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Biomechanical thresholds regulate inflammation through the NF-kappaB pathway: experiments and modeling.

Nam J, Aguda BD, Rath B, Agarwal S - PLoS ONE (2009)

Bottom Line: Experimental and computational results indicate that biomechanical signals suppress and induce inflammation at critical thresholds through activation/suppression of the NF-kappaB signaling pathway.These thresholds arise due to the bistable behavior of the networks originating from the positive feedback loop between NF-kappaB and its target genes.These findings lay initial groundwork for the identification of the thresholds in physical activities that can differentiate its favorable actions from its unfavorable consequences on joints.

View Article: PubMed Central - PubMed

Affiliation: Biomechanics and Tissue Engineering Laboratory, College of Dentistry, The Ohio State University, Columbus, OH, USA.

ABSTRACT

Background: During normal physical activities cartilage experiences dynamic compressive forces that are essential to maintain cartilage integrity. However, at non-physiologic levels these signals can induce inflammation and initiate cartilage destruction. Here, by examining the pro-inflammatory signaling networks, we developed a mathematical model to show the magnitude-dependent regulation of chondrocytic responses by compressive forces.

Methodology/principal findings: Chondrocytic cells grown in 3-D scaffolds were subjected to various magnitudes of dynamic compressive strain (DCS), and the regulation of pro-inflammatory gene expression via activation of nuclear factor-kappa B (NF-kappaB) signaling cascade examined. Experimental evidences provide the existence of a threshold in the magnitude of DCS that regulates the mRNA expression of nitric oxide synthase (NOS2), an inducible pro-inflammatory enzyme. Interestingly, below this threshold, DCS inhibits the interleukin-1beta (IL-1beta)-induced pro-inflammatory gene expression, with the degree of suppression depending on the magnitude of DCS. This suppression of NOS2 by DCS correlates with the attenuation of the NF-kappaB signaling pathway as measured by IL-1beta-induced phosphorylation of the inhibitor of kappa B (IkappaB)-alpha, degradation of IkappaB-alpha and IkappaB-beta, and subsequent nuclear translocation of NF-kappaB p65. A mathematical model developed to understand the complex dynamics of the system predicts two thresholds in the magnitudes of DCS, one for the inhibition of IL-1beta-induced expression of NOS2 by DCS at low magnitudes, and second for the DCS-induced expression of NOS2 at higher magnitudes.

Conclusions/significance: Experimental and computational results indicate that biomechanical signals suppress and induce inflammation at critical thresholds through activation/suppression of the NF-kappaB signaling pathway. These thresholds arise due to the bistable behavior of the networks originating from the positive feedback loop between NF-kappaB and its target genes. These findings lay initial groundwork for the identification of the thresholds in physical activities that can differentiate its favorable actions from its unfavorable consequences on joints.

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Regulation of pro-inflammatory gene expression by DCS.(A) NOS2 and (B) TNF-α expression in the cells subjected to various magnitudes of DCS for 45 minutes followed by 75 minutes of rest, in the absence (solid line) or presence (dotted line) of exogenous IL-1β (2 ng/ml). The figure shows that in the absence of IL-1β, the pro-inflammatory gene expression markedly increased after a threshold of the applied DCS, whereas in the presence of IL-1β, the gene expression was suppressed in response to the DCS up to a threshold, followed by an increase proportional to the magnitude of applied DCS.
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pone-0005262-g002: Regulation of pro-inflammatory gene expression by DCS.(A) NOS2 and (B) TNF-α expression in the cells subjected to various magnitudes of DCS for 45 minutes followed by 75 minutes of rest, in the absence (solid line) or presence (dotted line) of exogenous IL-1β (2 ng/ml). The figure shows that in the absence of IL-1β, the pro-inflammatory gene expression markedly increased after a threshold of the applied DCS, whereas in the presence of IL-1β, the gene expression was suppressed in response to the DCS up to a threshold, followed by an increase proportional to the magnitude of applied DCS.

Mentions: To examine how the magnitude of DCS differentially influences cellular responses, the gene expression of NOS2, one of the early-responsive pro-inflammatory genes was investigated. In the absence of inflammatory stimulus by IL-1β, the applied DCS induced NOS2 gene expression depending on the magnitude of applied forces (solid curve in Fig. 2A). At low magnitudes, the cells did not respond to the applied DCS. However, the NOS2 induction increased proportional to the applied DCS after a certain threshold, resulting in an approximately 300-fold increase at 30% DCS. On the other hand, exogenous IL-1β induced approximately 3000-fold increase in the NOS2 expression (dotted curve in Fig. 2A). Interestingly, the IL-1β-induced gene upregulation was gradually suppressed by the application of DCS up to a threshold, which nearly coincides with the magnitude that initiated NOS2 induction in the absence of the inflammatory cytokine. The gene response was parabolically related to the applied DCS having approximately 10–15% DCS estimated to result in the greatest suppression on IL-1β-induced NOS2 gene expression (dotted curve in Fig. 2A). High magnitudes of DCS were ineffective in suppressing the IL-1β-induced NOS2 gene expression; rather, they intensified the gene expression resulting in approximately 3800-fold increase at 30% DCS. Similar pro-inflammatory gene regulation by DCS was observed in TNF-α (Fig. 2B).


Biomechanical thresholds regulate inflammation through the NF-kappaB pathway: experiments and modeling.

Nam J, Aguda BD, Rath B, Agarwal S - PLoS ONE (2009)

Regulation of pro-inflammatory gene expression by DCS.(A) NOS2 and (B) TNF-α expression in the cells subjected to various magnitudes of DCS for 45 minutes followed by 75 minutes of rest, in the absence (solid line) or presence (dotted line) of exogenous IL-1β (2 ng/ml). The figure shows that in the absence of IL-1β, the pro-inflammatory gene expression markedly increased after a threshold of the applied DCS, whereas in the presence of IL-1β, the gene expression was suppressed in response to the DCS up to a threshold, followed by an increase proportional to the magnitude of applied DCS.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2667254&req=5

pone-0005262-g002: Regulation of pro-inflammatory gene expression by DCS.(A) NOS2 and (B) TNF-α expression in the cells subjected to various magnitudes of DCS for 45 minutes followed by 75 minutes of rest, in the absence (solid line) or presence (dotted line) of exogenous IL-1β (2 ng/ml). The figure shows that in the absence of IL-1β, the pro-inflammatory gene expression markedly increased after a threshold of the applied DCS, whereas in the presence of IL-1β, the gene expression was suppressed in response to the DCS up to a threshold, followed by an increase proportional to the magnitude of applied DCS.
Mentions: To examine how the magnitude of DCS differentially influences cellular responses, the gene expression of NOS2, one of the early-responsive pro-inflammatory genes was investigated. In the absence of inflammatory stimulus by IL-1β, the applied DCS induced NOS2 gene expression depending on the magnitude of applied forces (solid curve in Fig. 2A). At low magnitudes, the cells did not respond to the applied DCS. However, the NOS2 induction increased proportional to the applied DCS after a certain threshold, resulting in an approximately 300-fold increase at 30% DCS. On the other hand, exogenous IL-1β induced approximately 3000-fold increase in the NOS2 expression (dotted curve in Fig. 2A). Interestingly, the IL-1β-induced gene upregulation was gradually suppressed by the application of DCS up to a threshold, which nearly coincides with the magnitude that initiated NOS2 induction in the absence of the inflammatory cytokine. The gene response was parabolically related to the applied DCS having approximately 10–15% DCS estimated to result in the greatest suppression on IL-1β-induced NOS2 gene expression (dotted curve in Fig. 2A). High magnitudes of DCS were ineffective in suppressing the IL-1β-induced NOS2 gene expression; rather, they intensified the gene expression resulting in approximately 3800-fold increase at 30% DCS. Similar pro-inflammatory gene regulation by DCS was observed in TNF-α (Fig. 2B).

Bottom Line: Experimental and computational results indicate that biomechanical signals suppress and induce inflammation at critical thresholds through activation/suppression of the NF-kappaB signaling pathway.These thresholds arise due to the bistable behavior of the networks originating from the positive feedback loop between NF-kappaB and its target genes.These findings lay initial groundwork for the identification of the thresholds in physical activities that can differentiate its favorable actions from its unfavorable consequences on joints.

View Article: PubMed Central - PubMed

Affiliation: Biomechanics and Tissue Engineering Laboratory, College of Dentistry, The Ohio State University, Columbus, OH, USA.

ABSTRACT

Background: During normal physical activities cartilage experiences dynamic compressive forces that are essential to maintain cartilage integrity. However, at non-physiologic levels these signals can induce inflammation and initiate cartilage destruction. Here, by examining the pro-inflammatory signaling networks, we developed a mathematical model to show the magnitude-dependent regulation of chondrocytic responses by compressive forces.

Methodology/principal findings: Chondrocytic cells grown in 3-D scaffolds were subjected to various magnitudes of dynamic compressive strain (DCS), and the regulation of pro-inflammatory gene expression via activation of nuclear factor-kappa B (NF-kappaB) signaling cascade examined. Experimental evidences provide the existence of a threshold in the magnitude of DCS that regulates the mRNA expression of nitric oxide synthase (NOS2), an inducible pro-inflammatory enzyme. Interestingly, below this threshold, DCS inhibits the interleukin-1beta (IL-1beta)-induced pro-inflammatory gene expression, with the degree of suppression depending on the magnitude of DCS. This suppression of NOS2 by DCS correlates with the attenuation of the NF-kappaB signaling pathway as measured by IL-1beta-induced phosphorylation of the inhibitor of kappa B (IkappaB)-alpha, degradation of IkappaB-alpha and IkappaB-beta, and subsequent nuclear translocation of NF-kappaB p65. A mathematical model developed to understand the complex dynamics of the system predicts two thresholds in the magnitudes of DCS, one for the inhibition of IL-1beta-induced expression of NOS2 by DCS at low magnitudes, and second for the DCS-induced expression of NOS2 at higher magnitudes.

Conclusions/significance: Experimental and computational results indicate that biomechanical signals suppress and induce inflammation at critical thresholds through activation/suppression of the NF-kappaB signaling pathway. These thresholds arise due to the bistable behavior of the networks originating from the positive feedback loop between NF-kappaB and its target genes. These findings lay initial groundwork for the identification of the thresholds in physical activities that can differentiate its favorable actions from its unfavorable consequences on joints.

Show MeSH
Related in: MedlinePlus