Collagen gel-embedding culture of conjunctival epithelial cells

Three-Dimensional Human Cell Culture Models to Study the Pathophysiology of the Anterior Eye

In recent decades, the establishment of complex three-dimensional (3D) models of tissues has allowed researchers to perform high-quality studies and to not only advance knowledge of the physiology of these tissues but also mimic pathological conditions to test novel therapeutic strategies. The main advantage of 3D models is that they recapitulate the spatial architecture of tissues and thereby provide more physiologically relevant information. The eye is an extremely complex organ that comprises a large variety of highly heterogeneous tissues that are divided into two asymmetrical portions: the anterior and posterior segments. The anterior segment consists of the cornea, conjunctiva, iris, ciliary body, sclera, aqueous humor, and the lens. Different diseases in these tissues can have devastating effects. To study these pathologies and develop new treatments, the use of cell culture models is instrumental, and the better the model, the more relevant the results. Thus, the development of sophisticated 3D models of ocular tissues is a significant challenge with enormous potential. In this review, we present a comprehensive overview of the latest advances in the development of 3D in vitro models of the anterior segment of the eye, with a special focus on those that use human primary cells.

Poly-l/dl-lactic acid films functionalized with collagen IV as carrier substrata for corneal epithelial stem cells

Limbal epithelial stem cells (LESCs) are responsible for the renewal of corneal epithelium. Cultivated limbal epithelial transplantation is the current treatment of choice for restoring the loss or dysfunction of LESCs. To perform this procedure, a substratum is necessary for in vitro culturing of limbal epithelial cells and their subsequent transplantation onto the ocular surface. In this work, we evaluated poly-L/DL-lactic acid 70:30 (PLA) films functionalized with type IV collagen (col IV) as potential in vitro carrier substrata for LESCs. We first demonstrated that PLA-col IV films were biocompatible and suitable for the proliferation of human corneal epithelial cells. Subsequently, limbal epithelial cell suspensions, isolated from human limbal rings, were cultivated using culture medium that did not contain animal components. The cells adhered significantly faster to PLA-col IV films than to tissue culture plastic (TCP). The mRNA expression levels for the LESC specific markers, K15, P63α and ABCG2 were similar or greater (significantly in the case of K15) in limbal epithelial cells cultured on PLA-col IV films than limbal epithelial cells cultured on TCP. The percentage of cells expressing the corneal (K3, K12) and the LESC (P63α, ABCG2) specific markers was similar for both substrata. These results suggest that the PLA-col IV films promoted LESC attachment and helped to maintain their undifferentiated stem cell phenotype. Consequently, these substrata offer an alternative for the transplantation of limbal cells onto the ocular surface.

Concise Review: Comparison of Culture Membranes Used for Tissue Engineered Conjunctival Epithelial Equivalents

The conjunctival epithelium plays an important role in ensuring the optical clarity of the cornea by providing lubrication to maintain a smooth, refractive surface, by producing mucins critical for tear film stability and by protecting against mechanical stress and infectious agents. A large number of disorders can lead to scarring of the conjunctiva through chronic conjunctival inflammation. For controlling complications of conjunctival scarring, surgery can be considered. Surgical treatment of symblepharon includes removal of the scar tissue to reestablish the deep fornix. The surgical defect is then covered by the application of a tissue substitute. One obvious limiting factor when using autografts is the size of the defect to be covered, as the amount of healthy conjunctiva is scarce. These limitations have led scientists to develop tissue engineered conjunctival equivalents. A tissue engineered conjunctival epithelial equivalent needs to be easily manipulated surgically, not cause an inflammatory reaction and be biocompatible. This review summarizes the various substrates and membranes that have been used to culture conjunctival epithelial cells during the last three decades. Future avenues for developing tissue engineered conjunctiva are discussed.

Chitosan-gelatin biopolymers as carrier substrata for limbal epithelial stem cells

The aim of this work was to evaluate semi-synthetic biopolymers based on chitosan (CH) and gelatin (G) as potential in vitro carrier substrata for human limbal epithelial cells (hLECs). To that end, human corneal epithelial cells (HCE) were cultured onto different CH-G membranes. None of the polymers were cytotoxic and cell proliferation was higher when CH was functionalized with G. Expression levels of corneal epithelial markers (K3, K12, E-caherin, desmoplakin, and zonula occludens (ZO)-1) were better maintained in HCE cells grown on CH-G 20:80 membranes than other proportions. Consequently, CH-G 20:80 was chosen for the subsequent expansion of hLECs. Cells derived from limbal explants were successfully expanded on CH-G 20:80 membranes using a culture medium lacking components of non-human animal origin. The expression levels found for corneal (K3 and K12) and limbal epithelial stem cells (K15) specific markers were similar to or higher than those found in limbal cells grown onto the control substratum. Our results demonstrate that CH-G 20:80 membranes are suitable for the expansion and maintenance of stem cells derived from the limbal niche. These results strongly support the use of polymers as alternative substrata for the transplantation of cultivated limbal cells onto the ocular surface.

The use of human serum in supporting the in vitro and in vivo proliferation of human conjunctival epithelial cells

AIM

To evaluate the use of human serum (HS) in supporting the in vitro and in vivo proliferation of human conjunctival epithelial cells, and compare it with fetal bovine serum (FBS) and bovine pituitary extract (BPE).

METHODS

Conjunctival epithelial cells were cultivated in media supplemented with HS (5%, 10%), FBS (5%, 10%), and BPE (70 microg/ml, 140 microg/ml). The colony forming efficiency (CFE), bromodeoxyuridine (BrdU) ELISA proliferation assay, and cell generations were analysed. Cells were evaluated for keratin (K4, K19, and K3) and MUC5AC expression by immunostaining and RT-PCR. Conjunctival equivalents constructed on amniotic membranes were transplanted onto severe combined immune deficient (SCID) mice for 10 days and analysed histologically.

RESULTS

The proliferation assays of HS supplemented cultures (CFE, 6.7% (SD 1.8%); BrdU absorbance, 0.86 (0.16)) were comparable to FBS supplemented (CFE, 9.3% (1.8%); BrdU absorbance, 1.11 (0.18)) and BPE supplemented cultures (CFE, 5.9 (1.5); BrdU absorbance, 0.65 (0.12)). Goblet cell densities for HS, FBS, and BPE supplemented media were 52 cells/cm(2), 60 cells/cm(2), and 50 cells/cm(2), respectively. HS supplemented cultures formed stratified epithelial sheets in vivo following transplantation.

CONCLUSIONS

The proliferative capacity of conjunctival epithelial cells cultivated in HS supplemented cultures was comparable to FBS and BPE supplemented cultures. The elimination of animal material from the culture system is advantageous when cultivating cells for clinical transplantation.

Ex vivo produced human conjunctiva and oral mucosa equivalents grown in a serum-free culture system

PURPOSE

We sought to develop full-thickness ex vivo produced human conjunctiva and oral mucosa equivalents using a serum-free culture system without a feeder layer and to compare conjunctiva and oral mucosa equivalents to assess their suitability as graft materials for eyelid reconstruction.

MATERIALS AND METHODS

Human conjunctival and oral mucosal keratinocytes were cultured, expanded, and seeded onto AlloDerm (LifeCell Corp, Branchburg, NJ), a cadaveric, acellular dermis, to produce ex vivo produced full-thickness mucosa equivalents. Histology of equivalents and their expression of immunoreactive Ki-67, a proliferation marker, and GLUT1, a membrane antigen seen in barrier tissues, were examined at 4, 11, and 18 days after seeding onto AlloDerm.

RESULTS

Progressive epithelial stratification was observed on day 4, 11, and 18 conjunctiva and oral mucosa equivalents. Ki-67 immunoreactivity progressively increased with cultured time in both types of equivalent, indicating the continued presence of actively proliferating cells. GLUT1 immunoreactivity, concentrated in the basal keratinocytes of stratified epithelia of both types of equivalents, mimicked native tissue and indicated a high glycolytic state of the basal cells.

CONCLUSIONS

Conjunctival and oral mucosal equivalents are similar to native tissue and demonstrate high proliferative and glycolytic states. Due to the similarity to conjunctiva, oral mucosal equivalents may be useful for eyelid reconstruction. Their advantages for surgical reconstruction include 1) ease of obtaining autogenous oral epithelium for expansion in vitro without the possibility of contaminating cellular- or serum-borne biologic agents, 2) growth of intact, confluent epithelia on rigid, transplantable human allogeneic dermis that may be surgically transplanted, and 3) reduced donor site morbidity and surgical time.

Effects of collagen gel configuration on behavior of vascular smooth muscle cells in vitro: association with vascular morphogenesis

The growth, behavior, and contractile protein expression of rabbit aortic smooth muscle cells (SMC) grown on, between layers, or within a collagen gel was investigated by confocal laser scanning fluorescence microscopy and Western analysis. SMC grown on collagen gel behaved similarly to those on conventional culture dishes. However, when a second layer of collagen was overlaid, cells underwent an elongated quiescent phase before onset of proliferation and a more than threefold lower logarithmic growth rate was observed. These cells self-organized into a network with ring-like structures. With increasing culture time, some of the rings developed into funnel-like, incomplete or complete tubular structures. If a tubular template preexisted within the gel, the SMC established a cylinder-shaped tube with several circularly arranged muscular layers (similar to an artery wall). This behavior mimicked endothelial cells during angiogenesis in vitro. A similar phenomenon occurred in cultures in which SMC were randomly mixed in a collagen gel, but here their behavior and morphology varied with their position within the gel. Western blot analysis showed that the SMC differentiation marker, smooth muscle myosin heavy chain-2 (SM-2), rapidly decreased, disappearing by day 10 in SMC grown on collagen, but was still detectable until day 25 in cells cultured between or within the same gel. These findings indicate that like endothelial cells, vascular SMC can display blood vessel formation behavior in vitro when an appropriate three-dimensional matrix environment is provided to keep them in a relatively higher-differentiated and low-proliferative state.