MicroRNAs and the cellular response to rapamycin: Potential role in diagnosis and therapy

The mammalian target of rapamycin (mTOR) is a major regulator of cell growth, motility and angiogenesis that is often deregulated in malignancies. mTOR inhibitors have been approved for the treatment of renal cell carcinoma and mantle cell lymphoma. Currently, second generation mTOR inhibitors are under clinical evaluation. Major challenges remain in the identification of patients who will respond to mTOR inhibitors and the development of therapeutics that can overcome intrinsic resistance or acquired resistance. There are currently no biomarkers that predict tumor response to mTOR inhibitors. MicroRNAs (miRNAs) are endogenous small non-coding RNAs that regulate gene expression. MiRNAs participate in many biological processes including proliferation and apoptosis. miRNAs are often deregulated in cancer and act as tumor suppressors or oncogenes.2 Recently miRNAs emerged as diagnostic and prognostic markers to assess therapeutic responses giving rise to the field of miRNA pharmacogenomics.3 Numerous studies indicate that mTOR and its signaling pathway is regulated by miRNAs. However, little is known as to whether miRNAs play a role in the intrinsic tumor resistance or the development of acquired resistance to mTOR inhibitors. In our recent studies we used rapamycin resistant (RR1) variants of the murine brain tumor cell line BC3H1, developed by chronic rapamycin treatment

Physiology and pathophysiology of excitation–contraction coupling in skeletal muscle: the functional role of ryanodine receptor

Calcium (Ca2+) release from intracellular stores plays a key role in the regulation of skeletal muscle contraction. The type 1 ryanodine receptors (RyR1) is the major Ca2+ release channel on the sarcoplasmic reticulum (SR) of myocytes in skeletal muscle and is required for excitation–contraction (E–C) coupling. This article explores the role of RyR1 in the skeletal muscle physiology and pathophysiology

Ryanodine receptor studies using genetically engineered mice

AbstractRyanodine receptors (RyR) regulate intracellular Ca2+ release in many cell types and have been implicated in a number of inherited human diseases. Over the past 15years genetically engineered mouse models have been developed to elucidate the role that RyRs play in physiology and pathophysiology. To date these models have implicated RyRs in fundamental biological processes including excitation–contraction coupling and long term plasticity as well as diseases including malignant hyperthermia, cardiac arrhythmias, heart failure, and seizures. In this review we summarize the RyR mouse models and how they have enhanced our understanding of the RyR channels and their roles in cellular physiology and disease

Mitochondrial calcium overload is a key determinant in heart failure

Calcium (Ca2+) released from the sarcoplasmic reticulum (SR) is crucial for excitation-contraction (E-C) coupling. Mitochondria, the major source of energy, in the form of ATP, required for cardiac contractility, are closely interconnected with the SR, and Ca2+ is essential for optimal function of these organelles. However, Ca2+ accumulation can impair mitochondrial function, leading to reduced ATP production and increased release of reactive oxygen species (ROS). Oxidative stress contributes to heart failure (HF), but whether mitochondrial Ca2+ plays a mechanistic role in HF remains unresolved. Here, we show for the first time, to our knowledge, that diastolic SR Ca2+ leak causes mitochondrial Ca2+ overload and dysfunction in a murine model of postmyocardial infarction HF. There are two forms of Ca2+ release channels on cardiac SR: type 2 ryanodine receptors (RyR2s) and type 2 inositol 1,4,5-trisphosphate receptors (IP3R2s). Using murine models harboring RyR2 mutations that either cause or inhibit SR Ca2+ leak, we found that leaky RyR2 channels result in mitochondrial Ca2+ overload, dysmorphology, and malfunction. In contrast, cardiac-specific deletion of IP3R2 had no major effect on mitochondrial fitness in HF. Moreover, genetic enhancement of mitochondrial antioxidant activity improved mitochondrial function and reduced posttranslational modifications of RyR2 macromolecular complex. Our data demonstrate that leaky RyR2, but not IP3R2, channels cause mitochondrial Ca2+ overload and dysfunction in HF

A Fair Exchange: The Reciprocal Relationship Between Universities and Clinical Placement Supervisors

Clinical psychology training in the UK relies heavily upon supervised clinical practice placements. Placement supervisors have a significant responsibility for providing trainees with the learning experiences required for qualification. The role is demanding and whilst the university benefits greatly, it is less clear what supervisors receive in return. This is important when one considers how positive relationships and social action are influenced by reciprocity and a sense of belongingness. Despite its importance, no research has directly explored the relationship between supervisors and the university in a clinical psychology training context. This novel study sought to explore how supervisors perceive their role and their connectedness / belongingness to the university, and whether technology utilized by other areas of pedagogy led to improvements. Access to electronic resources was sent to clinical placement supervisors (n=100). A subset of these (n=7) signed up to complete a semi-structured interview. The interviews were analysed using template analysis. Common themes emerged, including perceived benefits of the supervisor role, such as feeling connected to the training course, despite significant challenges and demands. The provision of electronic resources was found to have the potential to enhance connectedness for all stakeholders. The implications of these findings are discussed

Genetically enhancing mitochondrial antioxidant activity improves muscle function in aging

Age-related skeletal muscle dysfunction is a leading cause of morbidity that affects up to half the population aged 80 or greater. Here we tested the effects of increased mitochondrial antioxidant activity on age-dependent skeletal muscle dysfunction using transgenic mice with targeted overexpression of the human catalase gene to mitochondria (MCat mice). Aged MCat mice exhibited improved voluntary exercise, increased skeletal muscle specific force and tetanic Ca(2+) transients, decreased intracellular Ca(2+) leak and increased sarcoplasmic reticulum (SR) Ca(2+) load compared with age-matched wild type (WT) littermates. Furthermore, ryanodine receptor 1 (the sarcoplasmic reticulum Ca(2+) release channel required for skeletal muscle contraction; RyR1) from aged MCat mice was less oxidized, depleted of the channel stabilizing subunit, calstabin1, and displayed increased single channel open probability (Po). Overall, these data indicate a direct role for mitochondrial free radi! cals in promoting the pathological intracellular Ca(2+) leak that underlies age-dependent loss of skeletal muscle function. This study harbors implications for the development of novel therapeutic strategies, including mitochondria-targeted antioxidants for treatment of mitochondrial myopathies and other healthspan-limiting disorders

Cholinergic Modulation of Locomotion and Striatal Dopamine Release Is Mediated by α6α4* Nicotinic Acetylcholine Receptors

Dopamine (DA) release in striatum is governed by firing rates of midbrain DA neurons, striatal cholinergic tone, and nicotinic ACh receptors (nAChRs) on DA presynaptic terminals. DA neurons selectively express α6* nAChRs, which show high ACh and nicotine sensitivity. To help identify nAChR subtypes that control DA transmission, we studied transgenic mice expressing hypersensitive α6^(L9’S*) receptors. α6^(L9’S) mice are hyperactive, travel greater distance, exhibit increased ambulatory behaviors such as walking, turning, and rearing, and show decreased pausing, hanging, drinking, and grooming. These effects were mediated by α6 α4* pentamers, as α6^(L9’S) mice lacking α4 subunits displayed essentially normal behavior. In α6^(L9’S) mice, receptor numbers are normal, but loss of α4 subunits leads to fewer and less sensitive α6* receptors. Gain-of-function nicotine-stimulated DA release from striatal synaptosomes requires α4 subunits, implicating α6α4β2* nAChRs in α6^(L9’S) mouse behaviors. In brain slices, we applied electrochemical measurements to study control of DA release by α6^(L9’S) nAChRs. Burst stimulation of DA fibers elicited increased DA release relative to single action potentials selectively in α6^(L9’S), but not WT or α4KO/ α6^(L9’S), mice. Thus, increased nAChR activity, like decreased activity, leads to enhanced extracellular DA release during phasic firing. Bursts may directly enhance DA release from α6^(L9’S) presynaptic terminals, as there was no difference in striatal DA receptor numbers or DA transporter levels or function in vitro. These results implicate α6α4β2* nAChRs in cholinergic control of DA transmission, and strongly suggest that these receptors are candidate drug targets for disorders involving the DA system