Effects of fasting on isolated murine skeletal muscle contractile function during acute hypoxia

Stored muscle carbohydrate supply and energetic efficiency constrain muscle functional capacity during exercise and are influenced by common physiological variables (e.g. age, diet, and physical activity level). Whether these constraints affect overall functional capacity or the timing of muscle energetic failure during acute hypoxia is not known. We interrogated skeletal muscle contractile properties in two anatomically distinct rodent hindlimb muscles that have well characterized differences in energetic efficiency (locomotory- extensor digitorum longus (EDL) and postural- soleus muscles) following a 24 hour fasting period that resulted in substantially reduced muscle carbohydrate supply. 180 mins of acute hypoxia resulted in complete energetic failure in all muscles tested, indicated by: loss of force production, substantial reductions in total adenosine nucleotide pool intermediates, and increased adenosine nucleotide degradation product-inosine monophosphate (IMP). These changes occurred in the absence of apparent myofiber structural damage assessed histologically by both transverse section and whole mount. Fasting and the associated reduction of the available intracellular carbohydrate pool (~50% decrease in skeletal muscle) did not significantly alter the timing to muscle functional impairment or affect the overall force/work capacities of either muscle type. Fasting resulted in greater passive tension development in both muscle types, which may have implications for the design of pre-clinical studies involving optimal timing of reperfusion or administration of precision therapeutics.

Temporal Association Between Ischemic Muscle Perfusion Recovery and the Restoration of Muscle Contractile Function After Hindlimb Ischemia

During incomplete skeletal muscle recovery from ischemia, such as that occurs with critical limb ischemia, the temporal relationship between recovery of muscle capillary perfusion and contractile function is poorly defined. We examined this relationship in BALB/cJ mice (N = 24) following unilateral hindlimb ischemia (HLI), which pre-clinically mimics the myopathy observed in critical limb ischemia patients. Specifically, we examined this relationship in two phenotypically distinct muscles (i.e., "oxidative" soleus - Sol and "glycolytic" extensor digitorum longus - EDL) 14- or 56-days after HLI. Although overall limb blood flow (LDPI) reached its' recovery peak (48% of control) by HLI d14, the capillary networks in both the Sol and EDL (whole mount confocal imaging) were disrupted and competent muscle capillary perfusion (perfused lectin⁺μm²/muscle μm²) remained reduced. Interestingly, both Sol and EDL muscles recovered their distinct capillary structures and perfusion (Con Sol; 0.056 ± 0.02 lectin⁺μm²/muscle μm², and Con EDL; 0.039 ± 0.005 lectin⁺μm²/muscle μm²) by HLI d56 (Sol; 0.062 ± 0.011 lectin⁺μm²/muscle μm² and EDL; 0.0035 ± 0.005 lectin⁺μm²/muscle μm²), despite no further improvement in limb blood flow (LDPI). Both muscles suffered severe myopathy, indicated by loss of dystrophin positive immunostaining and the absence of stimulation induced isometric force production at HLI d14. Dystrophin immunofluorescence returned at HLI d56, although neither myofiber CSA (μm²) nor isometric force production (58 and 28% sustained deficits, Sol and EDL, respectively) recovered completely in either muscle. In summary, we reveal that the temporal relationship between the restoration of muscle capillary perfusion and functional ischemic skeletal muscle regeneration favors competent muscle capillary perfusion recovery in BALB/c mice in a phenotypically non-distinct manner.

BAG3 (Bcl-2-Associated Athanogene-3) Coding Variant in Mice Determines Susceptibility to Ischemic Limb Muscle Myopathy by Directing Autophagy

BACKGROUND

Critical limb ischemia is a manifestation of peripheral artery disease that carries significant mortality and morbidity risk in humans, although its genetic determinants remain largely unknown. We previously discovered 2 overlapping quantitative trait loci in mice, Lsq-1 and Civq-1, that affected limb muscle survival and stroke volume after femoral artery or middle cerebral artery ligation, respectively. Here, we report that a Bag3 variant (Ile81Met) segregates with tissue protection from hind-limb ischemia.

METHODS

We treated mice with either adeno-associated viruses encoding a control (green fluorescent protein) or 2 BAG3 (Bcl-2-associated athanogene-3) variants, namely Met81 or Ile81, and subjected the mice to hind-limb ischemia.

RESULTS

We found that the BAG3 Ile81Met variant in the C57BL/6 (BL6) mouse background segregates with protection from tissue necrosis in a shorter congenic fragment of Lsq-1 (C.B6-Lsq1-3). BALB/c mice treated with adeno-associated virus encoding the BL6 BAG3 variant (Ile81; n=25) displayed reduced limb-tissue necrosis and increased limb tissue perfusion compared with Met81- (n=25) or green fluorescent protein- (n=29) expressing animals. BAG3Ile81, but not BAG3Met81, improved ischemic muscle myopathy and muscle precursor cell differentiation and improved muscle regeneration in a separate, toxin-induced model of injury. Systemic injection of adeno-associated virus-BAG3Ile81 (n=9), but not BAG3Met81 (n=10) or green fluorescent protein (n=5), improved ischemic limb blood flow and limb muscle histology and restored muscle function (force production). Compared with BAG3Met81, BAG3Ile81 displayed improved binding to the small heat shock protein (HspB8) in ischemic skeletal muscle cells and enhanced ischemic muscle autophagic flux.

CONCLUSIONS

Taken together, our data demonstrate that genetic variation in BAG3 plays an important role in the prevention of ischemic tissue necrosis. These results highlight a pathway that preserves tissue survival and muscle function in the setting of ischemia.

Diminished force production and mitochondrial respiratory deficits are strain-dependent myopathies of subacute limb ischemia

OBJECTIVE

Reduced skeletal muscle mitochondrial function might be a contributing mechanism to the myopathy and activity based limitations that typically plague patients with peripheral arterial disease (PAD). We hypothesized that mitochondrial dysfunction, myofiber atrophy, and muscle contractile deficits are inherently determined by the genetic background of regenerating ischemic mouse skeletal muscle, similar to how patient genetics affect the distribution of disease severity with clinical PAD.

METHODS

Genetically ischemia protected (C57BL/6) and susceptible (BALB/c) mice underwent either unilateral subacute hind limb ischemia (SLI) or myotoxic injury (cardiotoxin) for 28 days. Limbs were monitored for blood flow and tissue oxygen saturation and tissue was collected for the assessment of histology, muscle contractile force, gene expression, mitochondrial content, and respiratory function.

RESULTS

Despite similar tissue O₂ saturation and mitochondrial content between strains, BALB/c mice suffered persistent ischemic myofiber atrophy (55.3% of C57BL/6) and muscle contractile deficits (approximately 25% of C57BL/6 across multiple stimulation frequencies). SLI also reduced BALB/c mitochondrial respiratory capacity, assessed in either isolated mitochondria (58.3% of C57BL/6 at SLI on day (d)7, 59.1% of C57BL/6 at SLI d28 across multiple conditions) or permeabilized myofibers (38.9% of C57BL/6 at SLI d7; 76.2% of C57BL/6 at SLI d28 across multiple conditions). SLI also resulted in decreased calcium retention capacity (56.0% of C57BL/6) in BALB/c mitochondria. Nonischemic cardiotoxin injury revealed similar recovery of myofiber area, contractile force, mitochondrial respiratory capacity, and calcium retention between strains.

CONCLUSIONS

Ischemia-susceptible BALB/c mice suffered persistent muscle atrophy, impaired muscle function, and mitochondrial respiratory deficits during SLI. Interestingly, parental strain susceptibility to myopathy appears specific to regenerative insults including an ischemic component. Our findings indicate that the functional deficits that plague PAD patients could include mitochondrial respiratory deficits genetically inherent to the regenerating muscle myofibers.

Abstract 101: Mitochondrial and Cardiac Protection Evoked by a Novel Mitochondria-targeting Peptide-idebenone Conjugate

Dysfunction along the electron transport system contributes to cardiomyopathy in a number of mitochondrial diseases. Several pharmacological approaches are currently being tested for their ability to improve mitochondrial function, yet almost none of the leading candidates specifically target to mitochondria. In this study we determined the biological efficacy of a novel conjugate of idebenone and mitochondria-targeting peptide, SBT-61. Using a vertically-integrated approach we tested the ability of SBT-61 to improve functional recovery and bioenergetics in: perfused rat hearts subjected to ischemia-reperfusion, cultured cells exposed to hypoxia-reoxygenation injury, and isolated heart mitochondria where complexes I and/or III were inhibited. SBT-61 treatment preserved post-ischemic cardiac function as assessed by left ventricular developed pressure (40 ± 5 vs 24 ± 3 mmHg, P<0.0001), rate of contraction (1853 ± 236 vs. 1069 ± 109 mmHg/s, P<0.0001), rate of relaxation (-1349 ± 231 vs. -792 ± 52 mmHg/s, P<0.0001), and a 30% reduction in infarct size. In cells expressing an shRNA knockdown of glutathione reductase, treatment with SBT-61 normalized maximal mitochondrial respiration after hypoxia-reoxygenation. In isolated mitochondria with complexes I or III inhibited, SBT-61 stimulated respiration and was shown to directly reduce complex III and cytochrome c, indicating that SBT-61 can bypass defects in the electron transport system. These data highlight the cardioprotective potential of a mitochondria-targeted idebenone conjugate to stabilize mitochondrial bioenergetics.

Mitochondrial Regulation of the Muscle Microenvironment in Critical Limb Ischemia

Critical limb ischemia (CLI) is the most severe clinical presentation of peripheral arterial disease and manifests as chronic limb pain at rest and/or tissue necrosis. Current clinical interventions are largely ineffective and therapeutic angiogenesis based trials have shown little efficacy, highlighting the dire need for new ideas and novel therapeutic approaches. Despite a decade of research related to skeletal muscle as a determinant of morbidity and mortality outcomes in CLI, very little progress has been made toward an effective therapy aimed directly at the muscle myopathies of this disease. Within the muscle cell, mitochondria are well positioned to modulate the ischemic cellular response, as they are the principal sites of cellular energy production and the major regulators of cellular redox charge and cell death. In this mini review, we update the crucial importance of skeletal muscle to CLI pathology and examine the evolving influence of muscle and endothelial cell mitochondria in the complex ischemic microenvironment. Finally, we discuss the novelty of muscle mitochondria as a therapeutic target for ischemic pathology in the context of the complex co-morbidities often associated with CLI.

Muscle cell derived angiopoietin-1 contributes to both myogenesis and angiogenesis in the ischemic environment

Recent strategies to treat peripheral arterial disease (PAD) have focused on stem cell based therapies, which are believed to result in local secretion of vascular growth factors. Little is known, however, about the role of ischemic endogenous cells in this context. We hypothesized that ischemic muscle cells (MC) are capable of secreting growth factors that act as potent effectors of the local cellular regenerative environment. Both muscle and endothelial cells (ECs) were subjected to experimental ischemia, and conditioned medium (CM) from each was collected and analyzed to assess myogenic and/or angiogenic potential. In muscle progenitors, mRNA expression of VEGF and its cognate receptors (Nrp1, Flt, Flk) was present and decreased during myotube formation in vitro, and EC CM or VEGF increased myoblast proliferation. Angiopoietin-1 (Ang-1), Tie1, and Tie2 mRNA increased during MC differentiation in vitro. Exogenous Ang-1 enhanced myogenic (MyoD and Myogenin) mRNA in differentiating myoblasts and increased myosin heavy chain protein. Myotube formation was enhanced by MC CM and inhibited by EC CM. Ang-1 protein was present in CM from MCs isolated from both the genetically ischemia-susceptible BALB/c and ischemia-resistant C57BL/6 mouse strains, and chimeric Tie2 receptor trapping in situ ablated Ang-1's myogenic effects in vitro. Ang-1 or MC CM enhanced myotube formation in a mixed isolate of muscle progenitors as well as a myoblast co-culture with pluripotent mesenchymal cells (10T1/2) and this effect was abrogated by viral expression of the extracellular domain of Tie2 (AdsTie2). Furthermore, mesh/tube formation by HUVECs was enhanced by Ang-1 or MC CM and abrogated by Tie2 chimeric receptor trapping. Our results demonstrate the ability of muscle and endothelial cell-derived vascular growth factors, particularly Ang-1, to serve as multi-functional stimuli regulating crosstalk between blood vessels and muscle cells during regeneration from ischemic myopathy.

C3d enhancement of neutralizing antibodies to measles hemagglutinin

Measles remains a major cause of worldwide infant mortality despite the use of current live attenuated vaccines. New approaches to measles virus (MV) vaccine development are critical to interrupt the spread of MV. In this study, we report the results using a DNA vaccine expressing a fusion of the measles hemagglutinin (H) protein and the complement component, C3d, to enhance the titers of neutralizing antibody. Plasmids were generated that expressed a secreted (s) form of H and the same form fused to three tandem copies of the murine homologue of C3d (sH-3C3d). Analysis of titers of the antibody raised in vaccinated mice indicated that immunizations with the DNA expressing sH-3C3d had higher titers of anti-H antibodies compared to serum from mice vaccinated with DNA expressing sH only. In addition, sH-3C3d elicited higher neutralizing antibody titers that inhibited MV induced plaque formation.

Enhanced avidity maturation of antibody to human immunodeficiency virus envelope: DNA vaccination with gp120-C3d fusion proteins

DNA vaccination can elicit both humoral and cellular immune responses and can confer protection against several pathogens. However, DNA vaccines expressing the envelope (Env) protein of human immunodeficiency virus (HIV) have been relatively ineffective at generating high titer, long-lasting, neutralizing antibodies in a variety of animal models. In this study, we report that fusion of Env and the complement component, C3d, in a DNA vaccine, enhances the titers of antibody to Env. Plasmids were generated that expressed a secreted form of Env (sgp120) from three isolates of HIV and these same forms fused to three tandem copies of the murine homologue of C3d (sgp120-3C3d). Analyses of titers and avidity maturation of the raised antibody indicated that immunizations with each of the sgp120-3C3d-expressing DNAs accelerated both the onset and the avidity maturation of antibody to Env.

Accelerating antidepressant response in geriatric depression: a post hoc comparison of combined sleep deprivation and paroxetine versus monotherapy with paroxetine, nortriptyline, or placebo

Speed of response is an important clinical issue in the treatment of depressed elderly patients. Our objective was to compare rapid response rates in a study combining therapeutic sleep deprivation (TSD) with paroxetine with two earlier randomized, double-blind studies in late-life depression, one of paroxetine versus nortriptyline and another of nortriptyline versus placebo. We measured depressive symptoms with the 17-item Hamilton Rating Scale of Depression (HRSD), defining rapid response as an HRSD < or = 10 by 2 weeks. With combination therapy (TSD + paroxetine), 9 of 13 patients (69%) experienced a rapid response. In the nortriptyline versus paroxetine study, nortriptyline brought about rapid response in 12 of 37 (32%) and paroxetine in 11 of 43 patients (26%). In the third study, rapid response to nortriptyline occurred in 10 of 41 patients (24%) and to placebo in 6 of 39 patients (15%). The overall chi square, including the rate of rapid response to placebo, was 14.87 (P = .005). The chi square on the four active treatment groups, excluding placebo, was 10.28 (P = .016). This preliminary observation suggests that combined therapy with TSD plus paroxetine may be twice as successful at achieving rapid response in elderly depressed patients than conventional monotherapy with medication or placebo. A prospective, placebo-controlled evaluation of this dual therapy is warranted.

Causal attribution and affective response as mediated by task performance and self-acceptance

Predictions derived from cognitive consistency theories, self-esteem theories, and ego-serving-bias theory concerning how students would make attributional and affective responses to their academic performance were investigated. 202 university students completed a measure of self-acceptance of their college ability and made attributional and affective responses to an hypothetical examination performance. Analyses showed that students receiving positive feedback perceived greater internal causality and responded with greater positive affect than students receiving negative feedback. Self-acceptance did not moderate the attributions or affective reactions. The results supported the ego-serving-bias theory and provided partial support for self-esteem theory. Findings did not support predictions from cognitive-consistency theory.

Evaluation of a rapid peptide-based anti-human immunodeficiency virus-1 antibody immunoassay

A qualitative, visually interpreted, rapid, and synthetic peptide-based anti-human immunodeficiency virus-1 (HIV) antibody immunoassay has been developed that may be of value in situations in which rapid determination of HIV-1 status is important. Because questions have been raised about the accuracy of rapid anti-HIV-1 assays, the sensitivity, specificity, interobserver and intraobserver variability of the Genie HIV-1 assay (Genetics Systems, Seattle, WA) were determined. Sera from 56 patients with HIV-1 infections documented by enzyme immunoassay and western blot tested positive by this assay. Enzyme immunoassay- and western blot-negative sera from 30 visceral organ transplant donors were negative using the Genie assay. Specificity was examined further by testing sera from 29 patients hospitalized with a variety of medical disorders, including acute bacterial pneumonia, acute myocardial infarction, monoclonal gammopathy, and high titer antinuclear or antimitochondrial antibodies. Two of these patients were reactive with the enzyme immunoassay, both of which tested negative by western blot. All 29 tested negative using the Genie assay. In addition, sera from five patients with repeatedly reactive enzyme immunoassays and negative western blots tested negative by the Genie system. There was 100% agreement in interobserver and intraobserver studies. With the western blot as the reference method, the Genie assay exhibited 100% sensitivity and specificity and there was no observer variability.

Implicit versus Explicit Learning Processes in a Probabilistic, Continuous Fine-Motor Catching Task

We compared the influences of explicit instruction and uninstructed implicit learning of correlations among visual events, in a fine-motor task. The task required visual tracking of a small "ball" of light and "catching" it by means of joystick manipulation. A general pattern of improvement with practice for instructed and "noninstructed" conditions was found. Additionally, both instructed and noninstructed conditions evidenced use of the predictive relationships among stimulus events. The improvement in overall performance caused by explicit verbal instructions was less than the improvement seen with the implicit learning condition. Further, instructed and noninstructed conditions showed different patterns of joystick activity. These findings suggest a qualitatively different approach to visual information processing and task performance for the instructional conditions