The central nervous system (CNS) is organized into ensembles of cells that can be identified by their anatomy and physiology. That is, there are populations of cells with dedicated structure and function. Two fundamental questions about this organization are: (1) what are the mechanisms by which any particular neuronal ensemble establishes its identity and (2) what are the mechanisms by which ensembles find each other and establish their particular connectivity?
Considerable evidence has shown epigenetic factors to be important in regulating various aspects of development. The extracellular matrix (ECM) is a rich source of such signals. Laminins are key elements of the ECM and several human diseases are known to result from genetic disruptions in laminin genes or laminin receptor genes, including ocular diseases as well as congenital brain malformations.
We use the vertebrate retina as a "simple" model system to study the role of the ECM in CNS development. We have shown that laminins are critical to the normal development in the retina. Our data demonstrate that laminins and the coupled signaling cascades regulate a wide array of developmental events in the eye. Using in vivo and in vitro experimental manipulations, we have shown that deletion of various laminins result in retinal dysgenesis. The abnormalities that are present as a result of these deletions include photoreceptor dysplasia and photoreceptor synaptic disruption. Dysgenesis of retinal ganglion cells, Müller cells and microglia are also part of the complex phenotype following deletion. In addition to disruptions in the neural organization of the retina, there are profound disruptions in retinal vascular development. Analyses of these disruptions will contribute significantly to our understanding of the pathobiology of several retinal diseases.
Confirming the utility of the retina as a model for the rest of the brain, we have shown that cortical and cerebellar development is also disrupted in laminin mutants. Cortical lamination is disrupted in laminin mutant mice, along with radial glial organization, the principle cellular scaffold along which cortical neurons migrate. In addition, there are ectopic neurons on the surface of the brain. These malformations phenocopy some aspects of human cortical dysgenesis called cobblestone lissencephaly. Indeed, mutations in one laminin gene in humans, Lamc3, have been shown to cause a very restrictive human lissencephaly.
Our studies demonstrate that laminins and laminin-related genes are critical for normal CNS development, and they implicate the involvement of laminin mutations in a host of human diseases. Our immediate goal is to identify the signaling pathways involved in these processes with the goal of understanding both normal development and the role of laminins and the molecules with which they interact in human disease. Our long-term goal is to incorporate biologically active molecules into polymers that can be used in neural repair strategies.
Recent Selected Publications
Pinzón-Duarte, G., Daly, G., Yong, Li, Hunter, D.D., Koch, M. and Brunken, W.J. Defective formation of the inner limiting membrane in laminin β2- and γ3-null mice produces retinal dysplasia. Investigative Ophthalmology and Visual Sciences 51: 1773-1782 2010 PMID: 19907020
Hirrlinger, P.G., Pannicke, T., Winkler, U., Claudepierre, T., Varshney, S., Schulze, C., Reichenbach, R., Brunken, W.J., and Hirrlinger, J. Genetic deletion of laminin isoforms β2 and γ3 induces a reduction in Kir4.1 and aquaporin-4 expression and function in the retina. PLoS One. 6: e16106. 2011 PMID: 21283711
Barak. T., Kwan, K.Y., et al, Recessive LAMC3 mutations cause malformations of the occipital cortical development. Nature Genetics. 43:590-594. 2011 PMID: 21572413
Saghizadeh, M., Soleymani, S., Harounian, A., Bhakta, B., Troyanovsky, S.M., Brunken, W.J., Pellegrini,G., and Ljubimov, A.V. Alterations of epithelial stem cell marker patterns in human diabetic corneas and effects of c-met gene therapy. Molecular Vision 17:2177-2190. 2011 PMID: 21866211
Yebra, M., Diaferia, G.R., Montgomery, A.M., Kaido, T., Brunken, W.J., Koch, M., Hardiman, G., Crisa, L., and Cirulli, V. Endothelium-Derived Netrin-4 Supports Pancreatic Epithelial Cell Adhesion and Differentiation through Integrins α2β1 and α3β1. PLoS One 6:e22750. 2011 PMID: 21829502
Li, Y.N., Radner, S., French, M.M., Pinzón-Duarte, G., Daly, G.H., Burgeson, R.E., Koch, M, and Brunken, W.J. The γ3 chain of laminin is widely but differentially expressed in murine basement membranes: expression and functional studies. Matrix Biology 31:120-134. 2012 PMID: 22222602
Li, Y.N., Pinzón-Duarte, G., Dattilo, M., Claudepierre, T., Koch, M., and Brunken, W.J. The Expression And Function Of Netrin-4 In Murine Ocular Tissue. Experimental Eye Research 96: 24-35 2012 PMID: 22281059
Radner, S, Banos, C., Bachay, G., Li, Y.N., Hunter D. D., Brunken, W.J. and Yee, K.T. β2 and γ3 Laminins Are Critical Cortical Basement Membrane Components: Ablation of Lamb2 and Lamc3 Genes Disrupts Cortical Lamination and Produces Dysplasia. Developmental Neurobiology, 73: 209-229 2013 PMID: 22961762
Gnanaguru, G., Bachay, G., Biswas, S., Pinzón-Duarte, G.A., Hunter, D.D., and Brunken, W.J., Laminins Containing the β2 and γ3 Chains Regulate Astrocyte Migration And Angiogenesis In the Retina. Development 140: 2050-2061 2013 PMID: 23571221
Saghizadeh, M., Winkler, M.A., Kramerov, A.A., Hemmati, D., Ghiam, C.A., Dimitrijevich, S.D., Sareen, D., Ornelas. L., Ghiasi, H., Brunken, W.J., Maguen, E., Rabinowitz, Y.S., Svendsen, C.N., Jirsova, K., Ljubimov, A.V. A simple alkaline method for decellularizing human amniotic membrane for cell culture. PLoS One, 8(11): e79632. 2013.
Saghizadeh, M., Epifantseva, I., Hemmati, D., Ghiam, C.A., Brunken, W.J., and Ljubimov, A.V. (2013) Enhanced wound healing, kinase and stem cell marker expression in diabetic organ-cultured human corneas upon MMP-10 and cathepsin F gene silencing. Investigative Ophthalmology and Visual Sciences 54:8172-8180 2013.