No abstract

The NLRP3 inflammasome drives many inflammatory processes and mediates IL-1 family cytokine release. Inflammasome activators typically damage cells, and may release lysosomal and mitochondrial products into the cytosol. Macrophages triggered by the NLRP3 inflammasome activator nigericin show reduced mitochondrial function and decreased cellular ATP. Release of mitochondrial ROS leads to subsequent lysosomal membrane permeabilization (LMP). NLRP3-deficient macrophages show comparable reduced mitochondrial function and ATP loss, but maintain lysosomal acidity, demonstrating that LMP is NLRP3 dependent. A subset of WT macrophages undergo subsequent mitochondrial membrane permeabilization (MMP) and die. Both LMP and MMP are inhibited by potassium, scavenging mitochondrial ROS, or NLRP3 deficiency, but are unaffected by cathepsin B or caspase-1 inhibitors. In contrast, IL-1β secretion is ablated by potassium, scavenging mitochondrial ROS, and both cathepsin B and caspase-1 inhibition. These results demonstrate interplay between lysosomes and mitochondria that sustain NLRP3 activation, and distinguish cell death from IL-1β release.

Since their initial discovery over a century ago, our knowledge of the functions of myoglobin and the mitochondrion has gradually evolved. The mitochondrion, once thought to be solely responsible for energy production, is now known to be an integral redox and apoptotic signal tranducer within the cell. Likewise, myoglobin, traditionally thought of only as an oxygen store, has emerged as a physiological catalyst that can modulate reactive oxygen species levels, facilitate oxygen diffusion and scavenge or generate nitric oxide (NO) depending on oxygen tensions within the cell. By virtue of its unique ability to regulate O2 and NO levels within the cell, myoglobin can modulate mitochondrial function in energy-demanding tissues such as the beating heart and exercising muscle. In this review, we present the conventional functions of myoglobin and mitochondria, and describe how these roles have been reassessed and advanced, particularly in the context of NO and nitrite signaling. We present the mechanisms by which mitochondria and myoglobin regulate one another within the cell through their interactions with NO and oxygen and discuss the implications of these interactions in terms of health and disease.

Glutathione transport into mitochondria is mediated by oxoglutarate (OGC) and dicarboxylate carrier (DIC) in the kidney and liver. However, transport mechanisms in brain mitochondria are unknown. We found that both carriers were expressed in the brain. Using cortical mitochondria incubated with physiological levels of glutathione, we found that butylmalonate, a DIC inhibitor, reduced mitochondrial glutathione to levels similar to those seen in mitochondria incubated without extramitochondrial glutathione (59% of control). In contrast, phenylsuccinate, an OGC inhibitor, had no effect (97% of control). Additional experiments with DIC and OGC short hairpin RNA in neuronal-like PC12 cells resulted in similar findings. Significantly, DIC inhibition resulted in increased reactive oxygen species (ROS) content in and H(2)O(2) release from mitochondria. It also led to decreased membrane potential, increased basal respiration rates, and decreased phosphorus-to-oxygen (P/O) ratios, especially when electron transport was initiated from complex I. Accordingly, we found that DIC inhibition impaired complex I activity, but not those for complexes II and III. This impairment was not associated with dislodgment of complex subunits. These results suggest that DIC is the main glutathione transporter in cortical mitochondria and that DIC-mediated glutathione transport is essential for these mitochondria to maintain ROS homeostasis and normal respiratory functions.