ChlamydiaeChlamydiae Obligate intracellular pathogens.Obligate intracellular pathogens. Acute and/or persistent infections.Acute and/or persistent infections. C. trachomatisC. trachomatis – mucosal surfaces: – mucosal surfaces:

Ocular infections - trachomaOcular infections - trachoma

Genital infections - pelvic inflammation, Genital infections - pelvic inflammation, infertilityinfertility

Reactive arthritisReactive arthritis C. pneumoniaeC. pneumoniae

PneumoniaPneumonia

AtherosclerosisAtherosclerosis

Chlamydia Life CycleChlamydia Life Cycle Elementary body (EB)Elementary body (EB)

-metabolically inactive-metabolically inactive-highly infective stage-highly infective stage

Reticulate body (RB)Reticulate body (RB)-metabolically active-metabolically active-intracellular growth stage-intracellular growth stage

Persistent body (PB)Persistent body (PB)-life cycle pause between EB and RB -life cycle pause between EB and RB stagesstages-stable association with host cell-stable association with host cell

Apoptosis vs NecrosisApoptosis vs Necrosis

Apoptosis – programmed cell death.Apoptosis – programmed cell death.-eliminate and phagocytose cells in an orderly fashion.-eliminate and phagocytose cells in an orderly fashion.

-phosphatidylserine (PS) receptor on phagocytes -phosphatidylserine (PS) receptor on phagocytes increases anti-inflammatory cytokines TGF-beta and increases anti-inflammatory cytokines TGF-beta and IL-10.IL-10.

-needed for embryogenesis, immune system -needed for embryogenesis, immune system maintenance.maintenance.

Necrosis – non-programmed cell death.Necrosis – non-programmed cell death.-cellular debris is a ‘danger signal’ in the cell, so -cellular debris is a ‘danger signal’ in the cell, so

inflammatory response follows DSR interaction with inflammatory response follows DSR interaction with phagocytic cells.phagocytic cells.

Apoptosis vs Necrosis

How might apoptosis help How might apoptosis help pathogens?pathogens?

Facilitating pathogen propagationFacilitating pathogen propagation-pathogens within apoptotic cells can be -pathogens within apoptotic cells can be

taken up by other phagocytic cells without taken up by other phagocytic cells without the pathogen having to navigate the the pathogen having to navigate the extracellular environment.extracellular environment.

Avoiding inflammatory responsesAvoiding inflammatory responses-apoptosis can release anti-inflammatory -apoptosis can release anti-inflammatory

cytokines that down regulate the immune cytokines that down regulate the immune response.response.

Pathogen manipulation of Pathogen manipulation of apoptosisapoptosis

Viruses – often inhibit apoptosisViruses – often inhibit apoptosis- Oncogenic viruses destroys p53 surveillance Oncogenic viruses destroys p53 surveillance

systemsystem- Inhibit extrinsic and intrinsic apoptosis pathwaysInhibit extrinsic and intrinsic apoptosis pathways

Protozoa – often inhibit apoptosisProtozoa – often inhibit apoptosis- Toxoplasma, Trypanosomes, CryptosporidiumToxoplasma, Trypanosomes, Cryptosporidium- Heat shock proteins, NF-KBHeat shock proteins, NF-KB

Bacteria – often induce apoptosisBacteria – often induce apoptosis

- - Helicobacter, Shigella, SalmonellaHelicobacter, Shigella, Salmonella

- Toxins, protein synthesis inhibitors, TTSS- Toxins, protein synthesis inhibitors, TTSS

Mechanisms of ApoptosisMechanisms of Apoptosis

Extrinsic pathway – Receptor mediatedExtrinsic pathway – Receptor mediated- FasL-death receptor interactionsFasL-death receptor interactions- Initiator caspases – caspases 8, 9Initiator caspases – caspases 8, 9- Effector caspases – caspases 3, 6, 7Effector caspases – caspases 3, 6, 7

Intrinsic pathway – Intracellular originIntrinsic pathway – Intracellular origin- Caspase activation or intracellular stress Caspase activation or intracellular stress

signalssignals- Mitochondrial release of cytochrome cMitochondrial release of cytochrome c- Apoptosome formationApoptosome formation

Extrinsic pathwayExtrinsic pathway

Type I cells – activate initiator caspase 8, Type I cells – activate initiator caspase 8, then effector caspase 3, then apoptosis then effector caspase 3, then apoptosis commenses.commenses.

Type II cells – require mitochondrial Type II cells – require mitochondrial amplification. BAX, BAK stop being inhibited amplification. BAX, BAK stop being inhibited by BCL-2, BCL-X and cause mitochondrial by BCL-2, BCL-X and cause mitochondrial release of cytochrome c, then apoptosome release of cytochrome c, then apoptosome forms, activates caspase 3, and commenses forms, activates caspase 3, and commenses apoptosis (DNA fragmentation, nuclear apoptosis (DNA fragmentation, nuclear condensation, membrane blebbing, etc.)condensation, membrane blebbing, etc.)

Chlamydial apoptosis Chlamydial apoptosis manipulationmanipulation

When to inhibit apoptosis?When to inhibit apoptosis?

When to induce apoptosis?When to induce apoptosis?

Chlamydial apoptosis Chlamydial apoptosis manipulationmanipulation

When to inhibit apoptosis?When to inhibit apoptosis?

- for chronic or persistent infections- for chronic or persistent infections

- when intracellular growth stages - when intracellular growth stages dominatedominate

When to induce apoptosis?When to induce apoptosis?- for acute infectionsfor acute infections- when infectious Elementary Body stages when infectious Elementary Body stages

dominatedominate

How to manipulate How to manipulate apoptosis?apoptosis?

‘‘Chlamydia protein associating with death Chlamydia protein associating with death domains’ = CADD, is an oxidoreductase, domains’ = CADD, is an oxidoreductase, so accumulation of reactive oxygen so accumulation of reactive oxygen species could lead to necrosis, while species could lead to necrosis, while interactions with Fas could inhibit interactions with Fas could inhibit apoptosis.apoptosis.

Chlamydia interferes with mitochondrial Chlamydia interferes with mitochondrial apoptosis signals, perhaps by secreting apoptosis signals, perhaps by secreting Bcl-2 anti-apoptotic proteins or Bcl-2 anti-apoptotic proteins or inactivating pro-apoptotic proteins. Type inactivating pro-apoptotic proteins. Type III Secretion Systems available.III Secretion Systems available.

How to induce apoptosis?How to induce apoptosis? Caspase-independent apoptosis occurs.Caspase-independent apoptosis occurs. Necrosis occurs in some cases… by design or Necrosis occurs in some cases… by design or

accident?accident? Cell type specific interactions.Cell type specific interactions.

Over-expression of BAX, BAK cause cell Over-expression of BAX, BAK cause cell death. death. - BAX deficient cells and mice had fewer Chlamydial BAX deficient cells and mice had fewer Chlamydial

organisms, so perhaps BAX-induced apoptosis is organisms, so perhaps BAX-induced apoptosis is important for propagation of the infection.important for propagation of the infection.

Increased mitochondrial metabolism and Increased mitochondrial metabolism and oxidative stress observed in infected cells.oxidative stress observed in infected cells.

How to inhibit apoptosis?How to inhibit apoptosis?

Inhibit cytochrome c release from Inhibit cytochrome c release from mitochondria.mitochondria.

MEK/ERK – MAPK signalling pathways.MEK/ERK – MAPK signalling pathways.

NF-KB – as with MEK/ERK, upregulate NF-KB – as with MEK/ERK, upregulate transcription of anti-apoptotic genes.transcription of anti-apoptotic genes.

IAP – upregulate Inhibitors of Apoptosis IAP – upregulate Inhibitors of Apoptosis Proteins.Proteins.

Future WorkFuture Work

No methods exist for genetic transfer No methods exist for genetic transfer (yet), (yet),

so much is unknown about virulence so much is unknown about virulence and pathogenesis!and pathogenesis!

Is Chlamydiae-induced apoptosis Is Chlamydiae-induced apoptosis associated with acute disease while associated with acute disease while Chlamydiae-inhibited apoptosis is Chlamydiae-inhibited apoptosis is associated with chronic disease?associated with chronic disease?

You have the keys to unlock You have the keys to unlock

many of life’s mysteriesmany of life’s mysteries