Immunolocalization of Water Channel Proteins AQP1 and AQP4 in Rat Spinal Cord

Abstract

SummaryAquaporin (AQP) is a water-selective channel protein. In the brain, AQPs play critical roles in the production of cerebrospinal fluid and in edema formation. In contrast, the expression and role of AQPs in spinal cord are unclear. We aimed to investigate the localization of AQP1 and AQP4 in normal rat spinal cord compared with the expression of marker proteins for astrocytes, neurons, and endothelial cells. Immunohistochemistry demonstrated that AQP1 and AQP4 are expressed along all levels of the spinal cord from the cervical to lumbar levels. AQP1 immunolabeling was observed in the dorsal horns in the gray matter, whereas the labeling was weak and mainly seen close to glia limitans in the white matter. AQP1 was co-labeled with marker proteins for unmyelinated neuronal fibers (peripherin) and endothelial cells (RECA-1) of blood vessels that had penetrated through the glia limitans. In contrast, AQP1 did not colocalize with GFAP, an astrocyte marker, at any level of the spinal cord. AQP4 was exclusively localized at the astrocytes, but AQP4 expression in spinal cord exhibited a less polarized and more spatial distribution than that of brain astrocytes. The observed characteristic localization and expression patterns of AQP1 and AQP4 could provide insights toward gaining an understanding of the role of AQPs in the spinal cord. (J Histochem Cytochem 62:598-611, 2014)

Imaging Differences between Neuromyelitis Optica Spectrum Disorders and Multiple Sclerosis: A Multi-Institutional Study in Japan

“…35 Therefore, spinal cord lesions in humans may also be unchanged along all spinal levels. However, in this study, NMOSD spinal cord lesions showed a bimodal distribution with a high peak in thoracic regions, and more frequent (71%) and significantly longer lesions in thoracic regions than in cervical regions.…”

Aquaporins in the Spinal Cord

“…Intense AQP1 labeling was found in synaptical terminal membranes, but not in the area of synaptic density [23] (Figure 1C). In laminae III and IV, AQP1 was dominantly present at the lateral and medial boundaries of the dorsal horns and in lamina V, a tangled, filamental pattern of AQP1 immunolabeling was seen [21]. In contrast, in other parts of gray matter AQP1 was pretty scarce with slightly increased expression in the immediate surroundings of the central canal [14,21].…”

“…The cerebrovascular endothelium in the CNS lacks AQP1 [16,19] with the exception of the blood vessels in circumventricular organs [20] and small capillaries occasionally found in the brain and spinal cord parenchyma [20,21,22]. Outside of the brain, AQP1 expression was found in the dorsal horns of the spinal cord, in the dorsal root ganglia and its projecting nerves, particularly in the sciatic nerve (Table 1) [14,21,23]. A portion of AQP1 labeling in spinal cord was assigned to a population of the primary sensory neurons with small-diameter which are important in nociception and pain processing [21,23].…”

“…Outside of the brain, AQP1 expression was found in the dorsal horns of the spinal cord, in the dorsal root ganglia and its projecting nerves, particularly in the sciatic nerve (Table 1) [14,21,23]. A portion of AQP1 labeling in spinal cord was assigned to a population of the primary sensory neurons with small-diameter which are important in nociception and pain processing [21,23]. Moreover, other studies suggested a role of this water channel in the perception of inflammatory thermal pain and cold pain perception [24,25].…”

Effects of aquaporin 4 and inward rectifier potassium channel 4.1 on medullospinal edema after methylprednisolone treatment to suppress acute spinal cord injury in rats

“…Aquaporins (AQPs) are closely related to tissue edema and AQP4 is the most studied isoform in the central nervous system, as it is widely distributed in the brain and spinal cord; it is closely related to trauma-induced brain and medullospinal edema. Oklinski et al 3 found that AQP4 is mainly expressed in the astrocytes of the rat spinal cord, as well as in the gray matter and white matter of the spinal cord; it is most highly expressed on the membranes of perivascular astrocytes in the gray matter. AQP4 participates in the transportation of water molecules in the brain, as well as the regulation of electrolytes and osmotic pressure, in the physiological state; under pathological conditions, it is involved in tissue edema caused by bodily injury 4 .…”