"My main area of research explores questions related to the physiological control of water and ion homeostasis in mammals. The objectives of my studies aim to determine the functional importance of osmotically driven water movement through water channels, or Aquaporins. The graduate and undergraduate students who work with me in my laboratory, use the tools of molecular biology, genetics and physiology to address specific questions regarding the role of water channels in normal lung and vascular physiology in mammals, and freeze tolerance in anurans.
As the University Honors Program Associate Director for Honors Thesis Research I have the privilege of working with students from all majors across campus as they pursue independent, faculty-supervised Honors Thesis Projects as they earn an Honors Diploma. The depth and breadth of their interests and passions for learning and discovery, performance and creativity continue to amaze me."
Dr. Krane earned an Honors Bachelor of Science degree in Biochemistry in 1990 from Marquette University in Milwaukee WI, and a Doctoral degree in Molecular Genetics in 1996 from Washington University School of Medicine, in St. Louis, MO. Following a Post-doctoral fellowship in Molecular Physiology at the University of Cincinnati, College of Medicine, Dr. Krane joined the Department of Biology in 2001 as an Assistant Professor. Dr. Krane delivers upper-level undergraduate lecture and laboratory courses in Physiology (BIO 403 and BIO 403L), and is very active in mentoring graduate and undergraduate students in her laboratory. Dr. Krane also organizes the Careers in Biology Seminar Series in the Department of Biology and serves as an academic advisor to biology and premedical majors.
RESEARCH AREAS:
• Cryopreservation: Cold acclimation and Freeze Tolerance in Cope's Gray Treefrog, Hyla chrysoscelis
Some organisms inhabiting regions with sub-freezing temperatures are intolerant of freezing and avoid ice formation by mechanisms such as supercooling. Others, like Cope's gray treefrog H. chrysoscelis, tolerate actual freezing and implement mechanisms that minimize damage from the formation of ice crystals. Among these are the accumulation of solutes that may serve a variety of functions, including cryoprotection (stabilization of protein and/or membrane structure and function) and osmotic agent (regulating the distribution of water between intracellular and extracellular fluids). Upon freezing, a number of amphibian species liberate glucose to accomplish these physiological objectives. However, frogs of the gray treefrog complex - H. chrysoscelis and its tetraploid sister species H. versicolor - are unusual in that they also accumulate glycerol during cold acclimation before freezing. It is likely that this glycerol is synthesized by the liver and is eventually released to the circulation and distributed to tissues throughout the body. Glycerol may circulate at elevated concentration (and accumulate at high concentrations in tissues) in cold-acclimated organisms for weeks or months, as long as the animals remain cold. Although the function of this glycerol has not been definitively established-and other frogs that tolerate freezing do so without glycerol-the presumption is that this solute acts as a cryoprotectant as described above.
Thus, it is likely that glycerol transport across cell membranes-whether to exit hepatocytes, to enter other cells as a protective solute, or to be reabsorbed following glomerular filtration-is an important physiological demand during cold acclimation in this group of frogs. At the same time, pathways for water flux must be maintained, both for water balance during cold acclimation (e.g. renal water reabsorption, or potentially water redistribution) and for the eventuality of freezing (when water is likely distributed between fluid compartments, and which may well occur too quickly for upregulation of water transport pathways). Both glycerol and water transport can be accomplished via proteins from the MIP family. Some of these proteins (aquaporins, AQP) function as selective water channels, whereas others (glyceroporins, GLP) additionally transport small organic solutes like glycerol. We hypothesize that tissues from gray treefrogs would express AQPs and GLPs, and that the pattern of their expression among tissues would relate to roles in water and glycerol transport. To test these hypotheses and predictions we have cloned three novel AQPs. Our current efforts are focused on functionally characterizing these water channels using Xenopus oocyte expression assays. In addition, we are using quantitative real-time PCR and immunohistochemistry to characterize thermal and tissue regulation of the AQPs.
• Aquaporins in Vascular Physiology
Coronary artery disease is the most common type of heart disease, affecting ~385,000 Americans annually. Surgical treatments use the human saphenous vein (HSV) in coronary artery bypass graft (CABG) procedures. However, the long-term patency of the vein graft in an arterial environment is limited, thereby requiring a high percentage of autograft recipients to repeat the bypass surgery within 5 years. The main problem that ensues with HSV grafts is due to the development of intimal hyperplasia (IH) which compromises vessel function. The mechanistic reasons for the development of IH and limited HSV patency are not currently understood. Aquaporin 1 (AQP1), a water channel protein, is expressed in the plasma membrane of vascular endothelial cells. Aquaporin 1 protein abundance is upregulated in HSV explants that have been subjected to arterial environmental conditions ex vivo prior to the onset of IH. Therefore, we hypothesize that AQP1 may function as an early environmental sensor in HSV grafts. The goal of this study is to assess the effect of shear stress on AQP1 expression in cultured endothelial cells. Using primary endothelial cells from arterial and venous sources, we are currently examining the regulation of AQP1 as related to shear stress.
• Mammalian Fluid Homeostasis: Aquaporins
The maintenance of fluid homeostasis is a critical parameter in establishing and maintaining normal lung physiology. Control of membrane water flux through membrane water pores (aquaporins; AQP) is essential for the ability of an organism to adapt to changing fluid environments. We have found that perturbations in fluid handling in the lung can result in an asthma-like bronchoconstrictive response in a mouse model in which AQP5, a molecule important in water flow in the lung, has been disrupted. We do not currently understand how and why disruptions in this water channel result in an asthma-like pathophysiological state in mice.
The objectives of our studies are to determine the functional importance of AQP5 in fluid homeostasis in the context of whole animal physiology and pathophysiology using an Aqp5 knockout mouse. Using the tools of molecular biology and physiology, we have begun to address specific questions regarding the physiological role of AQP5 in mouse lung, as well as at the cellular and molecular levels. The major research interests in this arena include:
1. The molecular genetic analysis of the AQP5 gene from asthma patients for single nucleotide polymorphisms that may confer asthma susceptibility;
2. The molecular characterization of gene expression profiles and the gene regulatory events which are modified in the context of Aqp5 deletion;
3. The biological impact of these events that function to modulate normal physiological processes.
The insights gained from these studies have the potential to aid in the development of novel genetic and therapeutic resources for preventing and/or treating conditions of fluid dysregulation.