Injectable Neurotrophic Factor Delivery System Supporting Retinal Ganglion Cell Survival and Regeneration Following Optic Nerve Crush

Extracellular matrix stiffness mediates insulin secretion in pancreatic islets via mechanosensitive Piezo1 channel regulated Ca2+ dynamics

The pancreatic islet is surrounded by ECM that provides both biochemical and mechanical cues to the islet β-cell to regulate cell survival and insulin secretion. Changes in ECM composition and mechanical properties drive β-cell dysfunction in many pancreatic diseases. While several studies have characterized changes in islet insulin secretion with changes in substrate stiffness, little is known about the mechanotransduction signaling driving altered islet function in response to mechanical cues. We hypothesized that increasing matrix stiffness will lead to insulin secretion dysfunction by opening the mechanosensitive ion channel Piezo1 and disrupting intracellular Ca2+ dynamics in mouse and human islets. To test our hypothesis, mouse and human cadaveric islets were encapsulated in a biomimetic reverse thermal gel (RTG) scaffold with tailorable stiffness that allows formation of islet focal adhesions with the scaffold and activation of Piezo1 in 3D. Our results indicate that increased scaffold stiffness causes insulin secretion dysfunction mediated by increases in Ca2+ influx and altered Ca2+ dynamics via opening of the mechanosensitive Piezo1 channel. Additionally, inhibition of Piezo1 rescued glucose-stimulated insulin secretion (GSIS) in islets in stiff scaffolds. Overall, our results emphasize the role mechanical properties of the islet microenvironment plays in regulating function. It also supports further investigation into the modulation of Piezo1 channel activity to restore islet function in diseases like type 2 diabetes (T2D) and pancreatic cancer where fibrosis of the peri-islet ECM leads to increased tissue stiffness and islet dysfunction.

Optic nerve regeneration: Potential treatment approaches

The optic nerve, predominantly constituted by the axons of retinal ganglion cells (RGCs), lacks the ability to regenerate and re-establish function after injury. RGCs are crucial for visual function, and thus, RGC death contributes to the development of numerous progressive neurodegenerative optic neuropathies including glaucoma, ischemic optic neuropathy, and optic neuritis. Regenerating optic nerve axons poses numerous challenges due to factors such as the intricate and inhibitory conditions that exist within their environment, intrinsic breaks to regeneration, and the geometric tortuosity that offers physical hindrance to axon growth. However, recent research advancements offer hope for clinically meaningful regeneration for those who suffer from optic nerve damage. In this review, we highlight the current treatment approaches for optic nerve axon regeneration.

Ciliary neurotrophic factor mediated growth of retinal ganglion cell axons on PGS/PCL scaffolds

Ciliary neurotrophic factor (CNTF) promotes survival and/or differentiation of a variety of neuronal cells including retinal ganglion cells (RGCs). Delivery of CNTF requires a suitable medium capable of mediating diffusion and premature release of CNTF within the target tissue. Polymeric tissue-engineered scaffolds have been readily used as substrates for cell transplantation, expansion, and differentiation and, as carriers of cell growth factors. Their functions to CNTF release for RGC proliferation have remained so far unexplored, especially to CNTF affinity to the scaffold and subsequent RGC fate. Electrospunpoly(glycerol sebacate)/poly(ϵ-caprolactone) (PGS/PCL) biopolymer scaffolds have recently shown promising results in terms of supporting regeneration of RGC neurites. This work explores covalent immobilization of CNTF on PGS/PCL scaffold and the way immobilised CNTF mediates growth of RGC axons on the scaffold. Anex-vivothree-dimensional model of rodent optic nerve on PGS/PCL revealed that RGC explants cultured in CNTF mediated environment increased their neurite extensions after 20 d of cell culture employing neurite outgrowth measurements. The CNTF secretion on PGS/PCL scaffold was found bio-mimicking natural extracellular matrix of the cell target tissue and, consequently, has shown a potential to improve the overall efficacy of the RGC regeneration process.

Intraocular nano-microscale drug delivery systems for glaucoma treatment: design strategies and recent progress

Glaucoma is a leading cause of irreversible visual impairment and blindness, affecting over 76.0 million people worldwide in 2020, with a predicted increase to 111.8 million by 2040. Hypotensive eye drops remain the gold standard for glaucoma treatment, while inadequate patient adherence to medication regimens and poor bioavailability of drugs to target tissues are major obstacles to effective treatment outcomes. Nano/micro-pharmaceuticals, with diverse spectra and abilities, may represent a hope of removing these obstacles. This review describes a set of intraocular nano/micro drug delivery systems involved in glaucoma treatment. Particularly, it investigates the structures, properties, and preclinical evidence supporting the use of these systems in glaucoma, followed by discussing the route of administration, the design of systems, and factors affecting in vivo performance. Finally, it concludes by highlighting the emerging notion as an attractive approach to address the unmet needs for managing glaucoma.

Expression of the neuroprotective factors BDNF, CNTF, and FGF-2 in normal and oxygen induced retinopathy

INTRODUCTION

Oxygen-induced retinopathy is a type of retinal pathological neovascularization (NV) disease that leads to vision loss and translates to a significant societal cost. Anti-vascular endothelial growth factor (VEGF) and anti-inflammatory treatments have been widely used in the clinic, but the results have not been entirely satisfactory. It is necessary to explore other treatments for Ischemic retinal diseases.

METHODS

The oxygen-induced retinopathy (OIR) model was induced from P7 to P12 as described. Histology evaluation (HE) and retina flat mounts were checked at P17 to confirm the establishment of the OIR model. Retinal ganglion cell (RGC) degeneration was checked by transmission electron microscopy at P17 to confirm the neurological damage caused by OIR. Western blot analysis was performed at P12, P15, and P17 to study the expression of brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), and fibroblast growth factor 2 (FGF-2) in normal and OIR mice. Comparative analysis of the expressions of BDNF, CNTF, and FGF-2 in normal and OIR mice was performed.

RESULTS

There were many retinal NV and non-perfusion areas in OIR P17. RGCs were degenerated at OIR P17. The expressions of BDNF, CNTF, and FGF-2 gradually increased from P12 to P17 in normal mice and were much higher in OIR mice. The expression curves of BDNF, CNTF, and FGF-2 in the OIR model were inconsistent and did not correlate with each other.

DISCUSSION

This study provides evidence for changes in BDNF, CNTF, and FGF-2 in Oxygen-induced retinopathy.

Preliminary Results of a Reverse Thermal Gel Patch for Fetal Ovine Myelomeningocele Repair

BACKGROUND

Prenatal surgical closure of Myelomeningocele (MMC) is considered part of the current age armamentarium. Clinical data has demonstrated the need for innovative patches to maximize the benefits and decrease the risks of this approach. Our team has developed a minimally invasive reverse thermal gel (RTG) patch with cellular scaffolding properties. Here, we demonstrate the initial gross and microscopic histological effects of this RTG patch in the fetal ovine model of MMC.

MATERIALS AND METHODS

A fetal ovine MMC defect was created at 68-75 days gestation, RTG patch application or untreated at 100-103 days, and harvest at 135-140 days. The RTG was applied to the defect and secured in place with an overlay sealant. Defect areas underwent gross and microscopic analysis for inflammation and skin development. Brains were analyzed for hindbrain herniation and hydrocephalus.

RESULTS

The untreated fetus (n = 1) demonstrated an open defect lacking tissue coverage, evidence of spinal cord injury, increased caspase-3, Iba1 and GFAP in spinal cord tissues, and hindbrain herniation and ventricular dilation. RTG treated fetuses (n = 3) demonstrated defect healing with well-organized dermal and epidermal layers throughout the entire healed tissue area overlaying the defect with minimal inflammation, reduced caspase-3, Iba1 and GFAP in spinal cord tissues, and no hindbrain herniation or ventricular dilation.

CONCLUSION

An RTG patch applied to MMC defects in fetal sheep promoted skin coverage over the defect, was associated with minimal inflammation of the spinal cord tissues and prevented brain abnormalities. The present findings provide exciting results for future comprehensive radiological, functional, and mechanistic evaluation of the RTG.

The Pathogenesis and Therapeutic Approaches of Diabetic Neuropathy in the Retina

Diabetic retinopathy is a major retinal disease and a leading cause of blindness in the world. Diabetic retinopathy is a neurovascular disease that is associated with disturbances of the interdependent relationship of cells composed of the neurovascular units, i.e., neurons, glial cells, and vascular cells. An impairment of these neurovascular units causes both neuronal and vascular abnormalities in diabetic retinopathy. More specifically, neuronal abnormalities including neuronal cell death and axon degeneration are irreversible changes that are directly related to the vision reduction in diabetic patients. Thus, establishment of neuroprotective and regenerative therapies for diabetic neuropathy in the retina is an emergent task for preventing the blindness of patients with diabetic retinopathy. This review focuses on the pathogenesis of the neuronal abnormalities in diabetic retina including glial abnormalities, neuronal cell death, and axon degeneration. The possible molecular cell death pathways and intrinsic survival and regenerative pathways are also described. In addition, therapeutic approaches for diabetic neuropathy in the retina both in vitro and in vivo are presented. This review should be helpful for providing clues to overcome the barriers for establishing neuroprotection and regeneration of diabetic neuropathy in the retina.

Protective Effect of Total Panax Notoginseng Saponins on Retinal Ganglion Cells of an Optic Nerve Crush Injury Rat Model

Irreversible loss of retinal ganglion cells (RGCs) is a common pathological feature of various optic nerve degenerative diseases such as glaucoma and ischemic optic neuropathy. Effective protection of RGCs is the key to successful treatment of these diseases. Total Panax notoginseng saponins (TPNS) are the main active component of Panax notoginseng, which has an inhibitory effect on the apoptosis pathway. This study is aimed at assessing the protective effect of TPNS on RGCs of the optic nerve crush (ONC) model of rats and exploring the underlying mechanisms. The intraperitoneal or intravitreal injection of TPNS was used based on the establishment of the rat ONC model. Fifteen days after the injury, the cell membrane fluorescent probe (Fluoro-Gold) was applied to retrograde RGCs through the superior colliculus and obtain the number of surviving RGCs. TUNEL assay was also used to detect the number and density of RGC apoptosis after the ONC model. The expression and distribution of Bcl-2/Bax, c-Jun/P-c-Jun, and P-JNK in the retina were demonstrated by Western blot analysis. After the intervention of TPNS, the rate of cell survival increased in different retinal regions (p < 0.05) and the number of apoptosis cells decreased. Regarding the expression of Bcl-2/Bax, c-Jun/P-c-Jun, and P-JNK-related apoptotic proteins, TPNS can reduce the level of apoptosis and play a role in protecting RGCs (p < 0.05). These findings indicate that topical administration of TPNS can inhibit cell apoptosis and promote RGC survival in the crushed optic nerve.

An adherent drug depot for retinal ganglion cell protection and regeneration in rat traumatic optic neuropathy models

Traumatic optic neuropathy (TON) describes an injury to the optic nerve following either blunt or penetrating trauma, and remains an important cause of vision loss. No generalized treatment of TON has been established so far to restore the injured optic nerve. We developed an adherent drug-encapsulated bi-layered depot (DBP) as a dual drug vehicle for local treatment to protect the residual retinal ganglion cells (RGCs) and regenerate axons following optic nerve damage. The inner layer of the depot was prepared by co-electrospinning poly(d,l-lactide-co-glycolide acid) (PLGA: 75 : 25) and collagen (COL) with the hydrophobic corticosteroid triamcinolone acetonide (TA) loaded. The outer layer was made of PLGA and the hydrophilic neuroprotective agent Fasudil (FA). The DBP showed suitable morphology, hydrophilicity and mechanical properties, and slowly released TA and FA in vitro by undergoing time-dependent degradation and swelling. All depots showed good biocompatibility with L929 mouse fibroblasts, and DBP was helpful in maintaining the morphology of RGCs in vitro. In addition, direct implantation of DBP at the injured optic nerve in a rat model mitigated inflammation and the death of RGCs, and increased the expression of nerve growth-related protein GAP-43. Therefore, DBP maybe a promising local therapy against TON in future.

Localized co-delivery of CNTF and FK506 using a thermosensitive hydrogel for retina ganglion cells protection after traumatic optic nerve injury

Following the traumatic axonal injury in the optic nerve, the failure of retrograde axonal transport to continuously supply neurotrophins from the brain to retina results in deprivation of neurotrophins in retinal ganglion cells (RGCs), which in turn can modulate the fate of RGCs toward apoptosis and thereby impede axon regeneration. In this study, a ciliary neurotrophic factor (CNTF) loaded thermo-sensitive hydrogel was designed and developed as a localized drug depot to restore neurotrophins supply following axon injury. Besides, following traumatic axon injury, overactive immune responses cause neurotoxicity and induce scar formation which together constitutes the major hindrances for axon regeneration. Thus, the FK506, a hydrophobic macrolide immunosuppressant, was co-loaded into the hydrogel after encapsulating it into a polymeric micelle. The materials can undergo sol-to-gel transition within minutes under a physiological pH of 37 °C. The release of drugs from the hydrogel exhibited a sustainable profile in vitro. The optic nerve was exposed by surgical procedure and the animal model was prepared by crushing the nerve with a reverse clamp. For the localized delivery to the optic nerve, a pre-hydrogel liquid containing chitosan, FK506 (in micelle), CNTF, and the gelling agent was directly smeared on the injured site, which gelled under physiological condition. This co-delivery system exhibited in vivo RGCs protective effect against the adverse effects caused by traumatic optic nerve injury, indicating the potential of this drug delivery system for effective optic nerve repair and this strategy may provide promising platforms for localized drug delivery in various other therapies.

Biomimetic hydrogels with spatial- and temporal-controlled chemical cues for tissue engineering

Biomimetic hydrogels have emerged as the most useful tissue engineering scaffold materials. Their versatile chemistry can recapitulate multiple physical and chemical features to integrate cells, scaffolds, and signaling molecules for tissue regeneration. Due to their highly hydrophilic nature hydrogels can recreate nutrient-rich aqueous environments for cells. Soluble regulatory molecules can be incorporated to guide cell proliferation and differentiation. Importantly, the controlled dynamic parameters and spatial distribution of chemical cues in hydrogel scaffolds are critical for cell-cell communication, cell-scaffold interaction, and morphogenesis. Herein, we review biomimetic hydrogels that provide cells with spatiotemporally controlled chemical cues as tissue engineering scaffolds. Specifically, hydrogels with temporally controlled growth factor-release abilities, spatially controlled conjugated bioactive molecules/motifs, and targeting delivery and reload properties for tissue engineering applications are discussed in detail. Examples of hydrogels that possess clinically favorable properties, such as injectability, self-healing ability, stimulus-responsiveness, and pro-remodeling features, are also covered.

Improved Coverage of Mouse Myelomeningocele With a Mussel Inspired Reverse Thermal Gel

BACKGROUND

Myelomeningocele (MMC) is an open neural tube defect of the spinal column. Our laboratory previously introduced a reverse thermal gel (RTG) as the first in situ forming patch for in utero MMC application. To overcome the challenges of anchoring the RTG in the wet amniotic environment to improve MMC coverage, we modified the RTG to mimic the underwater adhesive properties of mussels. We have separated this study into three separate hypotheses-based components: CONCLUSIONS: The DRTG demonstrates increased elasticity, cellular scaffolding properties, and improved MMC coverage in the Grhl3 mouse model. Future studies will be translated to the preclinical ovine model to evaluate this novel gel.

Injectable Polymeric Delivery System for Spatiotemporal and Sequential Release of Therapeutic Proteins To Promote Therapeutic Angiogenesis and Reduce Inflammation

Myocardial infarction (MI) causes cardiac cell death, induces persistent inflammatory responses, and generates harmful pathological remodeling, which leads to heart failure. Biomedical approaches to restore blood supply to ischemic myocardium, via controlled delivery of angiogenic and immunoregulatory proteins, may present an efficient treatment option for coronary artery disease (CAD). Vascular endothelial growth factor (VEGF) is necessary to initiate neovessel formation, while platelet-derived growth factor (PDGF) is needed later to recruit pericytes, which stabilizes new vessels. Anti-inflammatory cytokines like interleukin-10 (IL-10) can help optimize cardiac repair and limit the damaging effects of inflammation following MI. To meet these angiogenic and anti-inflammatory needs, an injectable polymeric delivery system composed of encapsulating micelle nanoparticles embedded in a sulfonated reverse thermal gel was developed. The sulfonate groups on the thermal gel electrostatically bind to VEGF and IL-10, and their specific binding affinities control their release rates, while PDGF-loaded micelles are embedded in the gel to provide the sequential release of the growth factors. An in vitro release study was performed, which demonstrated the sequential release capabilities of the delivery system. The ability of the delivery system to induce new blood vessel formation was analyzed in vivo using a subcutaneous injection mouse model. Histological assessment was used to quantify blood vessel formation and an inflammatory response, which showed that the polymeric delivery system significantly increased functional and mature vessel formation while reducing inflammation. Overall, the results demonstrate the effective delivery of therapeutic proteins to promote angiogenesis and limit inflammatory responses.

An Injectable Reverse Thermal Gel for Minimally Invasive Coverage of Mouse Myelomeningocele

BACKGROUND

Myelomeningocele (MMC) results in lifelong neurologic and functional deficits. Currently, prenatal repair of MMC closes the defect, resulting in a 50% reduction in postnatal ventriculoperitoneal shunting. However, this invasive fetal surgery is associated with significant morbidities to mother and baby. We have pioneered a novel reverse thermal gel (RTG) to cover MMC defects in a minimally invasive manner. Here, we test in-vitro RTG long-term stability in amniotic fluid and in vivo application in the Grainy head-like 3 (Grhl3) mouse MMC model.

MATERIALS AND METHODS

RTG stability in amniotic fluid (in-vitro) was monitored for 6 mo and measured using gel permeation chromatography and solution-gel transition temperature (lower critical solution temperature). E16.5 Grhl3 mouse fetuses were injected with the RTG or saline and harvested on E19.5. Tissue was assessed for RTG coverage of the gross defect and inflammatory response by immunohistochemistry for macrophages.

RESULTS

Polymer backbone molecular weight and lower critical solution temperature remain stable in amniotic fluid after 6 mo. Needle injection over the MMC of Grhl3 fetuses successfully forms a stable gel that covers the entire defect. On harvest, some animals demonstrate >50% RTG coverage. RTG injection is not associated with inflammation.

CONCLUSIONS

Our results demonstrate that the RTG is a promising candidate for a minimally invasive approach to patch MMC. We are now poised to test our RTG patch in the large preclinical ovine model used to evaluate prenatal repair of MMC.