Divergent responses of chondrocytes and endothelial cells to shear stress: cross-talk among COX-2, the phase 2 response, and apoptosis

Diet and Cancer: Facts and Controversies

Evidence continues to mount that dietary components are important determinants of cancer risk and tumor behavior. Although these linkages are fascinating, numerous inconsistencies are also evident in the literature. Although multifactorial, these discrepancies likely reflect variation in the ability of food constituents to reach and/or modify critical molecular targets. Genetic polymorphisms can alter the response to dietary components (nutrigenetic effect) by influencing the absorption, metabolism, or site of action. Likewise, variation in DNA methylation patterns and other epigenomic events that influence overall gene expression can influence the biological response to food components and vice versa. Fluctuations in the ability of food components to increase or depress gene expression (nutritional transcriptomic effect) may also account for some of the inconsistencies in the response to foods. Functional proteomic studies that capture all of the proteins produced by a species and link them to physiological significance within the cell will be fundamental to understanding the relationship between dietary interventions, proteome changes, and cancer. Although a bioactive food component may influence a number of key molecular events that are involved with cancer prevention, to do so it must achieve an effective concentration within the target site, be in the correct metabolic form, and bring about a change in one or more small molecular weight signals in the cellular milleau (metabolomic effects). Fundamental to assessing and evaluating the significance of the interrelationships among bioactive food components with nutrigenetics, nutritional epigenomics, nutritional transcriptomics, proteomics, and metabolomics is knowledge about the appropriate tissue/cell or surrogate to evaluate and validated biomarkers that reflect changes in each. As the era of molecular nutrition grows, a greater understanding about the role of foods and their components on cancer risk and tumor behavior will surely unfold. Such information will be critical in the development of effective preemptive approaches to reduce the cancer burden.

Inhibition of caspase-9 reduces chondrocyte apoptosis and proteoglycan loss following mechanical trauma

OBJECTIVE

Chondrocyte death, a notable feature of osteoarthritis, may play a role in the initiation of cartilage degeneration. The present study was aimed at uncovering the nature and involvement of cell death in the initiation of cartilage degeneration induced by mechanical trauma.

METHODS

Articular cartilage discs obtained from healthy skeletally mature horses were subjected to a single-impact load (500 g from 50 mm) using a simple drop-tower device and cultured in vitro for 48 h. Chondrocyte death was examined using two independent methods: transmission electron microscopy and caspase-3 activity assay. To elucidate the signalling mechanisms involved in impact-induced cell death measured by terminal deoxynucleotidyl transferase-deoxyuridine triphosphate (dUTP) nick-end labelling (TUNEL), cartilage discs were incubated with specific caspase-3, -8 and -9 inhibitors prior to impact. Additionally, weight gain and glycosaminoglycan (GAG) release, markers of cartilage degeneration were monitored.

RESULTS

After 48 h, ultrastructural evidence of apoptosis was observed. Caspase-3 was activated after 12h of culture post-impact. When quantified by TUNEL, impact trauma induced death in 52.6% of superficial chondrocytes after 48 h in culture, compared to 4.2% in unimpacted controls. Specific caspases-3 and -9 inhibitors significantly reduced impact-induced apoptosis to 24.3% and 14.7%, respectively. Caspase-8 inhibition had no effect on chondrocyte death (60.3%). Impact-induced GAG release into the medium was significantly reduced by inhibition of cell death, but weight gain remained unaffected by caspase inhibition.

CONCLUSION

These results suggest that impact trauma-induced chondrocyte death is predominantly due to caspase-9-dependent apoptosis and is linked to cartilage degeneration.

EGFR-activated signaling and actin remodeling regulate cyclic stretch-induced NRF2-ARE activation

Cyclic stretch (CS) associated with mechanical ventilation (MV) can cause excessive alveolar and endothelial distention, resulting in lung injury and inflammation. Antioxidant enzymes (AOEs) play a major role in suppressing these effects. The transcription factor Nrf2, via the antioxidant response element (ARE), alleviates pulmonary toxicant- and oxidant-induced oxidative stress by up-regulating the expression of several AOEs. Although gene expression profiling has revealed the induction of AOEs in the lungs of rodents exposed to MV, the mechanisms by which mechanical forces, such as CS, regulate the activation of Nrf2-dependent ARE-transcriptional responses are poorly understood. To mimic mechanical stress associated with MV, we have cultured pulmonary alveolar epithelial and endothelial cells on collagen I-coated BioFlex plates and subjected them to CS. CS exposure stimulated ARE-driven transcriptional responses and subsequent AOE expression. Ectopic expression of a dominant-negative Nrf2 suppressed the CS-stimulated ARE-driven responses. Our findings suggest that actin remodeling is necessary but not sufficient for high-level CS-induced ARE activation in both epithelial and endothelial cells. We also found that inhibition of EGFR activity by a pharmacologic agent ablated the CS-induced ARE transcriptional response in both cell types. Additional studies revealed that amphiregulin, an EGFR ligand, regulates this process. We further demonstrated that the PI3K-Akt pathway acts as the downstream effector of EGFR and regulates CS-induced ARE-activation in an oxidative stress-dependent manner. Collectively, these novel findings suggest that EGFR-activated signaling and actin remodeling act in concert to regulate the CS-induced Nrf2-ARE transcriptional response and subsequent AOE expression.