miRNA-mediated gene regulation in lung development and homeostasis:
The long-term goal of my laboratory is to understand the gene regulatory networks required for proper lung development and homeostasis, focusing on the miRNA pathway. Characterizations of the expression, modification and functions of miRNAs and protein components of the miRNA pathway during lung development, and in response to injuries and stresses that are associated with pulmonary disorders, will potentially reveal novel mechanisms of lung formation and diseases. Ongoing analyses of function and targets of miRNAs have revealed a number of candidate networks potentially relevant to lung development and diseases, such as pulmonary fibrosis and hypertension. Investigation of the expression and function of Tnrc6 family members have revealed unexpected insights in the posttranscriptional regulation in ciliated cells of airway.
Jining Lu, Ph.D
Assistant Professor of Medical Sciences (in Medicine)
Tnrc6 gene family members in ciliogenesis
Ciliary defects in the respiratory tract caused by genetic mutations or pathological conditions, such as viral infection, often lead to secondary bacterial infection that is particularly problematic for infants or adults with other conditions. Despite recent advances, knowledge of mechanisms regulating proper differentiation or maintenance of ciliated cells is still limited. Trinucleotide repeats containing 6 (Tnrc6) family members are key components of miRNA-induced silencing complex (miRISC), which is required for miRNA-mediated gene silencing. Three paralogs have been described in human and mouse: Tnrc6a, also known as GW182 (because of its molecular weight and the presence of glycine (G) and tryptophan (W) repeats), Tnrc6b and Tnrc6c. Tnrc6 functions as a critical linker between Argonaute proteins (Agos) and the machinery for mRNAs degradation within the miRISC. In preliminary studies, we found selective enriched expression of Tnrc6a and Tnrc6b and the presence of a large number of centrosome-associated GW/P bodies in ciliated cells of the developing and adult murine airways. Currently, we are investigating their roles in airway epithelial cell differentiation using genetically modified mice. We are also studying potential specific miRNA pathway that depends on high levels of Tnrc6 family members in ciliated cells.
miR-449/34 and miR-92b in the ciliogenesis of airway epithelium
We have been collaborated with Dr. Cardoso’s group to identify miRNAs that are specifically enriched in different cell types of developing airways. We carried out miRNA array profiling for lungs from mice in which the Notch pathway is selectively disrupted in endoderm and the airways are overpopulated with ciliated and neuroendocrine cells. This allowed us to identify miRNAs specifically enriched ciliated cells, such as miR-449/34 and miR-92b. In this project, we will use both ex vivo and in vivo approaches to investigate their roles and responsible targets in ciliogenesis of airway epithelium.
Disruption of the miRNA pathway by respiratory syncytial virus (RSV) infection
Infection by respiratory virus, such as RSV leads to loss of cilia and ciliated cells in human airways or in lungs of animal models or in ex vivo cultured bronchial epithelial cells. Little is known about the mechanisms of RSV infection-induced loss of cilia or ciliated cells. In high plants or insects, the miRNA pathway is an important host-defense mechanism against viral infection. To disable this defense system, GW repeat domains of viral proteins were shown to hook Argonautes (Agos) to disrupt its activity in miRNA-mediated gene silencing. Since cellular GW repeats-containing proteins, such as Tnrc6 are important for miRNA activity by associating with Ago, these finding suggest that virus may use of GW mimicry to compete for and inhibit Ago activity. In this project, we will test the hypothesis that disruption of the Ago and Tnrc6 interaction within miRISC by RSV coding protein leads to defective cilia or ciliated cells.
miR-29 in pulmonary fibrosis
We have identified a number of miRNAs whose levels are altered in a bleomycin-induced pulmonary fibrosis model by Next Generation of Sequencing. Expression of miR-29 is reduced in association with the development of fibrosis in this mouse model, and its expression is suppressed by fibrotic growth factors or inflammatory cytokines in cultured cells in vitro. Moreover, endogenous miR-29 controls the expression of a large number of genes associated with extracellular matrix, indicating a critical role in modulating fibrotic responses. Currently, we are characterizing the lung phenotype of miR-29 null mice and investigating the role of miR-29 in pulmonary fibrosis in lung injury model.