Distribution of Aquaporin 4 in rodent spinal cord: Relationship with astrocyte markers and chondroitin sulfate proteoglycans

Abstract

Water balance between cells and extracellular compartments is essential for proper functioning of the central nervous system, as demonstrated by its perturbations in pathological conditions. Aquaporin 4 (AQP4) is the predominant water channel in brain and spinal cord, where it is present mainly on astrocytic endfeet contacting vessels. A role in water homeostasis control has been proposed also for the extracellular matrix, that in brain consists mainly of chondroitin sulfate proteoglycans (CSPGs). Using cytochemical and immunocytochemical techniques, we investigated their distribution in rodent spinal cord, to better understand the role of these two classes of molecules. The results show that in spinal gray matter AQP4 labeling is intense in all perivascular profiles and (1) displays a marked dorsoventral gradient in the neuropil; and (2) coexists extensively with glial glutamate transporter-1 (GLT-1) but scarcely with glial fibrillary acidic protein (GFAP). In white matter the overlap between AQP4, GLT-1, and GFAP is almost complete. Ultrastructural examination shows that AQP4-labeled astrocytic processes surround blood vessels, neuronal perikarya and processes, and both asymmetric and symmetric synapses, indicating that the protein may be involved in the regulation of water fluxes around both inhibitory and excitatory synapses. CSPGs, visualized by labeling with Wisteria floribunda agglutinin, show a distribution complementary to that of AQP4, being absent or weekly expressed in AQP4-enriched areas. These findings suggest that different mechanisms may contribute to the regulation of water homeostasis in different spinal cord regions.

Acute and chronic changes in aquaporin 4 expression after spinal cord injury

“…All reports have shown that AQP4 water channels are primarily expressed in spinal cord astrocytes, surrounding blood vessels and neurons (Vitellaro-Zuccarello et al, 2005;Rash et al, 1998Rash et al, ,1999Oshio et al, 2004). Consistent with those reports, we found robust expression of AQP4 in astrocytes forming barriers between the spinal cord parenchyma and blood or cerebrospinal fluid: in astrocytic processes surrounding blood vessels or in glia limitans externa and interna.…”

Astrocytic Plasticity and Patterned Oxytocin Neuronal Activity: Dynamic Interactions

“…The MER was accompanied by expression of AQP4 that was in parallel with GFAP changes. In spinal cord white matter, the overlap between AQP4 and GFAP is almost complete (Vitellaro-Zuccarello et al, 2005), suggesting that AQP4 is a binding partner of GFAP. Actin is a dynamic astrocytic cytoskeletal element (Wang and Hatton, 2007b).…”

Differential expression of several molecules of the extracellular matrix in functionally and developmentally distinct regions of rat spinal cord

“…For double-labeling experiments, mAbs to ECM components were used in combination with one of the following polyclonal rabbit antibodies: anti-calretinin (1:1,500), anticalbindin D-28k (1:1,500), and anti-parvalbumin (1:3,000), all from Swant (Bellinzona, Switzerland), used to label various subpopulations of local association neurons (Ren and Ruda 1994;Carr et al 1998); anti-potassium channel Kv3.1b subunit (Sigma; 1:250), considered a marker of fast-firing neurons (Rudy and McBain 2001;Baranauskas et al 2003); anti-aquaporin-4 (AQP4, Sigma; 1:800) identifying the main water channel expressed in the CNS (Amiry-Moghaddam and Ottersen 2003) and used to visualize astrocyte plasma membranes (Vitellaro-Zuccarello et al 2005). Motor neurons were labeled with mAb SMI 32 against a non-phosphorylated epitope of the neurofilament H subunit (NF-H, Sternberger Monoclonals, Lutherville, Md., USA; 1:500).…”