Expression and Distribution Pattern of Aquaporin 4, 5 and 11 in Retinas of 15 Different Species

Abstract

Aquaporins (AQPs) are small integral membrane proteins with 13 members in mammals and are essential for water transport across membranes. They are found in many different tissues and cells. Currently, there are conflicting results regarding retinal aquaporin expression and subcellular localization between genome and protein analyses and among various species. AQP4, 7, 9 and 11 were described in the retina of men; whereas AQP6, 8 and 10 were earlier identified in rat retinas and AQP4, 5 and 11 in horses. Since there is a lack of knowledge regarding AQP expression on protein level in retinas of different animal models, we decided to analyze retinal cellular expression of AQP4, 5 and 11 in situ with immunohistochemistry. AQP4 was detected in all 15 explored species, AQP5 and AQP11 in 14 out of 15. Interestingly, AQP4 was unambiguously expressed in Muller glial cells, whereas AQP5 was differentially allocated among the species analyzed. AQP11 expression was Muller glial cell-specific in 50% of the animals, whereas in the others, AQP11 was detected in ganglion cell layer and at photoreceptor outer segments. Our data indicate a disparity in aquaporin distribution in retinas of various animals, especially for AQP5 and 11.

Keywords: AQP; Muller glia; aquaporin 11; aquaporin 4; aquaporin 5; glial fibrillary acidic protein; glutamine synthase; immunohistochemistry; osmotic control; retina; tissue water flux; water channels.

Figure 1

Predominant expression of aquaporin 4 (AQP4, green) at Muller glial cells in retinas of different species (magnification ×40). ILM, inner limiting membrane (arrow); GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer; OLM, outer limiting membrane (arrowhead); POS, photoreceptor outer segments. (A) mouse; (B) rat; (C) guinea pig; (D) horse; (E) cow; (F) sheep; (G) deer; (H) pig; (I) cat; (J) dog; (K) pigeon; (L) chicken; (M) pheasant; (N) sturgeon; (O) char. Cell nuclei: blue ((4′,6-diamidino-2-phenylindole) DAPI).

Figure 2

Diverse distribution of AQP5 (green) in retinas of different species (magnification ×40). ILM, inner limiting membrane (arrow); GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer; OLM, outer limiting membrane (arrowhead); POS, photoreceptor outer segments. (A) mouse; (B) rat; (C) guinea pig; (D) horse; (E) cow; (F) sheep; (G) deer; (H) pig; (I) cat; (J) dog; (K) pigeon; (L) chicken; (M) pheasant; (N) sturgeon; (O) char. Cell nuclei: blue (DAPI).

Figure 3

Expression patterns of AQP11 (red) in retinas of different species (magnification ×40). ILM, inner limiting membrane (arrow); GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer; OLM, outer limiting membrane (arrowhead); POS, photoreceptor outer segments. (A) mouse; (B) rat; (C) guinea pig; (D) horse; (E) cow; (F) sheep; (G) deer; (H) pig; (I) cat; (J) dog; (K) pigeon; (L) chicken; (M) pheasant; (N) sturgeon; (O) char. Cell nuclei: blue (DAPI).

Figure 4

Overlay (yellow) of AQP11 (red) with Muller glial cell marker glial fibrillary acidic protein (GFAP, green; magnification ×40). ILM, inner limiting membrane (arrow); GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer; OLM, outer limiting membrane (arrowhead); POS, photoreceptor outer segments. (A) mouse; (B) rat; (C) guinea pig; (D) horse; (E) cow; (F) sheep; (G) deer; (H) pig; (I) cat; (J) dog; (K) pigeon; (L) chicken; (M) pheasant; (N) sturgeon; (O) char. Cell nuclei: blue (DAPI).

Figure 5

Overlay (yellow) of AQP11 (red) with Muller glial marker glutamine synthase (GS, green; magnification ×40). ILM, inner limiting membrane (arrow); GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer; OLM, outer limiting membrane (arrowhead); POS, photoreceptor outer segments. (A) horse; (B) mouse; (C) rat; (D) guinea pig; (E) cat; (F) chicken. Cell nuclei: blue (DAPI).