Brain aquaporin-4 in experimental acute liver failure.
Intracranial hypertension caused by brain edema and associated astrocyte swelling is a potentially lethal complication of acute liver failure (ALF). Mechanisms of edema formation are not well understood, but elevated levels of blood and brain ammonia and its by-product glutamine have been implicated in this process. Since aquaporin-4 (AQP4) has been implicated in brain edema in other conditions, we examined its role in a rat model of ALF induced by the hepatotoxin thioacetamide. Rats with ALF showed increased AQP4 protein in the plasma membrane (PM). Total tissue levels of AQP4 protein and mRNA levels were not altered, indicating that increased AQP4 is not transcriptionally mediated but likely reflects a more stable anchoring of AQP4 to the PM and/or interference with its degradation. An increase inAQP4 immunoreactivity in thePM was observed in perivascular astrocytes in ALF. Rats with ALF also showed increased levels of α-syntrophin, a protein involved in anchoringAQP4 to perivascular astrocytic end-feet. Increased AQP4 andα-syntrophin levels were inhibited by L-histidine, an inhibitor of glutamine transport into mitochondria, suggesting a role for glutamine in the increase of PM levels of AQP4. These results indicate that increased AQP4 PM levels in perivascular astrocytic end-feet are likely critical to the development of brain edema in ALF.
Rama Rao
Kakulavarapu V
KV
Department of Pathology, University of Miami, Miller School of Medicine, Miami, Florida 33101, USA.
Jayakumar
Arumugam R
AR
Tong
Xiaoying
X
Curtis
Kevin M
KM
Norenberg
Michael D
MD
D000641:Ammonia / Q000494:pharmacology; D000818:Animals; D051401:Aquaporin 4 / Q000235:genetics / Q000378:metabolism*; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D001921:Brain / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D001929:Brain Edema / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D006639:Histidine / Q000494:pharmacology; D017114:Liver Failure, Acute / Q000139:chemically induced / Q000150:complications / Q000378:metabolism* / Q000473:pathology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D013853:Thioacetamide / Q000494:pharmacology
C496032:Aqp4 protein, rat; D051401:Aquaporin 4; D002135:Calcium-Binding Proteins; D008565:Membrane Proteins; D009124:Muscle Proteins; D034741:RNA, Small Interfering; C091825:syntrophin alpha1; D013853:Thioacetamide; D006639:Histidine; D000641:Ammonia