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Expression of multiple AQP4 pools in the plasma membrane and their association with the dystrophin complex
Author(s) -
Nicchia Grazia Paola,
Cogotzi Laura,
Rossi Andrea,
Basco Davide,
Brancaccio Andrea,
Svelto Maria,
Frigeri Antonio
Publication year - 2008
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.2008.05302.x
Subject(s) - dystrophin , aquaporin 4 , duchenne muscular dystrophy , mdx mouse , membrane protein , caveolae , chemistry , polyacrylamide gel electrophoresis , skeletal muscle , dystroglycan , aquaporin , sodium dodecyl sulfate , biology , microbiology and biotechnology , biochemistry , membrane , genetics , endocrinology , extracellular matrix , enzyme , laminin
Altered aquaporin‐4 (AQP4) expression has been reported in brain edema, tumors, muscular dystrophy, and neuromyelitis optica. However, the plasma membrane organization of AQP4 and its interaction with proteins such as the dystrophin‐associated protein complex are not well understood. In this study, we used sucrose density gradient ultracentrifugation and 2D blue native/sodium dodecyl sulfate–polyacrylamide gel electrophoresis and showed the expression of several AQP4 multi‐subunit complexes (pools) of different sizes, ranging from ≫ 1 MDa to ∼500 kDa and containing different ratios of the 30/32 kDa AQP4 isoforms, indicative of orthogonal arrays of particles of various sizes. A high molecular weight pool co‐purified with dystrophin and β‐dystroglycan and was drastically reduced in the skeletal muscle of mdx3cv mice, which have no dystrophin. The number and size of the AQP4 pools were the same in the kidney where dystrophin is not expressed, suggesting the presence of dystrophin‐like proteins for their expression. We found that AQP2 is expressed only in one major pool of ∼500 kDa, indicating that the presence of different pools is a peculiarity of AQP4 rather than a widespread feature in the AQP family. Finally, in skeletal muscle caveolin‐3 did not co‐purify with any AQP4 pool, indicating the absence of interaction of the two proteins and confirming that caveolae and orthogonal arrays of particles are two independent plasma membrane microdomains. These results contribute to a better understanding of AQP4 membrane organization and raise the possibility that abnormal expression of specific AQP4 pools may be found in pathological states.