Gunnar P.H. Dietz

Intravenous TAT-GDNF Is Protective After Focal Cerebral Ischemia in Mice

Background and Purpose— Delivery of therapeutic proteins into tissues and across the blood-brain barrier is severely limited by their size and biochemical properties. The 11-amino acid human immunodeficiency virus TAT protein transduction domain is able to cross cell membranes and the blood-brain barrier, even when coupled with larger peptides. The present studies were done to evaluate whether TAT–glial line-derived neurotrophic factor (GDNF) fusion protein is protective in focal cerebral ischemia. Methods— Anesthetized male C57BL/6j mice were submitted to intraluminal thread occlusion of the middle cerebral artery. Reperfusion was initiated 30 minutes later by thread retraction. Laser Doppler flow was monitored during the experiments. TAT-GDNF, TAT-GFP (0.6 nmol each), or vehicle was intravenously applied over 10 minutes immediately after reperfusion. After 3 days (30 minutes of ischemia), animals were reanesthetized and decapitated. Brain injury was evaluated by histochemical stainings. Results— Immunocytochemical experiments confirmed the presence of TAT-GDNF protein in the brains of fusion protein–treated nonischemic control animals 3 to 4 hours after TAT fusion protein delivery. TAT-GDNF significantly reduced the number of caspase-3–immunoreactive and DNA-fragmented cells and increased the number of viable neurons in the striatum, where disseminated tissue injury was observed, compared with TAT-GFP– or vehicle-treated animals. Conclusions— Our results demonstrate that TAT fusion proteins are powerful tools for the treatment of focal ischemia when delivered both before and after an ischemic insult. This approach may be of clinical interest because such fusion proteins can be intravenously applied and reach the ischemic brain regions. This approach may therefore offer new perspectives for future strategies in stroke therapy.

TAT-BH4 and TAT-Bcl-xL Peptides Protect against Sepsis-Induced Lymphocyte Apoptosis In Vivo

Apoptosis is a key pathogenic mechanism in sepsis that induces extensive death of lymphocytes and dendritic cells, thereby contributing to the immunosuppression that characterizes the septic disorder. Numerous animal studies indicate that prevention of apoptosis in sepsis improves survival and may represent a potential therapy for this highly lethal disorder. Recently, novel cell-penetrating peptide constructs such as HIV-1 TAT basic domain and related peptides have been developed to deliver bioactive cargoes and peptides into cells. In the present study, we investigated the effects of sepsis-induced apoptosis in Bcl-xL transgenic mice and in wild-type mice treated with an antiapoptotic TAT-Bcl-xL fusion protein and TAT-BH4 peptide. Lymphocytes from Bcl-xL transgenic mice were resistant to sepsis-induced apoptosis, and these mice had a ∼3-fold improvement in survival. TAT-Bcl-xL and TAT-BH4 prevented Escherichia coli-induced human lymphocyte apoptosis ex vivo and markedly decreased lymphocyte apoptosis in an in vivo mouse model of sepsis. In conclusion, TAT-conjugated antiapoptotic Bcl-2-like peptides may offer a novel therapy to prevent apoptosis in sepsis and improve survival.

Cyclin-dependent kinase 5 is an upstream regulator of mitochondrial fission during neuronal apoptosis.

Under physiological conditions, mitochondrial morphology dynamically shifts between a punctuate appearance and tubular networks. However, little is known about upstream signal transduction pathways that regulate mitochondrial morphology. We show that mitochondrial fission is a very early and kinetically invariant event during neuronal cell death, which causally contributes to cytochrome c release and neuronal apoptosis. Using a small molecule CDK5 inhibitor, as well as a dominant-negative CDK5 mutant and RNAi knockdown experiments, we identified CDK5 as an upstream signalling kinase that regulates mitochondrial fission during apoptosis of neurons. Vice versa, our study shows that mitochondrial fission is a modulator contributing to CDK5-mediated neurotoxicity. Thereby, we provide a link that allows integration of CDK5 into established neuronal apoptosis pathways.

Granulocyte-colony stimulating factor is neuroprotective in a model of Parkinson's disease

We have recently shown that the hematopoietic Granulocyte‐Colony Stimulating Factor (G‐CSF) is neuroprotective in rodent stroke models, and that this action appears to be mediated via a neuronal G‐CSF receptor. Here, we report that the G‐CSF receptor is expressed in rodent dopaminergic substantia nigra neurons, suggesting that G‐CSF might be neuroprotective for dopaminergic neurons and a candidate molecule for the treatment of Parkinsons disease. Thus, we investigated protective effects of G‐CSF in 1‐methyl‐4‐phenylpyridinium (MPP+)‐challenged PC12 cells and primary neuronal midbrain cultures, as well as in the mouse 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) model of Parkinsons disease. Substantial protection was found against MPP+‐induced dopaminergic cell death in vitro. Moreover, subcutaneous application of G‐CSF at a dose of 40 μg/Kg body weight daily over 13 days rescued dopaminergic substantia nigra neurons from MPTP‐induced death in aged mice, as shown by quantification of tyrosine hydroxylase‐positive substantia nigra cells. Using HPLC, a corresponding reduction in striatal dopamine depletion after MPTP application was observed in G‐CSF‐treated mice. Thus our data suggest that G‐CSF is a novel therapeutic opportunity for the treatment of Parkinsons disease, because it is well‐tolerated and already approved for the treatment of neutropenic conditions in humans.

NF-κB factor c-Rel mediates neuroprotection elicited by mGlu5 receptor agonists against amyloid β -peptide toxicity

Opposite effects of nuclear factor-κB (NF-κB) on neuron survival rely on activation of diverse NF-κB factors. While p65 is necessary for glutamate-induced cell death, c-Rel mediates prosurvival effects of interleukin-1β. However, it is unknown whether activation of c-Rel-dependent pathways reduces neuron vulnerability to amyloid-β (Aβ), a peptide implicated in Alzheimers disease pathogenesis. We show that neuroprotection elicited by activation of metabotropic glutamate receptors type 5 (mGlu5) against Aβ toxicity depends on c-Rel activation. Aβ peptide induced NF-κB factors p50 and p65. The mGlu5 agonists activated c-Rel, besides p50 and p65, and the expression of manganese superoxide dismutase (MnSOD) and Bcl-XL. Targeting c-Rel expression by RNA interference suppressed the induction of both antiapoptotic genes. Targeting c-Rel or Bcl-XL prevented the prosurvival effect of mGlu5 agonists. Conversely, c-Rel overexpression or TAT-Bcl-XL addition rescued neurons from Aβ toxicity. These data demonstrate that mGlu5 receptor activation promotes a c-Rel-dependent antiapoptotic pathway responsible for neuroprotection against Aβ peptide.

Tat-Hsp70 protects dopaminergic neurons in midbrain cultures and in the substantia nigra in models of Parkinson's disease

Parkinson’s disease is characterized by the progressive loss of dopaminergic (DA) neurons in the substantia nigra. The heat‐shock protein 70 (Hsp70) reduces protein misfolding and aggregation. It has been shown to protect cells against oxidative stress and apoptotic stimuli in various neurodegenerative disease models. To deliver Hsp70 across cellular membranes and into the brain, we linked it to a cell‐penetrating peptide derived from the HIV trans‐activator of transcription (Tat) protein. In vitro, Tat‐Hsp70 transduced neuroblastoma cells and protected primary mesencephalic DA neurons and their neurites against MPP+‐mediated degeneration. In vivo, the systemic application of cell‐permeable Hsp70 protected DA neurons of the substantia nigra pars compacta against subacute toxicity of MPTP. Furthermore, Tat‐Hsp70 diminished the MPTP induced decrease in DA striatal fiber density. Thus, we demonstrate that systemically applied Tat‐Hsp70 effectively prevents neuronal cell death in in vitro and in vivo models of Parkinson’s disease. The use of Tat‐fusion proteins might therefore be a valuable tool to deliver molecular chaperones like Hsp70 into the brain and may be the starting point for new protective strategies in neurodegenerative diseases.

TAT-Hsp70-mediated neuroprotection and increased survival of neuronal precursor cells after focal cerebral ischemia in mice

Cerebral ischemia stimulates endogenous neurogenesis within the subventricular zone and the hippocampal dentate gyrus of the adult rodent brain. However, such newly generated cells soon die after cerebral ischemia. To enhance postischemic survival of neural precursor cells (NPC) and long-lasting neural regeneration, we applied the antiapoptotic chaperone heat shock protein 70 (Hsp70) fused to a cell-penetrating peptide derived from the HIV TAT to ensure delivery across the blood-brain barrier and the cell membrane. After transient focal cerebral ischemia in mice, TAT-Hsp70 was intravenously injected concomitant with reperfusion and additionally on day 14 after stroke. TAT-Hsp70 treatment resulted in smaller infarct size (27.1 ± 9.0 versus 109.0 ± 14.0 and 88.5 ± 26.0 mm3 in controls) and in functional improvement as assessed by the rota rod, tight rope, and water maze tests when compared with saline- and TAT-hemagglutinin-treated controls. In addition, postischemic survival of endogenous doublecortin (Dcx)-positive NPC was improved within the lesioned striatum of TAT-Hsp70-treated animals for up to 4 weeks after stroke without changing overall cell proliferation of BrdU+ cells. Thus, TAT-Hsp70 treatment after stroke may be a promising tool to act neuroprotective and improve postischemic functional outcome, and also to increase survival of endogenous NPC after stroke.

Application of a blood-brain-barrier-penetrating form of GDNF in a mouse model for Parkinson's disease.

Glial-cell-line-derived neurotrophic factor (GDNF) promotes mesencephalic dopaminergic neuronal survival in several in vitro and in vivo models. As the demise of dopaminergic neurons is the cause for Parkinsons disease (PD) symptoms, GDNF is a promising agent for its treatment. However, this neurotrophin is unable to cross the blood-brain barrier, which has complicated its clinical use. Therefore, ways to deliver GDNF into the central nervous system in an effective manner are needed. The HIV-1-Tat-derived cell-penetrating peptide (CPP) provides a means to deliver fusion proteins into the brain. We generated a fusion protein between the 11 amino acid CPP of Tat and the rat GDNF mature protein to deliver GDNF across the blood-brain barrier. We showed previously that Tat-GDNF enhances the neuroprotective effect of GDNF in in vivo models for nerve trauma and ischemia. Here, we tested its effect in a subchronic scheme of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) application into the mouse as a model for PD to evaluate the effect of Tat-GDNF fusion protein in dopaminergic neuron survival. We showed that the fusion protein did indeed reach the dopaminergic neurons. However, the in vivo application of Tat-GDNF did not provide neuroprotection of dopaminergic neurons, as revealed by immunohistochemistry and counting of the number of tyrosine-hydroxylase-immunoreactive neurons in the substantia nigra pars compacta. Possibly, GDNF does protect nigro-striatal projections of those neurons that survive MPTP treatment but does not increase the number of surviving dopaminergic neurons. A concomitant treatment of Tat-GDNF with an anti-apoptotic Tat-fusion protein might be beneficial.

Peptide-enhanced cellular internalization of proteins in neuroscience

Over the last 15 years, many publications described the use of peptide sequences that have been dubbed cell penetrating peptides (CPP), Trojan Horse peptides, protein transduction domains, or membrane-translocating sequences. These mostly positively charged domains bring attached cargo across biological membranes. One of the reasons for the interest in CPP is their potential as delivery tools to enhance the pharmacodynamics of drugs otherwise poorly bioavailable. In particular, the neuroscientist aiming to deliver a protein or other compound into the brain for analytical or therapeutic reasons is faced with the challenge that few drugs cross the blood-brain barrier. CPP are valuable tools to overcome the plasma membrane or the blood-brain barrier in basic research, and in relevant models of neural disease, and will hopefully help to increase the precious few treatments or even cures for people with diseases of the brain and nervous system. Here, we review applications in neuroscience and recent insights into the mechanism of CPP-mediated trafficking.

Transduction of Neural Precursor Cells with TAT‐Heat Shock Protein 70 Chaperone: Therapeutic Potential Against Ischemic Stroke after Intrastriatal and Systemic Transplantation

Novel therapeutic concepts against cerebral ischemia focus on cell‐based therapies in order to overcome some of the side effects of thrombolytic therapy. However, cell‐based therapies are hampered because of restricted understanding regarding optimal cell transplantation routes and due to low survival rates of grafted cells. We therefore transplanted adult green fluorescence protein positive neural precursor cells (NPCs) either intravenously (systemic) or intrastriatally (intracerebrally) 6 hours after stroke in mice. To enhance survival of NPCs, cells were in vitro protein‐transduced with TAT‐heat shock protein 70 (Hsp70) before transplantation followed by a systematic analysis of brain injury and underlying mechanisms depending on cell delivery routes. Transduction of NPCs with TAT‐Hsp70 resulted in increased intracerebral numbers of grafted NPCs after intracerebral but not after systemic transplantation. Whereas systemic delivery of either native or transduced NPCs yielded sustained neuroprotection and induced neurological recovery, only TAT‐Hsp70‐transduced NPCs prevented secondary neuronal degeneration after intracerebral delivery that was associated with enhanced functional outcome. Furthermore, intracerebral transplantation of TAT‐Hsp70‐transduced NPCs enhanced postischemic neurogenesis and induced sustained high levels of brain‐derived neurotrophic factor, glial cell line‐derived neurotrophic factor, and vascular endothelial growth factor in vivo. Neuroprotection after intracerebral cell delivery correlated with the amount of surviving NPCs. On the contrary, systemic delivery of NPCs mediated acute neuroprotection via stabilization of the blood‐brain‐barrier, concomitant with reduced activation of matrix metalloprotease 9 and decreased formation of reactive oxygen species. Our findings imply two different mechanisms of action of intracerebrally and systemically transplanted NPCs, indicating that systemic NPC delivery might be more feasible for translational stroke concepts, lacking a need of in vitro manipulation of NPCs to induce long‐term neuroprotection. STEM CELLS2012;30:1297–1310