OVERVIEW

There are four areas of research in my lab, which focus on: 1) nitric oxide metabolism, production, and elimination in the lungs, 2) would healing and tissue remodeling in the lungs, 3) pre-vascularization of implantable thick tissues, and 4) 3-D microtissues perfused with human capillaries in a high throughput design. For the studies related to the lungs, our approach is to consider the lung as an integrated whole organ, combining both cellular and whole organ studies as well as both experimental and theoretical techniques. For example, exhaled nitric oxide is a potential useful biomarker of inflammation, yet in order to interpret this signal one must understanding the exchange dynamics at the both the cellular and whole organ level. The cells of the lungs are the source of nitric oxide; thus, one must understand what changes in the local biochemical environment (i.e., inflammatory cytokines) alter these events. For nitric oxide to appear in the exhaled breath, it is advected through the larger airways of the lungs. This involves understanding the fluid mechanics of bifurcating tubes, mass transfer coefficients, and lung mechanics. New mathematical models must be developed to interpret the exhaled nitric oxide signal, and new models have unknown parameters, which must be estimated from experimental measurements. This combined approach to studying the lungs demands many skills, but provides exciting and challenging opportunities in the more general areas of signal processing, heat and mass transfer, parameter estimation, drug delivery, reaction kinetics, and tissue engineering. Below is a more detailed description of the individual projects.

SPECIFIC PROJECTS

Nitric Oxide Metabolism, Production, and Elimination in the Lungs.

Exhaled nitric oxide (NO) is a promising non-invasive tool to assess lung function, particularly in inflammatory diseases such as asthma. Traditional techniques, such as spirometry, are aimed at examining physical features of the lungs, such as airway caliber. In contrast, exhaled NO is derived from the lung tissue, and thus potentially provides important new physiological and clinical information. NO exchange occurs in both the airways and alveolar regions. Therefore, exhaled concentration alone depends strongly on exhalation flow rate and does not adequately reflect the rich features of NO exchange. Our lab utilizes an integrative approach in which cell and molecular data is combined with experiments on the whole organ to develop models of NO metabolism and exchange. We currently have projects that range from utilizing primary human bronchial epithelial cells in which we collect the "exhaled" gas, to experiments in human subjects, to integrative mathematical models. Our central hypothesis is that exhaled NO reflects the underlying biochemical processes of the airway epithelium which is modulated by inflammation.

Two-compartment model, experimental apparatus, exhaled profiles, effect of heliox experiment, effect of heliox theory

(Current Support: NIH R01 HL070645; Investigators: Anna Aledia, Jingjing Jiang, Jennifer Nguyen, Vivien Shi, and Ahrhamazd Tatavoosian)

Wound Healing and Extracellular Matrix Remodeling in the Lungs

Bronchial asthma afflicts more than 10% of the U.S. population, and the incidence and prevalence are on the rise. A critical feature of the disease is structural changes in the wall of the airways, which become more prominent as the disease progresses, and are correlated with disease severity and symptoms. It is not clear whether these changes are a normal response to an abnormal injury, or whether the response itself is abnormal. In addition, there is inadequate information describing the mechanisms of airway remodeling to determine whether the structural changes are reversible. The major changes in the airway wall include mucus cell hyperplasia, subepithelial fibrosis, angiogenesis, and smooth muscle cell hyperplasia. We are developing in vitro models to address all of these features, with a central hypothesis that the bronchial epithelial cell orchestrates and modulates each of these processes. The project combines conventional biological techniques (i.e., RT-PCR) with non-traditional non-invasive optical techniques (multi-photon laser scanning microscopy) utilizing the world class optical imaging facilities at the Beckman Laser Institute (BLI).

tissue model, phenotypic markers, healing wound, multiphoton microscopy wound, multiphoton microscopy fibroblast

(Current Support: NIH R01 HL067954; Investigators: Claire Robertson, Swee Lim, and Jian Zhou)

Pre-vascularizing an Implantable Tissue Construct.

Engineering artificial implantable tissues holds tremendous potential to restore tissue function following injury, illness, or trauma and thus significantly enhance our quality of life. The most successful applications of engineered tissues have been avascular, such as the epidermis of the skin, which are relatively thin and can survive by garnering oxygen and nutrients by passive diffusion. There remains an enormous need for more complex tissues such as cardiac tissue, blood vessels, liver, and skeletal muscle in which transplantation from whole donor organs is severely compromised by the short supply and immune-host response. The complexity of these tissues arises from not only maintaining a unique cellular phenotype, but by the geometric size and shape which precludes delivery of oxygen and nutrients by diffusion. Success in achieving implantable large complex tissues will require new strategies to overcome these mass transfer limitations. To date, strategies have largely relied on the in-growth of new vessels in vivo which limits the size and phenotype of the implantable tissue. Our central hypothesis is that pre-vascularizing a tissue construct prior to implant will enhance the delivery of essential nutrients and thus the physical dimensions of viable tissue following implantation.

prevascularized tissue concept, tissue model schematic, capillaries

(Current Support: Edwards Lifesciences Endowed Professor; Investigators: Lei Tian and Sean White)

3-D microtissues with perfused human capillaries.

Human tissue is three-dimensional, and requires convective transport of nutrients and waste through capillary networks to meet metabolic demands.  Chemical toxins are primarily absorbed through the microcirculation of the skin, lungs, and gastrointestinal tract.  However, there are no three-dimensional in vitro models of human tissue which contain perfused human capillaries.  Our project will create a high throughput platform of 3-D human microtissues (~ 1 mm3) that receive nutrients and eliminate waste products by perfused human capillaries.  Our strategy employs microfabrication technology to create the fluidic channels and pores, but is biology-inspired by mimicking the steps of in-vivo angiogenesis.  The resulting platform will contain > 1,000 microtissues on a single device no larger than 500 cm2, and is ideally suited for high throughput chemical toxicity screening in which > 50 different chemicals or chemical concentrations can be studied simultaneously.   The innovation of the proposal lies in the design strategy which combines microfabrication, microfluidics, optical imaging, and endothelial/stromal cell biology to achieve, for the first time, an in-vitro perfused human capillary bed.  Completion of the project will provide a high-throughput controlled platform to study the human microcirculation with direct application to high throughput chemical toxicity testing, but also a broad range of additional fields including drug discovery, normal and ischemic wound healing, adaptation to exercise, embryogenesis, oncogenesis, cell migration, and tissue engineering.

(Current Support: National Institutes of Health (NIEHS) RC1 ES-018361; Investigators: Lei Tian and Monica Moya)

Last Update:10/09