Daniela Kaufer

Acute stress facilitates long-lasting changes in cholinergic gene expression

Acute traumatic stress may lead to post-traumatic stress disorder (PTSD), which is characterized by delayed neuropsychiatric symptoms including depression, irritability, and impaired cognitive performance. Curiously, inhibitors of the acetylcholine-hydrolysing enzyme acetylcholinesterase may induce psychopathologies that are reminiscent of PTSD,. It is unknown how a single stressful event mediates long-term neuronal plasticity. Moreover, no mechanism has been proposed to explain the convergent neuropsychological outcomes of stress and of acetylcholinesterase inhibition. However, acute stress elicits a transient increase in the amounts released of the neurotransmitter acetylcholine and a phase of enhanced neuronal excitability. Inhibitors of acetylcholinesterase also promote enhanced electrical brain activity, presumably by increasing the survival of acetylcholine at the synapse. Here we report that there is similar bidirectional modulation of genes that regulate acetylcholine availability after stress and blockade of acetylcholinesterase. These calcium-dependent changes in gene expression coincide with phases of rapid enhancement and delayed depression of neuronal excitability. Both of these phases are mediated by muscarinic acetylcholine receptors. Our results suggest a model in which robust cholinergic stimulation triggers rapid induction of the gene encoding the transcription factor c-Fos. This protein then mediates selective regulatory effects on the long-lasting activities of genes involved in acetylcholine metabolism.

Blood–brain barrier breakdown as a therapeutic target in traumatic brain injury

Traumatic brain injury (TBI) is the leading cause of death in young adults and children. The treatment of TBI in the acute phase has improved substantially; however, the prevention and management of long-term complications remain a challenge. Blood–brain barrier (BBB) breakdown has often been documented in patients with TBI, but the role of such vascular pathology in neurological dysfunction has only recently been explored. Animal studies have demonstrated that BBB breakdown is involved in the initiation of transcriptional changes in the neurovascular network that ultimately lead to delayed neuronal dysfunction and degeneration. Brain imaging data have confirmed the high incidence of BBB breakdown in patients with TBI and suggest that such pathology could be used as a biomarker in the clinic and in drug trials. Here, we review the neurological consequences of TBI, focusing on the long-term complications of such injuries. We present the clinical evidence for involvement of BBB breakdown in TBI and examine the primary and secondary mechanisms that underlie such pathology. We go on to consider the consequences of BBB injury, before analyzing potential mechanisms linking vascular pathology to neuronal dysfunction and degeneration, and exploring possible targets for treatment. Finally, we highlight areas for future basic research and clinical studies into TBI.

Transcriptome Profiling Reveals TGF-β Signaling Involvement in Epileptogenesis

Brain injury may result in the development of epilepsy, one of the most common neurological disorders. We previously demonstrated that albumin is critical in the generation of epilepsy after blood–brain barrier (BBB) compromise. Here, we identify TGF-β pathway activation as the underlying mechanism. We demonstrate that direct activation of the TGF-β pathway by TGF-β1 results in epileptiform activity similar to that after exposure to albumin. Coimmunoprecipitation revealed binding of albumin to TGF-β receptor II, and Smad2 phosphorylation confirmed downstream activation of this pathway. Transcriptome profiling demonstrated similar expression patterns after BBB breakdown, albumin, and TGF-β1 exposure, including modulation of genes associated with the TGF-β pathway, early astrocytic activation, inflammation, and reduced inhibitory transmission. Importantly, TGF-β pathway blockers suppressed most albumin-induced transcriptional changes and prevented the generation of epileptiform activity. Our present data identifies the TGF-β pathway as a novel putative epileptogenic signaling cascade and therapeutic target for the prevention of injury-induced epilepsy.

Blood–brain barrier breakdown-inducing astrocytic transformation: Novel targets for the prevention of epilepsy

Epileptogenesis is common following brain insults such as trauma, ischemia and infection. However, the mechanisms underlying injury-related epileptogenesis remain unknown. Recent studies demonstrated impaired integrity of the blood-brain barrier (BBB) during epileptogenesis. Here we review accumulating experimental evidence supporting the potential involvement of primary BBB lesion in epileptogenesis. Data from animal experiments demonstrate that primary breakdown of the BBB prone animals to develop focal neocortical epilepsy that is followed by neuronal loss and impaired functions. The extravasation of albumin from the circulation into the brain neuropil was found to be sufficient for the induction of epileptogenesis. Albumin binds to transforming growth factor beta receptor 2 (TGFbetaR2) in astrocytes and induces rapid transcriptional modifications, astrocytic transformation and dysfunction. We highlight a novel cascade of events which is initiated by increased BBB permeability, eventually leading to neuronal dysfunction, epilepsy and cell loss. We review potential mechanisms and existing experimental evidence for the important role of astrocytes and the TGFbeta pathway in epileptogenesis. Finally, we review evidence from human clinical data supporting the involvement of BBB lesion in epilepsy. We propose that primary vascular injury, and specifically BBB breakdown and repair, are key elements in altered interactions within the neurovascular unit and thus may serve as new therapeutic targets.

Astrocytic dysfunction in epileptogenesis: consequence of altered potassium and glutamate homeostasis?

Focal epilepsy often develops following traumatic, ischemic, or infectious brain injury. While the electrical activity of the epileptic brain is well characterized, the mechanisms underlying epileptogenesis are poorly understood. We have recently shown that in the rat neocortex, long-lasting breakdown of the blood–brain barrier (BBB) or direct exposure of the neocortex to serum-derived albumin leads to rapid upregulation of the astrocytic marker GFAP (glial fibrillary acidic protein), followed by delayed (within 4–7 d) development of an epileptic focus. We investigated the role of astrocytes in epileptogenesis in the BBB-breakdown and albumin models of epileptogenesis. We found similar, robust changes in astrocytic gene expression in the neocortex within hours following treatment with deoxycholic acid (BBB breakdown) or albumin. These changes predict reduced clearance capacity for both extracellular glutamate and potassium. Electrophysiological recordings in vitro confirmed the reduced clearance of activity-dependent accumulation of both potassium and glutamate 24 h following exposure to albumin. We used a NEURON model to simulate the consequences of reduced astrocytic uptake of potassium and glutamate on EPSPs. The model predicted that the accumulation of glutamate is associated with frequency-dependent (>100 Hz) decreased facilitation of EPSPs, while potassium accumulation leads to frequency-dependent (10–50 Hz) and NMDA-dependent synaptic facilitation. In vitro electrophysiological recordings during epileptogenesis confirmed frequency-dependent synaptic facilitation leading to seizure-like activity. Our data indicate a transcription-mediated astrocytic transformation early during epileptogenesis. We suggest that the resulting reduction in the clearance of extracellular potassium underlies frequency-dependent neuronal hyperexcitability and network synchronization.

Blood-brain barrier dysfunction, TGFβ signaling, and astrocyte dysfunction in epilepsy.

Brain insults, including traumatic and ischemic injuries, are frequently followed by acute seizures and delayed development of epilepsy. Dysfunction of the blood‐brain barrier (BBB) is a hallmark of brain insults and is usually surrounding the core lesion. Recent studies from several laboratories confirmed that vascular pathology is involved in the development of epilepsy and demonstrate a key role for astroglia in this process. In this review, we focus on glia‐related mechanisms linking vascular pathology, and specifically BBB dysfunction, to seizures and epilepsy. We summarize molecular and physiological experimental data demonstrating that the function of astrocytes is altered due to direct exposure to serum albumin, mediated by transforming growth factor beta signaling. We discuss the reported changes and their potential role in the observed hyperexcitability as well as potential implications of these findings for the future development of new diagnostic modalities and treatments to allow a full implementation of the gained knowledge for the benefit of patients with epilepsy.

ARP, a peptide derived from the stress-associated acetylcholinesterase variant has hematopoietic growth promoting activities

BackgroundPsychological stress induces rapid and long-lasting changes in blood cell composition, implying the existence of stress-induced factors that modulate hematopoiesis. Here we report the involvement of the stress-associated “readthrough” acetylcholinesterase (AChE-R) variant, and its 26 amino acid C-terminal domain (ARP) in hematopoietic stress responses.Materials and MethodsWe studied the effects of stress, cortisol, antisense oligonucleotides to AChE, and synthetic ARP on peripheral blood cell composition and clonogenic progenitor status in mice under normal and stress conditions, and on purified CD341 cells of human origin. We employed in situ hybridization and immunocytochemical staining to monitor gene expression, and 5-bromo-2-deoxyuridine (BrdU), primary liquid cultures, and clonogenic progenitor assays to correlate AChE-R and ARP with proliferation and differentiation of hematopoietic progenitors.ResultsWe identified two putative glucocorticoid response elements in the human ACHE gene encoding AChE. In human CD341 hematopoietic progenitor cells, cortisol elevated AChE-R mRNA levels and promoted hematopoietic expansion. In mice, a small peptide crossreacting with anti-ARP antiserum appeared in serum following forced swim stress. Ex vivo, ARP was more effective than cortisol and equally as effective as stem cell factor in promoting expansion and differentiation of early hematopoietic progenitor cells into myeloid and megakaryocyte lineages.ConclusionsOur findings attribute a role to AChE-R and ARP in hematopoietic homeostasis following stress, and suggest the use of ARP in clinical settings where ex vivo expansion of progenitor cells is required.

Stress, social behavior, and resilience: Insights from rodents

The neurobiology of stress and the neurobiology of social behavior are deeply intertwined. The social environment interacts with stress on almost every front: social interactions can be potent stressors; they can buffer the response to an external stressor; and social behavior often changes in response to stressful life experience. This review explores mechanistic and behavioral links between stress, anxiety, resilience, and social behavior in rodents, with particular attention to different social contexts. We consider variation between several different rodent species and make connections to research on humans and non-human primates.

Restructuring the neuronal stress response with anti-glucocorticoid gene delivery

Glucocorticoids, the adrenal steroids released during stress, compromise the ability of neurons to survive neurological injury. In contrast, estrogen protects neurons against such injuries. We designed three genetic interventions to manipulate the actions of glucocorticoids, which reduced their deleterious effects in both in vitro and in vivo rat models. The most effective of these interventions created a chimeric receptor combining the ligand-binding domain of the glucocorticoid receptor and the DNA-binding domain of the estrogen receptor. Expression of this chimeric receptor reduced hippocampal lesion size after neurological damage by 63% and reversed the outcome of the stress response by rendering glucocorticoids protective rather than destructive. Our findings elucidate three principal steps in the neuronal stress-response pathway, all of which are amenable to therapeutic intervention.

Frequent Blood-Brain Barrier Disruption in the Human Cerebral Cortex

Abstract1. The blood–brain barrier (BBB) protects the brain from circulating xenobiotic agents. The pathophysiology, time span, spatial pattern, and pathophysiological consequences of BBB disruptions are not known.2. Here, we report the quantification of BBB disruption by measuring enhancement levels in computerized tomography brain images.3. Pathological diffuse enhancement associated with elevated albumin levels in the cerebrospinal fluid (CSF) was observed in the cerebral cortex of 28 out of 43 patients, but not in controls. Four patients displayed weeks-long focal BBB impairment. In 19 other patients, BBB disruption was significantly associated with elevated blood pressure, body temperature, serum cortisol, and stress-associated CSF “readthrough” acetylcholinesterase. Multielectrode electroencephalography revealed enhanced slow-wave activities in areas of focal BBB disruption. Thus, quantification of BBB disruption using minimally invasive procedures, demonstrated correlations with molecular, clinical, and physiological stress-associated indices.4. These sequelae accompany a wide range of neurological disorders, suggesting that persistent, detrimental BBB disruption is considerably more frequent than previously assumed.