Nuclear factor-kappaB p65 facilitates longitudinal bone growth by inducing growth plate chondrocyte proliferation and differentiation and by preventing apoptosis.
"Mice deficient in the NF-kappaB subunits p50 and p52 have retarded growth. Using cultured rat metatarsal bones and isolated growth plate chondrocytes, we studied the effects of two NF-kappaB inhibitors (pyrrolidine dithiocarbamate (PDTC) or BAY11-7082 (BAY)), p65 short interference RNA (siRNA), and of the overexpression of p65 on chondrocyte proliferation, differentiation, and apoptosis. NF-kappaB p65 and BMP-2 [interact] in chondrocytes. PDTC and BAY suppressed metatarsal linear growth{so you don't want to inhibit the NF-kappaB pathway}. Such growth inhibition resulted from decreased chondrocyte proliferation and differentiation and from increased chondrocyte apoptosis{so NF-kappaB pathway increases chondrocyte proliferation and differentiation and decreases chondrocyte apoptosis}. In cultured chondrocytes, the inhibition of NF-kappaB p65 activation (by PDTC and BAY) and expression (by p65 siRNA) led to the same findings observed in cultured metatarsal bones. overexpression of p65 in cultured chondrocytes induced chondrocyte proliferation and differentiation and prevented apoptosis. Although PDTC, BAY, and p65 siRNA reduced the expression of BMP-2 in cultured growth plate chondrocytes, the overexpression of p65 increased it. The addition of Noggin, a BMP-2 antagonist, neutralized the stimulatory effects of p65 on chondrocyte proliferation and differentiation, as well as its anti-apoptotic effect. NF-kappaB p65 expressed in growth plate chondrocytes facilitates growth plate chondrogenesis and longitudinal bone growth by inducing BMP-2 expression and activity."
NF-kappaB p65->BMP2->height.
"inhibition of the proteasomal function in growth plate chondrocytes results in decreased NF-κB activation and reduced chondrogenesis"
"NF-κB p65 subunit is expressed throughout the growth plate, predominantly in the epiphyseal and hypertrophic zones."
"In NF-κB p50/p52 double knockout mice, the expression of the BMP-2 mRNA in the growth plate is significantly decreased."<-So it's not likely to get around NF-kappaB deficiency by directly increasing BMP-2. Although it might still be possible.
Stimulatory effects of insulin-like growth factor-I on growth plate chondrogenesis are mediated by nuclear factor-kappaB p65.
"we first cultured rat metatarsal bones with IGF-I and/or pyrrolidine dithiocarbamate (PDTC), a known NF-kappaB inhibitor. The IGF-I-mediated stimulation of metatarsal growth and growth plate chondrogenesis was neutralized by PDTC. In rat growth plate chondrocytes, IGF-I induced NF-kappaB-p65 nuclear translocation. The inhibition of NF-kappaB-p65 expression and activity (by p65 short interfering RNA and PDTC, respectively) in chondrocytes reversed the IGF-I-mediated induction of cell proliferation and differentiation and the IGF-I-mediated prevention of cell apoptosis. The inhibition of the phosphatidylinositol 3-kinase and Akt abolished the effects of IGF-I on NF-kappaB activation."
"Mice deficient in both the NF-κB subunits p50 and p52 have retarded growth and shortened long bones"
"IGF-I increased the height of the growth plate epiphyseal and proliferative zones"
"Treatment with IGF-I increased the height of the growth plate hypertrophic zone and induced the mRNA expression of collagen X in the growth plate"
"Igf1 null mice demonstrate increased growth hormone and IGF-II expression and action"<-but they still have decreased length.
"the activation of NF-κB by PI3K/Akt [is] triggered by bone morphogenetic protein-2"
Dynamic compression alters NFkappaB activation and IkappaB-alpha expression in IL-1beta-stimulated chondrocyte/agarose constructs.
Dynamic compression alters NFkappaB activation and IkappaB-alpha expression in IL-1beta-stimulated chondrocyte/agarose constructs.
"Constructs were cultured under free-swelling conditions or subjected to dynamic compression for up to 360 min with IL-1beta and/or PDTC (inhibits NFkappaB activation). Nuclear translocation of NFkappaB-p65 was analysed. Gene expression of IkappaB-alpha, iNOS, IL-1beta and IL-4 was assessed.
Nuclear translocation of NFkappaB-p65 was concomitant with an increase in nuclear fluorescence intensity which reached maximum values at 60 min with IL-1beta. Dynamic compression or PDTC reduced nuclear fluorescence and NFkappaB nuclear translocation in cytokine-treated constructs. IL-1beta increased IkappaB-alpha expression at 60 min and either induced iNOS and IL-1beta or inhibited IL-4 expression at 360 min. These time-dependent events were partially reversed by dynamic compression or PDTC with IL-1beta. Co-stimulation by dynamic compression and PDTC favoured suppression (IkappaB-alpha, iNOS, IL-1beta) or induction (IL-4) of gene expression."
"Strained constructs were subjected to dynamic compression ranging from 0 to 15% strain in a sinusoidal waveform at a frequency of 1 Hz for 60, 120 and 360 min"
"Mechanical loading may induce factors which stabilise IκB-α or impair its degradation"
"cyclic mechanical stimulation induces the paracrine/autocrine secretion of IL-4, a process mediated by the α5β1 integrin"
"NFκB is located in the cytoplasm in an inactive form in which the heterodimer is bound to the inhibitory κB-α (IκB-α) protein. IκB-α has been shown to mask the nuclear localisation sequence, thereby preventing nuclear entry of both DNA-binding subunits. Stimulation with IL-1β leads to phosphorylation and subsequent degradation of IκB-α by two IκB-specific kinases, IKKα and IKKβ. The released NFκB is then translocated into the nucleus where it binds to specific consensus DNA sequences in target genes and initiates transcription. NFκB activity is regulated by IκB-α. Once expressed, newly synthesised IκB-α molecules migrate back into the nucleus to remove NFκB from DNA and transport the heterodimer into the cytosol to terminate transcription. IκB-α has both cytoplasmic and nuclear roles in regulating NFκB activation."
"The application of cyclic tensile strain downregulates expression of iNOS and COX-2 via inhibition of NFκB nuclear translocation in chondrocyte monolayers treated with IL-1β. iNOS and COX-2 expression [is downregulated] by dynamic compression in chondrocyte/agarose constructs cultured with IL-1β"
Discoidin domain receptor 2 mediates the collagen II-dependent release of interleukin-6 in primary human chondrocytes.
"We selectively knocked down the molecules of interest in primary human chondrocytes, induced the specified cascade by incubating primary human chondrocytes with collagen II, and observed the outcome, specifically the changes in interleukin-6 release. Knockdown was performed by siRNA-mediated gene silencing in the case of discoidin domain receptor 2 (DDR2) or by using specific inhibitors for the remainder of the molecules. Discoidin domain receptor 2 mediates the collagen II-dependent release of interleukin-6 in primary human chondrocytes. MAP kinases p38, JNK and ERK, [and] NFkappaB, are integral components of intracellular collagen II signalling."
"Phosphorylation of p38 and ERK could be verified 10 min after collagen II stimulation, whereas no phosphorylation of cPLA2 occurred in response to collagen II stimulation"
"IκB degradation could be detected 10 min after collagen stimulation"
A critical role for collagen II in cartilage matrix degradation: collagen II induces pro-inflammatory cytokines and MMPs in primary human chondrocytes.
"We tested the collagen II-dependent induction of pro-inflammatory cytokines and matrix metalloproteinases (MMPs) in PHCs. PHCs were incubated with or without monomeric (i.e., nonfibrillar) collagen II. Cells were then analyzed for the expression of MMP1, MMP3, MMP13, MMP14, and IL-1beta. [We] quantify IL-6 and IL-8 release. To examine the influence of collagen II signaling, specifically the role of MAPK p38, a p38-inhibitor was added prior to collagen treatment. Changes in IkappaB concentration were monitored to detect NFkappaB signaling. Incubation of PHCs with collagen II did produce a dose-dependent induction of MMP1, MMP3, MMP13, MMP14, as well as cytokines IL-1beta, IL-6, and IL-8. At the same time, inhibition of p38 and IkappaB degradation revealed that collagen II-dependent gene induction also involves MAPK p38 and NFkappaB signaling. Collagen II induces first MMPs and pro-inflammatory cytokines and then release of collagen II fragments from mature collagen II fibers. This, in turn, induces more pro-inflammatory cytokines and MMPs, and the process is repeated, which results in the acceleration and perpetuation of cartilage matrix degradation."
"collagen II can induce MMP13 in the immortalized human chondrocyte cell line C-28/I2, which transiently expresses discoidin domain receptor-2 (DDR-2) cDNA."
"The PHCs we used originated from osteoarthritic human knee and hip joints."
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