TGF-beta receptor-mediated albumin uptake into astrocytes is involved in neocortical epileptogenesis.

It has long been recognized that insults to the cerebral cortex, such as trauma, ischaemia or infections, may result in the development of epilepsy, one of the most common neurological disorders. Human and animal studies have suggested that perturbations in neurovascular integrity and breakdown of the blood-brain barrier (BBB) lead to neuronal hypersynchronization and epileptiform activity, but the mechanisms underlying these processes are not known. In this study, we reveal a novel mechanism for epileptogenesis in the injured brain. We used focal neocortical, long-lasting BBB disruption or direct exposure to serum albumin in rats (51 and 13 animals, respectively, and 26 controls) as well as albumin exposure in brain slices in vitro. Most treated slices (72%, n = 189) displayed hypersynchronous propagating epileptiform field potentials when examined 5-49 days after treatment, but only 14% (n = 71) of control slices showed similar responses. We demonstrate that direct brain exposure to serum albumin is associated with albumin uptake into astrocytes, which is mediated by transforming growth factor beta receptors (TGF-betaRs). This uptake is followed by down regulation of inward-rectifying potassium (Kir 4.1) channels in astrocytes, resulting in reduced buffering of extracellular potassium. This, in turn, leads to activity-dependent increased accumulation of extracellular potassium, resulting in facilitated N-methyl-d-aspartate-receptor-mediated neuronal hyperexcitability and eventually epileptiform activity. Blocking TGF-betaR in vivo reduces the likelihood of epileptogenesis in albumin-exposed brains to 29.3% (n = 41 slices, P < 0.05). We propose that the above-described cascade of events following common brain insults leads to brain dysfunction and eventually epilepsy and suggest TGF-betaRs as a possible therapeutic target.

[1]  Thomas D. Schmittgen,et al.  Analysis of relative gene expression data using real-time quantitative PCR and the 2(-Delta Delta C(T)) Method. , 2001, Methods.

[2]  P. Ramarao,et al.  Dementia of Alzheimer's disease and other neurodegenerative disorders--memantine, a new hope. , 2005, Pharmacological research.

[3]  T. Lehmann,et al.  Effects of barium, furosemide, ouabaine and 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS) on ionophoretically-induced changes in extracellular potassium concentration in hippocampal slices from rats and from patients with epilepsy , 2002, Brain Research.

[4]  A. Warth,et al.  Redistribution of the water channel protein aquaporin-4 and the K+ channel protein Kir4.1 differs in low- and high-grade human brain tumors , 2005, Acta Neuropathologica.

[5]  A. Bordey,et al.  Electrophysiological characteristics of reactive astrocytes in experimental cortical dysplasia. , 2001, Journal of neurophysiology.

[6]  G. Stoll,et al.  Time course of inwardly rectifying K+ current reduction in glial cells surrounding ischemic brain lesions , 2000, Brain Research.

[7]  Y. Kurachi,et al.  An inwardly rectifying K(+) channel, Kir4.1, expressed in astrocytes surrounds synapses and blood vessels in brain. , 2001, American journal of physiology. Cell physiology.

[8]  J. Simard,et al.  Transforming Growth Factor-β1 Regulates Kir2.3 Inward Rectifier K+ Channels via Phospholipase C and Protein Kinase C-δ in Reactive Astrocytes from Adult Rat Brain* , 2002, The Journal of Biological Chemistry.

[9]  D. Spencer,et al.  Loss of perivascular aquaporin 4 may underlie deficient water and K+ homeostasis in the human epileptogenic hippocampus. , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[10]  A. Friedman,et al.  Pyridostigmine enhances glutamatergic transmission in hippocampal CA1 neurons , 2003, Experimental Neurology.

[11]  C. Elger,et al.  Astrocytes in the hippocampus of patients with temporal lobe epilepsy display changes in potassium conductances , 2000, The European journal of neuroscience.

[12]  R. Pascual-Marqui,et al.  Focal Cortical Dysfunction and Blood–Brain Barrier Disruption in Patients With Postconcussion Syndrome , 2005, Journal of clinical neurophysiology : official publication of the American Electroencephalographic Society.

[13]  P A Salin,et al.  Chronic neocortical epileptogenesis in vitro. , 1994, Journal of neurophysiology.

[14]  M. Gutnick,et al.  Long-term changes in neocortical activity after chemical kindling with systemic pentylenetetrazole: an in vitro study. , 1994, Journal of neurophysiology.

[15]  D. Rifkin,et al.  Latent transforming growth factor-beta: structural features and mechanisms of activation. , 1997, Kidney international.

[16]  Cornford Em Epilepsy and the blood brain barrier: endothelial cell responses to seizures. , 1999 .

[17]  E. Neher,et al.  The equilibration time course of [K+]0 in cat cortex , 1973, Experimental Brain Research.

[18]  K. Vonck,et al.  Direct Medical Costs of Refractory Epilepsy Incurred by Three Different Treatment Modalities: A Prospective Assessment , 2002, Epilepsia.

[19]  Yoshihisa Kurachi,et al.  Differential Assembly of Inwardly Rectifying K+ Channel Subunits, Kir4.1 and Kir5.1, in Brain Astrocytes* , 2004, Journal of Biological Chemistry.

[20]  M. Gutnick,et al.  Hyperexcitability in a model of cortical maldevelopment. , 1996, Cerebral cortex.

[21]  P. Mcnaughton,et al.  Plasma albumin is a potent trigger of calcium signals and DNA synthesis in astrocytes. , 1995, Proceedings of the National Academy of Sciences of the United States of America.

[22]  Roberto Spreafico,et al.  Damage, Reorganization, and Abnormal Neocortical Hyperexcitability in the Pilocarpine Model of Temporal Lobe Epilepsy , 2002, Epilepsia.

[23]  S. Mildenberger,et al.  Transforming growth factor‐β1 reduces megalin‐ and cubilin‐mediated endocytosis of albumin in proximal‐tubule‐derived opossum kidney cells , 2003 .

[24]  Harald Sontheimer,et al.  Properties of human glial cells associated with epileptic seizure foci , 1998, Epilepsy Research.

[25]  Jens P Dreier,et al.  Lasting Blood-Brain Barrier Disruption Induces Epileptic Focus in the Rat Somatosensory Cortex , 2004, The Journal of Neuroscience.

[26]  M. Grigor,et al.  Serum albumin secretion in rat milk. , 1987, Journal of Physiology.

[27]  D A Pollen,et al.  Neuroglia: Gliosis and Focal Epilepsy , 1970, Science.

[28]  D. Prince,et al.  Synaptic activity in chronically injured, epileptogenic sensory-motor neocortex. , 2002, Journal of neurophysiology.

[29]  M. Nedergaard,et al.  The blood–brain barrier: an overview Structure, regulation, and clinical implications , 2004, Neurobiology of Disease.

[30]  E. Neuwelt Mechanisms of Disease: The Blood-Brain Barrier , 2004, Neurosurgery.

[31]  C. B. Ransom,et al.  Biophysical and pharmacological characterization of inwardly rectifying K+ currents in rat spinal cord astrocytes. , 1995, Journal of neurophysiology.

[32]  P. Crino,et al.  Epileptogenesis and Reduced Inward Rectifier Potassium Current in Tuberous Sclerosis Complex‐1–Deficient Astrocytes , 2005, Epilepsia.

[33]  D. Kaufer,et al.  Acute stress facilitates long-lasting changes in cholinergic gene expression , 1998, Nature.

[34]  A. Malik,et al.  Albumin endocytosis in endothelial cells induces TGF-β receptor II signaling , 2004 .

[35]  Hermona Soreq,et al.  Pyridostigmine brain penetration under stress enhances neuronal excitability and induces early immediate transcriptional response , 1996, Nature Medicine.

[36]  C. Steinhäuser,et al.  Lesion‐induced changes of electrophysiological properties in astrocytes of the rat dentate gyrus , 1999, Glia.

[37]  R. Jabs,et al.  Developmental regulation of Na+ and K+ conductances in glial cells of mouse hippocampal brain slices , 1995, Glia.

[38]  M. Morganti-Kossmann,et al.  Inflammatory response in acute traumatic brain injury: a double-edged sword , 2002, Current opinion in critical care.

[39]  F. Dudek,et al.  Increased excitatory synaptic activity and local connectivity of hippocampal CA1 pyramidal cells in rats with kainate-induced epilepsy. , 2004, Journal of neurophysiology.

[40]  U. Dirnagl,et al.  Turnover of Rat Brain Perivascular Cells , 2001, Experimental Neurology.

[41]  E. Hansson,et al.  Astrocyte–endothelial interactions at the blood–brain barrier , 2006, Nature Reviews Neuroscience.

[42]  W. J. Brown,et al.  Ultrastructural parameters of limbic microvasculature in human psychomotor epilepsy. , 1983, Clinical neuropathology.

[43]  I. Bechmann,et al.  Reactive astrocytes upregulate fas (CD95) and fas ligand (CD95L) expression but do not undergo programmed cell death during the course of anterograde degeneration , 2000, Glia.

[44]  W. Oldendorf,et al.  Epilepsy and the blood-brain barrier. , 1986, Advances in neurology.

[45]  Eva Syková,et al.  Voltage‐dependent potassium currents in hypertrophied rat astrocytes after a cortical stab wound , 2004, Glia.

[46]  D. Kaufer,et al.  Frequent Blood–Brain Barrier Disruption in the Human Cerebral Cortex , 2001, Cellular and Molecular Neurobiology.

[47]  D. Prince,et al.  Epileptogenesis in chronically injured cortex: in vitro studies. , 1993, Journal of neurophysiology.

[48]  Christian Steinhäuser,et al.  Astrocyte dysfunction in neurological disorders: a molecular perspective , 2006, Nature Reviews Neuroscience.

[49]  S. W. Kuffler,et al.  GLIA IN THE LEECH CENTRAL NERVOUS SYSTEM: PHYSIOLOGICAL PROPERTIES AND NEURON-GLIA RELATIONSHIP. , 1964, Journal of neurophysiology.

[50]  E. Mackenzie,et al.  Evidence of Type I and Type II Transforming Growth Factor‐β Receptors in Central Nervous Tissues: Changes Induced by Focal Cerebral Ischemia , 1998, Journal of Neurochemistry.

[51]  M S Grady,et al.  Impaired K+ Homeostasis and Altered Electrophysiological Properties of Post-Traumatic Hippocampal Glia , 1999, The Journal of Neuroscience.

[52]  Jerry Silver,et al.  Regeneration beyond the glial scar , 2004, Nature Reviews Neuroscience.

[53]  F. Battaini,et al.  PARP-1 inhibition to treat cancer, ischemia, inflammation. , 2005, Pharmacological research.