Current Projects

+Fungal Pathogenesis and Mucosal Immunology

Fungal diseases cause a tremendous burden of morbidity and mortality in humans. Invasive fungal infections account for more than one million deaths annually, and more than half of the deaths in patients with HIV/AIDS. The burden of fungal infections has been increasing as immunomodulatory therapies are increasingly used in the treatment of cancer, rheumatologic disease, solid organ transplant, and bone marrow transplant. Invasive fungal infections, such as invasive aspergillosis, are being increasingly reported in otherwise normal hosts following primary Influenza A or Influenza B infections. Furthermore, fungal infections are being recognized as driving significant morbidity through non-invasive infections and chronic colonization. Aspergillus fumigatus is a ubiquitous saprophytic fungus capable of causing a wide range of human pulmonary diseases including invasive aspergillosis, chronic aspergillosis, and allergic bronchopulmonary aspergillosis (ABPA). In patients with abnormal airways, Aspergillus can lead to the decline of lung function decline and death. This problem is particularly common in cystic fibrosis (CF) patients, in whom almost 50% are affected by Aspergillus colonization or infection. The determinants contributing to the development of different clinical presentations in response to Aspergillus infection remains poorly understood.

The innate immune system plays a critical role in controlling fungal infections through early recognition of fungal epitopes leading to pathogen phagocytosis, immune recruitment, and pathogen clearance. To better understand how phagocytic trafficking contributes to the response to fungal diseases, we developed a fluorescent method to tracking division of Candida glabrata yeast in macrophages (Front Immunology, 2018). C. glabrata causes invasive blood stream infections in both immunosuppressed and acutely ill human hosts. We applied this carboxyfluorescein succinimidyl ester (CFSE) labeling strategy to identify the role of spleen tyrosine kinase (Syk) phosphorylation in C. glabrata control by macrophages. For patients who develop invasive fungal infections, therapeutic options are limited and resistance to the available antibiotics has emerged. While much of our research is focused on discovering immunomodulatory strategies to combat or prevent infection, we are also trying to identify compounds that are either new antifungal agents or may potentiate known antibiotics. We reported that the widely used biguanide medication, metformin, potentiates the activity of antifungal agents against C. glabrata (Virulence, 2018)

When infectious fungal spores are inhaled, the airway epithelium becomes the first point of contact in the host lungs. Increasingly, the airway epithelium is being recognized as an immunologically active tissue that contributes to cytokine production, innate immune cell recruitment, and possibly pathogen phagocytosis and sequestration. Epithelial derangements in patients with CF contribute to the establishment of chronic infections, while also leading to neutrophilic mucus production and airway destruction. In the case of Aspergillus spp, it has been proposed that phagocytosis of inhaled spores by airway epithelial cells may protect the fungus from clearance by macrophages and neutrophils, thereby promoting infection. I recently reviewed the role of professional phagocytes, as well as non-professional phagocytes, including the airway epithelium, in response to fungal infections (Sem Cell Dev Biol, 2018).

+Airway Stem Cell Biology

Goblet cell hyperplasia and overproduction of mucus features in many human respiratory diseases including CF, ABPA and infections, chronic obstructive pulmonary disease and asthma. The overproduction of mucous impairs mucociliary clearance, causing retention of pathogens, allergens, and toxic particles. Inflammatory mediators released from goblet cells may act in an autocrine and paracrine manner, further enhancing inflammation in diseases and complex repair processes leading to persist airway remodeling. Indeed, the progression of airway diseases and decline in lung function is positively associated with the accumulation of inflammatory mucous and airflow obstruction. Several signaling pathways have been identified as important regulators of goblet cell differentiation such as the NOTCH signaling pathway and the epidermal growth factor (EGF) cascade. Recent studies have also linked the relevance of the GABAergic system to asthma and mucous production. In this context, c-aminobutyric acid (GABA) is secreted from pulmonary neuroendocrine cells (PNECs) in the lung and act on airway epithelial cells through the subtype A GABA receptor (GABAAR). The action of this autocrine-paracrine GABAergic system in the airway epithelial cells is essential to induce goblet cell hyperplasia in allergen-challenged mice and humans affected with asthma. In my first-author publication in the American Journal of Respiratory Cell and Molecular Biology, we identify transforming growth factor (TGF)-β superfamily canonical SMAD signaling as a critical pathway controlling goblet cell differentiation. BMP/TGF-β/SMAD signaling is exceptionally versatile and has been implicated in orchestrating multiple biological functions including organ development, tissue homeostasis, and injury repair. Previously, we reported that BMP and TGF-β signaling balances stem cell proliferation and differentiation in airway epithelium and in epithelia at large. We observed that the degree of SMAD signaling activation is associated with epithelial maturity. Suppression of BMP and TGF-β signaling activity is essential for maintaining p63+ basal cell stemness by impeding epithelial differentiation. Dual SMAD signaling inhibition can be deployed in cell culture in vitro to achieve prolonged expansion of murine and human cells, while maintaining their ability to differentiate into functional tissues. We demonstrate that although mucin-secreting goblet cells are post-mitotic differentiated cells, the SMAD signaling activity is largely suppressed. SMAD signaling inhibition markedly amplifies goblet cell hyperplasia induced by inflammatory mediators, whereas its activation restricts its production and facilitates its resolution. Furthermore, the inhibitory effects on goblet cell generation imposed by GABAergic system inhibitors can be overcome by SMAD signaling inhibition suggesting a functional relationship of these two pathways that are critical for goblet cell differentiation and regulation. Our data not only demonstrate the essential role of SMAD signaling pathway in regulating goblet cell fate determination, but also may lead to new therapeutic strategies for the management of allergic diseases.