Idiopathic pulmonary fibrosis (IPF) is a progressive, life-threatening, interstitial lung disease of unknown etiology. The median survival of patients with IPF is only 2 to 3 years, yet some patients live much longer. Respiratory failure resulting from disease progression is the most frequent cause of death. To date we have limited information as to predictors of mortality in patients with IPF, and research in this area has failed to yield prediction models that can be reliably used in clinical practice to predict individual risk of mortality. The goal of this concise clinical review is to examine and summarize the current data on the clinical course, individual predictors of survival, and proposed clinical prediction models in IPF. Finally, we will discuss challenges and future directions related to predicting survival in IPF.

The GAP models use commonly measured clinical and physiologic variables to predict mortality in patients with IPF.

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Idiopathic pulmonary fibrosis is a chronic fibrotic lung disease of unknown cause that occurs in adults and has a poor prognosis. Its epidemiology has been difficult to study because of its rarity and evolution in diagnostic and coding practices. Though uncommon, it is likely underappreciated both in terms of its occurrence (ie, incidence, prevalence) and public health impact (ie, health care costs and resource utilization). Incidence and mortality appear to be on the rise, and prevalence is expected to increase with the aging population. Potential risk factors include occupational and environmental exposures, tobacco smoking, gastroesophageal reflux, and genetic factors. An accurate understanding of its epidemiology is important, especially as novel therapies are emerging.

SUMMARY Background Patients with hypersensitivity pneumonitis (HP) may develop lung fibrosis, which is associated with reduced survival. Families with pulmonary fibrosis can present with members diagnosed with idiopathic pulmonary fibrosis (IPF) or chronic HP (cHP), suggesting that fibrotic HP may share risk factors with IPF. Methods In an observational study of two independent cohorts of patients with cHP (UCSF n=145, UTSW n=72), we measured two common single nucleotide polymorphisms associated with IPF (MUC5B rs35705950 & TOLLIP rs5743890) and peripheral blood leukocyte telomere length and evaluated their associations with cHP disease, survival, and clinical-radiograph-pathologic features. Findings The frequency of the MUC5B minor allele, but not the TOLLIP minor allele, was significantly increased in cHP patients in both cohorts (UCSF MAF 24.4% & UTSW MAF 32.3%) compared to healthy controls (MAF 10.7%; p-values for comparison = <0.0001 for both cohorts) and similar to IPF (UCSF MAF 33.3% & UTSW MAF 32.0%, p-values for comparison=0.10 & 0.95, respectively). The MUC5B minor allele (adjusted OR 1.91, p=0.045) and shorter telomere length (adjusted OR 0.23, p=0.002) were associated with extent of radiographic fibrosis and other measures of lung remodeling and fibrosis in the combined cHP cohorts. Shorter telomere length had a significant association (adjusted HR 0.18, p=0.001) with reduced survival in the combined cHP cohorts. Interpretation The MUC5B promoter polymorphism rs35705950 and shorter telomere length are associated with extent of fibrosis in cHP. Shorter telomere length is associated with histopathology findings typical of usual interstitial pneumonia and reduced survival in cHP. Funding NIH grants KL2TR001870, T32HL098040, UL1TR001105, R01HL093096, and the Nina Ireland Program for Lung Health.

Vesicular monoamine transporters (VMATs) mediate the transport of dopamine (DA), serotonin (5HT), and other monoamines into secretory vesicles. The regulation of mammalian VMAT and the related vesicular acetylcholine transporter (VAChT) has been proposed to involve membrane trafficking, but the mechanisms remain unclear. To facilitate a genetic analysis of vesicular transporter function and regulation, we have cloned the Drosophila homolog of the vesicular monoamine transporter (dVMAT). We identify two mRNA splice variants (DVMAT-A and B) that differ at their C-terminus, the domain responsible for endocytosis of mammalian VMAT and VAChT. DVMAT-A contains trafficking motifs conserved in mammals but not C. elegans, and internalization assays indicate that the DVMAT-A C-terminus is involved in endocytosis. DVMAT-B contains a divergent C-terminal domain and is less efficiently internalized from the cell surface. Using in vitro transport assays, we show that DVMAT-A recognizes DA, 5HT, octopamine, tyramine, and histamine as substrates, and similar to mammalian VMAT homologs, is inhibited by the drug reserpine and the environmental toxins 2,2,4,5,6-pentachlorobiphenyl and heptachlor. We have developed a specific antiserum to DVMAT-A, and find that it localizes to dopaminergic and serotonergic neurons as well as octopaminergic, type II terminals at the neuromuscular junction. Surprisingly, DVMAT-A is co-expressed at type II terminals with the Drosophila vesicular glutamate transporter. Our data suggest that DVMAT-A functions as a vesicular transporter for DA, 5HT, and octopamine in vivo, and will provide a powerful invertebrate model for the study of transporter trafficking and regulation.

This consensus-based approach for the diagnosis of cHP represents a first step towards the development of international guidelines for the diagnosis of cHP.