Down-regulation of semaphorin 3F in rat retinal ganglion cells in response to optic nerve crush

Spatial regulation of amacrine cell genesis by Semaphorin 3f

PURPOSE

The axonal projections of retinal ganglion cells (RGCs) of the eye are topographically organized so that spatial information from visual images is preserved. This retinotopic organization is established during development by secreted morphogens that pattern domains of transcription factor expression within naso-temporal and dorso-ventral quadrants of the embryonic eye. Poorly understood are the downstream signaling molecules that generate the topographically organized retinal cells and circuits. The secreted signaling molecule Semaphorin 3fa (Sema3fa) belongs to the Sema family of molecules that provide positional information to developing cells. Here, we test a role for Sema3fa in cell genesis of the temporal zebrafish retina.

METHODS

We compare retinal cell genesis in wild type and sema3fa CRISPR zebrafish mutants by in situ hybridization and immunohistochemistry.

RESULTS

We find that mRNAs for sema3fa and known receptors, neuropilin2b (nrp2b) and plexina1a (plxna1a), are expressed by progenitors of the temporal, but not nasal zebrafish embryonic retina. In the sema3fa^ca304/ca304 embryo, initially the domains of expression for atoh7 and neurod4, transcription factors necessary for the specification of RGCs and amacrine cells, respectively, are disrupted. Yet, post-embryonically only amacrine cells of the temporal retina are reduced in numbers, with both GABAergic and glycinergic subtypes affected.

CONCLUSIONS

These data suggest that Sema3fa acts early on embryonic temporal progenitors to control in a spatially-dependent manner the production of amacrine cells, possibly to allow the establishment of neural circuits with domain-specific functions. We propose that spatially restricted extrinsic signals in the neural retina control cell genesis in a domain-dependent manner.

Co-delivery of brinzolamide and miRNA-124 by biodegradable nanoparticles as a strategy for glaucoma therapy

Co-delivery nanoparticles with characteristics of intracellular precision release drug have been generally accepted as an effective therapeutic strategy for eye diseases. In this study, we designed a new co-delivery system (miRNA/NP-BRZ) as a lasting therapeutic approach to prevent the neuro-destructive after the long-term treatment of glaucoma. Neuroprotective and intraocular pressure (IOP) response were assessed in in vivo and in vitro models of glaucoma. At the meaning time, we describe the preparation of miRNA/NP-BRZ, drug release characteristics, intraocular tracing, pharmacokinetic and pharmacodynamics study and toxicity test. We found that miRNA/NP-BRZ could remarkably decrease IOP and significantly prevent retinal ganglion cell (RGC) damages. The new formula of miRNA-124 encapsulated in PEG-PSA-BRZ nanoparticles exhibits high encapsulation efficiency (EE), drug-loading capacity (DC), and stable controlled-release efficacy (EC). Moreover, we also verified that the miRNA/NP-BRZ system is significantly neuroprotective and nontoxic as well as lowering IOP. This study shows our co-delivery drug system would have a wide potential on social and economic benefits for glaucoma.

The role of semaphorins in small vessels of the eye and brain

Small vessel diseases, such as ischemic retinopathy and cerebral small vessel disease (CSVD), are increasingly recognized in patients with diabetes, dementia and cerebrovascular disease. The mechanisms of small vessel diseases are poorly understood, but the latest studies suggest a role for semaphorins. Initially identified as axon guidance cues, semaphorins are mainly studied in neuronal morphogenesis, neural circuit assembly, and synapse assembly and refinement. In recent years, semaphorins have been found to play important roles in regulating vascular growth and development and in many pathophysiological processes, including atherosclerosis, angiogenesis after stroke and retinopathy. Growing evidence indicates that semaphorins affect the occurrence, perfusion and regression of both the macrovasculature and microvasculature by regulating the proliferation, apoptosis, migration, barrier function and inflammatory response of endothelial cells, vascular smooth muscle cells (VSMCs) and pericytes. In this review, we concentrate on the regulatory effects of semaphorins on the cell components of the vessel wall and their potential roles in microvascular diseases, especially in the retina and cerebral small vessel. Finally, we discuss potential molecular approaches in targeting semaphorins as therapies for microvascular disorders in the eye and brain.

Sema3A inhibits axonal regeneration of retinal ganglion cells via ROCK2

Successful regeneration of injured axons in the adult mammalian central nervous system (CNS) is mainly limited by lesion-induced neuronal apoptosis and the inhibitory environment consisting of numerous extrinsic and intrinsic factors. Semaphorin 3A (Sema3A), a classic axonal guidance cue, contributes to the failure of axonal regeneration and can be neutralized to enhance axonal regeneration. Previous studies have suggested that blockage of rho-associated protein kinase 2 (ROCK2) also exerts a protective effect on the survival and axonal regeneration of retinal ganglion cells (RGC, RGCs) after injury. Yet unresolved question is the interaction between the two factors. We thus evaluated the role of Sema3A and ROCK2 in RGC axonal regeneration. In this study, we first examined the expression of Sema3A and ROCK2 against optic nerve crush in vivo and oxygen-glucose deprivation insult to RGCs in vitro at different time points. Then Sema3A, ROCK2 inhibitor Y-27632, combination of both and phosphate-buffered saline (PBS) only were injected into the vitreous cavity after optic nerve crush at various times in different experiments. In order to assess axonal regeneration, we detected the mRNA levels of small proline-rich protein 1A (Sprr1A) and growth-associated protein 43 (GAP43) by quantitative real time-polymerase chain reaction (RT-qPCR), evaluated visual function by Flash Visual Evoked Potentials (F-VEPs), and checked the protein level of GAP43 by immunofluorescent staining. Our results demonstrated that Sema3A significantly suppressed optic nerve regeneration and this effect can be attenuated via blocking ROCK2. Moreover, Sema3A promoted the phosphorylation of myosin light chain 2 (MLC2) (specific downstream effector of ROCK2 concerning neurite growth). Collectively, Sema3A may negatively regulate axonal regeneration through ROCK2 in RGCs.