Localization of aquaporin‐1 water channel in glial cells of the human peripheral nervous system

Abstract

The aquaporins (AQPs) are a family of water channel proteins with at least 13 mammalian members (AQPs 0-12) expressed in diverse fluid transporting tissues. AQP1, AQP4, and AQP9 have been identified in the central nervous system and demonstrated or proposed to play important roles in brain water homeostasis. Aquaporin expression in the peripheral nervous system is poorly studied. Here we report that the AQP1 water channel is specifically localized to glial cells of the peripheral nervous system by immunohistochemistry, RT-PCR, and immunoblotting. Paraffin-embedded biopsies of human pancreas, esophagus, and sciatic nerves were accessed by immunoperoxidase staining using affinity-purified AQP1, AQP4, and AQP9 antibodies. Strong AQP1 expression was identified in pancreatic nerve plexuses and in the submucosal and myenteric nerve plexuses in the esophagus. AQP1 was localized to the same cell population expressing glial fibrillary acidic protein (GFAP), but not to the neurons in the plexuses, indicating glial cell-specific expression. RT-PCR and immunoblot analysis of microdissected pancreatic ganglia confirmed the expression of AQP1 transcript and protein. Pancreatic and sciatic nerve bundles, which contain nonmyelinating and myelinating Schwann cells, respectively, were also selectively labeled by AQP1 antibody. AQP4 and AQP9, which are broadly expressed in astroglial cells in brain and spinal cord, were not localized in glial cells in the peripheral nerve plexuses. These results suggest that AQPs are differentially expressed in the peripheral versus central nervous system and that channel-mediated water transport mechanisms may be involved in peripheral neuronal activity by regulating water homeostasis in nerve plexuses and bundles.

Expression and function of aquaporins in peripheral nervous system

“…The vast majority of AQP1-bearing submucosal neurons were immunoreactive to substance P, suggesting that they are probably a subpopulation of sensory neurons. In both the rat and sheep studies, AQP1 expression was not detected in glial elements of submucosal plexus, which is different from the fi nding by Gao et al in the human esophagus [17] . These results further demonstrate species difference of AQP1 expression in enteric nervous system.…”

“…Many AQP1-positive nerve fi bers were also found both in the myenteric and submucosal plexuses in all regions of the ileum. The neuronal expression pattern of AQP1 in rat ileum is apparently different from the glial cell-specifi c expression seen in the nerve plexuses in human esophagus and pancreas [17] . In consistent with the above study, Ishihara et al confi rmed the localization of AQP1 in neurons and fibers of rat myenteric plexus [19] .…”

“…Gao et al first reported the expression pattern of AQP1 in human enteric nervous system by immunolocalization in 2006 [17] . Strong AQP1 expression was identifi ed in the submucosal and myenteric nerve plexuses in the esophagus.…”

Involvement of MAPK ERK Activation in Upregulation of Water Channel Protein Aquaporin 1 in a Mouse Model of Bell’s Palsy

“…*p<0.05 compared with that in the sham group (Gao et al 2006;Nandasena et al 2007), little is known about its expression in facial nerve. Several lines of evidence have revealed that Schwann cells are involved in regulating water and ion homeostasis to ensure an appropriate neuronal environment in the PNS, which is similar to the role of astrocytes in the CNS (Simard and Nedergaard 2004).…”

“…But, the expression and function of AQPs in the peripheral nervous system (PNS) are poorly understood. Gao et al have shown that AQP1 is the principle water channel in the PNS and is specifically localized to glial cells expressing glial fibrillary acidic protein (GFAP) (Gao et al 2006). AQP1 is also found in the PNS neuronal or glial elements such as dorsal root ganglion neurons, enteric neurons and glial cells, trigeminal ganglion neurons, and terminal Schwann cells, nodose ganglia neurons, nerve fiber bundles neurons and glial cells (Oshio et al 2006;Nandasena et al 2007;Shields et al 2007;Ma et al 2011).…”