Peripheral nerve implantation into a penetrating lesion of the eye: stimulation of the damaged retina

Matrix-bound nanovesicles prevent ischemia-induced retinal ganglion cell axon degeneration and death and preserve visual function

Injury to retinal ganglion cells (RGC), central nervous system neurons that relay visual information to the brain, often leads to RGC axon degeneration and permanently lost visual function. Herein this study shows matrix-bound nanovesicles (MBV), a distinct class of extracellular nanovesicle localized specifically to the extracellular matrix (ECM) of healthy tissues, can neuroprotect RGCs and preserve visual function after severe, intraocular pressure (IOP) induced ischemia in rat. Intravitreal MBV injections attenuated IOP-induced RGC axon degeneration and death, protected RGC axon connectivity to visual nuclei in the brain, and prevented loss in retinal function as shown by histology, anterograde axon tracing, manganese-enhanced magnetic resonance imaging, and electroretinography. In the optic nerve, MBV also prevented IOP-induced decreases in growth associated protein-43 and IOP-induced increases in glial fibrillary acidic protein. In vitro studies showed MBV suppressed pro-inflammatory signaling by activated microglia and astrocytes, stimulated RGC neurite growth, and neuroprotected RGCs from neurotoxic media conditioned by pro-inflammatory astrocytes. Thus, MBV can positively modulate distinct signaling pathways (e.g., inflammation, cell death, and axon growth) in diverse cell types. Since MBV are naturally derived, bioactive factors present in numerous FDA approved devices, MBV may be readily useful, not only experimentally, but also clinically as immunomodulatory, neuroprotective factors for treating trauma or disease in the retina as well as other CNS tissues.

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

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.

Embryonic retinal grafts have a beneficial effect on the damaged host retina

The adult rat retina was evaluated following surgical lesion and after transplantation of embryonic day 15 (E15) retinal tissue. While a surgical incision caused degeneration and ganglion cell death peripheral to lesion site, the addition of an embryonic retinal implant to the lesion site resulted in a reduction of this degenerative response. In addition, the embryonic graft also exerted a stimulatory effect in the central direction from the lesion site, as increases in layer thicknesses were seen. We speculate that putative diffusable factor(s) may mediate these effects.

Retinal transplants and optic nerve bridges: possible strategies for visual recovery as a result of trauma or disease

From the review of the current literature it is quite evident that some exciting prospects are on the horizon which will help to better explain the development and functioning of the visual system. In addition, the new technology of CNS tissue grafting coupled to other newly emerging technologies (i.e., microsurgical, microinjection, and micromanipulative techniques coupled with our knowledge of immunosuppressive methods) will allow for a realistic approach in exploring possible strategies for visual recovery as a result of trauma or disease within the near future. One specific area of research that hopefully will emerge from this new body of knowledge comes from the realization that at the present time there is no effective therapy for practically all types of hereditary retinal degenerative disorders in man. It would seem most appropriate to take advantage of the new neuronal transplantation technology mentioned in this article and the availability of hereditary retinal degeneration models in the hope of developing new methods for a therapeutic approach to this problem. Such an approach could involve replacing the abnormal, absent, and/or lost host retinal cells with tissue from healthy donors by means of a grafting technique with the goal of arresting and/or reversing the disease process. Of course, this is but one example of the many challenges in this area of research which increasingly appear to be within our grasp.

Peripheral nerve implant effects on survival of retinal ganglion layer cells after axotomy initiated by a penetrating lesion

A lesion paradigm involving a small penetrating incision made through the sclera, choroid and retina of the adult rat eye creates a unique environment for the study of the damaged retina. More specifically, the dependable formation of a small focal retinal lesion makes this an ideal model for the determination of conditions that may stimulate retinal regeneration, wound repair and/or cell survival. Our previous studies have indicated that the placement of a desheathed peripheral nerve implant (PNI) into the lesioned adult rat eye: (1) initiated the rescue of retinal tissue that would normally die due to trauma; and (2) maintained the thickness and organization of most retinal layers adjacent to the lesion site, particularly the retinal ganglion cell layer (RGL). We report in the present work that a more detailed analysis of the RGL revealed a significant increase in the survival of axotomized neurons within this layer in the presence of a PNI over an 8-week post-implantation period. More specifically, there was a 60% loss of control RGL cells axotomized by the lesion 3 weeks previously in contrast to only a 30% loss in those tissues exposed to a PNI. Additional RGL cell size distribution studies point to the fact that the PNI appeared to affect the increased survival of cells greater than or equal to 70 micron2. Also the PNI effect demonstrated a specificity of response when tested against the influence of a tendon or suture implant.(ABSTRACT TRUNCATED AT 250 WORDS)