Copyright ©The Author(s) 2015. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Exp Med. Aug 20, 2015; 5(3): 164-181
Published online Aug 20, 2015. doi: 10.5493/wjem.v5.i3.164
Use of siRNA molecular beacons to detect and attenuate mycobacterial infection in macrophages
Remo George, Renata Cavalcante, Celso Carvalho Jr, Elyana Marques, Jonathan B Waugh, M Tino Unlap
Remo George, Renata Cavalcante, Celso Carvalho Jr, Elyana Marques, Jonathan B Waugh, M Tino Unlap, Center for Teaching and Learning and the Department of Clinical and Diagnostic Sciences, University of Alabama at Birmingham, Birmingham, AL 35294-1212, United States
Author contributions: George R, Cavalcante R, Carvalho Jr C, Marques E, Waugh JB and Unlap MT equally contributed to this work; George R, Waugh JB and Unlap MT designed the research; George R, Cavalcante R, Carvalho Jr C, Marques E and Unlap MT performed the research; Waugh JB and Unlap MT analyzed the data; George R, Waugh JB and Unlap MT wrote the paper.
Conflict-of-interest statement: The authors have no conflict of interest to report.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:
Correspondence to: Jonathan B Waugh, PhD, Professor and Director, Department of Clinical and Diagnostic Sciences, University of Alabama at Birmingham, 1705 University Blvd., Birmingham, AL 35294-1212, United States.
Telephone: +1-205-9758344 Fax: +1-205-9757302
Received: February 26, 2015
Peer-review started: February 26, 2015
First decision: April 27, 2015
Revised: May 21, 2015
Accepted: June 9, 2015
Article in press: June 11, 2015
Published online: August 20, 2015

Tuberculosis is one of the leading infectious diseases plaguing mankind and is mediated by the facultative pathogen, Mycobacterium tuberculosis (MTB). Once the pathogen enters the body, it subverts the host immune defenses and thrives for extended periods of time within the host macrophages in the lung granulomas, a condition called latent tuberculosis (LTB). Persons with LTB are prone to reactivation of the disease when the body’s immunity is compromised. Currently there are no reliable and effective diagnosis and treatment options for LTB, which necessitates new research in this area. The mycobacterial proteins and genes mediating the adaptive responses inside the macrophage is largely yet to be determined. Recently, it has been shown that the mce operon genes are critical for host cell invasion by the mycobacterium and for establishing a persistent infection in both in vitro and in mouse models of tuberculosis. The YrbE and Mce proteins which are encoded by the MTB mce operons display high degrees of homology to the permeases and the surface binding protein of the ABC transports, respectively. Similarities in structure and cell surface location impute a role in cell invasion at cholesterol rich regions and immunomodulation. The mce4 operon is also thought to encode a cholesterol transport system that enables the mycobacterium to derive both energy and carbon from the host membrane lipids and possibly generating virulence mediating metabolites, thus enabling the bacteria in its long term survival within the granuloma. Various deletion mutation studies involving individual or whole mce operon genes have shown to be conferring varying degrees of attenuation of infectivity or at times hypervirulence to the host MTB, with the deletion of mce4A operon gene conferring the greatest degree of attenuation of virulence. Antisense technology using synthetic siRNAs has been used in knocking down genes in bacteria and over the years this has evolved into a powerful tool for elucidating the roles of various genes mediating infectivity and survival in mycobacteria. Molecular beacons are a newer class of antisense RNA tagged with a fluorophore/quencher pair and their use for in vivo detection and knockdown of mRNA is rapidly gaining popularity.

Keywords: Mammalian cell entry, Molecular beacons, siRNA, Mycobacterium tuberculosis, Macrophages

Core tip: This review paper looks at the current status of research of the role of mammalian cell entry gene products in mediating cholesterol mediated latency of mycobacteria and the potential use of short-interfering RNA molecular beacons in detecting and attenuating mycobacterial infections.