Learn more about the Kumar-Singh Laboratory
Combating Retinal Degeneration and Blindness
In public opinion polls over the previous 40 years, Americans have consistently identified fear of blindness as second only to fear of cancer. The long-term objective of our research laboratory is to develop therapies for retinal degeneration that lead to blindness. We have specific interests in age related macular degeneration (AMD), retinitis pigmentosa (RP) and diabetic retinopathy (DR). Collectively, these diseases account for the majority of blindness in the United States.
Gene Therapy Approaches to Retinal Degeneration
Although there are several environmental factors that govern the progression of AMD, RP or DR, the major contributing factor is genetic. Hence, in our laboratory we take a ‘gene therapy’ approach for the development of therapies for each of these diseases. As a consequence, our laboratory is heavily invested in the development and application of viral and non-viral gene transfer systems. In the case of viruses, we specialize in the use of adenovirus and adeno-associated virus vectors. While these are excellent methods of gene delivery, these viruses are sometimes associated with inflammation or other serious adverse events. Hence recently, we have made significant progress in the use of small cell-penetrating peptides for drug, protein and DNA delivery to ocular tissues. One particular peptide known as Peptide for Ocular Delivery or POD shows particular promise. POD forms 136nm homogenous nanoparticles in solution when complexed with DNA. Recently we have demonstrated that POD nanoparticles can be used to rescue retinal degeneration in murine models of RP.
Figure 1. Delivery of DNA across the nuclear membrane pore is considered a significant barrier for gene transfer to post mitotic cells such as neurons, including retinal cells. When POD is pegylated with a 25Kd polyethylene glycol and complexed with DNA, it spontaneously forms approximately 150nm nanoparticles in solution.These nanoparticles can deliver DNA to retinal cells in vivo following subretinal administration. These nanoparticles also effectively protect DNA from nucleases and can deliver DNA to the lung upon intravenous injection.
Therapy for AMD
AMD is a disease primarily of genetic origin and involves the complement system. Particularly, mutations in regulators of complement such as Factor H have been associated with AMD. Failed regulation of complement activation leads to the formation of the membrane attack complex (MAC) on host tissues and cells. These cells lyse and a series of events are initiated that lead to blindness. AMD affects approximately 1 in 3 people over the age of 65. Approximately 90% of AMD patients suffer from the ‘dry’ form of the disease for which there is currently no treatment available. We have demonstrated proof of principle that over-expression of a complement regulator known as CD59 on the surface of cells can block the formation of human MAC on murine ocular tissues. We propose that such a therapy may be a valid approach to treat dry AMD. We are also examining the potential use of CD46 and CD55 as methods to dampen local complement mediated damage to ocular tissues involved in AMD.
Figure 2. Normally, the membrane attack complex (MAC) would form holes in the membranes of pathogens and kill them. Human cells are naturally protected from MAC by the expression of complement inhibitory proteins such as CD59 on their surface. MAC has been found to be present on the retinal pigment epithelium as well as the choroid of AMD patients. Hence, one model for the progression or pathogenic trigger in AMD is that an imbalance between the activators and inhibitors of complement lead to damage to host ocular tissues through the formation of MAC.
The ultimate goal or ‘holy grail’ of gene therapy is to permanently correct the gene defect in vivo. Towards this goal, our laboratory is also interested in the development of designer zinc fingers that can home into pre assigned DNA ‘addresses’ in the human genome and correct the mutation. We have found this approach to be successful thus far only in cell culture studies and we are working towards being able to develop this technology for in vivo use.
Our laboratory is equipped with state of the art equipment, funded by the National Institutes of Health (NIH), several private not-for-profit organizations and private philanthropy. The research and development efforts are performed by a talented team of graduate students, post-doctoral fellows and research technicians. We always welcome applications from students and postdoctoral fellows that are interested in a career in ‘translational’ medicine.