Aquaporin 4 mRNA Levels in Neuromuscular Tissues of Wild-type and Dystrophin-deficient Mice

Abstract

Aquaporin (AQP) 4 is a water-specific channel protein and is abundant in central nervous tissues and skeletal muscles. Recently, the AQP4 molecule has been increasingly highlighted in its pathophysiological role of several neurological diseases, such as stroke, muscular dystrophy and neuromyelitis optica. We therefore measured the levels of AQP4 mRNA and glyceraldehyde-3 phosphate dehydrogenase mRNA (an internal control) in muscle and brain tissues of wild-type mice (C57BL10/ScSn) and age-matched dystrophindeficient mdx mice (C57BL10/ScSn mdx) by real-time quantitative RT-PCR. The relative AQP4 mRNA level was highest in the spinal cord among the neuromuscular tissues examined in wild-type mice. Among the muscle tissues of wild-type mice, the relative AQP4 mRNA level was higher in extensor digitorum longus (EDL) muscles, and its descending order was EDL, quadriceps femoris, soleus and heart muscles. It is noteworthy that there was no difference in the relative AQP4 mRNA levels in the brain tissues between wildtype mice and age-matched mdx mice. In contrast, the AQP4 mRNA level in the quadriceps femoris muscle was significantly lower in mdx mice than in wild-type mice. The fact that the spinal cord contains the highest AQP4 mRNA may be related to the pathogenesis of neuromyelitis optica, in which AQP4 protein is the target antigen. In addition, the low expression level of AQP4 mRNA in the mdx mouse muscle suggests a functional link between AQP4 and dystrophin in the muscle tissue. We suggest that a similar pathomechanism may underlie the phenotypic consequences of the mdx mouse and Duchenne muscular dystrophy. The water molecule is essential for the living organism. Aquaporins (AQPs) comprise a large family of integral membrane proteins that form a water channel in animals, plants and microorganisms. They play a role in bidirectional water movement in response to osmotic gradients created by ion pumping and are expressed widely in mammalian epithelia and endothelia. In skeletal muscle cells (Rash and Ellisman 1974) and brain astrocytes (Landis and Reese 1981), the freeze fracture electron microscopy revealed the presence of many orthogonal arrays (OAs) which are identified as aggregates of 4 or more 6-nm diameter particles in the P face and as aggregates of 4 or

Aquaporin-4 in the heart: expression, regulation and functional role in ischemia

“…With AQP4 being the most abundant aquaporin in the brain, the number of mRNA copies in murine cardiomyocytes has been estimated at around 11 % of that in the fast-twitch skeletal muscle and only 2.5 % of that in the cerebellum [38]. However, to evaluate the importance of function, cellular localization may be as significant as quantity.…”

“…AQP4 expression in the human heart was reported to be very low [7]. Only a few studies have addressed the expression and subcellular localization of AQP4 in the heart, with inconsistent results [7,38,44]. Thus, it is currently unclear in which cardiac cells AQP4 is located, where in the cell it is expressed, and how its expression is regulated.…”

Aquaporins in spinal cord injury: the janus face of aquaporin 4

“…There is little doubt that AQP4's normal function in astrocytes is to enable fast water influx or efflux, driven by osmotic or hydrostatic pressures (Solenov et al, 1997; Yang et al, 2008). It has been reported that rat spinal cord tissue has the highest expression levels of AQP4 among all AQP4-expressing organs, including several different brain regions as well as various muscles including heart tissue (Shibuya et al, 2008). Widespread and high expression levels of AQP4 in mammalian spinal cords suggest the importance of potentially altered AQP4 functions in different pathological spinal conditions.…”

Aquaporin 4 Expression in the mdx Mouse Diaphragm

“…The concentration of AQP4 mRNA content was estimated by real-time quantitative RT-PCR as described previously [20]. The oligonucleotide primers were designed from the mouse AQP4 sequence (Entrez U88623): sense strand, 5'-GAAAACCCCTTACCTGTGG-3'; antisense strand, 5'-AGCTGGCAAAAATAGTGA-3'.…”