Staphylococcus aureus Infects Osteoclasts and Replicates Intracellularly

Jennifer L. Krauss, Philip M. Roper, Anna Ballard, Chien Cheng Shih, James A.J. Fitzpatrick, James E. Cassat, Pei Ying Ng, Nathan J. Pavlos, Deborah J. Veis

Research output: Contribution to journalArticle

Abstract

Osteomyelitis (OM), or inflammation of bone tissue, occurs most frequently as a result of bacterial infection and severely perturbs bone structure. OM is predominantly caused by Staphylococcus aureus, and even with proper treatment, OM has a high rate of recurrence and chronicity. While S. aureus has been shown to infect osteoblasts, it remains unclear whether osteoclasts (OCs) are also a target of intracellular infection. Here, we demonstrate the ability of S. aureus to intracellularly infect and divide within OCs. OCs were differentiated from bone marrow macrophages (BMMs) by exposure to receptor activator of nuclear factor kappa-B ligand (RANKL). By utilizing an intracellular survival assay and flow cytometry, we found that at 18 h postinfection the intracellular burden of S. aureus increased dramatically in cells with at least 2 days of RANKL exposure, while the bacterial burden decreased in BMMs. To further explore the signals downstream of RANKL, we manipulated factors controlling OC differentiation, NFATc1 and alternative NF-κB, and found that intracellular bacterial growth correlates with NFATc1 levels in RANKL-treated cells. Confocal and time-lapse microscopy in mature OCs showed a range of intracellular infection that correlated inversely with S. aureus-phagolysosome colocalization. The propensity of OCs to become infected, paired with their diminished bactericidal capacity compared to BMMs, could promote OM progression by allowing S. aureus to evade initial immune regulation and proliferate at the periphery of lesions where OCs are most abundant.IMPORTANCE The inflammation of bone tissue is called osteomyelitis, and most cases are caused by an infection with the bacterium Staphylococcus aureus To date, the bone-building cells, osteoblasts, have been implicated in the progression of these infections, but not much is known about how the bone-resorbing cells, osteoclasts, participate. In this study, we show that S. aureus can infect osteoclasts and proliferate inside these cells, whereas bone-residing macrophages, immune cells related to osteoclasts, destroy the bacteria. These findings elucidate a unique role for osteoclasts to harbor bacteria during infection, providing a possible mechanism by which bacteria could evade destruction by the immune system.

Original languageEnglish
JournalmBio
Volume10
Issue number5
DOIs
Publication statusPublished - 15 Oct 2019

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Osteoclasts
Staphylococcus aureus
RANK Ligand
Osteomyelitis
Bone and Bones
Macrophages
Bacteria
Infection
Bone Marrow
Osteoblasts
Inflammation
Phagosomes
Bacterial Infections
Microscopy
Immune System
Flow Cytometry
Recurrence

Cite this

Krauss, J. L., Roper, P. M., Ballard, A., Shih, C. C., Fitzpatrick, J. A. J., Cassat, J. E., ... Veis, D. J. (2019). Staphylococcus aureus Infects Osteoclasts and Replicates Intracellularly. mBio, 10(5). https://doi.org/10.1128/mBio.02447-19
Krauss, Jennifer L. ; Roper, Philip M. ; Ballard, Anna ; Shih, Chien Cheng ; Fitzpatrick, James A.J. ; Cassat, James E. ; Ng, Pei Ying ; Pavlos, Nathan J. ; Veis, Deborah J. / Staphylococcus aureus Infects Osteoclasts and Replicates Intracellularly. In: mBio. 2019 ; Vol. 10, No. 5.
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Krauss, JL, Roper, PM, Ballard, A, Shih, CC, Fitzpatrick, JAJ, Cassat, JE, Ng, PY, Pavlos, NJ & Veis, DJ 2019, 'Staphylococcus aureus Infects Osteoclasts and Replicates Intracellularly' mBio, vol. 10, no. 5. https://doi.org/10.1128/mBio.02447-19

Staphylococcus aureus Infects Osteoclasts and Replicates Intracellularly. / Krauss, Jennifer L.; Roper, Philip M.; Ballard, Anna; Shih, Chien Cheng; Fitzpatrick, James A.J.; Cassat, James E.; Ng, Pei Ying; Pavlos, Nathan J.; Veis, Deborah J.

In: mBio, Vol. 10, No. 5, 15.10.2019.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Staphylococcus aureus Infects Osteoclasts and Replicates Intracellularly

AU - Krauss, Jennifer L.

AU - Roper, Philip M.

AU - Ballard, Anna

AU - Shih, Chien Cheng

AU - Fitzpatrick, James A.J.

AU - Cassat, James E.

AU - Ng, Pei Ying

AU - Pavlos, Nathan J.

AU - Veis, Deborah J.

PY - 2019/10/15

Y1 - 2019/10/15

N2 - Osteomyelitis (OM), or inflammation of bone tissue, occurs most frequently as a result of bacterial infection and severely perturbs bone structure. OM is predominantly caused by Staphylococcus aureus, and even with proper treatment, OM has a high rate of recurrence and chronicity. While S. aureus has been shown to infect osteoblasts, it remains unclear whether osteoclasts (OCs) are also a target of intracellular infection. Here, we demonstrate the ability of S. aureus to intracellularly infect and divide within OCs. OCs were differentiated from bone marrow macrophages (BMMs) by exposure to receptor activator of nuclear factor kappa-B ligand (RANKL). By utilizing an intracellular survival assay and flow cytometry, we found that at 18 h postinfection the intracellular burden of S. aureus increased dramatically in cells with at least 2 days of RANKL exposure, while the bacterial burden decreased in BMMs. To further explore the signals downstream of RANKL, we manipulated factors controlling OC differentiation, NFATc1 and alternative NF-κB, and found that intracellular bacterial growth correlates with NFATc1 levels in RANKL-treated cells. Confocal and time-lapse microscopy in mature OCs showed a range of intracellular infection that correlated inversely with S. aureus-phagolysosome colocalization. The propensity of OCs to become infected, paired with their diminished bactericidal capacity compared to BMMs, could promote OM progression by allowing S. aureus to evade initial immune regulation and proliferate at the periphery of lesions where OCs are most abundant.IMPORTANCE The inflammation of bone tissue is called osteomyelitis, and most cases are caused by an infection with the bacterium Staphylococcus aureus To date, the bone-building cells, osteoblasts, have been implicated in the progression of these infections, but not much is known about how the bone-resorbing cells, osteoclasts, participate. In this study, we show that S. aureus can infect osteoclasts and proliferate inside these cells, whereas bone-residing macrophages, immune cells related to osteoclasts, destroy the bacteria. These findings elucidate a unique role for osteoclasts to harbor bacteria during infection, providing a possible mechanism by which bacteria could evade destruction by the immune system.

AB - Osteomyelitis (OM), or inflammation of bone tissue, occurs most frequently as a result of bacterial infection and severely perturbs bone structure. OM is predominantly caused by Staphylococcus aureus, and even with proper treatment, OM has a high rate of recurrence and chronicity. While S. aureus has been shown to infect osteoblasts, it remains unclear whether osteoclasts (OCs) are also a target of intracellular infection. Here, we demonstrate the ability of S. aureus to intracellularly infect and divide within OCs. OCs were differentiated from bone marrow macrophages (BMMs) by exposure to receptor activator of nuclear factor kappa-B ligand (RANKL). By utilizing an intracellular survival assay and flow cytometry, we found that at 18 h postinfection the intracellular burden of S. aureus increased dramatically in cells with at least 2 days of RANKL exposure, while the bacterial burden decreased in BMMs. To further explore the signals downstream of RANKL, we manipulated factors controlling OC differentiation, NFATc1 and alternative NF-κB, and found that intracellular bacterial growth correlates with NFATc1 levels in RANKL-treated cells. Confocal and time-lapse microscopy in mature OCs showed a range of intracellular infection that correlated inversely with S. aureus-phagolysosome colocalization. The propensity of OCs to become infected, paired with their diminished bactericidal capacity compared to BMMs, could promote OM progression by allowing S. aureus to evade initial immune regulation and proliferate at the periphery of lesions where OCs are most abundant.IMPORTANCE The inflammation of bone tissue is called osteomyelitis, and most cases are caused by an infection with the bacterium Staphylococcus aureus To date, the bone-building cells, osteoblasts, have been implicated in the progression of these infections, but not much is known about how the bone-resorbing cells, osteoclasts, participate. In this study, we show that S. aureus can infect osteoclasts and proliferate inside these cells, whereas bone-residing macrophages, immune cells related to osteoclasts, destroy the bacteria. These findings elucidate a unique role for osteoclasts to harbor bacteria during infection, providing a possible mechanism by which bacteria could evade destruction by the immune system.

KW - bone

KW - intracellular bacteria

KW - osteoclasts

KW - osteomyelitis

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DO - 10.1128/mBio.02447-19

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Krauss JL, Roper PM, Ballard A, Shih CC, Fitzpatrick JAJ, Cassat JE et al. Staphylococcus aureus Infects Osteoclasts and Replicates Intracellularly. mBio. 2019 Oct 15;10(5). https://doi.org/10.1128/mBio.02447-19