Department of Pediatrics
McPherson Eye Research Institute
University of Wisconsin
Madison, WI

BASIC RESEARCH PROJECT

Treatment and prevention of PVR and retinal detachment

Current Research Interests

Retinal detachment (RD) is a vision-threatening condition that requires surgical treatment. Rhegmatogenous retinal detachment (RRD) is the most common surgically treated retinal detachment. Retinal scarring, specifically proliferative vitreoretinopathy (PVR), is the main reason for surgical retinal reattachment failure resulting in vision loss. Unfortunately, no drug treatment exists for PVR. Inflammation contributes to the development of PVR. Bcl-2 is an anti-apoptotic Bcl-2 family member known to enhance and prolong inflammation. Mononuclear phagocytes (MP) play essential roles in inflammation and scar formation.

RD is accompanied by inflammation that can lead to proliferative vitreoretinopathy (PVR) in up to 20% of patients. Since unchecked inflammation is a driving force in PVR, removal of unhelpful cells that fuel inflammation would be an important treatment in RD patients. Dr. Sorenson’s laboratory studies Bcl-2, a protein that prevents cells from dying. Increased Bcl-2 activity can cause cells to live longer than they should, contributing to persistent inflammation, new vessel growth and scarring. The innovation of this proposal is that it investigates whether increasing the clearance of cells that enhance inflammation, by decreasing Bcl-2 activity, improves vision outcomes for PVR patients by decreasing or reversing scar formation. A better understanding of the critical role Bcl-2 plays in this process will allow for the decrease in scar formation and reverse the scars that have already formed. This will be accomplished by decreasing Bcl-2 activity by gene deletion in inflammatory cells and with the FDA approved drug ABT-199, an inhibitor of Bcl-2 activity used to treat various cancers. The knowledge obtained from these studies should be translatable to PVR as well as other eye diseases in which scar formation is a major problem.

Specifically, the purpose of this project is to improve vision outcomes for PVR patients by preventing or decreasing scar formation. Thus, understanding the processes by which PVR-associated scars continue to form is crucial. Our data generated during the previous grant period shows that Bcl-2 expression facilitates PVR while Bim expression diminishes it. These studies have allowed us to begin to discern points of intervention to halt formation and induce regression of PVR-associated scars. During this next funding period we will assess whether decreasing or destabilizing Bcl-2 activity during scar formation or in established scars facilitate scar regression. The aim of this proposal is to delineate the fundamental role Bcl-2 plays in modulating and establishing retinal scars, which will allow us to greatly improve vision outcomes in RRD patients.

Plans for 2026

Utilizing the PVR dispase model, Dr. Sorenson has demonstrated an essential role for Bcl-2 driving fibrosis, and is now in an excellent position to execute the experiments proposed in the project. Examination of the efficacy of ABT-199 and anti-VEGF in both male and female mice during PVR has begun. Initial studies show that female mice develop more severe PVR compared to male mice. Dr. Sorenson’s lab team will administer anti-VEGF, ABT-199 and/or etomoxir to newly forming or established scars to determine the efficacy of these treatments for PVR. All these treatments have the potential to modulate Bcl-2 expression, including anti-VEGF.  Given the results observed in the lab’s experimental model, with increased severity in females and decreased treatment efficacy in male mice, they are initiating discussions with several University of Wisconsin School of Medicine and Public Health affiliated ophthalmologists, to determine if similar trends are seen in the clinic. These collaborative interactions will aid future investigations to improve treatment for these patients.

Specific Aims: The aim of this project is to delineate the fundamental role Bcl-2 plays in modulating retinal scar formation during PVR.

Progress in 2025

Utilizing Bcl-2^Flox/Flox (control) and Bcl-2^MP (lacking Bcl-2 expression in mononuclear phagocytes) mice, Dr. Sorenson demonstrated that lack of Bcl-2 significantly decreased fibrosis. Next, the team assessed whether lack of Bim expression in MP impacted fibrosis in the PVR model, noting a significant increase in the size of the fibrotic lesion in the PVR model in Bim^MPmice compared to their Bim^Flox/Flox counterpart. These data have been repeated and quantified. Thus, decreasing Bcl-2 expression to favor Bim function significantly mitigates PVR.

The lab also began testing the efficacy of ABT-199 (Bcl-2 inhibitor) to mitigate PVR. the team treated C57BL/6j mice with ABT-199 (25 mg/kg; intraperitoneal injection) daily beginning 2 days before the onset of PVR and continued treatment for an additional week. Noted was that a decrease in PVR that did not reach significance. Previously Dr. Sorenson had successfully utilized ABT-199 by intravitreal injection (100 μM; 1μl/eye) to prevent choroidal neovascularization. Therefore, next tried intravitreal ABT-199 injections one day prior to dispase administration and 3 days following were tried. Again, a decrease in PVR did not reach significance. It was felt that the number of injections received for these experiments may have been problematic. Given ABT-199 successfully treats established lung fibrosis, the next trial tried a single intravitreal injection of ABT-199 three days after dispase administration. These results were found to be encouraging in that a successful response in female mice was seen. These experiments are being followed up with a larger female cohort to improve significance but feel encouraged. The use of ABT-199 to reduce PVR after its onset is exciting, and further effort in this area will be expended to better understand the utility of this drug for this application. Next, to compare to ABT-199 treatment results, the lab team has begun to assess the ability of anti-VEGF to mitigate PVR. Anti-VEGF (25 ng/µl; 1 μl/eye) intravitreally injected 2 days prior to dispase administration mitigated formation of PVR. Next experiments will focus on whether anti-VEGF can decrease established fibrosis.

Resulting from Dr. Sorenson’s progress optimizing the PVR model throughout 2024, she  knows that female mice appear more susceptible to PVR, which makes them an  excellent resource for testing treatment modalities. The decreased response of male mice to PVR indicate they will aid in determining whether enhanced inflammation modulates PVR. The Sorenson lab will administer ABT-199 and/or etomoxir to newly forming or established scars to modulate Bcl-2 and determine the efficacy of these treatments for PVR. Next, the team will utilize mice lacking Bcl-2 in mononuclear phagocytes to delineate how decreasing the lifespan of this inflammatory subset impacts PVR. They will assess the clearance of mononuclear phagocytes from this area as well as whether M1 or M2 macrophage populations are impacted in a specific manner consistent with the decreased fibrosis we see in this area. Should Dr. Sorenson determine that Bcl-2 drives inflammation and scarring during the formation of PVR, her team will assess whether lack of Bcl-2’s opposing family member Bim enhances PVR. These mice are available in the laboratory. We have no plans to change the methodology for this proposal. Together these studies will give us a better understanding of the importance of modulating immune cell turnover to effectively treat PVR.

Specific Aim: The aim of this proposal is to delineate the fundamental role Bcl-2 plays in modulating inflammation and subsequent scar establishment which will allow us to greatly improve vision outcomes in RRD patients.

Progress in 2024

Dr. Sorenson made great progress in the past year. Her laboratory determined that for inducing PVR, dispase administration is more reproducible than mechanical method with a micro-knife (prepared from 30-gauge tungsten wire). The team found that administering an intravitreal injection of dispase (0.0015624 units/eye), harvesting retinas 1 week later, and staining with anti-collagen I was the best method to assess scar formation. They assessed whether Bcl-2 expression in mononuclear phagocytes influenced the amount of fibrosis in this PVR model in male and female mice. To this end, Dr. Sorenson utilized male and female Bcl-2Flox/Flox (control mice) and Bcl-2MP (mice lacking Bcl-2 expression in mononuclear phagocytes) to assess the level of fibrosis utilizing the PVR model. Her lab analyzed the data for Bcl-2Flox/Flox and Bcl 2MP for male mice only, female mice only and data combined for male and female mice, and determined that female mice demonstrated a larger scar (~20% larger) compared to male mice. Thus, the team analyzed the data by sex and as well as combined, and the data shows that lack of Bcl-2 in MP decreases the size of the scar.

These data have been repeated and are in the process of being quantified. We next assessed the efficacy of ABT-199 (inhibits Bcl-2 function) to inhibit PVR. Given female mice had a significant response to lack of Bcl-2 and a more pronounced response in the PVR model, we chose to utilize female mice only for our experiments. We have treated C57BL/6j female mice with ABT-199 daily beginning 2 days before PVR induction through the following week. This experiment has been completed and the samples are being processed and the data analyzed. We are excited to continue these studies and are intrigued by the enhanced PVR noted in female mice.

Progress in 2023

Dr. Sorenson made great progress optimizing the PVR model and staining protocol and now has a good-sized breeding colony of mice lacking Bcl-2 in mononuclear phagocytes that will be utilized to execute the experiments proposed in the grant. Mice lacking Bcl-2 in mononuclear phagocytes will be studied to delineate whether moderating the lifespan of this inflammatory subset diminishes PVR. In addition, the lab will administer ABT-199 and/or etomoxir to newly forming or established scars to modulate Bcl-2 and determine the efficacy of these treatments for PVR. Should it be determined that Bcl-2 drives inflammation and scarring during the formation of PVR, Dr. Sorenson will assess whether lack of Bcl-2’s opposing family member Bim enhances PVR. Together these studies will give us a better understanding of the importance of modulating immune cell turnover in treatment of PVR.

Specific Aims: To test the hypothesis that Bcl-2 expression and activity in
microglia and recruited myeloid cells plays an important role during retinal scar formation.

The major cell types of the retinal vasculature are endothelial cells, pericytes and astrocytes. Retinal astrocytes act as an intermediary between neural and vascular cells facilitating retinal vascular development, remodeling and maintaining normal function and neuronal integrity. Astrocytes surround maturing blood vessels, imparting barrier properties to the endothelia and facilitate revascularization following ischemia. Loss of retinal astrocytes aids retinal vascular rarefaction during the pathogenesis of retinopathy of prematurity (ROP) and diabetic retinopathy.

About 1,500 preterm infants in the United States become blind annually. Unfortunately, the main reason for the inherent sensitivity of the developing retinal vascular to changes in oxygen levels remains elusive. Preterm infants exposed to high levels of oxygen are predisposed to ROP due to attenuation of retinal vascular development and apoptotic loss of existing blood vessels. When infants return to room air the ischemic retina promotes pathologic growth of new blood vessels, which are fragile and leaky. Unfortunately intravitreal anti-VEGF enters the general circulation, leading to increased risk of systemic complications during this critical period of lung and kidney development.

Bim is a member of the Bcl-2 family of proteins, with important function in maintaining mitochondrial homeostasis and cell death. Bim not only regulates cell death but also influence the extracellular matrix (ECM) milieu, impacting cell adhesion and migration in a cell-type specific manner.

Progress in 2013

Dr. Sorenson hypothesized that enhanced astrocytic Bim expression in response to hyperoxia, facilitates retinal vascular rarefaction either locally during remodeling or on a larger scale during ROP. Her published studies demonstrate protection of the developing retinal vasculature from hyperoxia-mediated vessel obliteration, cessation of vascularization of the inner retina and ischemia-driven neovascularization in the absence of Bim.

She has found that Bim deletion in endothelial cells and/or pericytes was insufficient to prevent hyperoxia-mediated vessel obliteration. This study will test the hypothesis that Bim expression in astrocytes facilitates normal and pathologic retinal vessel remodeling. Enhancing astrocyte survival and function through decreasing Bim expression should prevent the first phase of ROP when normal blood vessels are being destroyed, preserving neuronal integrity and function.

Specific Aim: To test the hypothesis that Bim expression in astrocytes facilitates normal and pathologic retinal vessel remodeling.