Wearable Aptalyzer Integrates Microneedle and Electrochemical Sensing for in Vivo Monitoring of Glucose and Lactate in live Animals.

Continuous monitoring of clinically relevant biomarkers within the interstitial fluid (ISF) using microneedle (MN)-based assays, has the potential to transform healthcare. This study introduces the Wearable Aptalyzer, an integrated system fabricated by combining biocompatible hydrogel microneedle (HMN) arrays for ISF extraction with an electrochemical aptamer-based biosensor for in situ monitoring of blood analytes. The use of aptamers enables continuous monitoring of a wide range of analytes, beyond what is possible with enzymatic monitoring. The Wearable Aptalyzer is used for real-time and multiplexed monitoring of glucose and lactate in ISF. Validation experiments using live mice and rat models of Type 1 Diabetes demonstrate strong correlation between the measurements collected from the Wearable Aptalyzer in ISF and those obtained from gold-standard techniques for blood glucose and lactate, for each analyte alone and in combination. The Wearable Aptalyzer effectively addresses the limitations inherent in enzymatic detection methods as well as solid MN biosensors and addresses the need for reliable and multiplexed bioanalytical monitoring in vivo. This article is protected by copyright. All rights reserved.

Effects of lithium isotopes on sodium/lithium co-transport and calcium efflux through the sodium/calcium/lithium exchanger in mitochondria.

The effects of lithium (Li) isotopes and their impact on biological processes have recently gained increased attention due to the significance of Li as a pharmacological agent and the potential that Li isotopic effects in neuroscience contexts may constitute a new example of quantum effects in biology. Previous studies have shown that the two Li isotopes, which differ in mass and nuclear spin, have unusual different effects in vivo and in vitro and, although some molecular targets for Li isotope fractionation have been proposed, it is not known whether those result in observable downstream neurophysiological effects. In this work we studied fluxes of Li+, sodium (Na+) and calcium (Ca2+) ions in the mitochondrial sodium/calcium/lithium exchanger (NCLX), the only transporter known with recognized specificity for Li+. We studied the effect of Li+ isotopes on Ca2+ efflux from heart mitochondria in comparison to natural Li+ and Na+ using Ca2+-induced fluorescence and investigated a possible Li isotope fractionation in mitochondria using inductively coupled plasma mass spectrometry (ICP-MS). Our fluorescence data indicate that Ca2+ efflux increases with higher concentrations of either Li+ or Na+. We found that the simultaneous presence of Li+ and Na+ increases Ca2+ efflux compared to Ca2+ efflux caused by the same concentration of Li+ alone. However, no differentiation in the Ca2+ efflux between the two Li+ isotopes was observed, either for Li+ alone or in mixtures of Li+ and Na+. Our ICP-MS data demonstrate that there is selectivity between Na+ and Li+ (greater Na+ than Li+ uptake) and, most interestingly, between the Li+ isotopes (greater 6Li+ than 7Li+ uptake) by the inner mitochondrial membrane. In summary, we observed no Li+ isotope differentiation for Ca2+ efflux in mitochondria via NCLX but found a Li+ isotope fractionation during Li+ uptake by mitochondria with NCLX active or blocked. Our results suggest that the transport of Li+ via NCLX is not the main pathway for Li+ isotope fractionation and that this differentiation does not affect Ca2+ efflux in mitochondria. Therefore, explaining the puzzling effects of Li+ isotopes observed in other contexts will require further investigation to identify the molecular targets for Li+ isotope differentiation.

Indentation mechanics and native collagen content in the cartilaginous endplate: A comparison between porcine cervical and human lumbar spines.

This study characterized the regional indentation mechanics and native collagen content in cartilaginous endplates (CEPs) from the porcine cervical spine, young human lumbar spine, and aged human lumbar spine. Seventeen endplates were included in this study: six porcine cervical, nine young human lumbar, and two aged human lumbar. Width and depth measurements were obtained using a digital caliper and used to size-normalize and identify the central, anterior, posterior, and lateral regions. Regional microindentation tests were performed using a serial robot, where surface locations were loaded/unloaded at 0.1 mm/s and held at a constant 10 N force for 30 s. Loading stiffness and creep displacement were obtained from force-displacement data. Immunofluorescence staining for type I and type II collagen was subsequently performed on sagittal sections of all endplate regions. 255 images were obtained from which fluorescence intensity, sub-surface void area, and cartilage thickness were measured. CEPs from the young human lumbar spine were, on average, 27% more compliant, 0.891 mm thicker, had a lower fluorescence intensity for native collagen proteins within the cartilage (-58%) and subchondral bone (-24%), and had a sub-surface void area that was 19.7 times greater than porcine cervical CEPs. Compared to aged human lumbar CEPs, young human lumbar CEPs were 57% stiffer, 0.568 mm thicker, had a higher fluorescence intensity for native collagen proteins within the cartilage (+30%) and subchondral bone (+46%), and had a sub-surface void area that was 10.6 times smaller. Although not a perfect mechanical and structural surrogate, porcine cervical CEPs provided initial conditions that may be more representative of the young and healthy human lumbar spine compared to aged human cadaveric specimens. The indentation properties presented may have further applications to finite element models of the human lumbar spine.

Augmented mitochondrial apoptotic signaling impairs C2C12 myoblast differentiation following cellular aging through sequential passaging.

Aging is associated with the steady decline of several cellular processes. The loss of skeletal muscle mass, termed sarcopenia, is one of the major hallmarks of aging. Aged skeletal muscle exhibits a robust reduction in its regenerative capacity due to dysfunction (i.e., senescence, lack of self-renewal, and impaired differentiation) of resident muscle stem cells, called satellite cells. To replicate aging in vitro, immortalized skeletal muscle cells (myoblasts) can be treated with various agents to mimic age-related dysfunction; however, these come with their own set of limitations. In the present study, we used sequential passaging of mouse myoblasts to mimic impaired differentiation that is observed in aged skeletal muscle. Further, we investigated mitochondrial apoptotic mechanisms to better understand the impaired differentiation in these "aged" cells. Our data shows that sequential passaging (>20 passages) of myoblasts is accompanied with significant reductions in differentiation and elevated cell death. Furthermore, high-passage (HP) myoblasts exhibit greater mitochondrial-mediated apoptotic signaling through mitochondrial BAX translocation, CYCS and AIFM1 release, and caspase-9 activation. Finally, we show that inhibition of mitochondrial outer membrane permeability partly recovered differentiation in HP myoblasts. Together, our findings suggests that mitochondrial apoptotic signaling is a contributing factor to the diminished differentiation that is observed in aged myoblasts.

Initiation and accumulation of loading induced changes to native collagen content and microstructural damage in the cartilaginous endplate.

BACKGROUND CONTEXT: Injury to the cartilaginous endplate (CEP) is linked to clinically relevant low back disorders, including intervertebral disc degeneration and pain reporting. Despite this link to clinical disorders, the CEP injury pathways and the modulating effect of mechanical loading parameters on the pace of damage accumulation remains poorly understood. PURPOSE: This study examined the effect of cyclic loading on the initiation and accumulation of changes to native collagen content (type I, type II) and microstructural damage in the central region of cadaveric porcine CEPs. STUDY DESIGN: In vitro longitudinal study. METHODS: One hundred fourteen porcine cervical spinal units were included (N=6 per group). The study contained a control group (no cyclic loading) and 18 experimental groups that differed by loading duration (1,000, 3,000, 5,000 cycles), joint posture (flexed, neutral), and cyclic peak compression variation (10%, 20%, 40%). Multicolor immunofluorescence staining was used to quantify loading induced changes to type I (ie, subchondral bone) and type II (ie, endplate) native collagen content (fluorescence area, fluorescence intensity) and microstructural damage (pore area [transverse plane], void area along the CEP-bone border [sagittal plane]). RESULTS: Significant main effects of loading duration and posture were observed for fluorescence area and fluorescence intensity of type I and II collagen. In the transverse plane, type II fluorescence area significantly decreased following 1,000 cycles (-12%), but a significant change in fluorescence intensity was not observed until 3,000 cycles (-17%). Type II fluorescence area (-14%) and intensity (-10%) were both significantly less in flexed postures compared to neutral. Similar trends were observed for type I collagen in the sagittal plane sections. Generally, significant changes to fluorescence area were accompanied by the development of microstructural voids along the endplate-subchondral bone border. CONCLUSIONS: These findings demonstrate that microstructural damage beneath the endplate surface occurs before significant changes to the density of native type I and II collagen fibers. Although flexed postures were associated with greater and accelerated changes to native collagen content, the injury initiation mechanism appears similar to neutral. CLINICAL SIGNIFICANCE: Neutral joint postures can delay the initiation and pace of microdamage accumulation in the CEP during low-to-moderate demand lifting tasks. Furthermore, the management of peak compression exposures appeared relevant only when a neutral posture was maintained. Therefore, clinical low back injury prevention and load management efforts should consider low back posture in parallel with applied joint forces.

A Hydrogel Microneedle Assay Combined with Nucleic Acid Probes for On-Site Detection of Small Molecules and Proteins.

Point-of-care testing (POCT) of clinical biomarkers is critical to health monitoring and timely treatment, yet biosensing assays capable of detecting biomarkers without the need for costly external equipment and reagents are limited. Blood-based assays are, specifically, challenging as blood collection is invasive and follow-upprocessing is required. Here, we report a versatile assay that employs hydrogel microneedles (HMNs) to extract interstitial fluid (ISF), in a minimally invasive manner integrated with graphene oxide-nucleic acid (GO.NA)-based fluorescence biosensor to sense the biomarkers of interest in situ. The HMN-GO.NA assay is supplemented with a portable detector, enabling a complete POCT procedure. Our system could successfully measure four clinically important biomarkers (glucose, uric acid (UA), insulin, and serotonin) ex vivo, in addition, to accurately detecting glucose and UA in vivo.

Incidence of Compression-Induced Microinjuries in the Cartilage Endplate of the Spine.

STUDY DESIGN: In vitro biomechanical study. OBJECTIVE: This study investigated the incidence of microstructural endplate injuries caused by cyclic compression loading. The covarying effects of joint posture, loading duration, and peak compression variation were assessed. SUMMARY OF BACKGROUND DATA: The endplate is physiologically and functionally important for the maintenance of spine health. Despite the ability to radiographically diagnose and classify macroscopic endplate injuries, the mechanical mechanisms of injury initiation and progression remain largely unknown. METHODS: One hundred and fourteen porcine cervical spinal units were examined. All spinal units were exposed to preconditioning tests, followed by cyclic compression testing that differed by posture (flexed, neutral), loading duration (1000, 3000, 5000 cycles), and peak compression variation (10%, 20%, 40%). Microstructural injuries were examined via immunofluorescence staining for collagen I ( i.e. , subchondral bone) and collagen II ( i.e. , hyaline cartilage endplate). From the 678 acquired images, the incidence of node, avulsion, cartilage, and circumferential pore microinjuries were determined. The distribution of microinjuries between postures, spinal levels, and vertebrae were evaluated along with the associations of incidence and size of injuries with loading duration and variation. RESULTS: The incidence of avulsion injuries was significantly greater in caudal endplates (92%, P =0.006). No other injuries differed between vertebrae ( P ≥0.804) and no significant differences were observed between spinal units ( P ≥0.158). With respect to posture, 100% ( P <0.001) and 90% ( P <0.001) of avulsion and node injuries, respectively, occurred in flexed postures, whereas 82% ( P <0.001) of cartilage microinjuries occurred with neutral postures. Loading duration was significantly associated with microinjury incidence ( P <0.001) and lesion size ( P ≤0.003). CONCLUSION: Mechanical factors such as posture did not appreciably affect the incidence of endplate injury, but microinjury types were differently distributed between flexed and neutral postures. The duration of compression was shown to have an important role in the incidence of microinjury and lesion size.

Mitochondrial creatine sensitivity is lost in the D2.mdx model of Duchenne muscular dystrophy and rescued by the mitochondrial-enhancing compound Olesoxime.

Duchenne muscular dystrophy (DMD) is associated with distinct mitochondrial stress responses. Here, we aimed to determine whether the prospective mitochondrial-enhancing compound Olesoxime, prevents early-stage mitochondrial stress in limb and respiratory muscle from D2.mdx mice using a proof-of-concept short-term regimen spanning 10-28 days of age. As mitochondrial-cytoplasmic energy transfer occurs via ATP- or phosphocreatine-dependent phosphate shuttling, we assessed bioenergetics with or without creatine in vitro. We observed that disruptions in Complex I-supported respiration and mH2O2 emission in D2.mdx quadriceps and diaphragm were amplified by creatine demonstrating mitochondrial creatine insensitivity manifests ubiquitously and early in this model. Olesoxime selectively rescued or maintained creatine sensitivity in both muscles, independent of the abundance of respiration-related mitochondrial proteins or mitochondrial creatine kinase cysteine oxidation in quadriceps. Mitochondrial calcium retention capacity and glutathione were altered in a muscle-specific manner in D2.mdx but were generally unchanged by Olesoxime. Treatment reduced serum creatine kinase (muscle damage) and preserved cage hang-time, microCT-based volumes of lean compartments including whole body, hindlimb and bone, recovery of diaphragm force after fatigue, and cross-sectional area of diaphragm type IIX fiber, but reduced type I fibers in quadriceps. Grip strength, voluntary wheel-running and fibrosis were unaltered by Olesoxime. In summary, locomotor and respiratory muscle mitochondrial creatine sensitivities are lost during early stages in D2.mdx mice but are preserved by short-term treatment with Olesoxime in association with specific indices of muscle quality suggesting early myopathy in this model is at least partially attributed to mitochondrial stress.

Emerging role of mitophagy in myoblast differentiation and skeletal muscle remodeling.

Mitochondrial turnover in the form of mitophagy is emerging as a central process in maintaining cellular function. The degradation of damaged mitochondria through mitophagy is particularly important in cells/tissues that exhibit high energy demands. Skeletal muscle is one such tissue that requires precise turnover of mitochondria in several conditions in order to optimize energy production and prevent bioenergetic crisis. For instance, the formation of skeletal muscle (i.e., myogenesis) is accompanied by robust turnover of low-functioning mitochondria to eventually allow the formation of high-functioning mitochondria. In mature skeletal muscle, alterations in mitophagy-related signaling occur during exercise, aging, and various disease states. Nonetheless, several questions regarding the direct role of mitophagy in various skeletal muscle conditions remain unknown. Furthermore, given the heterogenous nature of skeletal muscle with respect to various cellular and molecular properties, and the plasticity in these properties in various conditions, the involvement and characterization of mitophagy requires more careful consideration in this tissue. Therefore, this review will highlight the known mechanisms of mitophagy in skeletal muscle, and discuss their involvement during myogenesis and various skeletal muscle conditions. This review also provides important considerations for the accurate measurement of mitophagy and interpretation of data in skeletal muscle.

Mitochondrial Apoptotic Signaling Involvement in Remodeling During Myogenesis and Skeletal Muscle Atrophy.

Mitochondria play a major role in apoptotic signaling. In addition to its role in eliminating dysfunctional cells, mitochondrial apoptotic signaling is implicated as a key component of myogenic differentiation and skeletal muscle atrophy. For example, the activation of cysteine-aspartic proteases (caspases; CASP's) can aid in the initial remodeling stages of myogenic differentiation by cleaving protein kinases, transcription factors, and cytoskeletal proteins. Precise regulation of these signals is needed to prevent excessive cell disassemble and subsequent cell death. During skeletal muscle atrophy, the activation of CASP's and mitochondrial derived nucleases participate in myonuclear fragmentation, a potential loss of myonuclei, and cleavage of contractile structures within skeletal muscle. The B cell leukemia/lymphoma 2 (BCL2) family of proteins play a significant role in regulating myogenesis and skeletal muscle atrophy by governing the initiating steps of mitochondrial apoptotic signaling. This review discusses the role of mitochondrial apoptotic signaling in skeletal muscle remodeling during myogenic differentiation and skeletal muscle pathological states, including aging, disuse, and muscular dystrophy.

Muscle weakness precedes atrophy during cancer cachexia and is linked to muscle-specific mitochondrial stress.

Muscle weakness and wasting are defining features of cancer-induced cachexia. Mitochondrial stress occurs before atrophy in certain muscles, but the possibility of heterogeneous responses between muscles and across time remains unclear. Using mice inoculated with Colon-26 cancer, we demonstrate that specific force production was reduced in quadriceps and diaphragm at 2 weeks in the absence of atrophy. At this time, pyruvate-supported mitochondrial respiration was lower in quadriceps while mitochondrial H2O2 emission was elevated in diaphragm. By 4 weeks, atrophy occurred in both muscles, but specific force production increased to control levels in quadriceps such that reductions in absolute force were due entirely to atrophy. Specific force production remained reduced in diaphragm. Mitochondrial respiration increased and H2O2 emission was unchanged in both muscles versus control while mitochondrial creatine sensitivity was reduced in quadriceps. These findings indicate muscle weakness precedes atrophy and is linked to heterogeneous mitochondrial alterations that could involve adaptive responses to metabolic stress. Eventual muscle-specific restorations in specific force and bioenergetics highlight how the effects of cancer on one muscle do not predict the response in another muscle. Exploring heterogeneous responses of muscle to cancer may reveal new mechanisms underlying distinct sensitivities, or resistance, to cancer cachexia.

Mechanically induced histochemical and structural damage in the annulus fibrosus and cartilaginous endplate: a multi-colour immunofluorescence analysis.

The annulus fibrosus (AF) and endplate (EP) are collagenous spine tissues that are frequently injured due to gradual mechanical overload. Macroscopic injuries to these tissues are typically a by-product of microdamage accumulation. Many existing histochemistry and biochemistry techniques are used to examine microdamage in the AF and EP; however, there are several limitations when used in isolation. Immunofluorescence may be sensitive to histochemical and structural damage and permits the simultaneous evaluation of multiple proteins-collagen I (COL I) and collagen II (COL II). This investigation characterized the histochemical and structural damage in initially healthy porcine spinal joints that were either unloaded (control) or loaded via biofidelic compression loading. The mean fluorescence area and mean fluorescence intensity of COL II significantly decreased (- 54.9 and - 44.8%, respectively) in the loaded AF (p ≤ 0.002), with no changes in COL I (p ≥ 0.471). In contrast, the EP displayed similar decreases in COL I and COL II fluorescence area (- 35.6 and - 37.7%, respectively) under loading conditions (p ≤ 0.027). A significant reduction (-31.1%) in mean fluorescence intensity was only observed for COL II (p = 0.043). The normalized area of pores was not altered on the endplate surface (p = 0.338), but a significant increase (+ 7.0%) in the void area was observed on the EP-subchondral bone interface (p = 0.002). Colocalization of COL I and COL II was minimal in all tissues (R < 0.34). In conclusion, the immunofluorescence analysis captured histochemical and structural damage in collagenous spine tissues, namely, the AF and EP.

Physical Exercise and Liver Autophagy: Potential Roles of IL-6 and Irisin.

Autophagic dysregulation contributes to liver diseases. Although some investigations have examined the effects of endurance and resistance exercise on autophagy activation, potential myokines responsible for skeletal muscle-liver crosstalk are still unknown. Based on experimental studies and bioinformatics, we hypothesized that interleukin 6 (IL-6) and irisin might be key players in the contraction-induced release of molecules that regulate liver autophagic responses.

Examining interindividual differences in select muscle and whole-body adaptations to continuous endurance training.

NEW FINDINGS: What is the central question of the study? Do interindividual differences in trainability exist for morphological and molecular skeletal muscle responses to aerobic exercise training? What is the main finding and its importance? Interindividual differences in trainability were present for some, but not all, morphological and molecular outcomes included in our study. Our findings suggest that it is inappropriate, and perhaps erroneous, to assume that variability in observed responses reflects interindividual differences in trainability in skeletal muscle responses to aerobic exercise training. ABSTRACT: Studies have interpreted a wide range of morphological and molecular changes in human skeletal muscle as evidence of interindividual differences in trainability. However, these interpretations fail to account for the influence of random measurement error and within-subject variability. The purpose of the present study was to use the standard deviation of individual response (SDIR ) statistic to test the hypothesis that interindividual differences in trainability are present for some but not all skeletal muscle outcomes. Twenty-nine recreationally active males (age: 21 ± 2 years; BMI: 24 ± 3 kg/m2 ; V̇O2peak ; 45 ± 7 ml/kg/min) completed 4 weeks of continuous training (REL; n = 14) or control (n = 15). Maximal enzyme activities (citrate synthase and ß-hydroxyacyl-CoA dehydrogenase), capillary density, fibre type composition, fibre-specific succinate dehydrogenase activity and substrate storage (intramuscular triglycerides and glycogen), and markers of mitophagy (BCL2-interacting protein 3 (BNIP3), BNIP3-like protein, parkin and PTEN-induced kinase 1) were measured in vastus lateralis samples collected before and after the intervention. We also calculated SDIR values for V̇O2peak , peak work rate and the onset of blood lactate accumulation for the REL group and a separate group that exercised at the negative talk test stage. Although positive SDIR values - indicating interindividual differences in trainability - were obtained for aerobic capacity outcomes, maximal enzyme activities, capillary density, all fibre-specific outcomes and BNIP3 protein content, the remaining outcomes produced negative SDIR values indicating a large degree of random measurement error and/or within-subject variability. Our findings question the interpretation of heterogeneity in observed responses as evidence of interindividual differences in trainability and highlight the importance of including control groups when analysing individual skeletal muscle response to exercise training.

Mitochondrial network remodeling: an important feature of myogenesis and skeletal muscle regeneration.

The remodeling of the mitochondrial network is a critical process in maintaining cellular homeostasis and is intimately related to mitochondrial function. The interplay between the formation of new mitochondria (biogenesis) and the removal of damaged mitochondria (mitophagy) provide a means for the repopulation of the mitochondrial network. Additionally, mitochondrial fission and fusion serve as a bridge between biogenesis and mitophagy. In recent years, the importance of these processes has been characterised in multiple tissue- and cell-types, and under various conditions. In skeletal muscle, the robust remodeling of the mitochondrial network is observed, particularly after injury where large portions of the tissue/cell structures are damaged. The significance of mitochondrial remodeling in regulating skeletal muscle regeneration has been widely studied, with alterations in mitochondrial remodeling processes leading to incomplete regeneration and impaired skeletal muscle function. Needless to say, important questions related to mitochondrial remodeling and skeletal muscle regeneration still remain unanswered and require further investigation. Therefore, this review will discuss the known molecular mechanisms of mitochondrial network remodeling, as well as integrate these mechanisms and discuss their relevance in myogenesis and regenerating skeletal muscle.

Increasing whole-body energetic stress does not augment fasting-induced changes in human skeletal muscle.

Fasting rapidly (≤ 6 h) activates mitochondrial biogenic pathways in rodent muscle, an effect that is absent in human muscle following prolonged (10-72 h) fasting. We tested the hypotheses that fasting-induced changes in human muscle occur shortly after food withdrawal and are modulated by whole-body energetic stress. Vastus lateralis biopsies were obtained from ten healthy males before, during (4 h), and after (8 h) two supervised fasts performed with (FAST+EX) or without (FAST) 2 h of arm ergometer exercise (~ 400 kcal of added energy expenditure). PGC-1α mRNA (primary outcome measure) was non-significantly reduced (p = 0.065 [ηp2 = 0.14]) whereas PGC-1α protein decreased (main effect of time: p < 0.01) during both FAST and FAST+EX. P53 acetylation increased in both conditions (main effect of time: p < 0.01) whereas ACC and SIRT1 phosphorylation were non-significantly decreased (both p < 0.06 [ηp2 = 0.15]). Fasting-induced increases in NFE2L2 and NRF1 protein were observed (main effects of time: p < 0.03), though TFAM and COXIV protein remained unchanged (p > 0.05). Elevating whole-body energetic stress blunted the increase in p53 mRNA, which was apparent during FAST only (condition × time interaction: p = 0.04). Select autophagy/mitophagy regulators (LC3BI, LC3BII, BNIP3) were non-significantly reduced at the protein level (p ≤ 0.09 [ηp2 > 0.13]) but the LC3II:I ratio was unchanged (p > 0.05). PDK4 mRNA (p < 0.01) and intramuscular triglyceride content in type IIA fibers (p = 0.04) increased similarly during both conditions. Taken together, human skeletal muscle signaling, mRNA/protein expression, and substrate storage appear to be unaffected by whole-body energetic stress during the initial hours of fasting.

Autophagy displays divergent roles during intermittent amino acid starvation and toxic stress-induced senescence in cultured skeletal muscle cells.

Due to the ever-expanding functions attributed to autophagy, there is widespread interest in understanding its contribution to human physiology; however, its specific cellular role as a stress-response mechanism is still poorly defined. To investigate autophagy's role in this regard, we repeatedly subjected cultured mouse myoblasts to two stresses with diverse impacts on autophagic flux: amino acid and serum withdrawal (Hank's balanced salt solution [HBSS]), which robustly induces autophagy, or low-level toxic stress (staurosporine, STS). We found that intermittent STS (int-STS) administration caused cell cycle arrest, development of enlarged and misshapen cells/nuclei, increased senescence-associated heterochromatic foci and senescence-associated ß-galactosidase activity, and prevented myogenic differentiation. These features were not observed in cells intermittently incubated in HBSS (int-HB). While int-STS cells displayed less DNA damage (phosphorylated H2A histone family, member X content) and caspase activity when administered cisplatin, int-HB cells were protected from STS-induced cell death. Interestingly, STS-induced senescence was attenuated in autophagy related 7-deficient cells. Therefore, while repeated nutrient withdrawal did not cause senescence, autophagy was required for senescence caused by toxic stress. These results illustrate the context-dependent effects of different stressors, potentially highlighting autophagy as a distinguishing factor.

Repeatability of training-induced skeletal muscle adaptations in active young males.

OBJECTIVES: Measurements of protein content, enzymatic activity, and/or capillarization are frequently utilized as markers of skeletal muscle adaptation following exercise training. Whether changes in these markers of muscle adaptation are repeatable when individuals are repeatedly exposed to the same training stimulus is unknown. The purpose of this study was to test the repeatability of skeletal muscle adaptations to two identical training periods. METHODS: Ten active young males (age: 22 ±â€¯2 years; VO2max: 57 ±â€¯7 ml/kg/min) were exposed to two identical four-week periods of supervised high-intensity interval running (4 × 4 min at 90-95% of HRmax interspersed with 3-min at 70-75% HRmax) separated by a 3-month wash-out period. Vastus lateralis biopsies were obtained before and after each training period for the measurement of protein content, enzyme activity, and capillary density. RESULTS: Training-induced changes in citrate synthase (CS) maximal activity, protein content (PGC-1α, OXPHOS, and LDH-A), and capillary density were not repeatable within individuals (r = -0.52-0.15; ICCs: -0.42-0.04; CVs: 11-67%). Several OXPHOS complex subunits also demonstrated dissimilar group-level adaptations (period × time interaction effects, p < 0.05) with large differences (ηp2 > 0.4) between training periods. A large (ηp2 = 0.65) increase in capillary density was apparent irrespective of training period (main effect of time, p = 0.05). CONCLUSIONS: An individual (or a group of individuals) may exhibit dissimilar skeletal muscle adaptations when re-exposed to the same training stimulus. Our findings challenge the utility of classifying of individuals as high/low responders using measurements of mitochondrial protein content, CS activity and/or capillary density following a single training period.