Reducing RBM20 activity improves diastolic dysfunction and cardiac atrophy

Impaired diastolic filling is a main contributor to heart failure with preserved ejection fraction (HFpEF), a syndrome with increasing prevalence and no treatment. Both collagen and the giant sarcomeric protein titin determine diastolic function. Since titin's elastic properties can be adjusted physiologically, we evaluated titin-based stiffness as a therapeutic target. We adjusted RBM20-dependent cardiac isoform expression in the titin N2B knockout mouse with increased ventricular stiffness. A ~50 % reduction of RBM20 activity does not only maintain cardiac filling in diastole but also ameliorates cardiac atrophy and thus improves cardiac function in the N2B-deficient heart. Reduced RBM20 activity partially normalized gene expression related to muscle development and fatty acid metabolism. The adaptation of cardiac growth was related to hypertrophy signaling via four-and-a-half lim-domain proteins (FHLs) that translate mechanical input into hypertrophy signals. We provide a novel link between cardiac isoform expression and trophic signaling via FHLs and suggest cardiac splicing as a therapeutic target in diastolic dysfunction. KEY MESSAGE: Increasing the length of titin isoforms improves ventricular filling in heart disease. FHL proteins are regulated via RBM20 and adapt cardiac growth. RBM20 is a therapeutic target in diastolic dysfunction

Strain Modulated Superlattices in Graphene

Strain engineering of graphene takes advantage of one of the most dramatic responses of Dirac electrons enabling their manipulation via strain-induced pseudo-magnetic fields. Numerous theoretically proposed devices, such as resonant cavities and valley filters, as well as novel phenomena, such as snake states, could potentially be enabled via this effect. These proposals, however, require strong, spatially oscillating magnetic fields while to date only the generation and effects of pseudo-gauge fields which vary at a length scale much larger than the magnetic length have been reported. Here we create a periodic pseudo-gauge field profile using periodic strain that varies at the length scale comparable to the magnetic length and study its effects on Dirac electrons. A periodic strain profile is achieved by pulling on graphene with extreme (>10%) strain and forming nanoscale ripples, akin to a plastic wrap pulled taut at its edges. Combining scanning tunneling microscopy and atomistic calculations, we find that spatially oscillating strain results in a new quantization different from the familiar Landau quantization observed in previous studies. We also find that graphene ripples are characterized by large variations in carbon-carbon bond length, directly impacting the electronic coupling between atoms, which within a single ripple can be as different as in two different materials. The result is a single graphene sheet that effectively acts as an electronic superlattice. Our results thus also establish a novel approach to synthesize an effective 2D lateral heterostructure - by periodic modulation of lattice strain.Comment: 18 pages, 5 figures and supplementary informatio

The Foreign Direct Investment Location Decision: A Contingency Model of the Foreign Direct Investment Location Decision-Making Process

Despite considerable prior research into foreign direct investment (FDI) location decisions, our understanding of the processes underlying such decisions is still limited. Findings from work based in the economics and behavioral theories of the multinational enterprise (MNE) both acknowledge that FDI is not a point-of-time decision but a gradual process that yields important changes over its duration. However, these competing traditions both fall short when attempting to portray the actual process by which FDI location decisions are made by managers in MNEs. This gap has been recently attributed to two interrelated limitations. Firstly, level of analysis concerns have artificially separated managerial decision-making processes from the organizational and environmental structures within which they are made. Secondly, because of the complexity inherent in the FDI location decision environment, the study of these decisions has not taken contextual factors into consideration. This study addresses three important questions in order to build our understanding of the FDI location decision-making processes: (1) What are the decision-making processes that lead to FDI location choice? (2) What is the impact of contextual variables on FDI location decision-making processes at different levels of analysis, and are there any patterns of variation in decision processes under different decision conditions? (3) What factors drive final FDI location choice, and can a useful framework or theory be developed that links FDI location decision-making processes and context to drivers of FDI location choice? In order to address level of analysis concerns, the study places the manager at the center of the FDI location decision in modeling and in research, a strategy recommended by an emerging stream of behavioral-focused international business research (Aharoni, 2010; Buckley et al., 2007; Devinney, 2011). By examining FDI location decisions from the perspective of the managers who implement them, it is possible to clarify the nature of processes that lead to FDI location choice, and identify the impact of different elements of decision maker, firm and environmental context on such processes. The conceptual framework builds on Aharoni’s (1966) pivotal research while incorporating findings from broader behavioral managerial decision models and international business research. The framework is based on the assumption that FDI location decision-making processes and final choice are contingent upon interactions between the environmental, firm and decision maker context under which the decision is made. The research was undertaken in three phases. Phase 1 included a literature review that covered research on the MNE, internationalization, and decision making. The findings of the review identified key aspects of FDI location decision context and led to the development of an initial contingency framework of strategic decision making. Phase 2 consisted of an exploratory case study of twenty four FDI location decisions. The initial contingency framework developed during the literature review was used during this stage to identify the relationship between decision-making processes and contextual variables at the case decisions. By drawing on results from the exploratory research, an initial conceptual model and a set of propositions were developed. In Phase 3, twenty case studies were theoretically sampled from a pool of MNEs of varying size and parent-country nationality within the knowledge-based industries. The data collection and analysis followed a process, event-driven approach to case study research involving the mapping of key sequences of events as well as within- and cross-case analysis. The results identify the key elements of the decision process that explain FDI location behavior and develop a framework that links them together and makes them sensible. The four key elements of the FDI location decision that comprise the framework include: (i) the process, (ii) the context, (iii) patterns, and (iv) location. Research findings show the FDI location decision process as comprising of five broad stages, the content of each driven by a dynamic and evolving interpretation of maximum subjective expected utility. Utility preferences are identified as the consequence of shifting and opaque goals, founded upon imperfect information, operating in an environment marked by uncertainty. Five variations in the overall orientation of utility at case decisions, classified in the study as ‘decision rules,’ proved to be more useful predictors of decision-making behavior than traditional notions of bounded rationality seeking rent extraction and profitability. Decision processes were found to vary in five prototypical patterns, according to clusters of contextual variables that together moderated the level of decision-maker autonomy, hierarchical centralization, rule formalization, commitment to strategy, and politicization of the decision. Patterns are described as FDI location decision-making models, and proposed as an initial step towards the development of a taxonomy of FDI location decision-making processes. Because of the dynamic and staged nature of the process, findings showed that factors that were important at one stage of the decision were not as important at the next. As such, the task of identifying universal drivers of FDI location was deemed an unfeasible one. In place of universal drivers, the initiating force of the investment, the purpose of investment and information sources and networks are identified as the key context-specific determinants of location in FDI decisions. Bounded by uncertainty, chance, the dynamics of the process and decision-maker effects, each of these aspects of the decision served to limit the possible consideration set for investment, and formed the value basis and measures from which to select the most attractive location choice. Despite the contextual differences in these drivers, however, the study revealed a strong pattern that showed that the importance of specific location considerations differed in much the same way across case decisions. During the first stage of case decisions primarily strategic aspects of locations were considered; during the second, considerations relating to the system; operational concerns in the third; implementation concerns in the fourth; and added value factors in the final choice. How each of these concerns was interpreted to reach final location choice differed according to the drivers mentioned previously, although the patterns were the same. This study develops a contingency framework for examining the FDI location decision-making processes of MNEs under different operating conditions. By identifying the four key components of the FDI location decision, their interrelationships and many sources of variance, this thesis shows that despite its complexity, the FDI location decision is amenable to useful conceptual structuring. From an academic standpoint, the framework answers Aharoni’s most recent call to action in ‘Behavioral Elements in Foreign Direct Investment’ (2010) by developing a replicable structure within which to think about incorporating managerial decision models and context into the theory of the MNE. These findings enhance understandings of decision making at MNEs, reconcile a number of inconsistencies between opposing perspectives of MNE theory, and thereby update extant theory so that it has greater relevance in today’s diverse international business environment. From a managerial standpoint, the thesis helps managers to recognize the opportunities and limitations posed by different aspects of decision context so that they are able to tailor their FDI location decision strategies to best suit their needs. Finally, from the perspective of policy markers, research findings provide great support for the use of investment attraction schemes through the use of targeted location marketing and investment incentives.

Modulation of Muscle Atrophy, Fatigue and MLC Phosphorylation by MuRF1 as Indicated by Hindlimb Suspension Studies on MuRF1-KO Mice

MuRF1 is a member of the TRIM/RBCC superfamily, a gene family that encompasses a large variety of proteins, all sharing the conserved TRIM (Tripartite Motive) sequential array of RING, B-box, and coiled-coil domains. Within this family, MuRF1(also named TRIM63) is a specialized member that contributes to the development of muscle atrophy and sarcopenia. Here we studied MuRF1's role in muscle atrophy during muscle unloading induced by hindlimb suspension. Consistent with previous studies, we found that MuRF1 inactivation leads to an attenuated muscle atrophy response. The amount of protection was higher as compared to the denervation model, and within the 10 day-suspension period the soleus muscle was spared from atrophy in MuRF1-KO mice. Contractility studies on hindlimb suspended muscle tissues suggested that MuRF1's functions extend beyond muscle trophicity and implicate MuRF1 in muscle fatigue and MLC phosphorylation control: soleus muscle from MuRF1-KO mice fatigued significantly faster and in addition showed a reduced posttetanic twitch potentiation. Thus the present work further established the role of MuRF1 in muscle atrophy and for the first time shows that MuRF1 plays a role in muscle fatigue and twitch potentiation

Tissue Triage and Freezing for Models of Skeletal Muscle Disease

Skeletal muscle is a unique tissue because of its structure and function, which requires specific protocols for tissue collection to obtain optimal results from functional, cellular, molecular, and pathological evaluations. Due to the subtlety of some pathological abnormalities seen in congenital muscle disorders and the potential for fixation to interfere with the recognition of these features, pathological evaluation of frozen muscle is preferable to fixed muscle when evaluating skeletal muscle for congenital muscle disease. Additionally, the potential to produce severe freezing artifacts in muscle requires specific precautions when freezing skeletal muscle for histological examination that are not commonly used when freezing other tissues. This manuscript describes a protocol for rapid freezing of skeletal muscle using isopentane (2-methylbutane) cooled with liquid nitrogen to preserve optimal skeletal muscle morphology. This procedure is also effective for freezing tissue intended for genetic or protein expression studies. Furthermore, we have integrated our freezing protocol into a broader procedure that also describes preferred methods for the short term triage of tissue for (1) single fiber functional studies and (2) myoblast cell culture, with a focus on the minimum effort necessary to collect tissue and transport it to specialized research or reference labs to complete these studies. Overall, this manuscript provides an outline of how fresh tissue can be effectively distributed for a variety of phenotypic studies and thereby provides standard operating procedures (SOPs) for pathological studies related to congenital muscle disease

Genetics of Mechanosensation in the Heart

Mechanosensation (the ultimate conversion of a mechanical stimulus into a biochemical signal) as well as mechanotransduction (transmission of mechanically induced signals) belong to the most fundamental processes in biology. These effects, because of their dynamic nature, are particularly important for the cardiovascular system. Therefore, it is not surprising that defects in cardiac mechanosensation, are associated with various types of cardiomyopathy and heart failure. However, our current knowledge regarding the genetic basis of impaired mechanosensation in the cardiovascular system is beginning to shed light on this subject and is at the centre of this brief review

Impairments in contractility and cytoskeletal organisation cause nuclear defects in nemaline myopathy

Nemaline myopathy (NM) is a skeletal muscle disorder caused by mutations in genes that are generally involved in muscle contraction, in particular those related to the structure and/or regulation of the thin filament. Many pathogenic aspects of this disease remain largely unclear. Here, we report novel pathological defects in skeletal muscle fibres of mouse models and patients with NM: irregular spacing and morphology of nuclei; disrupted nuclear envelope; altered chromatin arrangement; and disorganisation of the cortical cytoskeleton. Impairments in contractility are the primary cause of these nuclear defects. We also establish the role of microtubule organisation in determining nuclear morphology, a phenomenon which is likely to contribute to nuclear alterations in this disease. Our results overlap with findings in diseases caused directly by mutations in nuclear envelope or cytoskeletal proteins. Given the important role of nuclear shape and envelope in regulating gene expression, and the cytoskeleton in maintaining muscle fibre integrity, our findings are likely to explain some of the hallmarks of NM, including contractile filament disarray, altered mechanical properties and broad transcriptional alterations