Developing Extracellular Matrix Technology to Treat Retinal or Optic Nerve Injury(1,2,3)

Abstract

Adult mammalian CNS neurons often degenerate after injury, leading to lost neurologic functions. In the visual system, retinal or optic nerve injury often leads to retinal ganglion cell axon degeneration and irreversible vision loss. CNS axon degeneration is increasingly linked to the innate immune response to injury, which leads to tissue-destructive inflammation and scarring. Extracellular matrix (ECM) technology can reduce inflammation, while increasing functional tissue remodeling, over scarring, in various tissues and organs, including the peripheral nervous system. However, applying ECM technology to CNS injuries has been limited and virtually unstudied in the visual system. Here we discuss advances in deriving fetal CNS-specific ECMs, like fetal porcine brain, retina, and optic nerve, and fetal non-CNS-specific ECMs, like fetal urinary bladder, and the potential for using tissue-specific ECMs to treat retinal or optic nerve injuries in two platforms. The first platform is an ECM hydrogel that can be administered as a retrobulbar, periocular, or even intraocular injection. The second platform is an ECM hydrogel and polymer "biohybrid" sheet that can be readily shaped and wrapped around a nerve. Both platforms can be tuned mechanically and biochemically to deliver factors like neurotrophins, immunotherapeutics, or stem cells. Since clinical CNS therapies often use general anti-inflammatory agents, which can reduce tissue-destructive inflammation but also suppress tissue-reparative immune system functions, tissue-specific, ECM-based devices may fill an important need by providing naturally derived, biocompatible, and highly translatable platforms that can modulate the innate immune response to promote a positive functional outcome.

Keywords: ECM; axon regeneration; immunotherapy; regenerative medicine; retinal ganglion cell.

Figure 1.

Numerous barriers must be overcome to prevent neural degeneration. The low intrinsic regeneration capacity of RGCs, lost neurotrophic support, and an inflammatory immune response are three major factors leading to neurodegeneration. Therapies overcoming these barriers are showing promise in preclinical and clinical models, including stem cell delivery from both exogenous and endogenous sources; neurotrophin delivery; and immunomodulatory therapies using macrophage polarization, immunomodulatory drugs, and cytokines.

Figure 2.

ECMs can be derived from different animal tissues or organs, each with a unique compliment of proteins, carbohydrates, extracellular matrix molecules, growth factors, and cytokines. The ECM is a flexible platform that can be used as a natural material bioscaffold, an injectable hydrogel, or combined with polymeric materials to form biohybrid devices with controllable mechanical and biochemical properties. Each form can be augmented with cells or other bioactive molecules to improve the healing response.

Figure 3.

Images and H&E staining of different decellularized CNS ECMs derived from fetal porcine tissues.

Figure 4.

RGCs grow longer processes in ECM derived from younger, homologous tissue sources. A, Fluorescence images of purified primary rat RGCs cultured in adult or fetal brain ECMs. B, Quantification: p < 0.001, ANOVA.

Figure 5.

Extracellular matrix in two sheet forms. ECM biohybrid sheets can be made by dual-stream electrospinning. PEUU and ECM electrospinning setup consists of two syringe pumps and two high-voltage power supply units (not shown). A high positive voltage (+7-10 kV) is used to charge the steel capillary containing the polymer or ECM solution, and a high negative voltage (−4 kV) is used to charge the stainless steel mandrel (ω). The mandrel is rotated at 200 rpm with a slow lateral translation over a distance of 15 cm, A, Yielding a tubular, uniform PEUU/ECM sheet. B, Fetal urinary bladder sheet after vacuum pressing. C, D, Scanning electron microscopy showing the random fibers in the PEUU/ECM biohybrid wrap.

Figure 6.

ECM technology can promote positive tissue remodeling by modulating several factors that contribute to the default healing response in the CNS.