title: Focused ultrasound-mediated bbb disruption is associated with an increase in activation of AKT: experimental study in rats.
abstract: BACKGROUND
  The Blood Brain Barrier (BBB) maintains the homeostasis of central nervous system by preventing the free passage of macromolecules from the systemic circulation into the brain. This normal physiological function of the BBB presents a challenge for delivery of therapeutic compounds into the brain. Recent studies have shown that the application of focused ultrasound together with ultrasound contrast agent (microbubbles) temporarily increases the permeability of the BBB. This effect is associated with breakdown of tight junctions, the structures that regulate the paracellular permeability of the endothelial cell layer. The influence of this ultrasound effect on the activation of intracellular signaling proteins is currently not well understood. Therefore, the aim of this study was to investigate the activation of cell survival signaling molecules in response to ultrasound-mediated BBB opening;
  
  
  METHODS
  The BBB was disrupted in two four-spot lines (1-1.5 mm spacing) along the right hemisphere of rat brain with ultrasound beams (0.3 MPa, 120 s, 10 ms bursts, repetition frequency = 1 Hz) in the presence Definity microbubbles. Contrast-enhanced MRI images were acquired to assess the extent of BBB opening upon which the animals were sacrificed and the brains removed and processed for biochemical and immunohistochemical analyses;
  
  
  RESULTS
  Immunoblotting of sonicated brain lysates resolved by SDS-PAGE demonstrated an increase in phosphorylation of Akt and its downstream signaling molecule, GSK3β, while the phosphorylation of MAPK remained unchanged. The elevated levels of pAkt and pGSK3β are still evident after 24 hours post-sonication, a time point where the integrity of the BBB is known to be re-established. Furthermore, immunofluoresence staining localized this increase in pAkt and pGSK3β levels to neuronal cells flanking the region of the disrupted BBB;
  
  
  CONCLUSIONS
  Our data demonstrates that ultrasound-mediated BBB disruption causes an activation of the Akt signaling pathway in neuronal cells surrounding the disrupted BBB.
authors.affiliation: Molecular and Cellular Biology Research, Sunnybrook Research Institute, Sunnybrook Health Sciences Centre, Toronto, ON, Canada.
authors.forename: Shahrzad
authors.initials: S
authors.lastname: Jalali
authors.forename: Yuexi
authors.initials: Y
authors.lastname: Huang
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Dumont
authors.forename: Kullervo
authors.initials: K
authors.lastname: Hynynen
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001812:Blood-Brain Barrier / Q000000981:diagnostic imaging / Q000378:metabolism*; D015153:Blotting, Western; D003287:Contrast Media / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D047468:Immunoprecipitation; D008279:Magnetic Resonance Imaging; D008297:Male; D045423:Microbubbles; D009474:Neurons / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D013010:Sonication; D013997:Time Factors; D014463:Ultrasonography
chemical_list: D003287:Contrast Media; D000071679:Glycogen Synthase Kinase 3 beta; C000605508:Gsk3b protein, rat; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3