Restoration of Corneal Transparency by Mesenchymal Stem Cells

Abstract

Transparency of the cornea is indispensable for optimal vision. Ocular trauma is a leading cause of corneal opacity, leading to 25 million cases of blindness annually. Recently, mesenchymal stem cells (MSCs) have gained prominence due to their inflammation-suppressing and tissue repair functions. Here, we investigate the potential of MSCs to restore corneal transparency following ocular injury. Using an in vivo mouse model of ocular injury, we report that MSCs have the capacity to restore corneal transparency by secreting high levels of hepatocyte growth factor (HGF). Interestingly, our data also show that HGF alone can restore corneal transparency, an observation that has translational implications for the development of HGF-based therapy.

Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

Figures

Graphical abstract

Figure 1

MSCs Secrete High Levels of HGF upon Stimulation with IL-1β (A) Schematic showing injury model of mouse cornea created by mechanical removal of epithelium and anterior stroma, and effect of mesenchymal stem cell (MSC) administration on corneal opacity. (B) Micrographs showing MSC morphology in culture at second passage, and differentiation of MSCs into adipocytes. MSCs were cultured in adipogenic medium for 2 weeks and stained with oil red O dye; red-colored vacuoles (arrows) were observed within the cytoplasm, indicating their differentiation into adipocytes. Scale bar, 25 μm. (C) Phenotypic characterization of in vitro expanded MSCs using flow cytometry confirmed their surface phenotype of CD45–CD34–SCA1+CD29+CD105+ cells. (D) MSCs were cultured in medium alone or with IL-1β for 24 hr. mRNA expression of indicated genes in MSCs were analyzed using real-time PCR. (E) Protein expression of TGF-β1 and HGF was confirmed in culture supernatants of MSCs cultured in the presence or absence of IL-1β for 24 hr using ELISA. The values of mRNA and protein expression are shown as mean ± SD of three independent experiments. (F and G) In vitro expanded MSCs were intravenously injected into the C57BL/6 mice 1 hr after corneal injury. Healthy corneas without injury were used as normal control. Corneas were harvested after 3 days, and (F) mRNA and (G) protein expressions of HGF were measured using real-time PCR and ELISA, respectively. The values shown are mean ± SD and each corneal injury group consists of n = 6 mice. ∗p < 0.003, ∗∗p < 0.0001.

Figure 2

Restoration of Corneal Transparency Is Dependent upon HGF Expression by MSCs (A) Schematic of experimental design. (B) Real-time PCR analysis showing efficacy of Hgf-specific siRNA (siHGF) versus control siRNA (siCON) on downregulation of HGF expression in mesenchymal stem cells (MSCs). After corneal injury was induced in C57BL/6 mice, MSCs treated with control or Hgf-specific siRNA were intravenously administered 1 hr post injury and followed for 5 days. At days 1, 3, and 5 post injury, photographs of injured cornea with or without green fluorescein stain were captured using slit-lamp biomicroscopy. Corneal fluorescein staining was used to indicate epithelial defects and bright-field micrographs were used to evaluate corneal opacity. (C and D) Representative bright-field microscopic images of injured cornea (C) were quantitated using Image J software to measure the corneal opacity scores (D). (E) Representative biomicroscopic images showing green fluorescein-stained injured cornea. (F) The fluorescein-stained area was quantitated using ImageJ software. A smaller area of fluorescein staining represents faster repair of corneal injury. (G and H) At day 5 post injury, corneas were harvested. Total RNA was isolated from harvested corneas, and real-time PCR was performed to analyze mRNA expression of (G) α-Sma and (H) Tgf-β1. The values shown are mean ± SD and each corneal injury group consists of n = 6 mice. ∗p < 0.02, ∗∗p < 0.005.

Figure 3

HGF Alone Is Sufficient to Inhibit Corneal Opacity and Inflammation (A and B) A corneal fibroblast cell line (MK/T1) was stimulated with TGF-β1 in the presence or absence of HGF for 24 hr. α-SMA expression was assessed (A) at mRNA level using real-time PCR and (B) at protein level by immunohistochemistry. The values shown are the mean ± SD of three independent experiments. (C–K) Corneal injury was induced by mechanical removal of corneal epithelium and anterior stroma in C57BL/6 mice. Thereafter, 5 μL of 0.1% murine recombinant HGF in PBS per eye was applied topically to the injured eye twice a day up to 7 days after injury. A control group received a similar dosage of mouse serum albumin. At days 1, 3, 5, and 7 post injury, bright-field photographs of injured corneas were captured to evaluate corneal opacity using slit-lamp biomicroscopy. Representative bright-field images of injured corneas (C) were quantitated using Image J software to assess corneal opacity scores (D). Corneas were harvested at 7 days post injury. Cross-sections were stained with H&E to visualize corneal tissue structure and infiltration of inflammatory cells (E), and measure corneal tissue thickness (F). For immunocytochemistry analysis (G), cross-sections were immunostained with the fibrosis marker α-SMA (green). In addition, harvested corneas were analyzed for their mRNA expression of (H) α-Sma, (I) Tgf-β1, (J) Il-1β, and (K) Tnf-α using real-time PCR. The values shown are mean ± SD and each corneal injury group consists of n = 6 mice. ∗p < 0.01, ∗∗p < 0.005. Scale bars, 50 μm.