Triacylglycerols: Fuelling the Hibernating Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) has the remarkable ability to persist with a modified metabolic status and phenotypic drug tolerance for long periods in the host without producing symptoms of active tuberculosis. These persisters may reactivate to cause active disease when the immune system becomes disrupted or compromised. Thus, the infected hosts with the persisters serve as natural reservoir of the deadly pathogen. Understanding the host and bacterial factors contributing to Mtb persistence is important to devise strategies to tackle the Mtb persisters. Host lipids act as the major source of carbon and energy for Mtb. Fatty acids derived from the host cells are converted to triacylglycerols (triglycerides or TAG) and stored in the bacterial cytoplasm. TAG serves as a dependable, long-term energy source of lesser molecular mass than other storage molecules like glycogen. TAG are found in substantial amounts in the mycobacterial cell wall. This review discusses the production, accumulation and possible roles of TAG in mycobacteria, pointing out the aspects that remain to be explored. Finally, the essentiality of TAG synthesis for Mtb is discussed with implications for identification of intervention strategies

Use of an adipocyte model to study the transcriptional adaptation of Mycobacterium tuberculosis to store and degrade host fat

During its persistence in the infected host, Mycobacterium tuberculosis (Mtb) accumulates host-derived fatty acids in intracytoplasmic lipid inclusions as triacylglycerols which serve primarily as carbon and energy reserves. The Mtb genome codes for more than 15 triacylglycerol synthases, 24 lipase/esterases, and seven cutinase-like proteins. Hence, we looked at the expression of the corresponding genes in intracellular bacilli persisting amidst the host triacylglycerols. We used the Mtb infected murine adipocyte model to ensure persistence and transcripts were quantified using real-time reverse transcriptase polymerase chain reaction. Dormancy and glyoxylate metabolism was confirmed by the upregulated expression of dosR and icl, respectively, by intra-adipocyte bacilli compared with in vitro growing bacilli. The study revealed that tgs1, tgs2, Rv3371, and mycolyltransferase Ag85A are the predominant triacylglycerol synthases, while lipF, lipH, lipJ, lipK, lipN, lipV, lipX, lipY, culp5, culp7, and culp6 are the predominant lipases/esterases used by Mtb for the storage and degradation of host-derived fat. Moreover, it was observed that many of these enzymes are used by Mtb during active replication rather than during nonreplicating persistence, indicating their probable function in cell wall synthesis

Dendrogram based on the AFLP profile for EO/MC primer pair showing clustering of clinical isolates of and laboratory strains of , and BCG

<p><b>Copyright information:</b></p><p>Taken from "Combined use of Amplified Fragment Length Polymorphism and IS-RFLP in fingerprinting clinical isolates of from Kerala, South India"</p><p>http://www.biomedcentral.com/1471-2334/7/86</p><p>BMC Infectious Diseases 2007;7():86-86.</p><p>Published online 28 Jul 2007</p><p>PMCID:PMC1950308.</p><p></p> IScopy numbers of various isolates/strains are indicated

AFLP profiles generated by primer combinations EO/MT (panel A) and EG/MC (panel B)

<p><b>Copyright information:</b></p><p>Taken from "Combined use of Amplified Fragment Length Polymorphism and IS-RFLP in fingerprinting clinical isolates of from Kerala, South India"</p><p>http://www.biomedcentral.com/1471-2334/7/86</p><p>BMC Infectious Diseases 2007;7():86-86.</p><p>Published online 28 Jul 2007</p><p>PMCID:PMC1950308.</p><p></p> Lanes1-8: clinical isolates of , lanes 9&10: non tuberculous mycobacteria. The non-tuberculous mycobacteria have a very different profile from each other as well as from isolates. The primer pair EG/MC (panel B) shows fewer bands and more differences between the isolates as compared to EO/MT primer pair (panel A

AFLP profiles showing differences (arrows) between H37Rv (lane1), H37Ra (lane 2), (lane 3) and BCG (lane 4)

<p><b>Copyright information:</b></p><p>Taken from "Combined use of Amplified Fragment Length Polymorphism and IS-RFLP in fingerprinting clinical isolates of from Kerala, South India"</p><p>http://www.biomedcentral.com/1471-2334/7/86</p><p>BMC Infectious Diseases 2007;7():86-86.</p><p>Published online 28 Jul 2007</p><p>PMCID:PMC1950308.</p><p></p> The profiles shown are for EO/MC (panel A) and EO/MT (panel B) primer combinations

Loss of H3K9me3 Correlates with ATM Activation and Histone H2AX Phosphorylation Deficiencies in Hutchinson-Gilford Progeria Syndrome

Compelling evidence suggests that defective DNA damage response (DDR) plays a key role in the premature aging phenotypes in Hutchinson-Gilford progeria syndrome (HGPS). Studies document widespread alterations in histone modifications in HGPS cells, especially, the global loss of histone H3 trimethylated on lysine 9 (H3K9me3). In this study, we explore the potential connection(s) between H3K9me3 loss and the impaired DDR in HGPS. When cells are exposed to a DNA-damaging agent Doxorubicin (Dox), double strand breaks (DSBs) are generated that result in the phosphorylation of histone H2A variant H2AX (gammaH2AX) within an hour. We find that the intensities of gammaH2AX foci appear significantly weaker in the G0/G1 phase HGPS cells compared to control cells. This reduction is associated with a delay in the recruitment of essential DDR factors. We further demonstrate that ataxia-telangiectasia mutated (ATM) is responsible for the amplification of gammaH2AX signals at DSBs during G0/G1 phase, and its activation is inhibited in the HGPS cells that display significant loss of H3K9me3. Moreover, methylene (MB) blue treatment, which is known to save heterochromatin loss in HGPS, restores H3K9me3, stimulates ATM activity, increases gammaH2AX signals and rescues deficient DDR. In summary, this study demonstrates an early DDR defect of attenuated gammaH2AX signals in G0/G1 phase HGPS cells and provides a plausible connection between H3K9me3 loss and DDR deficiency