Compartmentalized, functional role of angiogenin during rickettsioses: Evidence of possible mediation by host tRNAderived small noncoding RNAs
University of Texas Medical Branch at Galveston, USA
Dr. Bin Gong has completed his MD and Ph.D. at the age of 29 years from the Second Military Medical College in Shanghai, China and Postdoctoral studies at the University of Texas Medical Branch at Galveston. He is an Assistant Professor in the Dept of Pathology and theDirector of Experimental Pathology and sncRNAomicscore at the Galveston National Laboratory at the UTMB. He has published more than 25 papers and has been serving as an editorial board member of reputed journals.
Microvascular endothelial barrier dysfunction is the central enigma in rickettsioses. Angiogenin (ANG) is one of the earliest identified angiogenic factors, of which some are relevant to the phosphorylation of VE-cadherins that serve as endothelial adherens proteins. Besides its nuclear role, ANG is thought to play a cytoplasmic role, owing to its RNase activity that cleaves tRNA to produce small RNAs. Recently, such tRNA-derived RNA fragments (tRFs) have been shown to be induced under stress conditions. All these observations raise an intriguing hypothesis about a novel cytoplasmic role of ANG, which is induced upon infection with Rickettsia and generates tRFs that may play roles in rickettsioses. C3H/HeN mice were infected intravenously with a sublethal dose of R. conoriifor IFstudies of R. and ANG.HUVEC cells were infected with R. conorii before incubation with 1microgm/ml ANG. HUVEC samples were subjected to IF, exogenous ANG translocation, endothelial permeability, and immunoprecipitation phosphorylation assays. To identify small non-coding RNAs (sncRNAs) upon rickettsial infection, RNAs from pulverized mouse lung tissues and HUVECs were subjected to library preparation and deep sequencing analysis using an Illumina 2000 instrument. Identified sncRNAs were confirmed by Northern hybridization, and their target mRNAs were predicted in silico using BLAST and RNAhybrid programs. We have demonstrated endothelial up-regulation of ANG, co-localized with rickettsial infection in vivo. We also have provided direct evidence that rickettsial infection sensitizes HUVECs to the translocation of exogenous ANG in a compartmentalized pattern at different times post-infection. Typically, exogenous ANG translocates into the nucleus at 24 hrs and to the cytoplasm at 72 hrs post-infection. The ANG cytoplasmic translocation enhances phosphorylation and destabilization of VE-cadherin and attenuates endothelial barrier function. Of note, deep sequencing analysis detected tRFs, mostly derived from the 5'-halves of host tRNAs, that are induced by ANG. Northern hybridization validates the two most abundantly cloned tRFs derived from tRNA-ValGTG and tRNA-GlyGCC, in both mouse tissues and human cells. Bioinformatics analysis predicted that these tRFs may interact with transcripts associated with the endothelial barrier, the host cell inflammatory response, and autophagy. Our data provide new insight into the role of compartmentalized ANG during SFG rickettsioses, and highlight its possible mediation through tRFs.
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