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Dr. Rizzolo received his Ph.D. in biochemistry from Duke University in 1977. He received postdoctoral training in biochemistry at Harvard Medical School and in cell biology at the New York University School of Medicine. Dr. Rizzolo joined the Yale faculty in 1993 where he serves as the Director of Medical Sciences for the Section of Anatomy, and Course Director of Human Anatomy and Development for first-year clinical students. He also holds a joint appointment in the Department of Ophthalmology and Visual Science. Dr. Rizzolo recently served on the Program Planning Committee of the Association for Research in Vision and Ophthalmology, and chaired the subcommittee on Retinal Cell Biology. He is currently on the editorial board of Molecular Vision. and a member of the Educational Affairs committee of the American Association of Anatomists.
The retinal pigment epithelium (RPE) plays a central role in retinal physiology by forming the outer blood-retinal barrier and supporting the function of the photoreceptors. Many retinopathies involve a disruption of the epithelium's interactions with the neural retina or its uncontrolled proliferation. Surgical interventions limit the progression of disease, but fail to restore function. Although encouraging progress has been made with RPE transplantation, it remains unclear how to restore RPE-retinal interactions or re-establish a blood-retinal barrier. To examine these interactions, We study a developmental model of chick RPE. We observed that the RPE develops gradually under the influence of the neighboring tissues. Because different interactions appear at different times of development, we are able to identify and investigate them.
We devised several primary cell and organ culture systems that model different aspects of development. We have shown that: 1) As the neural retina matures, it secretes factors that induce the RPE to form the outer blood-retinal barrier by decreasing the permeability of RPE junctions. 2) At the RPE/neural retina interface, extracellular matrix or cell-cell interactions regulate the distribution of certain integrins. These integrins are redistributed when the neural retina and its extracellular matrix mature. 3) Initially, diffusible factors produced by the neural retina maintain the apical polarity of the Na,K-ATPase. These retinal factors differ from those that decrease the permeability of the monolayer, and may act indirectly through effects on the structure of the apical microvilli.
Our current research focuses on the development and regulation of RPE tight junctions. Tight junctions are an integral part of any blood-tissue barrier, because they regulate diffusion across the paracellular spaces of an epithelial monolayer. Tight junctions form a network of anastomosing strands that encircles each cell and binds it to its neighbors in the monolayer. In the photo above, the RPE monolayer is viewed en face with the tight junctions illuminated by fluorescent tags for the tight junction protein, ZO-1, and the subadjacent circumferential band of actin. During embryonic development, the RPE and junctional functions develop gradually. Development is coordinated with the neural retina by two-way communications between the tissues. We continue to document changes in the expression of tight junctional proteins during development and wish to understand how the neural retina regulates the composition and function of the junction. To accomplish this, we established a unique culture model of development that has already led us to propose a refinement of the classical "pore" model of tight junctions. By freeze-fracture electron microscopy, we have gained evidence that the largest class of "pores" are actually discontinuities in the network of tight junctional strands. The chick model allows us to distinguish between the initial assemble of the strands from the remodeling that assembles strands into a continuous network. We partially characterized the retinal factors that regulate the permeability of tight junctions, and found at least two factors that act at different stages of development. Our interest is in how these factors regulate two modes of tight junction function that were revealed by our culture model. We recently cloned the avian form of the tight junction protein, ZO-2. Some regions of this protein are remarkably conserved among species, and we are using this insight to create dominant negative mutations for use in our culture system. Preliminary data indicate that different PDZ domains within ZO-2 have different regulatory functions. We are also pursuing the observation that the RPE expresses several isoforms of the tight junction protein, claudin, and that claudin expression is developmentally regulated. This is especially exciting, because the claudins are thought to lend specificity to tight junction function. Our experimental model allows us to alter function by changing the structure or the compostion the the tight junctions semi-independently.
With the completed sequence of the chick genome, we are able to combine the strengths of our experimental model with the emerging advances in bioinformatics. We are using microarrays to examine the proteins and regulatory pathways of the tight junctions during normal development and in our experimental model. The raw data from studies on the developmental time course from embryonic days 7-18 can be accessed in the Gene Expression Omnibus, GSE7176) and in the appendicies of Rizzolo, L.J., Chen, X., Weitzman, M., Sun, R. and Zhang, H. (2007).
These studies address fundamental issues about tissue interactions, cell polarity and the regulation of barrier function. Understanding these interactions will help us understand the proliferative retinopathies that result when these interactions are altered, and help us develop methods that insure these interactions are reestablished upon RPE or retinal transplantation.
Clinical education presents a daunting challenge. As we progress through a century of unprecedented advances in understanding the molecular basis of human health and disease, physicians must master an array of technical disciplines while retaining and expanding the interpersonal skills that make them caring, compassionate clinicians. The exponential growth of information and techniques that students must learn limits the time allowed for the basic sciences. In every corner of the curriculum, instruction must be maximally efficient or patient care will ultimately suffer. Our goal is to develop a short introductory anatomy course that prepares students for clinical training. We investigated the needs of the clinical faculty and learning styles of the students to design a course that would help students bridge the transition from the basic science years to the clinical years. Our web based course, Anatomy Clinic, uses clinical cases to drive what the student should learn. What is the anatomy behind the patient's presentation, physical exam, diagnostic imaging and surgical or medical resolution? By learning anatomy in the context in which it will be used, students find that Anatomy Clinic is a practicable reference, as they re-encounter basic anatomy in their clinical training.
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