Charge of the mito brigade. Focus on "Changes in mitochondrial surface charge mediate recruitment of signaling molecules during apoptosis"

Fluxomics reveals cellular and molecular basis of increased renal ammoniagenesis

The kidney plays a critical role in excreting ammonia during metabolic acidosis and liver failure. The mechanisms behind this process have been poorly explored. The present study combines results of in vivo experiments of increased total ammoniagenesis with systems biology modeling, in which eight rats were fed an amino acid-rich diet (HD group) and eight a normal chow diet (AL group). We developed a method based on elementary mode analysis to study changes in amino acid flux occurring across the kidney in increased ammoniagenesis. Elementary modes represent minimal feasible metabolic paths in steady state. The model was used to predict amino acid fluxes in healthy and pre-hyperammonemic conditions, which were compared to experimental fluxes in rats. First, we found that total renal ammoniagenesis increased from 264 ± 68 to 612 ± 87 nmol (100 g body weight)^-1 min^-1 in the HD group (P = 0.021) and a concomitated upregulation of NKCC2 ammonia and other transporters in the kidney. In the kidney metabolic model, the best predictions were obtained with ammonia transport as an objective. Other objectives resulting in a fair correlation with the measured fluxes (correlation coefficient >0.5) were growth, protein uptake, urea excretion, and lysine and phenylalanine transport. These predictions were improved when specific gene expression data were considered in HD conditions, suggesting a role for the mitochondrial glycine pathway. Further studies are needed to determine if regulation through the mitochondrial glycine pathway and ammonia transporters can be modulated and how to use the kidney as a therapeutic target in hyperammonemia.

Cationic antimicrobial peptide NRC-03 induces oral squamous cell carcinoma cell apoptosis via CypD-mPTP axis-mediated mitochondrial oxidative stress

Pleurocidin-family cationic antimicrobial peptide NRC-03 exhibits potent and selective cytotoxicity towards cancer cells. However, the anticancer effect of NRC-03 in oral squamous cell carcinoma (OSCC) and the molecular mechanism of NRC-03 induced cancer cell death is still unclear. This study focused to investigate mitochondrial oxidative stress-mediated altered mitochondrial function involved in NRC-03-induced apoptosis of OSCC cells. NRC-03 entered the OSCC cells more easily than that of normal cells and bound to mitochondria as well as the nucleus, causing cell membrane blebbing, mitochondria swelling, and DNA fragmentation. NRC-03 induced high oxygen consumption, reactive oxygen species (ROS) release, mitochondrial dysfunction, and apoptosis in OSCC cells. Non-specific antioxidant N-acetyl-l-cysteine (NAC), or mitochondria-specific antioxidant mitoquinone (MitoQ) alleviated NRC-03-induced apoptosis and mitochondrial dysfunction indicated that NRC-03 exerts a cytotoxic effect in cancer cells via inducing cellular and mitochondrial oxidative stress. Moreover, the expression of cyclophilin D (CypD), the key component of mitochondrial permeability transition pore (mPTP), was upregulated in NRC-03-treated cancer cells. Blockade of CypD by siRNA-mediated depletion or pharmacological inhibitor cyclosporine A (CsA) significantly suppressed NRC-03-induced mitochondrial oxidative stress, mitochondrial dysfunction, and apoptosis. NRC-03 also activated MAPK/ERK and NF-κB pathways. Importantly, intratumoral administration of NRC-03 inhibited the growth of CAL-27 cells-derived tumors on xenografted animal models. Taken together, our study indicates that NRC-03 induces apoptosis in OSCC cells via the CypD-mPTP axis mediated mitochondrial oxidative stress.

Renal acid-base regulation: new insights from animal models

Because majority of biological processes are dependent on pH, maintaining systemic acid-base balance is critical. The kidney contributes to systemic acid-base regulation, by reabsorbing HCO3 (-) (both filtered by glomeruli and generated within a nephron) and acidifying urine. Abnormalities in those processes will eventually lead to a disruption in systemic acid-base balance and provoke metabolic acid-base disorders. Research over the past 30 years advanced our understanding on cellular and molecular mechanisms responsible for those processes. In particular, a variety of transgenic animal models, where target genes are deleted either globally or conditionally, provided significant insights into how specific transporters are contributing to the renal acid-base regulation. Here, we broadly overview the mechanisms of renal ion transport participating to acid-base regulation, with emphasis on data obtained from transgenic mice models.