NPAS2 protein in IPF disease processes may be therapy target
Suppressing production of protein found to ease lung scarring in mice
Suppressing the production of a protein called NPAS2 eased signs of lung scarring (fibrosis) in a mouse model of idiopathic pulmonary fibrosis (IPF), a new study showed.
The NPAS2 gene, which codes for NPAS2, also was found to be more active in the lungs of IPF patients than in those of healthy people. And in cell culture studies, its activity was linked to specific cellular changes in alveolar type 2 (AT2) cells believed to underlie fibrosis in IPF.
Taken together, the findings point to the NPAS2 protein, and the gene of the same name, as potential therapeutic targets for IPF, according to the scientists.
“Our results suggest NPAS2 is a novel target gene … [in] pulmonary fibrosis,” the team wrote.
The study, “Downregulation of a potential therapeutic target NPAS2, regulated by p53, alleviates pulmonary fibrosis by inhibiting epithelial-mesenchymal transition via suppressing HES1,” was published in Cellular Signalling.
NPAS2 gene one of nearly 200 ID’d by researchers in study
In IPF, aberrant wound healing processes in lung tissue lead to the overactivation of myofibroblasts, the main cellular drivers of lung fibrosis. This results in the buildup of collagen and other components of the extracellular matrix (ECM), a network of proteins around cells that gives tissues their structure but also can contribute to tissue fibrosis.
Evidence suggests that loss or dysfunction of AT2 cells might be involved in this process. These stem cell-like cells line the air sacs responsible for gas exchange in the lungs (alveoli), where they are important for wound healing and tissue repair.
Particularly, it is thought that AT2 cells undergo a process called epithelial-mesenchymal transition (EMT), wherein epithelial cells such AT2 and others lining the surface of the lungs gain properties of a different type of cell, called mesenchymal cells.
In IPF, this EMT transition is believed to be a source of cells with myofibroblast-like features, which may contribute to lung fibrosis. Data from IPF animal models have shown that suppressing EMT in AT2 cells can alleviate lung fibrosis.
To identify genes involved in AT2 cell dysfunction or EMT in IPF, a team of scientists in China looked for gene activity differences between the lungs of IPF patients and those of healthy people using two available datasets. The scientists also examined differences in gene activity across the several stages of human AT2 cell maturation.
The results showed nearly 200 genes with significantly different activity between patients and healthy people that also were differentially activated between lung epithelial cells and matured AT2 cells.
A large number of these genes “were associated with ECM structural constituent and organization, which are also important during the process of fibrosis,” the researchers wrote.
Team focused in particular on role played by NPAS2 gene
The team was particularly interested in the potential role of one gene in particular — NPAS2 — whose activity was significantly elevated in the lung tissues of IPF patients relative to that of healthy lungs, but significantly reduced in AT2 cells compared with lung epithelial progenitors.
NPAS2 also was found to be significantly activated in the lungs of a mouse model of IPF.
The gene encodes for the production of a protein of the same name that’s responsible for maintaining circadian rhythms, or the biological changes that happen in 24-hour cycles. NPAS2 is a transcription factor, meaning it can regulate the activity of other genes, and it has been found to regulate genes associated with fibrosis.
These results suggested that NPAS2 was a contributor to IPF development and progression and a suppressor of AT2 cell maturation.
“NPAS2 might be involved in lung fibrosis through its functions in [AT2] cells,” the researchers wrote.
To test that, the team turned to cellular models of IPF, in which lab-grown human and mouse AT2 cells were exposed to a toxic chemical called bleomycin.
When the researchers silenced the NPAS2 gene in these cells — meaning they suppressed NPAS2 production — markers of EMT were reduced. This was found to be associated with NPAS2-induced increased activity of HES1, a gene linked to fibrosis.
Additional experiments indicated that the NPAS2 gene is activated by p53, a protein that has previously been found to promote fibrosis in animal models. A blockade of TP53, the gene coding for p53, suppressed EMT in the cellular models. This inhibitory effect was weakened when NPAS2 activity was boosted.
Altogether, these findings indicate that “NPAS2 is a novel downstream [target] of p53 in regulating EMT in [AT2] cells and pulmonary fibrosis,” the team wrote.
Given these data, the scientists hypothesized that suppressing NPAS2 production in the lungs of an IPF mouse model would reduce EMT and help to ease fibrosis. Indeed, NPAS2 silencing led to reductions in EMT markers, levels of collagen, a major ECM molecule, and overall lung fibrosis.
“Our studies shed light on revealing the role of NPAS2 in EMT in [AT2] cells and pulmonary fibrosis,” the researchers wrote, adding that suppressors of NPAS2 “will likely be used clinically to improve diseases in the future, including pulmonary fibrosis.”