Charlotte Nejad, Postgraduate Student, Centre for Innate Immunity and Infectious Diseases, Hudson Institute of Medical Research, Clayton, Australia
Charlotte received her Master of Science (M.Sc.) in Pharmaceutical Bioprocess Engineering from the Technical University in Munich, Germany at the end of 2014. Following this, Charlotte joined the laboratory of Dr. Michael Gantier at the Hudson Institute of Medical Research, Australia to pursue her postgraduate studies.
Charlotte’s Ph.D. investigates the modulation of microRNA function by immune responses, with a specific focus on the control of microRNA stability and its consequence for the use of microRNAs as biomarkers.
Her work, currently under consideration for publication, highlights a novel effect of type-I IFN on the stability of long microRNA isoforms. As such, type-I IFN stimulation promotes the sequence-specific decrease of select microRNA isoforms. These findings establish that microRNA variants can be dynamically regulated, thereby increasing the breadth of microRNA potentially used as biomarkers in disease contexts.
Charlotte was awarded a Young Investigator Award from the Victorian Infection and Immunity Network (VIIN) in 2016 and she was presented an award for best postgraduate presentation by the Australian Society of Medical Research (ASMR) in recognition of this work.
Abstract from Young Investigator Awards Session Presentation at Cytokines 2017 in Kanazawa, Japan:
Innate immune activation by pathogens promotes global transcriptional changes in infected cells, promptly affecting the levels of messenger RNAs (mRNAs) and non-coding RNAs such as microRNAs (miRNAs). As such, induced miRNAs cause rapid down regulation of mRNA targets, thereby controlling the duration and intensity of the immune response. Interestingly, there is evidence that upon type-I interferon (IFN) stimulation select miRNAs can be actively degraded, including the pro-inflammatory miR-221 and miR-222. However, the impact of these decreased miRNAs on IFN responses is currently not known.
In this work, we initially observed by RT-qPCR that the levels of miR-221, and not that of the co-expressed miR-222, were decrease by >80% following Toll-like receptor (TLR) 3/4 stimulation, but not that of other TLRs. This specific decrease of miR-221 was type-I IFN dependent, and ablated in IFN-α/β receptor 1 deficient bone marrow-derived macrophages (BMDMs). Unexpectedly, miR-221 decrease was restricted to its longer isoforms, a phenomenon also observed for miR-222. RNA sequencing (RNAseq) carried out on human fibroblasts treated with type-I IFN confirmed these observations, identifying a group of other miRNAs for which the longer isoforms were similarly impacted. Significantly, we identified a core motif in these miRNAs directly regulating their stability, upon IFN-β stimulation, which can be attributed to the exoribonuclease Pnpt1. In addition, the RNAseq data revealed an overall decrease >70% of miR-222 molecules with IFN-β.
Collectively, these findings suggest that sequence and length-dependent miRNA degradation helps control the overall abundance of miR-221/222, and their pro-inflammatory function during type-I IFN responses.