Role of mammalian target of rapamycin in regulating HIF-1α and vascular endothelial growth factor signals in glaucoma

Preparation and in vivo and ex vivo studies of sirolimus nano-in-situ gel ophthalmic formulation

Sirolimus (SR) is a macrolide with antifungal and antitumor immunosuppressant properties, classified as a selective inhibitor of mammalian target of rapamycin (mTOR). In this study, an ionic in situ gel of SR (SR-SUS-ISG) was formulated using gellan gum, exhibiting stability regardless of temperature and pH variations, causing minimal irritation. Harnessing the physiological conditions of the eye, SR-SUS-ISG underwent gelation upon contact with ions, increasing drug viscosity and prolonging retention on the ocular surface. Concurrently, SR-SUS-ISG displayed favorable shear dilution properties, reducing viscosity at ambient temperature, enhancing fluidity, and facilitating convenient packaging and transport. Biocompatibility assessments on both human corneal epithelial cells and rabbit eyes demonstrated that SR-SUS-ISG could well be tolerated. Pharmacokinetic investigations in rabbit ocular aqueous humor revealed sustained release, improved corneal penetration, and enhanced bioavailability. Additionally, in a rat corneal alkali burn model, SR-SUS-ISG exhibited inhibitory effects on corneal neovascularization, associated with decreased levels of the inflammatory factors VEGF and MMPs. These findings suggested that SR-SUS-ISG held promise as an effective ocular drug delivery system.

Pharmacological regulation of HIF-1α, RGC death, and glaucoma

Hypoxia can regulate oxygen-sensitive pathways that could be neuroprotective to compensate for the detrimental effects of low oxygen. However, prolonged hypoxia can activate neurodegenerative pathways. HIF-1α is upregulated/stabilized in hypoxic conditions, promoting alteration of gene expression, and ultimately leading to cell-death. Therefore, regulation of HIF-1α expression pharmacologically is a vital approach to mitigate cell death. In this review, we provide information showing the role of HIF-1α and its associated pathways in ocular retinopathies. We also discuss the beneficial roles of HIF-1α inhibitor, KC7F2, in ocular pathologies. Finally, we provided our own data demonstrating RGC neuroprotection by KC7F2 in glaucomatous animals.

The Anti-Inflammatory and Antioxidant Properties of Acebuche Oil Exert a Retinoprotective Effect in a Murine Model of High-Tension Glaucoma

Glaucoma is characterized by cupping of the optic disc, apoptotic degeneration of retinal ganglion cells (RGCs) and their axons, and thinning of the retinal nerve fiber layer, with patchy loss of vision. Elevated intraocular pressure (IOP) is a major risk factor for hypertensive glaucoma and the only modifiable one. There is a need to find novel compounds that counteract other risk factors contributing to RGC degeneration. The oil derived from the wild olive tree (Olea europaea var. sylvestris), also called Acebuche (ACE), shows powerful anti-inflammatory, antioxidant and retinoprotective effects. We evaluated whether ACE oil could counteract glaucoma-related detrimental effects. To this aim, we fed mice either a regular or an ACE oil-enriched diet and then induced IOP elevation through intraocular injection of methylcellulose. An ACE oil-enriched diet suppressed glaucoma-dependent retinal glia reactivity and inflammation. The redox status of the glaucomatous retinas was restored to a control-like situation, and ischemia was alleviated by an ACE oil-enriched diet. Notably, retinal apoptosis was suppressed in the glaucomatous animals fed ACE oil. Furthermore, as shown by electroretinogram analyses, RGC electrophysiological functions were almost completely preserved by the ACE oil-enriched diet. These ameliorative effects were IOP-independent and might depend on ACE oil's peculiar composition. Although additional studies are needed, nutritional supplementation with ACE oil might represent an adjuvant in the management of glaucoma.

Crosstalk between the mTOR pathway and primary cilia in human diseases

Autophagy is a fundamental catabolic process whereby excessive or damaged cytoplasmic components are degraded through lysosomes to maintain cellular homeostasis. Studies of mTOR signaling have revealed that mTOR controls biomass generation and metabolism by modulating key cellular processes, including protein synthesis and autophagy. Primary cilia, the assembly of which depends on kinesin molecular motors, serve as sensory organelles and signaling platforms. Given these pathways' central role in maintaining cellular and physiological homeostasis, a connection between mTOR and primary cilia signaling is starting to emerge in a variety of diseases. In this review, we highlight recent advances in our understanding of the complex crosstalk between the mTOR pathway and cilia and discuss its function in the context of related diseases.

Protective Effects of Pituitary Adenylate-Cyclase-Activating Polypeptide on Retinal Vasculature and Molecular Responses in a Rat Model of Moderate Glaucoma

Despite the high probability of glaucoma-related blindness, its cause is not fully understood and there is no efficient therapeutic strategy for neuroprotection. Vascular factors have been suggested to play an important role in glaucoma development and progression. Previously, we have proven the neuroprotective effects of pituitary adenylate-cyclase-activating polypeptide (PACAP) eye drops in an inducible, microbeads model in rats that is able to reproduce many clinically relevant features of human glaucoma. In the present study, we examined the potential protective effects of PACAP1-38 on the retinal vasculature and the molecular changes in hypoxia. Ocular hypertension was induced by injection of microbeads into the anterior chamber, while control rats received PBS. PACAP dissolved in vehicle (1 µg/drop) or vehicle treatment was started one day after the injections for four weeks three times a day. Retinal degeneration was assessed with optical coherence tomography (OCT), and vascular and molecular changes were assessed by immunofluorescence labeling. HIF1-α and VEGF-A protein levels were measured by Western blot. OCT images proved severe retinal degeneration in the glaucomatous group, while PACAP1-38 eye drops had a retinoprotective effect. Vascular parameters were deteriorated and molecular analysis suggested hypoxic conditions in glaucoma. PACAP treatment exerted a positive effect against these alterations. In summary, PACAP could prevent the severe damage to the retina and its vasculature induced by ocular hypertension in a microbeads model.

Rapamycin inhibits corneal inflammatory response and neovascularization in a mouse model of corneal alkali burn

Alkali burn-induced corneal injury often causes inflammation and neovascularization and leads to compromised vision. We previously reported that rapamycin ameliorated corneal injury after alkali burns by methylation modification. In this study, we aimed to investigate the rapamycin-medicated mechanism against corneal inflammation and neovascularization. Our data showed that alkali burn could induce a range of different inflammatory response, including a stark upregulation of pro-inflammatory factor expression and an increase in the infiltration of myeloperoxidase- and F4/80-positive cells from the corneal limbus to the central stroma. Rapamycin effectively downregulated the mRNA expression levels of tumor necrosis factor-alpha (TNF-α), interleukin-1beta (IL-1β), toll-like receptor 4 (TLR4), nucleotide binding oligomerization domain-like receptors (NLR) family pyrin domain-containing 3 (NLRP3), and Caspase-1, and suppressed the infiltration of neutrophils and macrophages. Inflammation-related angiogenesis mediated by matrix metalloproteinase-2 (MMP-2) and rapamycin restrained this process by inhibiting the TNF-α upregulation in burned corneas of mice. Rapamycin also restrained corneal alkali burn-induced inflammation by regulating HIF-1α/VEGF-mediated angiogenesis and the serum cytokines TNF-α, IL-6, Interferon-gamma (IFN-γ) and granulocyte-macrophage colony-stimulating factor (GM-CSF). The findings of this study indicated rapamycin may reduce inflammation-associated infiltration of inflammatory cells, shape the expression of cytokines, and balance the regulation of MMP-2 and HIF-1α-mediated inflammation and angiogenesis by suppressing mTOR activation in corneal wound healing induced by an alkali injury. It offered novel insights relevant for a potent drug for treating corneal alkali burn.

Natural History of Glaucoma Progression in the DBA/2J Model: Early Contribution of Müller Cell Gliosis

Glaucoma is a chronic optic neuropathy characterized by progressive degeneration of retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) and the resulting mechanical stress are classically considered the main causes of RGC death. However, RGC degeneration and ensuing vision loss often occur independent of IOP, indicating a multifactorial nature of glaucoma, with the likely contribution of glial and vascular function. The aim of the present study was to provide a comprehensive evaluation of the time course of neuro-glial-vascular changes associated with glaucoma progression. We used DBA/2J mice in the age range of 2-15 months as a spontaneous model of glaucoma with progressive IOP elevation and RGC loss typical of human open-angle glaucoma. We found that the onset of RGC degeneration at 10 months of age coincided with that of IOP elevation and vascular changes such as decreased density, increased lacunarity and decreased tight-junction protein zonula occludens (ZO)-1, while hypoxia-inducible factor (HIF)-1α and vascular endothelial growth factor (VEGF) were already significantly upregulated at 6 months of age together with the onset of Müller cell gliosis. Astrocytes, however, underwent significant gliosis at 10 months. These results indicate that Müller cell activation occurs well before IOP elevation, with probable inflammatory consequences, and represents an early event in the glaucomatous process. Early upregulation of HIF-1α and VEGF is likely to contribute to blood retinal barrier failure, facilitating RGC loss. The different time courses of neuro-glial-vascular changes during glaucoma progression provide further insight into the nature of the disease and suggest potential targets for the development of efficient therapeutic intervention aside from IOP lowering.

mTOR Signalling Pathway: A Potential Therapeutic Target for Ocular Neurodegenerative Diseases

Recent advances in the research of the mammalian target of the rapamycin (mTOR) signalling pathway demonstrated that mTOR is a robust therapeutic target for ocular degenerative diseases, including age-related macular degeneration (AMD), diabetic retinopathy (DR), and glaucoma. Although the exact mechanisms of individual ocular degenerative diseases are unclear, they share several common pathological processes, increased and prolonged oxidative stress in particular, which leads to functional and morphological impairment in photoreceptors, retinal ganglion cells (RGCs), or retinal pigment epithelium (RPE). mTOR not only modulates oxidative stress but is also affected by reactive oxygen species (ROS) activation. It is essential to understand the complicated relationship between the mTOR pathway and oxidative stress before its application in the treatment of retinal degeneration. Indeed, the substantial role of mTOR-mediated autophagy in the pathogenies of ocular degenerative diseases should be noted. In reviewing the latest studies, this article summarised the application of rapamycin, an mTOR signalling pathway inhibitor, in different retinal disease models, providing insight into the mechanism of rapamycin in the treatment of retinal neurodegeneration under oxidative stress. Besides basic research, this review also summarised and updated the results of the latest clinical trials of rapamycin in ocular neurodegenerative diseases. In combining the current basic and clinical research results, we provided a more complete picture of mTOR as a potential therapeutic target for ocular neurodegenerative diseases.

Identification of Immune Infiltration-Related ceRNAs as Novel Biomarkers for Prognosis of Patients With Primary Open-Angle Glaucoma

Glaucoma is the leading cause of irreversible blindness globally; hence, relevant clinical biomarkers are necessary to enable diagnosis, early detection, and development of novel therapies. The differentially expressed genes were annotated and visualized using Gene Ontology and Kyoto Encyclopedia. In addition, a competitive endogenous ribonucleic acids network was constructed using Cytoscape, which explained the regulation of gene expression in glaucoma. The CIBERSORT algorithm was employed to analyze the immune microenvironment. We validated that the core genes could predict glaucoma occurrence and development and identified potential molecular mechanism pathways, which were associated with immune infiltration and participated in endogenous regulation networks. Our data may partially explain the pathogenesis of glaucoma and they provide potential theoretical support for targeted therapy.

Prospective study of dietary intake of branched-chain amino acids and the risk of primary open-angle glaucoma

PURPOSE

Metabolomic and preclinical studies suggest that branched-chain amino acids (BCAA) may be inversely associated with neurodegenerative diseases including glaucoma. We therefore assessed the long-term association between dietary intake of BCAA and incident primary open-angle glaucoma (POAG) and POAG subtypes.

METHODS

We followed biennially participants of the Nurses' Health Study (NHS; 65 531 women: 1984-2016), Health Professionals Follow-up Study (42 254 men: 1986-2016) and NHSII (66 904 women; 1991-2017). Eligible participants were 40+ years old and reported eye examinations. Repeated validated food frequency questionnaires were used to assess dietary intake of BCAA. Incident cases of POAG and POAG subtypes defined by visual field (VF) loss and untreated intraocular pressure (IOP) were confirmed by medical record review. Multivariable-adjusted relative risks (MVRRs) and 95% confidence intervals (CIs) were estimated using Cox proportional hazards models.

RESULTS

We identified 1946 incident POAG cases. The pooled MVRRs of POAG for the highest quintile (Q5 = 17.1 g/day) versus lowest quintile (Q1 = 11.2 g/day) of total BCAA intake was 0.93 (95% CI, 0.73-1.19; p_trend  = 0.45; p_{heterogeneity by sex}  = 0.24). For subtypes of POAG defined by IOP level or POAG with only peripheral VF loss, no associations were observed for men or women (p_trend  ≥ 0.20); however, for the POAG subtype with early paracentral VF loss, there was a suggestion of an inverse association in women (MVRR_Q5versusQ1  = 0.80 [95% CI, 0.57-1.12; p_trend  = 0.12]) but not in men (MVRR_Q5versusQ1  = 1.38 [95% CI, 0.81-2.34; p_trend  = 0.28; p_{heterogeneity by sex}  = 0.06]).

CONCLUSION

Higher dietary intake of BCAA was not associated with POAG risk.

Rapamycin and Resveratrol Modulate the Gliotic and Pro-Angiogenic Response in Müller Glial Cells Under Hypoxia

Hypoxia and hypoxia-reoxygenation are frequently developed through the course of many retinal diseases of different etiologies. Müller glial cells (MGCs), together with microglia and astrocytes, participate firstly in response to the injury and later in the repair of tissue damage. New pharmacological strategies tend to modulate MGCs ability to induce angiogenesis and gliosis in order to accelerate the recovery stage. In this article, we investigated the variation in autophagy flux under hypoxia during 4 h, employing both gas culture chamber (1% O₂) and chemical (CoCl₂) hypoxia, and also in hypoxia-reoxygenation. Then, we delineated a strategy to induce autophagy with Rapamycin and Resveratrol and analysed the gliotic and pro-angiogenic response of MGCs under hypoxic conditions. Our results showed an increase in LC3B II and p62 protein levels after both hypoxic exposure respect to normoxia. Moreover, 1 h of reoxygenation after gas hypoxia upregulated LC3B II levels respect to hypoxia although a decreased cell survival was observed. Exposure to low oxygen levels increased the protein expression of the glial fibrillary acid protein (GFAP) in MGCs, whereas Vimentin levels remained constant. In our experimental conditions, Rapamycin but not Resveratrol decreased GFAP protein levels in hypoxia. Finally, supernatants of MGCs incubated in hypoxic conditions and in presence of the autophagy inductors inhibited endothelial cells (ECs) tubulogenesis. In agreement with these results, reduced expression of vascular endothelial growth factor (VEGF) mRNA was observed in MGCs with Rapamycin, whereas pigment epithelium-derived factor (PEDF) mRNA levels significantly increased in MGCs incubated with Resveratrol. In conclusion, this research provides evidence about the variation of autophagy flux under hypoxia and hypoxia-reoxygenation as a protective mechanism activated in response to the injury. In addition, beneficial effects were observed with Rapamycin treatment as it decreased the gliotic response and prevented the development of newly formed blood vessels.

[Anti-scarring effect of rapamycin following filtering surgery in rabbit eyes]

OBJECTIVE

To study the effect of rapamycin on scar formation in rabbit eyes following filtering operation and explore the possible mechanism.

METHODS

Ninety-six healthy adult rabbits were subjected to trabeculectomy of the left eye and subsequently randomly divided into 4 groups (n=24) for treatment with castor oil (control) or rapamycin (1%, 3%, or 5%) eye drops of the operated eyes 4 times a day. The morphology and function of the filtering blebs of the rabbits were compared at 7, 14, 21 and 28 days after the operation; at each of the time points, 6 rabbits from each group were euthanized for detection of expressions of proliferating cell nuclear antigen (PCNA) and α-smooth muscle actin (α-SMA) in the tissues in the surgical area using immunohistochemistry. Cultured rabbit subconjunctival fibroblasts (RTFSs) were treated with different concentrations of rapamycin (0.06, 0.25, 1, and 4 mg/L) and the cell apoptosis was detected using flow cytometry.

RESULTS

In the first, second and third weeks after the operation, the rate of functional follicle formation was significantly higher in the 3 rapamycin groups than in the control group (P < 0.05), and the number of α- SMA-positive fibroblasts decreased over time in the 3 rapamycin groups. In cultured RTFSs, treatment with rapamycin at different concentrations resulted in increased apoptosis of the cells, and rapamycin above 0.25 mg/L significantly increased the cell apoptosis in a dose-dependent manner.

CONCLUSIONS

Rapamycin can inhibit hyperplasia of the filtering passage tissue, helps to preserve the functional filtering blebs and prolong their life span, and induces apoptosis of RTFS.

NLRP12 collaborates with NLRP3 and NLRC4 to promote pyroptosis inducing ganglion cell death of acute glaucoma

BACKGROUND

Acute glaucoma, characterized by a sudden elevation in intraocular pressure (IOP) and retinal ganglion cells (RGCs) death, is a major cause of irreversible blindness worldwide that lacks approved effective therapies, validated treatment targets and clear molecular mechanisms. We sought to explore the potential molecular mechanisms underlying the causal link between high IOP and glaucomatous RGCs death.

METHODS

A murine retinal ischemia/ reperfusion (RIR) model and an in vitro oxygen and glucose deprivation/reoxygenation (OGDR) model were used to investigate the pathogenic mechanisms of acute glaucoma.

RESULTS

Our findings reveal a novel mechanism of microglia-induced pyroptosis-mediated RGCs death associated with glaucomatous vision loss. Genetic deletion of gasdermin D (GSDMD), the effector of pyroptosis, markedly ameliorated the RGCs death and retinal tissue damage in acute glaucoma. Moreover, GSDMD cleavage of microglial cells was dependent on caspase-8 (CASP8)-hypoxia-inducible factor-1α (HIF-1α) signaling. Mechanistically, the newly identified nucleotide-binding leucine-rich repeat-containing receptor (NLR) family pyrin domain-containing 12 (NLRP12) collaborated with NLR family pyrin domain-containing 3 (NLRP3) and NLR family CARD domain-containing protein 4 (NLRC4) downstream of the CASP8-HIF-1α axis, to elicit pyroptotic processes and interleukin-1β (IL-1β) maturation through caspase-1 activation, facilitating pyroptosis and neuroinflammation in acute glaucoma. Interestingly, processing of IL-1β in turn magnified the CASP8-HIF-1α-NLRP12/NLRP3/NLRC4-pyroptosis circuit to accelerate inflammatory cascades.

CONCLUSIONS

These data not only indicate that the collaborative effects of NLRP12, NLRP3 and NLRC4 on pyroptosis are responsible for RGCs death, but also shed novel mechanistic insights into microglial pyroptosis, paving novel therapeutic avenues for the treatment of glaucoma-induced irreversible vision loss through simultaneously targeting of pyroptosis.