Biomaterial substrates and transplantation materials for human embryonic stem cell derived retinal pigment epithelial cells

Event start date
Event start time
12.00
Place

Arvo building, auditorium F114, address: Lääkärinkatu 1.

Organiser(s)

Doctoral defence of DI Anni Sorkio

Biomaterial substrates and transplantation materials for human embryonic stem cell derived retinal pigment epithelial cells: Biomimetic approaches for retinal tissue engineering

The field of science of the dissertation is Cell and Tissue Technology.

The opponent is Professor Peter Coffey (University College London, UK). Adjunct Professor Heli Skottman acts as the custos.

The language of the dissertation defence is English.

Biomaterial substrates and transplantation materials for human embryonic stem cell derived retinal pigment epithelial cells

The retinal pigment epithelium (RPE) is a monolayer of polarized and pigmented cells that resides between the neural retina and the choroid. Together with the underlying Bruch’s membrane, the RPE has a pivotal role in the proper function, homeostasis and survival of the adjacent retinal photoreceptors. Irreversible damage and loss of the RPE is a fundamental factor in the development of degenerative retinal diseases such as age-related macular degeneration (AMD). In AMD, degeneration of the RPE and photoreceptors in the macular area of central vision lead to a gradual loss of visual acuity and eventually blindness. Currently, there is no treatment for the dry form of AMD. However, replacement of the dysfunctional and damaged RPE with a population of healthy cells is considered as a potential therapeutic strategy for AMD and related diseases. Cell transplants of human embryonic stem cell derived RPE (hESC-RPE) cells have shown potential for these cell therapies in animal models and are currently investigated in clinical setting.

An approach where cells are delivered to the subretinal space as a sheet on a biomaterial substrate, has shown improved cell survival upon transplantation. Several biomaterial substrates have been investigated as prospective carriers for RPE, but they often fail to fulfill the requirements set for subretinal implantation. Importantly, these substrates do not mimic the composition and structure of Bruch’s membrane, the natural environment of the RPE, which might affect their capacity to differentiate in vitro and subsequent performance in cell transplantation. Moreover, the majority of currently used biomaterial substrates contain animal-derived products. In addition, testing of these substrates is usually carried out with immortalized cells lines under culture conditions not suitable for clinical production.

The work presented in this dissertation aimed at finding and developing biomaterial substrates for hESC-RPE cells that bear a resemblance to the native microenvironment of the RPE. A special focus was paid to exploring biomaterial substrates of human or synthetic origin that would support the formation of mature hESC-RPE in serum-free culture conditions. Consequently, three approaches were developed to fabricate a biomimetic environment for hESC-RPE in vitro.

To begin with, the role of several human extracellular matrix (ECM) proteins found in the Bruch’s membrane and commercial basement membrane matrices was evaluated in adherent hESC-RPE cell differentiation and maturation cultures under serum-free conditions. Although there were no significant differences between the studied protein coatings in early-stage differentiation, the protein coatings had a major effect on the structure, function and basal lamina production of hESC-RPE cells upon further maturation of the cultures.

Thereafter, a biomimetic microenvironment simulating the layered structure of the Bruch’s membrane was fabricated with Langmuir-Schaefer technology from human derived collagens for the production of hESC-RPE cells. Only biocompatible components were involved in the manufacturing process. A thorough characterization of the substrate demonstrated that the fabricated collagen films had a layered structure with oriented fibers resembling the architecture of the two uppermost layers of Bruch’s membrane. Furthermore, the fabricated collagen films were superior in supporting hESC-RPE cell maturation and functionality compared to collagen IV dip-coated controls in serum-free culture conditions.

Finally, biodegradable biomaterial substrates were fabricated from synthetic polymer with an electrospinning method. The substrates were surface modified and coated with an additional collagen layer to increase hESC-RPE cell adhesion and maturation. The fabricated substrates consisted of unaligned fibers and were permeable for small molecular weight substance. Thus, these substrates bore a resemblance to the fibrous structure of Bruch’s membrane. Moreover, these biodegradable surface modified biomaterial substrates supported the formation of functional hESC-RPE in serum-free culture medium, therefore demonstrating the potential of biomaterial substrates for subretinal transplantation.

In conclusion, this dissertation has increased understanding of hESC-RPE cell interaction and performance on biomaterial substrates. Moreover, the results of this dissertation offer a range of methods to provide a biomimetic environment for the in vitro production of hESC-RPE cells without the use of animal-derived substrates and serum. These results can be exploited in future applications and biomaterial design for the retinal tissue engineering field.

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The dissertation is published in the publication series of Acta Universitatis Tamperensis; 2227, Tampere University Press, Tampere 2016. ISBN 978-952-03-0266-5, ISSN 1455-1616. The dissertation is also published in the e-series Acta Electronica Universitatis Tamperensis; 1727, Tampere University Press 2016. ISBN 978-952-03-0267-2, ISSN 1456-954X.

Additional information

Anni Sorkio, anni.sorkio@uta.fi