The Rao lab is interested in understanding how neurons and vasculature pattern themselves and interact with each other during development as well as in disease. Specifically, we are studying the role of circadian clocks and their contribution to retinal neurovascular development and function. We use the mouse eye as our model system mainly because of the presence of multiple vascular networks and their close association with the neurons. This interface between the neuronal and vascular systems is important for normal function and disruption can lead to pathologies. Circadian disruption is associated with wide range of metabolic syndromes and more recently has been implicated in the progression of certain diseases. Not much is known about the contribution of the circadian clock on retinal function. Our goal is to identify the molecular targets of the circadian clock within this retinal neurovascular unit and study the effects of the loss of these modulators on retinal development and maintenance. Though our studies are focused in the eye, our findings will have implications for the design of novel biological therapies for any tissue within the body.
Project 1: Circadian regulation of neuronal and vascular development in the eye.
We have recently demonstrated that environmental light plays an important role in the regulation of neuronal and vascular development in the eye. Based on our findings we proposed that light exposure during development is required to establish or entrain a circadian clock within the retina. Circadian clocks are biochemical oscillators that oscillate in phase with the solar day and night cycle. Thus a circadian oscillator could regulate and coordinate processes like cell cycle entry and exit or secretion of growth factors and hormones. Retinal development is a coordinated process of timed cell division, differentiation and growth.We hypothesize that this kind of synchronized activity within groups of cells must be due to the early timing cues provided by light. We use a variety of genetic, molecular and biochemical techniques to dissect the function of circadian clocks within different cell types of the retina.
Project 2: Circadian regulation of endocrine function.
An exciting and new area of research that has emerged from our analysis, is the observation that the circadian clock directly regulates enzymes that are responsible for controlling local thyroid hormone availability. The control of endocrine systems by the circadian clock is not surprising, sinceit allows for a systemic coordination of various physiological target systems according to the time of the day. Our data specifically shows that an enzyme called Dio2 (Deiodinase 2) is targeted by the circadian clock. Dio2 is responsible for locally converting the prohormone T4 to its active state. Thisresultsina spatial and temporal control of T3 mediated response, which is not always the case with the systemic release of the thyroid hormone. This interaction between the circadian clock and Dio2 prompted us to investigate if Dio2 has any role in ocular vasculature. We have identified a novel signaling axis that is controlled by thyroid hormone in regulation of arterial and venous blood vessels.
Current research is focused on identifying the downstream targets of thyroid hormone that play a significant role in vascular development and homeostasis. Our datasuggest that the notch signaling is affected by thyroid hormone signaling. Disruption in Notch pathway in humans results in arterial venous malformation. We will investigate if these malformations in an animal model can be rescued by providing thyroid hormone during the right time in development.The information gained from these experiments will help us to determineif manipulation of thyroid hormonecan be used to treat certain vascular diseases. Moreover, thyroid hormone signalingis extremely important in maintaining energy balance and controlling metabolism. The molecular information that we gain from this analysis can also be used in non-vascular tissues where energy metabolism is critical for the proper function of the tissue.
Project 3: Role of circadian clock in inflammation
The ocular vasculature is closely associated with resident macrophages and microglial cells. We are interested in understanding if circadian clocks within the microglia can regulate secretion of inflammatory molecules within the retina. Age related changes within the retina can lead to many retinal pathologies. Some pathologies have been associated with increased inflammation in the retina.We will investigate if clock disruption within the microglial cellsaffect or contribute to retinal patholgies. The ultimate goal of this project is to define a functional role for microglialclocksin maintenance and repair of neurons and vasculature
Research & Innovation
Our research was the first analysis that demonstrated a link between environmental light and proper development of the eye. Since then we have demonstrated that light exposure in first trimester is a risk factor for the development of severe retinopathy. We can use the information that we gather from these projects to consider early interventions in treatment of retinopathy of prematurity where it could have an enormous benefit. Furthermore, our current research investigating the role of clock genes which are important in the generation and maintenance of circadian rhythms will uncover novel roles for these genes and will provide us new targets for treatments of proliferative retinopathy.
In other words ...
Every living organism, have an internal timing mechanism that allows for certain physiological, behavioral and biochemical processes to occur in a rhythmic manner to coincide with the external environment. There is a growing body of evidence that shows a correlation between disruption of the internal timing and its negative impact on behavior and pathophysiology. We are interested in understanding how these internal timing cues affect tissue development and function and why do these disruptions lead to certain diseases. Our primary goal is to use the gained information to identify the targets of these clocks and design novel therapeutic that can be used to directly manipulate the targets. Though we study the eye, clocks are present in all the tissues within the body and this knowledge can be applied to any tissue within the body.
Onkar Sawant Ph.D.
Banumathi Tamilselvan Ph.D.
- Circadian clock gene Bmal1 controls thyroid hormone-mediated spectral identity and function of cone photoreceptors, Onkar B Sawant; Amanda M Horton; Olivia F Zucaro; Ricky Chan; Vera L Bonilha; Ivy S Samuels; Sujata Rao. In Press Cell Reports
- A mutagenesis-derived Lrp5 mouse mutant with abnormal retinal vasculature and low bone mineral density. Charette JR, Earp SE, Bell BA, Ackert-Bicknell CL, Godfrey DA, Rao S, Anand-Apte B, Nishina PM, Peachey NS, Mol Vis. 2017 Mar 18;23:140-148.
- Light regulated thyroid hormone signaling is required for rod photoreceptor development in the mouse retina. Sawant O, Horton AM, Shukla M, Rayborn ME, Peachey NS, Hollyfield JG, Rao S. Invest Ophthalmol Vis Sci., 2015 Dec 1;56 (13):8248-57. doi: 10.1167/iovs.15-17743.
- Wnt ligands from the embryonic surface ectoderm regulate 'bimetallic strip' optic cup morphogenesis in mouse.Carpenter AC, Smith AN, Wagner H, Cohen-Tayar Y, Rao S, Wallace V, Ashery-Padan R, Lang RA. Development, 2015 Mar 1;142(5):972-82. doi: 10.1242/dev.120022.
- Length of Day During Early Gestation as an Independent Predictor of Risk for Severe Retinopathy of Prematurity. Yang MB, Rao S, Copenhagen DR, Lang RL. Ophthalmology, 2013.
- A direct and melanopsin-dependent fetal light response regulates mouse eye development. Rao S, Chun C, Fan J, Kofron JM, Yang MB, Hegde RS, Ferrara N, Copenhagen DR, Lang RA.Nature, 2013 Feb 14;494 (7436):243-6. doi: 10.1038/nature 11823. Epub 2013 Jan 16.
- Macrophage Wnt- Calcineurin-Flt1 signaling regulates mouse wound angiogenesis and repair. Stefater JA 3rd, Rao S, Bezold K, Aplin AC, Nicosia RF, Pollard J, Ferrara N, Lang RA. Blood. 2013 Jan 9.
- Wntless functions in mature osteoblasts to regulate bone mass. Zhong Z, Zylstra-Diegel CR, Schumacher CA, Baker JJ, Carpenter AC, Rao S, Yao W, Guan M, Helms JA, Lane NE, Lang RA, Williams BO. PNAS 2012 Aug 14;109(33)197-204.
- Regulation of angiogenesis by a non-canonical Wnt-Flt1 pathway in myeloid cells. Stefater JA 3rd, Lewkowich I, Rao S, Mariggi G, Carpenter AC, Burr AR, Fan J, Ajima R, Molkentin JD, Williams BO, Wills-Karp M, Pollard JW, Yamaguchi T, Ferrara N, Gerhardt H, Lang RA. Nature, 2011 May 29;474(7352):511-5.
- Macrophages define dermal lymphatic vessel calibre during development by regulating lymphatic endothelial cell proliferation. Gordon EJ, Rao S, Pollard JW, Nutt SL, Lang RA, Harvey NL Development, 2010 Nov;137(22):3899-910.
- Generation of mice with a conditional null allele for Wntless. Carpenter AC, Rao S, Wells JM, Campbell K, Lang RA. Genesis. 2010 Sep;48(9):554-8.
- Macrophage Wnt7b is critical for kidney repair and regeneration.Lin SL, Li B, Rao S, Yeo EJ, Hudson TE, Nowlin BT, Pei H, Chen L, Zheng JJ, Carroll TJ, Pollard JW, McMahon AP, Lang RA, Duffield JS. PNAS, 2010 Mar 2;107(9):4194-9. Epub Feb16.
- Discovery and characterization of a small molecule inhibitor of the PDZ domain of disheveled. Grandy D, Shan J, Zhang X, Rao S, Akunuru S, Li H, Zhang Y, Alpatov I, Zhang XA, Lang RA, Shi DL, Zheng JJ. Journal of Biological Chemistry, 2009 Jun 12;284 (24):16256-63.
- Nrarp coordinates endothelial Notch and Wnt signaling to control vessel density in angiogenesis. Phng LK, Potente M, Leslie JD, Babbage J, Nyqvist D, Lobov I, Ondr JK, Rao S, Lang RA, Thurston G, Gerhardt H, Developmental Cell, 2009 Jan; 16(1); 70-82.
- Obligatory participation of macrophages in an angiopoietin 2-mediated cell death switch. Rao S, Lobov IB, Vallance JE, Tsujikawa K, Shiojima I, Akunuru S, Walsh K,Benjamin L, Lang RA. Development, 2007 Dec;134(24):4449-58. (Cover)
- WNT7b mediates macrophage-induced programmed cell death in patterning of the vasculature. Rao S*, Lobov IB*, Carroll TJ, Vallance JE, Ito M, Ondr JK, Kurup S, Glass DA, Patel MS, Shu W, Morrisey EE, McMahon AP, Karsenty G, Lang RA. Nature, 2005, Sep 15;437(7057):417-21. * Authors contributed equally.
- Unique biochemical and behavioral alterations in Drosophila shibire(ts1) mutants imply a conformational state affecting dynamin subcellular distribution and synaptic vesicle cycling. Chen ML, Green D, Liu L, Lam YC, Mukai L, Rao S, Ramagiri S, Krishnan KS, Engel JE, Lin JJ, Wu CF. Journal of Neurobiology, 2002 Nov 15;53(3):319-29.
- Two distinct effects on neurotransmission in a temperature-senstive SNAP-25 mutant. Rao S, Stewart BA, Rivlin PK, Vilinsky I, Watson BO, Lang C, Boulianne GL, Salpeter MM, Deitcher DL. EMBO, 2001 Dec 3;20(23):6761-71.
- Visualization of neuropeptide expression, transport and exocytosis in Drosophila melanogaster. Rao S, Lang C, Levitan ES, Deitcher DL. Journal of Neurobiology,2001 Nov 15;49(3):159-72.2001.
- Nuecleoside diphosphate kinase, a source of GTP, is required for dynamin dependent synaptic vesicle recycling. Krishnan KS, Rikhy R, Rao S, Shivalkar M, Mosko M, Narayan R, Etter P, Estes PS, Ramaswami M. Neuron, 2001 Apr;30(1):197-210.
- Drosophila stoned proteins regulate the rate and fidelity of synaptic vesicle internalization.Stimson DT, Estes PS, Rao S, Krishnan KS, Kelly LE, Ramaswami M. Journal of Neuroscience, 2001 May 1;2 (9):3034-44.
- Alleviation of the temperature-sensitive paralytic phenotype of shibire (ts) mutants in drosophila by sub-anesthetic concentration of carbon dioxide. Krishnan KS, Chakravarty S, Rao S, Raghuram V, Ramaswami M. Journal of Neurogenetics, 1996 Sept;10(4):221-38.
- Genetic studies on dynamin function in drosophila.Ramaswami, Rao S, van der Bliek A, Kelly RB, Krishnan KS. Journal of Neurogenetics, 1993 Dec;9(2):73-87.