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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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Related in: MedlinePlus

A transverse section of a whole smelt eye showing the cornea (c), lens (l), neural retina (nr), and rete mirabile (rm). The arrows indicate the junction between the rete mirabile and the choriocapillaris. Hematoxylin and Eosin, 50×. The composite image was created using tiling of multiple frames to capture the entire globe at a high resolution. The scale bar in the lower right corner of the figure represents 400 μm.
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f3: A transverse section of a whole smelt eye showing the cornea (c), lens (l), neural retina (nr), and rete mirabile (rm). The arrows indicate the junction between the rete mirabile and the choriocapillaris. Hematoxylin and Eosin, 50×. The composite image was created using tiling of multiple frames to capture the entire globe at a high resolution. The scale bar in the lower right corner of the figure represents 400 μm.

Mentions: Studies have yet to assess if hyperosmotic adaptation, which offers smelt protection from freezing, affects cellular permeability pathways that could impact molecular traffic in the eye. We sought to explore this by applying knowledge gained on retinal endothelial permeability pathways in mammalian systems to the smelt. A low power photomicrograph of the key elements in the smelt eye is presented in Figure 3. The smelt eye is similar to those reported in other teleost species [5,6] and includes the presence of a rete mirabile, the circulation of which is continuous with that of the choriocapillaris.


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)

A transverse section of a whole smelt eye showing the cornea (c), lens (l), neural retina (nr), and rete mirabile (rm). The arrows indicate the junction between the rete mirabile and the choriocapillaris. Hematoxylin and Eosin, 50×. The composite image was created using tiling of multiple frames to capture the entire globe at a high resolution. The scale bar in the lower right corner of the figure represents 400 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: A transverse section of a whole smelt eye showing the cornea (c), lens (l), neural retina (nr), and rete mirabile (rm). The arrows indicate the junction between the rete mirabile and the choriocapillaris. Hematoxylin and Eosin, 50×. The composite image was created using tiling of multiple frames to capture the entire globe at a high resolution. The scale bar in the lower right corner of the figure represents 400 μm.
Mentions: Studies have yet to assess if hyperosmotic adaptation, which offers smelt protection from freezing, affects cellular permeability pathways that could impact molecular traffic in the eye. We sought to explore this by applying knowledge gained on retinal endothelial permeability pathways in mammalian systems to the smelt. A low power photomicrograph of the key elements in the smelt eye is presented in Figure 3. The smelt eye is similar to those reported in other teleost species [5,6] and includes the presence of a rete mirabile, the circulation of which is continuous with that of the choriocapillaris.

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