title: Albumin causes increased myosin light chain kinase expression in astrocytes via p38 mitogen-activated protein kinase.
abstract: Myosin light chain kinase (MLCK) plays an important role in the reorganization of the cytoskeleton, leading to disruption of vascular barrier integrity in multiple organs, including the blood-brain barrier (BBB), after traumatic brain injury (TBI). MLCK has been linked to transforming growth factor (TGF) and rho kinase signaling pathways, but the mechanisms regulating MLCK expression following TBI are not well understood. Albumin leaks into the brain parenchyma following TBI, activates glia, and has been linked to TGF-β receptor signaling. We investigated the role of albumin in the increase of MLCK in astrocytes and the signaling pathways involved in this increase. After midline closed-skull TBI in mice, there was a significant increase in MLCK-immunoreactive (IR) cells and albumin extravasation, which was prevented by treatment with the MLCK inhibitor ML-7. Using immunohistochemical methods, we identified the MLCK-IR cells as astrocytes. In primary astrocytes, exposure to albumin increased both isoforms of MLCK, 130 and 210. Inhibition of the TGF-β receptor partially prevented the albumin-induced increase in both isoforms, which was not prevented by inhibition of smad3. Inhibition of p38 MAPK, but not ERK, JNK, or rho kinase, also prevented this increase. These results are further evidence of a role of MLCK in the mechanisms of BBB compromise following TBI and identify astrocytes as a cell type, in addition to endothelium in the BBB, that expresses MLCK. These findings implicate albumin, acting through p38 MAPK, in a novel mechanism by which activation of MLCK following TBI may lead to compromise of the BBB.
authors.affiliation: Department of Pediatrics, Divisions of Critical Care, Children's Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, IL 60614, USA.
authors.forename: Janet L
authors.initials: JL
authors.lastname: Rossi
authors.forename: Hantamalala
authors.initials: H
authors.lastname: Ralay Ranaivo
authors.forename: Fatima
authors.initials: F
authors.lastname: Patel
authors.forename: Maryann
authors.initials: M
authors.lastname: Chrzaszcz
authors.forename: Charu
authors.initials: C
authors.lastname: Venkatesan
authors.forename: Mark S
authors.initials: MS
authors.lastname: Wainwright
mesh_terms: D000418:Albumins / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects* / Q000378:metabolism; D001930:Brain Injuries / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology*; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009219:Myosin-Light-Chain Kinase; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D018709:Statistics, Nonparametric; D013997:Time Factors; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*; D054460:rho-Associated Kinases / Q000378:metabolism
chemical_list: D000418:Albumins; D004791:Enzyme Inhibitors; D005904:Glial Fibrillary Acidic Protein; D054460:rho-Associated Kinases; D009219:Myosin-Light-Chain Kinase; D048051:p38 Mitogen-Activated Protein Kinases