PhD student, Macquarie University
Glaucoma, a common retinal disorder
Why to do research on Glaucoma? The increasing prevalence of glaucoma represents a global challenge at multiple levels: personal, social and economic. Over 300,000 Australians live with glaucoma and the total related costs are expected to surge up to $4.3 billion p.a. by 2025. It is essential to understand mechanisms behind retinal ganglion cell loss and develop neuroprotective strategies.
Background: Glaucoma, a common neurodegenerative retinal disorder is the second leading cause of blindness. Glaucoma is often associated with increased intraocular pressure (IOP) and clinical management involves subsequent lowering of IOP which generally slows disease progression but some patients continue to deteriorate. Vision loss in glaucoma patients is primarily attributed to retinal ganglion cells (RGC) death. However, the precise reason of neurodegenerative mechanism underlying glaucoma is poorly understood. It is essential to understand mechanisms behind RGCs loss and develop neuroprotective strategies. Recently genome wide association has strongly linked variations in Caveolin1/2 gene loci as a risk factor in glaucoma pathogenesis. Cav1 comprises the main components of membrane lipid rafts caveolae, implicated in various signal transduction pathways and is ubiquitously expressed in almost all mammalian cells including majority of retinal cell types.
Research Aims: This study aims to investigate the role of Cav-1 in the inner retina in healthy and experimental glaucoma conditions.
Methods: Experimental glaucoma model will be generated in Cav-1 knockout and wildtype mice by weekly intracameral polystyrene microbead injections to induce high IOP. Retinal functional changes will be assessed by electrophysiological recordings. Histological assessment will reveal histological differences in retinal structure while Immunostaining will provide information regarding the expression profile of proteins involved in retinal survival signalling.
Conclusion: The project will help understand how caveolae help in maintaining the retinal function and architecture and outcomes will provide insights into the neuronal physiology with implications beyond glaucoma. The main theme of the current project is to improve the long-lasting knowledge for such neurodegenerative disorders, which is helpful for wellbeing of the aging world. This strategy may also find applications in other retinal diseases and additionally may help advance the field in other neurodegenerative conditions.
Abstract: Polymorphisms in the CAV1/2 genes that encode signature proteins of caveolae are associated with glaucoma, the second leading cause of blindness worldwide, and with its major risk factor, intraocular pressure (IOP). We hypothesized that caveolin-1 (Cav-1) participates in IOP maintenance via modulation of aqueous humor drainage from the eye. We localize caveolae proteins to human and murine conventional drainage tissues and show that caveolae respond to mechanical stimulation. We show that Cav-1-deficient (Cav-1(-/-)) mice display ocular hypertension explained by reduced pressure-dependent drainage of aqueous humor. Cav-1 deficiency results in loss of caveolae in the Schlemm's canal (SC) and trabecular meshwork. However, their absence did not appear to impact development nor adult form of the conventional outflow tissues according to rigorous quantitative ultrastructural analyses, but did affect cell and tissue behavior. Thus, when IOP is experimentally elevated, cells of the Cav-1(-/-) outflow tissues are more susceptible to plasma membrane rupture indicating that caveolae play a role in mechanoprotection. Additionally, aqueous drainage from Cav-1(-/-) eyes was more sensitive to nitric oxide (NO) synthase inhibition than controls, suggesting that excess NO partially compensates for outflow pathway dysfunction. These results provide a functional link between a glaucoma risk gene and glaucoma-relevant pathophysiology.
Pub.: 15 Nov '16, Pinned: 25 Aug '17
Abstract: Caveolae are specialized, invaginated plasma membrane domains that are defined morphologically and by the expression of signature proteins called, caveolins. Caveolae and caveolins are abundant in a variety of cell types including vascular endothelium, glia, and fibroblasts where they play critical roles in transcellular transport, endocytosis, mechanotransduction, cell proliferation, membrane lipid homeostasis, and signal transduction. Given these critical cellular functions, it is surprising that ablation of the caveolae organelle does not result in lethality suggesting instead that caveolae and caveolins play modulatory roles in cellular homeostasis. Caveolar components are also expressed in ocular cell types including retinal vascular cells, Müller glia, retinal pigment epithelium (RPE), conventional aqueous humor outflow cells, the corneal epithelium and endothelium, and the lens epithelium. In the eye, studies of caveolae and other membrane microdomains (i.e., "lipid rafts") have lagged behind what is a substantial body of literature outside vision science. However, interest in caveolae and their molecular components has increased with accumulating evidence of important roles in vision-related functions such as blood-retinal barrier homeostasis, ocular inflammatory signalling, pathogen entry at the ocular surface, and aqueous humor drainage. The recent association of CAV1/2 gene loci with primary open angle glaucoma and intraocular pressure has further enhanced the need to better understand caveolar functions in the context of ocular physiology and disease. Herein, we provide the first comprehensive review of literature on caveolae, caveolins, and other membrane domains in the context of visual system function. This review highlights the importance of caveolae domains and their components in ocular physiology and pathophysiology and emphasizes the need to better understand these important modulators of cellular function.
Pub.: 25 Sep '16, Pinned: 25 Aug '17
Abstract: Caveolin-1 (Cav-1), an integral component of caveolar membrane domains, is expressed in several retinal cell types, including photoreceptors, retinal vascular endothelial cells, Müller glia, and retinal pigment epithelium (RPE) cells. Recent evidence links Cav-1 to ocular diseases, including autoimmune uveitis, diabetic retinopathy, and primary open angle glaucoma, but its role in normal vision is largely undetermined. In this report, we show that ablation of Cav-1 results in reduced inner and outer retinal function as measured, in vivo, by electroretinography and manganese-enhanced MRI. Somewhat surprisingly, dark current and light sensitivity were normal in individual rods (recorded with suction electrode methods) from Cav-1 knock-out (KO) mice. Although photoreceptor function was largely normal, in vitro, the apparent K(+) affinity of the RPE-expressed α1-Na(+)/K(+)-ATPase was decreased in Cav-1 KO mice. Cav-1 KO retinas also displayed unusually tight adhesion with the RPE, which could be resolved by brief treatment with hyperosmotic medium, suggesting alterations in outer retinal fluid homeostasis. Collectively, these findings demonstrate that reduced retinal function resulting from Cav-1 ablation is not photoreceptor-intrinsic but rather involves impaired subretinal and/or RPE ion/fluid homeostasis.
Pub.: 28 Mar '12, Pinned: 25 Aug '17
Abstract: Tropomyosin-receptor-kinase B (TrkB receptor) activation plays an important role in the survival of retinal ganglion cells (RGCs). This study reports a novel finding that, SH2 domain-containing phosphatase-2 (Shp-2) binds to the TrkB receptor in RGCs and negatively regulates its activity under glaucomatous stress. This enhanced binding of TrkB and Shp2 is mediated through caveolin. Caveolin 1 and 3 undergo hyper-phosphorylation in RGCs under stress and bind to the Shp2 phosphatase. Shp2 undergoes activation under glaucomatous stress conditions in RGCs in vivo with a concurrent loss of TrkB activity. Inhibiting the Shp2 phosphatase restored TrkB activity in cells exposed to excitotoxic and oxidative stress. Collectively, these findings implicate a molecular basis of Shp2 mediated TrkB deactivation leading to RGC degeneration observed in glaucoma.
Pub.: 11 Aug '12, Pinned: 25 Aug '17