Polarized Secretion of Matrix Metalloproteinases and Their Inhibitors by Retinal Pigment Epithelium Derived from Induced Pluripotent Stem Cells During Wound Healing

Clinical value of combined serum MMP-2, MMP-9 and TIMP-1 for the prognosis of perianal fistula patients who received minimally invasive surgery

OBJECTIVE

This study aimed to investigate the clinical value of combined serum matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) for the prognosis of perianal fistula patients.

METHODS

Patients diagnosed and treated for perianal fistula by minimally invasive surgery (MIS) were enrolled. The concentrations of serum MMP-2, MMP-9 and TIMP-1 were measured at 24 h after surgery. Different levels of wound secretion, growth of granulation tissue and wound pain were used as criteria to evaluate surgical incision healing. The receiver operating characteristic curve was used to analyze the predicted assessment value.

RESULTS

The concentrations of serum MMP-2 and MMP-9 were significantly higher, while the concentrations of serum TIMP-1 at 24 h after surgery were significantly lower in the poor healing group than in the good healing group. It was further found that high levels of serum MMP-2 and MMP-9 were risk factors for poor healing, while high concentrations of serum TIMP-1 at 24 h after surgery were protective factors for poor healing.

CONCLUSION

High concentrations of serum MMP-2 and MMP-9 and low concentrations of serum TIMP at 24 h after surgery are risk factors for poor healing in perianal fistula patients who receive MIS, and the combined test has a higher predictive value.

Elastin turnover in ocular diseases: A special focus on age-related macular degeneration

The extracellular matrix (ECM) and its turnover play a crucial role in the pathogenesis of several inflammatory diseases, including age-related macular degeneration (AMD). Elastin, a critical protein component of the ECM, not only provides structural and mechanical support to tissues, but also mediates several intracellular and extracellular molecular signaling pathways. Abnormal turnover of elastin has pathological implications. In the eye elastin is a major structural component of Bruch's membrane (BrM), a critical ECM structure separating the retinal pigment epithelium (RPE) from the choriocapillaris. Reduced integrity of macular BrM elastin, increased serum levels of elastin-derived peptides (EDPs), and elevated elastin antibodies have been reported in AMD. Existing reports suggest that elastases, the elastin-degrading enzymes secreted by RPE, infiltrating macrophages or neutrophils could be involved in BrM elastin degradation, thus contributing to AMD pathogenesis. EDPs derived from elastin degradation can increase inflammatory and angiogenic responses in tissues, and the elastin antibodies are shown to play roles in immune cell activity and complement activation. This review summarizes our current understanding on the elastases/elastin fragments-mediated mechanisms of AMD pathogenesis.

Proline metabolism and transport in retinal health and disease

The retina is one of the most energy-demanding tissues in the human body. Photoreceptors in the outer retina rely on nutrient support from the neighboring retinal pigment epithelium (RPE), a monolayer of epithelial cells that separate the retina and choroidal blood supply. RPE dysfunction or cell death can result in photoreceptor degeneration, leading to blindness in retinal degenerative diseases including some inherited retinal degenerations and age-related macular degeneration (AMD). In addition to having ready access to rich nutrients from blood, the RPE is also supplied with lactate from adjacent photoreceptors. Moreover, RPE can phagocytose lipid-rich outer segments for degradation and recycling on a daily basis. Recent studies show RPE cells prefer proline as a major metabolic substrate, and they are highly enriched for the proline transporter, SLC6A20. In contrast, dysfunctional or poorly differentiated RPE fails to utilize proline. RPE uses proline to fuel mitochondrial metabolism, synthesize amino acids, build the extracellular matrix, fight against oxidative stress, and sustain differentiation. Remarkably, the neural retina rarely imports proline directly, but it uptakes and utilizes intermediates and amino acids derived from proline catabolism in the RPE. Mutations of genes in proline metabolism are associated with retinal degenerative diseases, and proline supplementation is reported to improve RPE-initiated vision loss. This review will cover proline metabolism in RPE and highlight the importance of proline transport and utilization in maintaining retinal metabolism and health.

Polarity and epithelial-mesenchymal transition of retinal pigment epithelial cells in proliferative vitreoretinopathy

Under physiological conditions, retinal pigment epithelium (RPE) is a cellular monolayer composed of mitotically quiescent cells. Tight junctions and adherens junctions maintain the polarity of RPE cells, and are required for cellular functions. In proliferative vitreoretinopathy (PVR), upon retinal tear, RPE cells lose cell-cell contact, undergo epithelial-mesenchymal transition (EMT), and ultimately transform into myofibroblasts, leading to the formation of fibrocellular membranes on both surfaces of the detached retina and on the posterior hyaloids, which causes tractional retinal detachment. In PVR, RPE cells are crucial contributors, and multiple signaling pathways, including the SMAD-dependent pathway, Rho pathway, MAPK pathways, Jagged/Notch pathway, and the Wnt/β-catenin pathway are activated. These pathways mediate the EMT of RPE cells, which play a key role in the pathogenesis of PVR. This review summarizes the current body of knowledge on the polarized phenotype of RPE, the role of cell-cell contact, and the molecular mechanisms underlying the RPE EMT in PVR, emphasizing key insights into potential approaches to prevent PVR.

Retinal pigment epithelium polarity in health and blinding diseases

The polarized phenotype of the retinal pigment epithelium is crucial for the outer retina-blood barrier and support of photoreceptors and underlying choroid, and its disruption plays a central role in degenerative retinopathies. Although the mechanisms of polarization remain mostly unknown, they are fundamental for homeostasis of the outer retina. Recent research is revealing a growing picture of interconnected tissues in the outer retina, with the retinal pigment epithelium at the center. This review discusses how elements of epithelial polarity relate to emerging apical interactions with the neural retina, basolateral cross-talk with the underlying Bruch's membrane and choriocapillaris, and tight junction biology. An integrated view of outer retina physiology is likely to provide insights into the pathogenesis of blinding diseases.

CLIC4 regulates late endosomal trafficking and matrix degradation activity of MMP14 at focal adhesions in RPE cells

Dysregulation in the extracellular matrix (ECM) microenvironment surrounding the retinal pigment epithelium (RPE) has been implicated in the etiology of proliferative vitreoretinopathy and age-related macular degeneration. The regulation of ECM remodeling by RPE cells is not well understood. We show that membrane-type matrix metalloproteinase 14 (MMP14) is central to ECM degradation at the focal adhesions in human ARPE19 cells. The matrix degradative activity, but not the assembly, of the focal adhesion is regulated by chloride intracellular channel 4 (CLIC4). CLIC4 is co-localized with MMP14 in the late endosome. CLIC4 regulates the proper sorting of MMP14 into the lumen of the late endosome and its proteolytic activation in lipid rafts. CLIC4 has the newly-identified “late domain” motif that binds to MMP14 and to Tsg101, a component of the endosomal sorting complex required for transport (ESCRT) complex. Unlike the late domain mutant CLIC4, wild-type CLIC4 can rescue the late endosomal sorting defect of MMP14. Finally, CLIC4 knockdown inhibits the apical secretion of MMP2 in polarized human RPE monolayers. These results, taken together, demonstrate that CLIC4 is a novel matrix microenvironment modulator and a novel regulator for late endosomal cargo sorting. Moreover, the late endosomal sorting of MMP14 actively regulates its surface activation in RPE cells.

Clinical-grade stem cell-derived retinal pigment epithelium patch rescues retinal degeneration in rodents and pigs

Considerable progress has been made in testing stem cell-derived retinal pigment epithelium (RPE) as a potential therapy for age-related macular degeneration (AMD). However, the recent reports of oncogenic mutations in induced pluripotent stem cells (iPSCs) underlie the need for robust manufacturing and functional validation of clinical-grade iPSC-derived RPE before transplantation. Here, we developed oncogenic mutation-free clinical-grade iPSCs from three AMD patients and differentiated them into clinical-grade iPSC-RPE patches on biodegradable scaffolds. Functional validation of clinical-grade iPSC-RPE patches revealed specific features that distinguished transplantable from nontransplantable patches. Compared to RPE cells in suspension, our biodegradable scaffold approach improved integration and functionality of RPE patches in rats and in a porcine laser-induced RPE injury model that mimics AMD-like eye conditions. Our results suggest that the in vitro and in vivo preclinical functional validation of iPSC-RPE patches developed here might ultimately be useful for evaluation and optimization of autologous iPSC-based therapies.

Fibrin hydrogels as a xenofree and rapidly degradable support for transplantation of retinal pigment epithelium monolayers

Recent phase 1 trials of embryonic stem cell and induced pluripotent stem cell (iPSCs) derived RPE transplants for the treatment of macular degeneration have demonstrated the relative safety of this process. However, there is concern over clumping, thickening, folding, and wrinkling of the transplanted RPE. To deliver a flat RPE monolayer, current phase 1 trials are testing synthetic substrates for RPE transplantation. These substrates, however, cause localized inflammation and fibrosis in animal models due to long degradation times. Here we describe the use of thin fibrin hydrogels as a support material for the transplantation of RPE. Fibrin was formed into a mechanically rigid support that allow for easy manipulation with standard surgical instruments. Using fibrinolytic enzymes, fibrin hydrogels were degraded on the scale of hours. The rate of degradation could be controlled by varying the fibrinolytic enzyme concentration used. RPE cells degraded fibrin spontaneously. To preserve the fibrin support during differentiation of iPSCs to RPE, media was supplemented with the protease inhibitor aprotinin. iPSC-RPE on fibrin gels remained viable, generated monolayers with characteristic cobblestone appearance and dark pigmentation, and expressed mRNA and protein markers characteristic of RPE in the eye. Following differentiation of the cells, addition of fibrinolytic enzymes fully and rapidly degraded the fibrin support leaving behind an intact, viable iPSC-RPE monolayer. In conclusion, human fibrin hydrogels provide a xeno-free support on which iPSCs can be differentiated to RPE cells for transplant which can be rapidly degraded under controlled conditions using fibrinolytic enzymes without adverse effects to the cells.

STATEMENT OF SIGNIFICANCE

Stem cell-derived retinal pigment epithelial (RPE) cell transplantation is currently in phase 1 clinical trials for macular degeneration (MD). A major obstacle in these studies is delivering the RPE as a living, flat sheets without leaving behind foreign materials in the retina. Here we investigate the suitability of using hydrogels made from human blood-derived proteins for RPE transplant. Our data shows that these fibrin hydrogels are rigid enough for use in surgery, support growth of stem cell-derived RPE, and are easily degraded within hours without damage to the RPE sheet. These fibrin hydrogels offer a promising solution to transplant RPE for patients with MD.