Towards retinal ganglion cell regeneration

Extracellular-Matrix Mechanics Regulate the Ocular Physiological and Pathological Activities

The extracellular matrix (ECM) is a noncellular structure that plays an indispensable role in a series of cell life activities. Accumulating studies have demonstrated that ECM stiffness, a type of mechanical forces, exerts a pivotal influence on regulating organogenesis, tissue homeostasis, and the occurrence and development of miscellaneous diseases. Nevertheless, the role of ECM stiffness in ophthalmology is rarely discussed. In this review, we focus on describing the important role of ECM stiffness and its composition in multiple ocular structures (including cornea, retina, optic nerve, trabecular reticulum, and vitreous) from a new perspective. The abnormal changes in ECM can trigger physiological and pathological activities of the eye, suggesting that compared with different biochemical factors, the transmission and transduction of force signals triggered by mechanical cues such as ECM stiffness are also universal in different ocular cells. We expect that targeting ECM as a therapeutic approach or designing advanced ECM-based technologies will have a broader application prospect in ophthalmology.

Resveratrol protects retinal ganglion cell axons through regulation of the SIRT1-JNK pathway

It is reported that Ischemia and reperfusion damage (I/R damage) can lead to retinal ganglion cell (RGC) death and neurodegeneration, which in turn can lead to irreversible vision loss. In this study, we sought to understand the neuroprotective effect of resveratrol, the important activator of sirtuin1 (SIRT1), on RGC survival in I/R damage model and the molecular mechanism that mediate this effect. Our results show that resveratrol could reverse axonal swelling, holes, and the chaos of the nucleus in axons of RGCs caused by I/R. At the same time, resveratrol could also reverse the activation of retinal astrocytes and the loss of RGCs caused by I/R. Resveratrol increased the expression of SIRT1 while decreasing the phosphorylation of N-terminal kinase (JNK). SP600125(JNK inhibitor) decreased the phosphorylation of JNK while increasing the expression of SIRT1, indicating that SIRT1 and JNK can interact with each other. Simultaneous administration of resveratrol and sirtinol (SIRT1 inhibitor) neither increased the expression of SIRT1 nor decreased the phosphorylation of JNK, indicating that resveratrol affects the phosphorylation of JNK by SIRT1. In total, our research shows that resveratrol treatment significantly reduces apoptosis and axonal degeneration of RGCs, and this protection is partly mediated through the SIRT1-JNK pathway.

Resveratrol protects retinal ganglion cells against ischemia induced damage by increasing Opa1 expression

Loss of idiopathic retinal ganglion cells (RGCs) leads to irreversible vision defects and is considered the primary characteristic of glaucoma. However, effective treatment strategies in terms of RGC neuroprotection remain elusive. In the present study, the protective effects of resveratrol on RGC apoptosis, and the mechanisms underlying its effects were investigated, with a particular emphasis on the function of optic atrophy 1 (Opa1). In an ischemia/reperfusion (I/R) injury model, the notable thinning of the retina, significant apoptosis of RGCs, reduction in Opa1 expression and long Opa1 isoform to short Opa1 isoform ratios (L-Opa1/S-Opa1 ratio) were observed, all of which were reversed by resveratrol administration. Serum deprivation resulted in reductions in R28 cell viability, superoxide dismutase (SOD) activity, Opa1 expression and induced apoptosis, which were also partially reversed by resveratrol treatment. To conclude, results from the present study suggest that resveratrol treatment significantly reduced retinal damage and RGC apoptosis in I/R injury and serum deprivation models. In addition, resveratrol reversed the downregulated expression of Opa1 and reduced SOD activity. Mechanistically, resveratrol influenced mitochondrial dynamics by regulating the L-Opa1/S-Opa1 ratio. Therefore, these observations suggest that resveratrol may exhibit potential as a therapeutic agent for RGC damage in the future.

Nanotechnology in regenerative ophthalmology

In recent years, regenerative medicine is gaining momentum and is giving hopes for restoring function of diseased, damaged, and aged tissues and organs and nanotechnology is serving as a catalyst. In the ophthalmology field, various types of allogenic and autologous stem cells have been investigated to treat some ocular diseases due to age-related macular degeneration, glaucoma, retinitis pigmentosa, diabetic retinopathy, and corneal and lens traumas. Nanomaterials have been utilized directly as nanoscaffolds for these stem cells to promote their adhesion, proliferation and differentiation or indirectly as vectors for various genes, tissue growth factors, cytokines and immunosuppressants to facilitate cell reprogramming or ocular tissue regeneration. In this review, we reviewed various nanomaterials used for retina, cornea, and lens regenerations, and discussed the current status and future perspectives of nanotechnology in tracking cells in the eye and personalized regenerative ophthalmology. The purpose of this review is to provide comprehensive and timely insights on the emerging field of nanotechnology for ocular tissue engineering and regeneration.

Inhibition of miR-21 ameliorates excessive astrocyte activation and promotes axon regeneration following optic nerve crush

Optic nerve injury is a leading cause of irreversible visual impairment worldwide and can even cause blindness. Excessive activation of astrocytes has negative effects on the repair and recovery of retinal ganglion cells following optic nerve injury. However, the molecular and cellular mechanisms underlying astrocyte activation after optic nerve injury remain largely unknown. In the present study, we explored the effects of microRNA-21 (miR-21) on axon regeneration and flash visual evoked potential (F-VEP) and the underlying mechanisms of these effects based on astrocyte activation in the rat model of optic nerve crush (ONC). To the best of our knowledge, this article is the first to report that inhibition of miR-21 enhances axonal regeneration and promotes functional recovery in F-VEP in the rat model of ONC. Furthermore, inhibition of miR-21 attenuates excessive astrocyte activation and glial scar formation, thereby promoting axonal regeneration by regulating the epidermal growth factor receptor (EGFR) pathway. In addition, we observed that the expression of tissue inhibitor of metalloproteinase-3, a target gene of miR-21, was inhibited during this process. Taken together, these findings demonstrate that inhibition of miR-21 regulates the EGFR pathway, ameliorating excessive astrocyte activation and glial scar progression and promoting axonal regeneration and alleviating impairment in F-VEP function in a model of ONC. This study's results suggest that miR-21 may represent a therapeutic target for optic nerve injury.

Toxicity of triphenyltin on the development of retinal axons in zebrafish at low dose

The impacts of triphenyltin (TPT) on ecological health are of particular concern due to the unexpectedly high levels found in wild fish around the world. Here, zebrafish embryos were exposed to TPT via in ovo nano-injection to study its toxicity on the development of retinal axons in fish. Lipophilic dye labeling revealed obvious defects in retinal axon development in larvae with normally shaped eyes, with incidences of 0, 1.08%, 2.66%, 4.26%, and 6.85% observed in the control, 0.8, 4.0, 20.0, and 100ng TPT-Cl/g wet weight (ww) exposure groups, respectively, showing a dose-dependent increase. Since the lowest observable effective concentration of TPT to induce retinal axon development defects was 0.8ng TPT-Cl/g ww, which is lower than the concentrations in wild fish eggs, this defect would occur in wild fish larvae. Alterations in the expressions of pax6 and ephrinBs, which regulate the establishment of retinal polarity, were correlated with defect incidence. Expression levels of the CYP26A1 gene and protein were significantly up-regulated in all exposure groups compared with the control, which may lead to significant decreases in concentrations of all-trans retinoic acid (atRA). Such a disruption of RA metabolism would, at least partly, contribute to the incidence of developmental defects in retinal axons. This study is the first to report that TPT can interfere with development of retinal axons in fish at low dose.

Neural Stem Cell-based Intraocular Administration of Pigment Epithelium-derived Factor Promotes Retinal Ganglion Cell Survival and Axon Regeneration after Optic Nerve Crush Injury in Rat: An Experimental Study

BACKGROUND

Pigment epithelium-derived factor (PEDF) is regarded as a multifunctional protein possessing neurotrophic and neuroprotective properties. PEDF has a very short half-life, and it would require multiple injections to maintain a therapeutically relevant level without a delivery system. However, multiple injections are prone to cause local damage or infection. To overcome this, we chose a cell-based system that provided sustained delivery of PEDF and compared the effect of weekly injections of PEDF and neural stem cell (NSC)-based intraocular administration of PEDF on retinal ganglion cell (RGC) survival and axon regeneration after optic nerve injury.

METHODS

Seventy-two rats were randomly assigned to 3 groups: group with injections of phosphate buffered saline (PBS) (n=24), group with weekly injections of PEDF (n=24), and group with NSC-based administration of PEDF (n=24). Western blot was used to analyze the PEDF protein level 2 weeks after injection. Retinal flat mounts and immunohistochemistry were employed to analyze RGC survival and axon regeneration 2 weeks and 4 weeks after injection. The data were analyzed with one-way ANOVA in SPSS (version 19.0). A P<0.05 was considered significant.

RESULTS

The PEDF protein level in the group with NSC-based administration of PEDF increased compared with that in the groups with injections of PEDF and PBS (P<0.05). The PEDF-modified NSCs differentiated into GFAP-positive astrocytes andβ-tubulin-III-positive neurons. NSC-based administration of PEDF effectively increased RGC survival and improved the axon regeneration of the optic nerve compared with weekly injections of PEDF.

CONCLUSION

Subretinal space transplantation of PEDF-secreting NSCs sustained high concentrations of PEDF, differentiated into neurons and astrocytes, and significantly promoted RGC survival and axon regeneration after optic nerve injury.

Restoration of Opa1-long isoform inhibits retinal injury-induced neurodegeneration

Optic atrophy 1 (Opa1) is a critical factor that regulates fusion and other important functions of mitochondria. In mitochondrion, the N-terminal mitochondrial targeting sequence of Opa1 precursors is removed to generate Opa1 long isoforms (L-Opa1), which are further cleaved into short isoforms (S-Opa1). In the present study, we found that retinal ischemia-reperfusion (I/R) injury and intravitreal injection of carbonylcyanide m-chlorophenyl hydrazone (CCCP) both dramatically induced Opa1 cleavage and caused loss of L-Opa1. In cultured neuronal cells under hypoxia-reoxygenation (H/R) injury, similar changes for Opa1 were also observed. In contrast, restoration of L-Opa1 level by overexpression of S1 cleavage site deletion Opa1 splice 1 (Opa1-ΔS1) not only normalized the H/R-induced mitochondrial morphology changes, but also inhibited the H/R-induced apoptosis, necrosis, and the intracellular ATP loss. Furthermore, recovering L-Opa1 level in the I/R-injured retina by intravitreal injection of genipin or overexpression of Opa1-ΔS1 inhibited apoptosis, necrosis, cell loss in the ganglion cell layer and retinal thickness reduction. Together, our data demonstrated the loss of L-Opa1 is involved in the development of retinal I/R injury, indicating restoring L-Opa1 level may be considered as a therapeutic target for I/R injury-related diseases, at least for the retina. Key messages: Retinal ischemia-reperfusion (I/R) or hypoxia-reoxygenation (H/R) injury induces L-Opa1 loss. Opa1-ΔS1 overexpression inhibits H/R-induced L-Opa1 loss. Opa1-ΔS1 overexpression inhibits H/R-induced mitochondria morphology change. Opa1-ΔS1 and genipin inhibit retinal I/R injury-induced necroptosis. Opa1-ΔS1 and genipin inhibit retinal I/R injury-induced neurodegeneration.

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.

MicroRNA-26a overexpression protects RGC-5 cells against H2O2-induced apoptosis

BACKGROUND

We intended to examine the functional role of microRNA 26 (miR-26a) in regulating H2O2-induced cytotoxicity and apoptosis in RGC-5 cells in vitro.

METHOD

Various concentrations of H2O2 (0-1000 μM) were added in RGC-5 culture. Cell cytotoxicity was monitored by viability assay and gene expression level of miR-26a examined by qRT-PCR. MicroRNA-26a mimic was then applied in the RGC-5 culture to examine its effect on upregulating endogenous miR-26a and rescuing H2O2-induced cytotoxicity. TUNEL immunostaining assay was used to further assess the protective effect of upregulating miR-26a on H2O2-induced apoptosis in RGC-5 cells. Direct targeting of miR-26a on Phosphatase and tensin homolog (PTEN) signaling pathway was assessed by luciferase assay and western blotting. PTEN was then ectopically over-expressed in RGC-5. And its effects on miR-26a mediated apoptosis protection in RGC-5 were investigated by western blot and TUNEL assay.

RESULTS

H2O2 induced cytotoxicity and down-regulated miR-26a in dose-dependent manner in RGC-5 cells. MiR-26a-mimic upregulated endogenous miR-26a gene levels, and then reduced H2O2-induced cytotoxicity, as well as H2O2-induced apoptosis in RGC-5 cells. PTEN was directly targeted by miR-26a. PTEN protein was upregulated, and phosphorylated AKT protein down-regulated while miR-26a was upregulated to reduce H2O2-induced apoptosis. Finally, overexpressing PTEN reversed the protective effect of miR-26a upregulation on RGC-5 apoptosis.

CONCLUSION

Upregulating miR-26a protects RGC-5 cell against cytotoxicity and apoptosis, probably through down-regulation of PTEN.