenty-eight days after stroke co-expression of BrdU(+) cells with the immature neuronal marker doublecortin was significantly increased in TAT-Bcl-x(L) animals. Although TAT-Bcl-x(L) treatment also resulted in an increased number of BrdU(+) cells expressing the mature neuronal marker NeuN, the total amount of these cells was low. These data show that TAT-Bcl-x(L) treatment yields both postischemic sustained hippocampal neuroprotection and increased survival of NPC rather than an induction of endogenous neurogenesis itself.

Dining in with BCL-2: new guests at the autophagy table

BCL-2 homologues are major regulators of apoptosis and, as such, play an active role in the survival of adult neurons following injury. In recent years, these proteins have also been associated with the regulation of autophagy, a catabolic process involved in the recycling of nutrients upon starvation. Basal levels of autophagy are also required to eliminate damaged proteins and organelles. This is illustrated by the accumulation of ubiquitin-positive aggregates in cells deficient in autophagy and, in the nervous system, this is associated with progressive cell loss and signs of neurodegeneration. Given the importance of both apoptosis and autophagy for neuronal survival in adult neurons, understanding how BCL-2 homologues co-ordinately regulate these processes will allow a better understanding of the cellular processes leading to neurodegeneration. In the present review, we will discuss the roles of BCL-2 homologues in the regulation of apoptosis and autophagy, focussing on their impact on adult neurons.