About our work
Glaucoma is the second leading cause of blindness in developed countries. It is a group of optic neuropathies characterized by the death of retinal ganglion cells (RGCs), leading to a specific deformation of the optic nerve head. Peripheral vision declines first in glaucoma, while central vision loss occurs much later. Elevated intraocular pressure (IOP) is one of the main risk factors in glaucoma, but it is not completely understood how elevated IOP kills RGCs. Several genes have been implicated in glaucoma pathogenesis but the search for other contributing genes continues. This section conducts basic research on glaucoma. We study genes, proteins and signaling pathways that might be essential for RGC and optic nerve development, function, survival, and regeneration.
Our interests are concentrated on early changes in the retina and the optic nerve during the course of glaucoma. Since it is hard to study such changes in the retina and optic nerve on human subjects, we use animal models of glaucoma for our investigations; subsequently we plan to confirm and apply our results to humans. Another main area of our research is the identification of new genes involved in glaucoma. This requires parallel studies on genes that are important for the function of the retina, the optic nerve and aqueous humor outflow system in the normal eye. We are particularly interested in genes encoding olfactomedin domain-containing proteins. To study function of these proteins we also use zebrafish as a model system.
Treatments currently available for glaucoma exert their effects by reducing IOP, the most important risk factor for the onset and progression of the disease, but have no direct effects on RGCs or the optic nerve and are not always optimally effective in slowing the progression of the disease. Thus, the development of novel, neuroprotective glaucoma therapies are of great importance. We are interested in investigating the potential neuroprotective benefits of stem cell transplantation, which has produced encouraging results in different models of CNS degeneration.
In addition to our own research, we collaborate extensively with other laboratories at the NEI, NIH, and the external community. Below is a brief summary of our research as of March 2014.
Functions of the olfactomedin domain-containing proteins
The family of olfactomedin domain-containing proteins is one of the main areas of our research. This family contains 13 members in mammals that segregate into seven subfamilies. Some family members, such as latrophilins and gliomedin, are membrane-bound proteins containing the olfactomedin domain in the extracellular N-terminal region, while the intracellular C-terminal domain of these proteins is essential for the transduction of extracellular signals to the intracellular signaling pathway. Other family members are secreted glycoproteins whose functions are mostly unknown. Several genes encoding olfactomedin domain-containing proteins are expressed in the eye. We focus our attention on the genes that are expressed in RGCs and eye angle tissues.
Myocilin (MYOC) was the first gene in which identified mutations were found to cause glaucoma. Mutations in MYOC are among the most common causes of inherited eye disease with a known molecular basis. Despite extensive studies by many laboratories for over 15 years since the discovery of a connection between mutations in MYOC and glaucoma, the physiological functions of myocilin in ocular and non-ocular tissues are poorly understood. We found new functions of myocilin in ocular and non-ocular tissues. We demonstrated that myocilin is involved in myelination of the optic and sciatic nerves acting through different signaling pathways. We found that myocilin is expressed in bone marrow-derived mesenchymal stem cells (MSCs) and affects their differentiation into osteoblasts. We discovered that myocilin increased cell proliferation and survival. Oppositely, expression of mutated myocilin sensitizes cells to apoptosis induced by oxidative stress. Our future plans involve the elucidation of possible involvement of myocilin in axon growth and regeneration.
Olfactomedin 1 (Olfm1) and the closely related genes Olfactomedin 2 (Olfm2) and Olfactomedin 3 (Olfm3) show overlapping expression patterns demonstrating preferential expression in the developing and adult neuronal tissues. RGCs are the main site of Olfm1-3 expression in the retina. We demonstrated that Olfm1 interacts with several proteins essential for neuronal and synaptic activity. Nogo-A receptor (NgR1) and subunits of ionotropic glutamate AMPA receptor (GluR1-GluR4) were among the most interesting Olfm1-interacting partners. We use a zebrafish model to study functions of Olfm1 in development. There are two olfm1 genes in zebrafish, each producing four different transcripts. Over-expression of Olfm1 in zebrafish embryos increased the thickness of the optic nerve and produced a more extended projection field in the optic tectum as compared with control embryos. We produced a zebrafish line with null mutations in both olfm1 genes showing interesting phenotype. The functions of Olfm1-3 proteins in formation, maintenance and activity of synapses and well in axon growth and regeneration is the main are of our current research
Neuroprotection in glaucoma
As one of the possible approaches to neuroprotection, we use stem cell transplantation. In addition to in vivo transplantation, we use the in vitro technique of retinal explant tissue culture as a model to assess cellular transplantation. We have demonstrated strong neuroprotection derived from MSC transplantation. Our recent experiments identified 11 secreted factors that were enriched in the MSC secretome. Treatment of retinal explants with a cocktail of these factors conferred RGC neuroprotection, with factors from the platelet-derived growth factor (PDGF) family being the most potent. Intravitreal injection of PDGF-AA or -AB led to profound optic nerve neuroprotection in vivo following experimental induction of elevated intraocular pressure. We concluded that an unexpectedly large effect size for PDGF-mediated neuroprotection may represent a neuroprotection target for the treatment of glaucoma that should be explored further and that direct injection of PDGF protein at regular intervals could represent a viable treatment option for late-stage glaucoma when conventional treatments have failed to arrest progression towards blindness. Our future plans involve elucidation of the molecular mechanisms responsible for RGC protection by PDGF.
MSCs may provide a temporal protective effect but are not the best candidates for RGC replacement therapy. The primary requirement for cell replacement therapy for glaucoma is the development of a reliable protocol capable of differentiating precursor cells into mature, functional RGCs. While a convincing in vitro differentiation of a mature RGC from a suitable precursor cell type has yet to be demonstrated, advances in driving stem cells, including induced pluripotent stem cells, towards an RGC-like fate are continually being made. Our current experiments are directed towards the generation of RGC precursors. We believe that production of such cells is a necessary step for subsequent RGC replacement therapy in glaucoma.
Kwon, H.-S., Nakaya, N., Abu-Asab, M., Kim, H.S., and Tomarev, S.I. (2014) Myocilin is involved in NgR1/Lingo-1-mediated oligodendrocyte differentiation and myelination of the optic nerve. J. Neurosci. In press.
Joe, M.-K., Kwon, H.S., Cojocaru, R., and Tomarev, S.I. (2014) Myocilin regulates cell proliferation and survival. J. Biol. Chem. 289, 10155-10167.
Johnson, T.V., DeKorver, N.W., Levasseur, V., Osborne, A., Tassoni, A., Lorber, B., Heller, J. P. Villasmil, R., Bull, N.D., Martin, K.R., and Tomarev, S.I. (2014) Identification of retinal ganglion cell neuroprotection conferred by platelet-derived growth factor (PDGF) through analysis of the mesenchymal stem cell secretome. Brain. 137, 503-519.
Nakaya, N., Sultana, A., Munasinghe, J., Cheng, A., Mattson, M.P., and Tomarev, S.I. (2013) Deletion in the N-terminal half of olfactomedin 1 modifies its interaction with synaptic proteins and causes brain dystrophy and abnormal behavior in mice. Exp. Neurol. 250, 205-218.
Kwon, H.-S., Johnson, T.V., Joe, M.K., Abu-Asab, M., Zhang, J., Chan, C.C., and Tomarev, S.I. (2013) Myocilin mediates myelination in the peripheral nervous system through ErbB2/3 signaling. J. Biol. Chem. 288, 26357-26371.
Kwon, H.-S, Johnson, T.V., and Tomarev, S.I. (2013) Myocilin stimulates osteogenic differentiation of human mesenchymal stem cells through MAPK signaling. J. Biol. Chem. 288, 16882-16894.
Suntharalingam, A., Abisambra, J.F., O’Leary, J.C., Koren, J., Joe, M.K., Blair, L.J., Hill, S.E., Jinwal, U.K., Cockman, M., Duerfeldt, A.S., Tomarev, S., Blagg, B.S.J., Lieberman, R.L., and Dickey, C.A. (2012) Grp94 triage of mutant myocilin through ERAD subverts a more efficient autophagic clearance mechanism. J. Biol. Chem. 287, 40661-40669.
Nakaya, N., Sultana, A., Lee, H.S., and Tomarev, S.I. (2012) Olfactomedin 1 interacts with the NOGO A receptor complex to regulate axon growth. J. Biol. Chem. 287, 37171-37184.
Joe, M.K., Changwon Kee, and Tomarev, S.I. (2012) Myocilin interacts with syntrophins and is a member of the dystrophin-associated protein complex. J. Biol. Chem. 287, 13216-13227.
Sultana, A., Nakaya, N., Senatorov, V.V., and Tomarev, S.I. (2011) Olfactomedin 2: expression in the eye and interaction with other olfactomedin domain-containing proteins. Invest. Ophthalmol. Vis. Sci. 52, 2584-2592.
Bull, N.D., Johnson, T.V., Welespar, G., DeKorver, N., Tomarev, S.I. and Martin, K.R. (2011) Use of an adult retinal explant model for screening of potential retinal ganglion cell neuroprotective therapies. Invest. Ophthalmol. Vis. Sci. 52, 3309-3320.
Kwon, H.-S. and Tomarev, S.I. (2011) Myocilin promotes cell migration through activation of integrin-focal adhesion kinase-serine/threonine kinase signaling pathway. J. Cell. Physiol. 226, 3392-3402.
Chi, Z.-L, Akahori1, M., Obazawa1, M., Minami1, M., Noda1, T., Nakaya, N., Tomarev, S., Kawase, K., Yamamoto, T., Noda, S., Sasaoka, M., Shimazaki, A., Takada, Y., and Iwata, T. (2010) Overexpression of optineurin E50K disrupts Rab8 interaction and leads to a progressive retinal degeneration in mice. Hum. Mol. Genet. 19, 2606-2615.
Li, L., Nakaya, N., Chavali, V.R.M., Ma, Z., Jiao, X., Sieving, P., Riazuddin, S., Tomarev, S.I., Ayyagari, R., Riazuddin, S.A., and Hejtmancik, J.F. (2010) A mutation in ZNF513, a putative regulator of photoreceptor development, causes autosomal recessive Retinitis Pigmentosa. Am. J. Hum. Genet. 87, 1-10.
Johnson, T.V., Bull, N.D., Tomarev, S.I., Hunt, D.P., and Martin, K.R. (2010) Local mesenchymal stem cell transplantation confers neuroprotection in experimental glaucoma. Invest. Ophthalmol. Vis. Sci. 51, 2051-2059.
Joe, M.-K and Tomarev, S.I. (2010) Expression of myocilin mutants sensitizes cells to oxidative stress-induced apoptosis: implication for glaucoma pathogenesis. Am. J. Pathol. 176, 2880-2890.
Tomarev, S.I. (2010) Animal models of glaucoma. In: Encyclopedia of the Eye, 1st Edition (Dartt. D. A., Beshrse. J. C. and Dana, R., Eds.). vol.1, pp. 106-111.
Johnson, T.V. and Tomarev, S.I. (2010) Rodent models of glaucoma. Brain Res. Bull. 81, 349-358.
Tomarev, S.I. and Nakaya, N. (2009) Olfactomedin domain-containing proteins: Possible mechanisms of action and functions in normal development and pathology. Mol. Neurobiol. 40, 122-138.
Kwon, H.-S., Lee, H.-S., Ji, Y., Rubin, J.S., and Tomarev, S.I. (2009) Myocilin is a modulator of Wnt signaling. Mol. Cell. Biol. 29, 2139-2154.
Nakaya, N., Lee, H.-S., Takada, Y., Tzchori, I., and Tomarev, S. I. (2008) Zebrafish olfactomedin 1 regulates retinal axon elongation in vivo and is a modulator of Wnt signaling pathway. J. Neurosci. 28, 7900-7910.
Zhou, Y., Grinchuk, O., and Tomarev, S. (2008) Transgenic mice expressing the Tyr437His mutant of human myocilin protein develop glaucoma. Invest. Ophthamol. Vis. Sci. 49, 1932-1939.