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Abstract Aims The conditions of hypoxia are suggested to induce permanent atrial fibrillation (AF). The regulation of COX4I2 and COX4I1 depends on oxygen availability in tissues. A role of COX4I2 in the myocardium of AF patients is supposed for pathogenesis of AF and subsequent alterations in the electron transfer chain (ETC) under hypoxia. Methods and results In vitro, influence of hypoxia on HeLa 53 cells was studied and elevated parts of COX 4I2 were confirmed. Myocardial biopsies were taken ex vivo from the patients' Right Atria with SR (n = 31) and AF (n = 11), respectively. RT‐ PCR for mRNA expresson, mitochondrial respiration by polarography and the protein content of cytochrome c oxidase (CytOx) subunit 4I1 and CytOx subunit 4I2 by ELISA were studied. Clinical data were correlated to the findings of gene expressions in parallel. Patients with permanent AF had a change in isoform 4I2/4I1 expression along with a decrease of isoform COX 4I1 expression. The 4I2/4I1 ratio of mRNA expression was increased from 0.630 to 1.058 in comparison. However, the protein content of CytOx subunit 4 was much lower in the AF group, whereas the respiration/units enzyme activity in both groups remained the same. Conclusions This study describes a possible molecular correlate for the development of AF. Due to the known functional significance of COX 4I2, mitochondrial dysfunction can be assumed as a part of the pathogenesis of AF.

In rats decreased bioavailability of nitric oxide induces oxidative stress and right heart failure. Oxidative stress can activate matrix metalloproteinase-2 (MMP2). We addressed the question whether increasing oxidative defense by administration of the SOD mimetic Tempol or direct inhibition of MMP2 activity by SB-3CT mitigates right heart failure. Rats received l-NAME for four weeks and during week three and four treatment groups received either Tempol or SB-3CT in addition. After four weeks heart function was analyzed by echocardiography, organ weights and expression of NPPB and COL1A1 were analyzed, oxidative stress was monitored by DHE-staining and MMP2 activity was quantified by proteolytic auto-activation, zymography, and troponin I degradation. l-NAME induced oxidative stress and MMP2 activity stronger in the right ventricle than in the left ventricle. Troponin I, a MMP2 substrate, was degraded in right ventricles. Tempol reduced oxidative stress and preferentially affected the expression of fibrotic genes (i.e. COL1A1) and fibrosis. Tempol and SB-3CT mitigated right but not left ventricular hypertrophy. Neither SB-3CT nor Tempol alone strongly improved right ventricular function. In conclusion, both MMP2 activity and oxidative stress contribute to right ventricular failure but neither is MMP2 activation linked to oxidative stress nor does oxidative stress and MMP2 activity have common targets.

Background: Obesity, a major component of cardiometabolic syndrome, contributes to the imbalance between pro- and anti-atherosclerotic factors via dysregulation of adipocytokine secretion. Among these adipocytokines, the C1q/TNF-related proteins (CTRPs) play a role in the modulation of atherosclerosis development and progression. Here, we investigated the vascular effects of CTRP13. Results: CTRP13 is not only expressed in adipose tissue but also in vessels/endothelial cells (ECs) of mice, rats, and humans. Obese individuals (mice, rats, and humans) showed higher vascular CTRP13 expression. Human Umbilical Vein Endothelial Cells (HUVECs), cultured in the presence of serum from obese mice, mimicked this obesity-associated effect on CTRP13 protein expression. Similarly, high glucose conditions and TNF-alpha, but not insulin, resulted in a strong increase in CTRP13 in these cells. Recombinant CTRP13 induced a reduction in EC proliferation via AMPK. In addition, CTRP13 reduced cell cycle progression and increased p53 phosphorylation and p21 protein expression, but reduced Rb phosphorylation, with the effects largely depending on alpha-2 AMPK as suggested by adenoviral overexpression of dominant-negative (DN) or wild-type (WT) alpha 1/alpha 2 AMPK. Conclusion: The present study demonstrates that CTRP13 expression is induced in ECs under diabetic conditions and that CTRP13 possesses significant vaso-modulatory properties which may have an impact on vascular disease progression in patients.

Serotonin effects on cardiac hypertrophy, senescence, and failure are dependent either on activation of specific receptors or serotonin uptake and serotonin degradation by monoamine oxidases (MAOs). Receptor-dependent effects are specific for serotonin, but MAO-dependent effects are nonspecific as MAOs also metabolize other substrates such as catecholamines. Our study evaluates the role of MAO-A in serotonin- and norepinephrine-dependent cell damage. Experiments were performed in vivo to study the regulation of MAOA and MAOB expression and in vitro on isolated cultured adult rat ventricular cardiomyocytes (cultured for 24 h) to study the function of MAO-A. MAOA but not MAOB expression increased in maladaptive hypertrophic stages. Serotonin and norepinephrine induced morphologic cell damage (loss of rod-shaped cell structure). However, MAO-A inhibition suppressed serotonin-dependent but not norepinephrine-dependent damages. Serotonin but not norepinephrine caused a reduction in cell shortening in nondamaged cells. Serotonin induced mitochondria-dependent oxidative stress. In vivo, MAOA was induced during aging and hypertension but the expression of the corresponding serotonin uptake receptor (SLC6A4) was reduced and enzymes that reduce either oxidative stress (CAT) or accumulation of 5-hydroxyindolacetaldehyde (ALDH2) were induced. In summary, the data show that MAO-A potentially affects cardiomyocytes’ function but that serotonin is not necessarily the native substrate.

CACNA1C encodes the pore-forming α1C subunit of the L-type Ca2+ channel, Cav1.2. Mutations and polymorphisms of the gene are associated with neuropsychiatric and cardiac disease. Haploinsufficient Cacna1c+/− rats represent a recently developed model with a behavioral phenotype, but its cardiac phenotype is unknown. Here, we unraveled the cardiac phenotype of Cacna1c+/− rats with a main focus on cellular Ca2+ handling mechanisms. Under basal conditions, isolated ventricular Cacna1c+/− myocytes exhibited unaltered L-type Ca2+ current, Ca2+ transients (CaTs), sarcoplasmic reticulum (SR) Ca2+ load, fractional release, and sarcomere shortenings. However, immunoblotting of left ventricular (LV) tissue revealed reduced expression of Cav1.2, increased expression of SERCA2a and NCX, and augmented phosphorylation of RyR2 (at S2808) in Cacna1c+/− rats. The β-adrenergic agonist isoprenaline increased amplitude and accelerated decay of CaTs and sarcomere shortenings in both Cacna1c+/− and WT myocytes. However, the isoprenaline effect on CaT amplitude and fractional shortening (but not CaT decay) was impaired in Cacna1c+/− myocytes exhibiting both reduced potency and efficacy. Moreover, sarcolemmal Ca2+ influx and fractional SR Ca2+ release after treatment with isoprenaline were smaller in Cacna1c+/− than in WT myocytes. In Langendorff-perfused hearts, the isoprenaline-induced increase in RyR2 phosphorylation at S2808 and S2814 was attenuated in Cacna1c+/− compared to WT hearts. Despite unaltered CaTs and sarcomere shortenings, Cacna1c+/− myocytes display remodeling of Ca2+ handling proteins under basal conditions. Mimicking sympathetic stress with isoprenaline unmasks an impaired ability to stimulate Ca2+ influx, SR Ca2+ release, and CaTs caused, in part, by reduced phosphorylation reserve of RyR2 in Cacna1c+/− cardiomyocytes.

Abstract Increased activation of sympathetic nervous system contributes to congestive heart failure (CHF) progression, and inhibition of sympathetic overactivation by beta-blockers is successful in CHF patients. Similarly, caloric restriction (CR) reduces sympathetic activity but mediates additional effects. Here, we compared the cardiac effects of CR (− 40% kcal, 3 months) with beta-blocker therapy (BB), diuretic medication (DF) or control diet in 18-months-old Wistar rats. We continuously recorded blood pressure, heart rate, body temperature and activity with telemetric devices and analysed cardiac function, activated signalling cascades and markers of apoptosis and mitochondrial biogenesis. During our study, left ventricular (LV) systolic function improved markedly (CR), mildly (BB) or even deteriorated (DF; control). Diastolic function was preserved by CR and BB but impaired by DF. CR reduced blood pressure identical to DF and BB and heart rate identical to BB. Plasma noradrenaline was decreased by CR and BB but increased by DF. Only CR reduced LV oxidative damage and apoptosis, induced AMPK and Akt phosphorylation and increased mitochondrial biogenesis. Thus, additive to the reduction of sympathetic activity, CR achieves protective effects on mitochondria and improves LV function and ROS damage in aged hearts. CR mechanisms may provide additional therapeutic targets compared to traditional CHF therapy.

Lysyl oxidase (LOX) is a secretory protein that catalyzes elastin and collagen cross-linking. Lowering LOX expression and activity in endothelial cells is associated with a high risk of aneurysms and vascular malformation. Interleukin-6 (IL-6), elevated in hypertension, is known to suppress LOX expression. The influence of anti-hypertensive medication on the plasma LOX concentration is currently unknown. In a cohort of 34 patients diagnosed with resistant hypertension and treated with up to nine different drugs, blood concentration of LOX was analyzed to identify drugs that have an impact on plasma LOX concentration. Key findings were confirmed in a second independent patient cohort of 37 patients diagnosed with dilated cardiomyopathy. Blood concentrations of aldosterone and IL-6 were analyzed. In vitro, the effect of IL-6 on LOX expression was analyzed in endothelial cells. Patients receiving aldosterone antagonists had the highest plasma LOX concentration in both cohorts. This effect was independent of sex, age, blood pressure, body mass index, and co-medication. Blood aldosterone concentration correlates with plasma IL-6 concentration. In vitro, IL-6 decreased the expression of LOX in endothelial cells but not fibroblasts. Aldosterone was identified as a factor that affects blood concentration of LOX in an IL-6-dependent manner.

The adipocytokine adiponectin and its structural homologs, the C1q/TNF-related proteins (CTRPs), increase insulin sensitivity, fatty acid oxidation and mitochondrial biogenesis. Adiponectin- and CTRP-induced signal transduction has been described to involve the adiponectin receptors and a number of co-receptors including the Low density lipoprotein receptor-related protein 1 (LRP1). LRP1 is another target of the proprotein convertase subtilisin/kexin-9 (PCSK9) in addition to the LDL-receptor (LDL-R). Here, we investigated the influence of PCSK9 on the metabolic effects of CTRP9, the CTRP with the highest homology to adiponectin. Knockdown of LRP1 in H9C2 cardiomyoblasts blunts the effects of CTRP9 on signal transduction and mitochondrial biogenesis, suggesting its involvement in CTRP9-induced cellular effects. Treatment of adult rat cardiomyocytes with recombinant PCSK9 but not knockdown of endogenous PCSK9 by siRNA results in a strong reduction in LRP1 protein expression and subsequently reduces the mitochondrial biogenic effect of CTRP9. PCSK9 treatment (24 h) blunts the effects of CTRP9-induced signaling cascade activation (AMP-dependent protein kinase, protein kinase B). In addition, the stimulating effects of CTRP9 on cardiomyocyte mitochondrial biogenesis and glucose metabolism (GLUT-4 translocation, glucose uptake) are largely blunted. Basal fatty acid (FA) uptake is strongly reduced by exogenous PCSK9, although protein expression of the PCSK9 target CD36, the key regulator of FA transport in cardiomyocytes, is not altered. In addition, only minor effects of PCSK9 were observed on CTRP9-induced FA uptake or the expression of genes involved in FA metabolism or uptake. Finally, this CTRP9-induced increase in CD36 expression occurs independent from LRP1 and LDL-R. In conclusion, PCSK9 treatment influences LRP1-mediated signaling pathways in cardiomyocytes. Thus, therapeutic PCSK9 inhibition may provide an additional benefit through stimulation of glucose metabolism and mitochondrial biogenesis in addition to the known lipid-lowering effects. This could be an important beneficial side effect in situations with impaired mitochondrial function and reduced metabolic flexibility thereby influencing cardiac function.

Background: Caloric restriction (CR) extends lifespan in many species, including mammals. CR is cardioprotective in senescent myocardium by correcting pre-existing mitochondrial dysfunction and apoptotic activation. Furthermore, it confers cardioprotection against acute ischemia-reperfusion injury. Here, we investigated the role of AMP-activated protein kinase (AMPK) in mediating the cardioprotective CR effects in failing, postinfarct myocardium. Methods: Ligation of the left coronary artery or sham operation was performed in rats and mice. Four weeks after surgery, left ventricular (LV) function was analyzed by echocardiography, and animals were assigned to different feeding groups (control diet or 40% CR, 8 weeks) as matched pairs. The role of AMPK was investigated with an AMPK inhibitor in rats or the use of alpha 2 AMPK knock-out mice. Results: CR resulted in a significant improvement in LV function, compared to postinfarct animals receiving control diet in both species. The improvement in LV function was accompanied by a reduction in serum BNP, decrease in LV proapoptotic activation, and increase in mitochondrial biogenesis in the LV. Inhibition or loss of AMPK prevented most of these changes. Conclusions: The failing, postischemic heart is protected from progressive loss of LV systolic function by CR. AMPK activation is indispensable for these protective effects.

The leading cause of death in Pulmonary Arterial Hypertension (PAH) is right ventricular (RV) failure. The tumor suppressor p53 has been associated with left ventricular hypertrophy (LVH) and remodeling but its role in RV hypertrophy (RVH) is unclear. The purpose of this study was to determine whether pharmacological activation of p53 by Quinacrine affects RV remodeling and function in the pulmonary artery banding (PAB) model of compensated RVH in mice. The effects of p53 activation on cellular functions were studied in isolated cardiomyocytes, cardiac fibroblasts and endothelial cells (ECs). The expression of p53 was examined both on human RV tissues from patients with compensated and decompensated RVH and in mouse RV tissues early and late after the PAB. As compared to control human RVs, there was no change in p53 expression in compensated RVH, while a marked upregulation was found in decompensated RVH. Similarly, in comparison to SHAM-operated mice, unaltered RV p53 expression 7 days after PAB, was markedly induced 21 days after the PAB. Quinacrine induced p53 accumulation did not further deteriorate RV function at day 7 after PAB. Quinacrine administration did not increase EC death, neither diminished EC number and capillary density in RV tissues. No major impact on the expression of markers of sarcomere organization, fatty acid and mitochondrial metabolism and respiration was noted in Quinacrine-treated PAB mice. p53 accumulation modulated the expression of Heme Oxygenase 1 (HO-1) and Glucose Transporter (Glut1) in mouse RVs and in adult cardiomyocytes. We conclude that early p53 activation in PAB-induced RVH does not cause substantial detrimental effects on right ventricular remodeling and function.

Background and AimsActivation of the cAMP/Epac signalling stabilises endothelial barrier function. Moreover, its activation is accompanied by an activation of PI3K/Akt and MEK/ERK signalling in diverse cell types but their impact on endothelial barrier function is largely unknown. Here the role of PI3K/Akt and MEK/ERK signalling in cAMP/Epac-mediated endothelial barrier stabilisation was analysed.MethodsEndothelial barrier function was analysed in cultured human umbilical vein endothelial cells (HUVECs) by measuring flux of albumin. A modified cAMP analogue 8-pCPT-2′-O-Me-cAMP (Epac agonist) was used to specifically activate cAMP/Epac signalling.ResultsEpac agonist reduces the basal and attenuates thrombin-induced endothelial hyperpermeability accompanied by an activation of PI3K/Akt and MEK/ERK signalling. The qPCR data demonstrate HUVECs express PI3Kα, PI3Kβ, and PI3Kγ but not PI3Kδ isoforms. The western blot data demonstrate Epac agonist activates PI3Kα and PI3Kβ isoforms. Inhibition of MEK/ERK but not PI3K/Akt pathway potentiates the endothelial barrier protective effects of cAMP/Epac signalling. Inhibition of MEK/ERK signalling in the presence of Epac agonist induces a reorganisation of actin cytoskeleton to the cell periphery, enhanced VE-cadherin localisation at cell-cell junctions, and dephosphorylation of myosin light chains (MLC) but not inhibition of RhoA/Rock signalling. Moreover, Epac agonist promotes endothelial cell (EC) survival via reduction in activities of pro-apoptotic caspases in a PI3K/Akt and MEK/ERK signalling-dependent manner.ConclusionOur data demonstrate that the Epac agonist simultaneously activates diverse signalling pathways in ECs, which may have differential effects on endothelial barrier function. It activates PI3K/Akt and MEK/ERK signalling which mainly govern its pro-survival effects on ECs. Inhibition of MEK/ERK but not PI3K/Akt signalling enhances barrier stabilising and barrier protective effects of cAMP/Epac activation.Chemical Compounds Used In This Study8-pCPT-2′-O-Me-cAMP (PubChem CID: 9913268); Akt inhibitor VIII (PubChem CID: 10196499); AS-252424 (PubChem CID: 11630874); IC-87114 (PubChem CID: 9908783); PD 98059 (PubChem CID: 4713); PIK-75 (PubChem CID: 10275789); TGX-221 (PubChem CID: 9907093); Thrombin (PubChem CID: 90470996); U0126 (PubChem CID: 3006531); Wortmannin (PubChem CID: 312145).

C1q/tumor necrosis factor -alpha-related proteins (CTRPs) have been shown to mediate protective cardiovascular effects, but no data exists on their effects on glucose and fatty acid (FA) metabolism in cardiomyocytes. In the present study, adult rat cardiomyocytes and H9C2 cardiomyoblasts were stimulated with various recombinant CTRPs. Glucose or FA uptake, expression of genes involved in glucose or FA metabolism and the role of the AMP-activated protein kinase (AMPK) and Akt were investigated. Although most CTRPs induced an increase in phosphorylation of AMPK and Akt in cardiomyocytes, mainly CTRP2, 7, 9 and 13 induced GLUT1 and GLUT4 translocation and glucose uptake in cardiomyocytes, despite high structural similarities among CTRPs. AMPK inhibition reduced the CTRPs-mediated activation of Akt, while Akt inhibition did not impair AMPK activation. In addition, CTRP2, 7, 9 and 13 mediated strong effects on the expression of enzymes involved in glucose or FA metabolism. Loss of adiponectin receptor 1, which has been suggested to be involved in CTRP-induced signal transduction, abolished the effects of some but not all CTRPs on glucose metabolism. Targeting the AMPK signaling pathway via CTRPs may offer a therapeutic principle to restore glucose homeostasis by acting on glucose uptake independent of the Akt pathway.

In the heart, connexins form gap junctions, hemichannels, and are also present within mitochondria, with connexin 43 (Cx43) being the most prominent connexin in the ventricles. Whereas the role of Cx43 is well established for the healthy and diseased left ventricle, less is known about the importance of Cx43 for the development of right ventricular (RV) dysfunction. The present article focusses on the importance of Cx43 for the developing heart. Furthermore, we discuss the expression and localization of Cx43 in the diseased RV, i.e., in the tetralogy of Fallot and in pulmonary hypertension, in which the RV is affected, and RV hypertrophy and failure occur. We will also introduce other Cx molecules that are expressed in RV and surrounding tissues and have been reported to be involved in RV pathophysiology. Finally, we highlight therapeutic strategies aiming to improve RV function in pulmonary hypertension that are associated with alterations of Cx43 expression and function.

The C1q/tumor necrosis factor-alpha-related protein 9 (CTRP9) has been reported to exert cardioprotective effects, but its role in the right ventricle (RV) remains unclear. To investigate the role of CTRP9 in RV hypertrophy and failure, we performed pulmonary artery banding in weanling rats to induce compensatory RV hypertrophy seven weeks after surgery and RV failure 22 weeks after surgery. CTRP9 expression, signal transduction and mechanisms involved in protective CTRP9 effects were analyzed in rat and human RV tissue and cardiac cells. We demonstrate that CTRP9 was induced during compensatory RV hypertrophy but almost lost at the stage of RV failure. RV but not left ventricular (LV) cardiomyocytes or RV endothelial cells demonstrated increased intracellular reactive oxygen species (ROS) and apoptosis activation at this stage. Exogenous CTRP9 induced AMP-activated protein kinase (AMPK)-dependent transcriptional activation of the anti-oxidant thioredoxin-1 (Trx1) and superoxide dismutase-2 (SOD2) and reduced phenylephrine-induced ROS. Combined knockdown of adiponectin receptor-1 (AdipoR1) and AdipoR2 or knockdown of calreticulin attenuated CTRP9-mediated anti-oxidant effects. Immunoprecipitation showed an interaction of AdipoR1 with AdipoR2 and the co-receptor T-cadherin, but no direct interaction with calreticulin. Thus, CTRP9 mediates cardioprotective effects through inhibition of ROS production induced by pro-hypertrophic agents via AMPK-mediated activation of anti-oxidant enzymes.

The cardiac expression of the mitochondrial uncoupling protein (UCP)-2 is increased in patients with heart failure. However, the underlying causes as well as the possible consequences of these alterations during the transition from hypertrophy to heart failure are still unclear. To investigate the role of UCP-2 mechanistically, expression of UCP-2 was silenced by small interfering RNA in adult rat ventricular cardiomyocytes. We demonstrate that a downregulation of UCP-2 by siRNA in cardiomyocytes preserves contractile function in the presence of angiotensin II. Furthermore, silencing of UCP-2 was associated with an upregulation of glucose transporter type (Glut)-4, increased glucose uptake, and reduced intracellular lactate levels, indicating improvement of the oxidative glucose metabolism. To study this adaptation in vivo, spontaneously hypertensive rats served as a model for cardiac hypertrophy due to pressure overload. During compensatory hypertrophy, we found low UCP-2 levels with an upregulation of Glut-4, while the decompensatory state with impaired function was associated with an increase of UCP-2 and reduced Glut-4 expression. By blocking the aldosterone receptor with spironolactone, both cardiac function as well as UCP-2 and Glut-4 expression levels of the compensated phase could be preserved. Furthermore, we were able to confirm this by left ventricular (LV) biopsies of patients with end-stage heart failure. The results of this study show that UCP-2 seems to impact the cardiac glucose metabolism during the transition from hypertrophy to failure by affecting glucose uptake through Glut-4. We suggest that the failing heart could benefit from low UCP-2 levels by improving the efficiency of glucose oxidation. For this reason, UCP-2 inhibition might be a promising therapeutic strategy to prevent the development of heart failure.

Purpose: According to the current therapeutic guidelines of the WHO physical activity and exercise are recommended as first-line therapy of arterial hypertension. Previous results lead to the conclusion, however, that hearts of spontaneously hypertensive rats (SHR) with established hypertension cannot compensate for the haemodynamic stresses caused by long-term exercise. The current study was initiated to investigate the effects of aerobic exercise on the cardiac remodeling as the sole therapeutic measure before and during hypertension became established.Methods: Beginning at their 6th week of life, six SHR were provided with a running wheel over a period of 6 months. Normotensive Wistar rats served as non-hypertensive controls.Results: In Wistar rats and SHR, voluntary exercise led to cardioprotective adaptation reactions that were reflected in increased mitochondrial respiration, reduced heart rate and improved systolic function. Exercise also had antioxidant effects and reduced the expression of maladaptive genes (TGF-β1, CTGF, and FGF2). However, at the end of the 6-months' training, the echocardiograms revealed that SHR runners developed a restrictive cardiomyopathy. The induction of lysyl oxidase (LOX), which led to an increased network of matrix proteins and a massive elevation in collagen III expression, was identified as the underlying cause.Conclusions: Running-induced adaptive mechanisms effectively counteract the classic remodeling of hearts subject to chronic pressure loads. However, with sustained running stress, signaling pathways are activated that have a negative effect on left ventricular relaxation. Our data suggest that the induction of LOX may play a causative role in the diagnosed filling disorder in trained SHR.

Aims: Parathyroid hormone-related protein (PTHrP) is involved in lung development and surfactant production. The latter one requires a paracrine interaction between type II alveolar cells and lipofibroblasts in which leptin triggers PTHrP-induced effects. Whether increased plasma leptin levels, as they occur in high fat diet, modify the expression of PTHrP remains unclear. Furthermore, the effect of high fat diet under conditions of forced pulmonary remodelling such as response to post myocardial infarction remains to be defined. Materials and methods: C57 bl/6 mice were randomized to either normal diet or high fat diet at an age of 6 weeks. Seven months later, the mice were euthanized and the lung was removed and frozen in fluid nitrogen until use. Samples were analyzed by real-time RT-PCR and western blot. Leptin deficient mice were used to investigate the effect of leptin on pulmonary expression of PTHrP more directly. A subgroup of mice with and without high fat diet underwent in vivo ischemia (45 min) and reperfusion (4 weeks). Finally, experiments were repeated with prolonged high-fat diet. Key findings: High fat diet increased plasma leptin levels by 30.4% and the pulmonary mRNA expression of PTHrP (1,447-fold), PTH-1 receptor (4.21-fold), and PTHrP-downstream targets ADRP (7.54-fold) and PPARγ (5.27-fold). Pulmonary PTHrP expression was reduced in leptin deficient mice by 88% indicating leptin dependent regulation. High fat diet further improved changes in pulmonary adaptation caused by ischemia/reperfusion (1.48-fold increased PTH-1 receptor protein expression). These effects were lost during prolonged high fat diet. Significance: This study established that physiological regulation of leptin plasma levels by high fat diet affects the pulmonary PTHrP expression and of PTHrP downstream targets. Modification of pulmonary expression of PTH-1 receptors by high fat diet after myocardial infarction suggests that the identified interaction may participate in the obesity paradox.

By producing H2O2, the NADPH oxidase Nox4 is involved in differentiation of mesenchymal cells. Exercise alters the composition of slow and fast twitch fibres in skeletal. Here we hypothesized that Nox4 contributes to exercise-induced adaptation such as changes in muscle metabolism or muscle fibre specification and studied this in wildtype and Nox4-/- mice.Exercise, as induced by voluntary running in a running wheel or forced running on a treadmill induced a switch from fast twitch to intermediate fibres. However the induced muscle fibre switch was similar between Nox4-/- and wildtype mice. The same held true for exercise-induced expression of PGC1α or AMPK activation. Both are increased in response to exercise, but with no difference was observed between wildtype and Nox4-/- mice.Thus, exercise-induced muscle fibre switch is Nox4-independent.