Dissecting the roles of mTORC1 and mTORC2 in the mouse heart

Mammalian target of rapamycin (mTOR) is an evolutionary conserved serine/threonine kinase that regulates cell growth and metabolism. mTOR occurs in cells in two complexes, termed mTORC1 and mTORC2. This thesis describes investigations into the in vivo functions of these two complexes in the mouse heart. The first part of the thesis focuses on the characterization of the role of mTORC1 in the adult heart. To inactivate mTORC1 for analysis of its cardiac functions, we ablated the mTORC1-specific and essential component raptor selectively and conditionally from cardiomyocytes using cre-loxP recombination. The resulting knockout mice showed decreased cardiac function at 3 weeks after gene deletion, culminating in heart failure and death after 5 weeks. Furthermore, the mice were exposed to voluntary wheel running exercise to trigger physiological cardiac growth, or to pathological stress, which was induced by aortic banding. Increased mortality was observed after exercise. In response to aortic banding, the raptor knockout mice lacked the phase of adaptive hypertrophic growth that normally occurs and went directly into dilated cardiomyopathy. In addition, the raptor knockout mice changed their cardiac mitochondrial gene expression pattern and switched from fatty acids to glucose as their primary source of energy. The decrease in cardiac function was accompanied by increased apoptosis and autophagy along with distorted mitochondrial structure. In conclusion, our findings establish mTORC1 as important regulator of cardiac homeostasis. The second part of the thesis describes the in vivo function of mTORC2 in the heart. We used a similar approach as for mTORC1 to delete the mTORC2-specific component rictor selectively from cardiomyocytes. At baseline, during adulthood, rictor deletion had no effect on cardiac function. Cardiac geometry was normal in the cardiac rictor knockout mice despite the fact that downstream of mTORC2, phosphorylated and total Akt and PKC levels were significantly reduced. In contrast, conditions of pathological stress induced by aortic banding caused decreased cardiac function in the rictor knockout mice. The mice had a phenotype of eccentric hypertrophy with changed chamber dimensions. Increased fibrosis and apoptosis were accompanied by enhanced reexpression of fetal genes compared to wild-type mice. On the other hand, deletion of rictor during postnatal growth did not show any functional or geometrical changes of the heart. Overall, the data demonstrates that rictor/mTORC2 is important for cardiac function during the adaptation to pathological stress

Cardiac mTOR complex 2 preserves ventricular function in pressure-overload hypertrophy

Mammalian target of rapamycin (mTOR), a central regulator of growth and metabolism, has tissue-specific functions depending on whether it is part of mTOR complex 1 (mTORC1) or mTORC2. We have previously shown that mTORC1 is required for adaptive cardiac hypertrophy and maintenance of function under basal and pressure-overload conditions. In the present study, we aimed to identify functions of mTORC2 in the heart.; Using tamoxifen-inducible cardiomyocyte-specific gene deletion, we generated mice deficient for cardiac rapamycin-insensitive companion of mTOR (rictor), an essential and specific component of mTORC2. Under basal conditions, rictor deficiency did not affect cardiac growth and function in young mice and also had no effects in adult mice. However, transverse aortic constriction caused dysfunction in the rictor-deficient hearts, whereas function was maintained in controls after 1 week of pressure overload. Adaptive increases in cardiac weight and cardiomyocyte cross-sectional area, fibrosis, and hypertrophic and metabolic gene expression were not different between the rictor-deficient and control mice. In control mice, maintained function was associated with increased protein levels of rictor, protein kinase C (PKC)βII, and PKCδ, whereas rictor ablation abolished these increases. Rictor deletion also significantly decreased PKCε at baseline and after pressure overload. Our data suggest that reduced PKCε and the inability to increase PKCβII and PKCδ abundance are, in accordance with their known function, responsible for decreased contractile performance of the rictor-deficient hearts.; Our study demonstrates that mTORC2 is implicated in maintaining contractile function of the pressure-overloaded male mouse heart

A Review- Dynamic Resource Allocation using Virtual Machines for Cloud Computing Environment

Abstract A cloud computing infrastructure is a complex system with a large number of shared resources. Cloud resource management requires complex policies and decisions for multi-objective optimization. In Cloud computing multiple cloud users can request number of cloud services simultaneously. In this paper virtualization is used to allocate resources based on client needs and also supports green computing concept. It offers the virtualized resources to the cloud users. The concept Skewness algorithm is used to measure the resource utilization of server and minimizing the Skewness can improve overall utilization of server. Overload avoidance is maintained using skewness and virtualization. This paper provides detailed description of the dynamic resource allocation techniques in cloud for cloud user

Role of minimally invasive surgery in cardiac valve disease

Introduction: Over the past decade minimally invasive cardiac surgery has gained significant popularity, more cases of valve, bypass and congenital surgery are being done by smaller incisions as experience increases. Materials & Methods: Between January 2013 and December 2015 a total of 50 cases were performed using ministernotomy or right thoracotomy. The patients were between 17-58 years of age and included 29 males, 21 females. Results: In Minimally invasive surgery average pump time was 20-60 minutes, cross clamp time 30-50 minutes, ventilation <8 hours, ICU stay < 1day, 2 or less units of blood required in majority of patients. Conclusion: Minimally invasive cardiac surgery results in smaller incisions, shorter ventilator time, ICU and hospital stay, faster recovery, less pain, lower incidence of infection and bleeding and better cosmesis

Role of thymectomy in myasthenia gravis

Aims and Objective: The aim of study is to show the effect of thymectomy with symptomatic improvement in patients and decrease in dose of medication requirement. To study the outcome of patients with respect to histology, duration of symptoms, remission of symptoms and post operative outcome. Methods: We prospectively analysed 28 patients with symptoms of myasthenia gravis with respect to patients profile, patients remission of symptoms with respect to age, and grade of disease, the response to thymectomy with respect to histology, and duration of symptoms. Result and Conclusion: Patients mainly present with easy fatigability, patients with mild disease respond well to surgery, hyperplasia is favorable histology for remission and lesser the duration of symptoms more are the chances of remission of disease

Cardiac mTOR complex 2 preserves ventricular function in pressure-overload hypertrophy

Abstract Aims Mammalian target of rapamycin (mTOR), a central regulator of growth and metabolism, has tissue-specific functions depending on whether it is part of mTOR complex 1 (mTORC1) or mTORC2. We have previously shown that mTORC1 is required for adaptive cardiac hypertrophy and maintenance of function under basal and pressure-overload conditions. In the present study, we aimed to identify functions of mTORC2 in the heart. Methods and results Using tamoxifen-inducible cardiomyocyte-specific gene deletion, we generated mice deficient for cardiac rapamycin-insensitive companion of mTOR (rictor), an essential and specific component of mTORC2. Under basal conditions, rictor deficiency did not affect cardiac growth and function in young mice and also had no effects in adult mice. However, transverse aortic constriction caused dysfunction in the rictor-deficient hearts, whereas function was maintained in controls after 1 week of pressure overload. Adaptive increases in cardiac weight and cardiomyocyte cross-sectional area, fibrosis, and hypertrophic and metabolic gene expression were not different between the rictor-deficient and control mice. In control mice, maintained function was associated with increased protein levels of rictor, protein kinase C (PKC)βII, and PKCδ, whereas rictor ablation abolished these increases. Rictor deletion also significantly decreased PKCε at baseline and after pressure overload. Our data suggest that reduced PKCε and the inability to increase PKCβII and PKCδ abundance are, in accordance with their known function, responsible for decreased contractile performance of the rictor-deficient hearts. Conclusion Our study demonstrates that mTORC2 is implicated in maintaining contractile function of the pressure-overloaded male mouse heart

Cardiac raptor ablation impairs adaptive hypertrophy, alters metabolic gene expression, and causes heart failure in mice.

Background- Cardiac hypertrophy involves growth responses to a variety of stimuli triggered by increased workload. It is an independent risk factor for heart failure and sudden death. Mammalian target of rapamycin (mTOR) plays a key role in cellular growth responses by integrating growth factor and energy status signals. It is found in 2 structurally and functionally distinct multiprotein complexes called mTOR complex (mTORC) 1 and mTORC2. The role of each of these branches of mTOR signaling in the adult heart is currently unknown. Methods and Results- We generated mice with deficient myocardial mTORC1 activity by targeted ablation of raptor, which encodes an essential component of mTORC1, during adulthood. At 3 weeks after the deletion, atrial and brain natriuretic peptides and β-myosin heavy chain were strongly induced, multiple genes involved in the regulation of energy metabolism were altered, but cardiac function was normal. Function deteriorated rapidly afterward, resulting in dilated cardiomyopathy and high mortality within 6 weeks. Aortic banding-induced pathological overload resulted in severe dilated cardiomyopathy already at 1 week without a prior phase of adaptive hypertrophy. The mechanism involved a lack of adaptive cardiomyocyte growth via blunted protein synthesis capacity, as supported by reduced phosphorylation of ribosomal S6 kinase 1 and 4E-binding protein 1. In addition, reduced mitochondrial content, a shift in metabolic substrate use, and increased apoptosis and autophagy were observed. Conclusions- Our results demonstrate an essential function for mTORC1 in the heart under physiological and pathological conditions and are relevant for the understanding of disease states in which the insulin/insulin-like growth factor signaling axis is affected such as diabetes mellitus and heart failure or after cancer therapy