Indiana University School of Optometry
Faculty Research: Joseph A. Bonanno, OD, PhD
Ion Transport of the Corneal Endothelium
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The goal of this research is to understand the mechanisms by which the corneal endothelial cells secrete fluid and how it is regulated. The corneal endothelium is responsible for maintaining the hydration of the cornea. This function is essential for good vision since a defective endothelium will lead to a reduction in corneal transparency. Devising rational medical treatments for endothelial dysfunction is needed to treat traumatized or diseased corneas.

We are identifying and characterizing ion transport mechanisms that are responsible for fluid secretion. We use combined physiological, molecular biological and biophysical approaches. See our latest publications for examples. Currently, our lab is focusing on signal transduction pathways that could stimulate ion transport. We have recently found that endothelial cells possess a HCO3-stimulated adenylyl cyclase called soluble AC (sAC). This enzyme appears to be responsible for basal levels of [cAMP] in the cells, which is important for stimulating cAMP dependent transport. For example, the presence of HCO3- leads to phosphorylation of the cystic fibrosis transmembrane conductance regulator (CFTR) and increased apical membrane chloride permeability. We would like to understand how this signaling pathway interacts with other autocrine signals, e.g., the adenosine pathway, in coordinating ion transport. These findings have major implications for fluid secretion in other HCO3- dependent epithelia. For example, the ciliary epithelium, which is responsible for secretion of aqueous humor, is also dependent on HCO3- and expresses sAC. New areas of research focus on the role of carbonic anhydrases in facilitating Lactate transport out of the cornea.

Current Model for Corneal Endothelial Fluid Pumping

diagram of the model

Figure 1. Endothelial Transport Model. At the basolateral membrane, HCO3- influx helps buffer H+ (facilitated by CAII) from lactate:H+ influx. At the apical membrane, HCO3- in the bath (aqueous humor) together with HCO3- transported by SLC26A- exchanger(s) buffer H+ (facilitated by CAIV) from lactate:H+ efflux. Net HCO3-and lactate flux contribute to fluid transport by local osmotic coupling and possibly cotransporter coupling. HCO3- and Cl- flux is stimulated by cAMP/Protein Kinase A (e.g., activation of soluble Adenylyl cyclase; A2b receptors) by increasing CFTR permeability and NBC activity. CaCC, Calcium activated chloride channels; CFTR, cystic fibrosis transmembrane regulator; SLC (solute carrier family); CAIV, Carbonic anhydrase IV attached to a Glycosophosphatidylinositol membrane stalk; MCT, monocarboxylate transporter; NHE1, Na+/H+ exchanger; AE2, anion exchanger 2; A2, adenosine receptor; AC, trans membrane bound adenylate cyclase; NBC1, 1Na+/2HCO3- cotransporter; NKCC1, Na+:K+:2Cl- cotransporter 1; CAII, carbonic anhydrase II; sAC, soluble adenylate cyclase; PKA, Protein kinase A.

Ongoing Projects

Recent Publications on Endothelial Function

  1. Sun X.C., McCutheon C., Bertram P., Xie Q. and Bonanno J.A. Studies on the expression of anion transport related proteins in corneal endothelial cells. Cur. Eye. Res., 22:1-7, 2001.
  2. Bonanno, J.A. Effects of contact lens-induced hypoxia on the physiology of the corneal endothelium. Optom Vis Sci. 78:783-790, 2001.
  3. Sun X.C. and Bonanno, J.A. Expression, Localization and Functional Evaluation of CFTR in Bovine Corneal Endothelial Cells. Am J Physiol (Cell Physiol) 282(4):C673-83, 2002.
  4. Zhang, Y, Xie, Q, Sun, X.C. and Bonanno, J.A. Enhancement of HCO3- permeability across the apical membrane of bovine corneal endothelium by multiple signaling pathways. Invest Ophthalmol. Vis. Sci., 43:1145-53, 2002.
  5. Xie, Q., Zhang, Y., Zhai, CB. and Bonanno, J.A. Calcium Influx Factor from Cytochrome P-450 Metabolism and Secretion-like Coupling Mechanisms for Capacitative Calcium Entry in Corneal Endothelial Cells. J. Biol. Chem. 277(19):16559-66, 2002.
  6. Bonanno, J.A., Identity and Regulation of Ion Transport Mechanisms in the Corneal Endothelium. Progress in Retina and Eye Research, 22: 69-94, 2003.
  7. Xing Cai Sun, Chang-Bin Zhai, Miao Cui, Yanqiu Chen, Lonny R. Levin, Jochen Buck, Joseph A. Bonanno. HCO3- Dependent Soluble Adenylyl Cyclase Activates the Cystic Fibrosis Transmembrane Conductance Regulator in Corneal Endothelium. Am J Physiol (Cell Physiol), 284: C1114-C1122, 2003.
  8. Sun XC, Bonanno JA. Identification and cloning of the Na/HCO3- cotransporter (NBC) in human corneal endothelium. Exp Eye Res. 2003 Sep; 77(3):287-95.
  9. Sun, XC, Cui, M, and Bonanno, JA. [HCO3-]-regulated expression and activity of soluble adenylyl cyclase in corneal endothelial and Calu-3 cells. BMC Physiol. 2004 Apr 29;4(1):8.
  10. Jinhua Li, Xing Cai Sun, and Joseph A Bonanno. Role of NBC1 in Apical and Basolateral HCO3- Permeabilities and Transendothelial HCO3- Fluxes in Bovine Corneal Endothelium. Am J Physiol Cell Physiol. 2005 Mar; 288(3):C739-46.
  11. Kah Y. Tan-Allen, Xing Cai Sun and Joseph A. Bonanno. Characterization of Adenosine Receptors in Bovine Corneal Endothelium. Exp Eye Res. 2005 May;80(5):687-96.
  12. Qiang Xie, Yan Zhang, Xing Cai Sun, Changbin Zhai, Joseph A. Bonanno. Expression and Functional Evaluation of Transient Receptor Potential Channel 4 in Bovine Corneal Endothelial Cells. Exp Eye Res. 2005 Jul;81(1):5-14.
  13. Srinivas SP, Ong A, Goon L, Goon L, Bonanno J. A. Lysosomal Ca2+ stores in bovine corneal endothelium. Invest Ophthalmol Vis Sci. 2002 Jul;43(7):2341-50.
  14. Srinivas SP, Ong A, Zhai CB and Bonanno JA. Inhibition of carbonic anhydrase activity in cultured bovine corneal endothelial cells by dorzolamide. Invest Ophthalmol Vis Sci 43: 3273-3278, 2002.16. Xie Q, Lin T, Zhang Y, Zheng J, Bonanno JA.
  15. Srinivas SP, Bonanno JA, Lariviere E, Jans D, Van Driessche W. Measurement of rapid changes in cell volume by forward light scattering. Pflugers Arch. 2003 Oct; 447(1):97-108.
  16. Xie Q, Lin T, Zhang Y, Zheng J, Bonanno JA. Molecular cloning and characterization of a human AIF-like gene with ability to induce apoptosis. J Biol Chem. 2005 May 20, 280:19673-19681.
  17. TRPC4 Knockdown Suppresses Epidermal Growth Factor-induced Store-operated Channel Activation and Growth in Human Corneal Epithelial Cells. Hua Yang, Stefan Mergler, Xingcai Sun, Zheng Wang, Luo Lu, Joseph A. Bonanno, Uwe Pleyer, and Peter S. Reinach. J. Biol. Chem. 2005; 280 32230-32237.
  18. Hypoxia preconditioning protects corneal stromal cells against induced apoptosis. Dongmei Xing, Xingcai Sun, Jinhua Li, Miao Cui, Kah Tan-Allen and Joseph A. Bonanno; Exp Eye Res 2006; 82:780.

Lab Personnel

Colin Cheng
Colin Cheng		 Miao Cui
Miao Cui		 Tracy Nguyen
Tracy Nguyen		 Kah Tan
Kah Tan-Allen		 Dongmei Xing
Dongmei Xing

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URL: http://www.opt.indiana.edu/people/faculty/bonanno/iontrans.htm
Revised: August 29, 2006
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