We use novel animal (mouse) models, cultured cells, and human samples to tease out pathways and mediators involved in these processes. There are a number of interrelated projects currently focused on the following themes:
1. Novel Models and Mechanisms of Lung Fibrosis
Mutations in some genes of the surfactant system have been associated with inherited forms of pulmonary fibrosis. We have shown that alterations in the proSP-C sequence that result in either misfolding or mistargeting of SP-C induce ER retention or formation of intracellular aggregates. Coincident with these observations, interstitial lung disease (ILD) in association with over 50 different heterozygous mutations in the SFTPC gene The majority of mutations fall into 2 domains
Aggregation prone mutants those with a structural homology with a protein associated with familial Alzheimer-like dementia (termed BRI domain)
Mutants which are mistrafficked away from the lamellar body
We are using these "rare" genetic variants to understand the broader question of how lung fibrosis develops and progresses in sporadic (non-inherited) forms of the disease. Using Surfactant Protein C (SP-C) as a model substrate, we are characterizing the mechanisms underlying the development of epithelial cellular dysfunction and relating these back to the development of pulmonary fibrosis in vivo using primary human cells and mice expressing disease causing SP-C mutations.
2. Epithelial Cell Dysfunction in the Pathogenesis of Pulmonary Fibrosis
In addition to disease causing variants in the SFTPC gene, we have explored the effects of mutations in other surfactant components (SP-A; ABCA3) as well as studied other monogenetic diseases that specifically affect lung epithelial cell function and have been associated with the development of pulmonary fibrosis. One such disease is Hermansky-Pudlak Syndrome (HPS). In an ongoing collaboration with Dr. Susan Guttentag at Vanderbilt Children’s Hospital (Nashville, TN), mechanistic link(s) between the gene defects of HPS and chronic inflammation/fibrosis in the lung are being studied. Current studies are directed at metabolic re-programming, alterations in macroautophagy and defective proteostasis as drivers of the dysfunctional AT2 phenotype.
3. The Role of Inflammatory Effector cells in Lung Injury / Repair
The phenotype of the mutant SFTPC mouse models includes an early inflammatory phase. Using high resolution techniques (FACS, RNAseq, etc) we are characterizing the role of the these effector cells and the signaling pathways that drive their recruitment to understand the pathogenesis of pulmonary fibrosis.
4. Alveolar Type 2 Cell Quality Control in Health and Disease
Cells utilize a variety of mechanisms and organelles to assure proper synthesis of correctly folded proteins. We are characterizing these "quality control " mechanisms in alveolar type 2 cellsusing “SFTPC BRICHOS mutations” as substrates. These proteins can induce induce cell dysfunction Figure 3 including formation of protein aggregates, generation of inflammation, and induction of apoptosis.
5. Biosynthetic Pathways for Surfactant Components
In a project spanning 20 years, we have been defining the cellular metabolism of pulmonary surfactant components including all 4 surfactant proteins with with a current emphasis on Surfactant Protein C and the regulation of its intracellular trafficking through its interactions with chaperones and the E3 ubiquitin ligase Nedd4-2.
[See Figure 1]
6. Biosynthesis and Function of ABCA3 in Health and Disease
The ATP-binding cassette transporter ABCA3 is a member of the ABC superfamily of transporters that function in the translocation of substrates across cell membranes. Predominantly localized in the limiting membrane of the lamellar bodies of lung alveolar type II cells, ABCA3 is believed to function as a lipid and phospholipid transporter. Recently, ABCA3 has received considerable attention because mutations in the gene are associated with various lung disorders including fatal surfactant deficiency and respiratory distress syndrome (RDS) in newborns and interstitial lung disease (ILD) in older children and adults. Our studies are focused both on the functional aspects of ABCA3 as a transporter and on the cellular responses and consequences in cellular and pulmonary homeostasis as a result of expressing mutant isoforms of ABCA3. The overall objective of this project program is to use both integrative and reductionist approaches to facilitate an understanding of the molecular mechanisms underlying ABCA3 biosynthesis, and to elucidate the consequences of expression of mutant isoforms of ABCA3 proteins associated with RDS and ILD. For more information please see Surafel Mulugeta, PhD.