Raf-1 Kinase Inhibitory Protein (RKIP) Promotes Retinal Ganglion Cell Survival and Axonal Regeneration Following Optic Nerve Crush

Rare variant analyses across multiethnic cohorts identify novel genes for refractive error

Refractive error, measured here as mean spherical equivalent (SER), is a complex eye condition caused by both genetic and environmental factors. Individuals with strong positive or negative values of SER require spectacles or other approaches for vision correction. Common genetic risk factors have been identified by genome-wide association studies (GWAS), but a great part of the refractive error heritability is still missing. Some of this heritability may be explained by rare variants (minor allele frequency [MAF] ≤ 0.01.). We performed multiple gene-based association tests of mean Spherical Equivalent with rare variants in exome array data from the Consortium for Refractive Error and Myopia (CREAM). The dataset consisted of over 27,000 total subjects from five cohorts of Indo-European and Eastern Asian ethnicity. We identified 129 unique genes associated with refractive error, many of which were replicated in multiple cohorts. Our best novel candidates included the retina expressed PDCD6IP, the circadian rhythm gene PER3, and P4HTM, which affects eye morphology. Future work will include functional studies and validation. Identification of genes contributing to refractive error and future understanding of their function may lead to better treatment and prevention of refractive errors, which themselves are important risk factors for various blinding conditions.

Axonal degeneration induces distinct patterns of phosphatidylserine and phosphatidylethanolamine externalization

Axonal degeneration is a common feature of multiple neurodegenerative diseases, yet the mechanisms underlying its various manifestations are incompletely understood. We previously demonstrated that axonal degeneration is associated with externalization of phosphatidylserine (PS), which precedes morphological evidence of degeneration, is redox-sensitive, and is delayed in Wallerian degeneration slow (Wld^S) mutant animals. Phosphatidylethanolamine (PE) is the other major membrane phospholipid in the inner leaflet of the cell membrane, and given that PS signals apoptosis, phagocytosis, and degeneration, we hypothesized that PS and PE membrane dynamics play distinct roles in axonal degeneration. To test this hypothesis, axonal degeneration was induced with calcium ionophores in postnatal rat retinal ganglion cells, and PS- and PE-specific fluorescent probes used to measure their externalization over time. In untreated cells, cell-surface PS was prominent in the cell body alone. Elevation of intracellular calcium with calcium ionophores resulted in significantly increased levels of PS externalization in the cell body, axon, and axon growth cone. Unlike PS, cell-surface PE was diffusely distributed in untreated cells, with comparable levels across the soma, axons, and axon terminals. After exposure to calcium ionophores, PE externalization significantly increased in the cell body and axon. Elevated intracellular calcium also resulted in the formation of axonal blebs which exclusively contained externalized PS, but not PE. Together, these results indicated distinct patterns of externalized PS and PE in normal and degenerating neurons, suggesting a differential role for these phospholipids in transducing neuronal injury.

Proteomics and systems biology in optic nerve regeneration

We present an overview of current state of proteomic approaches as applied to optic nerve regeneration in the historical context of nerve regeneration particularly central nervous system neuronal regeneration. We present outlook pertaining to the optic nerve regeneration proteomics that the latter can extrapolate information from multi-systems level investigations. We present an account of the current need of systems level standardization for comparison of proteome from various models and across different pharmacological or biophysical treatments that promote adult neuron regeneration. We briefly overview the need for deriving knowledge from proteomics and integrating with other omics to obtain greater biological insight into process of adult neuron regeneration in the optic nerve and its potential applicability to other central nervous system neuron regeneration.

Strategies to Promote Long-Distance Optic Nerve Regeneration

Mammalian retinal ganglion cells (RGCs) in the central nervous system (CNS) often die after optic nerve injury and surviving RGCs fail to regenerate their axons, eventually resulting in irreversible vision loss. Manipulation of a diverse group of genes can significantly boost optic nerve regeneration of mature RGCs by reactivating developmental-like growth programs or suppressing growth inhibitory pathways. By injury of the vision pathway near their brain targets, a few studies have shown that regenerated RGC axons could form functional synapses with targeted neurons but exhibited poor neural conduction or partial functional recovery. Therefore, the functional restoration of eye-to-brain pathways remains a greatly challenging issue. Here, we review recent advances in long-distance optic nerve regeneration and the subsequent reconnecting to central targets. By summarizing our current strategies for promoting functional recovery, we hope to provide potential insights into future exploration in vision reformation after neural injuries.

PEBP1/RKIP behavior: a mirror of actin-membrane organization

Phosphatidylethanolamine-binding protein 1 (PEBP1), a small 21 kDa protein, is implicated in several key processes of the living cell. The deregulation of PEBP1, especially its downregulation, leads to major diseases such as cancer and Alzheimer's disease. PEBP1 was found to interact with numerous proteins, especially kinases and GTPases, generally inhibiting their activity. To understand the basic functionality of this amazing small protein, we have considered several known processes that it modulates and we have discussed the role of each molecular target in these processes. Here, we propose that cortical actin organization, associated with membrane changes, is involved in the majority of the processes modulated by PEBP1. Furthermore, based on recent data, we summarize some key PEBP1-interacting proteins, and we report their respective functions and focus on their relationships with actin organization. We suggest that, depending on the cell status and environment, PEBP1 is an organizer of the actin-membrane composite material.

Extracellular Signal-Regulated Kinase 1/2 Pathway Is Insufficiently Involved in the Neuroprotective Effect by Hydrogen Sulfide Supplement in Experimental Glaucoma

Purpose

Glaucoma is a neurodegenerative eye disease characterized by gradually impaired visual field and irreversible blindness due to retinal ganglion cell (RGC) loss. Our previous studies have confirmed that hydrogen sulfide (H2S) takes part in the glaucomatous process and contributes to RGC protection. The present study aimed to further investigate the role of extracellular signal-regulated kinase 1/2 (ERK 1/2) pathway underlying the impact of H2S, to better understand the mechanism through which H2S exerts neuroprotection in glaucoma.

Methods

An established rat glaucoma model was used and 168 rats were qualified to undergo sodium hydrosulfide (NaHS, a H2S donor)/PD98059 (an ERK inhibitor) treatment. Then the survival and apoptosis of RGC were evaluated through retrograde labeling and TUNEL staining, along with activity evaluations of ERK 1/2 pathway, intrinsic apoptotic pathway, glial activation, nuclear factor kappa B (NF-κB) pathway, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, autophagy, and TNF-α production through immunohistochemistry, Western blotting, and ELISA.

Results

The study demonstrated that NaHS suppressed ERK 1/2 pathway activity similarly to PD98059 in retinas of experimental glaucoma rats, while PD98059 also similarly suppressed glial activation, NF-κB pathway, NADPH oxidase, and TNF-α production. However, PD98059 did not affect RGC survival, apoptotic regulation, or autophagy as NaHS did.

Conclusions

Our study indicated that inhibition of ERK 1/2 pathway might partly contribute to the neuroprotection by H2S in experimental glaucoma; however, it was insufficient to initiate the therapeutic effect on its own.

MEK inhibition prevents TGF‑β1‑induced myofibroblast transdifferentiation in human tenon fibroblasts

Subconjunctival fibrosis represents the primary cause of postoperative failure of trabeculectomy, and at present there is a lack of effective intervention strategies. The present study aimed to investigate the effect of the mitogen‑activated protein kinase kinase (MEK) inhibitor U0126 on human tenon fibroblast (HTF) myofibrosis transdifferentiation, and to illuminate the underlying molecular mechanisms involved. It was demonstrated that U0126 significantly inhibited the proliferation, migration and collagen contraction of HTFs stimulated with TGF‑β1. In addition, U0126 largely attenuated the TGF‑β1‑induced conversion of HTFs into myofibroblasts, as indicated by a downregulation of the mRNA and protein expression of α‑smooth muscle actin and zinc finger protein SNAI1, and by ameliorating the 3D‑collagen contraction response. Mechanistically, U0126 suppressed the TGF‑β1‑stimulated phosphorylation of mothers against decapentaplegic homolog 2/3, P38 mitogen‑activated protein kinase and extracellular signal‑regulated kinase 1/2, indicating that U0126 may inhibit HTF activation through the canonical and non‑canonical signaling pathways of TGF‑β1. Therefore, U0126 exhibits a potent anti‑fibrotic effect among HTFs, and the inhibition of MEK signaling may serve as an alternative intervention strategy for the treatment of trabeculectomy‑associated fibrosis.

Metabolomic changes in the mouse retina after optic nerve injury

In glaucoma, although axonal injury drives retinal ganglion cell (RGC) death, little is known about the underlying pathomechanisms. To provide new mechanistic insights and identify new biomarkers, we combined latest non-targeting metabolomics analyses to profile altered metabolites in the mouse whole retina 2, 4, and 7 days after optic nerve crush (NC). Ultra-high-performance liquid chromatography quadrupole time-of-flight mass spectrometry and liquid chromatography Fourier transform mass spectrometry covering wide spectrum of metabolites in combination highlighted 30 metabolites that changed its concentration after NC. The analysis displayed similar changes for purine nucleotide and glutathione as reported previously in another animal model of axonal injury and detected multiple metabolites that increased after the injury. After studying the specificity of the identified metabolites to RGCs in histological sections using imaging mass spectrometry, two metabolites, i.e., L-acetylcarnitine and phosphatidylcholine were increased not only preceding the peak of RGC death in the whole retina but also at the RGC layer (2.3-fold and 1.2-fold, respectively). These phospholipids propose novel mechanisms of RGC death and may serve as early biomarkers of axonal injury. The combinatory metabolomics analyses promise to illuminate pathomechanisms, reveal biomarkers, and allow the discovery of new therapeutic targets of glaucoma.

Specific Phospholipids Regulate the Acquisition of Neuronal and Astroglial Identities in Post-Mitotic Cells

Hitherto, the known mechanisms underpinning cell-fate specification act on neural progenitors, affecting their commitment to generate neuron or glial cells. Here, we show that particular phospholipids supplemented in the culture media modify the commitment of post-mitotic neural cells in vitro. Phosphatidylcholine (PtdCho)-enriched media enhances neuronal differentiation at the expense of astroglial and unspecified cells. Conversely, phosphatidylethanolamine (PtdEtn) enhances astroglial differentiation and accelerates astrocyte maturation. The ability of phospholipids to modify the fate of post-mitotic cells depends on its presence during a narrow time-window during cell differentiation and it is mediated by the selective activation of particular signaling pathways. While PtdCho-mediated effect on neuronal differentiation depends on cAMP-dependent kinase (PKA)/calcium responsive element binding protein (CREB), PtdEtn stimulates astrogliogenesis through the activation of the MEK/ERK signaling pathway. Collectively, our results provide an additional degree of plasticity in neural cell specification and further support the notion that cell differentiation is a reversible phenomenon. They also contribute to our understanding of neuronal and glial lineage specification in the central nervous system, opening up new avenues to retrieve neurogenic capacity in the brain.