| dc.description.abstract | Aging is associated with various diseases, such as neurodegenerative diseases. However,
individual risk of developing these age-related diseases clearly varies due to differences in
both genetic and environmental factors. Autophagy is a prosurvival mechanism that
contributes to restore cellular homeostasis by eliminating excessive or damaged proteins,
protein aggregates and organelles. Hence, autophagy is believed to be cytoprotective in
diseases associated with protein aggregates. Interestingly, studies of autophagy deficient
animal models have revealed that such animals develop various kinds of age-associated
diseases including early-onset neurodegeneration. Hence, acceleration the autophagy process
may be promising in disease prevention.
Diet is a major environmental factor that strongly influences human health. Several
epidemiological studies have indicated an inverse correlation between dietary intake of n-3
PUFAs and the risk of developing many pathologies. However, the disease-preventive
mechanisms mobilized by n-3 PUFAs are not completely understood, and for several of the
age-related diseases where n-3 PUFAs have a protective effect, loss of autophagy has the
opposite outcome. We were therefore interested in exploring if there was a direct relation
between n-3 PUFAs and increased autophagy in disease relevant cell models. In the context
of age-related macular degeneration (AMD) we found that physiologically relevant doses of
the n-3 PUFA docosahexaenoic acid (DHA) induced a transient increase in cellular reactive
oxygen species (ROS) levels that activated the oxidative stress response regulator nuclear
factor, erythroid derived 2, like 2 (NFE2L2). Simultaneously, a transient increase in
intracellular protein aggregates containing sequestosome 1 (SQSTM1) and increased
autophagy was observed. Pretreatment with DHA rescued the cells from cell cycle arrest
induced by misfolded proteins or oxidative stress. Together, these results suggest that DHAinduced
increase in endogenous antioxidants, and selective autophagy of misfolded proteins
may be relevant to reduce the risk of developing aggregate-associated diseases like AMD.
Interestingly, our results also emphasize that exogenous antioxidants may interfere with and
counteract some of the putative positive effects of DHA, including the activation of NFE2L2.
Most age-related diseases share an underlying low-grade inflammation that contributes
to their development and progression. Despite increasing evidence of the established antiinflammatory
effects of n-3 PUFAs, the underlying mechanisms are still largely unknown.
Hence, we further investigated if the DHA-specific effects observed in epithelial cells also
exist in macrophages, and whether this could contribute to the established anti-inflammatory effects of n-3 PUFAs. We report that DHA induced a transient increase in cytosolic
SQSTM1-positive speckles and protein quality control also in macrophages. Further, DHA
influenced the expression of some inflammatory genes. Especially the C-X-C motif
chemokine 10 (CXCL10) in lipopolysaccharide (LPS)-activated human macrophages was
repressed in a very potent manner. Surprisingly, SQSTM1 was found to be necessary for a
proper induction of CXCL10 by LPS. Finally, we demonstrated that Tax1 (human T-cell
leukemia virus type I) binding protein 1 (TAX1BP1) and tumor necrosis factor, alpha-induced
protein 3 (TNFAIP3) associated with SQSTM1-positive speckles in response to DHA.
TAX1BP1 and TNFAIP3 form a ubiquitin-editing complex known to downregulate
inflammatory signaling, and we suggest that this could contribute to the DHA-induced
repression of CXCL10 expression. From this, we propose a model that connects the
autophagic cargo receptor SQSTM1 to the ubiquitin-editing machinery involved in the
regulation of inflammatory signaling.
Autophagy is a cytoprotective mechanism that also may be utilized by cancer cells to
provide resistance towards various treatment regimes. Multiple myeloma is an incurable
cancer of the antibody-producing plasma cells. Despite that proteasome inhibitors have
improved treatment significantly; inherent and acquired drug resistance remains a problem.
The mechanisms of proteasome inhibitor-induced cytotoxicity have remained elusive.
Therefore, using myeloma cell lines and cancer cells isolated from patients, we wanted to
examine whether autophagy protected the cells from cell death induced by proteasome
inhibitors. Surprisingly, we found that inhibiting autophagy specifically potentiated the
cytotoxicity of irreversible proteasome inhibitors. On the other hand, the reversible
proteasome inhibitor bortezomib was highly dependent on intracellular glutathione (GSH)
levels. Our work indicate that clinical studies combining irreversible- and reversible
proteasome inhibitors with autophagy inhibitors and drugs reducing intracellular GSH levels,
respectively, might be beneficial. | nb_NO |
