Description of Research Expertise

General Scientific Interests
Airway cell biology and physiology, Extra-oral taste receptors, Regulation of motile cilia in the airway, Epithelial ion transport and fluid secretion, Bicarbonate secretion and intracellular pH regulation, Epithelial innate immunity, Live cell imaging of signal transduction using indicator dyes and fluorescent protein biosensors

Keywords: signal transduction, chronic rhinosinusitis, cystic fibrosis, allergy, live cell imaging, calcium signaling, nitric oxide signaling, cAMP signaling, cGMP signaling, antimicrobial peptides, g protein-coupled receptors

Description of Research
We study the physiology of the epithelial cells lining the upper airway (nose and sinuses) and the lower airway (lung) to understand how they sense and respond to pathogens. We combine biochemistry and molecular biology with real-time optical measurements of airway cell signaling and associated physiological responses, including ciliary beating, calcium signaling, fluid secretion, ion transport, nitric oxide production, and antimicrobial peptide secretion. Our goal is to better understand the cellular and molecular bases of airway diseases to identify novel molecular targets for new therapies.

There are two major diseases we focus on. The first is chronic rhinosinusitis (CRS), which affects 8-10% of the US population with direct healthcare costs of over 6 billion dollars annually. CRS has a major impact on individual quality of life as well as on public health; CRS accounts for 1 out of every 5 antibiotic prescriptions in adults in the US, making its treatment a major contributor to the emergence of antibiotic-resistant organisms. A continuing goal of our research is to identify new and better therapies to treat CRS and other airway diseases without the use of antibiotics, particularly through the stimulation of endogenous innate immune pathways. We also focus on cystic fibrosis (CF), the most common lethal genetic recessive disease in the US characterized by defective mucociliary transport due to altered ion transport and fluid secretion. CF is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) ion channel. Our goal is to better understand the molecular basis of CF and identify novel targets to restore or enhance airway function.

The close partnership we have with physicians at the Hospital of the University of Pennsylvania and the Philadelphia VA Medical Center allows ideas generated in our lab to be directly tested or evaluated in a real clinical setting, giving our research high translational potential.

Specific Areas of Focus
Regulation of Mucociliary Clearance: The primary physical defense of the airway is mucociliary clearance. Inhaled bacteria and viruses are trapped by mucus secreted by airway epithelial cells. Motile cilia line the airway, and coordinated ciliary beating transports debris-laden mucus from the respiratory passages toward the pharynx (throat), where it is cleared by swallowing or expectoration. Efficient mucociliary clearance requires the proper regulation of ciliary beating as well as mucus secretion and fluid homeostasis. When mucociliary clearance is not enough, it is complemented by the secretion of antimicrobial peptides and the generation of reactive oxygen and nitrogen species (ROS/RNS) that have direct antibacterial and antiviral effects.

These mechanisms are tightly regulated by G protein-coupled receptors (GPCRs) that respond to host and environmental cues. Our goal is to understand the basic science of airway epithelial cell GPCR signaling pathways and the receptors that activate them.

Role of Taste Receptors in Motile Cilia: How do airway epithelial cells detect the presence of invading pathogens? We recently discovered that this occurs partly through T2R bitter “taste” receptors in the cilia of epithelial cells in the nose and sinuses. T2Rs are G-protein–coupled receptors originally identified in type II taste cells of the tongue, where they function to protect against the ingestion of harmful compounds, including toxic bacterial products. One specific bitter taste receptor, T2R38, detects quorum-sensing compounds from invading bacteria and stimulates a nitric oxide-mediated innate immune defense response. Our observations suggest that bitter taste receptors are an “early warning” arm of airway innate immunity, activating responses within seconds to minutes of sensing these bitter bacterial products.

Because T2Rs have a uniquely high density of naturally-occurring, well-characterized genetic variants (polymorphisms) which underlie the complex individual variations in human taste preferences, we hypothesize that individual genetic differences in T2Rs may create variation in how efficiently airway cells from different individuals “sense” bacteria and contribute to varying susceptibility to respiratory infections.

Sweet Taste Receptor in Airway Physiology: Sweet taste (T1R) receptors are expressed in specialized solitary chemosensory cells in the sinonasal epithelium, where they inhibit innate defense responses stimulated by T2R bitter receptors. These receptors are activated by glucose in airway surface liquid as well as D-amino acids secreted by bacteria.

The sweet receptor in the nose may have important clinical relevance for CRS in patients with diabetes mellitus. Increased blood glucose levels are known to increase airway mucus glucose levels. CRS patients also have elevated nasal mucus glucose, likely due to increased leak from damage to their epithelial tissues as a result of chronic infection and inflammation. Diabetics are more prone to airway infections than non-diabetics, and this may potentially be due to higher nasal mucus glucose that overly-inhibits the airway solitary chemosensory cell defensive response.

Airway Submucosal Gland Bicarbonate Secretion: We also use optical methods to study fluid secretion, driven by chloride and bicarbonate transport, from living primary submucosal gland serous acinar cells. Our major focus is on defects in bicarbonate secretion due to defective CFTR ion channel

Potential Graduate Student Rotation Projects
Interested students should contact Rob to discuss a potential rotation project, which can be individually designed to fit the student’s interests within the context of active projects in the lab. Some example projects could be
1) Determining how inflammation and/or infection affects airway taste receptor expression
2) Examining the effects of hyperglycemia on airway cell physiology and innate immune mechanisms
3) Determining the signal transduction mechanism(s) and function(s) of chemosensory receptors within motile cilia
4) Examining if taste receptors regulate airway epithelial ion transport and/or fluid secretion
5) Elucidating mechanisms of nitric oxide generation by sinonasal epithelial cells in response to pathogens

Selected Publications

Miller ZA, Mueller A, Kim TB, Jolivert JF, Ma RZ, Muthuswami S, Park A, McMahon DB, Nead KT, Carey RM, Lee RJ.: Lidocaine Induces Apoptosis in Head and Neck Squamous Carcinoma Cells Through Activation of Bitter Taste Receptor T2R14 Cell Reports : 2023.

Kouakou YI and Lee RJ: Interkingdom detection of bacterial quorum sensing molecules by mammalian taste receptors Microorganisms 11 (5): 1295,2023.

Carey RM, Adappa ND, Palmer JN, Cohen NA, Lee RJ: Loss of CFTR Function Is Associated With Reduced Bitter Taste Receptor-Stimulated Nitric Oxide Innate Immune Responses in Nasal Epithelial Cells and Macrophages Frontiers in Immunology 14 : 1096242,2023.

McMahon DB, Jolivert JF, Kuek LE, Adappa ND, Palmer JN, Lee RJ: Savory Signaling: T1R Umami Receptor Modulates Endoplasmic Reticulum Calcium Store Content and Release Dynamics in Airway Epithelial Cells Nutrients 15 (3): 493,2023.

Carey RM, McMahon DB, Miller ZA, Kim TB, Rajasekaran K, Gopallawa I, Newman JG, Basu D, Nead KT, White EA, Lee RJ: T2R Bitter Taste Receptors Regulate Apoptosis and May Be Associated with Survival in Head and Neck Squamous Cell Carcinoma Molecular Oncology 16 (7): 1474-1492,2022.

Kuek LE, McMahon DB, Ma Z, Miller ZA, Jolivert JF, Adappa ND, Palmer JN, and Lee RJ: Cilia Stimulatory and Antibacterial Activities of T2R Bitter Taste Receptor Agonist Diphenhydramine: Insights Into Repurposing Bitter Drugs for Nasal Infections Pharmaceuticals 15 (4): 452,2022.

McMahon DB, Kuek LE, Johnson ME, Johnson PO, Horn RLJ, Carey RM, Adappa ND, Palmer JN, and Lee RJ: The Bitter End: T2R Bitter Receptor Agonists Elevate Nuclear Calcium and Induce Apoptosis in Non-Ciliated Airway Epithelial Cells Cell Calcium 101 : 102499,2022.

McMahon DB, Carey RM, Kohanski MA, Adappa ND, Palmer JN, and Lee RJ: PAR-2-activated secretion by airway gland serous cells: role for CFTR and inhibition by Pseudomonas aeruginosa American Journal of Physiology-Lung Cellular and Molecular Physiology 320 (5): L845-L879,2021.

Gopallawa I, Freund JR, and Lee RJ: Bitter Taste Receptors Stimulate Phagocytosis in Human Macrophages Through Calcium, Nitric Oxide, and Cyclic-GMP Signaling Cellular and Molecular Life Sciences 78 (1): 271-286,2021.

Kuek L, and Lee RJ: First Contact: The Role of Respiratory Cilia in Host-Pathogen Interactions in the Airways American Journal of Physiology-Lung Cellular and Molecular Physiology 319 (4): L603-L619,2020.

Academic Contact Information

Location:
Stellar-Chance Laboratories M13 (lab) and M8 (office)
Mailing Address:
UPHS, Department of ORL-HNS
3400 Spruce Street, 5 Ravdin Suite A
Philadelphia, PA 19104
Phone: 215-573-9766