Liraglutide Activates Type 2 Deiodinase and Enhances β3-Adrenergic-Induced Thermogenesis in Mouse Adipose Tissue

AimsLiraglutide is a long-acting glucagon-like peptide 1 (GLP-1) receptor agonist used as an anti-hyperglycemic agent in type 2 diabetes treatment and recently approved for obesity management. Weight loss is attributed to appetite suppression, but therapy may also increase energy expenditure. To further investigate the effect of GLP-1 signaling in thermogenic fat, we assessed adipose tissue oxygen consumption and type 2 deiodinase (D2) activity in mice treated with liraglutide, both basally and after β3-adrenergic treatment.MethodsMale C57BL/6J mice were randomly assigned to receive liraglutide (400 μg/kg, n=12) or vehicle (n=12). After 16 days, mice in each group were co-treated with the selective β3-adrenergic agonist CL316,243 (1 mg/kg, n=6) or vehicle (n=6) for 5 days. Adipose tissue depots were assessed for gene and protein expression, oxygen consumption, and D2 activity.ResultsLiraglutide increased interscapular brown adipose tissue (iBAT) oxygen consumption and enhanced β3-adrenergic-induced oxygen consumption in iBAT and inguinal white adipose tissue (ingWAT). These effects were accompanied by upregulation of UCP-1 protein levels in iBAT and ingWAT. Notably, liraglutide increased D2 activity without significantly upregulating its mRNA levels in iBAT and exhibited additive effects to β3-adrenergic stimulation in inducing D2 activity in ingWAT.ConclusionsLiraglutide exhibits additive effects to those of β3-adrenergic stimulation in thermogenic fat and increases D2 activity in BAT, implying that it may activate this adipose tissue depot by increasing intracellular thyroid activation, adding to the currently known mechanisms of GLP-1A-induced weight loss.

Beige Adipocyte As The Flame Of White Adipose Tissue: Regulation Of Browning And Impact Of Obesity

Beige adipocyte, the third and relatively new type of adipocyte, can emerge in white adipose tissue (WAT) under thermogenic stimulations that is termed as browning of WAT. Recent studies suggest that browning of WAT deserves more attention and therapies targeting browning of WAT can be helpful for reducing obesity. Beyond the major inducers of browning, namely cold and β3-adrenergic stimulation, beige adipocytes are affected by several factors, and excess adiposity per se may also influence the browning process. The objective of the present review is to provide an overview of recent clinical and preclinical studies on the hormonal and non-hormonal factors that affect the browning of WAT. This review further focuses on the role of obesity per se on browning process.

The RyR2-R2474S Mutation Sensitizes Cardiomyocytes and Hearts to Catecholaminergic Stress-Induced Oxidation of the Mitochondrial Glutathione Pool

Missense mutations in the cardiac ryanodine receptor type 2 (RyR2) characteristically cause catecholaminergic arrhythmias. Reminiscent of the phenotype in patients, RyR2-R2474S knockin mice develop exercise-induced ventricular tachyarrhythmias. In cardiomyocytes, increased mitochondrial matrix Ca2+ uptake was recently linked to non-linearly enhanced ATP synthesis with important implications for cardiac redox metabolism. We hypothesize that catecholaminergic stimulation and contractile activity amplify mitochondrial oxidation pathologically in RyR2-R2474S cardiomyocytes. To investigate this question, we generated double transgenic RyR2-R2474S mice expressing a mitochondria-restricted fluorescent biosensor to monitor the glutathione redox potential (EGSH). Electrical field pacing-evoked RyR2-WT and RyR2-R2474S cardiomyocyte contractions resulted in a small but significant baseline EGSH increase. Importantly, β-adrenergic stimulation resulted in excessive EGSH oxidization of the mitochondrial matrix in RyR2-R2474S cardiomyocytes compared to baseline and RyR2-WT control. Physiologically β-adrenergic stimulation significantly increased mitochondrial EGSH further in intact beating RyR2-R2474S but not in RyR2-WT control Langendorff perfused hearts. Finally, this catecholaminergic EGSH increase was significantly attenuated following treatment with the RyR2 channel blocker dantrolene. Together, catecholaminergic stimulation and increased diastolic Ca2+ leak induce a strong, but dantrolene-inhibited mitochondrial EGSH oxidization in RyR2-R2474S cardiomyocytes.

Loss of Awareness or Urinary Dysfunction? Investigating Amyloidosis and Urinary Physiology in a Transgenic Mouse

Alzheimer’s disease (AD) is a devastating disorder primarily affecting older adults and is the most common neurodegenerative disease in the US. More than one in three AD patients experience AD-associated urinary dysfunction (ADUD), which directly contributes to their institutionalization. While ADUD has been clinically regarded as a result of poor cognitive control over urinary function, the physiology underlying loss of urinary control remains unknown. We hypothesize that amyloidosis in the CNS results in pathologic changes in urinary structure and function. Tg-APP/PS1DE9 mice were used before plaque deposition (4-6 months) and after plaque accumulation (8-10 months) and compared to WT littermates. Behavioral assays (open field testing and voiding spot assays) were performed to assess cortical function. Pressure-flow cystometry was conducted under urethane anesthesia to assess autonomic control of urinary function without cortical influence. Pharmacomyography of bladder strips was used to determine tissue-level changes in the absence of CNS input. In Tg-APP/PS1DE9 mice, plaque accumulation resulted in significant cystometric changes to voiding phase parameters, but not storage phase parameters. Pharmacologic studies showed decreased sensitivity to adrenergic stimulation without change in muscarinic sensitivity. Behavioral assays demonstrated significant differences between transgenic animals and WT in locomotion and voiding spot sizes. We interpret our data to support AD-related pathology of Aβ accumulation results in a distinct urinary phenotype in our model, analogous to the ADUD observed in AD patients. Establishing and verifying models of ADUD may improve the efficacy of treating ADUD and increase quality of life for patients and their caregivers.

Avocado Oil Prevents Kidney Injury and Normalizes Renal Vasodilation after Adrenergic Stimulation in Hypertensive Rats: Probable Role of Improvement in Mitochondrial Dysfunction and Oxidative Stress

Hypertension impairs the function of the kidney and its vasculature. Adrenergic activation is involved in these processes by promoting oxidative stress and mitochondrial dysfunction. Thus, the targeting of mitochondrial function and mitochondrial oxidative stress may be an approach to alleviate hypertensive kidney damage. Avocado oil, a source of oleic acid and antioxidants, improves mitochondrial dysfunction, decreases mitochondrial oxidative stress, and enhances vascular function in hypertensive rats. However, whether avocado oil improves the function of renal vasculature during the adrenergic stimulation, and if this is related to improvement in renal damage and enhancement of mitochondrial activity is unknown. Thus, the effects of avocado oil on renal vascular responses to adrenergic stimulation, mitochondrial dysfunction, oxidative stress, and renal damage were compared with prazosin, an antagonist of α1-adrenoceptors, in hypertensive rats induced by L-NAME. Avocado oil or prazosin decreased blood pressure, improved endothelium—dependent renal vasodilation, prevented mitochondrial dysfunction and kidney damage in hypertensive rats. However, avocado oil, but not prazosin, decreased mitochondrial ROS generation and improved the redox state of mitochondrial glutathione. These results suggest that avocado oil and prazosin prevented hypertensive renal damage due to the improvement in mitochondrial function.

Loss of Mitochondrial Ca 2+ Uniporter Limits Inotropic Reserve and Provides Trigger and Substrate for Arrhythmias in Barth Syndrome Cardiomyopathy

Background: Barth syndrome (BTHS) is caused by mutations of the gene encoding tafazzin, which catalyzes maturation of mitochondrial cardiolipin and often manifests with systolic dysfunction during early infancy. Beyond the first months of life, BTHS cardiomyopathy typically transitions to a phenotype of diastolic dysfunction with preserved ejection fraction, blunted contractile reserve during exercise and arrhythmic vulnerability. Previous studies traced BTHS cardiomyopathy to mitochondrial formation of reactive oxygen species (ROS). Since mitochondrial function and ROS formation are regulated by excitation-contraction (EC) coupling, integrated analysis of mechano-energetic coupling is required to delineate the pathomechanisms of BTHS cardiomyopathy. Methods: We analyzed cardiac function and structure in a mouse model with global knockdown of tafazzin ( Taz -KD) compared to wild-type (WT) littermates. Respiratory chain assembly and function, ROS emission, and Ca 2+ uptake were determined in isolated mitochondria. EC coupling was integrated with mitochondrial redox state, ROS, and Ca 2+ uptake in isolated, unloaded or preloaded cardiac myocytes, and cardiac hemodynamics analyzed in vivo . Results: Taz -KD mice develop heart failure with preserved ejection fraction (>50%) and age-dependent progression of diastolic dysfunction in the absence of fibrosis. Increased myofilament Ca 2+ affinity and slowed cross-bridge cycling caused diastolic dysfunction, partly compensated by accelerated diastolic Ca 2+ decay through preactivated sarcoplasmic reticulum Ca 2+ ATPase (SERCA). Taz deficiency provoked heart-specific loss of mitochondrial Ca 2+ uniporter (MCU) protein that prevented Ca 2+ -induced activation of the Krebs cycle during β-adrenergic stimulation, oxidizing pyridine nucleotides and triggering arrhythmias in cardiac myocytes. In vivo , Taz -KD mice displayed prolonged QRS duration as a substrate for arrhythmias, and a lack of inotropic response to β-adrenergic stimulation. Cellular arrhythmias and QRS prolongation, but not the defective inotropic reserve, were restored by inhibiting Ca 2+ export via the mitochondrial Na + /Ca 2+ exchanger. All alterations occurred in the absence of excess mitochondrial ROS in vitro or in vivo . Conclusions: Downregulation of MCU, increased myofilament Ca 2+ affinity, and preactivated SERCA provoke mechano-energetic uncoupling that explains diastolic dysfunction and the lack of inotropic reserve in BTHS cardiomyopathy. Furthermore, defective mitochondrial Ca 2+ uptake provides a trigger and a substrate for ventricular arrhythmias. These insights can guide the ongoing search for a cure of this orphaned disease.

ROLE OF DRUG DISCOVERY IN CENTRAL NERVOUS SYSTEM DISORDERS: AN OVERVIEW

Central nervous system (CNS) stimulants are drugs, which produce a response that could be used to alleviate a particular medical condition. These are the agents, which speed up to treat conditions characterized by lack of adrenergic stimulation, including narcolepsy and neonatal apnea. The majority of CNS stimulants is chemically similar to the neurohormone norepinephrine and simulates the traditional "fight or flight" syndrome associated with sympathetic nervous system arousal. A small figure of added members of the CNS stimulant class do not fall into definite chemical groups. The review on central nervous system stimulants gives detail study of CNS stimulant drugs, their mechanism of action and in vivo models of CNS stimulants. The brain is a delicate tissue, and advancement built very effective methods to guard it. Unfortunately, the same mechanisms that protect it against intrusive chemicals can also upset therapeutic interventions. Many current medications are rendered unsuccessful in the treatment of cerebral maladies due to our incapability to efficiently deliver and sustain them within the brain. KEYWORDS: CNS Stimulants, Blood brain barrier (BBB), Drug toxicity, Drug Safety

RBM20-mutations induce disturbed splicing of calcium relevant genes and guides clinically therapy in different cardiomyopathies

Background Mutations in the splice factor RBM20 account for ∼3% of genetic cardiomyopathies. Mutations at position R634 in the hotspot RS-domain were found to cause dilative cardiomyopathy (DCM) (R634W) or left ventricular non-compaction cardiomyopathy (LVNC) (R634L), but the pathophysiological mechanisms that govern the heterogeneity in phenotype presentation remain unknown. Purpose We aimed here to identify the molecular events caused by the distinct RBM20 mutations from DCM and LVNC patients using a patient-specific induced stem cell model (iPSC) and test if the currently clinically used β-blockers (Metroprolol) are suitable for different RBM20-dependent cardiomyopathies. Methods We generated iPSC-cardiomyocytes of 2 DCM- and 2 LVNC-patients harboring the RBM20-mutations R634W (DCM) or R634L (LVNC). We investigated alternative splicing, sarcomeric regularity, cAMP-level, kinase-specific phosphorylation of Ca2+ players and Ca2+ handling. To investigate the impact of the genetic background, isogenic rescue lines were generated by CRISPR/Cas9. Different clinical drugs as Metoprolol and Verapamil were used to analyze the pharmacological improvement in vitro. Results We investigated the splicing pattern of the 2 RBM20 mutations in DCM and LVNC iPSC-CMs and observed common isoform changes in titin and a 24bp-insertion in the gene RYR2. The Ca2+ handling gene triadin is misspliced in LVNC-CMs, whereas the structural gene LDB3 is misspliced in DCM-CMs. As a possible consequence of splice defects in sarcomeric genes, both DCM and LVNC-CMs exhibited an irregular sarcomeric structure. The Ca2+ handling gene CAMK2δ was predominantly misspliced in LVNC-CMs leading to CAMK2δ-dependent hyperphosphorylation of its target PLN-Thr17 and subsequently to shortened Ca2+ elimination time and weakened response to β-adrenergic stimulation. By contrast, DCM-CMs exhibited increased Ca2+ sparks and decreased systolic and diastolic Ca2+ levels. RBM20 expression itself was decreased in LVNC-CMs, but not in DCM-CMs. This highlights that 2 distinct RBM20 mutations can lead to different pathological Ca2+ phenotypes. Isogenic CRISPR/Cas9 repair of both RBM20 mutations in LVNC and DCM demonstrated a rescue in gene missplicing, sarcomeric regularity and the Ca2+ handling aberrations and underscored the causative nature of the 2 mutations and their diverging effects. Ca2+ channel blockage with Verapamil showed a significant improvement of some of the LVNC disease characteristics compared to commonly clinically used β-blocker Metoprolol and underpins the potential clinical use of this drug in patients with LVNC. Conclusion We show the first iPSC-model of splice-defect associated RBM20-dependent LVNC and DCM. In summary, our results suggest that the molecular aberrations in alternative splicing differ depending on the distinct mutation in RBM20 and lead to shared and differential pathologies. Verapamil could be a good candidate in the treatment of RBM20-dependent LVNC. FUNDunding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Bunderministerium für Bildung und Forschung BMBFGerman Center for Cardiovascular Research DZHK