The interplay of inflammation, exosomes and Ca2+ dynamics in diabetic cardiomyopathy

Diabetes mellitus is one of the prime risk factors for cardiovascular complications and is linked with high morbidity and mortality. Diabetic cardiomyopathy (DCM) often manifests as reduced cardiac contractility, myocardial fibrosis, diastolic dysfunction, and chronic heart failure. Inflammation, changes in calcium (Ca²⁺) handling and cardiomyocyte loss are often implicated in the development and progression of DCM. Although the existence of DCM was established nearly four decades ago, the exact mechanisms underlying this disease pathophysiology is constantly evolving. Furthermore, the complex pathophysiology of DCM is linked with exosomes, which has recently shown to facilitate intercellular (cell-to-cell) communication through biomolecules such as micro RNA (miRNA), proteins, enzymes, cell surface receptors, growth factors, cytokines, and lipids. Inflammatory response and Ca²⁺ signaling are interrelated and DCM  has been known to adversely affect many of these signaling molecules either qualitatively and/or quantitatively. In this literature review, we have demonstrated that Ca²⁺ regulators are tightly controlled at different molecular and cellular levels during various biological processes in the heart. Inflammatory mediators, miRNA and exosomes are shown to interact with these regulators, however how these mediators are linked to Ca²⁺ handling during DCM pathogenesis remains elusive. Thus, further investigations are needed to understand the mechanisms to restore cardiac Ca²⁺ homeostasis and function, and to serve as potential therapeutic targets in the treatment of DCM.

Improved workflow for mass spectrometry-based metabolomics analysis of the heart

MS-based metabolomics methods are powerful techniques to map the complex and interconnected metabolic pathways of the heart; however, normalization of metabolite abundance to sample input in heart tissues remains a technical challenge. Herein, we describe an improved GC-MS-based metabolomics workflow that uses insoluble protein-derived glutamate for the normalization of metabolites within each sample and includes normalization to protein-derived amino acids to reduce biological variation and detect small metabolic changes. Moreover, glycogen is measured within the metabolomics workflow. We applied this workflow to study heart metabolism by first comparing two different methods of heart removal: the Langendorff heart method (reverse aortic perfusion) and in situ freezing of mouse heart with a modified tissue freeze-clamp approach. We then used the in situ freezing method to study the effects of acute β-adrenergic receptor stimulation (through isoproterenol (ISO) treatment) on heart metabolism. Using our workflow and within minutes, ISO reduced the levels of metabolites involved in glycogen metabolism, glycolysis, and the Krebs cycle, but the levels of pentose phosphate pathway metabolites and of many free amino acids remained unchanged. This observation was coupled to a 6-fold increase in phosphorylated adenosine nucleotide abundance. These results support the notion that ISO acutely accelerates oxidative metabolism of glucose to meet the ATP demand required to support increased heart rate and cardiac output. In summary, our MS-based metabolomics workflow enables improved quantification of cardiac metabolites and may also be compatible with other methods such as LC or capillary electrophoresis.

Abstract 807: Rad Ablation as a Treatment to Target Cardiac Inotropy via L-type Calcium Channel Function

The L-type Ca 2+ channel current (I Ca,L ) provides trigger Ca 2+ to contribute to cardiac contraction. Rad GTPase associates with the L-type Ca 2+ channel (LTCC) and serves as an endogenous inhibitor of LTCC activity. Overexpression of Rad blocks I Ca,L ; absence of Rad increases I Ca,L . Rad attenuates β-adrenergic receptor (β-AR) signaling. Chronic β-AR stimulation associates with Ca 2+ mishandling and can promote signaling that progresses towards heart failure. Early studies of global, constitutive Rad-knockout mice (gRadKO) suggested that elevated Ca 2+ dynamics leads to pathological cardiac hypertrophy; however, Rad is also expressed in non-cardiac tissues.

Our objective is to test the hypothesis that increased myocardial I Ca,L via Rad deletion safely enhances cardiac function without driving pathological remodeling.

We created a cardiac-restricted inducible Rad knockout mouse (Rad Δ/Δ ). In vivo function was measured with echocardiography. We examined I Ca,L through whole cell configuration of the patch clamp technique, assessed Ca 2+ handling, and sarcomere dynamics.

Unlike gRadKO, Rad Δ/Δ showed no elevation of fetal gene program, nor fibrosis, and no change to aortic pressure. Rad Δ/Δ had a sustained increase of inotropy without structural or functional remodeling (EF: Rad Δ/Δ =76 ± 2%, n=16; Rad fl/fl =59 ± 4%, n=7; p=0.001.) I Ca,L was significantly increased, with Rad loss mirroring a β-AR modulated phenotype on basal I Ca,L (max. conductance: Rad Δ/Δ =254 ± 19 pS/pF, n=15; Rad fl/fl =144 ± 12 pS/pF, n=18; p<10 -4 ). Contrary to models of chronic β-AR stimulation, Rad Δ/Δ retained β-AR signaling shown in vivo using isoproterenol, and by preserved phosphorylation of protein regulators of Ca 2+ reuptake and contractility. Rad Δ/Δ cardiomyocytes show enhanced cytosolic Ca 2+ handling (Decay of Ca 2+ transient: Rad Δ/Δ = 0.07 ± 0.003 (F 340 /F 380 )/s, n=67, Rad fl/fl = 0.10 ± 0.005, n=69; p<10 -4 ), increased contractile function, and elevated SERCA2a expression.

These new findings challenge the canonical assumption that increased myocardial Ca 2+ necessarily promotes pathology. We conclude that cardiac hypertrophy in gRadKO was caused by non-cardiac tissue effects, and myocardial Rad deletion is a promising cardiac inotropic therapeutic direction.

Myocardial-restricted ablation of the GTPase RAD results in a pro-adaptive heart response in mice

Existing therapies to improve heart function target β-adrenergic receptor (β-AR) signaling and Ca²⁺ handling and often lead to adverse outcomes. This underscores an unmet need for positive inotropes that improve heart function without any adverse effects. The GTPase Ras associated with diabetes (RAD) regulates L-type Ca²⁺ channel (LTCC) current (I_Ca,L). Global RAD-knockout mice (gRAD^-/-) have elevated Ca²⁺ handling and increased cardiac hypertrophy, but RAD is expressed also in noncardiac tissues, suggesting the possibility that pathological remodeling is due also to noncardiac effects. Here, we engineered a myocardial-restricted inducible RAD-knockout mouse (RAD^Δ/Δ). Using an array of methods and techniques, including single-cell electrophysiological and calcium transient recordings, echocardiography, and radiotelemetry monitoring, we found that RAD deficiency results in a sustained increase of inotropy without structural or functional remodeling of the heart. I_Ca,L was significantly increased, with RAD loss conferring a β-AR-modulated phenotype on basal I_Ca,L Cardiomyocytes from RAD^Δ/Δ hearts exhibited enhanced cytosolic Ca²⁺ handling, increased contractile function, elevated sarcoplasmic/endoplasmic reticulum calcium ATPase 2 (SERCA2a) expression, and faster lusitropy. These results argue that myocardial RAD ablation promotes a beneficial elevation in Ca²⁺ dynamics, which would obviate a need for increased β-AR signaling to improve cardiac function.

Mdivi-1 induced acute changes in the angiogenic profile after ischemia-reperfusion injury in female mice

The aim of this study is to determine the effects of mitochondrial division inhibitor 1 (Mdivi‐1), the mitochondrial fission inhibitor, on the angiogenic profiles after the ischemia reperfusion injury (IR injury) in female mice. Female mice were treated with Mdivi‐1 inhibitor, 2 days prior, on the day of IR injury and 2 days after IR injury, for a period of 5 days. Both control and treatment groups underwent 30 min of ischemia and 72 h of reperfusion. On the day 3, mice were sacrificed and the ischemic and nonischemic portions of heart tissue were collected. Relative levels of 53 angiogenesis‐related proteins were quantified simultaneously using Angiogenic arrays. Heart function was evaluated before and after 72 h of IR injury. Mdivi‐1 treatment ameliorated IR induced functional deterioration with positive angiogenic profile. The seminal changes include suppression of Matrix metalloproteinase (MMP3), tissue inhibitor of metalloproteases (TIMP1) and chemokine (C‐X‐C motif) ligand 10 (CXCL10) levels and prevention of connexin 43 (Cx43) loss and downregulation in the antioxidant enzyme levels. These changes are correlated with enhanced endothelial progenitor cell marker (cluster of differentiation (CD31), endothelial‐specific receptor tyrosine kinase (Tek), fMS‐like tyrosine kinase 4 (Flt4) and kinase insert domain protein receptor (Kdr)) presence. Our study is the first to report the role of mitochondrial dynamics in regulation of myocardial IR‐induced angiogenic responses. Inhibition of excessive mitochondrial fission after IR injury ameliorated heart dysfunction and conferred positive angiogenic response. In addition, there were improvements in the preservation of Cx43 levels and oxidative stress handling along with suppression of apoptosis activation. The findings will aid in shaping the rational drug development process for the prevention of ischemic heart disease, especially in females.

Exercise mitigates the effects of hyperhomocysteinemia on adverse muscle remodeling

Hyperhomocysteinemia (HHcy) is known for causing inflammation and vascular remodeling, particularly through production of reactive oxygen species (ROS) and matrix metalloproteinase-9 (MMP-9) activation. Although its effect on the skeletal muscle is unclear, HHcy can cause skeletal muscle weakness and functional impairment by induction of inflammatory mediators and macrophage mediated injury. Exercise has been shown to reduce homocysteine levels and therefore, could serve as a promising intervention for HHcy. The purpose of this study was to investigate whether HHcy causes skeletal muscle fibrosis through induction of inflammation and determine whether exercise can mitigate these effects. C57BL/6J (WT) and CBS+/- (HHcy) mice were administered a 6 weeks treadmill exercise protocol. Hindlimb perfusion was measured via laser Doppler. Measurement of skeletal muscle protein expression was done by western blot. Levels of skeletal muscle MMP-9 mRNA were determined by qPCR. Collagen deposition in the skeletal muscle was measured using Masson's trichrome staining. In CBS+/- mice, HHcy manifested with decreased body weight and femoral artery lumen diameter, as well as a trend of lower hindlimb perfusion. These mice displayed increased wall to lumen ratio, mean arterial blood pressure, collagen deposition, and elevated myostatin protein expression. Exercise mitigated the effects above in CBS+/- mice. Skeletal muscle from CBS+/- mice had elevated markers of remodeling and hypoxia: iNOS, EMMPRIN, and MMP-9. We conclude that HHcy causes skeletal muscle fibrosis possibly through induction of EMMPRIN/MMP-9 and exercise is capable of mitigating the pathologies associated with HHcy.

Dysbiosis and Disease: Many Unknown Ends, Is It Time to Formulate Guidelines for Dysbiosis Research?

Dysbiosis has been implicated in modulation of disease and treatment outcome. It also has been linked to the reproducibility concerns. However, research community needs guidelines on animal models and dysbiosis research to tackle the complexities associated with it. There is a necessity for multi-disciplinary collaborative approach in setting up certain guidelines to hasten the dysbiosis research in a hassle-free manner. J. Cell. Physiol. 232: 2929-2930, 2017. © 2016 Wiley Periodicals, Inc.

Interactions of hyperhomocysteinemia and T cell immunity in causation of hypertension

Although hyperhomocysteinemia (HHcy) is an independent risk factor for cardiovascular diseases (CVD), there is a debate on whether HHcy is a risk factor or just a biomarker. Interestingly, homocysteine lowering strategies in humans had very little effect on reducing the cardiovascular risk, as compared with animals; this may suggest heterogeneity in human population and epigenetic alterations. Moreover, there are only few studies that suggest the idea that HHcy contributes to CVD in the presence of other risk factors such as inflammation, a known risk factor for CVD. Elevated levels of homocysteine have been shown to contribute to inflammation. Here, we highlight possible relationships between homocysteine, T cell immunity, and hypertension, and summarize the evidence that suggested these factors act together in increasing the risk for CVD. In light of this new evidence, we further propose that there is a need for evaluation of the causes of HHcy, defective remethylation or defective transsulfuration, which may differentially modulate hypertension progression, not just the homocysteine levels.

Moderate intensity exercise prevents diabetic cardiomyopathy associated contractile dysfunction through restoration of mitochondrial function and connexin 43 levels in db/db mice

AIMS

Although the cardiovascular benefits of exercise are well known, exercise induced effects and mechanisms in prevention of cardiomyopathy are less clear during obesity associated type-2 diabetes. The current study assessed the impact of moderate intensity exercise on diabetic cardiomyopathy by examining cardiac function and structure and mitochondrial function.

METHODS

Obese-diabetic (db/db), and lean control (db/+) mice, were subjected to a 5 week, 300 m run on a tread-mill for 5 days/week at the speeds of 10-11 m/min. Various physiological parameters were recorded and the heart function was evaluated with M-mode echocardiography. Contraction parameters and calcium transits were examined on isolated cardiomyocytes. At the molecular level: connexin 43 and 37 (Cx43 and 37) levels, mitochondrial biogenesis regulators: Mfn2 and Drp-1 levels, mitochondrial trans-membrane potential and cytochrome c leakage were assessed through western blotting immunohistochemistry and flow cytometry. Ability of exercise to reverse oxygen consumption rate (OCR), tissue ATP levels, and cardiac fibrosis were also determined.

RESULTS

The exercise regimen was able to prevent diabetic cardiac functional deficiencies: ejection fraction (EF) and fractional shortening (FS). Improvements in contraction velocity and contraction maximum were noted with the isolated cardiomyocytes. Restoration of interstitial and micro-vessels associated Cx43 levels and improved gap junction intercellular communication (GJIC) were observed. The decline in the Mfn2/Drp-1 ratio in the db/db mice hearts was prevented after exercise. The exercise regimen further attenuated transmembrane potential decline and cytochrome c leakage. These corrections further led to improvements in OCR and tissue ATP levels and reduction in cardiac fibrosis.

CONCLUSIONS

Moderate intensity exercise produced significant cardiovascular benefits by improving mitochondrial function through restoration of Cx43 networks and mitochondrial trans-membrane potential and prevention of excessive mitochondrial fission.

Atherogenesis: hyperhomocysteinemia interactions with LDL, macrophage function, paraoxonase 1, and exercise

Despite great strides in understanding the atherogenesis process, the mechanisms are not entirely known. In addition to diet, cigarette smoking, genetic predisposition, and hypertension, hyperhomocysteinemia (HHcy), an accumulation of the noncoding sulfur-containing amino acid homocysteine (Hcy), is a significant contributor to atherogenesis. Although exercise decreases HHcy and increases longevity, the complete mechanism is unclear. In light of recent evidence, in this review, we focus on the effects of HHcy on macrophage function, differentiation, and polarization. Though there is need for further evidence, it is most likely that HHcy-mediated alterations in macrophage function are important contributors to atherogenesis, and HHcy-countering strategies, such as nutrition and exercise, should be included in the combinatorial regimens for effective prevention and regression of atherosclerotic plaques. Therefore, we also included a discussion on the effects of exercise on the HHcy-mediated atherogenic process.

Hyperhomocysteinemia: a missing link to dysfunctional HDL via paraoxanase-1

Paraoxanase-1 (PON1) is an HDL-associated enzyme that contributes to the antioxidant and antiatherosclerotic properties of HDL. Lack of PON1 results in dysfunctional HDL. HHcy is a risk factor for cardiovascular disorders, and instigates vascular dysfunction and ECM remodeling. Although studies have reported HHcy during atherosclerosis, the exact mechanism is unclear. Here, we hypothesize that dysfunctional HDL due to lack of PON1 contributes to endothelial impairment and atherogenesis through HHcy-induced ECM re-modeling. To verify this hypothesis, we used C57BL6/J and PON1 knockout mice (KO) and fed them an atherogenic diet. The expression of Akt, ADMA, and DDAH, as well as endothelial gap junction proteins such as Cx-37 and Cx-40 and eNOS was measured for vascular dysfunction and inflammation. We observed that cardiac function was decreased and plasma Hcy levels were increased in PON1 KO mice fed the atherogenic diet compared with the controls. Expression of Akt, eNOS, DDAH, Cx-37, and Cx-40 was decreased, and the expression of MMP-9 and ADMA was increased in PON1 KO mice fed an atherogenic diet compared with the controls. Our results suggest that HHcy plays an intricate role in dysfunctional HDL, owing to the lack of PON1. This contributes to vascular endothelial impairment and atherosclerosis through MMP-9-induced vascular remodeling.

Abstract P008: Impact of Hydrogen Sulfide on the Epigenetics of Diabetic Cardiomyopathy

Although Diabetic cardiomyopathy results in enhanced risk for heart failure, epigenetic changes leading to diabetic heart failure are unclear. Hydrogen sulfide (H2S) has been implicated in the preservation of heart function owing to its anti-inflammatory and positive metabolic changes. In the current study, we investigated whether or not chronic H2S treatment (by giving NaHS) reverses diabetic cardiomyopathy using mouse model of type-1 diabetes: Akita mice. Regulators of mitochondrial biogenesis, calcium handling and molecules that regulate post-ischemic recovery were assayed by western blotting and Q-PCR. Further, we considered epigenetic modifications such as microRNA expression changes and DNA methylation alterations to understand the causes of diabetic heart failure with and without NaHS treatment for 30 days. Our data indicated that chronic H2S treatment significantly reduced the mitochondrial fission inducers: Drp-1 (24%) and Fis-1 (17%) in the Akita mouse hearts. Further, there was enhancement (10%) in the SERCA2a expression after NaHS treatment in the diabetic hearts. Also, there was significant decrease (16%) in TNF-1α protein expression in diabetic hearts after NaHS treatment. In addition, there was significantly increased expression of post-ischemic recovery regulators such as: Notch3 (157%), C-JUN (160%), PGC-1α (173%), HIF-2α (72%) , and NRF-1 (149%) after NaHS treatment. These results suggest that the chronic NaHS treatment ameliorates diabetic cardiomyopathy through decreasing mitochondrial fission and inflammation and enhancing Ca2+ handling; as well as mitigating epigenetic changes leading to enhanced post-ischemic recovery potential.

Abstract P052: Homocysteine Increases Macrophage-Derived Paraoxonase -1 Expression Independent of CD68

Although atherosclerotic plaque rupture is the leading cause of myocardial infarction, the mechanisms are unclear. Macrophages burdened with oxidized LDL (oxLDL) become foam cells: hallmarks of plaque progression and instability. One of the main macrophage-specific receptors for oxLDL is CD68. Paraoxonase-1 (PON1) is a high-density lipoprotein (HDL)-associated lactonase capable of retarding/inhibiting LDL oxidation. Elevated levels of homocysteine (Hcy), an amino acid homologue and independent cardiovascular risk factor, is metabolized by Pon1.

Given the literature connections of oxLDL, Pon1, Hcy, and macrophages to atherosclerosis, we hypothesized that Pon1 is produced by murine macrophages and its expression is increased by Hcy via CD68.

Murine J774a.1 macrophages were treated with LDL, oxLDL, Hcy, or oxLDL+Hcy. Also, separate treatment groups included macrophages that had CD68 silenced by CD68 siRNA transfection. Cell lysates were analyzed for CD68 and Pon1 expression via Western blotting.

Pon1 is present in macrophages. Hcy along with oxLDL significantly increases Pon1 (51%, 1.51 vs 0.97) expression compared to controls than oxLDL alone. Pon1 expression is significantly decreased (33%, 0.67 vs 1) with silencing of CD68. Pon1 expression is significantly decreased more with oxLDL (82% 0.17 vs 1) in presence of CD68 silencing but is significantly increased with oxLDL+Hcy (24% 1.24 vs 1). CD68 expression tends to increase more with oxLDL+Hcy than oxLDL alone when compared to control and the tendency follows with silencing of CD68. Our results conclude that Hcy increases macrophage-derived Pon1 expression independent of CD68.

Homocysteine elicits an M1 phenotype in murine macrophages through an EMMPRIN-mediated pathway

Introduction: Hyperhomocysteinemia (HHcy) is associated with inflammatory diseases and is known to increase the production of reactive oxygen species (ROS), matrix metalloproteinase (MMP)-9, and inducible nitric oxide synthase, and to decrease endothelial nitric oxide production. However, the impact of HHcy on macrophage phenotype differentiation is not well-established. It has been documented that macrophages have 2 distinct phenotypes: the “classically activated/destructive” (M1), and the “alternatively activated/constructive” (M2) subtypes. We hypothesize that HHcy increases M1 macrophage differentiation through extracellular matrix metalloproteinase inducer (EMMPRIN), a known inducer of matrix metalloproteinases. Methods: murine J774A.1 and Raw 264.7 macrophages were treated with 100 and 500 μmol/L Hcy, respectively, for 24 h. Samples were analyzed using Western blotting and immunocytochemistry. Results: Homocysteine treatment increased cluster of differentiation 40 (CD40; M1 marker) in J774A.1 and Raw 264.7 macrophages. MMP-9 was induced in both cell lines. EMMPRIN protein expression was also increased in both cell lines. Blocking EMMPRIN function by pre-treating cells with anti-EMMPRIN antibody, with or without Hcy, resulted in significantly lower expression of CD40 in both cell lines by comparison with the controls. A DCFDA assay demonstrated increased ROS production in both cell lines with Hcy treatment when compared with the controls. Conclusion: Our results suggest that HHcy results in an increase of the M1 macrophage phenotype. This effect seems to be at least partially mediated by EMMPRIN induction.

Hyperhomocysteinemia inhibits satellite cell regenerative capacity through p38 alpha/beta MAPK signaling

Chronic failure in maintenance and regeneration of skeletal muscles leads to lower muscle mass (sarcopenia), muscle weakness, and poor response to injury. Evidence suggests that aberrant p38 MAPK signaling undermines the repair process after injury in aged mice. Previous studies have shown that hyperhomocysteinemia (HHcy) has been associated with muscle weakness and lower than normal body weights. However, whether or not HHcy condition also compromises skeletal muscle regenerative capabilities is not clear. In the current study, we show that CBS-/+ mice, a model for HHcy condition, exhibited compromised regenerative function and cell proliferation upon injury. However, there was no significant difference in Pax7 expression levels in the satellite cells from CBS-/+ mouse skeletal muscles. Interestingly, the satellite cells from CBS-/+ mice not only exhibited diminished in vitro proliferative capabilities, but also there was heightened oxidative stress. In addition, there was enhanced p38 MAPK activation as well as p16 and p21 expression in the CBS-/+ mouse satellite cells. Moreover, the C2C12 myoblasts also exhibited higher p38 MAPK activation and p16 expression upon treatment with homocysteine in addition to enhanced ROS presence. Tissue engraftment potential and regeneration after injury were restored to some extent upon treatment with the p38-MAPK inhibitor, SB203580, in the CBS-/+ mice. These results together suggest that HHcy-induced diminished satellite cell proliferation involves excessive oxidative stress and p38 MAPK signaling. Our study further proposes that HHcy is a potential risk factor for elderly frailty, and need to be considered as a therapeutic target while designing the alleviation interventions/postinjury rehabilitation measures for adults with HHcy.

Hyperhomocysteinemia associated skeletal muscle weakness involves mitochondrial dysfunction and epigenetic modifications

HHcy has been implicated in elderly frailty, but the underlying mechanisms are poorly understood. Using C57 and CBS+/- mice and C2C12 cell line, we investigated mechanisms behind HHcy induced skeletal muscle weakness and fatigability. Possible alterations in metabolic capacity (levels of LDH, CS, MM-CK and COX-IV), in structural proteins (levels of dystrophin) and in mitochondrial function (ATP production) were examined. An exercise regimen was employed to reverse HHcy induced changes. CBS+/- mice exhibited more fatigability, and generated less contraction force. No significant changes in muscle morphology were observed. However, there is a corresponding reduction in large muscle fiber number in CBS+/- mice. Excess fatigability was not due to changes in key enzymes involved in metabolism, but was due to reduced ATP levels. A marginal reduction in dystrophin levels along with a decrease in mitochondrial transcription factor A (mtTFA) were observed. There was also an increase in the mir-31, and mir-494 quantities that were implicated in dystrophin and mtTFA regulation respectively. The molecular changes elevated during HHcy, with the exception of dystrophin levels, were reversed after exercise. In addition, the amount of NRF-1, one of the transcriptional regulators of mtTFA, was significantly decreased. Furthermore, there was enhancement in mir-494 levels and a concomitant decline in mtTFA protein quantity in homocysteine treated cells. These changes in C2C12 cells were also accompanied by an increase in DNMT3a and DNMT3b proteins and global DNA methylation levels. Together, these results suggest that HHcy plays a causal role in enhanced fatigability through mitochondrial dysfunction which involves epigenetic changes.

Role of mitochondrial fission and fusion in cardiomyocyte contractility

BACKGROUND

Mitochondria constitute 30% of cell volume and are engaged in two dynamic processes called fission and fusion, regulated by Drp-1 (dynamin related protein) and mitofusin 2 (Mfn2). Previously, we showed that Drp-1 inhibition attenuates cardiovascular dysfunction following pressure overload in aortic banding model and myocardial infarction. As dynamic organelles, mitochondria are capable of changing their morphology in response to stress. However, whether such changes can alter their function and in turn cellular function is unknown. Further, a direct role of fission and fusion in cardiomyocyte contractility has not yet been studied. In this study, we hypothesize that disrupted fission and fusion balance by increased Drp-1 and decreased Mfn2 expression in cardiomyocytes affects their contractility through alterations in the calcium and potassium concentrations.

METHODS

To verify this, we used freshly isolated ventricular myocytes from wild type mouse and transfected them with either siRNA to Drp-1 or Mfn2. Myocyte contractility studies were performed by IonOptix using a myopacer. Intracellular calcium and potassium measurements were done using flow cytometry. Immunocytochemistry (ICC) was done to evaluate live cell mitochondria and its membrane potential. Protein expression was done by western blot and immunocytochemistry.

RESULTS

We found that silencing mitochondrial fission increased the myocyte contractility, while fusion inhibition decreased contractility with simultaneous changes in calcium and potassium. Also, we observed that increase in fission prompted decrease in Serca-2a and increase in cytochrome c leakage leading to mitophagy.

CONCLUSION

Our results suggested that regulating mitochondrial fission and fusion have direct effects on overall cardiomyocyte contractility and thus function.

Mechanisms of hyperhomocysteinemia induced skeletal muscle myopathy after ischemia in the CBS-/+ mouse model

Although hyperhomocysteinemia (HHcy) elicits lower than normal body weights and skeletal muscle weakness, the mechanisms remain unclear. Despite the fact that HHcy-mediated enhancement in ROS and consequent damage to regulators of different cellular processes is relatively well established in other organs, the nature of such events is unknown in skeletal muscles. Previously, we reported that HHcy attenuation of PGC-1α and HIF-1α levels enhanced the likelihood of muscle atrophy and declined function after ischemia. In the current study, we examined muscle levels of homocysteine (Hcy) metabolizing enzymes, anti-oxidant capacity and focused on protein modifications that might compromise PGC-1α function during ischemic angiogenesis. Although skeletal muscles express the key enzyme (MTHFR) that participates in re-methylation of Hcy into methionine, lack of trans-sulfuration enzymes (CBS and CSE) make skeletal muscles more susceptible to the HHcy-induced myopathy. Our study indicates that elevated Hcy levels in the CBS-/+ mouse skeletal muscles caused diminished anti-oxidant capacity and contributed to enhanced total protein as well as PGC-1α specific nitrotyrosylation after ischemia. Furthermore, in the presence of NO donor SNP, either homocysteine (Hcy) or its cyclized version, Hcy thiolactone, not only increased PGC-1α specific protein nitrotyrosylation but also reduced its association with PPARγ in C2C12 cells. Altogether these results suggest that HHcy exerts its myopathic effects via reduction of the PGC-1/PPARγ axis after ischemia.

Role of hydrogen sulfide in skeletal muscle biology and metabolism

Hydrogen sulfide (H2S) is a novel endogenous gaseous signal transducer (gasotransmitter). Its emerging role in multiple facets of inter- and intra-cellular signaling as a metabolic, inflammatory, neuro and vascular modulator has been increasingly realized. Although H2S is known for its effects as an anti-hypertensive, anti-inflammatory and anti-oxidant molecule, the relevance of these effects in skeletal muscle biology during health and during metabolic syndromes is unclear. H2S has been implicated in vascular relaxation and vessel tone enhancement, which might lead to mitigation of vascular complications caused by the metabolic syndromes. Metabolic complications may also lead to mitochondrial remodeling by interfering with fusion and fission, therefore, leading to mitochondrial mitophagy and skeletal muscle myopathy. Mitochondrial protection by H2S enhancing treatments may mitigate deterioration of muscle function during metabolic syndromes. In addition, H2S might upregulate uncoupling proteins and might also cause browning of white fat, resulting in suppression of imbalanced cytokine signaling caused by abnormal fat accumulation. Likewise, as a source for H(+) ions, it has the potential to augment anaerobic ATP synthesis. However, there is a need for studies to test these putative H2S benefits in different patho-physiological scenarios before its full-fledged usage as a therapeutic molecule. The present review highlights current knowledge with regard to exogenous and endogenous H2S roles in skeletal muscle biology, metabolism, exercise physiology and related metabolic disorders, such as diabetes and obesity, and also provides future directions.

Exercise mitigates the adverse effects of hyperhomocysteinemia on macrophages, MMP-9, skeletal muscle, and white adipocytes

Regular exercise is a great medicine with its benefits encompassing everything from prevention of cardiovascular risk to alleviation of different muscular myopathies. Interestingly, elevated levels of homocysteine (Hcy), also known as hyperhomocysteinemia (HHcy), antagonizes beta-2 adrenergic receptors (β2AR), gamma amino butyric acid (GABA), and peroxisome proliferator-activated receptor-gamma (PPARγ) receptors. HHcy also stimulates an elevation of the M1/M2 macrophage ratio, resulting in a more inflammatory profile. In this review we discuss several potential targets altered by HHcy that result in myopathy and excessive fat accumulation. Several of these HHcy mediated changes can be countered by exercise and culminate into mitigation of HHcy induced myopathy and metabolic syndrome. We suggest that exercise directly impacts levels of Hcy, matrix metalloproteinase 9 (MMP-9), macrophages, and G-protein coupled receptors (GPCRs, especially Gs). While HHcy promotes the M1 macrophage phenotype, it appears that exercise may diminish the M1/M2 ratio, resulting in a less inflammatory phenotype. HHcy through its influence on GPCRs, specifically β₂AR, PPARγ and GABA receptors, promotes accumulation of white fat, whereas exercise enhances the browning of white fat and counters HHcy-mediated effects on GPCRs. Alleviation of HHcy-associated pathologies with exercise also includes reversal of excessive MMP-9 activation. Moreover, exercise, by reducing plasma Hcy levels, may prevent skeletal muscle myopathy, improve exercise capacity and rescue the obese phenotype. The purpose of this review is to summarize the pathological conditions surrounding HHcy and to clarify the importance of regular exercise as a method of disease prevention.

Dysregulation of Mfn2 and Drp-1 proteins in heart failure

Therapeutic approaches for cardiac regenerative mechanisms have been explored over the past decade to target various cardiovascular diseases (CVD). Structural and functional aberrations of mitochondria have been observed in CVD. The significance of mitochondrial maturation and function in cardiomyocytes is distinguished by their attribution to embryonic stem cell differentiation into adult cardiomyocytes. An abnormal fission process has been implicated in heart failure, and treatment with mitochondrial division inhibitor 1 (Mdivi-1), a specific inhibitor of dynamin related protein-1 (Drp-1), has been shown to improve cardiac function. We recently observed that the ratio of mitofusin 2 (Mfn2; a fusion protein) and Drp-1 (a fission protein) was decreased during heart failure, suggesting increased mitophagy. Treatment with Mdivi-1 improved cardiac function by normalizing this ratio. Aberrant mitophagy and enhanced oxidative stress in the mitochondria contribute to abnormal activation of MMP-9, leading to degradation of the important gap junction protein connexin-43 (Cx-43) in the ventricular myocardium. Reduced Cx-43 levels were associated with increased fibrosis and ventricular dysfunction in heart failure. Treatment with Mdivi-1 restored MMP-9 and Cx-43 expression towards normal. In this review, we discuss mitochondrial dynamics, its relation to MMP-9 and Cx-43, and the therapeutic role of fission inhibition in heart failure.

Hyperhomocysteinemia attenuates angiogenesis through reduction of HIF-1α and PGC-1α levels in muscle fibers during hindlimb ischemia

Hyperhomocysteinemia (HHcy) is associated with elderly frailty, skeletal muscle injury and malfunction, reduced vascular integrity and function, and mortality. Although HHcy has been implicated in the impairment of angiogenesis after hindlimb ischemia in murine models, the underlying mechanisms are still unclear. We hypothesized that HHcy compromises skeletal muscle perfusion, collateral formation, and arteriogenesis by diminishing postischemic vasculogenic responses in muscle fibers. To test this hypothesis, we created femoral artery ligation in wild-type and heterozygous cystathionine β-synthase (CBS(+/-)) mice (a model for HHcy) and assessed tissue perfusion, collateral vessel formation, and skeletal muscle function using laser-Doppler perfusion imaging, barium angiography, and fatigue tests. In addition, we assessed postischemic levels of VEGF and levels of its muscle-specific regulators: hypoxia-inducible factor (HIF)-1α and peroxisome proliferator-activated receptor-γ coactivator (PGC)-1α. The observations indicated dysregulation of VEGF, HIF-1α, and PGC-1α levels in ischemic skeletal muscles of CBS(+/-) mice. Concomitant with the reduced ischemic angiogenic responses, we also observed diminished leptin expression and attenuated Akt signaling in ischemic muscle fibers of CBS(+/-) mice. Moreover, there was enhanced atrogene, ubiquitin ligases that conjugate proteins for degradation during muscle atrophy, transcription, and reduced muscle function after ischemia in CBS(+/-) mice. These results suggest that HHcy adversely affects muscle-specific ischemic responses and contributes to muscle frailty.

Abstract C142: Mortalin/HSPA9 regulates p21CIP1 expression in Raf/MEK/ERK-activated cancer cells

Dysregulated Raf/MEK/ERK signaling is a common hallmark of tumorigenesis. However intriguingly, aberrant Raf/MEK/ERK activation triggers senescence-like growth arrest as a primary response in many cell types. This response is recognized as an innate tumor suppressive mechanism, which should be bypassed for Raf/MEK/ERK to drive carcinogenesis. Therefore, understanding of the bypass mechanisms is likely to provide an opportunity to design a novel therapeutic strategy. In this study, we report that mortalin, a member of the heat shock protein 70 (HSP70) family, has a role in bypassing the Raf/MEK/ERK-induced growth inhibition in cancer. Using tandem affinity purification and proteomic mass spectrometry, we found that mortalin is present in the MEK1/2 proteome. A specific physical interaction between mortalin and MEK was validated by co-immunoprecipitation analyses and in vitro binding assays of recombinant proteins. Immunohistochemical analysis revealed that mortalin is upregulated in human melanoma biopsies in correlation with tumor malignancy. Of note, mortalin levels were inversely correlated with p21CIP1 levels in a number of Raf/MEK/ERK-activated cancer cell lines, suggesting a role for mortalin in p21CIP1 regulation. Indeed, mortalin depletion elicited increased p21CIP1 transcription and MEK/ERK activation which were accompanied by G2/M phase cell cycle arrest and cell death in different B-Raf or K-Ras mutated cancer cell lines. Remarkably, blocking MEK/ERK activation, using the MEK1/2 inhibitor, AZD6244, dominant negative mutants of MEK or ERK, or RNA interference, abrogated p21CIP1 induction by mortalin depletion in cancer cells harboring B-RafV600E regardless of their p53 status. In contrast, mortalin overexpression suppressed B-RafV600E or ΔRaf-1:ER-induced MEK/ERK activation, p21CIP1 expression, and cell cycle arrest in cell types exhibiting normal MEK/ERK status. Other HSP70 family chaperones could not effectively replace mortalin for the observed effects on p21CIP1 regulation, suggesting a unique role for mortalin. These findings suggest that mortalin upregulation is a mechanism that underlies p21CIP1 silencing in Raf/MEK/ERK-activated cancer, identifying mortalin as a novel negative regulator of the pathway signaling. Mortalin may provide a target to reactivate the tumor suppressive signaling of Raf/MEK/ERK in cancer.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C142.

Citation Format: Pui Kei Wu, Seung-Keun Hong, Sudhakar Veeranki, Mansi Karkhanis, Dmytro Starenki, Jose A. Plaza, Jong-In Park. Mortalin/HSPA9 regulates p21CIP1 expression in Raf/MEK/ERK-activated cancer cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C142.

Defective homocysteine metabolism: potential implications for skeletal muscle malfunction

Hyperhomocysteinemia (HHcy) is a systemic medical condition and has been attributed to multi-organ pathologies. Genetic, nutritional, hormonal, age and gender differences are involved in abnormal homocysteine (Hcy) metabolism that produces HHcy. Homocysteine is an intermediate for many key processes such as cellular methylation and cellular antioxidant potential and imbalances in Hcy production and/or catabolism impacts gene expression and cell signaling including GPCR signaling. Furthermore, HHcy might damage the vagus nerve and superior cervical ganglion and affects various GPCR functions; therefore it can impair both the parasympathetic and sympathetic regulation in the blood vessels of skeletal muscle and affect long-term muscle function. Understanding cellular targets of Hcy during HHcy in different contexts and its role either as a primary risk factor or as an aggravator of certain disease conditions would provide better interventions. In this review we have provided recent Hcy mediated mechanistic insights into different diseases and presented potential implications in the context of reduced muscle function and integrity. Overall, the impact of HHcy in various skeletal muscle malfunctions is underappreciated; future studies in this area will provide deeper insights and improve our understanding of the association between HHcy and diminished physical function.

LKB1 regulates development and the stress response in Dictyostelium

The serine/threonine kinase LKB1 is a master kinase that regulates a number of critical events such as cell transformation, polarization, development, stress response, and energy metabolism in metazoa. After multiple unsuccessful attempts of generating Dictyostelium lkb1-null cells, an RNAi-based knockdown approach proved effective. Depletion of lkb1 with a knockdown construct displayed severe reduction in prespore cell differentiation and precocious induction of prestalk cells, which were reminiscent of cells lacking GSK3. Similar to gsk3(-) cells, lkb1 depleted cells displayed lower GSK3 activity than wild type cells during development and compromised cAMP-mediated inhibition of the DIF-1 mediated ecmB induction. In response to stress insult, the kinase activity of LKB1, but not that of GSK3, increased. Therefore, LKB1 positively functions at the upstream of GSK3 during development and responds to stress insults independently from GSK3.

Interferon-inducible p200-family protein IFI16, an innate immune sensor for cytosolic and nuclear double-stranded DNA: regulation of subcellular localization

The interferon (IFN)-inducible p200-protein family includes structurally related murine (for example, p202a, p202b, p204, and Aim2) and human (for example, AIM2 and IFI16) proteins. All proteins in the family share a partially conserved repeat of 200-amino acid residues (also called HIN-200 domain) in the C-terminus. Additionally, most proteins (except the p202a and p202b proteins) also share a protein-protein interaction pyrin domain (PYD) in the N-terminus. The HIN-200 domain contains two consecutive oligosaccharide/oligonucleotide binding folds (OB-folds) to bind double stranded DNA (dsDNA). The PYD domain in proteins allows interactions with the family members and an adaptor protein ASC. Upon sensing cytosolic dsDNA, Aim2, p204, and AIM2 proteins recruit ASC protein to form an inflammasome, resulting in increased production of proinflammatory cytokines. However, IFI16 protein can sense cytosolic as well as nuclear dsDNA. Interestingly, the IFI16 protein contains a nuclear localization signal (NLS). Accordingly, the initial studies had indicated that the endogenous IFI16 protein is detected in the nucleus and within the nucleus in the nucleolus. However, several recent reports suggest that subcellular localization of IFI16 protein in nuclear versus cytoplasmic (or both) compartment depends on cell type. Given that the IFI16 protein can sense cytosolic as well as nuclear dsDNA and can initiate different innate immune responses (production of IFN-β versus proinflammatory cytokines), here we evaluate the experimental evidence for the regulation of subcellular localization of IFI16 protein in various cell types. We conclude that further studies are needed to understand the molecular mechanisms that regulate the subcellular localization of IFI16 protein.

IFI16 protein mediates the anti-inflammatory actions of the type-I interferons through suppression of activation of caspase-1 by inflammasomes

Background

Type-I interferons (IFNs) are used to treat certain inflammatory diseases. Moreover, activation of type-I IFN-signaling in immune cells inhibits the production of proinflammatory cytokines and activation of inflammasomes. However, the molecular mechanisms remain largely unknown. Upon sensing cytosolic double-stranded DNA, the AIM2 protein forms the AIM2-ASC inflammasome, resulting in activation of caspase-1. Given that the IFI16 and AIM2 proteins are IFN-inducible and can heterodimerize with each other, we investigated the regulation of IFI16, AIM2, and inflammasome proteins by type-I and type-II IFNs and explored whether the IFI16 protein could negatively regulate the activation of the AIM2 (or other) inflammasome.

Methodology/ Principal Findings

We found that basal levels of the IFI16 and AIM2 proteins were relatively low in peripheral blood monocytes (CD14⁺) and in the THP-1 monocytic cell line. However, treatment of THP-1 cells with type-I (IFN-α or β) or type-II (IFN-γ) IFN induced the expression levels of IFI16, AIM2, ASC and CASP1 proteins. The induced levels of IFI16 and AIM2 proteins were detected primarily in the cytoplasm. Accordingly, relatively more IFI16 protein bound with the AIM2 protein in the cytoplasmic fraction. Notably, increased expression of IFI16 protein in transfected HEK-293 cells inhibited activation of caspase-1 by the AIM2-ASC inflammasome. Moreover, the constitutive knockdown of the IFI16 expression in THP-1 cells increased the basal and induced [induced by poly(dA:dT) or alum] activation of the caspase-1 by the AIM2 and NLRP3 inflammasomes.

Conclusions/Significance

Our observations revealed that the type-I and type-II IFNs induce the expression of IFI16, AIM2, and inflammasome proteins to various extents in THP-1 cells and the expression of IFI16 protein in THP-1 cells suppresses the activation of caspase-1 by the AIM2 and NLRP3 inflammasomes. Thus, our observations identify the IFI16 protein as a mediator of the anti-inflammatory actions of the type-I IFNs.

Differential roles for the interferon-inducible IFI16 and AIM2 innate immune sensors for cytosolic DNA in cellular senescence of human fibroblasts

The IFN-inducible IFI16 and AIM2 proteins act as innate immune sensors for cytosolic double-stranded DNA (dsDNA). On sensing dsDNA, the IFI16 protein induces the expression of IFN-β whereas the AIM2 protein forms an inflammasome, which promotes the secretion of IL-1β. Given that the knockdown of IFI16 expression in human diploid fibroblasts (HDF) delays the onset of cellular senescence, we investigated the potential roles for the IFI16 and AIM2 proteins in cellular senescence. We found that increased IFI16 protein levels in old (vs. young) HDFs were associated with the induction of IFN-β. In contrast, increased levels of the AIM2 protein in the senescent (vs. old) HDFs were associated with increased production of IL-1β. The knockdown of type I IFN-α receptor subunit, which reduced the basal levels of the IFI16 but not of the AIM2, protein delayed the onset of cellular senescence. Accordingly, increased constitutive levels of IFI16 and AIM2 proteins in ataxia telangiectasia mutated (ATM) HDFs were associated with the activation of the IFN signaling and increased levels of IL-1β. The IFN-β treatment of the young HDFs, which induced the expression of IFI16 and AIM2 proteins, activated a DNA damage response and also increased basal levels of IL-1β. Interestingly, the knockdown of AIM2 expression in HDFs increased the basal levels of IFI16 protein and activated the IFN signaling. In contrast, the knockdown of the IFI16 expression in HDFs decreased the basal and dsDNA-induced activation of the IFN signaling. Collectively, our observations show differential roles for the IFI16 and AIM2 proteins in cellular senescence and associated secretory phenotype.

Systemic lupus erythematosus and increased risk to develop B cell malignancies: role of the p200-family proteins

Systemic lupus erythematosus (SLE), an autoimmune disease, develops at a female-to-male ratio of 10:1. Increased serum levels of type I interferons (IFN-alpha/beta) and induction of "IFN-signature" genes are associated with an active SLE disease in patients. Moreover, SLE patients exhibit three- to four-fold increase in the risk of developing malignancies involving B cells, including non-Hodgkin lymphoma (NHL) and Hodgkin's lymphoma (HL). Interestingly, homozygous mice expressing a deletion mutant (the proline-rich domain deleted) of the p53 develop various types of spontaneous tumors, particularly of B cell origin upon aging. The deletion is associated with defects in transcriptional activation of genes by p53 and inhibition of DNA damage-induced apoptosis. Notably, increased levels of the p202 protein, which is encoded by the p53-repressible interferon-inducible Ifi202 gene, in B cells of female mice are associated with defects in B cell apoptosis, inhibition of the p53-mediated transcription of pro-apoptotic genes, and increased lupus susceptibility. In this review we discuss how increased levels of the p202 protein (and its human functional homologue IFI16 protein) in B cells increase lupus susceptibility and are likely to increase the risk of developing certain B cell malignancies. A complete understanding of the molecular mechanisms that regulate B cell homeostasis is necessary to identify SLE patients with an increased risk to develop B cell malignancies.

Inducible priming phosphorylation promotes ligand-independent degradation of the IFNAR1 chain of type I interferon receptor

Phosphorylation-dependent ubiquitination and ensuing down-regulation and lysosomal degradation of the interferon alpha/beta receptor chain 1 (IFNAR1) of the receptor for Type I interferons play important roles in limiting the cellular responses to these cytokines. These events could be stimulated either by the ligands (in a Janus kinase-dependent manner) or by unfolded protein response (UPR) inducers including viral infection (in a manner dependent on the activity of pancreatic endoplasmic reticulum kinase). Both ligand-dependent and -independent pathways converge on phosphorylation of Ser(535) within the IFNAR1 degron leading to recruitment of beta-Trcp E3 ubiquitin ligase and concomitant ubiquitination and degradation. Casein kinase 1 alpha (CK1 alpha) was shown to directly phosphorylate Ser(535) within the ligand-independent pathway. Yet given the constitutive activity of CK1 alpha, it remained unclear how this pathway is stimulated by UPR. Here we report that induction of UPR promotes the phosphorylation of a proximal residue, Ser(532), in a pancreatic endoplasmic reticulum kinase-dependent manner. This serine serves as a priming site that promotes subsequent phosphorylation of IFNAR1 within its degron by CK1 alpha. These events play an important role in regulating ubiquitination and degradation of IFNAR1 as well as the extent of Type I interferon signaling.

The GPI-anchored superoxide dismutase SodC is essential for regulating basal Ras activity and for chemotaxis of Dictyostelium discoideum

A genetic screen for Dictyostelium mutant displaying high level of constitutive phosphatidylinositol (3,4,5)-trisphosphate led to the finding that the glycosylphosphatidylinositol (GPI)-anchored superoxide dismutase SodC regulates small GTPase Ras. Cells that lack SodC exhibited constitutively high levels of active Ras, more membrane localization of GFP-PHcrac, and defects in chemoattractant sensing, cell polarization and motility. These defects of SodC-lacking cells were partially restored by expression of wild-type SodC but not by the catalytically inactive mutant SodC (H245R, H247Q). Furthermore, an inhibition of PI3K activity in SodC-deficient cells by LY294002 only partially restored chemoattractant sensing and cell polarization, consistent with the fact that SodC-deficient cells have aberrantly high level of active Ras, which functions upstream of PI3K. A higher level of active GFP-RasG was observed in SodC-deficient cells, which significantly decreased upon incubation of SodC-deficient cells with the superoxide scavenger XTT. Having constitutively high levels of active Ras proteins and more membrane localization of GFP-PHcrac, SodC-deficient cells exhibited severe defects in chemoattractant sensing, cell polarization and motility.

The function of PP2A/B56 in non-metazoan multicellular development

DB56, the Dictyostelium B56 homolog, displayed high sequence homology to other eukaryotic B56 subunits of the PP2A and a specific association with the PP2A catalytic subunit. Cells lacking DB56, psrA(-), displayed higher PP2A phosphatase activity compared with the wild type, approximately 10 hr of delayed expression of ecmA and ecmB prestalk markers, and inefficient culmination. The prespore marker cotB declined as wild-type cells culminate, but no such decline was observed from psrA(-) cells. Interestingly, psrA(-) cells exhibited higher GSK3 kinase activity. Furthermore, the expression of the dominant negative GSK3 mutant (K84/85M) in psrA(-) cells improved both prestalk and prespore expression patterns similarly to wild-type cells. However, culmination was not restored in psrA(-) cells expressing dominant negative GSK3, which suggests that PP2A/DB56 has an extra target during terminal differentiation. This report shows that PP2A/DB56 controls not only metazoan development, but also non-metazoan cell fate decision processes.