Adaptations of mycobacteria for survival in macrophages

Sameer Tiwari

Flaunty

mycobacterium

Interaction of macrophage with mycobacteria

Peters J., Cell Host & Microbe, 2008

Cells involved in Phagocytosis

Kuby., Immunology, 4th Edi

Dendritic cellMonocyte Macrophage

Phagocytosis of a bacterium

Kuby, Immunology, Edi 4th

PAMP

CR

MR

CD14

Collectins

Scavengers

Fc receptors

M. tuberculosis recognition by membrane-bound receptors

O. Neyrolles, C. Guilhot ,Tuberculosis 91 (2011) 187-195

Entry of M. tuberculosis in macrophage

Phagocytosis of M.tb involves different receptors on the phagocytic cell which either bind to nonopsonized M.tb or recognize opsonins on the surface of M.tb.

Complement receptors (CRl, CR2, CR3 and CR4), mannose receptors (MR), CD14 receptor, collectins, scavenger receptors play important roles in binding of the organisms to the phagocytes (Schlesinger et al., 1996, Hoheisel et al., 1995, Gaynor et al., 1995).

Mycobacteria can invade host macrophages after opsonization with complement factor C3, which is followed by binding and uptake through CR1, CR3, and CR4 (Aderem et al., 1999, Hirsch et al., 1994, Schlesinger et al., 1993). In the absence of CR3, phagocytosis of M.tb by human macrophages and monocytes is reduced by approximately 70 to 80% in vitro (Schlesinger et al., 1993, Schlesinger et al., 1990).

Inhibition of phagosomal maturation

01

02

03

Phagosome-lysosome fusion block

Incomplete Luminal acidification

Absence of proton -ATPase

04 Absence of mature lysosomal hydrolase

Rab effectors & mycobacterial phagolysosomes

Rab5 & 7EEA1LAMP1Cathepsin DTACO

Role of Ca2+ in phagosomal maturation

Ca2+- binding protein calmodulin

recruitment of the PI3K hVPS34

interference with Ca2+ fluxes by LAM

PI3P and phagosomal maturation

Vergne I,et al,Traffic 2003;4:600–606

Other host mechanisms altered by mycobacteria

Antigen processing and presentation

Generation of ROI & RNI

MacMicking Nature Medicine 14, 809 - 810 (2008)

Vandal OH et al,JOURNAL OF BACTERIOLOGY, Aug. 2009, p. 4714–4721

Modulation of MAPK Signalling & JAK/STAT signalling

Modulation of macrophage signaling by mycobacteria

Mycobacteria alter host apoptotic pathways

Manipulation of host cell actin dynamics

Actin forms part of the eukaryotic cytoskeletal network

Migration Memabrane ruffling Cellular adherence

Activity of Coronin 1 in Macrophages

Protein Kinases

500 kinases

2% of all proteins

30% of all proteins modified by kinase activity

Phosphorylation occurs on serine, threonine & tyrosine residues

Human geome conatins

Variety of cellular processesIncluding protein trafficking

Protein Kinase C

Role of PKC in macrophage functions

Production of cytokines, chemokines and immune effector molecule

Role of PKC in mycobacterial infection

Reduced activation of MAP Kinases

Decreased production of NOS2 and TNF-α

Serine/Threonine Protein Kinases of Mtb

Alber T, Current Opinion in Structural Biology 2009,19:650–65

Model for Mtb receptor STPK regulation

Structural analysis of M.tb STPKs

PknA

Impairment in GTPase activity of FtsZ

phosphorylate FtsZ

PknB

Functional STPK expressed in active TB infection

Slow growth & cell morphology (cell shape)

PknD

Anchoring sensor domain

phosphorylate MmpL7 Virulence

MmpL7 is essential for virulence, it transports polyketide virulence factors such as phthiocerol dimycocerosate (PDIM) to the cell wall

PknE

Transduction of externa

l signals

PknF

Regulation in Glucose transport

Slow cell growth

Septum formation

PknH

Phosphorylation of EmbR (phosphoprotein recognition domain)

DNA binding activity towards promoter regions of embCAB genes

Differential expression of a mycobacterial kinase in response to stress conditions which can indicate its ability to regulate cellular events promoting bacterial adaptation to environmental change i.e. low pH & heat shock

PknK

Regulate the expression of the mycobacterial monooxygenase (mymA) operon

Expression of mymA operon genes is regulated through PknK-mediated phosphorylation of VirS

Phosphorylates FabD

PknG

Interfere with host signal transduction processes

Cellular glutamate and glutamine levels

Phosphorylate protein(s) possibly involved in host trafficking pathways

Blocking the maturation of mycobacterial phagosome into lysosomes

Establishment of an intracellular infection by blocking phagosome-lysosomal fusion within macrophages

Phosphorylated GarA (glutamate metabolism)

PknG in mycobacterial trafficking in macrophages

Conclusion

Knowledge of the mycobacterial tactics for survival inside macrophages might help not only to control tuberculosis and other mycobacterial diseases but also to uncover novel aspects of host cell biology

Further studies, with the help of new techniques in genomics and proteomics, will elucidate the precise mechanisms by which pathogenic mycobacteria are able to downregulate host-signalling pathways involving TLRs, MAPKs and JAK/STATs.

Mycobacterial gene products that disrupt host defences during infection represent potential drug targets.

Mycobacterial Kinases could be potential targets for the development of new TB drugs

THANKS