Research
The contractility of the actin cytoskeleton and extracellular matrix (ECM)-based tissue stiffness in the trabecular meshwork (TM) modulate aqueous humor (AH) drainage and intraocular pressure (IOP). In POAG, characteristic changes occur in the tissue structure of the AH outflow pathway, with major changes including increased contractility, excessive alterations in ECM organization in the JCT-TM region, and accumulation of sheath-like plaque material, leading to altered tissue stiffness. Current IOP-lowering strategies target the cytoskeleton and lower ECM accumulation.
At Indiana University School of Medicine, the Pattabiraman Lab studies significant knowledge gaps in the etiology and disease progression.
i) the regulatory controls of actin cytoskeleton-based TM cellular tension, 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
ii) investigates how compartmentalized metabolism contributes to cellular mechanobiology to regulate trabecular meshwork function and intraocular pressure homeostasis and dyshomeostasis.
iii) to bridge the gap between ocular hypertension and retinal dysfunction by defining novel disease mechanisms that can be leveraged for targeted therapeutic interventions.
These are done by studying enhancer elements, integrating epigenetic mechanisms via transcription factors, protein–RNA biochemistry, biomolecular condensate biology, and advanced cellular localization approaches to dissect how metabolic and signaling pathways reshape extracellular matrix structure and tissue stiffness in ocular disease. By combining mechanistic studies with translational strategies, Dr. Pattabiraman and his team aim to identify novel metabolic checkpoints and therapeutic targets to prevent vision loss and blindness due to glaucoma.
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 and to act as a chaperone protein that stabilizes cathepsin K (CTSK), which can hydrolyze the ECM. We explored the role of the clusterin-CTSK axis in regulating the ECM and IOP.
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 augmenting CTSK can decrease ECM and to underscore the importance of CTSK and ECM in regulating IOP, we inhibited CTSK with the pharmacological inhibitor balicatib, thereby significantly inducing ocular hypertension. Conversely, increasing CTSK function decreased ECM and, subsequently, IOP. Therefore, signifying the functional importance of CTSK activation and its availability, which can provide us with a novel therapeutic strategy to lower IOP.
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 for reversing elevated IOP.
3. Is clusterin a signaling protein?
Clusterin/apolipoprotein J can bind to various receptors, including heparan sulfate proteoglycans, TGFβR1, TGFβR2, VLDLR, LRP2, and LRP8. What is the signaling relevance of such binding?
4. How does lipid signaling regulate TM contractility?
The TM cell membrane plays an important role in modulating cellular properties. We are working to identify the significance of maintaining membrane and cellular cholesterol levels, as well as cellular communication, in achieving IOP homeostasis.
5. How does metabolism regulate IOP?
Maintaining a balance between energy demand and supply is crucial for maintaining good health. Glucose and lipids (fatty acids and ketone bodies), as sources of cellular energy, can compete and interact with each other. We are interested in understanding the metabolic reprogramming of the outflow pathway during ocular hypertension.
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 between AD and ED.
MAJOR INSTRUMENTS IN THE LAB:
Beckman Colter Optima MAX-XP Ultracentrifuge
Eppendorf Centrifuge 5415 R
AdInstruments - PowerLab, BridgeAMP, and LABCHART Software
FlexCell - FX-6000T™ Tension System
Quant Studio Flex 6/7 thermocycler
ChemiDoc MP imaging system
NikonEclipse Ts2 with camera
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 Ophthalmology, 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.
Dr. Jing Liu, Associate Professor, Department of Physics and Astronomy, Purdue University
Dr. Nuria Morral, Associate Professor, Department of Medical Genetics, Indiana University
Dr. Timothy F Osborne, Professor, Johns Hopkins, All Children's Hospital, St. Petersburg, Florida.
