Abstract: The retinal degenerative diseases retinitis pigmentosa and age-related macular degeneration are a leading cause of irreversible vision loss. Both present with progressive photoreceptor degeneration that is further complicated by processes of retinal remodeling. In this perspective, we discuss the current state of the field of retinal remodeling and its implications for vision-restoring therapeutics currently in development. Here, we discuss the challenges and pitfalls retinal remodeling poses for each therapeutic strategy under the premise that understanding the features of retinal remodeling in totality will provide a basic framework with which therapeutics can interface. Additionally, we discuss the potential for approaching therapeutics using a combined strategy of using diffusible molecules in tandem with other vision-restoring therapeutics. We end by discussing the potential of the retina and retinal remodeling as a model system for more broadly understanding the progression of neurodegeneration across the central nervous system.
We have a new collaborative manuscript out in iOVS, Peptide-Based Immunotherapy Against Oxidized Elastin Ameliorates Pathology In Mouse Model Of Smoke-Induced Ocular Injury. (pdf here)
Purpose: Age-related macular degeneration (AMD), the leading cause of blindness in western populations, is associated with an overactive complement system, and an increase in circulating antibodies against certain epitopes, including elastin. As loss of the elastin layer of Bruch’s membrane (BrM) has been reported in aging and AMD, we previously showed that immunization with elastin peptide oxidatively modified by cigarette smoke (ox-elastin), exacerbated ocular pathology in the smoke-induced ocular pathology (SIOP) model. Here we asked whether ox-elastin peptide-based immunotherapy (PIT) ameliorates damage.
Methods: C57BL/6J mice were injected with ox-elastin peptide at two doses via weekly subcutaneous administration, while exposed to cigarette smoke for 6 months. FcγR-/- and uninjected C57BL/6J mice served as controls. Retinal morphology was assessed by by electron microscopy, and complement activation, antibody deposition and mechanisms of immunological tolerance were assessed by Western blotting and ELISA.
Results: Elimination of Fcγ receptors, preventing antigen/antibody-dependent cytotoxicity, protected against SIOP. Mice receiving PIT with low dose ox-elastin (LD-PIT) exhibited reduced humoral immunity, reduced complement activation and IgG/IgM deposition in the RPE/choroid, and largely a preserved BrM. While there is no direct evidence of ox-elastin pathogenicity, LD-PIT reduced IFNγ and increased IL-4 within RPE/choroid. High dose PIT was not protective.
Conclusions: These data further support ox-elastin role in ocular damage in in part via elastin-specific antibodies, and support the corollary that PIT with ox-elastin attenuates ocular pathology. Overall, damage is associated with complement activation, antibody-dependent cell-mediated cytotoxicity, and altered cytokine signature.
Keywords: Age-related macular degeneration; Complement; Elastin; Peptide-based immunotherapy; Smoking.
We have a new manuscript out in iOVS, Subretinal Rather Than Intravitreal Adeno-Associated Virus–Mediated Delivery of a Complement Alternative Pathway Inhibitor Is Effective in a Mouse Model of RPE Damage. (pdf here)
Purpose: The risk for age-related macular degeneration has been tied to an overactive complement system. Despite combined attempts by academia and industry to develop therapeutics that modulate the complement response, particularly in the late geographic atrophy form of advanced AMD, to date, there is no effective treatment. We have previously demonstrated that pathology in the smoke-induced ocular pathology (SIOP) model, a model with similarities to dry AMD, is dependent on activation of the alternative complement pathway and that a novel complement activation site targeted inhibitor of the alternative pathway can be delivered to ocular tissues via an adeno-associated virus (AAV).
Methods: Two different viral vectors for specific tissue targeting were compared: AAV5-VMD2-CR2-fH for delivery to the retinal pigment epithelium (RPE) and AAV2YF-smCBA-CR2-fH for delivery to retinal ganglion cells (RGCs). Efficacy was tested in SIOP (6 months of passive smoke inhalation), assessing visual function (optokinetic responses), retinal structure (optical coherence tomography), and integrity of the RPE and Bruch’s membrane (electron microscopy). Protein chemistry was used to assess complement activation, CR2-fH tissue distribution, and CR2-fH transport across the RPE.
Results: RPE- but not RGC-mediated secretion of CR2-fH was found to reduce SIOP and complement activation in RPE/choroid. Bioavailability of CR2-fH in RPE/choroid could be confirmed only after AAV5-VMD2-CR2-fH treatment, and inefficient, adenosine triphosphate–dependent transport of CR2-fH across the RPE was identified.
Conclusions: Our results suggest that complement inhibition for AMD-like pathology is required basal to the RPE and argues in favor of AAV vector delivery to the RPE or outside the blood-retina barrier.
We have a new manuscript out in Investigative Ophthalmology & Visual Science, Immunization Against Oxidized Elastin Exacerbates Structural and Functional Damage in Mouse Model of Smoke-Induced Ocular Injury
Purpose: Age-related macular degeneration (AMD) is the leading cause of blindness in Western populations. While an overactive complement system has been linked to pathogenesis, mechanisms contributing to its activation are largely unknown. In aged and AMD eyes, loss of the elastin layer (EL) of Bruch’s membrane (BrM) has been reported. Elastin antibodies are elevated in patients with AMD, the pathogenic significance of which is unclear. Here we assess the role of elastin antibodies using a mouse model of smoke-induced ocular pathology (SIOP), which similarly demonstrates EL loss.
Methods: C57BL/6J mice were immunized with elastin or elastin peptide oxidatively modified by cigarette smoke (ox-elastin). Mice were then exposed to cigarette smoke or air for 6 months. Visual function was assessed by optokinetic response, retinal morphology by spectral-domain optical coherence tomography and electron microscopy, and complement activation and antibody deposition by Western blot.
Results: Ox-elastin IgG and IgM antibodies were elevated in ox-elastin immunized mice following 6 months of smoke, whereas elastin immunization had a smaller effect. Ox-elastin immunization exacerbated smoke-induced vision loss, with thicker BrM and more damaged retinal pigment epithelium (RPE) mitochondria compared with mice immunized with elastin or nonimmunized controls. These changes were correlated with increased levels of IgM, IgG2, IgG3, and complement activation products in RPE/choroid.
Conclusions: These data demonstrate that SIOP mice generate elastin-specific antibodies and that immunization with ox-elastin exacerbates ocular pathology. Elastin antibodies represented complement fixing isotypes that, together with the increased presence of complement activation seen in immunized mice, suggest that elastin antibodies exert pathogenic effects through mediating complement activation.
We have a new publication out, A Targeted Inhibitor Of The Alternative Complement Pathway Accelerates Recovery From Smoke-Induced Ocular Injury authored by Alex Woodell, Bryan W. Jones, Tucker Williamson, Gloriane Schnabolk, Stephen Tomlinson, Carl Atkinson and Bärbel Rohrer.
PURPOSE. Morphological and genetic evidence exists that an overactive complement system driven by the complement alternative pathway (CAP) is involved in pathogenesis of age- related macular degeneration (AMD). Smoking is the only modifiable risk factor for AMD. As we have shown that smoke-related ocular pathology can be prevented in mice that lack an essential activator of CAP, we ask here whether this pathology can be reversed by increasing inhibition in CAP.
METHODS. Mice were exposed to either cigarette smoke (CS) or filtered air (6 hours/day, 5 days/week, 6 months). Smoke-exposed animals were then treated with the CAP inhibitor (CR2-fH) or vehicle control (PBS) for 3 months. Spatial frequency and contrast sensitivity were assessed by optokinetic response paradigms at 6 and 9 months; additional readouts included assessment of retinal morphology by electron microscopy (EM) and gene expression analysis by quantitative PCR.
RESULTS. The CS mice treated with CR2-fH showed significant improvement in contrast threshold compared to PBS-treated mice, whereas spatial frequency was unaffected by CS or pharmacological intervention. Treatment with CR2-fH in CS animals reversed thinning of the retina observed in PBS-treated mice as analyzed by spectral-domain optical coherence tomography, and reversed most morphological changes in RPE and Bruch’s membrane seen in CS animals by EM.
CONCLUSIONS. Taken together, these findings suggest that CAP inhibitors not only prevent, but have the potential to accelerate, the clearance of complement-mediated ocular injury. Improving our understanding of the regulation of the CAP pathway is paramount to developing novel treatment approaches for AMD.
Alex Woodell, Beth Coughlin, Kannan Kunchithapautham, Sarah Casey, Tucker Williamson, W. Drew Ferrell, Carl Atkinson, Bryan Jones and Baerbel Rohrer have a new manuscript out, The Alternative Complement Pathway Deficiency Amerliorates Chronic Smoked-Induced Functional And Morphological Ocular Injury in PLOS One.
The short story is: Don’t smoke. But then you knew that. Where this paper contributes is that it provides clear findings that show ocular pathologies generated by cigarette smoke are dependent upon activation of the immune system, in particular complement and the alternative pathway which are critical findings in the treatment of AMD.
This abstract was presented today at the Association for Research in Vision and Opthalmology (ARVO) meetings in Seattle, Washington by Alexandra D. Butler, William D. Ferrell, Alex Woodell, Carl Atkinson, Baerbel Rohrer, Robert E. Marc and Bryan W. Jones.
Purpose: Smoking is the single largest risk factor for age-related macular degeneration, aside from age. Several of the main genetic risk factors for AMD are polymorphisms occurring in complement genes involved in the alternative, classical and common terminal pathways. To better understand the metabolic impact of smoking on the retina, we used computational molecular phenotyping (CMP) and examined the effects of cigarette smoke on wild type (wt) retinas and mice in which either the alternative pathway (complement factor B, CfB) or the common terminal pathway (complement component 3, C3) was removed.
Methods: Mice were exposed to either cigarette smoke or filtered air. Cigarette smoke (CS) was generated using an automated cigarette-smoking machine (Model TE-10, Teague Enterprises, Davis, CA) by burning 3R4F reference cigarettes (2.45 mg nicotine per cigarette; purchased from the Tobacco Health Research Institute, University of Kentucky, Lexington, KY). Mice were exposed to CS for 6 hours/day, 5 days/week for 6 months. Age matched room filtered air exposed mice were used as controls. Eyes were enucleated immediately post-mortem, fixed in 1% paraformaldehyde, 2.5% glutaraldehyde, dehydrated in graded methanols, embedded in eponates and histologically analyzed with CMP.
Results: Alterations in retinal small molecule signatures from mice exposed to cigarette smoke were observed compared to retinas from non-smoked mice in wt, CfB and C3 knockout mice. Signal changes with arginine, glutamine and glutathione progressively increased in the retinas of smoked exposed wt, CfB and C3 knockout mice, indicating increased response profiles to cell stress. Both Müller cells and photoreceptors of wt smoked retinas demonstrated changes relative to non- smoked retinas.
Conclusions: Arginine, glutamine and glutathione, amino acids known to be involved in cellular stress responses, were increased in retinal neurons and glial cells upon smoke exposure. Eliminating essential components of the complement system, a cascade required for the maintenance of the immune privilege of the eye, appears to exacerbate responses to cigarette smoke in oxidative damage response related pathways. Understanding complement-dependent alterations in the eye will aid in our understanding of AMD pathology and may open new avenues for novel treatment strategies.
Support: RPB CDA (BWJ), Thome AMD Grant (BWJ), NIH EY02576 (RM), NIH EY015128 (RM), NSF 0941717 (RM), NIH EY014800 Vision Core (RM), NIH EY019320 (BR), VA merit award RX000444 (BR), grant to MUSC from RPB