Research
The actin cytoskeleton contractility and extracellular matrix (ECM)-based tissue stiffness in the trabecular meshwork (TM) is known to modulate the aqueous humor (AH) drainage and intraocular pressure (IOP). In POAG, characteristic changes occur in the tissue structure of the AH outflow pathway and the major changes are increased contractility, excessive alterations in ECM organization in the JCT-TM region, and accumulation of sheath-like plaque materials leading to altered tissue stiffness. Current IOP lowering strategies, target the cytoskeleton and lower ECM accumulation.
The Pattabiraman Lab studies the significant knowledge gaps in the contribution of the actin and ECM in the regulation of outflow resistance.
i) the regulatory controls of actin cytoskeleton-based TM cellular tension,
ii) the molecular basis for ECM production, degradation, and clearance in the AH outflow pathway and the contributions of ECM-based tissue stiffness in the regulation of IOP, and
iii) the factors leading to actin cytoskeleton-ECM dysregulation in TM resulting in IOP elevation.
Additionally, we are identifying and developing novel therapeutics for IOP lowering.
Cell adhesion complexes, which bridge the intracellular cytoskeleton and the ECM, act as key force-sensing and -transducing units in cells. Cell adhesive interactions and cell-cell junctions influence the permeability characteristics of fluid flow through cells. Clusterin is known to regulate cell-matrix interactions as well as act as a chaperone protein to stabilize cathepsin k (CTSK) and CTSK can hydrolyze ECM. We explored the role of the clusterin-CTSK axis in the regulation of ECM and IOP.
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1. How does cathepsin k - a lysosomal cysteine protease - regulate IOP?
We study the role of CTSK in IOP regulation. CTSK is an ECM-degrading enzyme mainly found in osteoclasts. The problem that results in elevated IOP has increased ECM deposition. In a proof-of-concept study to show that by augmenting CTSK, we can decrease ECM, and to signify the importance of CTSK and ECM in regulating IOP, we inhibited CTSK using a pharmacological inhibitor balicatib, to significantly induce ocular hypertension. Contrarily increasing CTSK function decreased ECM and subsequently the IOP. Therefore, signifying the functional importance of CTSK activation and its availability, which can provide us with a novel therapeutic strategy to lower IOP.
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2. Can clusterin, a secretory chaperone protein, play a role in modulating IOP?
We are finding that clusterin regulates actin cytoskeleton - ECM interactions in the TM and the maintenance of IOP, thus making clusterin an interesting target to reverse elevated IOP.
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3. Is clusterin a signaling protein?
Clusterin/apolipoprotein J can bind to various receptors such as proteoglycan heparan sulfate, TGFβR1, TGFβR2, VLDLR, LRP2, and LRP8. What is the signaling relevance of such binding?
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4. How does lipid signaling regulate TM contractility?
TM cell membrane plays an important role in modulating cellular properties. We are working towards identifying the significance of maintaining membrane and cellular cholesterol levels and cellular communication for achieving IOP homeostasis.
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Another important question we are asking is if there are structural and functional differences in the trabecular outflow tissues in people of African and European Descent. Lacking is knowledge of differences in the ECM architecture and compaction in normal and POAG eyes in AD and ED. We will couple the structure of the TM (molecular and cellular) with its function (outflow facility) in non-glaucomatous and glaucomatous donor eyes to identify differences in ocular physiology among AD and ED.
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MAJOR INSTRUMENTS IN THE LAB:
Beckman CoulterOptima MAX-XP Ultracentrifuge
Eppendorf Centrifuge 5415 R
AdInstruments - PowerLab and BridgeAMP and LABCHART Software
FlexCell - FX-6000T™ Tension System
Quant Studio Flex 6/7 thermocycler
ChemiDoc MP imaging system
NikonEclipse Ts2 with camera
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COLLABORATORS:
Tim Corson, Associate Professor, Department of Ophthalmology, Indiana University School of Medicine
Michael Weiss, Professor, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine
Brian Blagg, Professor, Department of Chemistry and Biochemistry, University of Notre Dame
Carol Toris, Professor, Department of Opthalmology, Univ of Nebraska
Sanjoy Bhattacharya, Professor of Ophthalmology, Miami Integrative Metabolomics Research Center, Univ of Miami
Dr. Gregory Underhill, Associate Professor, Department of Biomedical Engineering, UI Urbana Champaign.
