Skeletal muscle Nox4 knockout prevents and Nox2 knockout blunts loss of maximal diaphragm force in mice with heart failure with reduced ejection fraction

Patients with heart failure with reduced ejection fraction (HFrEF) experience diaphragm weakness that contributes to the primary disease symptoms of fatigue, dyspnea, and exercise intolerance. Weakness in the diaphragm is related to excessive production of reactive oxygen species (ROS), but the exact source of ROS remains unknown. NAD(P)H Oxidases (Nox), particularly the Nox2 and 4 isoforms, are important sources of ROS within skeletal muscle that contribute to optimal cell function. There are reports of increased Nox activity in the diaphragm of patients and animal models of HFrEF, implicating these complexes as possible sources of diaphragm dysfunction in HFrEF. To investigate the role of these proteins on diaphragm weakness in HFrEF, we generated inducible skeletal muscle specific knockouts of Nox2 or Nox4 using the Cre-Lox system and assessed diaphragm function in a mouse model of HFrEF induced by myocardial infarction. Diaphragm maximal specific force measured in vitro was depressed by ∼20% with HFrEF. Skeletal muscle knockout of Nox4 provided full protection against the loss of maximal force (p < 0.01), while the knockout of Nox2 provided partial protection (7% depression, p < 0.01). Knockout of Nox2 from skeletal myofibers improved survival from 50 to 80% following myocardial infarction (p = 0.026). Our findings show an important role for skeletal muscle NAD(P)H Oxidases contributing to loss of diaphragm maximal force in HFrEF, along with systemic pathophysiological responses following myocardial infarction.

RNA-sequencing reveals transcriptional signature of pathological remodeling in the diaphragm of rats after myocardial infarction

The diaphragm is the main inspiratory muscle, and the chronic phase post-myocardial infarction (MI) is characterized by diaphragm morphological, contractile, and metabolic abnormalities. However, the mechanisms of diaphragm weakness are not fully understood. In the current study, we aimed to identify the transcriptome changes associated with diaphragm abnormalities in the chronic stage MI. We ligated the left coronary artery to cause MI in rats and performed RNA-sequencing (RNA-Seq) in diaphragm samples 16 weeks post-surgery. The sham group underwent thoracotomy and pericardiotomy but no artery ligation. We identified 112 differentially expressed genes (DEGs) out of a total of 9664 genes. Myocardial infarction upregulated and downregulated 42 and 70 genes, respectively. Analysis of DEGs in the framework of skeletal muscle-specific biological networks suggest remodeling in the neuromuscular junction, extracellular matrix, sarcomere, cytoskeleton, and changes in metabolism and iron homeostasis. Overall, the data are consistent with pathological remodeling of the diaphragm and reveal potential biological targets to prevent diaphragm weakness in the chronic stage MI.

Thermodynamic Switch in Binding of Adhesion/Growth Regulatory Human Galectin-3 to Tumor-Associated TF Antigen (CD176) and MUC1 Glycopeptides

A shift to short-chain glycans is an observed change in mucin-type O-glycosylation in premalignant and malignant epithelia. Given the evidence that human galectin-3 can interact with mucins and also weakly with free tumor-associated Thomsen-Friedenreich (TF) antigen (CD176), the study of its interaction with MUC1 (glyco)peptides is of biomedical relevance. Glycosylated MUC1 fragments that carry the TF antigen attached through either Thr or Ser side chains were synthesized using standard Fmoc-based automated solid-phase peptide chemistry. The dissociation constants (K_d) for interaction of galectin-3 and the glycosylated MUC1 fragments measured by isothermal titration calorimetry decreased up to 10 times in comparison to that of the free TF disaccharide. No binding was observed for the nonglycosylated control version of the MUC1 peptide. The most notable feature of the binding of MUC1 glycopeptides to galectin-3 was a shift from a favorable enthalpy to an entropy-driven binding process. The comparatively diminished enthalpy contribution to the free energy (ΔG) was compensated by a considerable gain in the entropic term. ¹H–¹⁵N heteronuclear single-quantum coherence spectroscopy nuclear magnetic resonance data reveal contact at the canonical site mainly by the glycan moiety of the MUC1 glycopeptide. Ligand-dependent differences in binding affinities were also confirmed by a novel assay for screening of low-affinity glycan–lectin interactions based on AlphaScreen technology. Another key finding is that the glycosylated MUC1 peptides exhibited activity in a concentration-dependent manner in cell-based assays revealing selectivity among human galectins. Thus, the presentation of this tumor-associated carbohydrate ligand by the natural peptide scaffold enhances its affinity, highlighting the significance of model studies of human lectins with synthetic glycopeptides.

Agonist-dependent cannabinoid receptor signalling in human trabecular meshwork cells

BACKGROUND AND PURPOSE

Trabecular meshwork (TM) is an ocular tissue involved in the regulation of aqueous humour outflow and intraocular pressure (IOP). CB1 receptors (CB1) are present in TM and cannabinoid administration decreases IOP. CB1 signalling was investigated in a cell line derived from human TM (hTM).

EXPERIMENTAL APPROACH

CB1 signalling was investigated using ratiometric Ca2+ imaging, western blotting and infrared In-Cell Western analysis.

KEY RESULTS

WIN55212-2, a synthetic aminoalkylindole cannabinoid receptor agonist (10-100 microM) increased intracellular Ca2+ in hTM cells. WIN55,212-2-mediated Ca2+ increases were blocked by AM251, a CB1 antagonist, but were unaffected by the CB2 antagonist, AM630. The WIN55,212-2-mediated increase in [Ca2+]i was pertussis toxin (PTX)-insensitive, therefore, independent of Gi/o coupling, but was attenuated by a dominant negative Galpha(q/11) subunit, implicating a Gq/11 signalling pathway. The increase in [Ca2+]i was dependent upon PLC activation and mobilization of intracellular Ca2+ stores. A PTX-sensitive increase in extracellular signal-regulated kinase (ERK1/2) phosphorylation was also observed in response to WIN55,212-2, indicative of a Gi/o signalling pathway. CB1-Gq/11 coupling to activate PLC-dependent increases in Ca2+ appeared to be specific to WIN55,212-2 and were not observed with other CB1 agonists, including CP55,940 and methanandamide. CP55940 produced PTX-sensitive increases in [Ca2+]i at concentrations>or=15 microM, and PTX-sensitive increases in ERK1/2 phosphorylation.

CONCLUSIONS AND IMPLICATIONS

This study demonstrates that endogenous CB1 couples to both Gq/11 and Gi/o in hTM cells in an agonist-dependent manner. Cannabinoid activation of multiple CB1 signalling pathways in TM tissue could lead to differential changes in aqueous humour outflow and IOP.