Theranostics 2014; 4(7):721-735. doi:10.7150/thno.9052

Research Paper

Luminescent Dual Sensors Reveal Extracellular pH-Gradients and Hypoxia on Chronic Wounds That Disrupt Epidermal Repair

Stephan Schreml1✉, Robert J. Meier2, Michael Kirschbaum3, Su Chii Kong4, Sebastian Gehmert5, Oliver Felthaus6, Sarah Küchler7, Justin R. Sharpe8, Kerstin Wöltje3, Katharina T. Weiß1, Markus Albert1, Uwe Seidl1, Josef Schröder9, Christian Morsczeck6, Lukas Prantl5, Claus Duschl3, Stine F. Pedersen4, Martin Gosau6, Mark Berneburg1, Otto S. Wolfbeis2, Michael Landthaler1, Philipp Babilas1

1. Department of Dermatology, University Medical Center Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany
2. Institute of Analytical Chemistry, Chemo- and Biosensors, University of Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany
3. Fraunhofer Institute for Biomedical Engineering, Branch Potsdam, Am Mühlenberg 13, 14476 Potsdam, Germany
4. Department of Biology, University of Copenhagen, 13 Universitetsparken, DK-2100 Copenhagen, Denmark
5. Center of Plastic Surgery, Department of Trauma Surgery, University Medical Center Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany
6. Department of Maxillofacial Surgery, University Medical Center Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany
7. Department of Pharmacy, Freie Universität Berlin, Königin-Luise-Str. 2-4, 14195 Berlin, Germany
8. Blond McIndoe Research Foundation, Queen Victoria Hospital, Holtye Road, East Grinstead RH19 3DZ, England, UK
9. Center for Electron Microscopy at the Institute of Pathology, University Medical Center Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany

Abstract

Wound repair is a quiescent mechanism to restore barriers in multicellular organisms upon injury. In chronic wounds, however, this program prematurely stalls. It is known that patterns of extracellular signals within the wound fluid are crucial to healing. Extracellular pH (pHe) is precisely regulated and potentially important in signaling within wounds due to its diverse cellular effects. Additionally, sufficient oxygenation is a prerequisite for cell proliferation and protein synthesis during tissue repair. It was, however, impossible to study these parameters in vivo due to the lack of imaging tools. Here, we present luminescent biocompatible sensor foils for dual imaging of pHe and oxygenation in vivo. To visualize pHe and oxygen, we used time-domain dual lifetime referencing (tdDLR) and luminescence lifetime imaging (LLI), respectively. With these dual sensors, we discovered centripetally increasing pHe-gradients on human chronic wound surfaces. In a therapeutic approach, we identify pHe-gradients as pivotal governors of cell proliferation and migration, and show that these pHe-gradients disrupt epidermal barrier repair, thus wound closure. Parallel oxygen imaging also revealed marked hypoxia, albeit with no correlating oxygen partial pressure (pO2)-gradient. This highlights the distinct role of pHe-gradients in perturbed healing. We also found that pHe-gradients on chronic wounds of humans are predominantly generated via centrifugally increasing pHe-regulatory Na+/H+-exchanger-1 (NHE1)-expression. We show that the modification of pHe on chronic wound surfaces poses a promising strategy to improve healing. The study has broad implications for cell science where spatial pHe-variations play key roles, e.g. in tumor growth. Furthermore, the novel dual sensors presented herein can be used to visualize pHe and oxygenation in various biomedical fields.

Keywords: fluorescence imaging, wound healing, cell migration, gradient sensing, proton transporters

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How to cite this article:
Schreml S, Meier RJ, Kirschbaum M, Kong SC, Gehmert S, Felthaus O, Küchler S, Sharpe JR, Wöltje K, Weiß KT, Albert M, Seidl U, Schröder J, Morsczeck C, Prantl L, Duschl C, Pedersen SF, Gosau M, Berneburg M, Wolfbeis OS, Landthaler M, Babilas P. Luminescent Dual Sensors Reveal Extracellular pH-Gradients and Hypoxia on Chronic Wounds That Disrupt Epidermal Repair. Theranostics 2014; 4(7):721-735. doi:10.7150/thno.9052. Available from http://www.thno.org/v04p0721.htm