minocycline and Glaucoma

Ocular hypertension (OHT) is a serious adverse effect of the widely prescribed glucocorticoid (GC) therapy and, if left undiagnosed, it can lead to glaucoma and complete blindness. Previously, we have shown that the small chemical chaperone, sodium-4-phenylbutyrate (PBA), rescues GC-induced OHT by reducing ocular endoplasmic reticulum (ER) stress. However, the exact mechanism of how PBA rescues GC-induced OHT is not completely understood. The trabecular meshwork (TM) is a filter-like specialized contractile tissue consisting of TM cells embedded within extracellular matrix (ECM) that controls intraocular pressure (IOP) by constantly regulating aqueous humor (AH) outflow. Induction of abnormal ECM deposition in TM is a hallmark of GC-induced OHT. Here, we investigated whether PBA reduces GC-induced OHT by degrading abnormal ECM deposition in TM using mouse model of GC-induced OHT, ex vivo cultured human TM tissues and primary human TM cells. We show that topical ocular eye drops of PBA (1%) significantly lowers elevated IOP in mouse model of GC-induced OHT. Importantly, PBA prevents synthesis and deposition of GC-induced ECM in TM. We report for the first time that PBA can degrade existing abnormal ECM in normal human TM cells/tissues by inducing matrix metalloproteinase (MMP)9 expression and activity. Furthermore, inhibition of MMPs activity by chemical-inhibitor (minocycline) abrogated PBA's effect on ECM reduction and its associated ER stress. Our study indicates a non-chaperone activity of PBA via activation of MMP9 that degrades abnormal ECM accumulation in TM.

Topics: Animals; Aqueous Humor; Cornea; Endoplasmic Reticulum Stress; Enzyme Activation; Extracellular Matrix; Eye Diseases; Fibronectins; Glaucoma; Glaucoma, Open-Angle; Humans; Intraocular Pressure; Male; Matrix Metalloproteinase 9; Mice; Mice, Inbred C57BL; Minocycline; Ocular Hypertension; Phenylbutyrates; Sodium; Trabecular Meshwork

Glaucoma is a leading cause of blindness, characterized by retinal ganglion cell (RGC) loss and optic nerve (ON) damage. Cumulative evidence suggests glial cell involvement in the degeneration of the ON and RGCs. We analyzed the contribution of microglial reactivity to early axoglial alterations of the ON in an induced model of ocular hypertension. For this purpose, vehicle or chondroitin sulfate (CS) were weekly injected into the eye anterior chamber from Wistar rats for different intervals. The amount of Brn3a(+) RGC significantly decreased in CS-injected eyes for 10 and 15 (but not 6) weeks. A reduction in anterograde transport of β-subunit cholera toxin was observed in the superior colliculus and the lateral geniculate nucleus contralateral to CS-injected eyes for 6 and 15 weeks. A disruption of cholera toxin β-subunit transport was observed at the proximal myelinated ON. A significant decrease in phosphorylated neurofilament heavy chain immunoreactivity, an increase in ionized calcium-binding adaptor molecule 1(+), ED1(+) (microglial markers), and glial fibrillary acidic protein (astrocytes) (+) area, and decreased luxol fast blue staining were observed in the ON at 6 and 15 weeks of ocular hypertension. Microglial reactivity involvement was examined through a daily treatment with minocycline (30 mg/kg, i.p.) for 2 weeks, after 4 weeks of ocular hypertension. Minocycline prevented the increase in ionized calcium-binding adaptor molecule 1(+), ED-1(+), and glial fibrillary acidic protein(+) area, the decrease in phosphorylated neurofilament heavy-chain immunoreactivity and luxol fast blue staining, and the deficit in anterograde transport induced by 6 weeks of ocular hypertension. Thus, targeting microglial reactivity might prevent early axoglial alterations in the glaucomatous ON. Cover Image for this issue: doi: 10.1111/jnc.13807.

Topics: Animals; Astrocytes; Disease Models, Animal; Geniculate Bodies; Glaucoma; Male; Microglia; Minocycline; Neuroglia; Optic Nerve; Rats, Wistar; Retina

Minocycline, a second-generation tetracycline with anti-inflammatory and anti-apoptotic properties, was reported to be neuroprotective in experimental glaucoma and optic nerve transection as well as in other neurodegenerative diseases. The purpose of this study was to investigate the mechanism underlying that neuroprotective effect in murine glaucoma.. Elevated intraocular pressure was induced in 159 rats by the translimbal photocoagulation laser model. Minocycline 22 mg/kg or saline was injected intraperitoneally starting 3 days before the induction of glaucoma, and continued daily until the animals were sacrificed. The effect of minocycline on gene expression was evaluated using a quantitative polymerase chain reaction (PCR) array for apoptosis. The involvement of selected pro-apoptotic, pro-survival, and inflammatory genes was further analyzed by quantitative real-time PCR at multiple time points. Immunohistochemistry was used to study the effect of minocycline on microglial activation and to localize Bcl-2 changes.. Minocycline significantly increased the anti-apoptotic gene Bcl-2 expression at day 8 and day 14 after the induction of glaucoma (p = 0.04 and p = 0.03 respectively), and decreased IL-18 expression in the retina at day 14 and day 30 (p = 0.04 and p < 0.001 respectively). PCR arrays suggested that additional genes were affected by minocycline, including Tp53bp2, TRAF4, osteoprotegerin, caspase 1 and 4, and members of the tumor necrosis factor superfamily. Additionally, minocycline decreased the amount of activated microglia in glaucomatous eyes.. These results suggest that minocycline upregulates pro-survival genes and downregulates apoptotic genes, thus shifting the balance toward the anti-apoptotic side in experimental glaucoma.

Topics: Animals; Anti-Bacterial Agents; Apoptosis Regulatory Proteins; bcl-2-Associated X Protein; bcl-Associated Death Protein; Disease Models, Animal; Gene Expression Regulation; Glaucoma; Injections, Intraperitoneal; Interleukin-18; Microglia; Minocycline; Optic Nerve Diseases; Proto-Oncogene Proteins c-bcl-2; Rats; Rats, Wistar; Real-Time Polymerase Chain Reaction; Retinal Ganglion Cells; Up-Regulation

Neuroinflammation underlies a wide variety of pathological processes in the central nerve system (CNS). Although previous experimental and clinical studies indicate that activation of neuroinflammatory signaling occurs early in glaucoma, the mechanisms controlling microglia activation are still poorly defined. In the present study, we investigated the role of the chemokine receptor Cx3cr1 in microglia activation and retinal ganglion cell (RGC) death in an experimental mouse glaucoma model with transient elevation of intraocular pressure (IOP). We demonstrated that retinal microglia played a pathogenic role in RGC death. Conversely, pharmacological suppression of microglia activation by minocycline increased RGC survival. Moreover, we found that Cx3cr1 deficiency enhanced microglial neurotoxicity and subsequently induced more extensive RGC loss, suggesting that Cx3cr1 suppressed microglial activation under elevated IOP. Overall, these findings provided novel insight into the mechanisms by which Cx3cr1 modulated microglia activation under elevated IOP. Suppression of microglia activation might be a potential treatment for slowing down the course of the disease and for increasing RGC survival in glaucoma patients.

Topics: Analysis of Variance; Animals; Antigens, CD; Calcium-Binding Proteins; CX3C Chemokine Receptor 1; Disease Models, Animal; Female; Gene Expression Regulation; Glaucoma; Green Fluorescent Proteins; Intraocular Pressure; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Microfilament Proteins; Microglia; Minocycline; Receptors, Chemokine; Retinal Ganglion Cells; RNA, Messenger; Tubulin

In the context of the retinal ganglion cell (RGC) axon degeneration in the optic nerve that occurs in glaucoma, microglia become activated, then phagocytic, and redistribute in the optic nerve head. The authors investigated the potential contribution of retinal microglia activation to glaucoma progression in the DBA/2J chronic mouse glaucoma model.. The authors treated 6-week-old DBA/2J mice for 25 weeks with minocycline, a tetracycline derivative known to reduce microglia activation and to improve neuronal survival in other models of neurodegenerative disease. They quantified RGC numbers and characterized microglia activation, gliosis, and both axonal integrity and retrograde tracer transport by RGCs in mice systemically treated with minocycline or vehicle only.. Minocycline reduced microglial activation and improved RGC axonal transport and integrity, yet it had no effect on the characteristic age-related ocular changes that lead to chronically elevated pressure and did not alter Müller or astrocyte gliosis. Specifically, minocycline increased the fraction of microglia with resting ramified morphology and reduced levels of Iba1 mRNA and protein, a microglia-specific calcium ligand linked to activation. The reduction in microglial activation was coupled to significant improvement in RGC axonal transport, as measured by neuronal retrograde tracing from the superior colliculus. Finally, minocycline treatment significantly decoupled RGC axon loss from increased intraocular pressure.. These observations suggest that in glaucoma, retina and optic nerve head microglia activation may be a factor in the early decline in function of the optic nerve and its subsequent degeneration.

Topics: Animals; Axonal Transport; Calcium-Binding Proteins; Cell Survival; Disease Models, Animal; Glaucoma; Gliosis; Injections, Intraperitoneal; Intraocular Pressure; Mass Spectrometry; Mice; Mice, Inbred DBA; Microfilament Proteins; Microglia; Minocycline; Neuroprotective Agents; Optic Nerve Diseases; Retina; Retinal Ganglion Cells; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger

To evaluate the effect of minocycline hydrochloride on the survival of retinal ganglion cells (RGCs) in glaucomatous rat eyes and rat eyes after optic nerve transection (ONT).. The effect of intraperitoneal injections of minocycline at dosages of 15 mg/kg per day, 22 mg/kg per day, and 45 mg/kg per day was evaluated and compared with saline in ONT (n = 174) and experimental glaucoma (n = 51).. The mean +/- SEM survival rate of RGCs 1 week after ONT was significantly higher with minocycline at dosages of 15 mg/kg per day (36% +/- 3%; n = 9; P = .04), 22 mg/kg per day (44% +/- 2%; n = 15; P = .001), and 45 mg/kg per day (39% +/- 3%; n = 10; P = .008) compared with saline (29% +/- 2%; n = 28). Minocycline at a dosage of 22 mg/kg per day was also significantly neuroprotective compared with saline 2 weeks after ONT (mean +/- SEM survival rate, 5% +/- 1% vs 3% +/- 0.4%, respectively; n = 20 [10 rats in each group]; P = .03). In experimental glaucoma, the mean +/- SEM percentage of RGCs after 4 weeks was 84% +/- 4% in the minocycline group (n = 15) compared with 65% +/- 4% in the saline group (n = 18) (P = .003). Apoptosis of RGCs was significantly delayed by minocycline 4 days and 1 week after ONT.. Minocycline significantly enhances the survival of RGCs after ONT and in experimental glaucoma by delaying the apoptosis pathway.. The safety record of minocycline and its ability to penetrate the blood-brain barrier suggest that this drug is a promising neuroprotective drug for optic nerve injuries.

Topics: Animals; Apoptosis; Cell Count; Cell Survival; Disease Models, Animal; Glaucoma; Injections, Intraperitoneal; Minocycline; Neuroprotective Agents; Optic Nerve Injuries; Rats; Rats, Wistar; Retinal Ganglion Cells