Modulation of contractility in human cardiac hypertrophy by myosin essential light chain isoforms

Cardiac hypertrophy is an adaptive response that normalizes wall stress and compensates for increased workload. It is accompanied by distinct qualitative and quantitative changes in the expression of protein isoforms concerning contractility, intracellular Ca(2+)-homeostasis and metabolism. Changes in the myosin subunit isoform expression improves contractility by an increase in force generation at a given Ca(2+)-concentration (increased Ca(2+)-sensitivity) and by improving the economy of the chemo-mechanical transduction process per amount of utilised ATP (increased duty ratio). In the human atrium this is achieved by partial replacement of the endogenous fast myosin by the ventricular slow-type heavy and light chains. In the hypertrophic human ventricle the slow-type beta-myosin heavy chains remain unchanged, but the ectopic expression of the atrial myosin essential light chain (ALC1) partially replaces the endogenous ventricular isoform (VLC1). The ventricular contractile apparatus with myosin containing ALC1 is characterised by faster cross-bridge kinetics, a higher Ca(2+)-sensitivity of force generation and an increased duty ratio. The mechanism for cross-bridge modulation relies on the extended Ala-Pro-rich N-terminus of the essential light chains of which the first eleven residues interact with the C-terminus of actin. A change in charge in this region between ALC1 and VLC1 explains their functional difference. The intracellular Ca(2+)-handling may be impaired in heart failure, resulting in either higher or lower cytosolic Ca(2+)-levels. Thus the state of the cardiomyocyte determines whether this hypertrophic adaptation remains beneficial or becomes detrimental during failure. Also discussed are the effects on contractility of long-term changes in isoform expression of other sarcomeric proteins. Positive and negative modulation of contractility by short-term phosphorylation reactions at multiple sites in the myosin regulatory light chain, troponin-I, troponin-T, alpha-tropomyosin and myosin binding protein-C are considered in detail

Impact of the PI3Kalpha inhibitor alpelisib on everolimus resistance and somatostatin receptor expression in an orthotopic pancreatic NEC xenograft mouse model

The mTORC1 inhibitor everolimus is one of the few approved therapies for locally advanced and metastatic neuroendocrine tumours (NETs). However, after initial disease stabilisation, most patients develop resistance within one year. Our aim was to overcome resistance to everolimus by additional treatment with the PI3Kalpha inhibitor alpelisib in an everolimus-resistant orthotopic pancreatic neuroendocrine carcinoma xenograft mouse model. Female SCID mice underwent laparoscopic pancreatic transplantation of everolimus-sensitive (BON1KDMSO) or everolimus-resistant (BON1RR2) NET cells. Both groups were further divided into 4 treatment groups: placebo, everolimus, alpelisib and everolimus + alpelisib (combination). Oral treatment was started at a tumour volume of approximately 140 mm3 and continued until 1900 - 2000 mm3, validated by weekly MRI. Somatostatin receptor expression and tumour viability were analysed by 68Ga-DOTATOC- and 18F-FDG PET/CT. Everolimus resistance of the BON1RR2 tumours was confirmed. In the everolimus-sensitive group, everolimus alone, alpelisib alone and combination treatment significantly prolonged survival, compared to placebo, while in the BON1RR2 group, only combination treatment significantly prolonged survival compared to placebo, but neither everolimus nor alpelisib alone. Placebo-treated everolimus-sensitive tumours grew more rapidly (median survival 45 d), compared to placebo-treated everolimus-resistant tumours (60 d). Within the everolimus-sensitive group, the combination-treated mice showed the longest median survival (52 d). Of all groups, the everolimus-resistant combination-treated group survived longest (69 d). Combination treatment with everolimus and alpelisib seems promising to overcome everolimus resistance in neuroendocrine neoplasms, and should be further examined in a clinical trial

Utrophin Binds Laterally along Actin Filaments and Can Couple Costameric Actin with Sarcolemma When Overexpressed in Dystrophin-deficient Muscle

Dystrophin is widely thought to mechanically link the cortical cytoskeleton with the muscle sarcolemma. Although the dystrophin homolog utrophin can functionally compensate for dystrophin in mice, recent studies question whether utrophin can bind laterally along actin filaments and anchor filaments to the sarcolemma. Herein, we have expressed full-length recombinant utrophin and show that the purified protein is fully soluble with a native molecular weight and molecular dimensions indicative of monomers. We demonstrate that like dystrophin, utrophin can form an extensive lateral association with actin filaments and protect actin filaments from depolymerization in vitro. However, utrophin binds laterally along actin filaments through contribution of acidic spectrin-like repeats rather than the cluster of basic repeats used by dystrophin. We also show that the defective linkage between costameric actin filaments and the sarcolemma in dystrophin-deficient mdx muscle is rescued by overexpression of utrophin. Our results demonstrate that utrophin and dystrophin are functionally interchangeable actin binding proteins, but that the molecular epitopes important for filament binding differ between the two proteins. More generally, our results raise the possibility that spectrin-like repeats may enable some members of the plakin family of cytolinkers to laterally bind and stabilize actin filaments

Global urban environmental change drives adaptation in white clover

Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural clines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale