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Biologic Significance (biologic + significance)
Selected AbstractsPerspective: Quantifying Osteoblast and Osteocyte Apoptosis: Challenges and Rewards,,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 10 2007Robert L Jilka Abstract Since the initial demonstration of the phenomenon in murine and human bone sections ,10 yr ago, appreciation of the biologic significance of osteoblast apoptosis has contributed greatly not only to understanding the regulation of osteoblast number during physiologic bone remodeling, but also the pathogenesis of metabolic bone diseases and the pharmacology of some of the drugs used for their treatment. It is now appreciated that all major regulators of bone metabolism including bone morphogenetic proteins (BMPs), Wnts, other growth factors and cytokines, integrins, estrogens, androgens, glucocorticoids, PTH and PTH-related protein (PTHrP), immobilization, and the oxidative stress associated with aging contribute to the regulation of osteoblast and osteocyte life span by modulating apoptosis. Moreover, osteocyte apoptosis has emerged as an important regulator of remodeling on the bone surface and a critical determinant of bone strength, independently of bone mass. The detection of apoptotic osteoblasts in bone sections remains challenging because apoptosis represents only a tiny fraction of the life span of osteoblasts, not unlike a 6-mo -long terminal illness in the life of a 75-yr -old human. Importantly, the phenomenon is 50 times less common in human bone biopsies because human osteoblasts live longer and are fewer in number. Be that as it may, well-controlled assays of apoptosis can yield accurate and reproducible estimates of the prevalence of the event, particularly in rodents where there is an abundance of osteoblasts for inspection. In this perspective, we focus on the biological significance of the phenomenon for understanding basic bone biology and the pathogenesis and treatment of metabolic bone diseases and discuss limitations of existing techniques for quantifying osteoblast apoptosis in human biopsies and their methodologic pitfalls. [source] Low Ki-67 proliferation index is an indicator of poor prognosis in gastric cancerJOURNAL OF SURGICAL ONCOLOGY, Issue 3 2010Hee Eun Lee MD Abstract Background and Objectives We designed this study to assess the biologic significance of Ki-67 proliferation index (PI) in gastric cancer. Methods Gastric cancer tissue from 245 patients were immunostained for Ki-67. Ki-67 PI was defined as the percentage of tumor cells positive for Ki-67. In addition, we have previously evaluated the expressions of nine epithelial mesenchymal transition (EMT)-related proteins. The relationship between Ki-67 PI and clinicopathologic parameters, patient survival, and EMT data were sought. Results Low Ki-67 PI was correlated with poorly differentiated histology (P,=,0.034), an advanced T stage (P,<,0.001), and lymph node metastasis (P,=,0.011). Also, the low PI group was found to have a significantly worse prognosis than the high PI group (P,=,0.003, log-rank test). Multivariate analysis revealed that Ki-67 PI remained as an independent prognostic factor (hazard ratio (95% CI),=,0.670 (0.450,0.999)). Furthermore, greater expressional changes of EMT-related proteins were found to be significantly associated with low Ki-67 PI (P,=,0.025). Conclusions These findings suggest that Ki-67 PI is an effective tool for predicting survival in gastric cancer. In addition, we found that an invasive property presented as EMT-related protein expressional changes was inversely correlated with a proliferative activity in gastric cancer. J. Surg. Oncol. 2010;102:201,206. © 2010 Wiley-Liss, Inc. [source] Aberrant hypertrophy in Smad3-deficient murine chondrocytes is rescued by restoring transforming growth factor ,,activated kinase 1/activating transcription factor 2 signaling: A potential clinical implication for osteoarthritisARTHRITIS & RHEUMATISM, Issue 8 2010Tian-Fang Li Objective To investigate the biologic significance of Smad3 in the progression of osteoarthritis (OA), the crosstalk between Smad3 and activating transcription factor 2 (ATF-2) in the transforming growth factor , (TGF,) signaling pathway, and the effects of ATF-2 overexpression and p38 activation in chondrocyte differentiation. Methods Joint disease in Smad3-knockout (Smad3,/,) mice was examined by microfocal computed tomography and histologic analysis. Numerous in vitro methods including immunostaining, real-time polymerase chain reaction, Western blotting, an ATF-2 DNA-binding assay, and a p38 kinase activity assay were used to study the various signaling responses and protein interactions underlying the altered chondrocyte phenotype in Smad3,/, mice. Results In Smad3,/, mice, an end-stage OA phenotype gradually developed. TGF,-activated kinase 1 (TAK1)/ATF-2 signaling was disrupted in Smad3,/, mouse chondrocytes at the level of p38 MAP kinase (MAPK) activation, resulting in reduced ATF-2 phosphorylation and transcriptional activity. Reintroduction of Smad3 into Smad3,/, cells restored the normal p38 response to TGF,. Phosphorylated p38 formed a complex with Smad3 by binding to a portion of Smad3 containing both the MAD homology 1 and linker domains. Additionally, Smad3 inhibited the dephosphorylation of p38 by MAPK phosphatase 1 (MKP-1). Both ATF-2 overexpression and p38 activation repressed type X collagen expression in wild-type and Smad3,/, chondrocytes. P38 was detected in articular cartilage and perichondrium; articular and sternal chondrocytes expressed p38 isoforms ,, ,, and ,, but not ,. Conclusion Smad3 is involved in both the onset and progression of OA. Loss of Smad3 abrogates TAK1/ATF-2 signaling, most likely by disrupting the Smad3,phosphorylated p38 complex, thereby promoting p38 dephosphorylation and inactivation by MKP-1. ATF-2 and p38 activation inhibit chondrocyte hypertrophy. Modulation of p38 isoform activity may provide a new therapeutic approach for OA. [source] Tumor necrosis factor , and interleukin-1, modulate calcium and nitric oxide signaling in mechanically stimulated osteocytesARTHRITIS & RHEUMATISM, Issue 11 2009A. D. Bakker Objective Inflammatory diseases often coincide with reduced bone mass. Mechanoresponsive osteocytes regulate bone mass by maintaining the balance between bone formation and resorption. Despite its biologic significance, the effect of inflammation on osteocyte mechanoresponsiveness is not understood. To fill this gap, we investigated whether the inflammatory cytokines tumor necrosis factor , (TNF,) and interleukin-1, (IL-1,) modulate the osteocyte response to mechanical loading. Methods MLO-Y4 osteocytes were incubated with TNF, (0.5,30 ng/ml) or IL-1, (0.1,10 ng/ml) for 30 minutes or 24 hours, or with calcium inhibitors for 30 minutes. Cells were subjected to mechanical loading by pulsatile fluid flow (mean ± amplitude 0.7 ± 0.3 Pa, 5 Hz), and the response was quantified by measuring nitric oxide (NO) production using Griess reagent and by measuring intracellular calcium concentration ([Ca2+]i) using Fluo-4/AM. Focal adhesions and filamentous actin (F-actin) were visualized by immunostaining, and apoptosis was quantified by measuring caspase 3/7 activity. Cell-generated tractions were quantified using traction force microscopy, and cytoskeletal stiffness was quantified using optical magnetic twisting cytometry. Results Pulsatile fluid flow increased [Ca2+]i within seconds (in 13% of cells) and NO production within 5 minutes (4.7-fold). TNF, and IL-1, inhibited these responses. Calcium inhibitors decreased pulsatile fluid flow,induced NO production. TNF, and IL-1, affected cytoskeletal stiffness, likely because 24 hours of incubation with TNF, and IL-1, decreased the amount of F-actin. Incubation with IL-1, for 24 hours stimulated osteocyte apoptosis. Conclusion Our results suggest that TNF, and IL-1, inhibit mechanical loading,induced NO production by osteocytes via abrogation of pulsatile fluid flow,stimulated [Ca2+]i, and that IL-1, stimulates osteocyte apoptosis. Since both NO and osteocyte apoptosis affect osteoclasts, these findings provide a mechanism by which inflammatory cytokines might contribute to bone loss and consequently affect bone mass in rheumatoid arthritis. [source] Pathogenic T cells in murine lupus exhibit spontaneous signaling activity through phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathwaysARTHRITIS & RHEUMATISM, Issue 4 2003Florin Niculescu Objective To determine the activation status of two cytoplasmic signaling pathways, phosphatidylinositol 3-kinase (PI 3-kinase) and the mitogen-activated protein kinase (MAPK) family. Methods We studied the pathogenic CD4+ T cells that drive disease in the parent-into-F1 mouse model of lupus-like chronic graft-versus-host disease (GVHD). We determined immunoprecipitated kinase activity for PI 3-kinase and MAPK members (Raf-1, extracellular signal,regulated kinase 1 [ERK-1], c-Jun N-terminal kinase 1 [JNK-1], and p38 MAPK) from either unfractionated splenocytes or purified donor CD4+ T cells. Uninjected normal mice served as negative controls, and acute GVHD mice served as positive controls. Results Compared with negative controls, unfractionated splenocyte kinase activity from chronic GVHD mice was significantly increased for PI 3-kinase and JNK-1, but not for Raf-1, p38 MAPK, or ERK-1. Increased PI 3-kinase and JNK-1 activity was also seen in acute GVHD splenocytes, as was increased Raf-1 and p38 MAPK activity. The pattern of increased PI 3-kinase and JNK-1 activity seen in unfractionated chronic GVHD splenocytes was also seen in isolated donor, but not host, CD4+ T cells from chronic GVHD mice, indicating that donor CD4+ T cell signaling activity accounted for at least a portion of the activity observed in unfractionated splenocytes. Increased ERK-1 activity was not seen in either donor or host CD4+ T cells. This pattern of cytoplasmic signaling pathway in donor CD4+ T cells was associated with increased T cell receptor membrane signaling activation (Lck and Fyn phosphorylation) and increased transcription activation (phosphorylation of inhibitor of nuclear factor ,B), confirming the biologic significance of these observations. Conclusion The pathogenic T cells driving disease in this murine model exhibit activation in the form of spontaneous cytoplasmic signaling pathway activity that can be detected without in vitro restimulation and involves a T cell,specific (PI 3-kinase) and a nonspecific stress/cytokine pathway (JNK-1). These results raise the possibility that a full characterization of the signaling pathways active in pathogenic lupus T cells might lead to new therapeutic targets. [source] | ||||||||||