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Absence of collagen XVIII in mice causes age-related insufficiency in retinal pigment epithelium proteostasis

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Abstract

Collagen XVIII has the structural properties of both collagen and proteoglycan. It has been found at the basement membrane/stromal interface where it is thought to mediate their attachment. Endostatin, a proteolytic fragment from collagen XVIII C-terminal end has been reported to possess anti-angiogenic properties. Age-related vision loss in collagen XVIII mutant mice has been accompanied with a pathological accumulation of deposits under the retinal pigment epithelium (RPE). We have recently demonstrated that impaired proteasomal and autophagy clearance are associated with the pathogenesis of age-related macular degeneration. This study examined the staining levels of proteasomal and autophagy markers in the RPE of different ages of the Col18a1 −/− mice. Eyes from 3, 6–7, 10–13 and 18 months old mice were enucleated and embedded in paraffin according to the routine protocol. Sequential 5 μm-thick parasagittal samples were immunostained for proteasome and autophagy markers ubiquitin (ub), SQSTM1/p62 and beclin-1. The levels of immunopositivity in the RPE cells were evaluated by confocal microscopy. Collagen XVIII knock-out mice had undergone age-related RPE degeneration accompanied by an accumulation of drusen-like deposits. Ub protein conjugate staining was prominent in both RPE cytoplasm and extracellular space whereas SQSTM1/p62 and beclin-1 stainings were clearly present in the basal part of RPE cell cytoplasm in the Col18a1 −/− mice. SQSTM1/p62 displayed mild extracellular space staining. Disturbed proteostasis regulated by collagen XVIII might be responsible for the RPE degeneration, increased protein aggregation, ultimately leading to choroidal neovascularization.

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Acknowledgments

This research was supported by VTR grand of Kuopio University Hospital, The Finnish Eye Foundation, Evald and Hilda Nissi Foundation and Janos Bolyai fellowship of the Hungarian Academy of Science (Sz. F.). We thank Ewen McDonald for checking the language and warmly acknowledge the importance of the critical technical help from Anne Seppänen, Tünde Pálné Terdik and Zoltán Hegyi.

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    Authors and Affiliations

    1. Department of Ophthalmology, Kuopio University Hospital and University of Eastern Finland, Kuopio, Finland

      Niko Kivinen, Kati Kinnunen & Kai Kaarniranta

    2. Department of Anatomy, Histology and Embryology, Dental Faculty, University of Debrecen, Debrecen, Hungary

      Szabolcs Felszeghy

    3. Biocenter Oulu and Faculty of Biochemistry and Molecular Medicine, Oulu Center for Cell-Matrix Research, University of Oulu, Oulu, Finland

      Aino I. Kinnunen, Mari Aikio & Taina Pihlajaniemi

    4. Department of Neurobiology, A. I. Virtanen Institute for Molecular Sciences, Biocenter Kuopio, University of Eastern Finland, Kuopio, Finland

      Aino I. Kinnunen

    5. Jyväskylä Central Hospital, Jyväskylä, Finland

      Niko Setälä

    6. Pathology and Forensic Medicine and Biocenter Kuopio and Cancer Center of Eastern Finland, University of Eastern Finland and Imaging Center, Clinical Pathology, Institute of Clinical Medicine, Kuopio University Hospital, Kuopio, Finland

      Reijo Sironen

    7. School of Pharmacy, University of Eastern Finland, Kuopio, Finland

      Anu Kauppinen

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    Niko Kivinen, Szabolcs Felszeghy, Anu Kauppinen and Kai Kaarniranta have contributed equally to this paper.

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    Kivinen, N., Felszeghy, S., Kinnunen, A.I. et al. Absence of collagen XVIII in mice causes age-related insufficiency in retinal pigment epithelium proteostasis. Biogerontology 17, 749–761 (2016). https://doi.org/10.1007/s10522-016-9647-7

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