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Osmotic pressure-adaptive responses in the eye tissues of rainbow smelt (Osmerus mordax).

Gendron RL, Armstrong E, Paradis H, Haines L, Desjardins M, Short CE, Clow KA, Driedzic WR - Mol. Vis. (2011)

Bottom Line: The effects that such massive changes in osmolarity have on both its visual system and its highly evolved and specialized circulation are not known.We propose a hypothesis that in a state of cold-induced hyperosmolarity, changes in ZO-1 expression are associated with the passage of small solutes from the plasma space to ocular fluid, while changes in Tbdn expression regulate the passage of proteins between the ocular fluid and plasma space.This work also provides fundamental insight into the mechanisms underlying the adaptation of the blood-retinal barrier to metabolically relevant compounds such as glycerol.

View Article: PubMed Central - PubMed

Affiliation: Division of BioMedical Sciences, Faculty of Medicine, Memorial University, St. John’s, NL, A1B 3V6, Canada. rgendron@mun.ca

ABSTRACT

Purpose: The rainbow smelt (Osmerus mordax), is a teleost fish, which avoids freezing by becoming virtually isosmotic with seawater. The effects that such massive changes in osmolarity have on both its visual system and its highly evolved and specialized circulation are not known. New knowledge about the osmotic adaptation of the rainbow smelt eye is highly relevant to the adaptation and survival of this species and to its ability to feed as a visual predator in the face of environmental pressures. Moreover, the molecular physiologic response of the smelt to osmotic stress might provide valuable insights into understanding and managing mammalian pathological hyperosmolarity conditions, such as diabetes. We undertook the present study to provide an initial assessment of gene expression in ocular vasculature during osmotic adaptation in rainbow smelt.

Methods: Immunohistochemistry with species cross reactive antibodies was used to assess blood vessel protein expression in paraffin sections. Western blotting was used to further verify antibody specificity for orthologs of mammalian blood vessel proteins in rainbow smelt. Thermal hysteresis and the analysis of glycerol concentrations in vitreous fluid were used to assess the physiologic adaptive properties of cold stressed eyes.

Results: Glycerol levels and osmotic pressure were significantly increased in the vitreal fluid of smelt maintained at <0.5 °C versus those maintained at 8-10 °C. Compared to the 8-10 °C adapted specimens, the rete mirabile blood vessels and connecting regions of the endothelial linings of the choroidal vessels of the <0.5 °C adapted specimens showed a higher expression level of Tubedown (Tbdn) protein, a marker of the endothelial transcellular permeability pathway. Expression of the zonula occludens protein ZO-1, a marker of the endothelial paracellular permeability pathway showed a reciprocal expression pattern and was downregulated in rete mirabile blood vessels and connecting regions in the endothelial linings of choroidal vessels in <0.5 °C adapted specimens. Smelt orthologs of the mammalian Tbdn and zoluna occludens protein 1 (ZO-1) proteins were also detected by western blotting using anti-mammalian antibodies raised against the same epitopes as those used for immunohistochemistry.

Conclusions: This work provides the first evidence that molecules known to play a role in ocular vascular homeostasis are expressed and may be differentially regulated during anti-freezing cold adaptation in smelt eyes. We propose a hypothesis that in a state of cold-induced hyperosmolarity, changes in ZO-1 expression are associated with the passage of small solutes from the plasma space to ocular fluid, while changes in Tbdn expression regulate the passage of proteins between the ocular fluid and plasma space. This work also provides fundamental insight into the mechanisms underlying the adaptation of the blood-retinal barrier to metabolically relevant compounds such as glycerol.

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Osmotic pressure in vitreous fluid in cold versus warm fish. A: Osmotic pressure in vitreous fluid in smelt at warm (8–10 °C) and cold (<0.5 °C) temperatures. B: Thermal hysteresis in vitreous fluid in smelt at warm (8–10 °C) and cold (<0.5 °C) temperatures. The values are presented as mean±SEM with n=3 for the warm group and n=5 for the cold group. * indicates a statistically significant difference.
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f2: Osmotic pressure in vitreous fluid in cold versus warm fish. A: Osmotic pressure in vitreous fluid in smelt at warm (8–10 °C) and cold (<0.5 °C) temperatures. B: Thermal hysteresis in vitreous fluid in smelt at warm (8–10 °C) and cold (<0.5 °C) temperatures. The values are presented as mean±SEM with n=3 for the warm group and n=5 for the cold group. * indicates a statistically significant difference.

Mentions: The osmotic pressure in vitreous fluid was significantly higher in cold versus warm fish—being twofold higher at cold versus warm temperatures (Figure 2A). The freezing point of the vitreous humor (calculated from the osmotic pressure) was −1.20±0.9 °C and −0.62±0.03 °C for cold and warm smelt, respectively. The freeze point depression was sufficient to prevent freezing in ambient water temperatures during winter. The difference in osmotic pressure of about 300 mOsmols could not be fully accounted for by glycerol accumulation, which was only about 125 mM higher in cold compared to warm fish. This implies that other osmolytes accumulate in the vitreous fluid as well as glycerol. These results indicate that, like the rest of a fish's body, a hyperosmotic physiologic adaptation—partly involving glycerol accumulation—protects the rainbow smelt eye from freezing in subzero water temperatures.


Osmotic pressure-adaptive responses in the eye tissues of rainbow smelt (Osmerus mordax).

Gendron RL, Armstrong E, Paradis H, Haines L, Desjardins M, Short CE, Clow KA, Driedzic WR - Mol. Vis. (2011)

Osmotic pressure in vitreous fluid in cold versus warm fish. A: Osmotic pressure in vitreous fluid in smelt at warm (8–10 °C) and cold (<0.5 °C) temperatures. B: Thermal hysteresis in vitreous fluid in smelt at warm (8–10 °C) and cold (<0.5 °C) temperatures. The values are presented as mean±SEM with n=3 for the warm group and n=5 for the cold group. * indicates a statistically significant difference.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3198499&req=5

f2: Osmotic pressure in vitreous fluid in cold versus warm fish. A: Osmotic pressure in vitreous fluid in smelt at warm (8–10 °C) and cold (<0.5 °C) temperatures. B: Thermal hysteresis in vitreous fluid in smelt at warm (8–10 °C) and cold (<0.5 °C) temperatures. The values are presented as mean±SEM with n=3 for the warm group and n=5 for the cold group. * indicates a statistically significant difference.
Mentions: The osmotic pressure in vitreous fluid was significantly higher in cold versus warm fish—being twofold higher at cold versus warm temperatures (Figure 2A). The freezing point of the vitreous humor (calculated from the osmotic pressure) was −1.20±0.9 °C and −0.62±0.03 °C for cold and warm smelt, respectively. The freeze point depression was sufficient to prevent freezing in ambient water temperatures during winter. The difference in osmotic pressure of about 300 mOsmols could not be fully accounted for by glycerol accumulation, which was only about 125 mM higher in cold compared to warm fish. This implies that other osmolytes accumulate in the vitreous fluid as well as glycerol. These results indicate that, like the rest of a fish's body, a hyperosmotic physiologic adaptation—partly involving glycerol accumulation—protects the rainbow smelt eye from freezing in subzero water temperatures.

Bottom Line: The effects that such massive changes in osmolarity have on both its visual system and its highly evolved and specialized circulation are not known.We propose a hypothesis that in a state of cold-induced hyperosmolarity, changes in ZO-1 expression are associated with the passage of small solutes from the plasma space to ocular fluid, while changes in Tbdn expression regulate the passage of proteins between the ocular fluid and plasma space.This work also provides fundamental insight into the mechanisms underlying the adaptation of the blood-retinal barrier to metabolically relevant compounds such as glycerol.

View Article: PubMed Central - PubMed

Affiliation: Division of BioMedical Sciences, Faculty of Medicine, Memorial University, St. John’s, NL, A1B 3V6, Canada. rgendron@mun.ca

ABSTRACT

Purpose: The rainbow smelt (Osmerus mordax), is a teleost fish, which avoids freezing by becoming virtually isosmotic with seawater. The effects that such massive changes in osmolarity have on both its visual system and its highly evolved and specialized circulation are not known. New knowledge about the osmotic adaptation of the rainbow smelt eye is highly relevant to the adaptation and survival of this species and to its ability to feed as a visual predator in the face of environmental pressures. Moreover, the molecular physiologic response of the smelt to osmotic stress might provide valuable insights into understanding and managing mammalian pathological hyperosmolarity conditions, such as diabetes. We undertook the present study to provide an initial assessment of gene expression in ocular vasculature during osmotic adaptation in rainbow smelt.

Methods: Immunohistochemistry with species cross reactive antibodies was used to assess blood vessel protein expression in paraffin sections. Western blotting was used to further verify antibody specificity for orthologs of mammalian blood vessel proteins in rainbow smelt. Thermal hysteresis and the analysis of glycerol concentrations in vitreous fluid were used to assess the physiologic adaptive properties of cold stressed eyes.

Results: Glycerol levels and osmotic pressure were significantly increased in the vitreal fluid of smelt maintained at <0.5 °C versus those maintained at 8-10 °C. Compared to the 8-10 °C adapted specimens, the rete mirabile blood vessels and connecting regions of the endothelial linings of the choroidal vessels of the <0.5 °C adapted specimens showed a higher expression level of Tubedown (Tbdn) protein, a marker of the endothelial transcellular permeability pathway. Expression of the zonula occludens protein ZO-1, a marker of the endothelial paracellular permeability pathway showed a reciprocal expression pattern and was downregulated in rete mirabile blood vessels and connecting regions in the endothelial linings of choroidal vessels in <0.5 °C adapted specimens. Smelt orthologs of the mammalian Tbdn and zoluna occludens protein 1 (ZO-1) proteins were also detected by western blotting using anti-mammalian antibodies raised against the same epitopes as those used for immunohistochemistry.

Conclusions: This work provides the first evidence that molecules known to play a role in ocular vascular homeostasis are expressed and may be differentially regulated during anti-freezing cold adaptation in smelt eyes. We propose a hypothesis that in a state of cold-induced hyperosmolarity, changes in ZO-1 expression are associated with the passage of small solutes from the plasma space to ocular fluid, while changes in Tbdn expression regulate the passage of proteins between the ocular fluid and plasma space. This work also provides fundamental insight into the mechanisms underlying the adaptation of the blood-retinal barrier to metabolically relevant compounds such as glycerol.

Show MeSH
Related in: MedlinePlus