Mitochondrial decay in aging

AbstractSeveral mitochondrial functions decline with age. The contributing factors include, the intrinsic rate of proton leakage across the inner mitochondrial membrane (a correlate of oxidant formation), decreased membrane fluidity, and decreased levels and function of cardiolipin, which supports the function of many of the proteins of the inner mitochondrial membrane. Oxidants generated by mitochondria appear to be the major source of the oxidative lesions that accumulate with age. Evidence supports the suggestion that age-associated accumulation of mitochondrial deficits due to oxidative damage is likely to be a major contributor to cellular, tissue, and organismal aging

Supercomplex Organization of the Electron Transfer System in Marine Bivalves, a Model of Extreme Longevity

The mitochondrial oxidative stress theory of aging suggests that the organelle’s decay contributes to the aging phenotype via exacerbated oxidative stress, loss of organ coordination and energetics, cellular integrity, and activity of the mitochondrial electron transfer system (ETS). Recent advances in understanding the structure of the ETS show that the enzymatic complexes responsible for oxidative phosphorylation are arranged in supramolecular structures called supercomplexes that lose organization during aging. Their exact role and universality among organisms are still under debate. Here, we take advantage of marine bivalves as an aging model to compare the structure of the ETS among species ranging from 28 to 507 years in maximal life span. Our results show that regardless of life span, the bivalve ETS is arrayed as a set of supercomplexes. However, bivalve species display varying degrees of ETS supramolecular organization with the highest supercomplex structures found in Arctica islandica, the longest-lived of the bivalve species under study. We discuss this comparative model in light of differences in the nature and stoichiometry of these complexes and highlight the potential link between the complexity of these superstructures and longer life spans

Cap-independent Nrf2 translation is part of a lipoic acid-stimulated detoxification stress response

AbstractLittle is known about either the basal or stimulated homeostatic mechanisms regulating nuclear tenure of Nf-e2-related factor 2 (Nrf2), a transcription factor that mediates expression of over 200 detoxification genes. Our data show that stress-induced nuclear Nrf2 accumulation is largely from de novo protein synthesis, rather than translocation from a pre-existing cytoplasmic pool. HepG2 cells were used to monitor nuclear Nrf2 24h following treatment with the dithiol micronutrient (R)-α-lipoic acid (LA; 50μM), or vehicle. LA caused a ≥2.5-fold increase in nuclear Nrf2 within 1h. However, pretreating cells with cycloheximide (50μg/ml) inhibited LA-induced Nrf2 nuclear accumulation by 94%. Providing cells with the mTOR inhibitor, rapamycin, decreased basal Nrf2 levels by 84% after 4h, but LA overcame this inhibition. LA-mediated de novo protein translation was confirmed using HepG2 cells transfected with a bicistronic construct containing an internal ribosome entry sequence (IRES) for Nrf2, with significant (P<0.05) increase in IRES use under LA treatment. These results suggest that a dithiol stimulus mediates Nrf2 nuclear tenure via cap-independent protein translation. Thus, translational control of Nrf2 synthesis, rather than reliance solely on pre-existing protein, may mediate the rapid burst of Nrf2 nuclear accumulation following stress stimuli

OLAM: A Wearable, Non-Contact Sensor for Continuous Heart-Rate and Activity Monitoring

A wearable, multi-modal sensor is presented that can non-invasively monitor a patient’s activity level and heart function concurrently for more than a week. The 4in² sensor incorporates both a non-contact heartrate sensor and a 5-axis inertial measurement unit (IMU), allowing simultaneous heart, respiration, and movement monitoring without requiring physical contact with the skin [1]. Hence, this Oregon State University Life and Activity Monitor (OLAM) provides the unique opportunity to combine motion data with heart-rate information, enabling assessment of actual physical activity beyond conventional movement sensors. OLAM also provides a unique platform for non-contact sensing, enabling the filtering of movement artifacts generated by the non-contact capacitive interface, using the IMU data as a movement noise channel. Intended to be used in clinical trials for weeks at a time with no physician intervention, the OLAM allows continuous noninvasive monitoring of patients, providing the opportunity for long-term observation into a patient’s physical activity and subtle longitudinal changes

Age-related loss of mitochondrial glutathione exacerbates menadione-induced inhibition of Complex I

The role of mitochondrial GSH (mGSH) in the enhanced age-related susceptibility to xenobiotic toxicity is not well defined. We determined mGSH status and indices of mitochondrial bioenergetics in hepatocytes from young and old F344 rats treated with 300 μM menadione, a concentration that causes 50% cell death in old. At this concentration, mGSH was significantly lost only in hepatocytes from old rats, and with near total depletion due to lower basal mGSH in aged cells. In old hepatocytes, menadione caused mitochondrial membrane potential to collapse, as well as significant deficits in maximal O2 consumption and respiratory reserve capacity, indicators of cellular bioenergetic resiliency. Further examination revealed that the menadione-mediated loss of respiratory reserve capacity in aged hepatocytes was from significant inhibition of Complex I activity and increased proton leak, for which an increase in Complex II activity was not able to compensate. These data demonstrate an age-related increase in mitochondrial susceptibility to a redox-cycling challenge, particularly in regards to Complex I activity, and provide a plausible mechanism to link this vulnerability to mGSH perturbations. Keywords: Aging, Redox cyclers, Mitochondria, Glutathione, Respiratory reserve capacit

Acetyl-L-carnitine supplementation reverses the age-related decline in carnitine palmitoyltransferase 1 (CPT1) activity in interfibrillar mitochondria without changing the L-carnitine content in the rat heart

The aging heart displays a loss of bioenergetic reserve capacity partially mediated through lower fatty acid utilization. We investigated whether the age-related impairment of cardiac fatty acid catabolism occurs, at least partially, through diminished l

Hepatocyte nuclear factor 1 is essential for transcription of sodium-dependent vitamin C transporter protein 1

Transport and distribution of vitamin C is primarily regulated by the function of sodium-dependent vitamin C transporters (SVCTs). SVCT1 is expressed in the small intestine, liver, and kidney, organs that play a vital role in whole body vitamin C homeostasis. Despite the importance of this protein, little is known about regulation of the gene encoding SVCT1, Slc23a1. In this study, we present the first investigation of the transcriptional regulation of human Slc23a1, identifying transcription factors that may influence its expression. A 1,239-bp genomic DNA fragment corresponding to the 5′-flanking region of Slc23a1 was isolated from a human hepatocarcinoma cell line (HepG2) and sequenced. When cloned into a reporter gene construct, robust transcriptional activity was seen in this sequence, nearly 25-fold above the control vector. Deletion analysis of the SVCT1 reporter gene vector defined the minimal active promoter as a small 135-bp region upstream of the transcriptional start site. While several transcription factor binding sites were identified within this sequence, reporter constructs showed that basal transcription required the binding of hepatic nuclear factor 1 (HNF-1) to its cognate sequence. Furthermore, mutation of this HNF-1 binding site resulted in complete loss of luciferase expression, even in the context of the whole promoter. Additionally, small interfering RNA knockdown of both members of the HNF-1 family, HNF-1α and HNF-1β, resulted in a significant decline in SVCT1 transcription. Together, these data suggest that HNF-1α and/or HNF-1β binding is required for SVCT1 expression and may be involved in the coordinate regulation of whole body vitamin C status