Effects of Modified Parvalbumin EF-Hand Motifs on Cardiac Myocyte Contractile Function.

Cardiac gene delivery of parvalbumin (Parv), an EF-hand Ca(2+) buffer, has been studied as a therapeutic strategy for diastolic heart failure, in which slow Ca(2+) reuptake is an important contributor. A limitation of wild-type (WT) Parv is the significant trade-off between faster relaxation and blunted contraction amplitude, occurring because WT-Parv sequesters Ca(2+) too early in the cardiac cycle and prematurely truncates sarcomere shortening in the facilitation of rapid relaxation. We recently demonstrated that an E → Q substitution (ParvE101Q) at amino acid 12 of the EF-hand Ca(2+)/Mg(2+) binding loop disrupts bidentate Ca(2+) binding, reducing Ca(2+) affinity by 99-fold and increasing Mg(2+) affinity twofold. ParvE101Q caused faster relaxation and not only preserved contractility, but unexpectedly increased it above untreated myocytes. To gain mechanistic insight into the increased contractility, we focused here on amino acid 12 of the EF-hand motif. We introduced an E → D substitution (ParvE101D) at this site, which converts bidentate Ca(2+) coordination to monodentate coordination. ParvE101D decreased Ca(2+) affinity by 114-fold and increased Mg(2+) affinity 28-fold compared to WT-Parv. ParvE101D increased contraction amplitude compared to both untreated myocytes and myocytes with ParvE101Q, with limited improvement in relaxation. Additionally, ParvE101D increased spontaneous contractions after pacing stress. ParvE101D also increased Ca(2+) transient peak height and was diffusely localized around the Z-line of the sarcomere, suggesting a Ca(2+)-dependent mechanism of enhanced contractility. Sarcoplasmic reticulum Ca(2+) load was not changed with ParvE101D, but postpacing Ca(2+) waves were increased. Together, these data show that inverted Ca(2+)/Mg(2+) binding affinities of ParvE101D increase myocyte contractility through a Ca(2+)-dependent mechanism without altering sarcoplasmic reticulum Ca(2+) load and by increasing unstimulated contractions and Ca(2+) waves. ParvE101D provides mechanistic insight into how changes in the Ca(2+)/Mg(2+) binding affinities of parvalbumin's EF-hand motif alter function of cardiac myocytes. These data are informative in developing new Ca(2+) buffering strategies for the failing heart.

Differential effects of S100 proteins A2 and A6 on cardiac Ca(2+) cycling and contractile performance.

Defective intracellular calcium (Ca(2+)) handling is implicated in the pathogenesis of heart failure. Novel approaches targeting both cardiac Ca(2+) release and reuptake processes, such as S100A1, have the potential to rescue the function of failing cardiac myocytes. Here, we show that two members of the S100 Ca(2+) binding protein family, S100A2 and S100A6 that share high sequence homology, differentially influence cardiac Ca(2+) handling and contractility. Cardiac gene expression of S100A2 significantly enhanced both contractile and relaxation performance of rodent and canine cardiac myocytes, mimicking the functional effects of its cardiac homologue, S100A1. To interrogate mechanism, Ca(2+) spark frequency, a measure of the gating of the ryanodine receptor Ca(2+) release channel, was found to be significantly increased by S100A2. Therapeutic testing showed that S100A2 rescued the contractile defects of failing cardiac myocytes. In contrast, cardiac expression of S100A6 had no significant effects on contractility or Ca(2+) handling. These data reveal novel differential effects of S100 proteins on cardiac myocyte performance that may be useful in application to diseased cardiac muscle.

Calcium mishandling in diastolic dysfunction: mechanisms and potential therapies.

Diastolic dysfunction is characterized by slow or incomplete relaxation of the ventricles during diastole, and is an important contributor to heart failure pathophysiology. Clinical symptoms include fatigue, shortness of breath, and pulmonary and peripheral edema, all contributing to decreased quality of life and poor prognosis. There are currently no therapies available that directly target the heart pump defects in diastolic function. Calcium mishandling is a hallmark of heart disease and has been the subject of a large body of research. Efforts are ongoing in a number of gene therapy approaches to normalize the function of calcium handling proteins such as sarcoplasmic reticulum calcium ATPase. An alternative approach to address calcium mishandling in diastolic dysfunction is to introduce calcium buffers to facilitate relaxation of the heart. Parvalbumin is a calcium binding protein found in fast-twitch skeletal muscle and not normally expressed in the heart. Gene transfer of parvalbumin into normal and diseased cardiac myocytes increases relaxation rate but also markedly decreases contraction amplitude. Although parvalbumin binds calcium in a delayed manner, it is not delayed enough to preserve full contractility. Factors contributing to the temporal nature of calcium buffering by parvalbumin are discussed in relation to remediation of diastolic dysfunction. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Cardiac Pathways of Differentiation, Metabolism and Contraction.

Evidence for the contribution of insulin resistance to the development of cachexia in tumor-bearing mice.

Cancer cachexia is a syndrome of unintentional weight loss that is characterized by wasting of both skeletal muscle and adipose tissue. Glucose intolerance and insulin resistance have been associated with cancer cachexia. However, it is unknown whether resistance to insulin has a role in the development of cachexia. In the present study, male CD2F1 mice with colon-26 adenocarcinoma tumors underwent an insulin tolerance test before the onset of weight loss. Compared to mice without tumors, mice with tumors had a profoundly blunted blood glucose response to insulin. Corroborating these findings, mice with tumors had decreased phosphorylation of Akt in quadriceps muscle and epididymal adipose tissue at the end of the study. Expression of Akt-regulated genes Atrogin-1, MuRF-1, and Bnip3 was increased in muscle, suggesting a role for decreased insulin signaling in the induction of both proteasomal proteolysis and autophagy in cachectic muscle. Rosiglitazone treatment increased serum adiponectin, insulin sensitivity, and body weight, and decreased Atrogin-1 and MuRF-1 expression in the skeletal muscle of tumor-bearing mice. In conclusion, insulin resistance is an early event in mice with cachexia induced by colon-26 tumors. Rosiglitazone improves insulin sensitivity and decreases early markers of cachexia. These data provide evidence that insulin resistance is not only present in cachexia, but also has a role in cachexia pathogenesis. Correction of insulin resistance may be a novel therapeutic target for the treatment of cancer cachexia.

Microtubule-Mediated Misregulation of Junctophilin-2 Underlies T-Tubule Disruptions and Calcium Mishandling in mdx Mice.

Cardiac myocytes from the mdx mouse, the mouse model of Duchenne muscular dystrophy, exhibit t-tubule disarray and increased calcium sparks, but a unifying molecular mechanism has not been elucidated. Recently, improper trafficking of junctophilin-2 on an altered microtubule network caused t-tubule derangements and calcium mishandling in a pressure-overload heart failure model. Mdx cardiac myocytes have microtubule abnormalities, but how this may affect junctophilin-2, t-tubules, and calcium handling has not been established. Here, we investigated the hypothesis that an inverse relationship between microtubules and junctophilin-2 underlies t-tubule disruptions and calcium mishandling in mdx cardiac myocytes. Confocal microscopy revealed t-tubule disorganization in mdx cardiac myocytes. Quantitative Western blot analysis demonstrated junctophilin-2 was decreased by 75% and showed an inverse hyperbolic relationship with α- and ß-tubulin, the individual components of microtubules, in mdx hearts. Colchicine-induced microtubule depolymerization normalized junctophilin-2 protein levels and localization, corrected t-tubule architecture, and reduced calcium sparks. In summary, these results suggest microtubule-mediated misregulation of junctophilin-2 causes t-tubule derangements and altered calcium handling in mdx cardiac myocytes.

Direct, differential effects of tamoxifen, 4-hydroxytamoxifen, and raloxifene on cardiac myocyte contractility and calcium handling.

Tamoxifen (Tam), a selective estrogen receptor modulator, is in wide clinical use for the treatment and prevention of breast cancer. High Tam doses have been used for treatment of gliomas and cancers with multiple drug resistance, but long QT Syndrome is a side effect. Tam is also used experimentally in mice for inducible gene knockout in numerous tissues, including heart; however, the potential direct effects of Tam on cardiac myocyte mechanical function are not known. The goal of this study was to determine the direct, acute effects of Tam, its active metabolite 4-hydroxytamoxifen (4OHT), and related drug raloxifene (Ral) on isolated rat cardiac myocyte mechanical function and calcium handling. Tam decreased contraction amplitude, slowed relaxation, and decreased Ca²âº transient amplitude. Effects were primarily observed at 5 and 10 µM Tam, which is relevant for high dose Tam treatment in cancer patients as well as Tam-mediated gene excision in mice. Myocytes treated with 4OHT responded similarly to Tam-treated cells with regard to both contractility and calcium handling, suggesting an estrogen-receptor independent mechanism is responsible for the effects. In contrast, Ral increased contraction and Ca²âº transient amplitudes. At 10 µM, all drugs had a time-dependent effect to abolish cellular contraction. In conclusion, Tam, 4OHT, and Ral adversely and differentially alter cardiac myocyte contractility and Ca²âº handling. These findings have important implications for understanding the Tam-induced cardiomyopathy in gene excision studies and may be important for understanding effects on cardiac performance in patients undergoing high-dose Tam therapy.

Noncanonical EF-hand motif strategically delays Ca2+ buffering to enhance cardiac performance.

EF-hand proteins are ubiquitous in cell signaling. Parvalbumin (Parv), the archetypal EF-hand protein, is a high-affinity Ca(2+) buffer in many biological systems. Given the centrality of Ca(2+) signaling in health and disease, EF-hand motifs designed to have new biological activities may have widespread utility. Here, an EF-hand motif substitution that had been presumed to destroy EF-hand function, that of glutamine for glutamate at position 12 of the second cation binding loop domain of Parv (ParvE101Q), markedly inverted relative cation affinities: Mg(2+) affinity increased, whereas Ca(2+) affinity decreased, forming a new ultra-delayed Ca(2+) buffer with favorable properties for promoting cardiac relaxation. In therapeutic testing, expression of ParvE101Q fully reversed the severe myocyte intrinsic contractile defect inherent to expression of native Parv and corrected abnormal myocardial relaxation in diastolic dysfunction disease models in vitro and in vivo. Strategic design of new EF-hand motif domains to modulate intracellular Ca(2+) signaling could benefit many biological systems with abnormal Ca(2+) handling, including the diseased heart.

Evidence for cardiac atrophic remodeling in cancer-induced cachexia in mice.

Cachexia is a common complication in cancer patients, which dramatically reduces quality of life and survival. In contrast to the well-studied feature of skeletal muscle loss, alterations in cardiac muscle are unclear. Recently, we reported that heart contractile function was significantly impaired in mice with colon-26 (C26) tumors, a widely used rodent model of cancer cachexia. In the present study, we investigated the potential underlying mechanisms for decreased heart function, specifically related to cardiac remodeling and atrophy. In cachectic mice bearing C26 tumors compared to mice without tumors, there was a gene expression pattern for cardiac remodeling, including increased BNP and c-fos, decreased PPARα and its responsive gene CPT1ß, and a switch from 'adult' isoforms (MHCα, GLUT4) to 'fetal' isoforms (MHCß and GLUT1). Echocardiography identified a decreased cardiac wall thickness. RT-PCR and Western blotting revealed a decreased amount of cardiac myofibrillar proteins MHC and troponin I, induced expression of E-3 ligases (MuRF-1 and Atrogin-1) and increased protein ubiquitination, providing evidence for cardiac atrophy in mice with cancer cachexia. Regulatory signaling pathways mediating these changes may include p44/42 MAPK. Together, these data provide evidence that pathways leading to cardiac remodeling and atrophy occur in mice with C26 cachexia.

Rosiglitazone delayed weight loss and anorexia while attenuating adipose depletion in mice with cancer cachexia.

Cachexia is characterized by severe weight loss, including adipose and muscle wasting, and occurs in a large percentage of cancer patients. Insulin resistance contributes to dysregulated metabolism in cachexia and occurs prior to weight loss in mice with colon-26 tumor-induced cachexia. Therefore, we hypothesized that the insulin sensitizer, rosiglitazone, would attenuate the loss of adipose and muscle to result in improved outcomes for mice with late-stage cachexia. Male CD2F1 mice were inoculated with colon-26 adenocarcinoma cells or vehicle. Treatments included vehicle, rosiglitazone (10 mg/kg body weight/day) or rosiglitazone plus pair-feeding to food intake of vehicle-treated mice with tumors. Rosiglitazone delayed weight loss onset by 2 d over the 16 d duration of this aggressive tumor model. This finding was associated, in part, with increased food intake. In addition, adipose mass, adipocyte cross-sectional area and inflammation were improved with rosiglitazone. However, at the time of necropsy 16 d after tumor inoculation rosiglitazone had no effect on retention of muscle mass, strength or proteolysis in late-stage cachexia. We did not measure stamina or endurance in this study. In early-stage cachexia, rosiglitazone normalized PDK4 and PPAR-delta mRNA in quadriceps muscle and rescued the decrease in insulin-stimulated glucose disappearance in mice with tumors. Rosiglitazone may delay weight loss onset by decreasing tumor-induced markers of metabolic change in early-stage cachexia. These changes predict for modest improvement in adipose, but no improvement in muscle strength in late-stage cachexia.

c9t11-Conjugated linoleic acid-rich oil fails to attenuate wasting in colon-26 tumor-induced late-stage cancer cachexia in male CD2F1 mice.

SCOPE: Cancer cachexia is characterized by muscle and adipose tissue wasting caused partly by chronic, systemic inflammation. Conjugated linoleic acids (CLAs) are a group of fatty acids with various properties including anti-inflammatory cis9, trans11 (c9t11)-CLA and lipid-mobilizing trans10, cis12 (t10c12)-CLA. The purpose of this study was to test whether dietary supplementation of a c9t11-CLA-rich oil (6:1 c9t11:t10c12) could attenuate wasting of muscle and adipose tissue in colon-26 adenocarcinoma-induced cachexia in mice. METHODS AND RESULTS: Loss of body weight, muscle and adipose tissue mass caused by tumors were not rescued by supplementation with the c9t11-CLA-rich oil. In quadriceps muscle, c9t11-CLA-rich oil exacerbated tumor-induced gene expression of inflammatory markers tumor necrosis factor-α, IL-6 receptor and the E3 ligase MuRF-1 involved in muscle proteolysis. In epididymal adipose tissue, tumor-driven delipidation and atrophy was aggravated by the c9,t11-CLA-rich oil, demonstrated by further reduced adipocyte size and lower adiponectin expression. However, expression of inflammatory cytokines and macrophage markers were not altered by tumors, or CLA supplementation. CONCLUSION: These data suggest that addition of c9t11-CLA-rich oil (0.6% c9t11, 0.1% t10c12) in diet did not ameliorate wasting in mice with cancer cachexia. Instead, it increased expression of inflammatory markers in the muscle and increased adipose delipidation.

Time-dependent effects of safflower oil to improve glycemia, inflammation and blood lipids in obese, post-menopausal women with type 2 diabetes: a randomized, double-masked, crossover study.

BACKGROUND & AIMS: Metabolic effects of dietary fat quality in people with type 2 diabetes are not well-understood. The study objective was to evaluate effects of conjugated linoleic acid (CLA) and safflower (SAF) oils on glycemia, blood lipids, and inflammation. The hypothesis we tested is that dietary oils improve glycemia, lipids, and inflammatory markers in a time-dependent way that follows accumulation of linoleic acid and CLA isomers in serum of subjects supplemented with dietary oils. METHODS: Fifty-five post-menopausal, obese women with type 2 diabetes enrolled, and 35 completed this randomized, double-masked crossover study. Treatments were 8 g daily of CLA and SAF for 16 weeks each. We used a multiple testing procedure with pre-determined steps analysis to determine the earliest time that a significant effect was detected. RESULTS: CLA did not alter measured metabolic parameters. SAF decreased HbA1c (-0.64 ± 0.18%, p = 0.0007) and C-reactive protein (-13.6 ± 8.2 mg/L, p = 0.0472), increased QUICKI (0.0077 ± 0.0035, p = 0.0146) with a minimum time to effect observed 16 weeks after treatment. SAF increased HDL cholesterol (0.12 ± 0.05 mmol/L, p = 0.0228) with the minimum time to detect an effect of SAF at 12 weeks. The minimum time to detect an increase of c9t11-CLA, t10c12-CLA, and linoleic acid in serum of women supplemented CLA or SAF, respectively, was four weeks. CONCLUSIONS: We conclude that 8 g of SAF daily improved glycemia, inflammation, and blood lipids, indicating that small changes in dietary fat quality may augment diabetes treatments to improve risk factors for diabetes-related complications.

Cardiac alterations in cancer-induced cachexia in mice.

Cachexia is a common syndrome in advanced cancer patients and causes up to 22% of cancer-related deaths. It remains elusive whether cancer cachexia causes heart failure. We investigated the effect of cancer cachexia on heart function and cardiac muscle structure in a mouse model. Male CD2F1 mice were inoculated with either colon-26 adenocarcinoma cells (Tumor group) or vehicle (PBS) (No Tumor group and Pair-fed group). Heart function as measured by fractional shortening in vivo using transthoracic echocardiography was performed on day 14 after tumor or PBS inoculation. At necropsy (day 17), hearts were collected for histology, transmission electron microscopy, RT-PCR and SDS-PAGE analysis. Mice from the Tumor group displayed a significantly reduced fractional shortening compared to mice in the No Tumor and Pair-fed groups. In hearts of the Tumor mice compared to the other groups, there was marked fibrosis and transmission electron microscopy revealed disrupted myocardial ultrastructure. Gene expression of troponin I, a regulator of cardiac muscle contraction, was reduced. Moreover, both mRNA and protein levels of myosin heavy chain (MHC) were altered whereby MHCalpha (adult isoform) was decreased and MHCbeta (fetal isoform) was increased indicating reactivation of the fetal gene expression pattern. In conclusion, heart function was diminished in mice with tumor-induced cachexia, and this impaired function was associated with increased fibrosis, disrupted myocardial structure and altered composition of contractile proteins of cardiac muscle.

Comparison of dietary conjugated linoleic acid with safflower oil on body composition in obese postmenopausal women with type 2 diabetes mellitus.

BACKGROUND: Weight loss may improve glucose control in persons with type 2 diabetes. The effects of fat quality, as opposed to quantity, on weight loss are not well understood. OBJECTIVE: We compared the effects of 2 dietary oils, conjugated linoleic acid (CLA) and safflower oil (SAF), on body weight and composition in obese postmenopausal women with type 2 diabetes. DESIGN: This was a 36-wk randomized, double-masked, crossover study. Fifty-five obese postmenopausal women with type 2 diabetes received SAF or CLA (8 g oil/d) during two 16-wk diet periods separated by a 4-wk washout period. Subjects met monthly with the study coordinator to receive new supplements and for assessment of energy balance, biochemical endpoints, or anthropometric variables. RESULTS: Thirty-five women completed the 36-wk intervention. Supplementation with CLA reduced body mass index (BMI) (P = 0.0022) and total adipose mass (P = 0.0187) without altering lean mass. The effect of CLA in lowering BMI was detected during the last 8 wk of each 16-wk diet period. In contrast, SAF had no effect on BMI or total adipose mass but reduced trunk adipose mass (P = 0.0422) and increased lean mass (P = 0.0432). SAF also significantly lowered fasting glucose (P = 0.0343) and increased adiponectin (P = 0.0051). No differences were observed in dietary energy intake, total fat intake, and fat quality in either diet period for either intervention. CONCLUSIONS: Supplementation with CLA and SAF exerted different effects on BMI, total and trunk adipose mass, and lean tissue mass in obese postmenopausal women with type 2 diabetes. Supplementation with these dietary oils may be beneficial for weight loss, glycemic control, or both.

Gamma-cyclodextrin lowers postprandial glycemia and insulinemia without carbohydrate malabsorption in healthy adults.

OBJECTIVE: Preliminary in vitro and animal studies have shown that gamma-cyclodextrin (GCD) is a slowly and completely digestible carbohydrate. The objective of this study was to determine the glycemic and insulinemic responses to GCD in humans. Breath hydrogen excretion was measured simultaneously to evaluate carbohydrate malabsorption. METHODS: Healthy adult subjects (N = 32) received 50 g of carbohydrate from GCD or a rapidly digested maltodextrin (MD) in a double-masked, randomized, crossover design. Plasma glucose (fingerstick) and serum insulin (venous) concentrations were measured at baseline and at 15, 30, 45, 60, 90, 120, 150, and 180 min postprandially. Breath hydrogen excretion was monitored hourly for 8 h postprandially. The severity of gastrointestinal symptoms (nausea, cramping, distension, flatulence) was rated by the subjects on a ranked scale for two 24-h periods postprandially. RESULTS: The mean baseline-adjusted peak plasma glucose concentration was 47% lower (P < 0.001), and the mean baseline-adjusted peak serum insulin concentration was decreased by 45% (P < 0.001) after subjects consumed GCD compared with MD. Positive incremental area under the curve (0-120 min) was reduced 45% for plasma glucose and 49% for serum insulin by GCD compared with MD (P < 0.001 in each case). There were no differences between GCD and MD in the proportion of positive breath hydrogen tests and both carbohydrates were equally well tolerated. CONCLUSIONS: GCD effectively lowers postprandial glycemia and insulinemia compared with MD, without resulting in appreciable carbohydrate malabsorption or gastrointestinal intolerance.