Glaucoma is a leading cause of irreversible vision loss due to retinal ganglion cell (RGC) degeneration that develops slowly with age. Elevated intraocular pressure (IOP) is a significant risk factor, although many patients develop glaucoma with IOP in the normal range. Mutations in microfibril-associated genes cause glaucoma in animal models, suggesting the hypothesis that microfibril defects contribute to glaucoma. To test this hypothesis, we investigated IOP and functional/structural correlates of RGC degeneration in mice of either sex with abnormal microfibrils due to heterozygous Tsk mutation of the fibrilin-1 gene (Fbn1Tsk /+). Although IOP was not affected, Fbn1Tsk /+ mice developed functional deficits at advanced age consistent with glaucoma, including reduced RGC responses in electroretinogram (ERG) experiments. While RGC density in the retina was not affected, the density of RGC axons in the optic nerve was significantly reduced in Fbn1Tsk /+ mice. However, reduced axon density correlated with expanded optic nerves, resulting in similar numbers of axons in Fbn1Tsk /+ and control nerves. Axons in the optic nerves of Fbn1Tsk /+ mice were significantly enlarged and axon diameter was strongly correlated with optic nerve area, as has been reported in early pathogenesis of the DBA/2J mouse model of glaucoma. Our results suggest that microfibril abnormalities can lead to phenotypes found in early-stage glaucomatous neurodegeneration. Thinning of the elastic fiber-rich pia mater was found in Fbn1Tsk /+ mice, suggesting mechanisms allowing for optic nerve expansion and a possible biomechanical contribution to determination of axon caliber.

Aims: The mechanisms underlying numerous biological roles of hydrogen sulfide (H 2 S) remain largely unknown. We have previously reported an inhibitory role of H 2 S in the L-type calcium channels in cardiomyocytes. This prompts us to examine the mechanisms underlying the potential regulation of H 2 S on the ion channels. Results: H 2 S showed a novel inhibitory effect on I to potassium channels, and this effect was blocked by mutation at the Cys320 and/or Cys529 residues of the Kv4.2 subunit. H 2 S broke the disulfide bridge between a pair of oxidized cysteine residues; however, it did not modify single cysteine residues. H 2 S extended action potential duration in epicardial myocytes and regularized fatal arrhythmia in a rat model of myocardial infarction. H 2 S treatment significantly increased survival by *1.4-fold in the critical 2-h time window after myocardial infarction with a protection against ventricular premature beats and fatal arrhythmia. However, H 2 S did not change the function of other ion channels, including I K1 and I Na . Innovation and Conclusion: H 2 S targets the Cys320/Cys529 motif in Kv4.2 to regulate the I to potassium channels. H 2 S also shows a potent regularizing effect against fatal arrhythmia in a rat model of myocardial infarction. The study provides the first piece of evidence for the role of H 2 S in regulating I to potassium channels and also the specific motif in an ion channel labile for H 2 S regulation. Antioxid. Redox Signal. 23, 129-147.

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To test whether mice with microfibril deficiency due to the Tsk mutation of fibrillin-1 (Fbn1 Tsk/+) have increased susceptibility to pressure-induced retinal ganglion cell (RGC) degeneration. METHODS. Intraocular pressure (IOP) elevation was induced in Fbn1 Tsk/+ and wild type (wt) mice by injecting microbeads into the anterior chamber. Mice were then followed up for four months, with IOP measurements every three to six days. Retinas were stained for Brn3a to determine RGC number. Optic nerve cross-sections were stained with pphenylene diamine to determine nerve area, axon number, and caliber and thickness of the pia mater. RESULTS. Microbead injection induced significant IOP elevation that was significantly less for Fbn1 Tsk/+ mice compared with wt. The optic nerves and optic nerve axons were larger, and the elastic fiber-rich pia mater was thinner in Fbn1 Tsk/+ mice. Microbead injection resulted in reduced optic nerve size, thicker pia mater, and a slight decrease in axon size. Fbn1 Tsk/+ mice had significantly greater loss of RGCs and optic nerve axons compared with wt (14.8% vs. 5.8%, P = 0.002, and 17.0% vs. 7.5%, P = 0.002, respectively). CONCLUSIONS. Fbn1 Tsk/+ mice had altered optic nerve structure as indicated by larger optic nerves, larger optic nerve axons and thinner pia mater, consistent with our previous findings. Despite lower IOP elevation, Fbn1 Tsk/+ mice had greater loss of RGCs and optic nerve axons, suggesting increased susceptibility to IOP-induced optic nerve degeneration in microfibril-deficient mice.