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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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Mathematical model predictions of k3eff and RNOS2.(A) Predicted k3eff as a function of m. (B) Model prediction of the steady states of RNOS2 (NOS2 mRNA) as a function of k3eff. The solid curve was generated by increasing k3eff slowly (with rate dk3eff/dt = 0.00001) and solving the set of differential equations in Table 2. The dotted curve was generated by decreasing k3eff (with rate dk3eff/dt = −0.00001) starting from the endpoint of the solid curve. Location labeled 1 corresponds to the point on the curve of Figure 6A for m = 0 and k3eff∼0.018. Initially as m increases the value of k3eff approaches zero, and this corresponds to the transition shown in the region 2 of the figure. As m increases further, hardly any change in RNOS2 is predicted (region 3 above) which corresponds to m between mth2 and mth1 in Figure 7A. Increasing m beyond mth1 leads to the transition from 3 to 4 corresponding to the sharp increase in RNOS2 (region 4 in the Fig. 7A). Initial values of parameters derived from the equilibrium state for P0 = 0 were RP = 0.00944, Pc = 0.000925, P0 = 0.259127, C = 0.001337, RI = 0.011025, Ic = 0.020399, In = 0.011686, Nc = 0.0000426, RNOS2 = 0.000616, Nn = 0.000647, Npc = 0.042536, and Npn = 0.000274.
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pone-0005262-g006: Mathematical model predictions of k3eff and RNOS2.(A) Predicted k3eff as a function of m. (B) Model prediction of the steady states of RNOS2 (NOS2 mRNA) as a function of k3eff. The solid curve was generated by increasing k3eff slowly (with rate dk3eff/dt = 0.00001) and solving the set of differential equations in Table 2. The dotted curve was generated by decreasing k3eff (with rate dk3eff/dt = −0.00001) starting from the endpoint of the solid curve. Location labeled 1 corresponds to the point on the curve of Figure 6A for m = 0 and k3eff∼0.018. Initially as m increases the value of k3eff approaches zero, and this corresponds to the transition shown in the region 2 of the figure. As m increases further, hardly any change in RNOS2 is predicted (region 3 above) which corresponds to m between mth2 and mth1 in Figure 7A. Increasing m beyond mth1 leads to the transition from 3 to 4 corresponding to the sharp increase in RNOS2 (region 4 in the Fig. 7A). Initial values of parameters derived from the equilibrium state for P0 = 0 were RP = 0.00944, Pc = 0.000925, P0 = 0.259127, C = 0.001337, RI = 0.011025, Ic = 0.020399, In = 0.011686, Nc = 0.0000426, RNOS2 = 0.000616, Nn = 0.000647, Npc = 0.042536, and Npn = 0.000274.

Mentions: It was shown previously that IKK is the key moleucule regulated by biomechanical signals [8], [10]. Low physiological magnitudes of biomechanical forces prevent phophorylation of TAK1 (TGF-β activating kinase), which in turn inhibits phosphorylation of IKK, resulting in attenuating further downstream NF-κB signaling cascade. Now we show that IKK activity, estimated from the phosphorylation of IκB-α, is regulated by DCS; initially it is suppressed as the magnitude of DCS increases and then increases again with further raising in magnitude (Fig. 3C and 3D). This observation of biphasic IKK activation is incorporated in the model of Figure 5 through the rate coefficient of activation of IKK, that is, k3f(m), where f(m) is a function of DCS magnitude (see Table 1). The factor k3f(m) is referred to as k3eff. A simple choice of the form of the function f(m) is the parabola a(m−m0)2, where a is set so that f(0) = 1, and m0 is set so that the observed threshold in the magnitude of DCS is approximated (Fig. 6A) A plot of RNOS2 (NOS2 mRNA) versus k3eff in steady states is given in Figure 6B. These steady states are the long-term levels of RNOS2, and are determined by setting all the differential equations in Table 2 to zero.


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

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

Mathematical model predictions of k3eff and RNOS2.(A) Predicted k3eff as a function of m. (B) Model prediction of the steady states of RNOS2 (NOS2 mRNA) as a function of k3eff. The solid curve was generated by increasing k3eff slowly (with rate dk3eff/dt = 0.00001) and solving the set of differential equations in Table 2. The dotted curve was generated by decreasing k3eff (with rate dk3eff/dt = −0.00001) starting from the endpoint of the solid curve. Location labeled 1 corresponds to the point on the curve of Figure 6A for m = 0 and k3eff∼0.018. Initially as m increases the value of k3eff approaches zero, and this corresponds to the transition shown in the region 2 of the figure. As m increases further, hardly any change in RNOS2 is predicted (region 3 above) which corresponds to m between mth2 and mth1 in Figure 7A. Increasing m beyond mth1 leads to the transition from 3 to 4 corresponding to the sharp increase in RNOS2 (region 4 in the Fig. 7A). Initial values of parameters derived from the equilibrium state for P0 = 0 were RP = 0.00944, Pc = 0.000925, P0 = 0.259127, C = 0.001337, RI = 0.011025, Ic = 0.020399, In = 0.011686, Nc = 0.0000426, RNOS2 = 0.000616, Nn = 0.000647, Npc = 0.042536, and Npn = 0.000274.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2667254&req=5

pone-0005262-g006: Mathematical model predictions of k3eff and RNOS2.(A) Predicted k3eff as a function of m. (B) Model prediction of the steady states of RNOS2 (NOS2 mRNA) as a function of k3eff. The solid curve was generated by increasing k3eff slowly (with rate dk3eff/dt = 0.00001) and solving the set of differential equations in Table 2. The dotted curve was generated by decreasing k3eff (with rate dk3eff/dt = −0.00001) starting from the endpoint of the solid curve. Location labeled 1 corresponds to the point on the curve of Figure 6A for m = 0 and k3eff∼0.018. Initially as m increases the value of k3eff approaches zero, and this corresponds to the transition shown in the region 2 of the figure. As m increases further, hardly any change in RNOS2 is predicted (region 3 above) which corresponds to m between mth2 and mth1 in Figure 7A. Increasing m beyond mth1 leads to the transition from 3 to 4 corresponding to the sharp increase in RNOS2 (region 4 in the Fig. 7A). Initial values of parameters derived from the equilibrium state for P0 = 0 were RP = 0.00944, Pc = 0.000925, P0 = 0.259127, C = 0.001337, RI = 0.011025, Ic = 0.020399, In = 0.011686, Nc = 0.0000426, RNOS2 = 0.000616, Nn = 0.000647, Npc = 0.042536, and Npn = 0.000274.
Mentions: It was shown previously that IKK is the key moleucule regulated by biomechanical signals [8], [10]. Low physiological magnitudes of biomechanical forces prevent phophorylation of TAK1 (TGF-β activating kinase), which in turn inhibits phosphorylation of IKK, resulting in attenuating further downstream NF-κB signaling cascade. Now we show that IKK activity, estimated from the phosphorylation of IκB-α, is regulated by DCS; initially it is suppressed as the magnitude of DCS increases and then increases again with further raising in magnitude (Fig. 3C and 3D). This observation of biphasic IKK activation is incorporated in the model of Figure 5 through the rate coefficient of activation of IKK, that is, k3f(m), where f(m) is a function of DCS magnitude (see Table 1). The factor k3f(m) is referred to as k3eff. A simple choice of the form of the function f(m) is the parabola a(m−m0)2, where a is set so that f(0) = 1, and m0 is set so that the observed threshold in the magnitude of DCS is approximated (Fig. 6A) A plot of RNOS2 (NOS2 mRNA) versus k3eff in steady states is given in Figure 6B. These steady states are the long-term levels of RNOS2, and are determined by setting all the differential equations in Table 2 to zero.

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