Gene expression changes in macrophages infected with pathogenic M. tuberculosis and non-pathogenic M. smegmatis and M. bovis BCG

Mpongoshe, Vuyiseka (2014-04)

Thesis (MScMedSc)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: The current anti-TB drugs have had success in decreasing the number of deaths caused by TB, however, this success is limited by the emergence of drug resistant TB strains. Therefore, a novel TB therapy that limits the development of resistance has become necessary in an attempt to effectively control TB. The anti-TB drugs directly target mycobacterial enzymes, and potentiate the development of this resistance, and have therefore provided the rationale for this study. The aim was therefore to identify host macrophage genes that affect M. tb intracellular survival. The proposed alternative anti-TB therapy potentially involves the application of RNA interference (RNAi) and RNA activation (RNAa) biological processes that will target host genes, thereby inducing an indirect bactericidal effect. We hypothesized that macrophage genes that are differentially expressed by pathogenic and non-pathogenic mycobacterial species may be important in the regulation of M. tb intracellular survival. The lipid-rich mycobacterial cell wall is implicated in the excessive clumping of the mycobacterial cells in liquid culture. In order to minimize this, Tween 80 detergent was supplemented (mycobacteriaT). However, due to substantial evidence emphasising the detrimental effects of Tween 80 on the mycobacterial cell wall, mycobacteria were also cultured without Tween 80 (mycobacteriaNT), in order to investigate if the perturbed mycobacterial cell wall induced by Tween 80 affects the transcriptional response of macrophages. We endeavoured to develop a new method to culture mycobacteria without Tween 80 that will still generate single cells. We further hypothesized that the macrophage gene expression profile induced by mycobateriaNT differs from the response induced by mycobacteriaT. Differentiated THP-1 (dTHP-1) cells were infected with pathogenic and non-pathogenic mycobacteria (for 3 h, 24 h and 48 h with M. tb and M. bovis BCG, and 3 h and 8 h with M. smegmatis) cultured in the presence or absence of Tween 80. The expression of 12 macrophage genes, selected based on their involvement in the phagocytic pathway and autophagy, as well as their general involvement in the immune response, was determined by qRT-PCR and further analysed on the REST programme. The expression of each target gene was normalised relative to the expression of the reference gene (Beta actin). We observed that out of the 12 genes, TLR7 and VAMP7 were consistently downregulated in dTHP-1 cells infected with M. tbNT and upregulated in dTHP-1 cells infected with M. smegmatisNT. Their response to M. bovis BCG was inconsistent and not significantly different, and therefore could not be interpreted. Furthermore, CCL1 was upregulated by all the mycobacterial species. However, its expression was more pronounced in response to mycobacteriaNT, when compared to mycobacteriaT. Differential gene expression of TLR7 and VAMP7 in response to pathogenic and non-pathogenic mycobacteriaNT suggests that these 2 genes may be potential targets for RNAa-based anti-TB therapy, even though we could not conclude whether their response was specific to macrophages. In addition, the observed difference in the expression of CCL1 induced by mycobacteriaNT, compared to mycobacteriaT suggests that the perturbation caused by Tween 80 on the mycobacterial cell wall most likely affected the response of macrophages to infection with mycobacteria. Furthermore, this study has demonstrated a feasible method by filtration to generate single cells from mycobacteriaNT, which should be considered for future mycobacterial infection studies.

AFRIKAANSE OPSOMMING: Die huidige anti-tuberkulose middels se sukses lê daarin dat dit die aantal sterftes verminder maar hierdie sukses word weer beperk met die ontstaan van middel-weerstandige M.tb stamme. Daarom is nuwe middels nodig wat die ontwikkeling van middel-weerstandigheid beperk in ʼn poging om effektiewe TB behandeling te bewerkstellig. Anti-tuberkulose middels teiken hoofsaaklik mycobakteriële ensiemsisteme en ontlok sodoende weerstandigheid in M.tb stamme en dit vorm die rasionale vir hierdie studie. Die doel was om gasheer makrofaag gene te identifiseer wat M.tb oorlewing intrasellulêr bewerkstellig. Die voorgestelde alternatiewe anti-TB behandeling sal dan behels die toepassing van RNA intervensie (RNAi) en RNA aktivering (RNAa) tegnologie wat gasheer selgene teiken (inaktiveer) en sodoende ʼn bakterisidiese respons induseer. Die kanse is skraal dat mycobakterieë weerstandigheid sal kan ontwikkel onder hierdie omstandighede. Ons hipotetiseer dus dat makrofaag gene wat differensieel uitgedruk word deur patogeniese en nie-patologiese mycobakteriële spesies belangrik mag wees vir die oorlewing van M.tb intrasellulêr. Die lipiedryke selwand van mycobakterieë word geïmpliseer in die oormatige sameklomping van die bakterieë in vloeistofkulture. Om hierdie effek te minimaliseer word Tween 80 normaalweg tot die medium gevoeg (mycobakterieëT). Maar weens genoegsame bewyse dat Tween-80 die selwand van bakterieë nadelig beïnvloed, is mycobakterieë ook in die afwesigheid van Tween 80 gekultureer (mycobakterieëNT) om te bepaal of die nadelige effek van Tween 80 op die selwand die transkripsionele respons in makrofage beïnvloed post-infeksie. Dit was daarom ook ons doelstelling om ʼn nuwe tegniek te ontwikkel om mycobakterieë te kultureer in die afwesigheid van Tween 80 wat ook enkelselle sal genereer vir beter gekontroleerde makrofaag infeksie. Ons hipotetiseer ook verder dat makrofaag geenuitdrukking-profiele verskil afhangende of infeksie gedoen is met mycobakterieë wat in die afwesigheid of teenwoordigheid van Tween 80 gekultureer is. Gedifferensieerde THP-1 (dTHP-1) was geïnfekteer met patogeniese en nie-patogeniese mycobakterieë (vir 3 h, 24 h en 48 h met M.tb en M.bovis BCG, en 3 h en 8 h met M.smegmatis) gekultureer in die teenwoordigheid en afwesigheid van Tween 80. Die uitdrukking van 12 makrofaag gene, geselekteer op grond van hul betrokkenheid in die fagositose meganisme en in outofagie asook hul betrokkenheid in die immuunrespons, is gekwantifiseer met qRT-PCR en daaropvolgens geanaliseer met die REST-program. Die uitdrukking van elke geen is genormaliseer relatief tot die uitdrukking van die verwysingsgeen (Beta actin). Daar is bevind dat van die 12 gene, TLR7 en VAMP7 deurlopend afgereguleer was in dTHP-1 selle geïnfekteer met M.tbNT en opgereguleer was in dTHP selle geïnfekteer met M.smegmatisNT. Selrespons met M.bovis BCG was onbeduidend en derhalwe kon geen gevolgtrekking hier gemaak word nie. Ook, CCL1 was opgereguleer met infeksie deur enige van die mycobakteriële spesies, maar CCL1 se uitdrukking was groter in respons tot mycobakterieëNT wanneer vergelyk word met respons tot mycobakterieëT. Differensiële geenuitdrukking van TLR7 en VAMP7 in respons tot patogeniese en nie-patogeniese mycobakterieëNT impliseer dat hierdie twee gene potensiële teikens kan wees vir RNAa-gebaseerde anti-TB behandeling, alhoewel ons nie kon beslis of hierdie respons spesifiek vir makrofage was nie. Ook, die verskille waargeneem in die uitdrukking van CCL1 geïnduseer deur mycobakterieëNT, vergeleke met mycobakterieëT, impliseer dat die steuring in die selwand veroorsaak deur Tween 80, heelwaarskynlik die respons van die makrofaag beïnvloed het. Hierdie studie beskryf ook ʼn filtrasiemetode om enkele mycobakteriële selle te genereer wat oorweeg moet word by toekomstige mycobakteriële infeksiestudies.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/86729
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